This PDF file contains the front matter associated with SPIE Proceedings Volume 12292, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

This paper describes the direct print Extreme Ultra Violet (EUV) technology used for lithographic patterning of 30-36 nm pitch metal layers of Intel 18A technology node. Direct print EUV delivers cost effective pitch scaling to enable flexible design rules and ease of use for layout designers. Careful co-optimization of the illumination source, photoresist and lithography stack is essential to resolve the tightest pitches. Optimum CDSEM metrology conditions and EUV specific requirements such as full field correction with thru slit, flare and black border compensation are critical to improve the quality of the optical proximity correction (OPC) flows. OPC algorithms were used to maximize the process window by using width sizing and pitch shifting to meet lithographic printability criteria while pushing mask manufacturability constraints to their healthy limits. The sizing of metal lines is modelled and fed to the RC extraction flows to close the fabdesign house feedback loop to improve accuracy of timing closure. Multiple test masks were specifically designed to increase sensitivity of defect metrology and accelerate yield learning. Our results from multiple product vehicles demonstrate achievement of technology readiness milestones.

The trade-off between resist sensitivity and local critical dimension uniformity (LCDU) of contact hole (C/H) patterning is one of the most challenging issues facing cost effective high-numerical aperture (NA) high volume manufacturing. The focus margin at 0.55 NA is only 36% of that at 0.33 NA, which raises significant concerns about defocus-induced LCDU degradation. A chemically amplified resist (CAR_B) which resolved 24 nm pitch showed zero useful depth of focus (DOF) when considering LCDU specification for 32-nm pitch contact holes. If we relax the LCDU target to 18% of half pitch (or 2.88 nm), a useful DOF of 30 nm was obtained with CAR_B at 32 nm pitch contact hole. If we relax the LCDU target to 20% of half pitch (or 2.8 nm), a useful DOF of less than 10 nm was achieved with CAR_A for 28-nm pitch contact hole. Non-CAR positive-tone resist (PTR) was worse than CAR PTR in terms of LCDU at 32-nm pitch and 28-nm pitch dense contact holes. Non-CAR negativetone resist (NTR) has a demerit of ~8% lower NILS caused by usage of clear-tone mask. For sub 30-nm pitch dense contact hole patterning, it is highly recommended to develop positive-tone non-CAR material and to develop new additional processes that improve LCDU for high-NA implementation.

In recent years the promise of EUV lithography became a high-volume-manufacturing reality. With already more than 160 EUV scanners in the field worldwide (and counting!), EUV lithography has now a solid footing in market and is currently the main enabler for the latest generations of chips we all know and use. To enable the future generations of chips, with even smaller feature sizes than what we currently have on the market, ZEISS and ASML are developing a new generation of EUV tools, where the numerical aperture (NA) of their optics is increased from the current 0.33 to 0.55. These high-NA tools will allow the shrink prescribed by the Moore's Law to continue well into this decade, by allowing the lithographers to print 8nm half-pitch in a single exposure. In this presentation we will remind briefly on high-NA optics concepts as compared to its 0.33-NA predecessor. We will give insight into how advanced the current production status at ZEISS is: not only into mirror surface polishing, coating, metrology, but also mirror handling and integration as well as shipment. Moreover, besides what happens in high-NA program, you will also see the current status and ongoing improvements to 0.33-NA optics.

Herein, we investigated the chemical reactions associated with low-energy electron exposures on an inorganic-organic hybrid thin film system deposited using molecular atomic layer deposition (MALD) for EUV photoresist applications. Using the hybrid thin films consisting of trimethylaluminum (TMA) and hydroquinone (HQ), we determined the critical doses and thickness contrast of the hybrid materials at various electron energies (up to 400 eV). The custom-built in-situ Fourier-Transform Infrared (FTIR) spectroscopy system, equipped with an electron flood gun and gas residual analyzer (RGA), was employed to monitor the chemical changes induced by low-energy electrons in the hybrid thin films. Based on the in-situ FTIR and RGA results, potential chemical reaction mechanisms responsible for the change in solubility of the TMA/HQ material are proposed.

