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This PDF file contains the front matter associated with SPIE Proceedings volume 7639, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.
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Thirty five years have passed since the first lithography process models were presented, and since that time
there has been remarkable progress in the predictive power, performance, and applicability of these models
in addressing many different challenges within the semiconductor industry. The impact has been profound,
and this paper will attempt to highlight some of the key contributions which have been made, particularly
as patterning simulation has moved beyond the realm of process development to full chip production
enablement. In addition, this paper will outline the new process simulation challenges which emerge as
the industry approaches sub-0.25 k1 patterning. These challenges lie principally in driving towards ever
improved accuracy for an expanding set of processes and failure modes, while maintaining or improving
full chip data preparation cycle times.
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Methods for improving lithography performance with optimization of resist materials and formulation for negative tone
development (NTD) process are discussed. Narrow pitch lithography performance comparison with NTD and PTD
process for initial platform for NTD revealed the not enough maturity of the resist for NTD. Dissolution rate study
suggested the optimizations of molecular weight and solvent parameter to NTD process are important to improve
dissolution property. Larger dissolution rate and larger γ value in contrast curve gave larger process window at 40 nm
half pitch dense contact hole pattern with double exposure and single development step.
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We present an overview of lithography results achieved for materials to support "leave-on-chuck" double-exposure
pitch-division patterning. These materials attempt to make use of a non-reciprocal photoresponse in which the same
number of absorbed 193nm photons can produce different remaining levels of resist, depending upon whether the
photons are received all at once or in two separate exposures. This, in principle, allows for the use of two exposures,
using independent masks and without removing the wafer from the chuck, to produce non-regular patterning down to
one half the pitch limit of the scanner. Such behavior could be produced, for example, by a reversible two-stage
Photoacid Generator (PAG) or other non-reciprocal mechanisms.
Several stages of lithography screening were done on a large number of candidate systems. Initially, thermal stability,
casting behavior, and single-exposure (SE) contrast curves were investigated to determine whether the system behaved
as a usable photoresist. The next stage of testing probed non-reciprocal response, in the form of double-exposure (DE)
contrast curves, typically with an intervening whole-wafer flood exposure at a longer wavelength to enact the nonreciprocity.
The key criterion for the material to pass this stage was to show a shifted contrast curve (difference in
photospeed) for DE vs. SE. Such a shift would then imply that pitch-division imaging would be possible for this
material.
After identifying materials which exhibited this SE vs. DE contrast curve shift, the next step was actual DE patterning.
Since the laboratory tool used for these exposures does not have the precise alignment needed to interleave the two
exposures for pitch division, we employed a technique in which the second exposure is rotated slightly with respect to
the first exposure. This results in a Moiré-type pattern in which the two aerial images transition between overlap and
interleave across the wafer.
One particular PAG + sensitizer did indeed show the desired DE vs. SE contrast curve shift and pitch-divided imaging (k1 = 0.125). This system appears to operate on a scheme based on the creation of a photobase generator between the first and second exposures. Unfortunately, the quality of the pitch-divided images degrades quickly as the pitch is decreased, showing severe LER and bridging defects at a final pitch of 220nm. We postulate that this is caused by the diffusion of one or more key photoproducts. Accompanying papers report on both the photochemical details of the reaction pathways of these materials as well as modeling of the reaction kinetics.
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The drive to sustain the improvements in productivity that derive from following Moore's law has
led the semiconductor industry to explore new technologies that enable production of smaller and
smaller features on semiconductor device. Pitch division techniques and double exposure lithography
are approaches that print features beyond the fundamental resolution limit of state-of-art lenses by
modifying the lithographic process. This paper presents a new technique that enables pitch division in
the printing of gratings using only a single exposure that is fully compatible with the current
manufacturing tools. This technique employs a classical photoresist polymer together with a
photoactive system that incorporates both a photoacid generator (PAG) and a photobase generator
(PBG). The PBG is added to the resist formulation in higher molar concentration than the PAG, but has
a base production rate that is slower than the acid production rate of the PAG. The PBG functions as a
dose-dependent base quencher, which neutralizes the acid in high dose exposure regions but not in the
low dose regions. This photoactive system can be exploited in the design of both positive tone and
negative tone resist formulations that provide a developed image of a grating that is twice the
frequency of the grating on the mask. A simulation of this process was performed for a 52 nm line and
space pattern using PROLITH and customized codes. The results showed generation of a 26 nm half
pitch relief image after development. Through this new technique, a 45 nm half pitch line and space
pattern was experimentally achieved with a mask that produces a 90 nm half pitch aerial image. This
corresponds to a k1 factor of 0.13. The principles, the materials design and the first lithographic
evaluations of this system are reported.
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Double patterning processes are techniques that can be used to form etching mask patterns for 32nm node and possibly
for 22nm node as well. The self-aligned spacer process has drawn much attention as an effective means of enabling the
formation of repetitive patterns. The self-aligned spacer process is now being used in actual device manufacturing, but it
has many process steps driving up process cost while also assuming a 1D pattern. This paper demonstrates extensions of the self-aligned spacer process by an enhanced 2D positive spacer process and a newly developed spacer DP process using a 1D negative spacer.
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Double exposure (DE) and double patterning (DP) have emerged as leading candidates to fill the technology gap
between water immersion and EUV lithography. Various approaches of them are proposed to achieve 3x-nm half-pitch
dense lines and beyond. Both DE with two resist processes and double patterning (DP) require two separate exposures,
and they are faced very tight overlay margin by the scanner tool. By contrast, self-aligned double patterning (SADP)
requires one exposure only, and provides high feasibility for 3x-nm node at this moment. However, a sequential order of
multiple non-lithographic steps (film deposition, etch, and CMP) cause a complicated and expensive process of SADP.
Instead of using complicated sacrificial layers, the spacers are directly formed at the sidewall of the resist patterns by
low-temperature CVD deposition or spin on sidewall (SoS) material coating. In this paper, lower cost-of-ownership of
SoS material are studied for SADP process.
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Several methods to improve sensitivity of EUV resist, with a couple of key points of acid generation efficiency and deprotection
reaction efficiency. Larger loading of PAG to increase the secondary electron absorption possibility, cation
unit design to lower the lowest unoccupied molecular orbital of cation, and lowering ionization potential of polymer to
enable efficient secondary electron generation, were discussed in the viewpoint of acid generation efficiency. Larger
size of anion structure design on PAG was applied to special formulation of small loading of quencher to minimize
necessary generated acid concentration to give enough de-protection reaction amount, and to higher PEB temperature
resist process to maximize de-protection reaction efficiency.
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The higher energy associated with extreme ultraviolet (EUV) radiation coupled with the high absorptivity of most
organic polymers at these wavelengths should lead to increased excited state population and higher quantum yields of
photoproducts. Polymers representative of those commonly employed in resists as well as some model polymers were
selected for this study. Polymer photochemistry at EUV was catalogued as to the effect of absorbed 13.4-nm radiation
on a polymer's quantum yield of chain scission (Φs) and crosslinking (Φx). In selected cases, the chain scission and
crosslinking quantum yields were also compared to those previously determined at 157-, 193- and 248-nm. It was found
that quantum yield values were over a magnitude greater at EUV relative to optical wavelengths.
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We investigated the relationship between line edge roughness (LER) and the chemical gradient using the fourth Selete
Standard Resist (SSR4). Two-dimensional (half-pitch and exposure dose) matrices of resist line width and LER were
analyzed on the basis of the sensitization mechanisms of chemically amplified resists for extreme ultraviolet (EUV)
lithography. The latent images of resist patterns were successfully reproduced by assuming that LER is inversely proportional to the chemical gradient. The product of LER and normalized chemical gradient was approximately 0.2 for SSR4.
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By combining chemical and thermal curing techniques, we developed a simple "hybrid" curing system which offers
precise CD control of the first patterns after double patterning. This hybrid curing system involves thermal curing
followed by a liquid rinse process using a double patterning primer (DPP). DPP is an aqueous solution formulated with
surface curing agent (SCA) components and enhances "positive" interaction between L1 and L2 patterns. Taking
advantage of the CD growth with DPP treatment, we further developed three advanced patterning schemes: 1. "Shrink
Process Assisted by Double Exposure" (SPADE I), 2. "Space Patterning Assisted by Double Exposure" (SPADE II), and
3. "Sidewall Patterning Assisted by Double Exposure" (SPADE III). Using SPADE I, contact hole CD was reduced by
10~30nm and excellent through pitch performance was achieved. Using SPADE II, the first example of self-aligned
double patterning of contact holes has been demonstrated. After SPADE II, the contact hole pitch was reduced by 30%.
A novel method was developed to form sidewalls on the existing patterns using SPADE III. The 2D sidewall patterning
with contact holes was demonstrated and ~40nm sidewalls were formed using SPADE III. This can also be applied to
form sidewall patterns on line and space patterns to self-aligned double patterning of lines. In this paper, our recent
progress with SPADE technology is described and its potential use in the advanced patterning schemes is discussed.
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Photoacid generators (PAGs) are a key component in chemically amplified resists used in photolithography.
Perfluorooctanesulfonates (PFOS) and other perfluoroalkylsulfonates (PFAS) have been well adopted as PAGs in 193
nm photoresist. Recently, concerns have been raised about their environmental impact due to their chemical persistency,
bioaccumulation and toxicity. It is a general interest to find environmentally benign PAGs that are free of fluorine atoms.
Here we describe the design, synthesis and characterization of a series of novel fluorine-free onium salts as PAGs for
193 nm photoresists. These PAGs demonstrated desirable physical and lithography properties when compared with
PFAS-based PAGs for both dry and immersion exposures.
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The trend of ever decreasing feature sizes in subsequent lithography generations is paralleled by the need to reduce resist
thickness to prevent pattern collapse. Thinner films limit the ability to transfer the pattern to the substrate during etch
steps, obviating the need for a hardmask layer and thus increasing processing costs. For the 22 nm node, the critical
aspect ratio will be less than 2:1, meaning 40-45 nm thick resists will be commonplace. To address this problem, we
have developed new inorganic nanocomposite photoresists with significantly higher etch resistance than the usual
polymer-based photoresists. Hafnium oxide nanoparticles are used as a core to build the inorganic nanocomposite into an
imageable photoresist. During the sol-gel processing of nanoparticles, a variety of organic ligands can be used to control
the surface chemistry of the final product. The different ligands on the surface of the nanoparticles give them unique
properties, allowing these films to act as positive or negative tone photoresists for 193 nm or electron beam lithography.
The development of such an inorganic resist can provide several advantages to conventional chemically amplified resist
(CAR) systems. Beyond the etch resistance of the material, several other advantages exist, including improved depth of
focus (DOF) and reduced line edge roughness (LER). This work will show etch data on a material that is ~3 times more
etch-resistant than a PHOST standard. The refractive index of the resist at 193 nm is about 2.0, significantly improving
the DOF. Imaging data, including cross-sections, will be shown for 60 nm lines/spaces (l/s) for 193 nm and e-beam
lithography. Further, images and physical characteristics of the materials will be provided in both positive and negative
tones for 193 nm and e-beam lithography.
