Extreme ultraviolet lithography (EUVL) technology continues to progress and remains a viable candidate for next generation lithography1, which drives the need for EUV resists capable of high resolution with high sensitivity and low LWR. While chemically amplified resists (CARs) have demonstrated the ability to pattern 12nm half-pitch features2, pattern collapse continues to limit their ultimate resolution. We have taken multiple approaches to extend resist capabilities past these limits. Recent results in pattern collapse mitigation using a resist encapsulation and etch back strategy will be discussed. We continue to investigate EUV patterning of semi-inorganic resists to simultaneously increase EUV photon absorption and extend mechanical strength beyond CAR capabilities. The limitations of metal oxide-based nanoparticle photoresists have been investigated, and have provided key insights to further understanding the mechanism of this class of materials.
Recently, both PSI<sup>1</sup> and ASML<sup>2</sup> illustrated champion EUVL resolution using slow, non-chemically amplified inorganic resists. However, the requirements for EUVL manufacturing require simultaneous delivery of high resolution, good
sensitivity, and low line edge/width roughness (LER/LWR) on commercial grade hardware. As a result, we believe that
new classes of materials should be explored and understood. This paper focuses on our efforts to assess metal oxide based
nanoparticles as novel EUV resists<sup>3</sup>. Various spectroscopic techniques were used to probe the patterning
mechanism of these materials. EUV exposure data is presented to investigate the feasibility of employing inorganic
materials as viable EUV resists.
One of the key challenges to high resolution resist patterning is pattern collapse. Using a new scanning probe microscopy (SPM), Peak Force<sup>TM</sup> tapping, we map nano-mechanical properties-- modulus, adhesion, and dissipation-- of the exposed/developed resist structures with sub-10 nm resolution. Properties are compared across a carbon based negative resist with and without cross-linking. The SPM technique reveals that cross-linking significantly enhances the mechanical properties to give a champion resolution of sub 20 nm half-pitch in a chemically amplified negative resist system. Beyond mechanical properties, surface morphology and redistribution kinetics were examined using complementary techniques and reveal additional benefits with cross-linking.
Here, we report the highest recorded resolution for a negative-tone, carbon-based, chemically amplified (CA) resist of 20 nm half-pitch (HP) using both E-beam and EUV exposure systems. The new chemistry incorporates variable amounts of oxetane (0, 5, 10 and 20%) cross-linker into a base of Noria-MAd (methyl-admantane) molecular resist. Cross-linkable resists showed simultaneous improvements in surface energy, structural integrity, and swelling to ensure collapse free 20nm HP patterns and line-edge roughness (LER) down to 2.3 nm. EUV exposed Noria-Ox (5%) cross-linked resist patterns demonstrated 5 times improvement in Z-factor (for 24 nm HP) over Noria-MAd alone.
Modern high-resolution lithography, which employs a chemically amplified resist (CAR) at either 193 or 13.5 nm wavelength, is often limited by pattern collapse. While the general concepts of how CAR platforms work are widely understood, the influence of composition on pattern collapse has been studied to a lesser extent. In addition, the subject is often further complicated by non-disclosure of the resist chemistry used in the lithographic evaluation. Open-source photoresist platforms can be beneficial for fundamental studies on how individual components influence pattern collapse. Such platforms should mimic a typical CAR, containing-apart from the polymer-additional components such as photo acid generators (PAGs) and base quenchers. Here, 193 nm and extreme ultraviolet lithography open-source platforms are presented wherein the chemistry, composition, and concentration are all disclosed. With the aim of fundamentally understand how resist composition and behavior influences pattern collapse, the molecular weight of the polymer backbone and the concentration of both PAG and base quencher were varied. These sets of resists were exposed using high-end optical lithography scanners. The results are presented such that the probability of pattern collapse is derived as a function of the exposure wavelength, chemistry, and component concentrations.
Modern high-resolution lithography, which employs a chemically amplified resist (CAR) at either 193 or 13.5 nm
wavelength, is often limited by pattern collapse. While the general concepts of how CAR platforms work are widely
understood, the influence of composition on pattern collapse has been studied to a lesser extent. In addition, the subject
is often further complicated by non-disclosure of the resist chemistry used in the lithographic evaluation. Open-source
photoresist platforms can be beneficial for fundamental studies on how individual components influence pattern collapse.
