The present disclosure provides a method for making metal gate stacks of a semiconductor device. The method includes applying a first dry etching process to a semiconductor substrate in an etch chamber through openings of a patterned mask layer defining gate regions, removing a polysilicon layer and a metal gate layer on the semiconductor substrate; applying a H2O steam to the semiconductor substrate in the etch chamber, removing a capping layer on the semiconductor substrate; applying a second dry etching process to the semiconductor substrate in the etch chamber, removing a high k dielectric material layer; and applying a wet etching process to the semiconductor substrate to remove polymeric residue.