Ion beam nitridation of indium phosphide (100) substrates was studied using x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Argon ion bombardment of the InP(100) surface removes the native oxides and induces the formation of three-dimensional indium clusters. After cleaning, the samples were nitrided in an ultrahigh vacuum chamber using a home-made radiofrequency plasma source (13.56 MHz) that allows nitridation at low pressures (10 −4 Pa). We have studied the influence of temperature on the nitridation mechanisms. For low temperature (T < 200• C), no variation of the metallic indium droplets was observed; for high temperature (T > 270 • C), the first layers of the substrate were damaged. The optimal temperature for the nitridation of InP(100) was found to be 250 • C.