Finite Element Analysis of Alternating Phase-Shift Masks Subjected to Dynamic Pressure Loading Due to Megasonic Cleaning

The mechanical response of alternating phase-shift mask (APSM) microstructures to dynamic pressure loading during megasonic cleaning was analyzed with the finite element method (FEM). A parametric study of the effects of microstructure dimensions, pressure amplitude, and loading frequency on the mask structural integrity was performed for two typical chromium/quartz APSM patterns. Damage due to microfracture and plastic deformation processes encountered during megasonic cleaning was examined for frequencies of 1, 5, and 10 MHz. FEM results provide insight into possible damage modes and critical microstructure dimensions for catastrophic failure. Damage scenarios revealed by FEM results are in qualitative agreement with experimental observations. The results of this study have direct implications in the design of extreme ultraviolet lithography masks and the optimization of the megasonic cleaning process.