Cost benefits from going chromeless
"UMC's 90nm silicon success, using Cr-less PSMs and 193nm lithography tools, shows that we have moved Cr-less PSM technology out of the experimental stage," says SW Sun, head of UMC's Central R&D (CRD) division. "With the Cr-less approach, we have achieved improved critical-dimension uniformity and line-edge roughness control, which means that layout patterns are more accurately being printed onto silicon," he adds.
The Cr-less PSM is unlike traditional binary chrome masks. Non-chrome sub-resolution phase shifters delineate the pattern. Two-phase edges are required instead of one to define single-line patterns. The contrast of the image is enhanced through destructive interference at each phase edge, which leads to an enhanced exposure intensity gradient. This in turn results in improved resolution and critical dimension control of the advanced lithography process.
UMC says that the Cr-less technology is also proving to be more cost effective in manufacturing than the alternating PSM (altPSM) approach. The altPSM process requires a double exposure and two masks for each pattern layer. UMC is also evaluating the use of Cr-less PSM technology beyond 65nm, along with several other resolution enhancement (RET) candidates.