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We have developed a new silicon-containing resist for 193-nm immersion lithography. This resist is compatible with
topcoats used in the industry today for immersion lithography. Most of the current topcoats contain 4-methyl-2-
pentanol as a solvent. Our evaluations indicated that the previously developed silicon-containing resists are not
compatible with the current topcoats because of their solubility in 4-methyl-2-pentanol. In the new resist polymers,
we have incorporated high percentage (> 60 mol%) of lactone monomers to prevent them from dissolving in this
solvent. In order to increase the lactone content in a silicon polymer, we have incorporated lactone containing acidlabile
functionalities in addition to widely used acid-inert lactone monomers. Utilizing these polymers, we have
demonstrated a functional silicon-containing photoresist for immersion lithography.
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Future demands of the semiconductor industry call for robust patterning strategies for critical dimensions
below twenty nanometers. The self assembly of block copolymers stands out as a promising, potentially lower cost
alternative to other technologies such as e-beam or nanoimprint lithography. One approach is to use block
copolymers that can be lithographically patterned by incorporating a negative-tone photoresist as the majority
(matrix) phase of the block copolymer, paired with photoacid generator and a crosslinker moiety. In this system,
poly(α-methylstyrene-block-hydroxystyrene)(PαMS-b-PHOST), the block copolymer is spin-coated as a thin film,
processed to a desired microdomain orientation with long-range order, and then photopatterned. Therefore, selfassembly
of the block copolymer only occurs in select areas due to the crosslinking of the matrix phase, and the
minority phase polymer can be removed to produce a nanoporous template. Using bulk TEM analysis, we
demonstrate how the critical dimension of this block copolymer is shown to scale with polymer molecular weight
using a simple power law relation. Enthalpic interactions such as hydrogen bonding are used to blend inorganic
additives in order to enhance the etch resistance of the PHOST block. We demonstrate how lithographically
patternable block copolymers might fit in to future processing strategies to produce etch-resistant self-assembled
features at length scales impossible with conventional lithography.
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As device scaling continues according to Moore's Law, an ongoing theme in the semiconductor industry is the need for
robust patterning solutions for advanced device manufacture. One particularly attractive solution for implant lithography
is the use of a developable BARC (DBARC) to improve reflection control while still affording an "implant ready"
substrate following development. Going forward, these two features of DBARC technology are key to successful
implant patterning as the industry standard TARC process begins to falter due to poor substrate reflection control leading
to profile degradation, shrinking process windows and poor CDU.
In this paper, we report our progress in the design and development of production worthy DBARCs for implant
lithography. In addition to outlining our general design concepts, we describe our fundamental approach to
characterizing DBARCs and share key performance data showing our DBARC technology is surpassing the capability of
a traditional TARC process for both KrF and ArF implant applications. Key performance metrics include CD swing, CD
control over varying oxide thickness, active to field CD bias and footing over topography.
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In this work, the conventional via-first dual damascene (DD) patterning scheme is replaced by a cost-efficient
Multi-Level Multiple Exposure (MLME) patterning and etching approach. A two-layer positive-tone photoresist stack is
sequentially imaged using 193 nm dry lithography, to produce a DD resist structure that is subsequently transferred into
an auxiliary dual organic underlayer stack, and then further into a dielectric layer. This novel integration approach
eliminates inter-tool wafer exchange sequences as performed in a conventional litho-etch-litho-etch process flow, while
simultaneously being applicable to all back-end-of-the-line (BEOL) levels, ensuring throughput increase. The top and
bottom resist layers are chemically designed in such a way that they feature differential solubility in organic solvents
making it possible to coat the top photoresist onto the bottom resist layer without intermixing to enable a strict litholitho-
etch processing sequence. Independent registration of the via and trench structures in the bottom and top resist
layers is achieved by selective photospeed decoupling of the respective layers, so that the bottom resist is largely
insensitive at nominal resist exposure dose for the top resist. Imaging performance evaluation of the newly introduced
MLME technology includes the resist materials selection process and their required properties (solvent compatibility,
adhesion, photospeed, defectivity and correction of via dose bias due to trench exposure) as well as metrology work.
Image transfer of the patterned DD resist structure into an underlying transfer layer stack and then further into a
dielectric layer using Reactive Ion Etching (RIE) followed by electroplating, polishing and electrical testing was also
thoroughly investigated and is described in detail in an accompanying paper.
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In this paper, we wish to report, for the first time, on a simple, low-cost, novel way to form dual-damascene copper (Cu)
on-chip interconnect or Back-End-Of-the-Line (BEOL) structures using a patternable low dielectric constant (low-κ)
dielectric material concept. A patternable low-κ dielectric material combines the functions of a traditional resist and a
dielectric material into one single material. It acts as a traditional resist during patterning and is subsequently converted
to a low-κ dielectric material during a post-patterning curing process. No sacrificial materials (separate resists or
hardmasks) and their related deposition, pattern transfer (etch) and removal (strip) are required to form dual-damascene
BEOL patterns. We have successfully demonstrated multi-level dual-damascene integration of a novel patternable low-κ
dielectric material into advanced Cu BEOL. This κ=2.7 patternable low-κ material is based on the industry standard
SiCOH-based (silsesquioxane polymer) material platform and is compatible with 248 nm optical lithography. Multilevel
integration of this patternable low-κ material at 45 nm node Cu BEOL fatwire levels has been demonstrated with
very high electrical yields using the current manufacturing infrastructure.
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As the semiconductor industry approaches smaller and smaller features, applications that previously used top antireflective
coatings have now begun using developer-soluble bottom anti-reflective coatings (BARCs). However, there
are several drawbacks to a wholly developer-soluble system, mainly because many of these systems exhibit isotropic
development, which makes through-pitch and topography performance unsatisfactory. To solve this problem, we have
developed several photosensitive BARC (PS BARC) systems that achieve anisotropic development. One issue with the
PS BARC, as with traditional dry BARCs, is resist compatibility. This effect is compounded with the photosensitive
nature of our materials. The acid diffusion and quenching nature of the resists has been shown to have a significant
effect on the performance of the acid-sensitive PS BARC. Some resists contain a highly diffusive acid that travels to the
PS BARC during the post-exposure bake and aids in clearance. Others show the opposite effect, and the same PS BARC
formulation is not able to clear completely. To address the lack of compatibility and to further improve the PS BARC,
we have developed a solution that properly matches PS BARC and photoresist performance.
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Chemically amplified photoresists require a post exposure bake (PEB), typically on a hot plate at 90-150°C for 30-120
seconds, to catalytically deprotect the polymer backbone. During PEB, excessive diffusion of the photo-generated acid
results in loss of line edge definition, blurring of latent images and changes in the line edge roughness. Both acid
diffusion and deprotection are thermally activated processes, with the relative rates affected by the time/temperature
profile of the PEB. In this work, we introduce an alternate PEB method involving 500 μs time scale heating over a
temperature range of 130°C to 450°C using a continuous wave CO2 laser. A methodology is developed for characterizing
this laser PEB and comparing the behavior with conventional hot plate PEB. The thermal stability of several polymer
and photoacid generator (PAG) resist systems were studied and shown to be stable at these high temperatures due to the
short heating duration. Sensitivity of resists under hot plate and laser PEB were measured. Under moderate temperatures,
the laser PEB sensitivity can exceed that of hot plate PEB by an order of magnitude. Quantitative determination of the
acid diffusion was obtained using resist bilayers (PAG loaded / PAG free). Despite the five orders of magnitude
difference in PEB time, systems with l-PEB and hot-plate PEB exhibit comparable imaging quality under deep ultraviolet exposure.
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This paper describes construction of a chemically amplified resist model across 248nm, 193nm and EUV imaging
wavelengths. Using resist absorbance input as obtained from experiment and modeling, only the acid formation kinetics
are allowed to vary across imaging wavelengths. This very constraining system affords very good fitting results, which
provides high confidence that the extracted parameters from the model have actual physical significance. The quantum
efficiency for acid formation in EUV is found to be ~8X higher than at 248 or 193nm, due to the excitation mechanism
by secondary electrons. Most notably for the polymer bound PAG system under study the model provides an extremely
low acid diffusion length (~7nm), suggesting an excellent inherent resolution for this material.
Next, resist models are created for a series of sensitizer containing polymer bound PAG formulations, where the
sensitizer loading is systematically varied. Compared to the reference polymer bound PAG resist without sensitizer the
efficiency of acid formation is significantly increased, without a negative impact on either resolution or line width
roughness. For the materials the quantum efficiency of acid formation in EUV is found to be ~12X higher than at 248nm.
In these formulations the impact of sensitizer loading on the sizing dose is found to be rather moderate. This may suggest
that even at the lowest sensitizer loading studied the energy of the secondary electrons is already efficiently transferred to the PAGs.
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A series of negative tone molecular resists was investigated for use in both organic solvent and aqueous base
development. Molecular resists designed purely for solvent development showed half-pitch resolution down to 25 nm
with sensitivities of 50 μC/cm2 and LER (3σ) down to 2.3 nm. Aqueous developable designs that used epoxide
functionalized molecules that are intrinsically water soluble showed improved contrast and comparable sensitivity, but
suffered from significant dewetting during baking due to their low molecular weight and high polarity. This inability to
form high quality films prevented their use as high resolution resists. Aqueous developable designs that used molecules
with both cross-linking and base solubilizing groups were also investigated; the initial example of this design is DPA-
2Ep, a molecular resist containing two epoxides and one carboxylic acid per molecule. It formed high quality films and
showed improved contrast compared to the purely solvent developed designs. Even after complete cross-linking of the
epoxide groups, several free carboxylic acids still remained in the network. These free acids tend to imbibe developer and appear to retain the tetramethylammonium carboxylates even after rinsing and drying the film. This imbibing of developer leads to significant failure during high resolution patterning due to swelling.
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Linear and star-shaped ArF photoresists were prepared and preliminary lithographic comparison was performed
using electron-beam exposure. An oligo-initiator based on saccharose forms the core of the star shaped photoresist
from which three standard ArF photoresist monomers, α-gamma butyrolactone methacrylate (GBLMA), methyl
adamantyl methacrylate (MAMA) and hydroxyl adamantyl methacrylate (HAMA) were polymerized. Conditions
were adjusted to obtain a low polydispersity, 6 kg/mol star polymer with a degree of polymerization of approximately five mers per arm. For comparison, a linear photoresist control was prepared using the same scheme. The star resist architecture was found to improve roughness without reducing sensitivity or resolution.
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We prepared three different kinds of polymers. The first was the STAR polymers having various length of the arms
connected to the single core which could be decomposed by the acid. The second was the Linear polymers based on
p-hydroxystylene (HS) which was also used for the arms of the STAR polymer. The other was the non-decomposable
STAR polymer which had a quite similar shape to the STAR polymer and of which core structure could not be
decomposed.
Using those materials, lithographic performance obtained using a Micro Exposure Tool (MET) was compared with
thermal property, and it was found that STAR-9mer-H having the 9 HS unit arms provided best overall performance,
24 nm of ultimate resolution, 4.3 nm of line width roughness and 4.6x10-8 mJ•nm3 of Z factor on MET evaluation. In
addition to this, the specific resist based on the STAR polymer could achieve 26 nm resolution with quite wider
process window capability that the control resist consisting of partially protected poly(p-hydroxystyrene) on the Alpha
Demo Tool evaluation with conventional illumination.
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This paper summarizes the development of EUV resists based on various new materials: the lithographic evaluation results of EUV resists from resist material manufacturers using the small field exposure tool (SFET). We discuss the screening results of new resin materials based on
calix[4]resorcinarene, "Noria" and fullerene.
