Extreme Ultraviolet Pellicle Research Articles

Development and optimization of metal silicide EUV pellicle for 400W EUV lithography.

In the extreme ultraviolet lithography (EUVL) process, extreme ultraviolet (EUV) pellicles serve as thin, transparent membranes that shield the photomask (reticle) from particle contamination, thereby preserving photomask pattern integrity, reducing chip failure risks, and enhancing production yields. The production of EUV pellicles is highly challenging due to their mechanical fragility at nanometer-scale thicknesses and the need to endure the rigorous conditions of the EUVL environment, which include high temperatures and hydrogen radicals. Consequently, extensive research has been conducted on a variety of materials, such as carbon-based and silicon-based substances, for the development of EUV pellicles. This study explores the feasibility of implementing molybdenum silicide (MoSix) pellicles for high-power EUVL applications. We successfully fabricated MoSix pellicles in two dimensions: a 10 mm x 10 mm sample and a full-size 110 mm x 144 mm pellicle. We then evaluated their optical, mechanical, thermal, and chemical properties, as well as their lifespan. The pellicles demonstrated over 90% transmittance and less than 0.02% reflectance. The films exhibited a deflection of 300 μm under a 2 Pa differential pressure and an ultimate tensile strength (UTS) exceeding 2 GPa. The thermal emissivity was measured at 0.3. Additionally, the durability of the pellicles was validated through exposure to 20,000 wafers using a 400W EUV power (offline test: 20W/cm²). The transmittance variations of the pellicles were evaluated by comparing the measurements obtained before and after exposure to 400W EUV power.

Theoretical study of extreme ultraviolet pellicles with nanometer thicknesses

Extreme ultraviolet (EUV) pellicles are required for EUV defectivity management in high volume manufacturing (HVM). Theoretical analysis of EUV pellicles of nanometer thickness is helpful for these fabrications. In this paper, for maximum transverse deflection, an analytical–numerical method is contrasted against the finite element method (FEM) due to the ratio of thickness and width length of EUV pellicles. The difference was increased at a thickness of micron unit. Single- and multiple-variable methods of linear regression in deep learning were used to overcome the ANSYS limitation based on FEM, such as the meshing of more than 10 μm thickness, and shear loading, an error in FEM resulting from the impact on the stiffness matrix caused by variations in the length-to-thickness ratio increases in the beam element, respectively.

Evaluation of H2 Plasma‐Induced Damage in Materials for EUV Lithography

AbstractUltrafine semiconductor fabrication by lithography has undergone a significant transition from deep ultraviolet (DUV) to extreme ultraviolet (EUV) processes, which presents new challenges. Specifically, the damage caused to components utilized in an EUV system, such as multilayer mirrors, reticles, and pellicles within lithography equipment, owing to EUV‐induced H2 plasma, is a critical issue that directly affects the process yield and equipment lifespan. To address these issues, it is crucial to establish an environment similar to that of EUV‐induced plasma and develop a method to evaluate the resulting damage. Accordingly, an evaluation method is developed for assessing the material damage caused by hydrogen radicals and ions in inductively coupled H2 plasma. In these systems, the electron density ranged from 5 × 108 to 3.5 × 1010 cm−3, the electron temperature ranged from 1 to 4 eV, and the ion energy ranged from several to tens of eV; these conditions closely align with the environment of an EUV‐induced H2 plasma. The damage to Mo2C, a potential EUV pellicle material, is quantitatively analyzed by measuring the fraction of the pore area and examining the chemical characteristics after exposing the samples to various plasma conditions, including electron density, gas pressure, and exposure time.

Comparative Study of the Thermal Stability of Be-Based Extreme Ultraviolet Pellicles

Comparative Study of the Thermal Stability of Be-Based Extreme Ultraviolet Pellicles

Study on ZrSi2 as a Candidate Material for Extreme Ultraviolet Pellicles.

