Proposal for an etching mechanism of InP in CH4-H2 mixtures based on plasma diagnostics and surface analysis

Abstract

The influence of CH4-H2 mixture composition and rf power input on the etching mechanism of InP is discussed. Argument is based on etch rate measurements, plasma diagnostics (optical emission spectroscopy and mass spectrometry) and quasi in situ x-ray photoelectron spectroscopy (XPS) surface analysis. Results show that the key mechanistic parameters are the CH3 flux density and the ion energy flux density on the InP surface. The In removal mechanism is the most important feature as it is the one which limits the effective etching and controls the surface stoichiometry. This mechanism depends mostly upon the CH3 flux but needs ion assistance. On another hand, the P removal mechanism appears to be strictly controlled by the ion energy flux. Based on these observations an analytical model is proposed to describe the etching. The mechanism can be described as an ion-assisted chemical etching mechanism. Its originality is that In and P removal mechanisms are considered separately although they are strongly interdependent as indicated by XPS. A quantitative determination of the CH3 flux and the ion energy flux density on the InP surface by means of mass spectrometry allow to show that the model is applicable in a wide range of gas mixture composition and rf power. Moreover, it gives an estimation of the number of In atom etched per incident CH3 in agreement with the generally admitted assumption that trimethylindium is the major etch product of In, and allows an estimation of the surface coverage in methyl radicals.