The plasma–surface interaction duringCH4–H2reactive ion etching processing of InP is described in detail by means of plasmadiagnostics (optical emission spectroscopy and mass spectrometry) and x-ray photoelectronspectroscopy (XPS) surfaceanalysis. The influence of the input power is carried out for differentCH4–H2mixtures in terms of InP etch rate,etch product andCH3radical detection and surface damage characterization. In particular detailed XPS results allow the study of the changes in the stoichiometry andamorphization of the surface with the input power. In addition, for a given power, the quality of the etched surface improves by increasing the fraction of methane in the gas mixture. Asan example, the best surface stoichiometry(InP0.86)is obtained for a pure methane plasma running ata high power (300 W). In general, it is shown that the lower the P depletion, the lower the amorphization, which is indicative of a general improvement of the etched surface quality.Based on the XPS results, a three-layer model is proposed for the representation of the surface in thecourse of etching. The damaged layer situated over the bulk InP is composed of a superficial P-depleted layer and of a stoichiometric amorphized InP layer. Using thecurve-fitting of theP 2pspectra, the thickness of the different layers is estimated. As an example, a damaged layer as low as 37 Å thick is obtained for puremethane plasma at 15 mTorrand a power of 300 W, whereas our standard conditions (10%CH4–H2,50 mTorr, and 80 W) give a damaged layer of 90 Å. The experimental observations give evidence of the need for both ion bombardment and activeneutral species to obtain etching. The improvement of the etch process is then explained by an improved In removal rate which is actually the limiting step in theetching mechanism of InP.