Numerical Simulation Method for Plasma-Induced Damage Profile in SiO2 Etching

Abstract

We developed a numerical simulation method for the depth profiles of plasma-induced physical damage to SiO2 and Si layers during fluorocarbon plasma etching. In the proposed method, the surface layer is assumed to consist of two layers: a C–F polymer layer and a reactive layer. Physical and chemical reactions in the reactive layer divided into several thin slabs and in the deposited C–F polymer layer, which depend on etching parameters, such as etching time, gas flow rate, gas pressure, and ion energy (Vpp), are considered in detail. We used our simulation method to calculate the SiO2 etch rate, the thickness of the C–F polymer layer (TC–F), and the selectivity of SiO2 to Si during C4F8/O2/Ar plasma etching. We confirmed that the calculated absolute values and their behavior are consistent with experimental data. We also successfully predicted depth profiles of physical damage to the Si and SiO2 layers introducing our re-gridding method. We found that much Si damage is generated in the pre- and early stages of the overetching step of SiO2/Si layer etching despite the high selectivity. These simulation results suggest that the TC–F value and the overetching time must be carefully controlled by process parameters to reduce damage during fluorocarbon plasma etching. The results have also provided us with useful knowledge for controlling the etching process.