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Molecular resists are expected to offer the advantages of high resolution and low line width roughness (LWR) for the
next-generation lithography. We developed a new molecular resist that showed high resolution by introducing an
efficient acid-leaving group to an amorphous molecule, 1,3,5-Tris(p-(p-hydroxy- phenyl) phenyl) benzene (THTPPB).
The lithographic properties such as sensitivity, developing rate, and adhesion are considered to be controlled using a
suitable acid-leaving group. A molecular resist of THTPPB to which is attached with an alicyclic acid-leaving group,
hyperlactyl vinyl ether group (HPVE) showed a high resolution for electron beam (EB) lithography and good etch resistance. Half-pitch 36 nm line-and-space (1:1) positive pattern was fabricated using 100 keV EB with chemically amplified molecular resist based on HPVETPPB.
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We developed negative-tone chemically amplified molecular resists based on a fullerene derivative and evaluated the
lithographic performance using 75 keV electron beam (EB) exposure tool to explore the potential of fullerene derivatives
as a negative-type EB resist with high resolution and high etching durability. The etching rate of fullerene derivatives is
lower than that of conventional resist materials such as PHS, ZEP530 and UVIII. Although a dose of 800 μC/cm2 is
required, 60 nm line resolution and aspect ratio five was obtained in best of four kinds of fullerene derivative films. Also,
the effect of acid generators to a fullerene derivative resists were investigated. Fullerene derivative resists are a
promising candidate for nanolithography because it is essential for next generation lithography to have high aspect ratio related collapse of high resolution pattern and high etching durability in ultra-thin films.
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The feasibility of three polymer systems for use as non chemically amplified resists for 193 nm lithography are
discussed. The three systems are polycarbonates, polyphthalaldehydes and polysulfones. In general it was found that
increased absorbance resulted in higher sensitivity to 193 nm light. However, the exception to this was the
polycarbonates, which were found to undergo crosslinking due to an alkene group present in the polymer backbone.
Although polyphthalaldehydes were very sensitive, their absorbance values were too high to be useful in a commercial
environment. Absorbing polysulfones were found to be sensitive to 193 nm light and initial patterning results have been presented.
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As the critical pitch continues to shrink for advanced technology nodes and the EUV tool is
not yet mature, the demand for ArF high-contrast resist becomes stronger than ever. In this paper,
we discuss the impact of photosensitive quenchers to lithographic performance. Two types of
photosensitive quencher, photo-base generator (PBG) and photo decomposable quencher (PDQ),
are studied for its ability to extend the life of immersion ArF lithography. With conventional
photoresists using normal non-photosensitive quenchers, the aerial image was substantially
linearly transferred to the acid image of the photoresist stimulated by photo acid generator (PAG).
The new PBG or PDQ serves as one additional photosensitive component. Such photosensitive
quencher changes its base level after exposure. Thus, it modifies the aerial image for better
imaging performance. We will present and discuss the imaging results from various formulations
of photosensitive quencher and variation in its concentration. The defect performance of these
new approaches will also be characterized.
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The development of double patterning processes/schemes are widely in progress for 2x nm node and beyond by using
193nm immersion lithography. It is realized that a resist shrink step is necessary in many double patterning process cases
due to the resolution limit of the 193nm immersion exposure tool.
As the development work progresses into the mass-product transition phase, the requirement for technical performances
has become more difficult to be achieved by existing resist shrink technologies.
In order to overcome these difficulties, we have developed "wet slimming" process based on our coater/developer
technologies including the platform. The process is optimized for CD uniformity and defectivity. The process also has
good robustness to the various possible resist materials and/or exposure conditions used by industry.
In this paper, we introduce the scheme of wet slimming process together with basic performance data such as CD
controllability, CD uniformity, defectivity and I-D bias. The evaluation data on actual double patterning processed
wafers is reported as well.
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20 nm contact hole (C/H) patterning is applicable for sub-22 nm technology node applications. Dependence of C/H
CD window on critical process parameters is important for process stability and repeatability. Post applied baking
(PAB) condition, resist thickness, develop time, and dry etch rate are considered to be the most important process
parameters for e-beam chain scission resist ZEP520A C/H patterning. In this paper, PAB temperatures (TPAB) are
investigated at temperatures between lower than glass transition temperature (TG) and much higher than TF. Effects of these process parameters on 20 nm +/-10% C/H CD window for various pattern densities and e-beam doses are
studied. The critical process parameters are determined by their effects on CD window size, C/H sidewall profile,
proximity effect immunity, ΔCD/ΔDose slope, and etch selectivity.
Experimental results are summarized below. Thinnest ZEP520A film has the largest 20nm +/-10% CD window on
D-D plot for various L/S ratios and doses. The dosage window of smaller C/H CD is larger. The proximity effect is
negligible for 50 nm ZEP520A baked at 200°C/300 sec. No apparent effect is found in CD window on D-D plot for develop time as short as 30 sec. PAB condition is most critical than the other process parameters in determining resist density and polymerization which affect e-beam scattering and chain scission in resist film and therefore affects CD resolution and window. PAB condition of 140°C/60 sec is most desirable in terms of CD window on D-D plot, C/H sidewall profile, dry etch rate and proximity effect.
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Organic electronics has recently gained attention as a new field promising cheaper, flexible, and large-scale
devices. Although photolithography has proven to be a high-resolution and high-throughput patterning method with
excellent registration capabilities, the emerging field of organic electronics has been largely unsuccessful in adapting this
well-established method as a viable approach to patterning. Chemical compatibility issues between organic materials and
the processing solvents and chemicals required by photolithography have been the main problem. This challenge has led
us to identify a set of non-damaging processing solvents and to develop alternative imaging materials in order to extend
photolithographic patterning methods to organic electronics.
We have identified supercritical carbon dioxide and hydrofluoroether (HFE) solvents as chemically benign to
organic electronic materials and which are also suitable as processing solvents. We refer to these solvents as orthogonal
in that they do not substantially interact with traditional aqueous and organic solvents. Multi-layered devices are easily
realized by exploiting this orthogonality property; subsequent layers are deposited and patterned without damaging or
otherwise adversely affecting previously deposited underlying layers. We have designed and synthesized novel
photoresists, which are processible in these benign solvents.
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Microlens arrays are used on CMOS image sensors to focus incident light onto the appropriate photodiode and thus
improve the device quantum efficiency. As the pixel size shrinks, the fill factor of the sensor (i.e. ratio of the
photosensitive area to the total pixel area) decreases and one way to compensate this loss of sensibility is to improve the
microlens photon collection efficiency. This can be achieved by developing zero-gap microlens processes. One elegant
solution to pattern zero-gap microlenses is to use a grayscale reticle with varying optical densities which locally
modulate the UV light intensity, allowing the creation of continuous relief structure in the resist layer after development.
Contrary to conventional lithography for which high resist contrast is appreciated to achieve straight resist pattern
profiles, grayscale lithography requires smooth resist contrast curve. In this study we demonstrate the efficiency of
grayscale lithography to generate sub-2μm diameter microlens with a positive-tone photoresist. We also show that this
technique is resist and process (film thickness, development normality and exposure conditions) dependent. Under the
best conditions, spherical zero-gap microlenses as well as aspherical and off-axis microlenses, which are impossible to
obtain with the conventional reflow method, were obtained with satisfying process latitude.
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A newly developed chemically amplified (CA) i-line positive resist is designed to reflow the resist structures at relatively
low temperatures while eliminating thermal crosslinking mechanisms. The resist can reflow to form clear spherical
lenses having greater than 90° contact angles. This is demonstrated by thermally reflowing squared resist posts, 50μm
and 80μm in size printed in 48μm resist thickness and 10μm posts in 15μm thickness at 120°C. The resulting lenses have
smooth surfaces, free of any wrinkling or residual resist corners.
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The chemical waste generated in today's microelectronic fabrication processes has driven the need to develop a more
environmentally benign process. Supercritical CO2 (scCO2) has been evaluated as an environmentally friendly solvent for photoresist development. It is nontoxic, nonflammable, and inert under most conditions. It also possesses advantages
such as liquid-like densities, gas-like diffusivity, and zero surface tension. Although scCO2 is a poor solvent for most
polymers, certain fluorine-and silicon-containing polymers have shown solubility in scCO2. Previously, negative-tone
patterns of 100nm have also been developed in scCO2 using conventional photoresists such as ESCAP and PBOCST
with the aid of fluorinated quaternary ammonium salts (QAS). However, the incorporation of fluorine degrades plasma
etch resistance, and because of their persistence in nature, fluorinated compounds are coming under increased scrutiny.
In order to make the process more environmentally benign, the elimination of fluorine is desirable. Some molecular glass
photoresists without the incorporation of fluorine and silicon have thus been designed and synthesized to be processed in
scCO2. In addition to scCO2, another environmentally friendly, low VOC solvent, decamethyltetrasiloxane has also been investigated to develop conventional photoresists. In this paper, we demonstrate the patterning of photoresists in both
scCO2 and decamethyltetrasiloxane.
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HSQ island formed by directly e-beam exposure (DE) and wet development is used as a dry etching mask material.
However, the HSQ islands with high aspect ratio are susceptible to collapse during wet development process due to
surface tension. To improve this, HSQ-rod and HSQ-Tip structures were achieved by dry stripping of ZEP520A
after thermal reflow of ultra-thin HSQ (hydrogen silsesquioxane) gap-filled (GF) ZEP520A contact holes (C/H) in
previous study. Aspect ratio of HSQ island formed by latter process is higher than that by the former since the latter
is without wet develop procedure which tends to washout the HSQ island. In this paper, gap-fill processes followed
by a hardening process to prevent bending of HSQ island are studied to form sub-50 nm HSQ islands (rod or tip)
with high aspect ratio. Diluted HSQ is used to gap-fill the exposed ZEP520A C/H or C/H after thermal reflow. The
hardening processes include high temperature baking and e-beam curing with high beam current.
Experimental results are summarized below. Aspect ratio of GF type HSQ-rod larger than 7 is obtained. Bending of
GF type HSQ island (rod or tip) with high aspect ratio is also observed. HSQ-rod hardened by high temperature
baking tends to fracture. E-beam curing proves to be efficient for HSQ island (rod or tip) hardening and the required curing doses are dependent on HSQ-rod CD. Smallest HSQ-Tip CD hardened by e-beam curing is ~12.5nm. It is found that e-beam curing of GF type HSQ island and e-beam exposure of DE type HSQ island has the same effect and mechanism in cross-linking of HSQ molecules to increase mechanical strength.
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The reduction of line width roughness (LWR) is a critical issue in developing resist materials for EUV lithography and
LWR represents a trade-off between sensitivity and resolution. Additional post pattern processing is expected as an LWR
reduction technique without impact to resolution or sensitivity. This paper reports the LWR reducing effect of a post-development
resist-smoothing process. Approximately 20% improvement in LWR for ArF immersion exposed resist patterns was achieved for two types of resist and two illumination conditions. The LWR after BARC etching in which
resist-smoothing was applied was decreased relative to the case in which smoothing was not applied. Resist-smoothing
process also reduced LWR of an EUV exposure resist pattern by approximately 10%. These results confirm that resistsmoothing
process is robust for different resists and illumination conditions.
