In micro/nano electro-mechanical system, silicon nitride (SiN x ) membrane has been widely used in sensors, energy harvesting and optical filters because of its mechanical/chemical stability. However, it is necessary to verify mechanical and thermal properties of nanoscale SiNx membranes to ensure the desirable reliability and durability of a device because the properties of nanoscale films vary with thickness which is severely depending on changes in density, grain size, and crystallinity. In this paper, SiN x membranes were fabricated by low pressure chemical vapor deposition followed by reactive ion etching and KOH wet etching. The composition, surface roughness, thickness uniformity and residual stress of the deposited SiN x films were measured to confirm the reliability of the deposition process. Plane-strain modulus, failure stress and emissivity were evaluated by bulge test and heat load test. As a result, the failure stress of the membrane was enhanced by decreasing SiN x thickness while the plane-strain modulus was insensitive to the thickness variation. Through the UV laser heat-load test, it was found that the thermal durability of the thinner membrane deteriorated due to decreased emissivity. To investigate the emissivity depending on membrane thickness, a finite element method simulation was performed based on the experimental results. The calculated emissivity of each membrane coincided with the reported values within 8% difference.

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.

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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.

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