This PDF file contains the front matter associated with SPIE Proceedings Volume 11854, including the Title Page, Copyright information, and Table of Contents.

Quantum computing is one of the grand challenges of the 21st century and promises to transform almost every industry. As quantum computing technology exits the academic research phase into manufacturing, the goal is not to build single, unique qubits, but millions of interconnected, identical qubits capable of performing fully error corrected, general purpose calculations. Photon-based qubits offer a path to such a general-purpose machine by leveraging the mature silicon photonics high-volume manufacturing ecosystem. Creating quantum devices from silicon photonics components requires patterning innovation to bring leading-edge nanolithography to near macroscopic scale, a unique challenge for an industry where the future relies on progressive device shrink.

While EUV systems equipped with a 0.33 Numerical Aperture (NA) lens are being applied in high volume manufacturing, ASML and ZEISS are in parallel ramping up their activities on an EUV exposure tool with an NA of 0.55. The purpose of this so-called high-NA scanner, targeting an ultimate resolution of 8nm, is to extend Moore’s law for another decade. A novel lens design, capable of providing the required Numerical Aperture, has been identified; this so called anamorphic lens will provide 8nm resolution in all orientations. Paired with new, faster stages and more accurate sensors providing the tight focus and overlay control needed it enables future nodes. In this paper we will outline the advantages of High-NA, especially for managing the needed extreme low defect printing rates while maximizing the effective throughput for patterning economics. The imaging performance is being simulated based on expected surface figures of the illumination and projection optics. Next to this, an update will be given on the status of the developments at ZEISS and ASML. Buildings, cleanrooms and equipment are being constructed, mirror production is ramping up, many tests are carried out to ensure a smooth implementation.

ASML NXE:3400 scanners are now commonly used for High Volume Manufacturing (HVM) of 7nm and 5nm logic devices as well as D1z memory devices. This year, ASML has introduced the NXE:3600D scanner to the market, targeting 3nm logic and D1a and D1b nodes. In this paper we will share the latest performance of these systems, including excellent overlay, critical dimension (CD) control, stability, reliability, and high productivity. Furthermore, we will address the ASML roadmap for meeting the requirements for the 2 nm node and beyond.

State-of-the-art EUV exposure systems utilize EUV radiation around 13.52 nm with a full band spectrum extend- ing from 13.2 nm to 13.8 nm. The variation of the wavelength in this range modifies the diffraction angles with an impact on the image blur and non-telecentricity effects. Dispersion of the materials on the EUV mirrors and on the 3D mask introduce an additional sensitivity of the imaging characteristics to the exposure wavelength. We employed the simulation models of the Fraunhofer IISB lithography simulator Dr.LiTHO in combination with measured optical material data from PTB to quantify the resulting image impact and to differentiate between the identified contributors to polychromatic imaging effects.

Contact holes are traditionally designed as squares or rectangles on the mask. The lithography tool acts as a low-pass filter of the spatial frequencies and is not able to image the corners. Therefore, the contact holes will appear as circles or ellipses on the wafer, even if they are square on the mask. Nevertheless, the presence of the designed corners imposes a limit to the center-to-center distance that can be obtained in certain contact hole configurations. Indeed, as the distance between contact holes is decreased, these corners are the first features to create violations in the Mask Rule Check (MRC). Rounded contact hole corners therefore give more design freedom. The recent introduction of multi-beam mask writing makes writing curvilinear shapes on actual masks practical, including contact holes with corner rounding. While the benefits to design freedom are obvious, there is a need for studies identifying the impact of this additional corner rounding parameter on the imaging properties. In this work, we investigate the imaging impact of corner rounding on pitch-40nm contact holes, exposed with an EUV scanner (ASML NXE:3400B at imec). The study aims to experimentally establish the difference in imaging quality introduced by the corner rounding. More specifically, we first characterize the pattern fidelity on the mask by means of mask CD-SEM images. Next, we assess the impact of corner rounding on imaging properties such as Local Critical Dimension Uniformity (LCDU), Mask Error Enhancement Factor (MEEF) and Exposure Latitude.

New resists are needed to advance EUV lithography. Tailored design of efficient photoresist is impossible without fundamental understanding of EUV induced chemistry. The absorption of an EUV photon by a thin film resist leads to emission of primary and secondary electrons. The electrons may travel up to tens of nanometers before losing their kinetic energy via collisions which initiate chemical reactions. The “blur” of an aerial image is directly related to the distance that electrons are able to travel and initiate chemistry in the resist. Thus, identifying how to measure and influence the absorption of EUV photons, emission of electrons, and distance traveled by the secondary electrons is extremely beneficial to the resist community. In this work, we present several experimental techniques to probe model polymer materials to investigate the impact of specific chemical groups on three critical resist properties: EUV absorption, electron emission, and the electron attenuation length (EAL). EUV absorption dictates the efficiency of the film to absorb photons. Total electron yield (TEY) provides information on the conversion of absorbed EUV photons to electrons, whereas photoelectron spectroscopy (PES) provides information on energies and abundance of generated electrons. The EAL corresponds to the thickness of a material required to reduce the number of emitted electrons to 1/e of the initial value. The EAL reveals the distance the electrons can travel in a resist film, which is directly related to the electron blur. Correlations between the obtained experimental values is discussed.