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Research has been conducted to develop alternatives to chemically amplified 193 nm photoresist materials that will be
able to achieve the requirements associated with sub-32 nm device technology. New as well as older photoresist design
concepts for non-chemically amplified 193 nm photoresists that have the potential to enable improvements in line edge
roughness while maintaining adequate sensitivity, base solubility, and dry etch resistance for high volume manufacturing
are being explored. The particular platforms that have been explored in this work include dissolution inhibitor
photoresist systems, chain scissioning polymers, and photoresist systems based on polymers incorporating
formyloxyphenyl functional groups. In studies of two-component acidic polymer/dissolution inhibitor systems, it was
found that compositions using ortho-nitrobenzyl cholate (NBC) as the dissolution inhibitor and poly norbornene
hexafluoro alcohol (PNBHFA) as the base resin are capable of printing 90 nm dense line/space patterns upon exposure to
a 193 nm laser. Studies of chain scission enhancement in methylmethacrylate copolymers showed that incorporating
small amounts of absorptive a-cleavage monomers significantly enhanced sensitivity with an acceptable increase in
absorbance at 193 nm. Specifically, it was found that adding 3 mol% of α-methyl styrene (α-MS) reduced the dose to
clear of PMMA-based resist from 1400 mJ/cm2 to 420 mJ/cm2. Preliminary data are also presented on a direct
photoreactive design concept based on the photo-Fries reaction of formyloxyphenyl functional groups in acrylic copolymers.
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In a 2009 analysis of microbridging defectivity, a design of experiment methodology was used to show the effect of
filtration parameters on microbridging defectivity, specifically focusing on filter retention rating, filter media and design,
filtration rate, and controlled filtration pressure. In that analysis it was shown that different filter architectures provide
the most effective filtration of microbridging and that different filter architectures show different levels of microbridging
defects even when optimally tuned. Ultimately, filter choice and filtration setup matter in removal of microbridging
defects.
In the new analysis, a similar approach was taken with additional filter types. However, in the new study the retention rating of the filters was kept constant at 10nm while other filter parameters were varied, including membrane material and design. This study will show the specific effect of the membrane material and design on microbridging defectivity in addition to the effects of filtration setup.
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While immersion lithography has been rapidly implemented in manufacturing environments around the world, a few
defect challenges still remain. Bubble and watermark defects are well understood and have been addressed by
equipment manufacturers. However, a few defects still bewilder the lithography community, including residues and
microbridging. These defects are difficult to completely eliminate as they may have many root causes. However,
through effective point-of-use filtration, they can be greatly reduced.
Point-of-use filtration has traditionally focused on selecting a filter membrane at a specific pore size that is compatible
with the resist chemistry being utilized in the process. The research hereby discussed indicates that in addition to these
important point-of-use filter choices, careful filtration parameter setup can improve defectivity results and impact the coating process.
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A novel back-end-of-line (BEOL) patterning and integration process termed Multi-Level Multiple Exposure
(MLME) technique is herein introduced. The MLME technique simplifies BEOL dual damascene (DD) integration while
simultaneously being applicable to all BEOL levels. It offers a patterning resolution reaching into the sub-100nm region
and improves semiconductor manufacturing cost and throughput. MLME employs a dual-layer imaging stack (via + trench resists) cast onto a customized etch transfer multilayer stack. This process implements a strict litho-litho-etch sequence for transferring the trench- and via-patterns into the dielectric layer. Under the MLME scheme, two imaging
steps (i.e. via- and trench-level patterning) are executed consecutively followed by a dry etch process that transfers the
lithographically-formed patterns into the customized etch transfer multilayer stack and further into the dielectric layer.
The MLME integration scheme not only decreases the number of overall process steps for the full DD BEOL process but
also eliminates several inter-tool wafer exchange sequences as performed in a conventional litho-etch-litho-etch process
flow. All MLME process steps were demonstrated i.e. combined 193nm-dry dual-resist layer MLME via- and trench-lithography,
full pattern transfer of via- and trench-patterns into the dielectric layer using reactive ion etching (RIE), as
well as electroplating and polishing of the DD patterns. This paper provides a detailed description of both post-lithography
steps of the DD process for a DD BEOL structure, i.e. (i) the RIE-pattern transfer process with the customized multilayer stack, and (ii) the metallization process completing the DD process for one BEOL layer.
Furthermore, the integration capabilities of the MLME technique were demonstrated and characterized by generating an
electrically functional via-chain connecting two neighboring BEOL layers fabricated by subsequently applying the MLME approach to both layers. An exhaustive description and evaluation of MLME lithographic patterning is given in an accompanying paper.
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In a conventional lithography process, the resist pattern is removed by dry strip or wet
chemical etch. The wet chemical etch includes sulfuric peroxide etch and solvent etch. The
wet chemical etch process is always combined with the dry strip process to meet the residue
process spec. However, in some applications, only the wet-etch process can be used to
avoid substrate damage during the plasma step. However, organic residue can be found
from particle surface scan and TGA/DSC after normal solvent strip.
In this paper, we investigate polymer residue stripping using only solvent as well as solvent
in combination with UV treatment. For solvents only, some solvents different from the
conventional PGMEA/PGME mixture in polarity, also exhibited stripping ability but the
efficiency is not as good as PGME/PGMEA mixture. When supplemented with UV
treatment, the organic residue can be further decomposed and removed completely. The UV
we used contains 185nm and 254nm wavelengths. Ozone is generated during UV
exposure and acts as oxidant. The organic residue is thus decomposed and removed. It has been proven as an effective method to cleave the C-C bond without damaging the wafer substrate. The organic residue on the wafer surface can be easily stripped away under UV-ozone exposure. Its defect performance is also discussed in this paper.
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By copolymerization of 2-(2-diazo-3-oxo-3-(4-dimethylaminophenyl)propionyloxy)ethyl methacrylate (DODMAPPEA), methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA), a photoactive polymer for negative-tone resist is synthesized and its photolithographic properties are investigated. Since the maximum-absorption wavelength of the photoactive monomer DODMAPPEA is 356nm and it still has a comparatively large absorption at 365nm (I-line), the copolymer poly(DODMAPPEA -co-MMA-co-HEMA) is anticipated to be used in
I-line single component negative-tone resist. Upon irradiaton, the diazoketo groups which are in the side chains of
the copolymers undergo the wolff rearrangement, affording ketenes that react with hydroxyl to provide cross-linking
photoproducts and a negative image is obtained. Besides that, cross-linking agent hexamethoxymethylmelamine (HMMM) is added to the resist system and high sensitivity is expected. This kind of copolymer has great value in I-line non-CARs, TFT-LCD and IC discrete devices processing and the anti-dry etching ability is enhanced by the introduction of the benzene ring. In addition, this copolymer still has potential value in Ultra-violate lithographic plate.
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Nanoimprint lithography is a newly developed patterning method that employs a hard template for the patterning of
structures at micron and nanometerscales. This technique has many advantages such as cost reduction, high resolution,
low line edge roughness (LER), and easy operation. However, resist peeling, defects, low degree of planarization, and
low throughput issues present challenges that must be resolved in order to mass produce advanced nanometer-scale
devices. In this study, the new approach of using spin-on hard mask materials under the resist to modify its adhesion
during a UV irradiation process in nano imprint lithography was proposed to increase process latitudes. The performance of this process is evaluated by using step and flash imprint lithography. We expect that these spin-on hard mask materials (NCI-NIL-U series) under organic resist will be one of the most promising materials in the next generation of nano imprint lithography.
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In today's competitive lithography market, resist manufacturers are always striving to create a product to meet
lithographic challenges while maintaining a low inherent defect level. While bulk filtration used in resist manufacturing
removes a majority of the inherent defectivity, point-of-use filtration is still required to ensure that defects are not passed
from the bottle to the wafer. As Moore's law drives lithographers to ever decreasing dimensions, resist manufacturers
must find new ways of filtering their chemistries to make sure that the smallest defects cannot create the biggest yield
detractors. In addition, IDMs must use new innovations to explore point-of-use filtration techniques to protect their
valuable patterns.
This paper will show the conditions that can reduce defectivity in an immersion lithography scheme. More specifically,
advanced point-of-use filtration techniques, including revolutionary filter membrane technology and advanced filtration
settings, will be explored to understand potential 22nm node defect performance. By thinking ahead about the filtration
needs of the future, resist manufacturers, IDMs, and equipment manufacturers can all work toward an understanding of the complex nature of filtration, ultimately yielding a new, low defectivity regime at the smallest pattern sizes.
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A new method for rating retention in lithography process filters has been developed. The method employs a gold
nanoparticle contaminant challenge, inductively coupled plasma mass spectrometry as a concentration detector, and
dynamic light scattering as a particle size detector, all of which enable accurate, reliable filter retention rating below 30
nm. There is good agreement between results obtained with the new method and results obtained with a conventional
polystyrene latex bead challenge. A filter that was rated at 10 nm using extrapolative methods was confirmed to be 10
nm using the new challenge test. Microbridge removal efficiency of polyethylene filters rated by the new method was
studied in a 193 nm (dry) lithography process and the new method was verified. When applied to commercially available filters that are rated below 30 nm, the new method revealed significant differences in removal efficiency among similarly labeled filters.
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It has become clear that although line edge roughness and resolution are important for future lithographic technology
nodes, other issues such as pattern collapse must be addressed as well. One of the primary modes of pattern collapse is
pattern collapse caused by loss of adhesion of the resist from the substrate. The main forces which govern pattern
collapse by adhesion failure are related to substrate/resist interactions. Though several methodologies to improve pattern
collapse have been investigated, such as the use of surfactants during the final rinse, the use of such methods virtually all
suffer from some serious drawback. To this end, we have developed a reactive surface modifier capable of covalently
attaching to a positive tone resists containing hydroxystyrene groups. A vinyl-ether-modified silane was prepared and
effectively applied using a solution silanization reaction. A hydroxystyrene-based positive tone copolymer resist was
applied and subjected to a post apply bake to allow sufficient time for reaction with the surface modifier to occur prior to
patterning using e-beam lithography. Ultimately, it was determined that covalent attachment of the surface modifier to
the photoresist during the post apply bake resulted in enhanced resist/substrate adhesion of photoresist lines as evidenced
by improved pattern collapse performance in high resolution imaging experiments.
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As integrated circuit fabrication continues to advance towards the 32 nm node and below, it has become increasingly
apparent that the use of ultrathin films and polymer features will be required. Though it has been widely accepted that
the properties of polymers on the nanoscale can differ significantly from their bulk counterparts, the extent of such
deviation is the subject of much debate and concern. Furthermore, most studies have focused on elucidating the
differences in the thermal properties of micro- and nano-scale polymer films as determining the mechanical properties of
ultrathin films can be somewhat cumbersome. In order to study the modulus of polymer thin films we have implemented
a thin film buckling technique wherein a polymer film is floated onto a pre-strained PDMS substrate. Release of the
strain, results in the buckling of the polymer film and provides the opportunity to accurately determine the modulus of
polymer thin films with thicknesses down to 20 nm. This thin film buckling strategy was also used to probe the effect of
thickness on the modulus of the ESCAP-1 thin films. Finally, a reactive rinse method was employed whereby the hydroxyl functional groups of the resist were cross-linked via a dicarboxylic acid using carbodiimide chemistry as a potential method to ultimately enhance lithographic patterning performance. The effect of the reactive rinse on the modulus of the ESCAP-1 thin films was analyzed and it was found that the application of the reactive rinse resulted in a clear increase in the modulus of the polymer films. Also, quartz crystal microbalance (QCM) supporting the confinement of the crosslinking agents to the surface will be discussed.