An extreme ultraviolet (EUV) pellicle is an ultrathin membrane at a stand-off distance from the reticle surface that protects the EUV mask from contamination during the exposure process. EUV pellicles must exhibit high EUV transmittance, low EUV reflectivity, and superior thermomechanical durability that can withstand the gradually increasing EUV source power. This study proposes an optimal range of optical constants to satisfy the EUV pellicle requirements based on the optical simulation results. Based on this, zirconium disilicide (ZrSi2), which is expected to satisfy the optical and thermomechanical requirements, was selected as the EUV pellicle candidate material. An EUV pellicle composite comprising a ZrSi2 thin film deposited via co-sputtering was fabricated, and its thermal, optical, and mechanical properties were evaluated. The emissivity increased with an increase in the thickness of the ZrSi2 thin film. The measured EUV transmittance (92.7%) and reflectivity (0.033%) of the fabricated pellicle satisfied the EUV pellicle requirements. The ultimate tensile strength of the pellicle was 3.5 GPa. Thus, the applicability of the ZrSi2 thin film as an EUV pellicle material was verified.

Extreme ultraviolet pellicle wrinkles influence on mask 3D effects: experimental demonstration.

Extreme ultraviolet (EUV) lithography uses reflective optics and a thick mask absorber, leading to mask 3D (M3D) effects. These M3D effects cause disparities in the amplitudes and phases of EUV mask diffractions, impacting mask imaging performance and reducing process yields. Our findings demonstrate that wrinkles in the EUV pellicle can exacerbate M3D effects. This imbalance results in critical dimension variation, image contrast loss, and pattern shift in mask images. Therefore, the use of a pellicle material with thermodynamic characteristics that minimize wrinkles when exposed to EUV rays is imperative.

Investigation of EUV pellicle deflection and mechanical stress within EUV inner pod under vacuum activity

Controlling defectivity caused by airborne debris on extreme ultraviolet (EUV) masks is crucial, and the use of EUV pellicles has become practice for this purpose. While the behavior of EUV pellicles alone has been extensively studied, the investigation of mechanical stress inside EUV inner pod (EIP) remains relatively unexplored. Here, we introduce a new approach using a chromatic confocal sensor to address this issue. The sensor enables precise detection of the pellicle surface by analyzing the reflected light wavelength, providing an axial resolution of 22 nm. A modified load-deflection Timoshenko relationship considering geometric effect was applied to evaluate the residual stress of EUV pellicle. To simulate the pump/vent characteristics as per core EUV scanners, a conductance tester was utilized. Throughout the pump/vent cycle, ranging from atmospheric pressure to 300 Pa and vice versa, the EUV pellicle exhibited deflection from −808 μm to +307 μm. Deflection and corresponding residual stress on the deformed pellicle were further analyzed through numerical simulations and theoretical calculations. Notably, such stress of 192 kPa evaluated was discovered to contribute a net pellicle deflection of +100 μm on vacuum environment. Overall, our study presents a successful demonstration to enable comprehensive examination of EUV pellicle behavior within EIP.

Transverse Deflection for Extreme Ultraviolet Pellicles.

Defect control of extreme ultraviolet (EUV) masks using pellicles is challenging for mass production in EUV lithography because EUV pellicles require more critical fabrication than argon fluoride (ArF) pellicles. One of the fabrication requirements is less than 500 μm transverse deflections with more than 88% transmittance of full-size pellicles (112 mm × 145 mm) at pressure 2 Pa. For the nanometer thickness (thickness/width length (t/L) = 0.0000054) of EUV pellicles, this study reports the limitation of the student's version and shear locking in a commercial tool-based finite element method (FEM) such as ANSYS and SIEMENS. A Python program-based analytical-numerical method with deep learning is described as an alternative. Deep learning extended the ANSYS limitation and overcame shear locking. For EUV pellicle materials, the ascending order of transverse deflection was Ru<MoSi2=SiC<SiNx<ZrSr2<p-Si<Sn in both ANSYS and a Python program, regardless of thickness and pressure. According to a neural network, such as the Taguchi method, the sensitivity order of EUV pellicle parameters was Poisson's ratio<Elastic modulus<Pressure<Thickness<Length.

Investigating the Degradation of EUV Transmittance of an EUV Pellicle Membrane.

The extreme ultraviolet (EUV) pellicle is a freestanding membrane that protects EUV masks from particle contamination during EUV exposure. Although a high EUV transmittance of the pellicle is required to minimize the loss of throughput, the degradation of EUV transmittance during the extended exposure of the pellicle has been recently reported. This may adversely affect the throughput of the lithography process. However, the cause of this phenomenon has not yet been clarified. Therefore, we investigated the cause of the degradation in the EUV transmittance by observing the compositional change when the Ru/SiNx pellicle composite was heated in an emulated EUV scanner environment. The Ru thin film that was deposited at high pressure had more void networks but was not oxidized, whereas the SiNx thin film was oxidized after heating. This was because the void network in the Ru thin film served as a preferential diffusion path for oxygen and caused oxidation of the SiNx thin film. It was confirmed that the degradation of the EUV transmittance was due to the oxidation of SiNx. The results verified the effect of diffusivity in the thin film due to the void network on oxidation and EUV transmittance.

