This PDF file contains the front matter associated with SPIE Proceedings Volume 13215, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

In this study, the development of a dry process for vertically tailored hybrid multilayer EUV photoresists using hexafluoroacetylacetone (HFAA) as a chemical vapor developer is investigated. Unexposed regions of the resist were effectively removed, resulting in well-defined patterns, as confirmed by AFM and XPS analyses. The consistent line thickness was maintained, and high development selectivity was demonstrated. The patterned resist was successfully transferred onto a SiO2 substrate. Future research will be focused on optimizing both the dry development and etching conditions to further enhance the precision and applicability of this technique for next-generation lithography.

In 2019, finally, extreme ultraviolet (EUV) lithography has been applied to high volume manufacturing (HVM). 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. The critical issues were the stochastic, which will be become defectivity. The classification of the stochastic factors in EUV lithography was reported, which are photon stochastic and chemical stochastic. In the past, speaking of the stochastic issue of EUV lithography was basically considered from low photon number from EUV light source, photon shot noise. It was still critical concerning point of the stochastic issue, even with recent progress on source power improvement. However, the stochastic issue is not only from them but also from EUV materials and processes, called chemical stochastic. The chemical stochastic, like materials uniformity in the film, reactive uniformity in the film, and dissolving behavior with the developer must be improved for next generation. For chemical stochastic reduction, newly proposed novel formulated organic solvent-based developer for negative-tone development of chemically amplified resist (CAR) with EUV exposure, called EUV CAR-NTD, were effective and reported in last conference. In this paper, recent progress of EUV CAR-NTD will be updated including lithographic performances.

Stochasticity is increasingly recognized as the critical factor affecting EUV lithography performances, while it’s also been recognized that the usable k1-factor is lower for EUV than for DUV exposures. This paper explores the problems in EUV from a statistical viewpoint. Relationships between probability density functions (PDF) for chemo-physical events in image-exposed resist films and practical lithography performances, such as the RLS tradeoff relationship are explored based on stochastic simulations. The developments of PDFs for a series of chemo-physical events in lithography processes (from radio-chemical reactions to dissolutions) show the contrast enhancement as the event step proceeds, showing the ability of the resist process to achieve rectangular resist profiles from sinusoidal image profiles regardless of the differences in photon energies and reaction mechanisms. This is because the number of photons contributing to each event generation increases with proceeding the event steps through the multi-photon-induced molecular-solubility-switching and the collaborative dissolution. PDF distributions near pattern edges are blurry in EUV; however, this is because of the increased inhomogeneities in event distributions due to localized secondary electron generation and the interaction among molecules in dissolution processes. Both degrade the dissolution-rate slope near edges and increase the LER. Further, the situation worsens when they are combined. Statistical variations in reaction-dissolution event densities in resist films and molecular interactions in dissolution dominate the ultimate resolution of EUV. We discuss the effectiveness of increasing contributing photons through increasing required reaction density and molecular interaction for suppressing intrinsic inhomogeneity and enhancing the contrast at the expense of resist sensitivity.

The cost of EUV lithography in chip production calls for imaging solutions that increase scanner throughput via dose reduction. By enhancing imaging via alternative low-n mask absorber materials, the imaging mask becomes a knob for dose reduction. Current low-n masks have an absorber thickness of 40 to 50nm. Thinning down the absorber results in image contrast losses, limiting their dose reduction potential in EUV lithography. Here we present wavefront optimization enabling thinning down low-n mask absorbers to 24 to 26nm. For single print EUV logic applications, this achieves a dose reduction of 20 to 30% compared to current low-n and Ta-based mask absorber thicknesses. In this simulation study, we first show that pole-to-pole image shifts drive the observed contrast losses at reduced low-n absorber thickness. Using wavefront optimization to overcome such image shifts, we then demonstrate that the low-n absorber thickness can be further reduced. The imaging potential of thinner low-n masks for current (0.33NA) and future (0.55NA) metal logic applications is evaluated by rigorous simulation overlapping process window (oPW) analysis. We also show that source/mask/wavefront co-optimization can enable a superior oPW depth of focus for the thinner low-n mask compared to the current generation of Ta-based and low-n masks. Finally, we propose available absorber materials with suitable optical properties for the practical implementation of thinner low-n masks and show their imaging strategy can be achieved at full illumination efficiency for single patterning metal logic applications down to a dense pitch of 20nm. In conclusion, our results prove that by employing wavefront optimization, thinner low-n masks provide similar or improved imaging at a much lower exposure dose.

“Low-n” bright field masks are key to enabling single exposure in 0.55NA at lower dose and improved contrast. However, these masks come with best focus shifts (BFS) for isolated features and an increased risk of assist feature (AF) printing. In this paper we describe how segmentation of AFs can minimize their printing risk without violating mask manufacturing limits for simple line spaces. They can also be used to address BFS and increase the depth of focus. The trade-off between AF print margin and the DOF performance is also considered. Finally, the impact of assist feature in reducing sensitivity to process variations is demonstrated on a logic clip.

The new high numerical aperture (0.55NA) Extreme Ultraviolet Lithography (EUVL) machine has been developed by ASML, which is using an anamorphic projection system with the demagnification of 4× in x-direction and 8× in y-direction. Due to the unchanged 6-inch mask, 0.55NA EUVL reduces the exposure field size to half-field (26×16.5mm²). Therefore, the in-die stitching between two exposures might be needed for the applications requiring larger than half-field size. To enable High-NA EUV in die stitching, a complete mask data correction flow is needed. In this paper, we will investigate the in-die stitching effects and solution by using Ta-based dark field mask. We will show the impact of pattern types and decomposition rules on the stitching strategy, in addition to methods for correcting these stitching effects in optical proximity correction from an EDA perspective.