Continued lithographic scaling using high-NA EUV scanners requires materials and processes with sufficient resolution and stochastic performance to translate the aerial image into thin film photoresist material. Amongst these key processes is photoresist dissolution that converts latent exposure chemistry in the photoresist into a developed pattern. However, co-optimization of resist materials and the develop process is difficult due to the challenge of directly measuring resist dissolution at the nanometer spatial and sub-second temporal scales on which it occurs. Most metrology of the dissolution process thus ignores either the temporal component by measuring just the final developed structure, or the spatial component as is done in most dissolution rate monitoring experiments. To overcome these challenges, we have developed an in-situ dissolution rate monitoring technique using high-speed atomic force microscopy (AFM). As opposed to pioneering work using AFM to monitor the dissolution process, our technique incorporates the use of a specially-designed flow cell which provides precise control of the time at which developer is introduced to the photoresist material, as well as delivery of nearly full-strength developer in fractions of a second. Our system thus offers the ability to probe the spatially-dependent nature of the dissolution process at conditions close to those in the fab, providing insight into exposure-dependent dissolution rate gradient, material swelling, and other potentially lithographically relevant phenomena such as polymer entanglement. In doing so, we provide another technique to aid in the design and study of photoresist materials for future lithographic nodes.

Understanding the interaction of resist materials with the underlayers is important for the development of highly resolving resist materials. The effect of the surface free energy of the organic underlayer on the dissolution kinetics of poly(4-hydroxystyrene) (PHS) film in a tetramethylammonium hydroxide (TMAH) aqueous developer was investigated by the quartz crystal microbalance (QCM) method. By using 0.95 wt% TMAH standard developer, we observed the correlation between the polar component of the surface free energy of the underlayer and the interaction area of the QCM chart (impedance) near the end of PHS dissolution. The interaction area was defined by the product of impedance change and time. The interaction of the hydroxyl groups of PHS with the underlayer increased with the polar component of the surface free energy of the underlayer. The analytical method developed in this study is useful for the investigation of the resist-underlayer interaction during development.

In this contribution, the authors present the design and fabrication of optimized phase-shifting transmission masks for high-resolution nanopatterning with a compact EUV exposure tool. Several influencing factors on the achievable resolution are determined and characterized, paving the way towards the theoretical resolution limit in the sub-10 nm range. Applications that require high resolution patterns are numerous, leading to an increasing demand for compact exposure tools and lithographic concepts. The realized exposure tool is a compact and versatile setup, that can be operated either at an exposure wavelength of 10.9 nm or 13.5 nm addressing both large area nanopatterning with maximized throughput and industrial resist qualification with highest resolution. For partially coherent radiation as provided by the utilized discharge-plasma produced (DPP) EUV radiation source of the setup, the (achromatic) Talbot lithography has proven to be the most suitable lithographic approach with a demonstrated resolution in the sub-30 nm regime and a theoretical resolution limit below 10 nm. To maximize the contrast of the resulting intensity distribution in wafer plane, the material composition and geometry of the mask are optimized by means of rigorous coupled-wave (RCWA) simulations. Different influencing factors on the achievable resolution are identified and presented. In addition to the simulative optimization of the phase-shifting masks, the fabrication of the dense periodic nanopatterns becomes more and more challenging for smaller periods. In this contribution the mask fabrication process is optimized to create stable and high-resolution periodic mask patterns, leading to record resolution for both line and pinhole periodic nanopatterns with the presented setup.

The mask pattern is created on the multilayer reflection mirror in the EUV lithography. This is the origin of the issues such as the absorber shadowing (mask-3D) and contrast loss at high-NA tool. To solve these issues, this paper presents conceptual discussions on a new configuration which employs rotating mirror (precession beam) to illuminate the mask from normal direction with small tilt angle matches to the numerical aperture: 8.3 deg at 0.55 NA and 11.3 deg at 0.71 NA, both angles are acceptable for multi-layer mirror of the mask. Unlike current EUV machine design, all optical components are axial symmetric and aligned on axis (in-line), and thus form a plane-parallel resonator configuration. xand y-magnifications are same 4x, and full-field 33 mm x 26 mm may be possible at high-NA as high as 0.71. Annular slit at the back focal plane acts as Fourier spatial filter, which removes 3D components, thus resulting image becomes longitudinally projected mask pattern without shadows. The system becomes a both-side telecentric camera, providing long depth-of-focus and high contrast image. As the objective mirror, Schwarzschild objective or Wolter telescope will be a suitable candidate. Wolter telescope is axisymmetric and lighter than conventional solid concave mirror, therefore, a larger diameter mirror can be fabricated in high precession. After the objective mirror, all diffractions have the same angles to the axis (cone beam) including the illumination beam. A new concept “the generalized interference lithography” will be introduced as the working principle of pattern writing on the wafer.

