Charging Effect in Plasma Etching Mask of Hole Array

It has already been found that the round shape of holes can be changed into hexag- onal shape during plasma etching processes. This work aims to understand the mechanism behind such a shape change using particle simulation method. The distribution of electric field produced by electrons was calculated for different heights from the mask surface. It is found that the field strength reaches its maximum around a hole edge and becomes the weakest between two holes. The field strength is weakened as moving away from the surface. The spatial distribution of this electric field shows obvious hexagonal shape around a hole edge at some distances from the surface. This charging distribution then affects the trajectories of ions that fall on a mask surface so that the round hole edge is etched to become a hexagonal hole edge. The changing of this hole shape will again alter the spatial distribution of electric field to enhance the charging effect dynamically.