Impact of MEF on 0.15-μm KrF lithography

Abstract

We studied the mask error enhancement factor (MEF) for four 0.15-micrometers patterns, isolated lines, line and space (L and S), isolated holes, and dense holes, for various process conditions. The MEF for isolated lines was the smallest of all. The MEF for L and S was not as small as that of the isolated lines. We obtained a less than 15-nm wafer critical dimension (CD) variation, when we reduced the mask CD variation to 20 nm. For the isolated-hole patterns using an attenuated phase shift mask (PSM) with large mask biasing can reduce the wafer CD variation. On the other hand, it is very difficult to reduce the MEF and the wafer CD variation for the dense-hole patterns. The alternating PSM was the best of the evaluated process, but it was not good enough to reduce the mask CD variation.