Image contrast is an important measure of image quality, especially for EUV lithography where high contrast can mitigate stochastic process fluctuations1 such as Line-Edge Roughness (LER), Line Width Roughness (LWR), Local CD Uniformity (LCDU) and stochastic defects. In this paper, several aspects of image contrast for EUV lithography are discussed. We will look at some of the fundamental mechanisms which degrade image contrast, including resist blur from acid diffusion. We assume the imaging of dense line/space images with k₁<0.5. This assumption guarantees that the image is a simple sinusoid, and implies that the exposure latitude is proportional to the image contrast. We then consider various methods to experimentally measure image contrast. The classic measure would be to measure the exposure latitude from a Focus/Exposure Matrix (FEM) wafer. The exposure latitude is generally giving a contrast measure which is averaged over some portion of the wafer. In this paper, we propose the use of MEEF (Mask Error Enhancement Factor) targets to track contrast at specific locations on the wafer. In principle, one could measure many points across the image field (or even across the whole wafer) to map out the spatial variation of contrast, i.e. a contrast map. The paper includes experimental contrast measurements that relate to stage fading, source shape and resist blur from different processes. We will also briefly look at fading from the Pole-to-Pole image shift, and how to mitigate this with a novel exposure method called Dual Monopole.

Currently various materials are being tested as new EUV mask absorber for next-generation EUV lithography. The materials can roughly be divided into two groups: low-n and high-k. In order to determine what material to use, various properties such as wafer printability and mask process needs to be considered. In this work, wafer printability of low-n and high-k material was compared with current tantalum based conventional absorber by simulation. Material chosen from the n & k value showing promising results in the simulation where tested for durability in mask usage condition. Also, the chosen material was patterned with conventional tool applied for current photomask process, testing the etchability and resolution with temporal process used for initial testing.

Mask defectivity continues to be a critical challenge to full industrialization of extreme ultraviolet (EUV) lithography. The most concerning defects are those that originate from the blank substrate or multilayer deposition process and are not easily repaired or compensated for. These can best be avoided by hiding them underneath the unexposed absorber regions of the reticle layout. In this paper, we present a comprehensive blank defect avoidance solution that substantially mitigates the risk of printing blank defects. In the first step of this solution, we apply an automatic defect classification to all available blank inspections, categorizing defects into various critical and noncritical bins. In the second step, we register these defects to very high accuracy using a mask registration tool. In the final step, we use a fast polygon-based nonlinear optimization algorithm that outputs the best possible placement of all critical defects so that they are located under the absorber patterns. It does so by optimizing the global mask pattern shift and rotation and accounts for uncertainty in defect positioning and E-beam writing. After the optimal reticle shift and rotation are computed, they are verified by simulating possible wafer print impact. An overall impact score is computed for that specific combination of blank and pattern file and done so for all available blanks in the unused blank database. The E-beam writer operator can then select the blank with the lowest impact score or least risk of printing. Integrated within the KLA RDC and KlearView™ systems, this comprehensive extreme ultraviolet (EUV) blank defect avoidance solution has been validated in pilot production. By maximizing entitlement of EUV blanks across various grade levels, this solution has helped reduce costs and improve yields.