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Non-conventional chemically amplified (CA) resist was designed. Photo-induced thiol/ene radical reaction
was used to insolubilize the resist based on multifunctional thiol and poly(4-hydroxystyrene) (PHS) derivatives.
Hydroxy groups of PHS were modified with allyl or propargyl moiety. Dissolution property of the
modified-PHS in TMAHaq solution was affected by the modification degree. Resist was prepared by mixing
the modified-PHS, multifunctional thiol compound, and photoradical generator. Photosensitivity of the resist
was studied at 254 and 13.5 nm. The sensitivity was strongly affected by the modification degree of PHS,
molecular weight of PHS, molecular weight distribution of PHS, amounts of thiol compound and photoradical generator added. It was found that the present resist system was highly sensitive to EUV exposure.
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In chemically amplified resists for extreme ultraviolet (EUV) and electron beam (EB) lithographies, the reaction
mechanism of acid generation is different from that for photolithography. However, details of acid generation are still
unclear. In particularly, details of the deprotonation dynamics of radical cations in solid resist films have not been
investigated. The dynamics of radical cations of resist polymer is important for understanding proton generation.
Poly(4-hydroxystyrene) (PHS) is a typical polymer for EUV and EB lithographies. We observed the dynamics of PHS radical cation in PHS film by using pulse radiolysis.
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Extreme ultraviolet (EUV) lithography is the most favorable process for high volume manufacturing of semiconductor
devices at 22nm half-pitch and below. Many efforts have revealed that the phenolic hydroxyl groups of polymers are
also an effective proton source in acid generation in EUV resists, and the effective proton generation and the control of
the generated acid diffusion are required to improve the breakthrough of the resolution - line width roughness -
sensitivity (RLS) trade-off. To clarify the lithographic performance of these derivatives, we synthesized the acrylic
terpolymers containing phenolic and alcoholic hydroxyl derivatives as model photopolymers and exposed the resist
samples based on these polymers to EUV and electron beam (EB) radiation. On the basis of the lithographic performances of these resist samples, we evaluated the characteristics of phenolic and alcoholic derivatives upon exposure to EUV radiation. We discuss the relationship between the chemical structures of these derivatives and lithographic performance.
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Molecular resists are of increasing interest as a route to improving the resolution - line width roughness - sensitivity
trade-off of resists for next generation lithography. We have previously presented a three component fullerene derivative
based negative tone chemically amplified resist capable of ~12 nm sparse feature size, ~20 nm half pitch, sub 5 nm line
width roughness, sub 10 μC/cm2 sensitivity, and high etch durability with electron beam lithography. In order to further
improve the performance of the resist we have studied the use of acid quenchers on the performance of the resist. We
evaluated six quenching additives including five base additives and a triphenylsulfonium photoacid generator that also
shows a quenching effect. The sensitivity and resolution of the resist were evaluated as the proportion of the quencher
was varied with respect to the other resist components. Certain quenchers were seen to strongly suppress the sensitivity
of the resist, even at low concentrations, whilst an amide base actually enhanced the sensitivity at the cost of resolution.
Improvements over the previous best feature width and half pitch were not achieved, but it was possible to reduce the effects of beam defocusing on sidewall angle indicating an improvement in contrast for certain additives.
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Fundamental studies on polymer bounded PAG and polymer - PAG blend type were carried out with the viewpoint of
dissolution property, lithographic performance, and blur. These materials were prepared to be able to directly compare
and to discuss the difference between blend and bounded PAG, with different PAG loading amount. Dissolution
property revealed the clear difference of these materials tendency to the PAG loading amount variation. Lithographic
performance difference corresponds to the dissolution property difference, and there found the strategy to improve
lithographic performance with polymer bounded PAG type resist. Blur study suggests the advantage in polymer bounded PAG in resolution.
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Vertical distribution of photo acid generator (PAG) inside CA-type photoresist is inferred from X-ray reflectivity (XRR)
analysis which gives the information on the vertical electron density profile of thin film. The difference between the
density distribution of normal photoresist and pure resin indicates the approximate distribution of PAG. The electron
density profile of each film is obtained by fitting method for the XRR results based on distorted wave Born
approximation (DWBA) approach. In this study, trends in density distributions varied by concentration of PAG suggest that the inhomogeneous distributions of PAG near the surface or interface of photoresist film occurs due to interactions between PAG molecules and substrate, or polymer resin. Distributions with low concentration of PAG (2 wt%) show that the PAG molecules tend to be concentrated near the surface of photoresist, while over-load of PAG (20 wt%) results in the density increase near the interface region.
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Process parameter influence in resist process with negative tone development (NTD) to pattern size (CD), CD
uniformity (CUD), and defectivity are studied to estimate the impact for process stability in high volume manufacturing
(HVM) of semiconductor devices. Since double exposure process is one of the candidates in contact hole patterning,
exposure to exposure delay was studied. There is a possibility to design the off-line system with NTD process,
therefore, exposure - PEB delay and PEB - development delay were studied. As basic development parameter studies, development time, developer temperature, developer volume, and rinse time dependency on CD, CDU, and defectivity were investigated.
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Double patterning process with ArF immersion lithography has been developed as one of the most promising candidate
for hp32 node and beyond. However the complicated process flow and cost of ownership are the critical issue for this
process. LELE (Litho-Etch-Litho-Etch) is the one of the standard process, but in order to reduce the process and cost,
that LPLE(Litho-Process-Litho-Etch) process have been investigated as the alternative process. In these processes,
organic Bottom-Anti-Reflective Coating (BARC) is used two times with same film in both 1st Litho and 2nd lithography
process. In 2nd lithography process, resist pattern will be printed at space area where exposed and developed in 1st
lithography process. Therefore, organic BARC needs to have process stability in photo and development step to keep
good litho performance between 1st and 2nd lithography in LPLE process.
This paper describes the process impact of 1st exposure and development for organic BARC, and the LPLE
performance with optimized organic BARC will be discussed.
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Contact hole patterning is more difficult than line/space patterning as mask error factor is higher in contact hole
patterning which has 2-dimensional patterns. As the industry moves towards 40nm node and beyond, the challenges
associated with contact hole having a manufacturable process window have become increasingly difficult. Current
1.35NA ArF lithography is capable of printing 50nm contact hole with a stable process window at best. Conventional
contact hole patterning processes such as resist reflow and RELACS are no longer able to be used for half-pitch 40nm
contact hole pattern because we have to shrink not only hole diameter but also pattern pitch. In this paper, we will
demonstrate and compare the patterning performance of the mesh patterning processes including litho-etch-litho-etch, cap freezing and self freezing process.
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Although numerical aperture (NA) has been significantly improved to 1.35 by the introduction of water-bases
immersion 193-nm exposure tools, the realistic minimum feature size is still limited to 40 nm even with the help of
robust resolution enhancement techniques (RETs). Double patterning processes are techniques that can be used for
fabricating etching mask patterns for 32-nm nodes and possibly for 22-nm nodes as well. Although several double
patterning processes have been introduced such as LELE[1], LLE[2] and the self-aligned spacer process, LELE and
LLE suffer from the need for high overlay accuracy. The self-aligned spacer process[3], meanwhile, has drawn much
attention as an effective means of forming repetitive patterns easily. This paper presents results of innovative
experiments on the fabrication of 22-nm node patterns by the DP spacer process.
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Numerical aperture (NA) has been significantly improved to 1.35 by the introduction of water-based immersion
193-nm exposure tools, but the realistic minimum feature size is still limited to 40 nm even with the help of robust
resolution enhancement techniques (RETs). Double patterning processes are techniques that can be used for
fabricating etching mask patterns for 32-nm nodes and possibly for 22-nm nodes as well, but the aspect ratio of
such etching mask patterns have been reduced with scaling. At the same time, dramatic improvements in the
etching durability of photo resist have not been made. This paper introduces a robust pattern-slimming process that
maintains pattern height.
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Double patterning is one of the enabling techniques to allow for further shrinking of
devices in the future. Many different solutions, like LELE (Litho-Etch-Litho-Etch) and
LPL (Litho-Process-Litho), have been investigated in the past years. In this paper a simplified - "Litho-Cluster-Only" - solution for double patterning is presented. This topcoat-less thermal freeze process has high capability of reaching 26 nm 1:1 LS. In addition it is shown that defect counts for the thermal freeze process approach defect numbers for high end immersion processes.
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Double patterning techniques are one of the dominant method to achieve the 32 nm node and beyond and Litho-Litho-
Etch (LLE) process is a strong candidate for double patterning method. Contact hole resolution is limited by the low
image contrast using dark field masks. Cross-line contact hole process using LLE process is applicable to image fined
contact holes. Contact hole patterns are formed by first line and space patterns and orthogonal second line and space
patterns. Furthermore LLE process flow should be simple as possible as it can for cost reduction. Thus LLE process
without freezing process is ideal one.
In this paper, we examine the process performance using latest material for freezing free LLE process, exposure tool
and novel coater/developer system. The latest resist materials can form cross-line contact hole with good pattern fidelity
and CD uniformity. It will be shown that novel coater/developer hardware is effective on enhancement of lithography
performance like CD control and defect control toward double Patterning technology for 193-nm immersion lithography.
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The implementation of double patterning processes in 193 immersion lithography is moving forward. The industry is
examining several methods of producing robust double pattern images. These methods include thermal cure resists and
the use of a spin on chemical to cure the layer 1 resist image. Thermal cure resist systems require fewer processing steps
than a chemical curing process. An effective thermal cure process improves process throughput, reduces chemical costs
and reduces process complexity In either case, producing wafers with adequate CD Uniformity (CDU) relies on the
ability of the layer 1 resist to remain inert during subsequent processing steps.
The goal of this paper is to isolate and optimize the critical processing steps using thermal cured resists in order to
improve CDU. The system includes a layer 1 thermal cured resist and a traditional layer 2 resist. Processing was done
using a TEL Lithius I+ and an ASML XT Twinscan 1900i. The feature of interest is a 42 nm x-Hatch contact hole
produced by horizontal lines exposed with layer 1 and vertical lines exposed with layer 2.
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We present a simple reaction rate analysis of lithographic patterning using the Non-Reciprocal Photo Base Generation
(NRPBG) scheme of Bristol (Bristol, et. al., to be published in Proceedings of the SPIE - The International Society for
Optical Engineering, 2010, presentation 7639-4). Multistep reaction kinetics simulations demonstrate that the NRPBG
scheme produces clear pitch division upon 193 nm double-exposure, over a range of photochemical reaction rate
constants.
