Effects of Mask Pattern Geometry on Plasma Etching Profiles

Abstract

Two-dimensional etching profile evolution in two different geometries, namely an axisymmetric hole and an infinitely long trench, has been simulated with the cellular algorithm, to clarify the effects of geometrically different structures on etching profile evolution. The simulation assumed SiO2 etching using CF4 plasmas, owing to the widely employed fluorocarbon plasmas for the fabrication of contact and via holes. Numerical results indicated that the two mask pattern geometries give some differences in profile evolution, depending on condition parameters such as ion energy, mask pattern size, mask height, and reflection probability on mask surfaces. The profile evolution is slower and more anisotropic in a hole than in a trench; in practice, the profile of a trench tends to have prominent lateral etches such as an undercut and a bowing on sidewalls. Moreover, the reactive ion etching lag is less significant for a hole than for a trench. These differences are ascribed to the geometrical shadowing effects of the structure for neutrals, where the incident flux of neutrals is more significantly reduced in a hole than in a trench. The differences are also attributed to the anisotropy of the velocity distribution of neutrals; in effect, the velocity distribution is more anisotropic in a hole, because more particles interact with mask sidewalls to adsorb or reflect thereon in a hole, so that more anisotropic neutrals are transported onto bottom surfaces after passing mask features.