EUV chemically amplified resists (CARs) have had big problems about a trade-off relationship between resolution, line width roughness (LWR), and sensitivity (RLS trade-off). The RLS trade-off problems have come to a head with the progress of pattern miniaturization. Moreover, etching durability of CARs are also gradually surfaced as an issue due to reducing film thickness to prevent pattern collapse. Previously, we proposed a novel chemically amplified resist platform that consists of polarity changer, cross linker and organotin compound. Polymers having triarylsulfonium cations, diarylmethanol and organotin compound as side chains were designed to realize a negative imaging property by using crosslinking through the acid catalytic etherification. It demonstrated RLS trade -off mitigation and low LER property by using two concentration of acetonitrile aqueous solution developer. Moreover, it could be observed two or threefold sensitization by using a UV flood exposure after EB lithography process applying new sulfonium cation structure which can be converted to UV absorbing structure by acid catalytic reaction.

EUV lithography is becoming established in high volume manufacturing but there are still many challenges to be overcome within the ecosystem including next generation exposure tools and the materials used in the patterning stack. EUV photoresists with the appropriate capability to support future roadmap requirements such as high-NA remain a high priority area of research. EUV photons have significantly higher energy than in previous photolithographic techniques, and the resist is exposed by radiation chemistry routes rather than the well-known photochemistry from earlier nodes. In addition, resists must contend with much higher photon-shot noise, require high EUV absorbance to offset the need for very thin films, especially in High-NA EUV, where the depth of focus will be less than 20 nm, and ultimately the theoretical resolution limits of EUV will approach the size of typical photoresist molecules. We are developing a new type of photoresist based on the multi-trigger concept, which seeks to suppress line edge roughness using a new photoresist mechanism, and which is based on molecular rather than polymeric materials to maximize resolution. Here we present results showing improved lithography accomplishments due to the enhancement of the highopacity multi trigger resist system. We present a range of process conditions and formulation variations including substrate changes which impact roughness and defectivity. The lithographic performance at pitch 28 nm patterned on an ASML NXE3400 scanner is presented on a variety of substrates. Lines with a width of 12.5 nm can be patterned at 59 mJ/cm2 with a biased LWR of 3.9 nm using a resist spun on the Brewer Optistack AL412 underlayer (12 nm thickness). We also present results on SOG/SOC stacks and the optimization required of the substrate to improve LWR and decrease defectivity. We further present results where we have been targeting sub-30 mJ/cm2 patterning. Introducing an alternative PAG but maintaining constant formulation and process conditions has enabled the patterning of p28 lines lines/spaces, with 12 nm lines having been patterned at a dose of 17.5 mJ/cm² and a film thickness of 14.5 nm. Work is continuing to reduce the LWR whilst maintaining a sub 30 mJ/cm² dose. Multi-trigger resist has also been used to pattern pillars arranged in a hexagonal pattern. We show results at pitch 36 nm, again patterned on an ASML NXE3400, exposed at 66 mJ/cm² to obtain a pillar diameter of 18 nm with a biased LCDU of 3.6 nm. We also show pitch 34 nm hexagonal pillars, patterned at 65 mJ/cm² to obtain a pillar diameter of 17 nm with a biased LCDU of 3.6 nm with a focus window of over 60 nm. A film thickness of 22 nm was used. Additionally, carefully controlling the rates of the various reactions in the MTR mechanism, we have shown that we can reduce the dose required for 19 nm diameter hexagonally arranged pillars at p34 to 28 mJ/cm2 with a biased LCDU of 4.3 nm using a 17 nm resist film thickness.

In 2019, finally, extreme ultraviolet (EUV) lithography has been applied to high volume manufacturing (HVM) for preparing advanced semiconductor devices. That was very important year for EUV enthusiasts and semiconductor industry. Because it takes for a long time, more than 30 years, to study EUV lithography for realizing HVM. With recent rapid progress on the source power improvement, EUV lithography development including photoresist materials has been achieved HVM requirements. However, the performance of EUV resist materials are still not enough for the expected HVM requirements, even by using the latest qualifying EUV resist materials. One of the critical issues is the stochastic issues, which will be become ‘defectivity’, like a nano-bridge or a nano-pinching. The analyzing summary of the stochastic factors in EUV lithography, and their improvement status are described in this paper. 2 (two) major stochastic issues, which are photon stochastic and chemical stochastic, were observed in the lithography steps. And the improvement status of each stochastic issues including lithographic results are also described.