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Materials and processes for double patterning using 193nm immersion lithography has been developing for the 32/22
nm node device generations. As for double patterning , some patterning methods such as LELE (Litho Etch Litho Etch)
process and LFLE (Litho Freeze Litho Etch) process have already been reported. LELE process is complicated and is a
low throughput process compared to LFLE process. On the other hand, freezing process and freezing material are needed
in LFLE process. Contact hole (C/H) and trench pattern resolution are limited by low aerial image contrast. Then, we
examined the process and the material that was able to form a minute pattern without increasing the number of processes
as much as possible. So image reverse process has one of technique to form the fine hole pattern and trench pattern. The
pillar pattern is obtained by the X-Y double line exposures. Then, the reverse material is applied on the pillar pattern and
the subsequent process (dry etching or wet etching process) converts the pillar pattern into a hole pattern. In this paper,
we studied the reverse process and materials. Methyl isobutyl carbinol (MIBC) was selected as a slovent for the Si
contained reverse material. MIBC solvent system has no damege for PR film and pattern. Plannarizaion of reverse material is important for image reverse and pattern transfer.
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This study reports on post develop defect on TC-less immersion resist system. There are major defects on TC-less resist
system, for example micro-Bridging, Blob and pattern collapse defect, as is well known. Among these defect, we
reported Blob and pattern collapse defect could be reduced by Acid rinse involving CO2. However, we also reported
there was the difference in the effect for each resist.
In this work, we show the great effective and slight effective case for post develop defect and we discuss the cause of
difference in acid rinse effect. We evaluated and confirmed the effect on each resist, pattern, exposed area location,
develop process and so on. Furthermore, we made a mechanism of defect appearing based on the analysis of defect
components and the measurement of resist surface condition for each develop process.
Finally we show the novel approach to post develop defect reduction on TC-less immersion resist system.
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A topcoat material plays a significant role in achieving technology nodes below 45 nm via ArF immersion lithography.
Switching the exposure medium between the lens and the photoresist (PR) film from gas (air, n=1) to liquid (H2O,
n=1.44) may lead to leaching of the polymer, the photoacid generator (PAG), or the solvent. These substances can
contaminate the lens or cause bubbles, which can lead to defects during the patterning. Previously reported topcoat
materials mainly use hydrophobic fluoro-compounds and carboxylic acids to provide high dissolution rates (DR) to basic
developers as well as high receding contact angles (RCA). Recently, the demand for a new top-coat material has risen
since current materials cause water-mark defects and decreases in scan speeds, due to insufficient RCA's. However,
RCA and DR are in a trade-off relationship as an increase in RCA generally results in a lower DR. To overcome this, a
novel polymer with high-fluorine content was synthesized to produce a topcoat material with improved DR (120 nm/s in 2.38 wt% TMAH) and RCA (>70°). In addition, a strategy to control the pattern profile according to needs of customers was found.
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This work is the summary of improvements in processing capability implemented and tested on the LITHIUS ProTM -i /
TWINSCANTM XT:1950Hi litho cluster installed at ASML's development clean room at Veldhoven, the Netherlands.
Process performance with regards to CD uniformity (CDU) and defectivity are investigated to confirm adherence to
ITRS roadmaps specifications. Specifically, imaging capabilities are tested for 40nm line 80nm pitch with the new
bake plate hardware for below hp 3Xnm generation. For defectivity, the combination of Coater/Developer defect
reduction hardware with the novel immersion hood design will be tested.
For CDU improvements, the enhanced Post Exposure Bake (PEB) plate hardware was verified versus performance of the
previous technology plate. Additionally, after the PEB improvement, a remaining across wafer signature was reduced
with an optimized develop process. The total CDU budget was analyzed and compared to previous results. Finally the
optimized process was applied to a non top coat resist process. For defectivity improvements, the effectiveness of
ASML's new immersion hood and TEL's defect reduction hardware were evaluated. The new immersion hood
performance was optimal on very hydrophobic materials, which requires optimization of the track hardware and process.
The high contact angle materials could be shown to be successfully processed by using TEL's Advanced Defect
Reduction (ADR) for residues related to the high contact angle and optimized bevel cut strategy with new bevel rinse hardware. Finally all the optimized processes were combined to obtain defect counts on a highly hydrophobic resist well within manufacturing specifications.
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ArF immersion lithography has been introduced in mass production of 55nm node devices and beyond as the post ArF
dry lithography. Due to the existence of water between the resist film and lens, we have many concerns such as leaching
of PAG and quencher from resist film into immersion water, resist film swelling by water, keeping water in the
immersion hood to avoid water droplets coming in contact with the wafer, and so on. We have applied to the ArF dry
resist process an immersion topcoat (TC) process in order to ensure the hydrophobic property as well as one for
protecting the surface. We investigate the TC-less resist process with an aim to improve CoO, the yield and productivity
in mass production of immersion lithography.
In this paper, we will report TC-less resist process development for the contact layer of 40nm node logic devices. It is
important to control the resist surface condition to reduce pattern defects, in particular in the case of the contact layer.
We evaluated defectivity and lithography performance of TC-less resist with changing hydrophobicity before and after
development. Hydrophobicity of TC-less resist was controlled by changing additives with TC functions introduced into
conventional ArF dry resist. However, the hydrophobicity control was not sufficient to reduce the number of Blob
defects compared with the TC process. Therefore, we introduced Advanced Defect Reduction (ADR) rinse, which
was a new developer rinse technique that is effective against hydrophobic surfaces. We have realized Blob defect
reduction by hydrophobicity control and ADR rinse. Furthermore, we will report device performance, yield, and immersion defect data at 40nm node logic devices with TC-less resist process.
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The Back-side Surface Treatment ("BST") is a module that cleans the backside of a wafer just before a process on
the exposure system. To support immersion lithography, Tokyo Electron introduces a bevel cleaning function to
this module. This enables cleaning of both wafer backside and bevel section at the same time. We evaluate the new
BST module for wafer cleaning performance, wafer backside cleaning performance and wafer topside particle
control performance. The effectiveness of the BST module is tested in an actual production line. It is proved that the
introduction of the BST module reduces defocus and blocked images.
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Fluoroalcohol-containing materials have found considerable use in 193 nm immersion topcoat and topcoat-free
immersion resist materials due to their good water contact angles and base-dissolution properties.
Trifluoromethanesulfonamide-containing materials are another alternative which have been explored for use in 193 nm
photoresist and immersion topcoat applications; however, fluorosulfonamide materials have suffered from issues such as
low water contact angles. In this paper, we report the synthesis of a series of fluorosulfonamide-containing methacrylate materials with water contact angle and base dissolution performance that rivals or exceeds that of comparable fluoroalcohol-based materials.
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Developer-soluble bottom anti-reflective coating (DBARC) BSI.W09008 has provided promising lithography results
with five different 193-nm photoresists, with the accomplishments including 120-nm L/S (1:1) and 130-nm L/S
through-pitch (i.e., 1:1, 1:3, and isolated line). This DBARC is not inherently light sensitive and depends on diffusing
photoacid from the exposed photoresist for development. With undercutting being an issue for the PAG-less DBARC
with some resists, the shapes of 130-nm lines (both dense and isolated) were improved by either a) incorporating a small
amount of a base additive in the BSI.W09008 formulation or b) altering the structure of the DBARC's binder polymer.
With selected photoresist(s) and/or resist processing conditions, either photoacid diffusion or photoacid activity is
inadequate to give DBARC clearance and BSI.W09008 performs more as a dry BARC. The post-development residue
obtained from BSI.W09008 on a silicon substrate is much less dependent on the initial DBARC film thickness and the
exposure dose than for earlier-generation photosensitive (PS)-DBARC BSI.W07327A, using the same photoresist.
BSI.W09008 also gives less post-development residue than BSI.W07327A using the same resist on a silicon nitride
substrate at exposure doses of 14-25 mJ/cm2.
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In hyper NA immersion lithography which has over 1.0 numerical aperture (NA) exposure system, reflectivity control
between PR and substrate is key technique to overcome resolution limit. Trilayer resist process, which has two layers of
spin-on hard mask (SOH) composed of silicon and carbon, was introduced and applied to various generation of ArF
lithography from dry to immersion process. However, lack of adhesion between PR (hydrophobic) and Si-SOH
(hydrophilic) can cause pattern collapse problem. Moreover, PR profile was not easily adjusted to optimum shape
because some side reaction may be occurred at the interfacial layer between PR and Si-SOH. Herein, we studied how to
control interfacial side reaction between PR and Si-SOH layer in Trilayer process. We approached three conceptual
items: acidity control to PR, uniformity control of Si-SOH itself, and intermixing control of Si-SOH with PR. First, we
checked PR lifting margin with line and space pattern. Although vertical profile was obtained in contact pattern, it was
useless if line pattern was collapsed. With first screening tests, we made a conclusion that a major factor for side reaction
at interfacial layer was penetration of proton into Si-SOH layer produced exposed region. To solve that problem,
intermixing control of Si-SOH with PR was the best solution. We introduced network structure formation with Si-O-Si
bond by cross-linking catalyst. AFM and contact angle data showed improved surface morphology. We could obtain improved pattern profiles with several PR samples. This result can be optimized to various generations of ArF immersion lithography and further more.
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Developable BARCs (DBARCs) are useful for implant layers because they eliminate the plasma etch step avoiding
damage to the plasma sensitive layers during implantation. It is expected that DBARC will also be used for non-implant
layers and double exposure technology. AZ has pioneered DBARC based on photosensitive cleave as well as
crosslink/decrosslink mechanisms. In this paper, we focus on various processing factors for 193nm DBARC and discuss
the influences of prewet, thickness, topography and substrates on lithographic performance. Prewet of DBARC before
resist coating deteriorated performance, however, it was resolved by modifying DBARC formulations. The optimized
DBARC showed both optical and lithographic performance comparable to conventional BARCs. DBARCs minimized reflection from the substrates and notching of patterns was improved observed on silicon oxide topography. This paper includes simulation, DBARC contrast curve analyses, and recent dry and immersion exposure results of DBARC.
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Minimizing defects in spin-on lithography coatings requires a careful understanding of the interactions between the spin-on
coating material and the filtration and dispense system used on the coating track. A wet-developable bottom anti-reflective
coating (BARC) was examined for its interaction with polyamide and UPE media when utilizing the Entegris IntelliGen Mini dispense system. In addition, a new method of priming the filter and pump is described which improves
the wetting of the filter media, preventing bubbles and other defect-generating air pockets within the system. The goal is
to establish plumb-on procedures that are material and hardware specific to avoid any defect problems in the coating
process, as well as to gain a better understanding of the chemical and physical interactions that lead to coating defects.
Liquid particle counts from a laboratory-based filtration stand are compared with on-wafer defects from a commercial
coating track to establish a correlation and allow better prediction of product performance. This comparison in turn will
provide valuable insight to the engineering process of product filtration and bottling at the source.
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Dual damascene technique has been widely applied to IC device fabrication in copper interconnect
process. For traditional via-first dual damascene application, a fill material is first employed to fill via to protect
over-etching and punch-through of the bottom barrier layer during the trench-etch process. Etch-back process is then
applied to remove excess overfill thickness and maintain a greater planar topography. To get better CD control, a thin
organic BARC is finally coated to reduce reflectivity for trench patterning but not in this study. It is a multi-step and
costly dual damascene process. In this study, a new gap-filling BARC material with good via fill and light
absorption features was adopted to explore the via-first dual damascene process by skipping etch-back and BARC
coating steps. The results show not only the reduction of process cycle time and cost saving but also the CP yield
improvement based on data from pilot production of 0.11/0.13 μm logic device.
