Patent ID: 8679392

Claim:
A method for forming a diffraction grating, comprising steps of: forming a plurality of semiconductor layers on a semiconductor substrate; evaluating inhomogeneity in an etching rate of said semiconductor layers, said etching rate showing a distribution within said semiconductor layers, preparing a mold that includes a particular pattern reflecting a diffraction grating having an aspect ratio, a duty ratio and a pitch, said mold including a plurality of regions each having one said aspect ratio specific to said region and different from other regions, wherein said aspect ratios in said regions have a distribution that compensates said distribution of said etching rate in said semiconductor layers; coating a resist on said semiconductor layers; printing said particular pattern of said mold on said resist to form a resist pattern by pressing said pattern of said mold on said resist and hardening said resist while keeping said mold pressed on said resist; and etching said semiconductor layers to reflect said particular pattern of said mold on said semiconductor layers by using said resist pattern as an etching mask.