Damage on the mask surface caused by charging effect during plasma etching process continues to attract much attention currently. For example, the round shape of holes can be changed into hexagonal shape. In our previous paper, the reason for this phenomenon has been explained through a particle simulation approach [P. Zhang et al., Plasma Sci. Technol. 15 (2013) 570]. However, it has been observed that the round shape of holes in a mask can also be etched into an asymmetric shape due to factors such as nonuniform plasma source, inclination or vibration of sample platform, etc. This work further aims to explore the charging effect when the round-shaped holes in a mask have been changed into asymmetric-shaped ones by particle simulation method. The distribution of electric field produced by electrons was calculated for different shaped isolated holes (round, hexagonal and asymmetric shapes) in a mask as well as various heights from the mask surface. It is found that the field strength reaches its maximum around a hole edge and presents uniform distribution for the round hole and nonuniform distribution for the hexagonal- and asymmetric-shaped holes. The nonuniform electric field distribution can affect the trajectories of ions falling on the mask surface, further enhancing the asymmetry of the mask hole shape. Additionally, the charging effect on a mask of asymmetric holes aligned in a hexagonal array is also studied. It is found that due to the alignment of holes, the charging effect is quite different from the case in an isolated hole.
Exploring the evolution of asymmetric pattern of mask hole during plasma etching process by particle simulation method
