This year, papers from TEL and Samsung/Synopsys have revealed that EUV light that has not been absorbed by the resist but transmitted through to the underlayer can release electrons that can contribute significantly to the exposure of the resist. In particular, TEL found that dose to size for 28 nm pitch lines and spaces was reduced from 81.4 mJ/cm2 to 42.6 mJ/cm2, nearly 50%, by changing the underlayer. Since the underlayer electron exposure effectively originates from some distance below the resist layer, even if the image is focused within the resist layer, the underlayer electron exposure comes from a defocused, blurred image some distance below. Therefore, the underlayer’s electron yield and mean free path has become the most significant factor in EUV lithography performance.
frederickchen.substack.com
EUV Resists are Getting Exposed by More than EUV Light
Electrons from underneath the EUV resist are reducing dose-to-size by over 30%
frederickchen.substack.com