Pattern dependence of mask topography effect in alternating phase-shifting masks

We compared the topography effect of two types of alternating PSMs; single-trench type with side etching and dual-trench type. The side etching value and dual-trench depth were adjust to give same linewidth in 0 degrees and 180 degrees regions for 0.2 mu m L/S pattern. Several test patterns having different width and length were formed on these alternating PSMs. These two PSMs were evaluated by using an x4, 0.6 NA, KrF exposure tool. For longer patterns (similar to L/S pattern), pattern size differences were very small; the mask topography effect was negligible. However, pattern size differences of shorter patterns (similar to window pattern) were large with both Alt PSMs. Therefore, optimization of the side etching value or the trench depth is required for each mask pattern.