Abstract: In order to obtain a method for low damage and steaty mesa structures, the damage mechanism of InGaAs by Cl2/N2 ICP etching was studied in this paper. The surfaces of InGaAs before and after etching was investigated using Raman spectroscopy and X-ray diffraction(XRD) technology. The results indicate that lattice defects are the main damages. The surface damage of different treatment process was characterised and analysed by the method of microwave photoconductivity decay measurement. The results show that the surface defects and broken bonds of etching damage are decreased to a certain extent by wet etching and surface sulfur treatment, but deep defects still cannot be avoided.