LOW-TEMPERATURE DRY-ETCHING OF TUNGSTEN, DIELECTRIC, AND TRILEVEL RESIST LAYERS ON GAAS

Dry etching of common masking materials used in GaAs device technology was examined down to temperatures of -30 degrees C. The etch rates of SiNx, siO(2), and W in SF6/Ar are reduced below 0 degrees 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 degrees C, but much lower increases at -30 degrees C substrate temperature. The underlying GaAs surface shows increased S and F coverage after low-temperature etching, but these species are readily removed either by an ex-situ wet chemical cleaning step or an in-situ H-2 plasma exposure. Photoresist etching is less sensitive to temperature, and anisotropic profiles are produced between -30 and +60 degrees C in pure O-2 discharges.