For EUV lithography, hemicellulose EUV resist was proposed and studied the relationship between lithography performance and resist structure. The key parameters of hemicellulose resist for improvement of EUV lithography performance are hemicellulose content and resist structure (EUV sensitivity unit and sensitivity enhanced unit). OPAL-R4 which has 3 times the hemicellulose content and special resist structure compared with OPAL-R1 is the best performance. For high-NA EUV lithography, hemicellulose EUV resist has a potential of high performance.

In the photolithographic process of semiconductor manufacture, a photoresist is exposed to light and then developed to create a pattern on the photoresist surface. After development, a rinse step is necessary to prevent pattern collapse and to remove polymer residues that linger after development. Surfactants are essential in these rinse solutions and help mobilize polymer residues while also minimizing capillary forces that are responsible for pattern collapse. An ideal surfactant system interacts with the polymer surface enough to mobilize debris particles, but not enough to cause swelling and shift the critical dimension; while at the same time creating a surface tension and contact angle to prevent pattern collapse. In this work, we investigated various non-fluorinated surfactants and their interaction with EUV photoresists by measuring surface tension, contact angle, and photoresist swelling. Although the difference of solubility parameters (DSP) between surfactants and photoresists were shown to correlate to photoresist swelling. No correlation between resist swelling and the difference of solubility parameters was found in the study. Through this work, we identified that ideal surfactant rinse properties can be achieved in a fluoro-free surfactant formulation. Ideal fluoro-free EUV surfactant rinse formulations achieve no pattern collapse, low CD-shift, and good residue clean performance for an EUV photolithographic process.

The goal of this work is to prepare process readiness towards High NA EUV lithography, by using 0.33NA exposures on NXE3400B scanner. We focus on photoresists, underlayers and etch processes mitigation of P24nm Line Space patterns. Etch transfer has been validated for Metal Oxide Resist (MOR). Furthermore, we investigate challenges to accelerate Chemically Amplified Resist (CAR) P24nm Line Space processes. Also, here, promising patterning results have been achieved. Thin film metrology-friendly methods like Atomic Force Microscopy (AFM) have been performed to characterize and improve the CAR-based etch processes.

EUV (extreme ultraviolet) lithography is progressively being inserted in high volume manufacturing of semiconductors to keep up with node shrinkage. However, defectivity remains one big challenge to address in order to be able to exploit its full potential. As in any type of lithographic process, processing failures and in-film particles are contributors that need to be reduced by the optimization of coating and development processes and improved dispense systems. On top of these defects, stochastic failures, due to photon shot noise or non-uniformities in the resist, are another major contribution to the defectivity. To support their mitigation, etch process can be used to avoid their transfer to underlying layers. However, it requires a sufficient resist mask thickness. For line and space patterns, providing more resist budget comes with a trade-off which is the increase of pattern collapse failures, especially with shrinking critical dimensions. Collapse mitigation approaches are therefore very important to enable tight pitches and were explored. Stack engineering and especially optimization of resist under layers will be crucial components to enable patterning and defect reduction of shrinking pitches. Finally, as an alternative to traditional chemically amplified resists, metal containing resists are also promising because of their inherent high etch resistance. Dedicated hardware and processes were developed the use of such materials and prevent metal contamination to other tools during further processing steps. In this report will be presented the latest solutions to further decrease defectivity towards manufacturable levels and provide more process margin to achieve better quality patterning towards the limits of NA 0.33 EUV exposure. Furthermore, technologies to improve CD uniformity and stability, which are required for mass production, will also be reported.

In this work we studied the impact of stochastic resist defects on electrical measurements of BEOL structures, and seek to demonstrate that large electrical test structures, built with a relatively simple patterning flow, can be used in the early stages of resist, and patterning development, as the electrical failures are almost exclusively caused by resist defects. To that end, single-layer electrically testable metal patterns at minimum metal pitch of 28nm were created using a single 0.33NA-EUV exposure and a metal damascene process flow. A bright field mask was exposed with a metal-organic, negative-tonedevelopment resist process to create trench structures that are transferred into an oxide dielectric layer. Following this, the trenches were filled with ruthenium (Ru) for electrical testing of meander resistor and fork-fork structures.

The continued need to satisfy the Power-Performance-Area requirements in advanced technologies resulted in a steady and rapid increase in manufacturing costs in the last years. Indeed, novel process integration schemes can require advanced tools and/or new materials, further aggravating cost. In addition, several dimensions are slowing down reaching a plateau due to physical limitations, which can impact the resulting die cost. Therefore, in this work we analyze advanced technology nodes from a cost perspective, considering different patterning and integration schemes at 3 nm and 2 nm node as this is becoming more and more important. Also, possible scenarios regarding the introduction of high-NA EUV lithography at the 2 nm node are explored, showing promising results from both a cost and a yield perspective.

