CHEMICAL DRY-ETCHING OF GAAS(100) BY HCL - PRODUCTS, RATE, AND A KINETIC-MODEL

The chemical dry etching of GaAs by HCl has been studied using molecul ar beam scattering techniques. Unlike Cl2 which etches GaAs at room te mperature, HCl does not etch GaAs at a measurable rate below 670 K. Fo r an incident HCl flux of 3.6 monolayers/s and surface temperatures of 670-870 K, the major volatile reaction products are GaCl and As2. Abo ve 850 K, GaAs evaporation also produces Ga atoms. Quantitative analys is of the product mass spectra and angular distributions shows that th e product evolution rates are consistent with stoichiometric etching. Studies of the etching kinetics by modulated molecular beam scattering (MMBS) indicate that the rate of arsenic evolution limits GaAs etchin g to temperatures above 670 K. A simple reaction model which utilizes kinetic parameters derived from independent studies in the literature quantitatively reproduces the etching products, rate, and kinetics und er both steady state and modulation conditions with only one adjustabl e parameter.