Renewable single-walled carbon nanotube membranes for extreme ultraviolet pellicle applications

We propose a facile, cost-efficient, environmentally friendly, and scalable process to renew single-walled carbon nanotube membranes serving as extreme ultraviolet (EUV) protective pellicles. The method comprises of high-temperature treatment of the membrane by Joule (resistive) heating at temperatures higher than 1000 °C and pressure below 0.3 Pa. Using model Sn aerosol nanoparticles, the primary contaminant from extreme ultraviolet light sources, we demonstrate the proposed method to clean the membrane with the power consumption as low as 20 W/cm2. We show the proposed method to cause no harm to carbon nanotube structure, opening a route towards multiple membrane renovation. We confirm the applicability of the approach using in situ deposition from the semi-industrial EUV light source and subsequent Sn-based contaminant removal, which restores the EUV-UV-vis-NIR transmittance of the film and, therefore, the light source performance. The proposed method supports pulse-cycling opening an avenue for enhanced protection of the lithography mask and stable performance of the EUV light source. Additionally, the approach suits other composite contaminants based on such species as Pb, In, Sb, etc.

Development of nanometer-thick graphite film extreme ultraviolet pellicle with hydrogen-resistant TiN capping layer

TiN has beneficial physicochemical properties, such as high hardness, good chemical inertness, and good corrosion resistance. TiN has been used for optical filters and protective coatings to exploit these properties. We deposited TiN using atomic layer deposition as a capping layer for a pellicle. We investigated the hydrogen plasma resistance using Raman spectroscopy, transmission electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy. As the hydrogen plasma exposure time increased, bonds formed between the TiN film and nitrogen compounds. With long-term exposure, the thickness of the TiN film decreased owing to etching.

Investigation of the Resistivity and Emissivity of a Pellicle Membrane for EUV Lithography.

A pellicle is a thin membrane structure that protects an extreme ultraviolet (EUV) mask from contamination during the exposure process. However, its limited transmittance induces unwanted heating owing to the absorption of EUV photons. The rupture of the EUV pellicle can be avoided by improving its thermal stability, which is achieved by improving the emissivity of the film. However, the emissivity data for thin films are not easily available in the literature, and its value is very sensitive to thickness. Therefore, we investigated the dependence of emissivity on structural parameters, such as thickness, surface roughness, and grain size. We found a correlation between resistivity and emissivity using theoretical and experimental approaches. By changing the grain size of the Ru thin film, the relationship between resistivity and emissivity was experimentally verified and confirmed using the Lorentz–Drude model. Finally, we present a method to develop an EUV pellicle with better thermal stability that can withstand high-power EUV light sources.

Impact of thermal expansion coefficient on the local tilt angle of extreme ultraviolet pellicle

Background: A local tilt angle of <300 mrad results in a critical dimension uniformity (CDU) impact below 0.1 nm when a pellicle is used for extreme ultraviolet (EUV) lithography. However, the thermomechanical property guidelines satisfying this specification have not yet been established. Aim: We present the thermomechanical property guidelines that yield a CDU impact below 0.1 nm. Approach: The peak temperature ranges of the EUV pellicle, as a function of the emissivity, were calculated through experimental, numerical, and finite element method analyses. The wrinkle profiles were evaluated as a function of the coefficient of thermal expansion (CTE) within these temperature ranges. The emissivity and CTE values satisfying the specifications were obtained using the CDU impact caused by the wrinkled EUV pellicle. Results: The wrinkle amplitude in the EUV pellicle exhibited 45% attenuation with a twofold decrease in the CTE. The maximum local tilt angles for the 17, 16, and 15 nm half-pitch patterns were 290.2, 286.1, and 272.3 mrad, respectively. CTE below 2 × 10 − 5 K − 1 and emissivity above 0.1 are suggested for the EUV pellicle. Conclusions: The CTE and emissivity guidelines satisfying the CDU impact specifications can be used for developing next-generation EUV pellicles.