Measuring EPE on logic devices is challenging due to the large variety of features given its random environment and layout. One has to measure an enormous amount of unique features to estimate CD, PPE, LCDU, and LPE of each feature making it impractical for EPE monitoring due to the large metrology load. We developed a simulation-based pattern clustering method that identifies and classifies features with similar EPE behavior to address this challenge. Both geometric design and imaging behavior of the patterns were taken into account to effectively cluster similar features. We report here the verification results of the clustering method which is measured on-wafer for both random layout lines-spaces and vias. With this we make a step towards identification and selection of EPE critical patterns for logic devices, which can be used further for monitoring and control.

Mask defectivity remains a key focus area for the enablement of extreme ultraviolet (EUV) lithography in high-volume manufacturing (HVM) at both mask and IC manufacturing facilities. To improve defect detection on EUV patterns, both mask and wafer inspection tools are operated with high sensitivity and advanced algorithms, coupled with mask SEM and wafer e-beam review tools, all of which generate substantial amounts of data. This data must be thoroughly examined to identify any possible defect source information and improve the overall performance of mask outgoing, fab incoming, and requalification inspections. In this paper, the complete integration of a centralized reticle and wafer data management solution is presented, providing real-time analytics to help identify defect sources, monitor changes in defectivity due to exposure and reticle handling, and recognize systematic patterns of defectivity resulting from reticles used in an HVM flow. By combining reticle data from both the mask shop and requalification line with inline wafer inspection data, including wafer print checks, operators can make correct and timely go/no-go decisions for EUV reticles, minimizing any wafer impact, while engineering teams can obtain detailed information across reticle and wafer lots for defect reduction efforts. By integrating the mask-centric KlearView^™ Fab with the wafer-centric Klarity^® defect software systems, this comprehensive data management solution improves time to results, enhances the capability to trace defectivity to its source, and improves data continuity between mask and reticle manufacturing sites, thereby enabling EUV manufacturability and production yield.

The lithography process in semiconductor manufacturing demands precise control over focus and exposure parameters to achieve optimal lithographic outcome for the structures being printed. It has become increasingly important to fully characterize the resist (3 dimensional) profile after development, since it is known that the optimum focus level and exposure dose may differ according to the parameter in question. For example, the optimal settings for CD and for minimizing stochastics effects may not be the same. In this study, we demonstrate the use of Rapid Probe Microscopy (RPM) to evaluate a Focus-Exposure-Matrix (FEM) in EUV lithography. RPM offers deep sub nanometre resolution and true 3-dimensional measurement, enabling the characterisation of variations critical to the lithographic process.

A single exposure EUV patterning process has been optimized for hexagonal contact holes (CHs) at pitch 36nm and SRAM via. Defect inspection results are reported using after etch voltage contrast (VC) metrology as well as after metallization. By comparing top-down scanning electron microscopy (SEM) and VC images, the VC technique was proven to detect the close defective CHs not only on the top surface but also at the bottom of CHs. This is confirmed on cross section inspection using transmission electron microscopy (TEM) metrology. To quantify the number of defects (NoDs) per million CHs, both a greyscale analysis and a computer vision-based defect analysis algorithm are used and exhibits the dependence of NoDs on CHs mean CD. This algorithm is capable of detecting, classifying, and incrementally counting the occurrence of defect instances as closed, partially open and open CHs. An advantage of this algorithm is its distortion invariance and independence from GDS alignment.

It has been several years since EUV lithography technology was introduced to advanced semiconductor manufacturing, and the production use of EUV pellicles also has recently been promoted. To maximize production yield and throughput, higher EUV transmittance and lifetime performance are required. To meet these requirements, NGK has initiated the development of pellicle membranes made of beryllium metal. In this presentation, we introduce the prototype manufacturing and evaluation results of a free-standing beryllium core membrane. Beryllium, a light metal, has long been used as a material for X-ray transmission. Additionally, beryllium possesses high stiffness and excellent heat dissipation properties, making it a strong candidate to meet the high-performance requirements as an EUV pellicle material. NGK is one of the few companies worldwide capable of manufacturing beryllium products and has succeeded in producing the world's first large, ultra-thin, free-standing beryllium core membrane. We manufactured and evaluated the ultra-thin membrane, achieving greater than 90% EUV transmittance. The membrane’s lifetime (durability) was also assessed under conditions equivalent to 600W EUV power (30W/cm2) in a hydrogen atmosphere, with the pellicle membrane withstanding EUV irradiation for more than 50,000 wafers. Additionally, regarding the toxicity of beryllium, which is generally a concern, we have confirmed that it meets international safety standards.

Extreme-ultraviolet (EUV) lithography is a critical technology for producing the finest patterns in semiconductor manufacturing, and the development of reliable EUV pellicle is crucial to prevent mask contamination and ensuring pattern quality. However, achieving stability over 5000 wafer exposures with more than 90% EUV transmittance in thin film is challenging. Although research on porous pellicles using carbon nanotubes (CNTs) is being ongoing, these materials still face difficulties with durability in hydrogen radical environments. To address these issues, we present a multilayer structure that enhances EUV transmittance while also improving thermo-mechanical stability. Our findings demonstrate that stacking layers of MoSi2/Si pellicle can improve the ultimate tensile strength (UTS), achieving 2.1 GPa compared to the single layered MoSi₂ pellicle targeting the same EUVT of 90%. Meanwhile, although the MoSi₂/Si multilayer structure consists of thinner emission layers, minimal loss of emissivity was confirmed due to the cumulative contribution of emission from each stacked layer.

