Optical Spectroscopy Studies of the Reactive Ion Etching of Silicon and Gallium-Arsenide in Halomethane-Based Discharges

Abstract

The Reactive Ion Etching (RIE) behavior of Si and GaAs in d.c. halomethane-based discharges has been investigated using Glow Discharge Optical Spectroscopy in both emission and absorption modes. The etching of GaAs was found to be anisotropic and a carbon layer formed on the etched surfaces. A post etch in-situ surface analysis technique was developed to measure the functional dependence of etching parameters on the carbon surface layer which forms during RIE. A model was formulated which related the carbon coverage thickness to the fraction of incident halide atoms which actually assist in etching the target material. Using this model one can identify two modes of etching behavior: etchant surface unsaturated and saturated. The RIE of Si is an example of the former, while the RIE of GaAs in fluorinated discharges operates in an etchant saturated mode and proceeds through the ion assisted desorption of otherwise nonvolatile gallium fluoride.