Driving down imaging-induced edge placement error (EPE) is a key enabler of semiconductor technology node scaling1-3. From the 5 nm node forward, stochastic edge placement error (SEPE) is predicted to become the biggest contributor to total edge placement error. Many previous studies have established that LER, LCDU, and similar variability measurements require corrections for metrology artifacts and noise as well as mask variability transfer to more accurately represent wafer-level stochastic variability. In this presentation, we will discuss SEPE band behavior based on a methodology that allows local extraction of SEPE from total measured local variability (LEPU) in a generalized way along 2D contours.

To further increase the resolution of EUV scanners ZEISS is working on next generation EUV optics with an increased NA of 0.55. This next generation optics consists of a highly flexible illumination system and projection optics with NA 0.55 to allow scaling beyond the next decade. In this presentation we will present the status of the high-NA optics program at ZEISS. We report on the high NA infrastructure including mirror polishing, coating, surface figure metrology, mirror handling, and integration tooling. Progress in manufacturing of mechanics, frames and mirrors at ZEISS for both illuminator and POB will be shown.

To enable cost-effective shrink of future devices, a new High-NA EUV platform is being developed. The High-NA EUV scanner employs a novel POB design concept with 0.55NA that enables 8nm HP resolution and a high throughput. In this paper we will discuss the imaging performance and technology solutions to support our customers device roadmap from High-NA insertion towards low-k1 extension for critical Logic/MPU and DRAM layers. We will address various technology solutions that enable a high contrast through focus for decreasing feature size, such as mask stack optimization, computational litho solutions and advanced illumination shapes.

A series of experiments was conducted to study how defectivity depends on NILS, aerial image intensity and depth-offocus. Three sets of illuminations were designed to vary only one of these parameters while keeping the others constant for a 48 nm pitch orthogonal contact hole array. The focus was on the after etch defectivity, for which two different etch processes were studied. Both on-wafer LCDU and defectivity for the two etch processes were correlated to the different illumination settings. In summary, we found that defect levels correlate best with the maximum intensity for missing holes and minimum intensity for merging holes. Depth-of-focus appears to have little or no impact on defectivity for the nominal focus condition.

This paper extends the 2019 and 2020 symposium contributions clearly showing that (local) mask defects and non-local mask defects (NLMDs) act as triggers for increased stochastic failure probability on the EUV printed wafer. The present work focuses on anamorphic imaging at 0.55 NA, including horizontal and vertical pattern orientations, and comprises defocus conditions and line breaking as a second failure mechanism. Two roughness type NLMDs are studied: multilayer (ML) ripple relates to a non-fully planar coating of the ML mask stack. Mask absorber line-edge roughness is addressed as a second roughness type NLMD. The longer-term intent is to inspire defining limits to their impact, from the perspective that an increased mask contribution to stochastics of high-NA EUV lithography must be avoided.

Over 85 EUV scanners are installed at customer factories and being used in high volume manufacturing (HVM) of leading semiconductor devices. The latest generation of EUV sources are operating at 250W with 92% availability, while meeting all performance requirements. Future EUV scanners are projected to require even higher power to meet throughput requirements. In this paper, we provide an overview of a the latest advances in the laboratory for tin laser-produced-plasma (LPP) extreme-ultraviolet (EUV) sources at 13.5nm enabling HVM at the N5 node and beyond, highlighting crucial EUV source technology developments needed to meet future requirements for EUV power and stability. This includes the performance of subsystems designed for critical source functions such as collector protection and continuous tin droplet supply.

The extreme ultraviolet (EUV) light source has been developed together with the lithography EUV scanner. As tool with a 10 W EUV light source, ASML shipped the “a-demo tool” in 20071) and Nikon shipped EUV-1 in 20082). Then ASML developed the b-tool, NXE-3100, at the beginning of 2011 with a 100 W EUV light source.3)4) Requirement of the EUV exposure tool is now covered by the g-tool; NXE3300 (for high volume manufacturing (HVM))5). The required EUV power is 250 W clean power (after purifying infrared (IR) and deep ultra violet (DUV) spectra) at intermediate focus (IF). However, the demonstrated power level was around 80 W6)7) in 2013.

The Laser-assisted Discharge-produced Plasma (LDP) EUV source has been developed as a light source for actinic mask inspection and beamline application and deployed in the field. LDP EUV source enables to generate high brightness with relatively larger EUV plasma by discharged plasma triggered by laser on one electrode disc which is coated by tin film. As EUVL process is used more in mass-production process, the requirement for EUV source for mask inspection is required more. USHIO LDP source has overcome various issues specialized from LDP source and realized high reliability 24/7 based operation with high brightness maintained.

An ERL(energy recovery linac)-based EUV-FEL can provide EUV power of more than 1 kW for multiple scanners to overcome stochastic noise and to achieve higher throughput. An IR-FEL project started at the KEK cERL for the purpose of developing high-power IR lasers for high-efficiency laser processing, and it can demonstrate proof of concept of the EUV-FEL for future lithography. We will briefly review the EUV-FEL and present construction and commissioning of the cERL IR-FEL including future work.