The Laser-assisted Discharge-produced Plasma (LDP) EUV source has been developed as a light source for actinic mask inspection and is currently deployed in the field. As the EUVL process is used more in the mass-production process, the requirement for EUV source for mask inspection is required more. LDP source enables the generation of high brightness with relatively large EUV plasma to fulfill these requirements. Ushio LDP source has overcome various issues specialized from LDP source and realized high reliability 24/7 based operation with high brightness maintained. In this paper, we address the followings: (1) LDP source configuration and its monitoring system, (2) Features of LDP source for inspection purposes, (3) Recent availability in the field, (4) Improvement of source stability and cleanliness, and (5) Roadmap of source availability.

Algebraic models using Poisson statistics are used to investigate phenomena contributing to missing contacts and pillars, assess progress in their mitigation, and provide guidance for technology pathfinding for sub-10nm. Fitting the missing rate versus dose clearly shows the dominant EUV photon absorption stochastics, enables scaling from 10-4 to 10-13 error rates, and gives an equivalent number of dissolution aiding events for diagnosing physical phenomena. This number for 20 nm contacts in CAR is about 300 and suggest the possible presence of reaction enhanced diffusion or reaction enhanced solvent penetration and gel extrusion prior to disentanglement dissolution. Metal oxide resists are more complex and data on missing pillars is just becoming available. The use of similar characterization techniques can pursue phenomena that are more Gaussian in nature and more beneficial for reducing error rates.

Background: thin resists, below 30 nm, suffer from reduced imaging contrast and signal-to-noise ratio (SNR). This has an impact on the unbiased Line Width Roughness (uLWR) estimation, which becomes artificially low and hence is inaccurate when the SNR drops below certain limit, while reaching an accurate plateau value at higher SNR. Aim: improve the SNR of Scanning Electron Microscope (SEM) images in order to achieve a more reliable and robust roughness measurements on the thin resist, without having to increase the measurement electron dose. Approach: apply an unsupervised machine learning denoising algorithm to SEM raw images of thin resists on two different underlayers. The images were captured using different frame averaging (4, 8, 16, 32, and 64 frames). A systematic analysis is performed to compare the measurements before and after denoising. Results: after denoising, the SNR is improved, the mean CD stayed unchanged, and the roughness using smaller number of frames got closer to the accurate values, obtained using a larger number of frames. Conclusions: we have demonstrated that the use of a machine learning-based denoising algorithm enhances the SNR of SEM images without changing the mean CD and is beneficial for accurate and robust roughness measurements of thin resist.

We demonstrate the use of EPE (Edge Placement Error) as an early defect detection metric in an EUV self-aligned lithoetch-litho-etch (eSALELE) patterning process. Pitch 21nm test structures were investigated on an eSALELE flow consisting of 4 EUV exposures, 2 of which are lines-spaces while the other 2 exposures are for block patterns that defines the tip-to-tip. An HMI eP5 SEM with large field-of-view (8x8µm FOV) was used to measure critical dimension (CD) on wafer at each critical processing step while the overlay between multiple exposures were measured optically on uDBO marks using a YieldStar (YS). On top of CD metrology, patterning defects were measured at the final patterning transfer into dielectric material using an eP5 SEM and built-in defect inspection capability. Line-break defects are reported. Although each metric like CD, LWR or OVL is expected to contribute to the defect performance of the final pattern transfer, using only one information or another is not fully descriptive. Combining these information into an EPE metric on this complicated patterning process showed better correlation to the defect rates at dielectric transfer.

Low-n masks have gained strong interest due to their potential to simultaneously improve dose and imaging contrast for dense clips. We’ve presented before that for the imaging of isolated features mask bias and assist features are crucial to minimize the focus range through pitch. In this paper we elaborate on aberration sensitivity for different mask absorber types. We observe that even aberration sensitivities can change significantly by changing the mask absorber type for the same use case. We show that even aberration sensitivity and best-focus shifts are coupled and that they can also be solved together by applying mask & target bias and/or assist features. Finally we show how assist-feature position optimization can reduce the impact of odd aberrations on two-bar features.