The EUV lithography started to be used for the high-volume manufacturing of the advanced semiconductor devices such as logic 7nm device and DRAM 1a device by using the conventional EUV masks and blanks with Ta absorber. We developed the new EUV masks and blanks suitable for DRAM 1a and beyond. This new EUV masks and blanks that we developed employs the unique absorber material in order to realize the higher EUV scanner throughput than the conventional EUV masks and blanks, which we think one of advantages of the new EUV masks and blanks. On the other hand, this new EUV masks and blanks can use the similar mask fabrication process to the conventional EUV masks and blanks that we have experiences. In this paper, the fundamental properties of this unique absorber material are reported such as the dry etching performance, the durability to the wet cleaning process and the hydrogen durability. The mask pattern fidelity and the EUV scanner performance are also reported in comparison with the conventional EUV mask and blanks to show the advantage of the new EUV mask and blanks.

New absorber materials are currently being developed for next-generation EUV lithography. In particular, the demand for low-refractive-index (low-n) materials has been increasing in recent years. There are many types of low-n materials, but deciding which material to use requires considering both wafer lithography and mask making perspectives. In this study, various types of low-n materials were evaluated through wafer lithography simulations and mask making assessments. Simulations were conducted and revealed the inherent strengths and weaknesses of each material, thereby providing a balanced perspective on their performance. In addition to the evaluation based on simulations, the actual mask processability of the absorbers was assessed.

Metal oxide resists (MORs) have shown excellent performance in EUV lithography, offering high resolution, low line-edge roughness, and low EUV dose sensitivity. These attributes make them strong candidates for advanced patterning solutions. While the basic molecular mechanisms of Sn-based MORs are relatively well understood, environmental factors—such as the presence of moisture and other gases—have been found to influence reactions, leading to variations in critical dimension (CD) stability. Researching these phenomena is challenging because EUV exposures occur in vacuum environments, while conventional measurement techniques like Fourier Transform Infrared (FTIR) spectroscopy are typically conducted on off-line tools. This offline process can introduce variability due to uncontrolled environmental factors, such as atmospheric moisture and time delays. To enable a more detailed investigation of MOR reactions under controlled conditions, imec has developed the BEFORCE* tool. Built on an existing system that already includes EUV exposure and Residual Gas Analysis (RGA) capabilities, the BEFORCE tool integrates FTIR spectroscopy and hotplate units, allowing for post-exposure bake under different gas atmospheres and varying levels of humidity. Additionally, the system employs transfer arms to move MOR samples between units under controlled environments, such as vacuum or dry nitrogen. In this paper, we will clarify the chemical changes in model MORs induced by EUV exposure, baking, and environmental conditions. The high signal-to-noise ratio of the FTIR measurements enables precise quantification of processes such as ligand removal and the presence of water. Moreover, measurements conducted within the BEFORCE tool’s controlled environment were found to be significantly more stable than those taken with off-line FTIR, which are susceptible to delays and environmental variability. * BEFORCE: Bake and Exposure system with FTIR and Outgas measurement for Resist evaluation in Controlled Environment

As technology nodes shrink, EUV photoresists are critical for high-resolution nanopatterning. However, slow electrons (below 20 eV) generated during EUV exposure can cause electron blur and defect formation through unintended chemical reactions. Understanding the behavior of these electrons is crucial for improving resist performance. This work aims to study how different resist materials, particularly photoacid generators (PAGs) and quenchers, influence electron-induced chemistry under EUV exposure. Additionally, the goal is to develop high-throughput methods to screen hundreds of samples efficiently. Simultaneous total electron yield (TEY) and residual gas analysis (RGA) were used to investigate electron behavior in various polymers and model resists during EUV exposure. TEY measured electron generation and capture, while outgassing experiments explored molecular bond scission. The methods are designed for high-throughput analysis, allowing rapid sample evaluation. TEY measurements showed that PAGs and quenchers significantly affect electron generation and capture. Combined TEY and outgassing results revealed insights into EUV-induced molecular bond scission and the correlation to the resist sensitivity. This study highlights the importance of optimizing resist composition to control slow-electron behavior and outgassing. The developed high-throughput screening methods can accelerate the evaluation and development of next-generation EUV photoresists.

Understanding the fundamental properties of photoresists used in extreme ultraviolet (EUV) photolithography is crucial, particularly regarding the complex dynamics of electron emission during EUV exposure. This knowledge is essential in semiconductor manufacturing as lithographic requirements intensify with the ongoing miniaturization of semiconductor devices. In our study, we aimed to investigate the factors influencing the yield of slow electrons emitted by EUV-exposed photoresists, focusing on how different materials with varying properties, such as electron affinity, affect this process. To achieve this, we incorporated a variety of chemical substances with similar molecular weights or chemical structures into our model photoresists to better simulate real-world conditions. We then conducted total electron yield and photoelectron spectroscopy measurements on each resist sample to assess both the intensities of total electron yield and the ratios of slow electrons (with energies below 20eV) to fast electrons emitted during EUV exposure. We revealed a trend of decreasing slow electron emission from the photoresist during EUV exposure when substances with low ionization energies or high chemical reactivity, such as onium salts, are added. This finding suggests which material properties should be targeted to decrease the electron-induced blur of the aerial image, potentially impacting the lithographic performance of EUV photoresists.

The development process is important to lithography, particularly as the size of pattern features continues to shrink. The traditional developer, tetramethylammonium hydroxide (TMAH), has faced challenges with these reductions in size. The quartz crystal microbalance (QCM) method is commonly employed to measure the dissolution rate of the resist. Additionally, changes in the impedance of QCM can monitor energy loss during development. However, the potential of impedance information has not been fully exploited. This study uses simulation to analyze the changes in frequency and impedance throughout the development process, focusing on the diffusion process of polymer molecules. The reproduction of QCM charts revealed that impedance can provide insights not only into the dissolution rate of the resist but also into the viscosity near the interface between the developer and the top layer of the resist. Moreover, the diffusion constant of polymer molecules in developers can also be estimated for various developers.