Such platforms should mimic a typical CAR, containing - apart from the polymer - additional components such as photo
acid generators (PAGs) and base quenchers. In this paper, 193 nm and EUVL open-source platforms are presented
wherein the chemistry, composition, and concentration are all disclosed. With the aim to fundamentally understand how
resist composition and behavior influences pattern collapse, the molecular weight of the polymer backbone and the
concentration of both PAG and base quencher were varied. These sets of resists were exposed using both high-end
optical lithography scanners. The results are presented such that the probability of pattern collapse is derived as a
function of the exposure wavelength, chemistry, and component concentrations.
Current work in lithographic patterning has been carried out using 193 nm excitation sources, limiting the pitch division
to approximately λ/2 and, thus, the advancement of Moore's law. Recently, double patterning has emerged as a potential
extension of 193 nm techniques as two lines can be patterned in one exposure. In this contribution, the double patterning
features of single component carbamate photoacid/photobase generators (PAG/PBG) are examined. At lower exposure
doses, sulfonic acid is generated, while at higher doses, a photochemical rearrangement is initiated to activate the PBG.
Optimally, at intermediate doses, photoacid and photobase components can exist concurrently resulting in the desired
dual tone lithographic features. The energy required to initiate dual tone behavior can be tailored through co-added
amine quenchers and carbamate concentration. Using ellipsometry, the energy required for the resists to have the first
sign of photoacid generation (film dissolution), E<sub>0</sub>, and at the energy required for photobase activation (E<sub>n</sub>) were
determined, as this value dictates the ability to achieve the desired pitch division.
Pitch division lithography (PDL) with a photobase generator (PBG) allows printing of grating images with twice
the pitch of a mask. The proof-of-concept has been published in the previous paper and demonstrated by
others. Forty five nm half-pitch (HP) patterns were produced using a 90nm HP mask, but the image had line
edge roughness (LER) that does not meet requirements. Efforts have been made to understand and improve the
LER in this process. Challenges were summarized toward low LER and good performing pitch division.
Simulations and analysis showed the necessity for an optical image that is uniform in the z direction in order for
pitch division to be successful. Two-stage PBGs were designed for enhancement of resist chemical contrast. New
pitch division resists with polymer-bound PAGs and PBGs, and various PBGs were tested. This paper focuses on
analysis of the LER problems and efforts to improve patterning performance in pitch division lithography.
The semiconductor industry is pursuing several process options that provide pathways to printing images smaller
than the theoretical resolution limit of 193 nm projection scanners. These processes include double patterning, side
wall deposition and pitch division. Pitch doubling lithography (PDL), the achievement of pitch division by addition
of a photobase generator (PBG) to typical 193 nm resist formulations was recently presented.<sup>1</sup> Controlling the net
acid concentration as a function of dose by incorporating both a photoacid generator (PAG) and a PBG in the resist
formulation imparts a resist dissolution rate response modulation at twice the frequency of the aerial image.
Simulation and patterning of 45 nm half pitch L/S patterns produced using a 90 nm half pitch mask were reported.<sup>2</sup>
Pitch division was achieved, but the line edge roughness of the resulting images did not meet the current standard.
To reduce line edge roughness, polymer bound PBGs and polymer bound PAGs were investigated in the PDL resist
formulations. The synthesis, purification, analysis, and functional performance of various polymers containing PBG
or PAG monomers are described herein. Both polymer bound PBG with monomeric PAG and polymer bound PAG
with monomeric PBG showed a PDL response. The performance of the polymer bound formulations is compared to
the same formulations with small molecule analogs of PAG and PBG.
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
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
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 (k<sub>1</sub> = 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.
A new type of scissionable polymer based on main-chain acid-labile acetal linkages is reported as a photoresist for
e-beam and EUV lithography. Four kinds of copolymers were synthesized via ring-opening metathesis polymerization
(ROMP) using various ratios of acetal and norbornene-derivative monomers. Differential scanning calorimetry (DSC)
analysis demonstrated that incorporation of bulky structure, i.e., norbornene-derivatives, provided copolymers with high
T<sub>g</sub>. According to thermogravimetric analysis (TGA), these copolymers had slight weight loss in the temperature range
from 100 to 250°C. This weight loss is tentatively assigned to a cleavage process due to the presence of the acetal units.
