New concept phase shifting masks based on projection lens design

For the purpose of shortening turn around time (TAT) and costs of phase-shifting mask (PSM) fabrication, we proposed a new concept of PSM composed of an opaque pattern substrate and a phase shifter substrate. It was considered that this PSM has the disadvantage of high wave-front aberration. In order to solve this problem, we have designed a high NA (0.75), very low aberration (0.0017 λ) reduction projection lens system. Based on this design, we found that wave-front aberration of phase shifter substrate (0.09 inches thickness) between the mask and projection lens was reduced from 0.3314 λ to 0.0089 λ by projection lens system optimization of mask and imaging positions. We measured the intensity profiles of this prototype PSM using AMIS (Zeiss optical simulation microscope) and checked the intensity profiles of this PSM were better than that of the conventional PSM.