Lithography accounts for the highest total CO₂ equivalent emissions for imec N3 technology node and the second highest emissions for imec N5 technology node. Additionally, the resolution-line edge roughness (LER)-sensitivity i.e., the RLS trade-off will push the EUV dose higher to improve lithographic performance. All these factors combined will result in increased costs and increased CO₂ emissions as the industry shifts toward advanced technology nodes. Reducing the EUV exposures dose while maintaining LER and defectivity with respect to the reference process can be one of the most impactful ways to achieve cost reduction, throughput improvement and CO₂ emission reduction. In this paper, we experimentally tested various ways to reduce EUV dose for CAR and MOR to print pitch 28nm line-space structures while minimizing the impact on LER and defectivity. The impact of several tuning knobs for dose reduction was explored: resist formulation, post-exposure pattern rectification, underlayer, post-exposure bake (PEB), development, mask CD bias and mask material type. Using only material and post-exposure process optimizations, up to 26% EUV dose reduction was observed with comparable performance in terms of line roughness and defectivity. Similarly, by optimizing the mask CD bias and mask material type, we can expect about 12% EUV dose reduction while also improving the peak normalized image log slope (NILS), as confirmed by simulation results. Finally, we will demonstrate that the ‘low dose process’ that we obtained, can be transferred from printing pitch 28 nm line-space structures to printing regular tip-to-tip structures with similar reduction in EUV dose at comparable tip-to-tip LCDU performance with respect to the reference process. It is critical that we consider the impact of these changes on the climate, so these process changes will also be evaluated relative to the baseline with respect to changes in equivalent CO₂ emissions.

Phasing out PFAS from semiconductor industry is a formidable undertaking driven both by sustainability concerns and by government regulations. Lithography process nowadays use PFAS-containing chemicals for rinsing the wafer at the end of the development process of chemically amplified resist patterned with EUV lithography. To evaluate the readiness and performance of novel PFAS-free alternative rinse liquids, we tested a concrete case of pitch 24nm dense lines/spaces patterned on CAR by EUV lithography. In previous technological nodes, rinse performance was linked to the minimization of the capillary force acting in the liquid meniscus between lines; but in pitch 24nm we found that model to be inadequate to explain the experimental observations. A larger design of experiment is proposed: by screening more than 25 rinse liquids of varying chemical composition we demonstration how each component of the rinse impacts the line breaks and pattern collapse probability, opening new ways to optimize the formulation of PFAS-free rinse.

In EUV lithography, the underlayers (ULs) play a crucial role for EUV exposure dose reduction as well as the prevention of the pattern collapse of the resist. In this work, we have focused on the EUV exposure dose reduction which is important for cost reduction and productivity enhancement. To accomplish so, we have developed an dry deposited underlayer engineered for metal oxide resist (MOR). A series of ULs with various chemistry, thickness, and processing conditions were screened with MOR resist using ASML’s NXE3400 EUV exposure system to print 14nm dense line CD. We observed a 27% dose reduction on the best deposited underlayer compared to spin on glass (SOG) UL. In addition to the exposure dose reduction, we observed that unbiased roughness values (LWR 2.44nm and LER1.86 nm) is maintained the same as SOG UL (LWR: 2.49 nm and LER 1.86 nm). Furthermore, the defect free window is comparable to the SOG process. Considering all these advantages, the dry deposited ULs could be one of the underlayer candidates for high NA EUV lithography.

Advanced lithography is transitioning to the high-NA EUV era with highly valuable technological advancements. We explored the limits of hexagonal contact hole and pillar patterning for memory device by utilizing holistic patterning technology of materials and process optimization, pattern rectification by directed self-assembly of block copolymer, and phase shift mask with low-n that can maximize patterning resolution in 29nm pitch design, which is the inflection point of high-NA EUV patterning. Focusing on pattern transfer, we were able to secure contact hole patterning, contact hole DSA rectification and pillar patterning in the 0.33NA process. It was also confirmed that phase shift mask can improve local CD uniformity by more than 23% compared to binary mask. In addition, we demonstrated dose and local CD uniformity in 0.55NA EUV resulting from changes in stochastic impact following the imaging contrast improvement of 0.55NA. This paper presents our latest patterning experience for 29nm pitch hexagonal contact hole and pillar array patterning and outlook for the future transition to the high-NA EUV process.

Increasing source power levels to meet higher throughput targets, in combination with tightened overlay requirements, drives the need to mitigate reticle heating and enhance performance. Improvements to the EUV scanner will prevent or compensate for overlay impact resulting from reticle heating; however, improving reticle blank thermal properties also plays a role in improving overlay and scanner performance. Reticle heating is a significant contributor to the overlay budget. EUV reticle blanks are made of a Low Thermal Expansion Material (LTEM) which is relatively insensitive to temperature changes. This makes these reticles suitable to use in EUV scanners such as the NXE:4000F, where strong temperature gradients (clamp cooling water temperature) are experienced between the image field and unexposed reticle areas. Reticle blanks have an average zero crossing temperature (ZCT), or temperature of the minimal reticle deformation, of 22 °C. The rate of the thermal expansion as a function of temperature (ZCT slope) is uniform across the reticle and can vary from 1.0 to 1.85 ppb/K². Local ZCT variations in the reticle, inherent to the manufacturing process, can also create non-uniform thermal expansion, degrading overlay. Reticle heating experiments have been performed to investigate these effects. Mask substrates were fabricated from two different LTEM manufacturing processes with different ZCT slopes and levels of ZCT non-uniformity to isolate the deformation of the reticles and the effects of LTEM thermal properties on overlay. The study shapes our understanding of how reticle heating affects overlay through comparison of simulation models with experimental data. This will enable LTEM vendors to optimize materials for future EUV systems. We provide a recommendation for material requirements to achieve minimal reticle heating impact for over 500W systems.

