The present disclosure provides a method of semiconductor device fabrication including removing a sacrificial gate structure formed on a substrate to provide an opening. A metal gate structure is then formed in the opening. The forming of the metal gate structure includes forming a first layer (including metal) on a gate dielectric layer, wherein the first layer includes a metal and performing a stress modulation process on the first layer. The stress modulation process may include ion implantation of a neutral species such as silicon, argon, germanium, and xenon.