Effect of neutral transport on the etch product lifecycle during plasma etching of silicon in chlorine gas

Abstract

In this article, we report a computer simulation of silicon etching in chlorine gas. We focus on the lifecycle of silicon containing etch products and how this lifecycle is affected by neutral transport. The lifecycle of silicon in an etch reactor consists of etching, fragmentation by gas phase chemistry, deposition on the walls and wafer, and removal from the reactor. All of these processes are affected by neutral transport. Flow rate and reactor geometry are varied, and the characteristics of the resulting flow fields are analyzed. With the reactor inlet located at the center of the top dielectric, there is significant convective flow at the wafer surface at a chlorine feed rate of 500 sccm. The convective flow helps remove etch products from the reactor. This reduces etch product fragmentation to depositing species in the plasma; thereby reducing wall and wafer deposition. With a showerhead inlet, or with an inlet located at the outer rim of the top dielectric, there is little convective flow at the wafer for any of the simulated flow rates. This results in diffusion dominated transport of etch products. The diffusion is driven by species gradients induced by gas phase and surface reactions. As flow rate decreases, the primary redeposition precursor shifts from SiCl (at 500 sccm) to Si (at 45 sccm), changing the profile of redeposition on the wafer.