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We have developed negative-tone molecular resist based on C-4-cyclohexylphenylcalix[4]resorcinarene(MGR108) and positive-tone molecular resist based on protected C-4-isopropylphenylcalix[4]resorcinarene (MGR104P). Both MGR108 and MGR104P showed high solubility in both conventional resist solvents such as propylene glycol monomethyl ether and conventional alkaline developer of 0.26N TMAHaq. In this paper, we show current performance of resists by EB lithography (EBL) and EUV lithography (EUVL).
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As the semiconductor industry moves forward, resolution limits are being pushed to the sub-30 nm regime. In order to
meet these demands, radical new resist design and processes must be explored. We have developed a molecular glass
system for all-dry processing conditions. Physical vapor deposition (PVD) has been used for film formation onto silicon
wafers. PVD deposits a uniform film of controlled thickness free from impurities that are often introduced by casting
solvents used in traditional spin coating methods. Thermal development is used as an alternative to processing in
solvents in order to prevent resist swelling and pattern collapse by capillary forces. The deposited molecule is designed
to crosslink upon E-beam irradiation without additives, and therefore form a homogeneous, single component film.
PAG-attached molecular glasses have been synthesized in order to promote film homogeneity as well. By tethering PAG
directly to the molecular glass core, issues such as PAG aggregation can be remedied. Acid migration, which increases
blur and LER, can also be hindered.
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Recent years increasing attention has been given to molecular glass resist materials. In this paper, maleopimaric acid,
cycloaddition reaction product of rosin with maleic anhydride, was reacted with hydroxylamine and then further
esterified with 2-diazo-1-naphthoquinone-4-sulfonyl chloride to give N-hydroxy maleopimarimide sulfonate. The
carboxylic acid group of the compound was then protected by the reaction of this compound with vinyl ethyl ether or
dihydropyran. Thus obtained compounds were amorphous. When irradiated with i-line light, the 2,1,4-DNQ group
undergo photolysis not only to give off nitrogen gas but also generate sulfonic acid which can result in the decomposition of the acid labile group. So, a novel chemically amplified positive i-line molecular glass photoresists can be formed by the compound and other acidolytic molecular glass compounds. The lithographic performance of the resist materials is evaluated.
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A series of Adamantanephenol derivatives was synthesized from adamantinetriphenol /
adamantinetrimethylhydroquinone and vinylether compound. Solubility for resist solvent or alkali developer of those
materials and thermal properties were examined. Adamantanetrimethylhydroquinone cross-linked with divinylether
(AmHQ-CL) had excellent properties as positive tone resist material. We evaluated lithographic properties of AmHQ-CL
with photo acid generator and base. Line and space pattern was formed with EB exposure followed with post exposure
bake and alkali development. Pattern of smooth wall surface was obtained by removing high molecular weight
component from AmHQ-CL. Line width roughness (LWR) of the pattern AnHQ-CL nMWD was less than 30 nm. It was very small value compared with that of traditional polymer resist.
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Two different types of non-traditional molecular resists were synthesized and characterized. A positive-tone cross-linked
molecular resist was made that functions by first forming an etch resistant film via thermal cross-linking of vinyl ether
functionalized small molecules followed by patterning of the film via acid catalyzed cleavage of the resulting acetal
bonds. DPA-2VE, a single multi-functional molecular resist of this type, showed DUV sensitivity of 7 mJ/cm2 and a
contrast of 5.2 for development in either organic solvent or aqueous base. Using high resolution patterning with a 100
keV e-beam, it was possible to demonstrate feature resolutions down to 40 nm. When 0.26N TMAH was used as a
developer, the dose-to-size was 84 μC/cm2 with a 3σ LER of 14.2 nm. Using MIBK as a developer, the dose-to-size was 104 μC/cm2 and the 3σ LER was 7.4 nm. A series of non-chemically amplified molecular resists based on using 2-
nitrobenzyl ethers as photosensitive protecting groups were also made. One formulation showed a DUV sensitivity of 1 mJ/cm2, while another formulation which showed the best contrast of 8.3 obtained at a sensitivity of 10 mJ/cm2.
However, under 100 keV e-beam patterning, the 2-nitrobenzyl ether protected materials showed little to no response even up to 3000 μC/cm2.
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A three-dimensional kinetic Monte Carlo model has been developed to simulate design and processing effects on the line
edge roughness and patterning of photoresists. The model is capable of simulating most all of the important parameters
involved in resist processing from film formation and exposure to development. It can be used to examine the effect of
photoacid generator loading, photoacid diffusion, deprotection reaction, quencher loading, base diffusion, and acid/base
reactions, with the flexibility to add more physics as needed. The model is able to reproduce experimentally observed
trends of the effect of base loading on LER through all levels of base loading and the effect of reduced aerial image
contrast on the LER of resists. It also shows good agreement with experimental results on the effect of PAG loading
through around 20% PAG loading. The scaling factors for LER were also examined. It was found that the gradient in
polymer protection (dP/dx) provides a very good predictor for LER in some cases, but is insufficient for other conditions
when the dominant cause of LER changes such as non-uniformity along the line edge from things like PAG or polymer
aggregation.
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The examination of the roughness evolution of open-surface resist films during development may elucidate the material
origins of Line Edge Roughness. In this paper, a stochastic simulator of resist development is used and the surface
roughness evolution is analyzed with dynamic scaling theory. A power-law increase of rms roughness and correlation
length is found for resists with homogeneous solubility. The scaling exponents are shown to obey the dynamical scaling
hypothesis of Family-Viscek. The insertion of inhomogeneity in the solubility of resist causes much larger increase of rms roughness and anomalous scaling behaviour. Comparison with experimental results shows good agreement with the simulation predictions.
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Pattern doubling by cross-linking of a spacer triggered by residual acid diffusion from a previously developed
primary structure into the spacer is a possible option to create structure widths below the nominal resolution of
the optical process. An advantage of such a process step would be the self-alignment to the primary structure,
which would render a second exposure step unnecessary. Using macroscopic and stochastic modeling approaches, we demonstrate that it may be possible to control the width of the secondary structure created by cross-linking by the amount of quencher base added.
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Current minimum feature sizes in the microelectronics industry dictate that molecular interactions affect process fidelity
and produce stochastic excursions like line edge roughness (LER). The composition of future resists is still unknown at
this point, and so simulation of various resist platforms should provide useful information about resist design that
minimizes LER. In the past, researchers developed a mesoscale model for exploring representative 248 nm resist
systems through dynamic Monte Carlo methods and adaptation of critical ionization theory. This molecular modeling
uses fundamental interaction energies combined with a Metropolis algorithm to model the full lithographic process (spin
coat, PAB, exposure, PEB, and development). Application of this model to 193 nm platforms allows for comparison
between 248 and 193 nm resist systems based on molecular interactions. This paper discusses the fundamental
modifications involved in adapting the mesoscale model to a 193 nm platform and investigates how this new model
predicts well-understood lithographic phenomena including the relationship between LER and aerial image, the
relationship between LER and resist components, and the impact of non-uniform PAG distribution in the resist film.
Limited comparisons between the 193 nm system and an analogous 248 nm platform will be discussed.
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The concepts of dynamical scaling in the study of kinetic roughness are applied to the problem of photoresist development. Uniform, open-frame exposure and development of photoresist corresponds to the problem of quenched noise and the etching of random disordered media and is expected to fall in the Kadar-Parisi-Zhang (KPZ) universality class for the case of fast development. To verify this expectation, simulations of photoresist development in 1+1 and 2+1 dimensions were carried out with various amounts of random, uncorrelated noise added to an otherwise uniform development rate. The resulting roughness exponent α and the growth exponent β were found to match the KPZ values nearly exactly. The impact of the magnitude of the underlying development randomness on the values of these exponents was also determined and an empirical expression for predicting the kinetic roughness over a wide range of conditions is presented.
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Since the top-down approaches, such as the extremely ultraviolet (EUV) technique and the high-index fluid-based
immersion ArF lithography, may be cover one or two generations, these lithography technology are getting more severe
for the feature size scaling down to sub-10 nm. The directed self-assembly technology of block copolymers is one of the
candidates for next-generation lithography. The process simulation can help to solve the easy process, the low critical
dimension (CD) variation, the low edge roughness, the high throughput, and the low number density of pattern defects
for the directed self-assembly technology.
In this paper, a directed self-assembly lithography process of block copolymers is modeled and simulated in molecular
scale. The sub-10 nm patterns can be formed by using the precise pattern placement of conventional "top-down" lithography methods with the well-defined nanostructures and self-healing properties of "bottom-up" block copolymer self-assembly. For 35-nm pattern formation, simulation results are similar with experiment results.
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In the electron-beam lithography and extreme-ultraviolet lithography, electrons above ionization energy collide with
resist materials and bring out the ionization and electronic excitations of resist molecules. The energy degradation
mechanism of the incident primary electrons in resists plays the important role to determine the resist properties. The
Monte Carlo simulation using the binary-encounter-collision cross section was performed to determine the electron
trajectory in resist materials. The distributions of product species had an edge around 500 eV of incident energy of
primary electron. The product distributions of ions and singlets became the narrower in electronic excited states with decrease in incident energy and with increase of the electron generations. Main product of triplets was in the lowest excited state. Triplets had the longer scattering length than singlets and ions.
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Pattern collapse is becoming a critical issue as integrated circuit fabrication continues to advance towards the 32 nm
node and below. Though line edge roughness and resolution are certainly important in moving forward, pattern collapse
by both deformation and adhesion failure must be addressed. In this work, a post-development strategy to reduce pattern
collapse by bending was developed whereby the hydroxyl functional groups on the surface of the resist were crosslinked
via a dicarboxylic acid using carbodiimide chemistry. The pattern collapse of a hydroxystyrene-based, positive tone
resist was then studied before and after the application of the reactive rinse. SEM analysis of the samples showed that
application of the reactive rinse resulted in a clear increase in the printing capabilities of the resist, as the photoresist
lines could be printed with smaller space widths corresponding to higher stresses after the rinse treatment.
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Many recent publications have highlighted pattern density effects as a problem in both electron-beam and optical
lithography. These effects are manifested as a systematic variation in critical dimension as a function of position on the
wafer. It is becoming an increasing problem as the pattern density and diminishing critical dimensions are needed for
production nodes 32nm and beyond.
One potential source of pattern density effects is acid volatility, where acid is presumed to redeposit during exposure or
bake; here we refer to this effect as chemical flare. Another source of density effects is develop loading which refers to
the impact of local depletion of developer in highly exposed regions. Both develop loading and chemical flare can cause
deviations in feature size that may be difficult to correct for by adjustment of the exposure process.
Here we describe a method that allows the detrimental effects of chemical flare and develop loading to be separately characterized. The method makes use of arrays of 248 nm exposure sites and a controlled develop process within a custom liquid flowcell; this combination enables a systematic study of these effects.
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Measurements of the sidewall morphology of commercial resist lines (3D Line Edge Roughness) after lithography and
before etching by CD-AFM and SEM show that they exhibit anisotropy in the form of striations perpendicular to line
direction. When this anisotropy of post-litho resist sidewalls is included in the models for trimming and pattern transfer
proposed in [V. Constantoudis et al., Proc SPIE 7273, 72732J (2009)], then the models predict the beneficial role of
trimming process in LER reduction during pattern transfer in agreement with experimental results. Furthermore,
experimental and simulation studies show that the CD-AFM measurements of the 3D Line Width Roughness may overestimate the correlation length. Taking into account this finding in the model for trimming, we found that model predictions approach further the experimental results.
