Extreme-ultraviolet (EUV) lithography is a crucial technology in semiconductor manufacturing, and the development of effective pellicles is essential to prevent mask contamination and ensure patterning accuracy. Traditional approaches to improving pellicle transmittance have faced limitations, prompting exploration into novel strategies such as CNT, graphitelike film, or structural modification. In this study, we investigate the mechanical stability and imaging impact of porous pellicles, which can overcome the limitations of conventional structures. Our findings reveal that while porous pellicles induce stress variations, overall residual stress is almost maintained. Imaging simulations demonstrate minimal impact on pattern fidelity, highlighting compatibility with existing lithographic systems. Additionally, we fabricated the silicon nitride porous pellicles and measured EUV transmittance. Experimental results confirm significant increases in EUV transmittance with porous structures, validating their potential for next-generation lithography applications.
As the EUV pellicle becomes more widely applied in the semiconductor industry, efforts are carried out to develop an EUV pellicle with a transmittance of over 90% and a heat emission efficiency that can withstand the increasing EUV source power. A metal silicide applied to such a pellicle can form crystal structures exhibiting different thermal properties depending on it. In this paper, the rapid thermal annealing process was performed to crystallize the MoSi2 pellicle composite and subsequent thermal property evaluation confirmed the change in heat emission efficiency depending on the crystal structure. On the SiNx membrane fabricated through KOH wet etching, MoSi2 and SiNx were deposited through co-sputtering and reactive sputtering, respectively. The composite films were annealed at various temperatures and time conditions through a rapid thermal annealing process. The crystallinity and resistivity of the films were analyzed using XRD and 4-point probe. Heat load tester was introduced to evaluate heat emission efficiency. The temperature of the pellicle surface was measured by optical pyrometer under 808 nm laser irradiation conditions, emulating the EUV exposure process. It was confirmed that the hexagonal and tetragonal structures of MoSi2 were formed in the pellicle according to the annealing temperature. Structural change due to the heat treatment alters the band structure, which leads to a change in free-electron density. According to the Drude model, these variations in free electron density can affect the thermal emissivity of nano-membrane structures. For the heat load test, the tetragonal structured MoSi2 pellicle with low resistivity reached lower temperature at the same thermal load, thereby confirming the higher heat emission efficiency compared to that of the hexagonal structure.
To boost the productivity of extreme ultraviolet (EUV) lithography, the development of an EUV pellicle that not only has excellent optical properties such as high EUV transmittance and low reflectance but also can withstand
high-power EUV light sources is in progress. In this paper, zirconium silicide (ZrSi2)-based pellicles were fabricated and optical, mechanical, and thermal properties were evaluated to verify their applicability to EUV pellicle materials.
ZrSi2 composite pellicle was fabricated by depositing ZrSi2 on a silicon nitride (SiNx) free-standing membrane. The heat load test that emulates EUV exposure conditions was performed to evaluate the thermal properties. The optical and mechanical properties were evaluated by an EUV microscope and bulge test, respectively.
As a result of the thermal load test, the emissivity of ZrSi2 was measured to be 0.18-0.29 at a ZrSi2 thickness of 10-40 nm, and the emissivity increased as the thickness increased. The ZrSi2-based pellicle of Si/ZrSi2/SiNx structure meets optical requirements with EUV transmittance and EUV reflectance of 92.7% and 0.04% or less, respectively. In addition, the ultimate tensile strength (UTS) of this composite pellicle was measured to be about 3.5 GPa. From these results, it is expected that ZrSi2 can be used as an EUV pellicle material.
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.
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.
Possibility of localized thermal gradient near particles on pellicle surface during EUV-induced heat load was investigated. Optical/thermo-mechanical simulations were performed to calculate EUV/UV absorbance and thermal stress distribution of a particle contaminated pellicle. Ru/SiNx double-stack pellicles were fabricated and contaminated by particles of Ti, C, Fe which are the main contamination species in a EUV scanner. As a result, a localized thermal stress was induced by particles and a shorter lifetime was observed for a membrane contaminated with larger particles.
Molybdenum disilicide (MoSi2) pellicle membrane was fabricated and its optical/thermal properties were compared with Ru-capped pellicle and SiNx pellicle. EUV reflectance was measured through EUV Coherent Scattering Microscope, and thermal stability was evaluated using 355nm laser source emulating EUV exposure condition. As a result, it was confirmed that MoSi2 pellicle showed sufficiently lower reflectance and comparable thermal durability under 300 W EUV matched source power compares with the Ru-capped SiNx pellicle. Further study is now underway to improve emissivity and mechanical stability.
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