Lithographic effects due to particles on high-NA EUV mask pellicle

Abstract

Defectivity in EUV scanners gains much more importance as they move towards the high-volume manufacturing. The reticle (mask) needs to be protected from particle contamination, both inside and outside the scanner environment. One widely used method to realize this is to make use of a thin protective layer on top of the mask, which is called pellicle. In this work we investigate the impact on printed features caused by particles laying on top of the pellicle for a High-NA EUV scanner. The study was supported by simulations using the most up to date High-NA EUV scanner projected design. The most relevant lithographic metrics (namely, change in Critical Dimension, Normalized Intensity Log Slope, dose sensitivity, non-Telecentricity, Pattern Shift and Mask Error Enhancement Factor) have been considered in the study. An experimentally calibrated simulation model is used to predict the particle transmission as function of the particle size. The goal is to set a well-reasoned (based on imaging requirements) maximum particle size specification for production of pellicles and cleanliness inspection. Some sets of mask patterns and sources (use cases) that likely will be used in high volume manufacturing are considered. Furthermore, a comparison with existing 0.33 NA EUV simulation results is done.