A semiconductor device includes a semiconductor substrate and a transistor formed in the substrate, the transistor having a gate stack that has an interfacial layer formed on the substrate, a high-k dielectric layer formed over the interfacial layer, a metal layer formed over the high-dielectric layer, a capping layer formed between the interfacial layer and high-k dielectric layer; and a doped layer formed on the metal layer, the doped layer including at least F.