InP surface properties under ICP plasma etching using mixtures of chlorides and hydrides

InP wafers after etching in an ICP (Inductively-Coupled Plasma) reactor with different kinds of reactant gases have been carefully studied using surface sensitive techniques, in order to gain insight into the mechanisms that control the process. Two types of reactive gas systems have been investigated, namely Cl₂/CH₄/Ar mixtures on one side, and CH₄/H₂ on the other. In both cases, the composition (flow rate) of the different components was varied. X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM) and micro-Raman were the techniques used. From the XPS data, information like the surface overall enrichment (in P or In depending on the nature of the etching gases), quantitative surface stoichiometry, and detailed chemical analysis could be derived. AFM images provided an estimate of the roughness increase, while micro-Raman results were used to get indications on the surface structural disordering associated with the etching process, as well as the changes induced in the electronic properties of the InP material (Surface Recombination velocity - SRV - and modifications of the free carrier densities)