Historically, the block layers are considered "non critical ", as ones requiring less challenging ground rules.
However, continuous technology-driven scaling has brought these layers to a point, where resolution, tolerance and
aspect ratio issue of block masks now present significant process and material challenges. Some of these challenges will
be discussed in this paper.
In recent bulk technology nodes, the deep well implants require an aspect ratio of up to 5:1 in conventional
resist leading to small process margin for line collapse and/or residue. New integration schemes need to be devised to
alleviate these issues, i.e. scaling down the energy of the implant and the STI deep trench to reduce resist thickness, or
new hard mask solutions with high stopping power to be dry etched.
Underlying topography creates severe substrate reflectivity issues that affect CD, tolerance, profiles and
defectivity. In addition to the CD offset due to the substrate, the implant process induces CD shrinkage and resists profile
degradation that affects the devices. Minimizing these effects is paramount for controlling implant level processes and
meeting overall technology requirements. These "non-critical" layers will require the development of more complex
processes and integration schemes to be able to support the future technology nodes. We will characterize these process
constraints, and propose some process / integration solutions for scaling down from 28nm to 20 nm technology node.
As patterning of implant layers becomes increasingly challenging it is clear that the standard resist/Top Antireflective
Coating (TARC) process may be soon be limited in terms of its ability to meet implant targets at future nodes. A
particularly attractive solution for patterning implant levels is the use of a Developable Bottom Anti-Reflective Coating
(DBARC). Similar to a conventional BARC, a DBARC controls reflectivity from the underlying substrate by absorbing
the incident radiation thereby minimizing detrimental effects of reflected light. However, unlike a conventional Bottom
Anti-Reflective Coating (BARC) which requires a BARC open etch step, the DBARC is developed with the resist in a
single step leaving the substrate ready for implantation. These properties make DBARC very attractive for implant
In this paper, we report on the development of KrF and ArF DBARCs for implant applications. Our primary interest is
in developing solutions for patterning Post-Gate implant levels. We briefly describe our fundamental design concepts
and demonstrate the concepts are robust as we develop AR<sup>TM</sup>602 DBARC to address the criteria for a production worthy
DBARC. This includes data on EBR performance, drain line compatibility, sublimation and footing coverage over
topography. In terms of lithographic performance, we demonstrate improved capability over the incumbent SLR/TARC
process in many key areas. This includes through pitch performance, process window and profile integrity over
topography for both KrF and ArF DBARC solutions. Several strategies to enhance profile by resist/DBARC matching
are also demonstrated. From a platform robustness standpoint, we show that AR602 DBARC is ready for high volume
manufacturing in terms of batch to batch control and shelf life.
Implant level photolithography processes are becoming more challenging each node due to everdecreasing
CD and resist edge placement requirements, and the technical challenge is exacerbated
by the business need to develop and maintain low-cost processes. Optical Proximity Correction
(OPC) using models created based on data from plain silicon substrate is not able to accommodate
the various real device/design scenarios due to substrate pattern effects. In this paper, we show our
systematic study on substrate effect (RX/STI) on implant level lithography CD printing. We also
explain the CD variation mechanism and validate by simulation using well calibrated physical resist
model. Based on the results, we propose an approach to generate substrate-aware OPC rules to
correct for such substrate effects.
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.
In recent years, implant (block) level lithography has been transformed from being widely viewed as non-critical into
one of the forefronts of material development. Ever-increasing list of substrates, coatings and films in the underlying
stack clearly dictates the need for new materials and increased attention to this challenging area. Control of the substrate
reflectivity and critical dimension (CD) on topography has become one of the key challenges for block level lithography
and is required in order to meet their aggressive requirements for developing 32nm technology and beyond.
The simulation results of wet-developable bottom anti-reflective coating (dBARC) show better reflectivity control on
topography than the conventional top anti-reflective materials (TARCs), and make a convincing statement as to viability
of dBARC as a working solution for block level lithography.1 Wet-developable BARC by definition offers substrate
reflectivity and resist adhesion control, however there is a need to better understand the fundamental limitations of the
dBARC process in comparison to the TARC process. In addition, some specific niche dBARC applications as facilitating
adhesion to challenging substrates, such as capping layers in the high-k metal gate (HK/MG) stack, can also be
envisioned as most imminent dBARC applications.2 However, most of the engineering community is still indecisive to
use dBARC in production, bound by uncertainties of the robustness and lack of experience using dBARC in production.
This work is designed to inspire more confidence in the potential use of this technology. Its objective is to describe
testing of one of dBARC materials, which is not a photosensitive type, and its implementation on 32nm logic devices.
The comparison between dBARC and TARC processes evaluates impacts of dBARC use in the lithographic process,
with special attention to OPC behavior and reflectivity for controlling CD uniformity. This work also shows advantages
and future challenges of dBARC process with several 248nm and 193nm resists on integrated wafers, which have
shallow trench isolation (STI) and poly gate pattern topography.
Developable bottom anti-reflective coating (DBARC) technology holds promise in two main areas of lithography. The
first application of DBARC is in implant lithography where patterning implant levels would greatly benefit from
improved reflection control such as provided by a conventional BARC. However, implant layers cannot withstand
BARC open etch thereby making DBARC an attractive solution as the resist and DBARC are simultaneously dissolved
during the development step leaving the underlying substrate ready for implantation. In comparison to current implant
processes with top anti-reflective coatings (TARC), DBARCs are anticipated to offer improvements in reflection control
which would translate to improved CDU and increased process window for both KrF and ArF implants. Indeed, this area
has long been considered the ideal insertion point for DBARC technology.
