Plasma parameters, gas-phase chemistry and Si/SiO2 etching mechanisms in HBr + Cl-2 + O-2 gas mixture: Effect of HBr/O-2 mixing ratio

Abstract

Features of plasma chemistry as well as peculiarities of etching mechanisms for Si and SiO2 in the HBr + Cl-2 + O-2 gas mixture with variable HBr/O-2 mixing ratio were investigated using a combination of experimental and theoretical approaches. Plasma diagnostics by Langmuir probe and 0-dimensional (global) plasma modeling provided the information on gas-phase plasma parameters, formation/decay kinetics of plasma active species and the steady-state plasma composition. It was found that the substitution of HBr for O-2 at constant Cl-2 fraction in a feed gas 1) leads to a weak increase in electron density, ion density and the ion energy flux; 2) influences the kinetics of neutral species through reactions involving O atoms and their reaction products; and 3) results in increasing total halogen atom density. It was shown also that the change in HBr/O-2 mixing ratio causes the opposite behaviors of Si and SiO2 etching rates and lifts the SiO2/Si etching selectivity up to similar to 10 in highly oxygenated plasmas. The analysis of Si and SiO2 etching kinetics with model-predicted fluxes of plasma active species indicated the different etching mechanisms for these materials.