An improved work function layer and a method of forming the same are disclosed. In an embodiment, the method includes forming a semiconductor fin extending from a substrate; depositing a dielectric layer over the semiconductor fin; depositing a first work function layer over the dielectric layer; and exposing the first work function layer to a metastable plasma of a first reaction gas, a metastable plasma of a generation gas, and a metastable plasma of a second reaction gas, the first reaction gas being different from the second reaction gas.