A Diagnostic Approach to Plasma‐Etching Kinetics: Determination of Atom Concentrations

Abstract

The concentrations of titanium atoms and fluorine atoms in an plasma were measured as a function of pressure during plasma etching of a titanium sheet. Absorption of emission from a hollow cathode lamp at 399.86 nm was used to determine the titanium atom concentration. F‐atom concentrations were determined by argon actinometry. A kinetic model was also developed. According to the model, the etching is due to fluorine atoms produced in the plasma, resulting in the formation of a radical. Both physical and chemical processes were important in the etching, with the diffusion of gaseous constituents dominating at lower pressures and reactions in the gas phase dominating at higher pressures. The etching rate was found to be proportional to the fluorine atom concentration. The model, established by use of steady‐state approximations, was fitted to the experimental data for titanium atom concentrations. From the model, the concentration of fluorine atoms was determined to be proportional to the square of the pressure, as determined experimentally. The titanium atom concentrations were related to the total pressure by the expressionThe rate constant for the reaction of with Ti or was estimated to be . Absorption measurements on atoms are simply made, and provide one approach to understanding the kinetics of plasma etching.