Overbake: sub-40nm gate patterning with ArF lithography and binary masks

摘要

Recently, we have shown that process effects induced by extending the post-exposure bake time ('overbake') in the process flow of chemically amplified photoresists can lead to significant improvements in Depth-of-Focus (DOF) and small line printing capability. Due to improved acid dose contrasts and a balanced optimization of acid diffusion in the presence of quencher, overtaking has enabled the printing of sub-50nm lines with a large DOF, using binary masks and 193nm lithography. In this paper, the results and findings of a full patterning process in a device flow, using 'overbake' as a process enhancement, are presented. The objective is a sub-40nm gate patterning demonstration, using 0.75 NA ArF lithography with phase shift masks as well as with binary masks. Lithographic process latitudes, proximity behaviour, CD linearity, line end shortening, line edge roughness and resist profiles of an overbake process and a standard process are evaluated. Then, the gate patterning capabilities as well as the CD uniformities of ultra-narrow gates obtained by an overbake process are investigated and compared to a standard resist process.