The introduction of novel photoresists is a critical enabler of future technology nodes, including the upcoming high-NA EUVL deployment. The development of EUV materials is investigated within the scope of a resist screening program between ASML and PSI. In this work, the EUV interference lithography tool at PSI is used to study materials performance in terms of the resolution-roughness-sensitivity tradeoff, with an emphasis on ultimate resolution. Here, we review the development status of different platforms by considering recent results obtained in the first half of 2021 (H1-2021). Patterning resolution of 11 nm half-pitch is achieved with both CAR and non-CAR materials, which indicates steady progress in the global resist development. Perspectives of this work are discussed towards enabling 8 nm half-pitch resolution solutions.

Zeon developed ZER02#04 resists with main chain scission reaction to enhance patterning performance for EUVL. This presentation focuses on the patterning performance of contact hole patterns with ZER02#04DM at ADI and AEI. For example, at P40nm orthogonal C/H in ADI, the resolution at 17.5 nm in hole CD was achieved at the exposure dose of 76 mJ/cm2, giving a LCDU of 2.77 nm. And it could transfer P40nm orthogonal C/H patterns to SiO2 by etching. The LCDU in AEI was enhanced at 2.47 nm. Additionally, the results with novel resist for next generation plan to be introduced at my presentation.

One approach for a novel EUV resist is the multi-trigger concept wherein a reaction will only occur when multiple elements of the resist are initiated concurrently and in close spatial proximity. We present results focused on the enhancement of the high-opacity MTR resist which shows a decrease in dose and improvement in Z-factor using a higher activation energy MTR molecule for pitch 32nm dense lines. We present pillars at p40 with a diameter of 24nm, dose of 72mJ/cm2, with a CDU of 2.63nm.

In the development of highly resolving and highly sensitive resist materials, stochastic phenomena (LER and stochastic defect generation) are a critical issue. In this study, the dependences of chemical gradient (an indicator of LER) on the half-pitch of line-and-space patterns, the thermalization distance of secondary electrons, EUV optical contrast, the photoacid generator (PAG) concentration, the photodecomposable quencher (PDQ) concentration, and the effective reaction radius for deprotection were investigated using a simulation on the basis of the sensitization and reaction mechanisms of chemically amplified EUV resists. The relationships between resolution, LER, and sensitivity were formulated in terms of thermalization distance.

With EUV lithography now a stable part of the chip Industry production processes, the attention and demand for higher productivity is more pressing than ever. To support customers' demands, ASML has developed the next generation EUV pellicle, increasing the EUV transmittance and lifetime standards. Thanks to its unparalleled performance, the new generation pellicle boosts the scanner productivity more than 20% compared to the previous one.

Sometimes the biggest impact can be made in the smallest details. Canatu pioneers the future of semiconductor manufacturing and extreme ultraviolet (EUV) lithography with its freestanding carbon nanotube (CNT) membrane pellicles that protect photomasks from particles and defects, enhancing precision, shortening processing, and increasing production efficiency per wafer. When the already remarkable 1-dimensional intrinsic properties of virtually defect-free CNTs are expanded into a 2-dimensional network, this added degree of freedom results in a membrane with an unequaled combination of optical and mechanical properties, that may truly provide solutions for the extreme physics of EUV at increasing powers. Here, we demonstrate the extensive customizability and versatility of Canatu’s CNT synthesis and freestanding network fabrication processes. For example, the fine structure and chemistry of individual tubes, as well as the mesoscopic morphology of the network can be optimized extensively. In practice, this enables precise control over the size and type of catalyst particles, as well as the diameter of the tube and the number of walls in the carbon nanotube (Single, Double, or Multi-walled). The orientation of the CNTs in the network can also be controlled, and the CNTs can be induced to form either larger or smaller bundles, resulting in dense or sparse networks with constant optical transmittance. CNT surfaces can be further treated or coated in response to specific chemical or optical requirements. In summary, this high degree of tunability is becoming increasingly critical in applications where strict particle and impurity filtering requirements must be met with minimal optical disturbances.

Extending 0.33NA EUV single patterning to pitch 28nm will enable metal layers cost-efficiency and significantly shorter process flow for N2 node. At the same time, EUV single patterning becomes very challenging in terms of stochastic defectivity and process window. In this paper, the lithographic performance of the M1 layer of an imec N3 (foundry N2 equivalent) random logic layout is evaluated by means of source mask optimization on these three mask candidates: a standard binary Ta-based absorber mask, a high extinction (high-k) absorber mask and a low-n attenuated phase-shift mask. The impact of mask tonality (bright field vs. dark field) and insertion of sub-resolution assist features on pattern fidelity and process window is evaluated.