In follow-up of related contributions at the past three symposium editions, our simulation study arrived at this question. As shown before, (local) mask defects and non-local mask deficiencies (NLMDs) act as triggers for increased stochastic failure probability on the EUV imaged resist pattern on wafer. Mask roughness is such an NLMD. The three types studied comprise multilayer (ML) ripple, which relates to a non-fully planar coating of the ML mask stack, mask absorber lineedge roughness and roughening of the ML. For the latter the study was restricted to roughening of the ruthenium capping layer only, which may already happen during the patterning step of the absorber during mask making. Each of the 3 roughness types is studied standalone and in combination. An alternative technique is presented that allows to define tolerance limits for mask roughness, without requiring massive, time-consuming stochastic simulations. It is based on studying how roughness-induced background light is passing through the projection optics. Our results, for anamorphic imaging at 0.55 NA, suggest the importance of limiting mask roughness beyond state-of-the-art.

The introduction of Extreme Ultraviolet Lithography (EUVL) has been an extraordinary achievement in keeping Moore’s law alive, as it minimizes the cost, time, and number of patterning steps required for device fabrication. However, as the advanced technology nodes require further scale down of the semiconductor devices, the current state-of-art EUVL tool, equipped with 0.33 Numerical Aperture (NA) and 13.5nm wavelength cannot print the features of interest with an acceptable yield. As a solution, a new generation of EUVL tool has been proposed (High-NA EUVL), having 0.55 NA and 8nm resolution. As a result of the increased NA, the depth of focus is reduced, thus thinner resist is required. Moreover, we need to restrict the aspect ratio of the features to avoid pattern collapse. For instance, resist thickness of approximately 30nm, which is typically used to print a 16nm half-pitch feature, cannot be applied to print an 8nm half-pitch feature, resist thickness must be lowered significantly to circumvent pattern collapse. However, the use of thin resist may have several negative effects on metrology and defect inspection. In this paper, we will discuss the influence of resist thickness and underlayer films on Scanning Electron Microscope (SEM) using ASML’s eP5. For this study, we prepared a set of wafers with 16nm line-space (LS) patterns at different resist thicknesses using either Metal-Oxide Resist (MOR) or Chemically Amplified Resist (CAR). The case study compares both resist platforms on Spin on Glass (SoG) and Organic Underlayer (OUL). To conduct this study our BKM ADI eP5 SEM condition has been used. We observed that thinning down film thickness leads to deterioration of SEM image quality as well as loss of defect sensitivity during the inspection. In addition, varying the underlayers greatly affects both image quality and sensitivity. By decreasing the resist thickness, MOR and CAR were observed to behave in the same way, in terms of both image degradation and loss of sensitivity, although image quality did not degrade in the same way in the two cases.

Digital Flex Illu is a fully digital solution which provides SMO functionality to the AIMS® EUV system by combining an adaptation of the already built-in system metrology with a powerful algorithm and most importantly, without changing the machine hardware. In this paper, we will present the concept of Digital Flex Illu functionality, its significant advantages in combination with a binary aperture-based illumination concept, together with showing imaging results obtained on the AIMS® EUV prototype system. This digital solution is a paradigm change for the AIMS® EUV usability and final user, it allows ZEISS to guarantee an agile roadmap for the AIMS® EUV with limited development effort and great benefits in sustainability and roadmap scaling.

EUV lithography is currently being used in semiconductor high volume manufacturing, however, performing non-destructive metrology at the nanoscale for different types of structures and materials is still an extremely challenging task. The EUV reflective grazing incidence nanoscope (REGINE) is a new synchrotron end-station dedicated to non-destructive EUV metrology at the nanoscale for surface/layered structures with different material compositions. REGINE is being developed at the Swiss Light Source synchrotron and aims to enable grazing-incidence coherent diffraction imaging (CDI), scatterometry, and reflectometry in the energy range of 80 to 200 eV. In this work, we present the concept of the REGINE tool and the results of its commissioning experiments.

