The optimization of a grapho-epitaxy process flow for lamellar phase block copolymer frequency multiplication on full 300 mm wafers is discussed. The process uses a dedicated photoresist that, after hardening, allows direct coating and annealing of the block copolymer over it. Some of the critical parameters for optimization of this process were found to be the selection of the neutral layer material and reduction of the prepattern resist height. Process window analysis was done by determining the best dose and focus settings for generating high quality directed self-assembly structures with the prepattern process. A very small process window for good self-assembly and an offset in the optimum dose and focus settings for these two stages of the process were found. Finally, the sensitivity of the process to programmed prepattern imperfections was studied. Programmed protrusions in the prepattern as small as 6 nm were found to cause self-assembly defects.
Directed self-assembly (DSA) has the potential to extend scaling for both line/space and hole patterns. DSA has shown
the capability for pitch reduction (multiplication), hole shrinks, CD self-healing as well as a pathway towards line edge
roughness (LER) and pattern collapse improvement [1-4]. The current challenges for industry adoption are materials
maturity, practical process integration, hardware capability, defect reduction and design integration. Tokyo Electron
(TEL) has created close collaborations with customers, consortia and material suppliers to address these challenges with
the long term goal of robust manufacturability.
This paper provides a wide range of DSA demonstrations to accommodate different device applications. In
collaboration with IMEC, directed line/space patterns at 12.5 and 14 nm HP are demonstrated with PS-b-PMMA
(poly(styrene-b-methylmethacrylate)) using both chemo and grapho-epitaxy process flows. Pre-pattern exposure
latitudes of >25% (max) have been demonstrated with 4X directed self-assembly on 300 mm wafers for both the lift off
and etch guide chemo-epitaxy process flows. Within TEL's Technology Development Center (TDC), directed selfassembly
processes have been applied to holes for both CD shrink and variation reduction. Using a PS-b-PMMA hole
shrink process, negative tone developed pre-pattern holes are reduced to below 30 nm with critical dimension uniformity
(CDU) of 0.9 nm (3s) and contact edge roughness (CER) of 0.8 nm. To generate higher resolution beyond a PS-b-PMMA system, a high chi material is used to demonstrate 9 nm HP line/ space post-etch patterns. In this paper, TEL presents process solutions for both line/space and hole DSA process integrations.
Directed Self-Assembly (DSA) is gaining momentum as a means for extending optical lithography past its current limits.
There are many forms of the technology, and it can be used for creating both line/space and hole patterns.1-3 As with any
new technology, adoption of DSA faces several key challenges. These include creation of a new materials infrastructure,
fabrication of new processing hardware, and the development of implementable integrations. Above all else,
determining the lowest possible defect density remains the industry's most critical concern. Over the past year, our
team, working at IMEC, has explored various integrations for making 12-14nm half-pitch line/space arrays. Both
grapho- and chemo-epitaxy implementations have been investigated in order to discern which offers the best path to high
volume manufacturing. This paper will discuss the manufacturing readiness of the various implementations by
comparing the process margin for different DSA processing steps and defect density for the entirety of the flow. As part
of this work, we will describe our method for using programmed defectivity on reticle to elucidate the mechanisms that
drive self-assembly defectivity on wafer.
In this paper the Arrhenius behavior of blur upon extreme ultraviolet (EUV) exposure is investigated through variation of the post-exposure bake (PEB) temperature. In this way, thermally activated parameters that contribute to blur (such as acid/base diffusion) can be separated from nonthermally activated parameters (such as secondary electron blur). The experimental results are analyzed in detail using multiwavelength resist modeling based on the continuum approach and through fitting of the EUV data using stochastic resist models. The extracted blur kinetics display perfectly linear Arrhenius behavior, indicating that there is no sign for secondary electron blur at 22-nm half pitch. At the lowest PEB setting the total blur length is ∼4 nm, indicating that secondary electron blur should be well below that. The stochastic resist model gives a best fit to the current data set with parameters that result in a maximum probability of acid generation at 2.4 nm from the photon absorption site. Extrapolation of the model predicts that towards the 16-nm half pitch the impact on sizing dose is minimal and an acceptable exposure latitude is achievable. In order to limit the impact on linewidth roughness at these dimensions it will be required to control acid diffusion to ∼5 nm.
In this paper the Arrhenius behavior of blur upon EUV exposure is investigated through variation of the PEB
temperature. In this way, thermally activated parameters that contribute to blur (such as acid/base diffusion) can be
separated from non-thermally activated parameters (such as secondary electron blur). The experimental results are
analyzed in detail using multi-wavelength resist modeling based on the continuum approach and through fitting of the
EUV data using stochastic resist models. The extracted blur kinetics display perfectly linear Arrhenius behavior,
indicating that there is no sign for secondary electron blur at 22nm half pitch. At the lowest PEB setting the total blur
length is ~4nm, indicating that secondary electron blur should be well below that. The stochastic resist model gives a
best fit to the current data set with parameters that result in a maximum probability of acid generation at 2.4nm from the
photon absorption site. Extrapolation of the model predicts that towards the 16nm half pitch the impact on sizing dose is
minimal and an acceptable exposure latitude is achievable. In order to limit the impact on line width roughness at these
dimensions it will be required to control acid diffusion to ~5nm.
The goal of this work is to use a combination of experiment and calibrated resist models to understand the impact of photo-acid generator (PAG) and sensitizer loading on the performance of a polymer bound PAG resist based processes for extreme ultraviolet (EUV) lithography. This paper describes construction of a chemically amplified resist model across 248 nm, 193 nm, 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 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 ∼8× higher than at 248 or 193 nm, 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 (∼8 nm), 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 linewidth roughness. For these materials the quantum efficiency of acid formation in EUV is found to be ∼12× higher than at 248 nm. 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.
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.
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.
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.
This paper discusses the optimization of process conditions on a 193 nm immersion lithography cluster tool to minimize
defects. A 45 nm gate process was selected for optimization but a 65nm reticle was used for defect testing so that a nonimmersion
baseline could be collected for comparison. Previous testing has shown defect counts and density are
sensitive to rinsing of wafers before and after exposure. This sensitivity was dependent on the topcoat contact angle
and resist-plus-topcoat porosity. This paper expands on that study in several ways. (1) The immersion process was
simulated by scanning a develop rinse nozzle to observe, with a microscope, any peeling that could cause contamination
in the exposure tool. (2) Different EBR strategies were compared to reduce defects causing by edge residue while
maximizing the productive area of the wafer. (3) The appearance of some defect types was found to be related to the
delay between exposure and post rinse. (4) Bake time and temperature were also added to the testing to determine if the
impact to the film composition would influence the number of defects. (5) The addition of HMDS before BARC was
tested as a way to control defects caused by delaminating at the edge of the wafer. The paper distinguishes between
defects which are specific to the immersion process and those that would still be expected to occur in dry processing.
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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