Application of multistep quartz etching method to strong PSMs

Before strong plastic shifting masks (PSMs) are used in production mode, several problems, such as (Delta) CD, X- phenomenon, and phase non-uniformity must be resolved. Among these problems, the phase non-uniformity on the mask plate is the main topic in our study. A quartz substrate is not embedded with any etching stopper layer, which leads to inherent etching depth non-uniformity across the mask plate. In this paper, we carry out simulation on the dependency of phase variation for tolerable margin. The simulation result shows that the phase should be controlled within +/- 2 degree(s) off a targeted phase. Through some experiments, it is confirmed that the etching non-uniformity results from etching species' reaction with resist. Employment of a multi-step dry etching gives rise to remarkable improvement of the phase uniformity compared with a single-step etching.