Photolithography plays a major role in leading-edge semiconductor fabrication. Due to the tighter photolithography specification, leading-edge 1γ (1-gamma) DRAM needs the EUV technology. There is a stringent defectivity requirement to meet critical specifications for photolithography. Any failure mode left undetected leads to yield loss and prevents cycles of learning during the early technology development phase and pilot line manufacturing. Due to tighter pitches and a high aspect ratio etch process, EUV lithography levels are prone to defects such as bridging and toppling. Photolithography Track Equipment leads the way in reducing defectivity using advanced processes and hardware optimization. Traditional bare silicon-based PMON (particle monitor) for critical tools and process monitoring is insufficient for leading-edge photolithography. It is unreliable for monitoring chemical interaction-based defectivity. Enabling Photo track monitoring (PTM) shortened cycles of learning and aided in optimizing the photolithography processes for development and production.

LCDU is a known measurable metric for studying imaging contrast in semiconductor lithography. It is rather common to separate it into systematic and stochastic subcomponents using ANOVA decomposition technique. In this work we present several experiments performed on an ASML NXE scanner to showcase what practical learnings this type of decomposition can bring, and how it could potentially be useful in process setup, monitoring and diagnostics. Firstly, we study reticle impact on the LCDU systematics and local MEEF, and demonstrate the consequences for process correctability using standard scanner tuning knobs such as dose and focus. Secondly, we highlight experimentally the difference between how strongly resist parameters, such as layer thickness, affect systematic and stochastic LCDU terms, and compare our data with scaling laws from an established model. Finally, we make an observation on how a classical ANOVA-based method to determine metrology contribution has limitations due to random destructive resist-SEM beam interaction, and discuss ramifications for interpreting the overall measured LCDU values.

To accommodate the A10 node a further scaling down of the metal line pitch towards MP16 is envisaged. As high NA will be close to its practical limit for direct P16 L/S patterning, low NA self-aligned double patterning (SADP) from P32 towards P16 was explored. First, lithography conditions such as source and stack were optimized by investigating process windows, uLER/uLWR and ebeam defectivity throughout the P32 core patterning process. Then, with the optimized lithography conditions a CDU wafer was subjected to SADP patterning.

In this work, the TiO₂ film was deposited on periodic Mo/Si bilayer at various temperatures (70~90°C) by atomic layer deposition (ALD). The H₂O and Tetrakis(dimethylamino)titanium (TDMAT) were be used for precursors. Effects of substrate temperature and thickness of TiO₂ film on the microstructure, surface roughness, and optical properties were investigated by field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), high resolution transmission electron microscope (HRTEM), and extreme ultraviolet (EUV) spectrometer, respectively. It was found that the surface roughness of the TiO₂ film at substrate temperature 70°C was obviously larger than the others. The surface roughness of TiO₂ film was under 0.2nm at the substrate temperature was above 80°C. The reflectivity of periodic Mo/Si bilayer was 66% by EUV spectrometer. We found that the reflectivity of Mo/Si/TiO₂ films was decreased with increased the thickness of TiO₂ film. The reflectivity of the films was maintain 65.97% as the TiO₂ film was 1.8nm. However, the reflectivity of the films was decreased to 59.27% when the TiO₂ film was 3nm. Based on the results of the reflectivity investigation, the TiO₂ thin film by ALD as the protective film for highly reflective EUV mirror was been confirmed.

The novel developers with low biotoxicity have attracted considerable attention to ensuring environmental sustainability. In this study, the dissolution dynamic of poly (4-hydroxylstyrene) (PHS) partially protected with t-butoxycarbonyl (t-Boc) group in alkyl-trimethyl-ammonium hydroxide (A-TMAH, 0.26N) and tetraethyl-ammonium hydroxide aqueous solutions (TEAH, 0.26N) were investigated by the quartz crystal microbalance (QCM) method. One of the methyl groups of tetramethyl-ammonium hydroxide (TMAH) was substituted by ethyl, propyl, and butyl groups. The dissolution dynamics of PHS and t-Boc PHS films showed different tendencies with the developers. In addition, the diffusion constant of PHS and t-Boc PHS in different developers was obtained from the result of dynamic light scattering (DLS), quantificationally determining their difference in dissolution rates.

Since a high-NA EUV scanner has a half field size, two masks are necessary for exposing a chip larger than the half field. However, it takes long time until exposing the 2nd half field after the 1st half exposure since many wafers need to be exposed before changing the mask not to reduce the throughput. We proposed a new scan method which enables to contact the two exposed areas using two masks which are held at a single mask stage. This gives almost no delay time for the 2nd exposure. Moreover, the throughput is improved by 1.5 to 1.7 times, which is ~90% of that of a scanner with a 6”x12” mask. However, since holding the two masks on the stage completely coaxially is difficult, a substitute exposure method is considered based on the two-mask stage. At first, the 1st exposure is provided for all the chips in a wafer with the 1st mask. Next, the 2nd exposure is provided for all the chips on the same wafer with the 2nd mask. Since switching the illuminated mask can be quick, the throughput is still higher than a single 6”x6” mask stage scanner.