We employ the hybrid mask model of the Fraunhofer IISB simulator Dr.LiTHO to investigate the role of the absorber and multilayer for the observed image blur and contrast loss mechanisms. Hybrid mask model decomposes the EUV mask into the absorber and multilayer part. Both parts can be described by real 3D objects or idealized 2D objects. An idealized absorber is specified by the transmission tr and phase of the transmitted light. An idealized multilayer mirror is characterized by a certain reflectivity value, by an angular range or bandwidth (BW) where the light is reflected and by a distance Zeff from the absorber. The diffraction of the incident light by the absorber, the reflection of the diffracted light by the multilayer mirror, and the second diffraction of the reflected light by the absorber are combined by transfer matrices. The obtained superposed diffraction orders provide characteristic diffraction efficiencies and phase values of discrete orders. The presented analysis of the light diffraction from EUV mask and resulting imaging metrics provides several novel insights into the root causes of M3D effects in high NA EUV imaging. The combination of double diffraction by an ideal (thin) absorber and reflection by an ideal (thin) multilayer with a limited reflectivity range (BW <= 15°) explains the peculiarities of the optimum phase of attenuated PSM for EUV. In contrast to phase shift masks for DUV with an optimum phase of 180°, the optimum phase of attenuated phase shift mask for EUV is in the range between 200° and 250°. The optimum value varies with the pitch and a chosen trade-off between large image contrast (normalized image log slope - NILS) and large threshold to size. The real 3D absorber and multilayer contribute to the specific value of the best absorber thickness and phase as well, This finding explains previous observations of this phenomenon. Waveguide effects in real absorbers with low refractive index n are at the basis of the good imaging performance of low n materials. Low n absorber materials exhibit significant sensitivity to illumination direction and feature size. The described double diffraction of light by the absorber introduces characteristic jumps in the optimum bias (and other imaging metrics) versus pitch. The optimized phase/thickness of low n (low k) absorbers can extend the performance of high NA EUV imaging to pitches below 10 nm.

The EUV Photomask in its state of the art architecture reveals a contradiction in design. Two seemingly disparate functions are juxtaposed to form the foundation of the EUV mask. On the one hand a highly reflective multilayer is required to transmit maximum light to the wafer. On the other hand an inscribed absorber layer pattern spatially selectively blocks the transmission of light to transcribe the pattern of the IC on the wafer. Limitations in the performance of materials result in an inelegant solution with side effects. In this presentation we explore the feasibility of an alternative homogenous mask design with a highly engineered multilayer that can perform the same function as today’s EUV photomasks.

It seems like EUV is at the center stage of semiconductor industry nowadays. Several leading companies has already established manufacturing foothold on EUV and add the number of equipment steadily where double-digit number of tools are already operational in their realm. Mostly logic and foundry sectors have moved earlier for EUV high volume manufacturing but memory makers are also following suit. In the presentation, it will be reviewed what specific aspects has differentiated the memory sector from logic and foundry in view of EUV adoption. The value of EUV lithography by comparing that of ArF immersion based multiple patterning techniques will be examined. It will be also touched on the current status and future extendibility of EUV lithography in view of DRAM manufacturing will be briefly addressed also.

Extreme ultraviolet lithography (EUV) materials and processes are constantly evolving and maturing, making sub-30 nm pitch single-exposure yield feasible. Characterization methodologies for stochastic variations are well-documented at this stage, with most employing critical dimension scanning electron microscopy (CDSEM) and a form of defect inspection to quantify line edge roughness (LER), local critical dimension uniformity and patterning failures. In this paper, the link between LER and stochastic defectivity is explored at a deeper level, as we probe the possibility of nucleating stochastic failures with programmed LER structures at 30 nm pitch using CDSEM, optical inspection and electrical yield data. First, we characterize LER post-develop and post-etch using unbiased LER measurements. Second, we study the defectivity and optical characteristics of the programmed LER pattern post hard mask open using optical inspection. Specifically, we measure the optical noise induced by programmed LER, the inspection performance in terms of defect capture and nuisance rate, and the predictive capability of optical inspection through a comparison of defectivity with electrical yield data.

As we strive toward smaller and smaller pitches and new 3D constructs to enable device scaling, thorough defect characterization at wafer scale is essential during the early phases of process optimization. Often CD (critical dimension) variations and roughness lead to high SEM (scanning electron microscope) inspection noise. It is important to suppress this noise and increase DOI (defect of interest) SNR (signal-to-noise ratio) for better detection efficiency while maintaining high speed for meaningful wafer coverage. In this work, we describe experiments and show characterization results for capturing EUV (extreme ultraviolet) stochastic defects across various test structures of 28nm pitch devices that have been patterned using single exposure 0.33NA EUV lithography. We have used KLA eSL10TM for SEM inspection and analysis. The tool can also be used for high resolution and high-speed metrology, providing quick feedback on observed defect signatures and further root cause analysis.

The feasibility of using extreme ultra violet (EUV) lithography in high volume manufacturing makes the technology a very strong candidate for sub 20nm patterning. However defect control remains a major challenge even today. The aim of this paper is to understand propagation of the programmed defects present on the EUV mask to wafer to get an understanding of how stochastic defects may evolve through processes and how we can mitigate it. The evolution of the defects from mask to wafer post lithography and post etch has been studied both theoretically by calculating change in defect area from a script on images taken with e-beam inspection and other metrology techniques like atomic force microscopy. The end goal is to study the propagation of these programmed defects from post lithography to post etch on wafer through parameters like defect area, defect sizes and stack height information[1][2].

