Comparative study of Cl2 + O2 and HBr + O2 plasma chemistries in respect to silicon reactive-ion etching process

Abstract

The comparative study of Cl2 + O2 and HBr + O2 plasma chemistries in respect to Si reactive-ion etching process was carried out. Both plasma diagnostics and modeling tools were applied to compare effects of gas mixing ratios on steady-state plasma parameters and densities of active species as well as to determine key processes in respect to Cl and Br atom kinetics. It was found that a) the variation of Cl2/O2 and HBr/O2 mixing ratios produces opposite changes in both electrons-related and ions-related plasma parameters in corresponding gas systems; b) the stepwise dissociation pathways, such as Cl2 + O/O(1D) → ClO + Cl and HBr + O/O(1D) → OH + Br, have no principal influence on the halogen atom formation rates; and c) the higher formation rate and the lower recombination frequency for Cl atoms always provide the condition [Cl] > [Br]. The data on fluxes of plasma active species provided the analysis of Si etching kinetics in terms of process-condition-dependent reaction probability and etching yield. It was suggested that both parameters are sensitive to O atom flux through the oxidation of reaction products into the lower volatile SiClxOy and SiBrxOy compounds. © 2021 Elsevier Ltd