The surface composition, etch rates, and surface roughness of indium phosphide (InP) surfaces treated in radio frequency (rf) hydrogen and hydrogen/argon/methane plasmas have been investigated using in situ Auger spectroscopy and ex situ scanning electron microscopy and atomic force microscopy. In agreement with most previous studies, hydrogen plasmas are found to completely remove surface carbon and oxygen impurities, but at the expense of some degree of surface phosphorus depletion. This depletion can be minimized by utilizing brief plasma exposure times and low rf power settings. Oxygen removal is found to be rate limiting in the production of a clean surface. InP etching in hydrogen/argon/methane can be performed either in a low density, capacitively coupled plasma mode, or in a high density, inductively coupled plasma mode. For operation in the low density regime, the etched surfaces have a constant and nearly stoichiometric composition, independent of plasma parameters. Etch rates vary from similar to 20-400 Angstrom/min, while the root mean square (rms) surface roughness varies from similar to 20 to >400 Angstrom. Both of these quantities show definite trends with changing plasma parameters, and, in particular, high etch rates and low surface roughness are both favored by increasing total plasma pressure and methane how rate. Within the ranges studied, the etch rate is most strongly affected by the amount of hydrocarbon species reaching the surface, which can remove indium in the form of indium alkyl products. However, sputtering effects are also shown to be significant. Etching InP in the high density plasma mode gives an etch rate of similar to 700 Angstrom/min, but only at the expense of severe surface phosphorus depletion and rms surface roughness of similar to 2000 Angstrom. The breakdown of methane within the plasma under these conditions may serve to inhibit indium alkyl formation, and hence lead to the observed phosphorus depletion.