High Numerical Aperture (NA) EUV lithography will require very thin resist films. This reduction in thickness will challenge most metrology techniques, except for Atomic Force Microscopy (AFM). Indeed, thinner resist films allow AFM to reach a better depth accuracy and a higher throughput. In this work, we demonstrate the capabilities of AFM metrology on 16-nm half-pitch resist lines obtained with 5 resist film thicknesses ranging from 10 to 30 nm. As we show, AFM provides relevant information about the pattern dimensions (resist height, line top roughness) as a function of exposure dose, and even about the bottom trench roughness on films with thickness < 10 nm.

Contour detection of an object is a fundamental computer vision problem in image processing domain. The goal is to find a concrete boundary for pixel ownership between an OOI (object-of-interest) and its corresponding background. However, contour extraction from low SN SEM images is a very challenging problem as different sources of noise shadow the estimation of underlying structural geometries. As device scaling continues to 3nm node and below, the extraction of accurate CD contour geometries from SEM images especially ADI (after developed inspection) is of utmost importance for a qualitative lithographic process as well as to verify device characterization in aggressive pitches. In this paper, we have applied a U-Net architecture based unsupervised machine learning approach for de-noising CD-SEM images. Unlike other discriminative deep-learning based de-noising approaches, the proposed method does not require any ground-truth as clean/noiseless images or synthetic noiseless images for training. Simultaneously, we have also attempted to demonstrate how de-noising is helping to improve the contour detection accuracy. We have analyzed and validated our result by using a programmable tool (SEMSuiteTM) for contour extraction. We have de-noised SEM images with categorically different geometrical patterns such as L/S (line-space), T2T (tip-to-tip), pillars with different scan types etc. and extracted the contours in both noisy and de-noised images. The comparative analysis demonstrates that de-noised images have higher confidence contour metric than their noisy twins while keeping the same parameter settings for both data input. When the ML algorithm is applied, the contour extraction results would have higher confidence numbers comparing with the ones only applied the conventional Gaussian or Median blur de-noise method. The final goal of this work is to establish a robust de-noising method to reduce the dependency of SEM image acquisition settings and provide more accurate metrology data for OPC calibration.

Experimental results demonstrated that the EUV low-n mask improves both LCDU and dose for dense features. For semi-isolated and isolated features best-focus shifts through pitch can occur with the low-n mask as well as with the Tabased mask. In this paper, we show how mask-3D induced phase offsets between diffraction orders lead to best focus shifts for dense and (semi-) isolated features. Subsequently we investigate what are the options to mitigate best focus shifts. First, when the pitch is large enough, sub-resolution assist features (SRAFs) can significantly improve contrast and reduce best-focus shifts. Second, optimizing the target and mask bias, is very effective for focus-shift mitigation. Especially the low-n mask shows a strong response to target and mask bias. Third, using bright field imaging instead of dark-field imaging generally also results in smaller best focus shifts through pitch. Using source-mask optimization (SMO) examples through pitch, we show how these mitigation strategies are effectively applied to through pitch use cases. We find NILS DOF improvements up to 65% with the low-n mask and optimized retargeting.

Novel reticle absorber materials are required for high-NA EUV lithography. TNO and ASML developed an assessment for the compatibility of novel high-NA reticle absorber materials with conditions that mimic the EUV scanner environment^[1]. Four candidate reticle absorber materials were evaluated, TaCo, RuTa, PtMo and Pt2Mo alloys, in a joint research program. For the compatibility tests, dedicated samples with silicon wafer substrates were fabricated. The silicon wafers were coated with a Mo-Si multilayer coating, followed by a Ru capping layer and finally the absorber material.

Chemical outgassing tests, in presence of hydrogen radicals, did not show chemical outgassing for the TaCo and PtMo alloys. RuTa and Pt₂Mo alloys were not tested, based upon their elemental composition chemical outgassing is not expected. Next, all four materials were exposed in a hydrogen plasma resistance test equivalent to an EUV exposure of at least 250 thousand wafers** in the EUV scanner. No plasma-induced defects, like blistering or delamination, were found that were related to the intrinsic absorber properties.

The RuTa and PtMo alloys were selected for EUV exposure in the EBL2 facility at TNO. Both materials were exposed to an 9.6 kJ/mm² EUV peak dose at an EUV peak intensity of 450 mW/mm² in a hydrogen environment. This EBL2 EUV exposure of 6 hours represents about 1-2 months of EUV dose (at least 150 thousand wafers) in a NXE or EXE scanner with a 300 W source. Both materials showed good performance during EUV exposure. Relevant surface defects and chemical outgassing were not observed. The few observed blisters in the low EUV intensity areas are likely provoked by particle contamination or coating defects.

