A process of forming a first mask on a first region of a metal film formed on a surface of a substrate, a process of modulating a work function of a first exposed region of the metal film, using plasma of a first process gas, a process of removing the first mask, a process of forming a second mask on a second region of the metal film, and a process of modulating the work function of a second exposed region of the metal film, using plasma of a second process gas are executed.