Mercury cadmium telluride (MCT) CH4-H-2 based chemistry inductively coupled plasma (ICP) etching mechanisms are investigated. The effect of Ar and N-2 addition in the mixture on plasma and MCT surface characteristics are studied by Langmuir probe, mass spectrometry, and x-ray photoelectron spectroscopy (XPS). In the authors' conditions, the HgTe faster removal than CdTe leads to the formation of a CdTe rich layer in the first 30 s of plasma exposure. Ion flux intensity and composition are only slightly influenced by N-2 addition while a strong effect is shown on neutral species by the formation of NH3, HCN, and the increase in CH3 radical density. At the opposite, Ar addition to the gas mixture leads to a total ion flux increase and promote CH3+ formation while small changes are observed on neutral species. In our low pressure and high density conditions, same order of magnitude of ion and neutral CH3 flux on MCT surface is found, suggesting a chemical contribution of CH3+ ions in MCT etching. This is confirmed by a strong correlation of the MCT etching yield versus total (neutral and ionic) CH3 flux. These results suggest that the etching is limited by the supply of CH3 to the surface. (C) 2009 American Vacuum Society. [DOI: 10.1116/1.3147219]