EUV lithography plays a critical role in semiconductor manufacturing, and EUV pellicles are essential for preventing defects caused by photomask contamination during semiconductor production. As closed film-type membranes face limitations, interest in porous structures, such as carbon nanotubes (CNTs), is growing. Our team has been developing breathable porous silicon nitride (SiN) membranes with hole patterns. We explored wet etching techniques using KOH and TMAH for silicon etching, alongside dry etching technology for deep silicon etching. Although we attempted to create large field-size membranes, fabricating larger membranes proved difficult. So we investigated the contour of the silicon-etched side and improved the abnormal step height at the membrane edges. In a bulge test, we confirmed that the maximum deflection was 27.3μm, and the maximum pressure difference sustained was 7Pa. Remarkably, the membrane did not fracture during the bulge test. Specifically, a 40nm SiN membrane with 100nm hole patterns exhibited a 3.0 percentage point increase in transmittance compared to the 79% of a typical closed-type membrane.

With advances in cutting-edge IT technology, such as artificial intelligence and augmented reality, ultrafine lithography using extreme ultraviolet (EUV) sources has been important for high-volume manufacturing of high-performance chips. To implement EUV lithography, it is important to develop EUV components such as photoresists, pellicles, and reflective mirrors, and performance testing of them is essentially needed. In this work, a performance testing system for EUV components is introduced, and it consists of a Z-pinch EUV source, an optical system, and a sample test chamber. We focused on optical properties such as the emission spectrum of the Z-pinch EUV source and optical fluence on the surface of materials. A spectrometer was set to calibrate referred to a reference gas, source diagnosis. As monitoring the optical spectrum, optical power with a wavelength of 13.5nm was maximized by optimizing the parameters of DC pulse power, a repetition rate, and loss by absorption to the gases. As a result, the optical fluence reaches 30mJ/cm2. In conclusion, we configured a performance testing system for EUV lithography components, and it can be widely utilized to verify newly developed photoresists.

Gigaphoton Inc. presents a Sn-LPP EUV light source for mask inspection tools. This light source uses a minimum-mass Sn droplet generator with an in-line Sn fuel supply system, a double-pulse laser irradiation scheme with precise shooting control and a debris mitigation technology with H₂ buffer-gas flow. During 1500 hours of continuous operation, a brightness of 120W/mm²sr at the plasma point, a stable EUV energy 3σ-value below 5% and a high availability of 99% have been obtained without reflectivity degradation of the EUV collector mirror. We are currently developing key components for higher repetition rate to further increase the brightness.

To elucidate the thermal and magnetic dimensional stability of Cr-based Invar, the effects of various alloying elements on thermal expansion and magnetic properties were investigated. The Cr-Fe-Mn alloys exhibit low thermal expansion characteristics near room temperature, with the addition of Mn significantly elevating the Néel temperature. Specifically, the addition of approximately 0.89% Mn adjusted the low thermal expansion region to be close to room temperature, while 1.4% Sn raised it to temperatures below 0°C. The average thermal expansion coefficient (CTE) of Cr-based Invar at a temperature range between 20 and 30°C was found to be 1.7ppm/°C, comparable to the 0.90ppm/°C of conventional Invar, and approached nearly zero around 50 to 60°C. Magnetic measurements indicated that Cr-based Invar exhibits negligible magnetization compared to conventional Invars, with magnetization less than one-thousandth of Invar 36. This low magnetization results in minimal magnetostriction, making Cr-based Invar suitable for applications requiring both thermal and magnetic stability. Under a magnetic field strength of 796kA/m, Cr-based Invar showed a slight contraction behavior, unlike other Invars which expanded. This contraction is attributed to the antiferromagnetic nature of Cr, where magnetic moments align in opposite directions, leading to a net magnetization of zero.

Extreme ultraviolet (EUV) lithography is one of the essential technologies for the 5nm and below technology nodes. However, the presence of aberrations in the system severely affects the exposure results, which can lead to wafer rework and increase costs. In order to investigate the impact of aberrations in EUV lithography systems on exposure results, this paper conducts research on the impact of aberrations on exposure results of patterns that commonly used in EUV single-exposure for the 5nm technology node. A large number of aberration experiments are performed, and the distribution of critical dimension (CD), normalized image log-slope (NILS), Pattern Shift (PS), and process variation band (PVB) of exposure results in relation to all Zernike terms variation within ±50mλ is statistically analyzed. We find that aberrations lead to worse exposure results generally, and the distribution of results does not strictly follow a Gaussian distribution but exhibits significant "tail" phenomena. And the impact of aberrations varies for different patterns. Furthermore, the relationship between the distribution of exposure results and the magnitude of aberrations are investigated. It is observed that as the aberration RMS increases, the probability of deteriorated exposure results also increases. Spherical aberration has a significant impact on CD and PVB, while x-direction coma has a significant impact on the PS of vertical line-space patterns, and y-direction coma has a significant impact on the PS of vertical tip to tip patterns. X-direction astigmatism has a higher probability of causing positive PS, while y-direction astigmatism has a higher probability of causing negative PS. Relatively speaking, the effects of 3-foil, 4-foil, and 5-foil aberrations are smaller. This paper provides a clear reference for the influence of various aberrations on exposure results and can contribute to the future development and aberration control of lithography systems.

In advanced lithography nodes, variations in the sidewall angle and height deformation of photoresists can significantly impact production quality, presenting new challenges for metrology techniques. To address these challenges, we first developed a 3D nano-structure modeling toolkit, T3S, capable of generating a wide range of 3D models with diverse nano-structural features. We then employed a Monte Carlo simulator to generate SEM images of these nano-structures under various primary electron energies and detector settings. Then we analyzed the grayscale profiles of these images. By applying fast Fourier transform, we extracted the frequency domain information from the grayscale profiles of the SEM images, successfully establishing a comprehensive SEM frequency domain database of nano-structures with varying 3D features and SEM operating conditions. Furthermore, we developed a frequency domain-based algorithm to match and predict 3D nano-structural features, such as sidewall angle and height, from unknown SEM images. This database and algorithm enable the rapid and reliable assessment of photoresist shape quality, enhancing process control in advanced lithography nodes.

