Model-based breakdown of resist and mask contributions to local CDU for sub-30-nm contact holes in EUV lithography

Abstract

The resist and mask contributions to the local critical dimension uniformity (L.CDU) of 30-nm contact holes (CHs) printed using extreme ultra-violet lithography (EUVL) are decomposed quantitatively by three independent budget breakdown methods. An asymptotic behavior model is proposed for the prediction of the resist-only contribution via a shifted and averaged multiple exposure (SAME) method that statistically averages out the collective mask local contributions. The other two budget breakdown methods of assessing, the variance of site-to-site difference for the derivation of resist-only contribution and the global mask error enhancement factor (G.MEEF) for the mask-only contribution, are performed and compared to the resist and mask contributions from the SAME method. The three budget breakdown methods consistently indicate that approximately 75–80% of L.CDU is attributed to the resist and process regardless of the process conditions, such as post exposure bake (PEB) temperature, PEB time, and exposure dose. L.CDU exhibits a linear correlation with 1/sqrt(dose), which is a potential indication that photon shot noise (PSN) could be a key contributor to the L.CDU on a wafer. Although a significant reduction of the total L.CDU is observed in the low PEB temperature process, i.e., high exposure dose, a relatively small change in the ratio of the resist-to-mask contribution may be observed because the chemical contrast enhancement by acid diffusion reduction is relatively small compared to PSN reduction.