Dry etching of GaAs with Cl₂: correlation between the surface Cl coverage and the etching rate at steady state

While dry etching of GaAs with chlorine is technologically important for manufacturing semiconductor devices, little is known conclusively about the surface chemical reactivity responsible for this etching process. In this work, modulated molecular beam scattering (MMBS) has been combined with temperature-programmed reaction (TPR) and Auger electron spectroscopy (AES) to study the reaction of molecular chlorine with GaAs. The MMBS and AES results indicate that the surface coverage of chlorine during steady state etching over the temperature range of 350-650 K is in the monolayer regime. Above 700 K the surface is chlorine free. A direct correlation is observed between the number of vacant surface sites and the Cl₂ reaction probability. This result suggests a Langmuir adsorption model for the surface reaction, and it is shown that such a model combined with the product evolution kinetics determined from TPR studies successfully simulates the temperature dependence of the chlorine evolved from the surface during modulated molecular beam scattering.