This article presents the first spectral responsivity calibration system in the EUV region in Taiwan. This system enables local foundries to adjust the exposure parameters of an EUV exposure machine with more certain knowledge, and thus could simplify the dose calibration processes and save energy consumption. This system utilizes the EUV radiation generated from synchrotron radiation light source, covering a wavelength range from 10nm (123.98eV) to 15nm (82.66eV), including the commonly used 13.5nm (91.84eV). This article mainly focuses on the performance evaluation of the current calibration system. Several measurement uncertainty sources will be determined and compared to identify the dominant measurement uncertainty sources for future improvement. The relative expanded uncertainty of the spectral responsivity calibration at 13.5nm is 4.6% (k=2), which meets the industrial tolerance for exposure dose determination.

Extreme ultraviolet lithography (EUVL) is employed in the mass production of advanced semiconductor devices, and the development of the high numerical aperture (NA) system for future 3 nm nodes is underway. However, the current tantalum (Ta)-based EUV masks face limitations in imaging performance for finer patterns, necessitating the exploration of alternative EUV mask absorbers. Furthermore, several promising absorber materials present challenges in etching during mask fabrication, leading to delays in their utilization. In this study, we propose a novel approach-the introduction of ion implantation processes in EUV mask fabrication to enhance the etching performance of absorber materials. We employed argon (Ar) ion implantation to enhance the etchability of platinum-tungsten (Pt-W) alloys. We not only acquired an implantation energy and dose condition that had negligible impact on film characteristics, but also confirmed that the etching rate of PtW increased by approximately 1.4 times after ion implantation, resulting in higher sidewall angles in patterns. In conclusion, the ion implantation process offers a practical solution for improving etchability without compromising film characteristics, demonstrating the potential for manufacturing EUV masks with absorbers featuring low etching performance.

While metal oxide resists showing good patterning performance and etching durability have been developed for a next generation resist as negative type resist, high performance positive tone resists are still needed for logic device manufacturing. We recently developed an organometal resist based on polarity change and chain scission, which resolved 22nm HP L/S pattern in EB drawing. However, it has some problems including film thickness loss and scum formation after development in the unexposed and exposed area, respectively. In this work, to resolve these problems, we attempted modification of our polymer-type resists in terms of chemical reactions that occurs in the exposed area. The results were discussed from their dissolution behavior by QCM method and printability by EB patterning. We found that newly designed anion D improved dissolution rate of exposed area and suppressed scum formation in exposed area. Our resist in this work resolved less than 20nm line and space patterns by such alkyl acetates as butyl acetate and PGMEA as developers.

The development of compact radiation sources for extreme ultraviolet (EUV) radiation has enabled a multitude of lab-size applications, especially in the field of metrology, that were previously only possible at synchrotron facilities. Plasma-based and high-harmonic generation (HHG) sources are widely used and well characterized at their application specific wavelength ranges in the EUV regime. The spectrum of the emitted radiation from these sources extends to a broader wavelength range, even into the visible and infrared bands and their full spectral composition is not sufficiently characterized. Therefore, a broadband spectral characterization of the source emission is of utmost importance for the investigation of photon-induced processes and metrology. In this study, the authors present a unique setup and corresponding measurement results for the high-resolution broadband spectral characterization of radiation sources covering the extensive wavelength range from 5nm to 1μm. For the vacuum wavelength range (5nm to 200nm) the setup employs a combination of three flat-field diffraction gratings with varying line density as dispersive elements. Higher diffraction orders are filtered out by a selection of thin film filters. The wavelength range above 200nm is measured with two Czerny-Turner spectrometer modules. The resulting spectra are combined to obtain the full spectrum without any contributions from higher diffraction orders. Here, the overall design, wavelength calibration, and the relative and absolute intensity calibration of the measured spectra are presented.

Phase retrieval from diffraction data is an inverse problem which is in principle ill-posed and is made tractable by appropriately introducing constraints in the problem formulation. Particularly, phase retrieval is often formulated as an optimization problem which attempts to find a solution that simultaneously fulfills two sets of constraints. For example, the support constraint can be exploited in real space, by enforcing knowledge about the object boundaries. Similarly, the diffracted intensity measured in the far–field offers a constraint that is exploited upon propagation of the optical field from the near to the far zone. In the context of Extreme Ultraviolet (EUV) mask/wafer metrology, the fabricated nanostructures are often periodic and known a–priori by their nominal design. These structures are realized on top of a substrate whose optical properties are usually known, to some degree, in advance. We consider the case of an EUV photomask with a patterned field of periodic absorber nanostructures on top of a multilayer and present simulation results that illustrate that by developing inversion schemes that account for both the periodicity of the target and the expected multilayer reflectivity value, the phase of the reflected wave can be better determined, thereby enabling imaging where the traditional inversion algorithms (e.g. ER, HIO, Ptychography) struggle.

Extreme ultraviolet (EUV) lithography, utilizing a 13.5nm wavelength, has significantly advanced the semiconductor industry. Key to this progress are developments in chemically amplified photoresists (CAR), though challenges like stochastic effects in photoresists complicate achieving required resolution and line edge roughness. To address these issues, the study explores polymethyl methacrylate (PMMA) as a model system, focusing on the impact of polymer molecular weight on roughness and defectivity. The paper investigates how variations in molecular weight influence the dissolution rate of PMMA in a developer, using commercial PMMA samples mixed with varying molecular weights to assess their dissolution behavior under EUV exposure.

