A method includes forming a dummy gate stack over a semiconductor substrate, wherein the semiconductor substrate is comprised in a wafer. The method further includes removing the dummy gate stack to form a recess, forming a gate dielectric layer in the recess, and forming a metal layer in the recess and over the gate dielectric layer. The metal layer has an n-work function. A portion of the metal layer has a crystalline structure. The method further includes filling a remaining portion of the recess with metallic materials, wherein the metallic materials are overlying the metal layer.