Doping level selective photochemical dry etching of GaAs

Abstract

The first observation of a highly selective photochemical dry etching process which discriminates between semiconductor materials differing in dopant concentrations by less than a factor of 5 is reported here. A photochemical reaction of GaAs with gas phase reactive Cl species occurs when the surface is irradiated with low-intensity light of band gap or greater quantum energies. Application of an appropriate negative bias to a GaAs sample can almost totally suppress the photochemical reaction of heavily doped n-GaAs, while less heavily doped n-GaAs or p-GaAs continue to etch at undiminished rates under the same conditions. This is the first reported etching process to produce greater than 20:1 selectivity for doping levels differing by less than a factor of 5. A mechanism which may explain the origin of the photochemical reaction and the voltage-controlled doping level selectivity which it displays is presented here. The potential significance of these observations for other semiconductor materials, such as Si, is discussed.