In optical lithography process, a critical step involves projecting the optimal dose of energy onto the photoresist to fabricate the patterns of integrated circuits. These precise energy doses utilized for pattern projection across the wafer unavoidably induce local temperature increases, resulting in nano-level thermal deformation. The industry attempted to mitigate the effects of wafer heating by applying thermal actuators on the wafer chuck system. However, the criticality of wafer heating issue lies in the variation of thermal deformation across die and wafer, contingent upon the underlayer structures and materials employed. Even with equivalent dose, the gap of thermal deformation stemming from the underlayer configurations could contribute significantly to overlay budget constraints. Thermal deformation could constitute a large portion of the entire overlay budget when the same application is used for different underlayer structures without deformation correction.

Given that the energy of photons in Extreme Ultraviolet (EUV) is significantly higher than in Deep Ultraviolet (DUV), EUV photoresists undergo exposure via photo-ionization. In this process, high-energy photons are absorbed by the photoresist, which ionizes the polymer and subsequently generates photoelectrons. These photoelectrons produce more secondary electrons through scattering. Furthermore, compared to DUV, the number of incident photons in EUV is fewer for the same exposure dose, leading to more significant stochastic effects, such as Line Edge Roughness (LER). Therefore, modeling these stochastic effects in EUV is a noteworthy issue. Due to the complexity of the secondary electron scattering, it is extremely challenging to establish a strict EUV stochastic model from first principles. The current approach to simulating the stochastic behavior in EUV photoresist is primarily conducted through Monte Carlo dynamics-based stochastic methods, which have been proven to be an accurate method. However, these approaches necessitate conducting repeated simulations to obtain the statistical distribution of LER, which can be time-consuming. Using a semi-empirical approach to equivalently process secondary electron scattering is a worthwhile method. In this paper, we employ the Gaussian function to equivalently process the energy distribution after the scattering of secondary electrons. Subsequently, based on the PEB model that incorporates physical mechanisms, the statistical distribution of LER is derived through the transmission of variance. The model is calibrated using the statistical results of the Monte Carlo dynamics-based stochastic methods. The result shows that this approach can quickly predict the statistical distribution of LER in EUV with high accuracy.

High-NA EUV lithography is essential for advanced semiconductor manufacturing, particularly for DRAM contact hole patterning. One of the primary challenges in High-NA systems is the intensity variation between the center and edges of the slit. Additionally, critical dimension differences in the x and y directions are further complicated by anamorphic optics and arc-slit illumination configurations, adding to the overall process complexity in High-NA lithography. To address these challenges, we conducted source optimization using a rigorous lithography simulation tool for contact hole patterns, with whole arc-slit configuration. This optimization, considering the full arc-slit effect, successfully reduced intensity variation across the slit. Further refinement in pattern fidelity through threshold level light intensity adjustments improved process margins for both vertical and horizontal patterns. By minimizing the need for optical proximity correction and mask bias, our approach simplifies the pattern transfer process from mask to wafer, enhancing accuracy. Additionally, source optimization combined with precise illumination control significantly improves the process window, particularly when dealing with the arc-slit configuration, facilitating the manufacturability of DRAM patterns in high NA EUV lithography.

There is a rapidly growing need for new materials for extreme ultra-violet, EUV, lithography which incorporate high EUV absorbing atoms. Hybrid resists which are a combination of inorganic and organic moieties are promising as they offer both high EUV sensitivity and high etch resistance. However, there is a glaring lack of methods to examine the uniformity of these important materials at the nanoscale. Here we examine the capabilities of Nano-Projectile Secondary Ion Mass Spectrometry (NP-SIMS) to investigate hybrid resists. NP-SIMS is a mass spectrometry-based technique with high lateral resolution. Using NP-SIMS, a surface is probed stochastically with a suite of individual projectiles, 10⁶⁻⁷ in total, separated in time and space. Examining these individual mass spectra allows for nanoscale investigation of the uniformity of the surface. We evaluated the performance NP-SIMS using samples of polymethyl methacrylate, PMMA, infiltrated with varying amounts of InO_x via vapor-phase infiltration (VPI). We found that NP-SIMS measurements contained abundant characteristic ions related to both the PMMA and infiltrated In. The intensity of In atomic ions increased linearly with the number of infiltration cycles, however the uniformity of In and PMMA varied with the number of infiltration cycles. After one cycle we found that both the PMMA and In were relatively inhomogeneous. The homogeneity improved with subsequent infiltration cycles. Overall, the results show that NP-SIMS is capable of examining both the inorganic and organic moieties in a hybrid resist and will be an important method for understanding the performance of these materials for use in EUV lithography.

The lifetime of pellicles is difficult to predict accurately due to the influence of various factors. However, even an approximate estimation would be highly useful. To address this, we proposed a criterion for comparing pellicle lifetimes using a fatigue curve. By modeling the EUV exposure environment, we calculated the thermal stress on pellicles and applied it to the fatigue curves to analyze the lifetime variations based on pellicle materials, structures, source power, and defects. As a result, the metal silicide and carbon nanotube structures had stable lifetimes even under high source power, showing their potential as next-generation pellicle materials. Furthermore, we found that pinhole defects within the pellicles significantly reduced their lifetimes.

A high-resolution all-dry resist process is presented that utilizes amorphous zinc-imidazolate (aZnMIm) films deposited by atomic/molecular layer deposition (ALD/MLD), patterned with electron beam lithography (EBL), and developed with a low temperature gas phase etchant, hexafluoroacetylacetone (hfacH), to achieve well-resolved 16nm thick, 20nm pitch lines when using an organic-based underlayer. This work is a continuation of previous efforts that explored deposition, dry development, and pattern transfer. Previously, minimum feature sizes of 29nm thick lines with 40nm pitch were observed, but here, the use of an underlayer was able to shrink critical feature dimensions to 16nm.