Energy dispersive x-ray (EDX) spectroscopy coupled to transmission electron microscopy (TEM) is used to analyze the passivation layer deposited on the sidewall of InP submicron patterns etched in Cl-2-H-2 and HBr inductively coupled plasmas. It is shown that a thin Si-containing layer is deposited on the sidewalls of the etched patterns, resulting from the reaction of Cl-2 or HBr with the Si wafer used as the sample tray. For Cl-2-containing plasma, the deposition layer becomes thicker when hydrogen is added to the gas mixture, leading to highly anisotropic InP etching at an optimized H-2 percentage. A similar effect is obtained in HBr plasma by increasing the ICP power. When O-2 is added to the gas mixture, the deposited layer is changed from Si rich to more stoichiometric silicon oxide (SiO2) and the passivation effect is enhanced. EDX-TEM analysis has also been carried out on InP samples etched in Cl-2-N-2 plasma for comparison. A similar impact of the coverplate material on the sidewall profile is evidenced, the InP sidewall being moreover strongly In deficient in this case. These results give useful guidelines to define anisotropic etching processes scalable to large-diameter InP wafers. (C) 2008 American Vacuum Society.