Effect of Grain-Size Control on Mechanical and Optical Properties of ZrSi2 Membranes for Extreme Ultraviolet Pellicles

Abstract

Extreme ultraviolet (EUV) pellicles must exhibit high optical transmittance, thermal, and mechanical stability to withstand the demands of semiconductor fabrication. ZrSi2 has attracted attention as a pellicle material due to its excellent optical characteristics. The thickness of ZrSi2 films is being reduced to enhance EUV transmittance (EUVT). Since the mechanical strength of nanoscale thin films can be influenced by grain-size effects described by either the Hall–Petch or inverse Hall–Petch relationship, grain-size control becomes critical. In this study, ZrSi2/SiNx free-standing membranes with different ZrSi2 grain sizes were fabricated by sputter deposition followed by annealing at 425–600 °C. Grazing incidence X-ray diffraction analysis confirmed that the ZrSi2 thin films retained their orthorhombic structure up to 600 °C. Scanning transmission electron microscopy showed a gradual increase in grain size with increasing annealing temperature. EUVT remained almost unchanged regardless of the ZrSi2 grain size. In contrast, the ultimate tensile strength increased with grain size up to 64 nm and decreased with further grain growth. These results indicate that although the optical properties of ZrSi2-based EUV pellicles are grain-size independent, their mechanical strength can be optimized through microstructural engineering, consistent with the Hall–Petch relationship.