Pattern dependence optical phase effect on alternating phase shift mask

A comprehensive study of alternating phase shifting mask (Alt-PSM) including mask making, 3-dimensional aerial image simulation, and wafer printing is reported in this paper. For the mask making, we found that the micro-loading effect will be greatly improved using the etching recipe with high Reactive Ion Etching (RIE) power and low Inductively Coupled Plasma (ICP) power. However, this recipe has side effects of Cr film damage and rough quartz side wall. Due to the 3-dimensional mask complex effect, the optimal phase difference is not simply π calculated using optical path difference but is varied with mask features. The optimal phase difference is 165° other than 180° for hole patterns, while it is 176° for line-and-space patterns. The micro-loading effect with variant 2-dimensional complexities is also studied in this paper.