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

Abstract

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.