Low-temperature dry etching of tungsten, dielectric, and trilevel resist layers on GaAs

Abstract

Dry etching of common masking materials used in GaAs device technology, was examined down to temperatures of −30°C. The etch rates of SiNx, SiO2, and W in SF6/Ar are reduced below 0°C, but the anisotropy of the etching is improved at low temperature. Microwave enhancement of the SF6/Ar discharges produces increases in etch rates of several times at 25°C, but much lower increases at −30°C substrate temperature. The underlying GaAs surface shows increased S and F coverage after low-temperature etching, but these species are readily removerd either by anex-situ wet chemical cleaning step or an in-situ H2 plasma exposure. Photoresist etching is less sensitive to temperature, and anisotropic profiles are produced between −30 and +60°C in pure O2 discharges.