Stochastic side-lobe printing in EUV lithography: a simulation study

Abstract

Background: Extreme ultraviolet (EUV) phase shifting masks (PSMs) may be introduced at the N3 node as alternative to double patterning or high-NA exposures. To be optically advantageous, PSMs may have to come with phase different from 180 deg and high transmission. Aim: The main concern is how such exposures could be affected by stochastic side-lobe printing. Approach: We present a simulation study where we compare stochastic distributions for contact layers with different mask approaches: binary mask, PSM with and without assist features, and TriTone masks. The purpose of this work is to evaluate whether PSMs in EUV lithography may become a valuable option to further extend single-exposure EUV at NA = 0.33. Results: We identify the best exposure conditions for lowest stochastic defectivity for each of the masks considered and perform a large-scale study at these conditions. We report CD and placement error distribution parameters, along with frequencies of observed defects. Conclusions: We find that PSMs are more limited in range of CDs that can be printed without stochastic defects, compared with binary masks. When compared at target CD that is optimal for PSM, proposed phase shift masks did not exhibit a clear advantage, suggesting careful consideration of stochastic defects will be needed during future process development.