Fundamentals of EUV stack for improving patterning performance

Extreme ultraviolet (EUV) lithography has already utilized for high volume manufacturing, and miniaturization by numerical aperture (NA) 0.33 is approaching to the limit. Pitch 24 nm line and space (L/S) resist patterns can be resolved with single exposure at even NA 0.33. However, etch transfer performance to underlayer materials is one of the issues. Especially, in narrow pitch case, it is very difficult to etch due to the lack of resist mask resistance. Therefore, resist pattern thickening process with optimized development process and underlayer state was studied and verified the pattern height impact at our past paper. As a result, it found that combination of the underlayer (UL) kinds and their status was one of the key points to lead high-quality patterns. In this paper, optimized stack structure narrow pitch pattern and lithography performance. As a result, in experiments toward High NA EUV, 24 nm pitch L/S pattern could be patterned (near smallest size by NA 0.33) by selecting the optimal ML/UL combination, and some defect free process windows were kept between defect cliffs.