Both GPC and NMR analyses revealed that the main-chain of these copolymers was steadily chopped at scission
moieties of acetal units by strong acids in solution, and was also chopped by photo-generated acid from PAG in thin-film.
A steric barrier to the scissionable moiety is considered to hinder acidolysis, leading to improvement of main-chain
stability. These copolymers were confirmed to make fine patterns by e-beam exposure, demonstrating them to be
promising materials as photoresists for EUV lithography. Significant improvements are needed to meet the required resolution and photospeed performance for incorporation into viable EUV resists.
Extreme ultraviolet (EUV) lithography has gained momentum as the method of choice for <32-nm half-pitch device
fabrication. In this paper, we describe our initial attempts to increase an EUV resist's sensitivity without compromising
resolution and line roughness via introduction of a thermally crosslinkable underlayer. The main purpose is to test the
possibility of using a combination of photoacid generators (PAGs) and EUV sensitizers (phenol type) in the underlayer
designs to enhance the overall performance of EUV resists. We have demonstrated the possible benefits of adding an
EUV underlayer into the regular EUV litho stack and investigated the effect of PAG types and loadings on the
photospeed and litho performance of three different EUV resists.
We present the results of both theoretical and experimental investigations of materials for application either as a
reversible Contrast Enhancement Layer (rCEL) or a Two-Stage PAG. The purpose of these materials is to enable Litho-
Litho-Etch (LLE) patterning for Pitch Division (PD) at the 16nm logic node (2013 Manufacturing). For the rCEL, we
find from modeling using an E-M solver that such a material must posses a bleaching capability equivalent to a Dill A
parameter of greater than 100. This is at least a factor of ten greater than that achieved so far at 193nm by any usable
organic material we have tested.
In the case of the Two-Stage PAG, analytical and lithographic modeling yields a usable material process window, in
terms of reversibility and two-photon vs. one-photon acid production rates (branching ratio). One class of materials,
based on the cycloadduct of a tethered pair of anthracenes, has shown promise under testing at 193nm in acetonitrile.
Sufficient reversibility without acid production, enabled by near-UV exposure, has been achieved. Acid production as a
function of dose shows a clear quadratic component, consistent with a branching ratio greater than 1. The experimental
data also supports a acid contrast value of approximately 0.05 that could in principle be obtained with this molecule
under a pitch division double-exposure scenario.
EUV lithography (EUVL) is a leading candidate for printing sub-32 nm hp patterns. In order for EUVL to be
commercially viable at these dimensions, a continuous evolution of the photoresist material set is required to
simultaneously meet the aggressive specifications for resolution, resist sensitivity, LWR, and outgassing rate.
Alternative PAG designs, especially if tailored for EUVL, may aid in the formation of a material set that helps
achieve these aggressive targets. We describe the preparation, characterization, and lithographic evaluation of
aryl sulfonates as non-ionic or neutral photoacid generators (PAGs) for EUVL. Full lithographic
characterization is reported for our first generation resist formulation using compound H, MAP-1H-2.5. It is
benchmarked against MAP-1P-5.0, which contains the well-known sulfonium PAG, triphenylsulfonium
triflate (compound P). Z-factor analysis indicates nZ<sub>32</sub> = 81.4 and 16.8 respectively, indicating that our first
generation aryl sulfonate formulations require about 4.8x improvement to match the results achieved with a
model onium PAG. Improving the acid generation efficiency and use of the generated byproducts is key to
the continued optimization of this class of PAGs. To that end, we believe EI-MS fragmentation patterns and
molecular simulations can be used to understand and optimize the nature and efficiency of electron-induced
The synthesis and characterization data for a new sulfonium photoacid generator (PAG),
diphenyltrimethylsilylmethylsulfonium triflate (I), is reported. It is shown that the molecule undergoes rapid silyl group
transfer to water or phenol in the presence of a strong, nucleophilic base such as trioctylamine (TOA). The resulting
PAG, diphenyl-methylsulfonium triflate (II), is subsequently degraded by TOA via methyl group transfer from S to N
leading to the formation of Ph2S and methyltriocylammonium triflate. Both I and II are stable when non-nucleophilic
base quenchers are used. Dose-to-clear and patterning results obtained from EUV exposures at Intel-MET are presented,
illustrating that increased sensitivity can be obtained with PAGs I and II relative to triphenylsulfonium triflate (TPSOTf),
but that LWR is compromised.