In the process of simultaneously etching a polysilicon layer in a groove of a memory cell section and a polysilicon layer in a peripheral circuit section, a Cl2/HBr-based gas is used as a first etching step, and this etching is performed until polysilicon in the peripheral section is removed. Next, the gas is switched to a C12/HBr/O2-based gas to remove an etched particulate resist film having accumulated in the groove. As a final step, the polysilicon layer remaining in the groove is etched with a HBr/O2-based gas having a high selectivity ratio against an oxide film.