Metal Gate Stack Having TaAlCN Layer

A method includes forming a gate stack over a semiconductor substrate; forming an interlayer dielectric layer surrounding the gate stack; and at least partially removing the gate stack, thereby forming an opening. The method further includes forming a multi-function wetting/blocking layer in the opening, a work function layer over the multi-function blocking/wetting layer, and a conductive layer over the work function layer. The work function layer, the multi-function wetting/blocking layer, and the conductive layer fill the opening. The multi-function wetting/blocking layer includes aluminum, carbon, nitride, and one of: titanium and tantalum.