A method of processing a substrate includes a first step, a second step and a third step. The substrate includes an etching layer and a mask. The mask is formed on a first surface of the etching layer. The first step forms a first film on a second surface of the mask. The second step forms a second film having a material of the etching layer on the first film by etching the first surface of the etching layer. The third step removes the first film and the second film by exposing the substrate after the second step to plasma of a processing gas. The first film has an electrode material. The processing gas includes oxygen.