Comparative study of the thermal stability of Be-based extremeultraviolet pellicles

We demonstrate the possibility of manufacturing Be-basedultrathin films with high transmission at wavelengths of 11.4 and 13.5 nm. For free-standing films of Be and Be-based multilayer structures (Si/Be,ZrSi2/Be, Be/BexNy, Zr/Be, Ru/Be, Mo/Be), we determine the thresholds of theabsorbed power at which over a short period (tens of minutes) of vacuumannealing, initially sagging free-standing films became visibly stretchedover the hole. Of the film structures tested here, the Be/BexNy structure(with beryllium nitride interlayers) showed the highest threshold for theabsorbed power (1 W/cm2). However, due to the low strength of thisstructure, ZrSi2/Be, Mo/Be, and Be films seem to be more promising for themanufacture of a full-size pellicle. Long-term vacuum annealing of Mo/Beand Be ultrathin films showed that they could withstand 24 hours of vacuumheating at an absorbed power density of 0.2 W/cm2 (film temperature 250oC)without noticeable changes in EUV transmission or sagging of films. Withcomparable transmission (~83% at 13.5 nm and ~88% at 11.4 nm), a multilayerMo/Be structure with a thickness of 30 nm appears to be preferable, as itshows less brittleness than a monolayer Be film with a thickness of 50 nm. Keywords: Be-based pellicle, multilayer thin film, EUV lithography,thermal stability\

Fabrication of extreme ultraviolet lithography pellicle with nanometer-thick graphite film by sublimation of camphor supporting layer

An extreme ultraviolet (EUV) pellicle consists of freestanding thin films on a frame; these films are tens of nanometers in thickness and can include Si, SiN X , or graphite. Nanometer-thick graphite films (NGFs), synthesized via chemical vapor deposition on a metal catalyst, are used as a pellicle material. The most common method to transfer NGFs onto a substrate or a frame is to use polymethyl methacrylate (PMMA) as a supporting layer. However, this PMMA-mediated technique involves several disadvantages in term of manufacturing NGF EUV pellicles. When removing the PMMA using acetone or O2 plasma, defects or deflections can occur in the NGFs. Furthermore, PMMA residues are generally present on large-area NGFs. In this study, a transfer method using camphor instead of PMMA as the supporting layer was developed to overcome these problems. After the camphor/NGF was formed on the frame, camphor was removed via sublimation in an atmosphere of ethanol vapor. This study investigated the deposition and sublimation of camphor, and confirmed that no residue was present and no deflection or defects were observed in the NGFs. Thus, a large-area NGF pellicle was successfully fabricated using the camphor transfer process.

Reduced lifetime of EUV pellicles due to defects

Background: Extreme ultraviolet (EUV) pellicles are affected by heat deformation due to energy absorption during EUV exposure. Defects can accelerate thermal deformation, thereby shortening pellicle lifetime. Aim: We compared the thermal stress and thermomechanical stability with different defects, focusing on the internal defects that occur during the fabrication of EUV pellicles. Approach: Pellicles resistant to high thermal stress can be fabricated based on mechanical properties. To evaluate this, we compared the mechanical stability based on robustness against thermal stress during exposure. Results: Our results show that external contaminants had a greater contribution than internal defects on the mechanical stability of pellicles. However, pellicles with internal defects exhibited increased thermal stress and decreased mechanical stability compared with defect-free pellicles during EUV exposure. Conclusions: Thermal stress is used as an indicator in most studies to predict pellicle lifetime, but evaluation of thermomechanical stability including thermal stress and mechanical durability is required because the material can break under low thermal stress depending on the mechanical properties, and pellicle defects can be a major cause of shortening the lifetime of pellicles.

Carbon nanotube EUV pellicle tunability and performance in a scanner-like environment