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We propose novel inactivation technologies which improve resolution. Base generators have been developed, which
inactivate acid by thermal treatment or exposure. This thermal inactivation technology realizes simple
litho-inactivation-litho-etch (LILE) process with good fidelity. After 1st patterning, acid is inactivated by amine released
from the thermal base generator under low temperature baking of less than 150°C. Just adding one simple low
temperature bake process, LILE has two advantages; i) keeping high throughput, and ii) avoidance of pattern
deformation. 32nm line and space (l&s) pattern is successfully delineated. The inactivation technology has been
expanded to frequency doubling patterning. Photo base generator (PBG) is used to inactivate acid generated by exposure.
Acid concentration in both of low and high exposed area is precisely controlled by base generation efficiency of PBG.
The dual tone resist successfully delineates 32.5nm l&s pattern using 65nm l&s mask patterns with single exposure.
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Double patterning with 193nm immersion lithography becomes to most promising candidate for 32nm half pitch node
and possibly below 32nm half pitch. Several double patterning methods have been suggested such as LELE (Litho-Etch
-Litho-Etch), LLE (Litho-Litho-Etch) and Spacer defined process, however, LLE process is pointed out as low cost
double patterning technique because of its simplicity. But LLE process needs new method to maintain 1st lithography
pattern and additional freezing processes have been suggested
In SPIE Advanced Lithography 2009, freezing free "Posi/Posi" process was introduced as candidate for LLE process.
This is LLE process that uses two different positive tone photoresists without freezing process. The resist for 2nd
lithography contains a specific solvent to prevent the mixing of two resists and there is an activation energy gap
between 1st and 2nd resists to maintain 1st lithography pattern. The double patterning can be successfully processed by
these specific resists without freezing process.
In this study, the performance of this freezing free "Posi/Posi" process is investigated for pitch splitting pattern using
1.35 NA exposure tool. The imaging results including CD control capability, and etching results are collected for 32nm
half pitch and below. Additionally the two-dimensional pattern imaging is also obtained for 76nm minimum pitch.
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To extend immersion based lithography to below 32nm half pitch, the implementation of Double-Patterning
lithography requires that cost be contained by as many means possible. In addition to CDU and defectivity, simplifying
the process flow is a viable approach to helping accomplish cost containment. For Litho-Litho-Etch processes, this
entails replacing the flows that require spin-on chemical freeze with a solely thermally cured resist approach, thereby
eliminating materials and several process steps from the flow. As part of ongoing efforts to allow Double-Patterning
techniques to further scale semiconductor devices, we use DETO (Double-Expose-Track-Optimized) methods for producing pitch-split patterns capable of supporting 16 and 11-nm node semiconductor devices. In this paper we present the assessment from a series of thermal cure double-patterning resist systems; with a focus on process latitude, CDU, and resolution limit.
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Lithographic scaling beyond the 22 nm node requires double patterning techniques to achieve
pitch values below 80nm. The semiconductor industry is focusing on the development of several process
techniques including track-only lithographic processing methods in order to reduce cost, cycle time and
defects. Initial efforts for track-only double expose processes have relied on the use of chemical freeze
materials to prevent inter-mixing of resists, and also by means of thermal curable materials. These two
techniques may be complementary, in the sense that a chemical freeze may be very robust for protection of
exposed regions, while thermal cure systems may provide strong protection of large unexposed areas.
We will describe our results with mainly the thermal-cure double patterning resist materials, and
the application of these materials to the fabrication of sub-80 nm pitch semiconductor structures. We will summarize the process window and defect capability of these materials, for both line/space and via applications.
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Double patterning is one of the most promising techniques for sub-30nm half pitch device manufacturing. Several
techniques such as dual-trench process (litho-etch-litho-etch: LELE) and dual-line process (litho-litho-etch : LLE) have
been reported. Between them, the dual-line process attracts a great deal of attention due to its higher throughput. The key
issue in the dual-line process is preventing damage of the first resist pattern during the second lithography process. As a
solution, we have developed a process to alleviate this issue using a chemical material called "freezing agent." More
recently, we have further simplified the process by developing a simple freezing technique called "self-freezing" or
"thermal-freezing." The "self-freezing resist" material can accomplish the freezing process by applying only one bake to
the resulting first pattern. In addition, our self-freezing resist also has added water shedding properties to meet non-topcoat
(non-TC) immersion resist requirements, which further simplifies the process and materials.
In this study, imaging results of Non-TC self-freezing resist including critical dimension uniformity, defectivity and
processing properties of the resulting patterns is shown.
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Litho-Etch-Litho-Etch double patterning requires aggressive shrink of each sub-pattern's critical dimensions
to enable inter-digitation and pitch doubling. Application of this double patterning technique to elliptical contacts
introduces a new constraint to the CD shrink processes as controlling the 2-D aspect ratio of elliptical contacts is critical
for both device performance and yield. The impact of a track-applied chemical shrink and reactive ion etch [RIE] shrink
processes to pre/post RIE 2-D aspect ratios [2-D AR] have been evaluated. A methodology for controlling 2-D aspect
ratios with an aggressive CD shrink target is described using a 2:1 aspect ratio test pattern resulting in the successful
fabrication of 2:1 aspect ratio bottom CD contacts with 65% bias from the lithographic CD.
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In this paper a previously developed Line Width Roughness (LWR) analysis techniques is used to characterize postlitho
process LWR reduction methods in the frequency domain.
Post-litho processes are likely to be required to reach the ITRS 3σLWR target for the 32nm and 22nm half pitch
technological node. The aim of these lithographic processes is to mitigate the roughness of the resist and ultimately the etched patterns without a dramatic change in Critical Dimensions (CD). Various techniques are discussed: in-track
chemical processes, ion beam sputtering, thermal and plasma treatments as dedicated etch-step. Each technique manifests
a characteristic smoothing in the frequency domain reducing the LWR up to 35%. Exploiting LWR reduction at the different frequencies, and combining these techniques, our target is to determine whether 50% overall LWR reduction is feasible.
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In this paper, a stochastic modeling approach is used to predict the results of the exposure
and post-exposure bake of a chemically amplified photoresist. The statistics of photon shot
noise, chemical concentration, exposure, reaction-diffusion, and amplification are derived.
The result, though preliminary, is a prediction of the standard deviation of the final deprotection level of polymer molecules in the resist using simple, analytical expressions. Combining this result with ongoing work to characterize the stochastics of resist development will eventually lead to a full model of the line-edge roughness of a resist feature. The current model is used to elucidate the impact of acid diffusion on line-edge roughness.
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To study the line edge roughness, we developed the simulation method of formation process of line edge based on the
meso-scale simulation of dissipative particle dynamics (DPD) method. We modeled the development and rinse processes
based on the coarse-grained polymer model. It is important that the block copolymer in which the soluble and insoluble
blocks are bonded exists at the line edge. Though the soluble part of this block copolymer is stretched out in the developing process, it becomes shrunk in the rinse process. The shrunk polymers contribute to the formation of line edge, and LER was much influenced by these polymers. These simulations will represent the formation process of line edge based on the polymer chain dynamics.
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A lattice-type Monte Carlo based mesoscale model and simulation of the lithography process has been described
previously [1]. The model includes the spin coating, post apply bake, exposure, post exposure bake and development
steps. This simulation has been adapted to study the insoluble particle generation that arises from statistically
improbable events. These events occur when there is a connected pathway of soluble material that envelops a volume of
insoluble material due to fluctuations in the deprotection profile that occur during the post exposure bake [2].
Development erodes the insoluble material into the developer stream as an insoluble particle. This process may produce
a cavity on the line edge that can be far larger than a single polymer molecule. The insoluble particles generated may
coalesce in developer to form large aggregates of insoluble material that ultimately deposit on the wafer surface and the
tooling. The recent modifications made in mesoscale models for the PEB and dissolution steps, which have enabled this
study are briefly described. An algorithm that was used for particle detection in the current study is also discussed. The
effect of the resist formulation and the different lithographic steps, namely, exposure, post exposure bake and
development, on the extent of particle generation is analyzed. These simulations can be used to set process variables to
minimize the extent of particle generation.
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A recently developed stochastic resist model, implemented in the PROLITH X3.1 lithography
simulation tool, is fitted to experimental data for a commercially available immersion ArF photoresist, EPIC
2013 (Dow Electronic Materials). Calibration is performed using the mean CD and LWR values through
focus and dose for three line/space features of varying pitch (dense, semi-dense and isolated). An unweighted
Root Mean Squared Error (RMSE) of approximately 1.6 nm is observed when the calibrated model is
compared to the experimental data. Although the model is calibrated only to mean CD and LWR values, it is
able to accurately predict highly accurate CDU distributions at fixed focus and dose conditions for 1D and 2D
(line end shortening) pattern. It is also shown how the stochastic model can be used to describe the bridging
behavior often observed at marginal focus and exposure conditions.
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Anti-reflection coatings are commonly used in advanced photolithography in order to minimize CD
variability caused by deviations in resist thickness and in the films and structures comprising the
substrate. For a planar film stack, reflectivity calculations are a critical tool for optimization of
parameters such as coating thicknesses and optical properties of anti-reflection coatings (TARCs and
BARCs). However, with the exception of the first lithography layer, all layers on a production wafer
have some degree of topography, so that reflectivity calculations for a planar film stack are not
strictly correct. In this study, we evaluate three different reflectivity metrics that can be applied to
wafers with topography: reflectivity for simplified planar film stacks, standing wave amplitude, and
reflected diffraction efficiencies. Each of these metrics has a simple, physical meaning that will be described in detail in the presentation. We then evaluate how well these reflectivity metrics correlate with CD variability for two different example lithography steps: implant layers with STI (where a developable BARC might be used), and Litho-Etch-Litho-Etch style double patterning.
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Chemically Amplified resists are complex systems. If the main mechanisms implied have already been described, the
challenge to even better control and model these formulations remains important as performance requirements become
more and more stringent and critical dimensions get smaller and smaller. This paper tries to assess and deconvolute some
of the main potential mechanisms involved during the process of a 193 nm chemically amplified resist, before correlating
them with the final lithographic results obtained.
A formulation was selected in order to offer a large range of film physical properties, thus allowing the resist film to switch from non-annealing to annealing conditions. The use of thermal analysis as the main characterization technique allowed correlation between the variations in physico-chemical properties and process conditions. This investigation also included a study of the behavior of some additives during bake steps. In so doing, it became possible to correlate the variations of the resist properties under different bake conditions to the changes in its final lithographic performance, i.e. contrast, sensitivity and line edge roughness.
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In recent years ArF immersion lithography in memory devices, topcoat process has become baseline process in mass
production in spite of its additional process steps and high cost-of-ownership. In order to overcome low process
efficiency of topcoat process, high throughput scanner with higher scan speed and advanced rinse modules for
decreasing defectivity are under development. Topcoat-less resist is also upgraded gradually which contains
hydrophobic additives enables the extreme patterning without topcoat and high speed scanning. But current topcoat-less
process has not matured yet for the dark-field mask compared to bright-field because of the blob defect in unexposed area. To minimizing blob defect level both material and process sequence should be optimized effectively. The authors have focused on blob defect and litho performance of topcoat-less resist process for dark field application in 2Xnm node devices.
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