Abstract: Effects of mask on the quality of facets etched on InP-based materials by ICP dry etching technique were studied extensively. Photoresist, SiO₂, and Si₃N₄ films were used as etching mask and their properties were compared. It is found that the smoothness and the verticality of the mask sidewall are of great importance to the quality of etched facets. Si₃N₄ mask with smooth and vertical edge is formed by dry etching method. Smooth and vertical InP etched-facets of 7μm -deep are achieved by C1₂/CH₄/Ar ICP dry etching with this dry-etched Si₃N₄ mask, and the selectivity over Si₃N₄ is as high as 15:1.