Exploring the Effects of Placement and Electron Angular Distribution on Two Adjacent Mask Holes During Plasma Etching Process

Abstract

The charging effect generated by the accumulation of negative charges on a mask surface strongly limits the perfect pattern transfer from the mask to the substrate during the plasma etching process, which leads to the deformation of etched features and severely damages the mask pattern. This study first verified that various placements of the holes will result in different distributions of the electric filed (E-field) and the etching rate. This work next shows that the electron angular distribution (EAD) is closely related to the damage to the mask pattern. Based on a reliable modeling framework, the effects of changing the EAD on the distributions of spatial E-field and the etching rate were examined focusing on two adjacent and asymmetrically-shaped mask holes. Specifically, both the E-field strength and the etching rate around the edge of the two mask holes can be greatly reduced by narrowing the EAD, meanwhile, the number of electrons penetrating into the bottom of two holes will be significantly increased. These results will reduce the mask pattern damage and improve the etching of high-aspect-ratio features into a substrate. In the cases of different EADs, the simulated evolution rates of these two mask holes and the E-field strength inside the holes verify these conclusions. The mechanism is discussed in detail. This work will greatly help to optimize the etching technique.