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.
High NA immersion and EUV lithography processes are challenged to meet stringent control requirements for the 22 nm
node and beyond. Lithography processes must balance resolution, LWR and sensitivity (RLS) performance tradeoffs
while scaling resist thickness to 100 nm and below. Hardware modules including coat, bake and development seek to
enable resist processes to balance RLS limitations. The focus of this paper is to study the fundamentals of the RLS
performance tradeoffs through a combination of calibrated resist simulations and experiments.
This work seeks to extend the RLS learning through the creation of calibrated resist models that capture the exposure
kinetics, acid diffusion properties, deprotection kinetics and dissolution response as a function of PAG loading in a 193
nm polymer system. The calibrated resist models are used to quantify the resolution and sensitivity performance
tradeoffs as well as the degradation of resist contrast relative to image contrast at small dimensions.
Calibrated resist simulations are capable of quantifying resolution and sensitivity tradeoffs, but lack the ability to model
LWR. LWR is challenging to simulate (lattice models) and to measure; due to the dependence on spectral frequency.
This paper seeks to use micro-bridging experiments as means to better understand the statistical nature of LWR. Microbridging
analysis produces a statistical distribution of "discrete bridging events" that encompasses practical variations
across scanner, track and resist. Micro-bridging and LWR experiments are done using a 1.2 NA immersion system on 45
nm space structures (90 nm pitch) as a means to demonstrate the concept, but the methodology can also be used to study
EUVL processes as the technology matures. The understanding of the RLS performance tradeoffs enables TEL to
develop future hardware and processes that support industry scaling goals.
As lithographic technology is moving from single pattern immersion processing for 45nm node to double patterning for
the next generation and onward to EUV processing, TEL is committed to understanding the fundamentals and improving
our technology to enable customers to meet roadmap expectations. With regards to immersion and double patterning
technology, TEL has presented a wide variety of technologies to advance the processing capability of our customers.
With regards to EUV technology, we have previously presented work for simulation and modeling of an EUV resist
system1 in order to further our understanding of the differences between resist performance from previous platforms and
currently available EUV resists. As it's currently unknown which direction resist suppliers will take with regards to
platform in order to surpass the current limitations in resolution, roughness and sensitivity trade off's, we need to
consider the implications of such kinds of novel platforms to track processing capabilities. In this work, we evaluated
two of the more promising materials, to determine processing sensitivities necessary for the development of new
hardware and process applications. This paper details the initial study complete for understanding the track process
parameters such as dissolution characteristics and the impact of film hydrophobicity. Fundamental processing
knowledge from 193 and 248nm technology is applied to understand where processing deviates from known sensitivities
and will require more development efforts.
Determination of the optimal double patterning scheme depends on cost, integration complexity, and performance. This
paper will compare the overall CDU performance of litho-etch-litho-etch (LELE) versus a spacer approach. The authors
use Monte Carlo simulation as a way to rigorously account for the effect of each contributor to the overall CD variation
of the double patterning process. Monte Carlo simulation has been applied to determine CD variations in previous
studies1-2, but this paper will extend the methodology into double patterning using a calibrated resist model with
topography.
The ever-shrinking circuit device dimensions challenge lithographers to explore viable patterning for the 32 nm halfpitch
node and beyond. Significant improvements in immersion lithography have allowed extension of optical
lithography down to 45 nm node and likely into early 32 nm node development. In the absence of single-exposure
patterning solutions, double patterning techniques are likely to extend immersion lithography for 32 nm node
manufacturing. While several double patterning techniques have been proposed as viable manufacturing solutions, cost,
along with technical capability, will dictate which candidate is adopted by the industry.
Dual-tone development (DTD) has been proposed as a potential cost-effective double patterning technique.1 Dual-tone
development was reported as early as in the late 1990's by Asano.2 The basic principle of dual-tone imaging involves
processing exposed resist latent images in both positive tone (aqueous base) and negative tone (organic solvent)
developers. Conceptually, DTD has attractive cost benefits since it enables pitch doubling without the need for multiple
etch steps of patterned resist layers. While the concept for DTD technique is simple to understand, there are many
challenges that must be overcome and understood in order to make it a manufacturing solution.
This work presents recent advances and challenges associated with DTD. Experimental results in conjunction with
simulations are used to understand and advance learning for DTD. Experimental results suggest that clever processing
on the wafer track can be used to enable DTD beyond 45 nm half-pitch dimensions for a given resist process. Recent
experimental results also show that DTD is capable of printing <0.25 k1-factor features with an ArF immersion scanner.
Simulation results showing co-optimization of process variables, illumination conditions, and mask properties are
presented.
As the industry extends immersion lithography to the 32 nm node, the limits of image and resist contrast will be
challenged. Image contrast is limited by the inherent numerical aperture of a water based immersion lithography system.
Elements of resist design and processing can further degrade the final deprotected image contrast1,2. Studies have been
done to understand the effects of image contrast on line width roughness (LER) for dry 193 nm lithography3. This paper
focuses on the impacts of image and resist contrast on the formation of defects and LER in an immersion lithography
process.
Optical and resist simulations are combined with experiments to better understand the relationship between image
quality, resist design, scanner/track processing and defect formation. The goal of this work is to develop a relationship
between resist contrast metrics and defect formation for immersion processes.
Utilizing de-ionized water as the medium between the wafer and lens of the exposure system and realizing high numerical aperture (NA), 193-nm immersion lithography is being developed at a great pace towards practical application. Recent improvements in materials, processing and exposure systems have dramatically reduced the defectivity levels in immersion processing. However, in order to completely eradicate immersion related defects and achieve defectivity levels required for ideal productivity, further investigation into the defect generation mechanism and full understanding of the improvements garnered so far is required. It is known that leaching of resist component materials during exposure and penetration of remaining water from the immersion scanning process are two key contributors towards immersion related defects. Additionally, the necessity to increase the hydrophobicity of the resist materials has had a signification effect on remaining resist residues. In order to more fully understand the generation of defects from the these contributions, it is necessary not only to analyze properties of the defects, but also investigate the change in composition originating from advanced processing techniques that have shown improvements in defectivity performance.
As the integration of semiconductor devices continues, pattern sizes required in lithography get smaller and smaller. To achieve even more scaling down of these patterns without changing the basic infrastructure technology of current cutting-edge 193-nm lithography, 193-nm immersion lithography is being viewed as a powerful technique that can accommodate next-generation mass productions needs. Therefore this technology has been seriously considered and after proof of concept it is currently entering the stage of practical application. In the case of 193-nm immersion lithography, however, because liquid fills the area between the projection optics and the silicon wafer, several causes of concern have been raised - namely, diffusion of moisture into the resist film due to direct resist-water interaction during exposure, dissolution of internal components of the resist into the de-ionized water, and the influence of residual moisture generated during exposure on post-exposure processing. To prevent these unwanted effects, optimization of the three main components of the lithography system: materials, track and scanner, is required. For the materials, 193nm resist formulation improvements specifically for immersion processing have reduced the leaching and the sensitivity to water related defects, further benefits can be seen by the application of protective top coat materials. For the track component, optimization of the processing conditions and immersion specific modules are proven to advance the progress made by the material suppliers. Finally, by optimizing conditions on the 3rd generation immersion scanner with the latest hardware configuration, defectivity levels comparable to dry processing can be achieved. In this evaluation, we detail the improvements that can be realized with new immersion specific track rinse modules and formulate a hypothesis for the improvements seen with the rinsing process. Additionally, we show the current status of water induced immersion specific defect reduction using the latest advances in technology.
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