All four absorber materials, TaCo, RuTa, PtMo and Pt₂Mo alloys performed well in the compatibility tests that were executed. Not all compatibility tests could be performed on each absorber material within the scope of our research program. Further testing would be needed to complete the compatibility assessment, including an EUV exposure on a patterned reticle.

We present a comparison of the properties of the Mo/Si multilayers deposited by three techniques: secondary ion beam deposition (IBD), DC magnetron sputtering (MS), and biased-target ion beam deposition (BTIBD). Based on sputter simulations, we demonstrate that the energetics of the depositing adatoms and the intermixing depth depend strongly on the target/beam voltage, process pressure and target-to-substrate distance. XRR measurements indicate that the multilayers deposited by MS are much rougher than those deposited by IBD and BTIBD. SIMS and RBS measurements suggest that the Mo layers have low contamination of Fe and Al indicating insignificant beam overspray onto the target mounting material, as well as minimal Ar implantation. High-resolution TEM analysis shows intermixed layer thickness in the range of 0.3 to 1.9 nm and interfacial roughness in the range of 100 to 500 pm. Optical calculations suggest that the observed level of contamination is expected to have minimal impact on the EUV peak reflectivity. The intermixed layers could result in a 2-5% decrease in peak reflectivity. Further, the optical simulations predict that the 100-200pm range interfacial roughness in IBD and BTIBD cause a <0.5% reduction in peak reflectivity, whereas the 200-500pm range interfacial roughness in MS films is expected to compromise the peak reflectivity by up to 5%. This comparison of a variety of thin film techniques for the deposition of Mo and Si has allowed us to gain a deeper insight into the challenges faced during the fabrication of EUV mask blanks.

Optical masks are classified based on the transmittance of the absorber. The optical density of binary masks is over three. This means that the transmittance is less than 0.1 %. Long experience in developing optical phase-shift masks (PSMs) has shown that the optimum transmittance of PSMs is 5~15 %. High transmittance PSMs are avoided due to the unwanted sidelobe printing. In the same way, EUV masks can be classified based on the reflectance of the absorber. Assuming the phase-shift value of the absorber to be π, the reflectance relative to ML is calculated by exp(-2πk/(1-n)), where n+ik is the complex refractive index of the absorber. Therefore, EUV masks are classified by the ratio of the complex refractive index k/(1-n). We classify EUV masks into four categories, i) binary mask: 1 < k/(1-n), ii) low-R PSM: 0.5 < k/(1-n) < 1, iii) PSM: 0.3 < k/(1-n) < 0.5, and iv) high-R PSM: k/(1-n) < 0.3. Conventional TaN absorber is a low-R PSM where k/(1-n) = 0.58. It is not a binary mask as it requires black borders. The benefit of PSMs is that they reduce dose. The drawback of PSMs is that they increase edge placement error (EPE). Especially in high NA optics, the error cannot be compensated by illumination optimization. On the other hand, binary masks reduce EPE at the expense of increased dose. There is a tradeoff between dose and EPE. The optimum absorber selection depends on the pattern layout. In CH applications, PSMs are favorable to reduce dose. Binary masks are suitable for L/S applications to suppress EPE.

As EUV lithography becomes the new standard for electronic chip manufacturing, identifying suitable materials for higher resolution patterning stands out as a prominent challenge to reach future technology nodes. Innovative approaches to patterning are becoming more and more relevant as conventionally used photoresists approach their limitations. In this work we use the Interference Lithography tool at the Paul Scherrer Institute (Swiss Light Source) for screening of EUV Lithography materials. We highlight the EUV lithography exposure mechanism of secondary electron chemistry and its versatility in inducing a solubility switch in photosensitive materials by using a chicken egg-white albumin protein cluster as a resist to obtain sub-100 nm patterns.

The continuous need to shrink dimensions using EUV lithography has posed challenges and opportunities for patterning materials and processes. Scaling BEOL interconnect structured is a key element to performance improvement of functional devices. In this paper, we investigate the impact of various factors on the patterning of EUV single exposure vias, to find effective strategies to shrink critical dimension (CD) with improved critical dimension uniformity (CDU), local critical dimension uniformity (LCDU) and decrease in defectivity. This work is based on patterning a system on chip (SoC) random logic via layer at minimum horizontal interconnect wire pitch of 28nm, which is the limit of single exposure interconnect with 0.33 NA EUV tools. This design uses aggressive CPP/Mx gear ratio of 3/2 which is equivalent to 38nm to 34nm pitch orthogonal via arrays, thus, examining the impact of the primary patterning parameter and illumination source co-optimized with OPC treatment of rectangular vias. The via patterns are transferred to bottom dielectrics to study the evolution of LCDU and defectivity through etch.

