A method for fabricating a gate stack of a semiconductor device comprises forming a first dielectric layer over a channel region of the device, forming a first nitride layer over the first dielectric layer, depositing a scavenging layer on the first nitride layer, forming a capping layer over the scavenging layer, removing portions of the capping layer and the scavenging layer to expose a portion of the first nitride layer in a n-type field effect transistor (nFET) region of the gate stack, forming a first gate metal layer over the first nitride layer and the capping layer, depositing a second nitride layer on the first gate metal layer, and depositing a gate electrode material on the second nitride layer.