Background: An extreme ultraviolet (EUV)-transparent pellicle must be used during lithography to protect the photomask from fall-on particles. A pellicle made of free-standing carbon nanotube (CNT) films stops particles despite the presence of gaps while demonstrating high EUV transmission, mechanical stability, low EUV scattering and reflectivity, and DUV transmission that enables through-pellicle mask inspection. Aim: The CNT EUV pellicle properties can be tailored based on the diversity of CNT structures and tunability of their configuration within the CNT film (density, bundle size, composition, etc.) as shown in this work. A remaining challenge is extending the CNT EUV pellicle lifetime in the scanner environment of EUV-induced hydrogen-based plasma, and the effects on different CNT films are explored here. Approach: Optical and thermal properties of different CNT pellicles with respect to the CNT material type, density, composition, and bundle size were explored. The ability of uncoated CNT EUV pellicles to withstand high EUV powers in the hydrogen-based environment was tested. Transmission, spectroscopic, and chemical mapping of the exposed CNT membranes were performed to explore the material modifications under various exposure conditions. Results: Uncoated CNT pellicles withstand 600-W source power equivalent in the EUV scanner-like gas environment but exhibit structural changes with prolonged exposure. Multiwalled CNT pellicles exhibit less EUV transmission change as compared to single-walled CNT pellicles under the same exposure conditions. The protection of CNT material from structural degradation by means of coating was shown. Conclusions: These investigations add to the understanding of CNT EUV pellicle tunability for optimal performance and lifetime limiters of CNT pellicles under the influence of EUV radiation and plasma. We anticipate the need for coating the CNT pellicle to protect the CNT material against plasma damage for the current scanner conditions. Optimization of both the CNT membrane and its coating is in progress.

Carbon nanotube pellicles: imaging results of the first full-field extreme ultraviolet exposures

Extreme ultraviolet (EUV) lithography was recently implemented in high-volume wafer production. Consequently, maximizing yield is gaining importance. One key component to achieving optimal yield is using a pellicle to hold particles out of the focal plane and thereby minimizing the printing of defects. The carbon nanotube (CNT) pellicle is a membrane consisting of a network of CNTs with a demonstrated EUV transmission (EUV-T) of up to 98%. The challenge is balancing the CNT material parameters for optimal performance in the EUV scanner: low probability for particles to pass, low impact on imaging through scattered light, and high durability in the scanner environment, while maintaining high transmission. We report results of the first full-field CNT pellicle exposures on an EUV scanner. We demonstrate handling of the pellicles, without breakage, and provide a first assessment of their imaging behavior. Multiple single- and double-walled uncoated CNT pellicles with EUV-T of up to 97.7% were exposed on the EUV scanner at imec, and minimal impact on the imaging was confirmed. In these exposures, uncoated CNT pellicles that do not yet meet the specifications regarding lifetime were used. Therefore, ongoing developments focus on CNT durability in scanner environments. The presented demonstration proves the value of a CNT-based EUV pellicle solution.

Impact of residual stress on the deflection of extreme ultraviolet pellicles

Extreme ultraviolet (EUV) pellicles are in high demand for improving the yield of EUV lithography. However, when the EUV pellicle membrane is destroyed inside the scanner, machine availability is significantly affected. The deflection of EUV pellicle membranes needs to be thoroughly studied, because when the membrane deflects beyond its limit, the membrane contacts the scanner components and leads to failure. To propose guidelines for sustaining the EUV pellicle membrane during lithography, the deflection of the EUV pellicle membrane with a range of mechanical properties should be investigated. We verified the feasibility of the finite element method (FEM) analysis by comparing the analysis results with the experimental results. Subsequently, the impact of the mechanical properties on the deflection of a full-sized (110 mm × 143 mm) membrane was investigated using the FEM analysis. The residual stress showed 6.28 and 2.9 times higher impact on the deflection compared to the Poisson’s ratio and elastic modulus, respectively. Finally, the deflection results for 84 different mechanical properties are presented. The residual stress was determined to be a crucial and controllable parameter. The presented guidelines can be used as a design rule for developing EUV pellicle membranes.

Through-pellicle imaging of extreme ultraviolet mask with extreme ultraviolet ptychography microscope

Background: An extreme ultraviolet (EUV) pellicle is necessary to increase the process yield even though the declining throughput is a big concern. However, an EUV metrology/inspection tool for this pellicle has not been commercialized yet. Aim: The goal of this study is to verify the pellicle/mask inspection feasibility of EUV scanning lensless imaging (ESLI) and verify the impact of contaminants on pellicles depending on their size. Approach: Through-pellicle imaging was implemented by using ESLI, which uses a high-order harmonic generation EUV source and ptychography. Optical characteristics of various sizes of Fe-contaminated EUV pellicles were evaluated to verify their impact on wafer images. Results: Large size (∼10 μm) contaminants on the pellicle were found to contribute to the final wafer pattern loss. However, small size (2 to 3 μm) contaminants on the pellicle do not have substantial impact on the wafer image. Conclusions: The defect detection capability of ESLI for pellicle and mask was confirmed. Therefore, ESLI is useful in applications like pellicle qualification and EUV mask inspection metrology.