The second area where DBARC technology can make a significant impact is in non-implant lithography. In this large
segment, the ability to replace a conventional BARC with a DBARC affords the device maker the ability to simplify
both lithographic and integration processes. By replacing the BARC with a DBARC, the BARC open etch is negated.
Furthermore, by applying this strategy on multilayer stacks it is possible to greatly simplify the process by avoiding both
CVD steps and pattern transfer steps thereby easing integration. In this area, DBARC technology could have merit for
low k1 KrF and ArF (dry) lithography as well as in immersion ArF processes.
This paper describes our results in designing production worthy DBARCs for both implant and non-implant applications.
A newly developed KrF DBARC platform is evaluated for logic implant applications and compared to a standard TARC
implant process. Post develop residue and defectivity are checked for the new platform and the results compared to
production worthy BARC and implant resists. A new ArF platform was also developed and initial lithographic results
are reported for an implant application. Several non-implant applications were also investigated and results are reported
for high resolution KrF and ArF (dry) lithography as well as an immersion ArF process.
We report here, new non-acetal containing low bake (PEB < 100° C ) resists that are suitable for immersion
lithography. These resists are based on novel low activation energy (low-E<sub>a</sub>) tertiary ester protecting
groups. One major obstacle to imaging in the sub-50 nm regime using chemically amplified resists is the
diminished image integrity in the pattern ("image blur") due to photo-generated acid diffusion into
unexposed regions. Low processing temperatures are predicted to decrease the degree of photoacid
diffusion and, in turn, decrease the image blur. Even though many low bake resist compositions have
previously been reported, they are all based on acetal/ketal protecting groups. Unfortunately, these
materials require a stoichiometric amount of water for the photoacid-catalyzed deprotection reaction to
proceed. It is usually assumed that the water for the reaction comes from the environment in the bake
station. However, fluctuations in humidity could affect the performance of the resist. Furthermore,
acetal/ketal-based resists generally lack storage stability. For these reasons, acetal/ketal-based resists did
not receive widespread acceptance in the lithography community. With the introduction of water based
immersion lithography, acetal/ketal-based resists are expected to have further performance difficulties.
Therefore, we targeted the development of new "low blur" resists for 193nm lithography that do not
contain acetal/ketal protecting groups.
Over a period of last several years 193 nm immersion lithography from a remote and unlikely possibility
gradually became a reality in many fabrication facilities across the globe and solid candidate for high volume
manufacturing for the next generation technology node. It is being widely understood in the industry that top-coatless
resist approach is a desirable final stage of the immersion process development. However creating low-defect high
performance top-coatless resist materials requires understanding of the fundamental material properties of the top layer,
responsible for leaching suppression, immersion fluid meniscus stability, and in this way enabling high speed low-defect
While a lot of progress has been made in implementing specific top coat materials into the process flow, clear
understanding effects of the top coat properties on the lithographic conditions and printing capability is still lacking. This
paper will discuss top coat materials design, properties and functional characteristics in application to novel
fluoroalcohol polymer-based immersion top coat.
We have used our fluoroalcohol based-series designs (titled MVP top coat materials further on in the paper) as a
test vehicle for establishing correlations between top coat performance and its physical and chemical properties including
hydrophobicity, molecular weight/dispersity etc. Effects of polymer-solvent interactions on the contact angle and
characteristics of the top coat material are explored, providing valuable understanding transferable to design of new
generation top coats and top-coatless materials. Our resultant new designs demonstrated excellent lithographic
performance, profiles and low leaching levels with commercially available resist and high receding contact angles,
comparable to the commercial top coat materials.
Scaling of designs to the 45nm or future nodes presents challenges for KrF lithography. The purpose of this work was to
explore several aspects of ArF lithography for implant layers. A comparison of dark loss seen in a KrF resist and TARC
system to that seen in an ArF system showed significant differences. While the KrF resist yielded dark loss that varied
with CD and pitch, the ArF resist showed very little dark loss and no significant variation through the design space. ArF
resist were observed to have marginal adhesion to various substrates. Improvements in adhesion performance were
shown by pre-treating the substrate with various processes, of which an ozone clean provided the best results.
Optimization of the HMDS priming conditions also improved adhesion, and it was observed that the HMDS reaction
proceeds at different rates on different subsatrates, which is particularly important for implant layers where the resist
must adhere to both Si and SiO<sub>2</sub>. The effect of ArF resist profile with varying reflectivity swing position is shown, and
some investigation into reflectivity optimization techniques was performed. Low-index ArF TARC was shown to
reduce the CD variation over polysilicon topography, and wet developable BARC was demonstrated to provide
consistent profiles on both Si and SiO<sub>2</sub> substrates. Finally, a comparison of ArF and KrF resists after As implant
indicates that the ArF resist showed similar shrinkage performance to the KrF resist.
The combination of immersion lithography and reticle enhancement techniques (RETs) has extended 193nm
lithography into the 45nm node and possibly beyond. In order to fulfill the tight pitch and small critical dimension
requirements of these future technology nodes, the performance of 193nm resist materials needs to further improve. In
this paper, a high performance 193nm photoresist system based on fluorosulfonamide (FSM) is designed and
developed. The FSM group has good transparency at 193nm. Compared to the commonly used hexafluoroalcohol
(HFA) group, the trifluoromethyl sulfonamide (TFSM) functionality has a lower pKa value and contains less fluorine
atoms. Polymers containing the TFSM functionality have exhibited improved dissolution properties and better etch
resistance than their HFA counterparts. Resists based on the FSM-containing polymers have shown superior
lithographic performance for line, trench and contact hole levels under the 45nm node exposure conditions. In
addition, FSM resists have also demonstrated excellent bright field and dark field compatibility and thereby make it
possible to use one resist for both bright field and dark field level applications. The structure, property and lithographic
performance of the FSM resist system are reported.