Applications that require high resolution patterns are numerous, leading to an increasing demand for compact patterning tools and alternative lithographic concepts. For many scientific applications like biosensing or fabrication of metamaterials, or artificial crystals, the achievable resolution and the patterned area of the fabrication process are of main importance. In the field of high-volume manufacturing, there is a need for high-resolution patterning at the industrial exposure wavelength of 13.5 nm. The main industrial application for compact exposure tools is EUV photoresist development and its related process optimization. The overall patterned area is of minor interest. Instead, the focus is placed on the achievable resolution and quality of the intensity distribution used for the patterning tests. The realized EUV dual beamline allows to address both application fields in a single in-lab setup. By operating the source with an argon/xenon (Ar/Xe) gas mixture, a narrowband spectrum with a main wavelength of 10.9 nm is created without the need of spectral filtering. The resulting intensity of up to 2 mW/cm² in wafer plane allows large area patterning with highest throughput of several mm²/min. Single exposure fields of 2 x 2 mm² can be stitched together to achieve an overall patterned area of up to several cm² with minimal stitching borders of ~ 1 μm. By inserting a customized multilayer mirror into the beamline, the emission spectrum of the DPP source (operated with pure Xe gas) is in-band filtered to 13.5 nm, thus allowing qualification of industrial photoresists regarding sensitivity, contrast and resolution. The mask-wafer positioning system for the 13.5 nm beamline is designed for maximum rigidity to minimize relative movements between the mask and wafer that would lower the achievable resolution. Multi-field resolution test masks are created in-house and are exposed in a parallel manner to determine the achievable resist resolution in an efficient manner. Transmission mask designs are optimized by a rigorous simulation model. By tuning the pattern geometry on mask, different patterns like contact holes or nanopillars can be created on the wafer, tailored to the required application.

We present performance metrics for the commercially available TEUS product line. TEUS-S is a high-brightness EUV LPP light source based on a fast rotating liquid metal target with EUV collection angle of 0.05sr. The TEUS-S100 and S400 models employing 100W and 400W of average laser power respectively have been characterized wi0th particular attention to the collector optics lifetime. It is estimated that 10% mirror reflectivity degradation will occur after 2 years for the TEUS-S100 and after 0.5 year for the TEUS-S400 in 24/7operation mode. The TEUS-S400 source provides more than 30 mW of in-band (±1%) EUV radiation after the debris mitigation system.

The flatness of the silicon wafers used to manufacture integrated circuits (IC) is controlled to tight tolerances to help ensure that the full wafer is sufficiently flat for lithographic processing. Advanced lithographic patterning processes require a detailed map of the wafer shape to avoid overlay errors caused by depth-of-focus issues. A large variety of new materials are being introduced in Back-End of Lines (BEOL) to ensure innovative architecture for new applications. The standard in-line control plan for the BEOL layer deposition steps is based on film thickness and global stress measurements which can be performed on blanket wafers to check the process equipment performance. However, the challenge remains to ensure high performance metrology control for process equipment during high volume manufacturing. With the product tolerance getting tighter and tighter and architecture more and more complex, there is an increasing demand for knowledge of the wafer shape. In this paper we present Wave Front Phase Imaging (WFPI), a new wafer geometry technique, where 7.65 million data points were acquired in 5 seconds on a full 300mm wafer enabling a lateral resolution of 96μm.

Significant efforts have been dedicated to the development of inorganic-organic hybrid materials for next-generation EUV resists. Among the various synthesis, vapor-phase infiltration of metal source into existing e-beam photoresists using ALD process has drawn great attention. In this work, we have demonstrated the vapor-phase infiltration of both Hf and Al precursors into PMMA and HSQ resists, respectively. For example, under the electron exposure with 100 eV, both hybrid resists show relatively higher EUV absorption, increasing positive and negative tone. The detailed photochemical reactions of on electron exposure were investigated using an in-situ FTIR equipped with electron gun capability.

As the industry continues to push the limits of integrated circuit fabrication, reliance on EUV lithography has increased. Additionally, it has become clear that new techniques and methods are needed to mitigate pattern defectivity and roughness at Litho and Etch together with eliminating film-related defects. These approaches require further improvements to the process chemicals and the lithography process equipment to achieve finer patterns. In particular improvements in the coater/developer hardware and process are required to enable the use of a wide variety of chemicals as well as compatibility with existing systems. This paper reviews the ongoing progress in coater/developer processes that are required to enable EUV patterning sub-30nm line and space by using MOR (Metal Oxide Resist).

We investigate atomic structure and atomic processes of Sn and heavier elements for present and future extension of EUV source. We investigate experimental and theoretical spectrum to identify the average wavelength, width and strength of combined 4d-4f and 4p-4d transition arrays from which intense EUV emission is obtained. We investigate the spectrum taking the effect configuration interaction (CI), as well as the effect of emission from multiply and inner-shell excited states. We will discuss data driven approaches, with that fast and accurate methods to predict spectral property of the plasma is explored.

Even though the EUV pellicle has less than 0.04% EUV reflectivity, it could be locally increased at wrinkles on the pellicle and the intensified light could cause a local CD variation. we confirmed that the reflectivity was increased by more than 4 times due to the pellicle wrinkle and it caused the mask CD variation. Therefore, although the pellicle satisfies the EUV reflectivity requirement, we also need to qualify the wrinkle of the pellicle for the CD variation issue during the exposure process.