Wet chemical etching of compound semiconductors

Abstract

Typically the wet etching of III-V materials involves use of an oxidant to oxidize the surface, followed by dissolution of a soluble reaction product. The resultant etching tends to be basically isotropic in nature.In the case of III-V compounds, differential etch rates for crystallographic directions containing predominantly one or the other elements can lead to a degree of anisotropy and different sidewall shapes. The etch rate may be limited by the diffusion of the active etchant species to the semiconductor surface, or by the diffusion away of the soluble product In this case the etching is termed diffusion-limited, and its characteristic include a square root dependence of etch depth on etch time, an activation energy ≤6 kCal.mol-1 and a strong dependence of etch rate on solution agitation. This mode of etching is not desirable for device fabrication, because of the difficulty in obtaining reproducible rates.The other rate-limiting step may be the chemical reactions at the surface. In this case, the etch depth depends linearly on time, the activation energy is ≥6 kCal.moL-1 and the rate is independent of solution agitation. This is the preferred mode of etching for device fabrication, since only temperature and solution composition need to be controlled.In this paer we will summarize wet etching approaches for a wide variety of semiconductors of interest in high speed electronic and photonic devices.