On product overlay (OPO) is one of the most critical parameters for the continued scaling according to Moore’s law. Without good overlay between the mask and the silicon wafer inside the lithography tool, yield will suffer. As the OPO budget shrinks, non-lithography process induced stress causing in plane distortions (IPD) becomes a more dominant contributor to the shrinking overlay budget. To estimate the process induced in-plane wafer distortion after cucking the wafer onto the scanner board, a high-resolution measurement of the freeform wafer shape of the unclamped wafer with the gravity effect removed is needed. Measuring both intra and inter die wafer distortions, a feed-forward prediction algorithm, as has been published by ASML, minimizes the need for alignment marks on the die and wafer and can be performed at any lithography layer. Up until now, the semiconductor industry has been using Coherent Gradient Sensing (CGS) interferometry or Fizeau interferometry to generate the wave front phase from the reflecting wafer surface to measure the free form wafer shape. In this paper, we present a new method to generate a very high-resolution wave front phase map of the reflected light from a patterned silicon wafer surface that can be used to generate the free form wafer shape. We show data using a WFPI patterned wafer geometry tool to acquire 3.4 million data points on a 200mm patterned silicon wafer with 96µm spatial resolution with a data acquisition time of 5 seconds.

Achieving commercial viability for extreme ultraviolet lithography (EUVL) demands a homogeneous polymeric materials platform for fine pattern microelectronics. However, current polymer systems possess a heterogeneity length scale larger than the 13.5 nm range desired for EUVL leading to line-edge roughness close to the size of a single polymer molecule in less than a nanometer. In this report, we develop polypeptoids in a high-yielding polymer synthesis with low stochastics and enable a high sensitivity environmentally stable chemically amplified photoresist (ESCAP) for large-scale manufacturing using DUV/EUVL. Polypeptoids are bio-inspired, sequence-defined polymers that minimize molecular size and compositional and sequence statistics. Functional monomers, such as photosensitizers, solubility switches, etchresistant units, and Tg modulators, have been programmed to be precisely distributed into the polymer structure using a robotic synthesizer. Positive-tone polypeptoids ESCAPs can thus be tuned via chemical and sequence design. In particular, the arrangement of solubility-switch functional groups relative to adhesion-promoting groups influences synthetic yield and lithographic patternability. Other functional groups, such as phenolic and aromatic, promote a resist’s physical properties, film quality, adhesive characteristics, and pattern development by tuning the polymer’s polarity, depending on the sequence within the polymer chain. This work bridges the materials design of bioinspired polymers, high throughput manufacturing techniques, and nanolithography enabling polymer uses with high processing fidelity for nanotechnologies.

For imaging methods based on Fourier transform, such as coherent diffraction imaging (CDI), in the case where the sampling rate of the diffraction data satisfies Nyquist sampling theorem, phase retrieval algorithm can effectively recover the phase lost in the image acquisition process. In general, ptychography is used to ensure the adequate sample. But in the imaging system of EUV mask defect inspection, the acquisition of more sampling data requires multiple exposures of the mask, which increases the sampling time resulting in low throughput and causes mask irradiation damage. To solve the problem, we propose a machine learning scheme to reconstruct the profile of phase defect using a single diffraction intensity. Combining the physical model of CDI and neural network framework, the method transforms the phase retrieval problem into a regression model of machine learning. Integrating the constraints of the traditional CDI and the gradient descent algorithms in neural network framework, our approach can accelerate the convergence of the model. The performance of the method is confirmed by comparing with the conventional iterative method in the condition of sufficient sampling rate. This novel method provides a new idea of combining computational imaging with machine learning, which can simplify the data acquisition process and accelerate the iteration of algorithm in EUV mask defect inspection.

The pellicle prevents image errors due to contaminated particles in the EUV mask and protects the mask for a stable process. However, the lifetime of the pellicle could be shortened due to deformation and destruction caused by the collision of the particle defects in the chamber. Therefore, in order to increase the lifetime of the pellicle, it is required to develop an optimal pellicle material and structure that is resistant to deformation and destruction and has excellent mechanical stability. Accordingly, it is necessary to know the deformation caused by the particle collision and estimate the lifetime of the pellicles with different mechanical stability. In this study, we simulate the collision of particle defects for the pellicle and compare the mechanical stability depending on the single-layer pellicle materials.

Extreme ultraviolet (EUV) lithography is part of the high-volume manufacturing (HVM) processes for devices beyond 7 nm node. However, the technology still has several issues for HVM. Especially, RLS (Resolution, LWR, and Sensitivity) trade-off remains as one of the obvious problems for EUV Lithography. In which, resist pattern collapse is one of the hurdles that is preventing a process window/margin for resist patterning. Resist, under-layer, and rinse materials are continuously being developed to mitigate resist pattern collapse. In such status, rinse materials for chemically amplified resist (CAR) in the development process are known well as one approach for mitigation of the pattern collapse. In this study, we focused on the effectiveness of rinse material against lithography performance with parameters, such as surface tension and affinity with resist. In the paper, Rinse material considering low surface tension and low affinity with resist exhibited significant pattern collapse mitigation and wide process window at 28nm pitch. In addition to the rinse study, a new rinse process was investigated focusing on resist surface modification for more pattern collapse mitigation than the conventional process by suppression of water droplet generation. Furthermore, New rinse process exhibited better pattern collapse margin than the conventional rinse process.

Our previous studies focused on ways to measure simulation parameters for EUV resists, including development parameters, Dill's C parameter, the diffusion length of PAG-derived acids, and parameters for deprotection reactions. Through EUV resist simulations based on these parameters, we examined conditions for reducing LER and improving resolution. This paper presents the results of our investigations of methods for determining the refractive index n and extinction coefficient k of photoresists for EUV light (wavelength 13.5 nm), parameters generally considered difficult to measure, and for calculating an absorption parameter known as the Dill's B parameter. We investigated three types of photoresists: polymer decomposition type resist, chemically amplified resist, and EUV metal resist.

With the introduction of high-numerical aperture extreme ultraviolet lithography, the thickness of layers in the lithographic stack will scale owing to reduced depth of focus and etch budget. While several studies have explored the impact of thickness scaling on photoresists, the consequence of thinning down underlayers for extreme ultraviolet (EUV) lithography has been scarcely investigated. In this work we assessed the readiness of nine state-of-the-art underlayers, spin-on and dry deposited, scaled in thickness series down to 4 nm nominal (~3 nm actual). Dose-to-size and exposure latitude changed by less than 5 % when thickness of underlayer was decreased. In summary, most of EUV underlayers investigated in this work showed minimal impact on the physical and chemical properties as well as the patterning performance when scaling in view of high numerical aperture extreme ultraviolet lithography.

As the industry continues to scale DRAM cell size, EUV lithography techniques have been considered in one or multiple steps. We have explored a single mask solution to pattern the bit-line-periphery (BLP) and the storage node landing pad (SNLP). Normally, for such varied types of structures as honeycomb arrays, SWD, S/A and Core, multiple masks are required. In this paper, we have explored a single EUV mask approach. First, a freeform EUV light source (in the source mask optimization, or SMO, process) was generated targeting a 36nm pitch honeycomb array and BLP structures. Then, curvilinear optical proximity correction (OPC) was applied to the target design (as shown in Figure 1) such that the performance meets qualified process window variation bands (PVBs) with proper curvilinear mask rule check (MRC). It is important to note that only an optical model was used for SMO and OPC without a resist model in this task. For the wafer process, we have used a dark field mask and metal oxide resist (MOR) photoresist and negative tone development (NTD). This was followed by transferring the pattern into a suitable hardmask for optical defect characterization using the KLA broadband plasma (BBP) 29xx tool as shown in Figure 2. Process window characterization was done to discover a unified defect-free window for both honeycomb array and BLP structures.

Gigaphoton has developed LPP EUV light source which is the most promising solution as the 13.5nm high power light source for HVM EUVL. Unique and original technologies including; combination of pulsed CO2 laser and Sn droplets, dual wavelength pico second laser pulses for shooting and debris mitigation by magnetic field have been applied. We have demonstrated high average power CO2 laser more than 25kW at output power in cooperation with Mitsubishi Electric. Pilot#1 demonstrated HVM capability; <300W operation data (short-term) and actual collector mirror reflectivity degradation rate is less than 0.15%/Gp by using real collector mirror around 125W (at I/F clean) in burst power < 10 Billion pulses operation. Long-term operation over 270W is also successful. Also we are developing small LPP light source for new application. I will report this new LPP light source at the conference.