An integrated circuit device includes a semiconductor substrate; and a gate stack disposed over the semiconductor substrate. The gate stack further includes a gate dielectric layer disposed over the semiconductor substrate; a multi-function blocking/wetting layer disposed over the gate dielectric layer, wherein the multi-function blocking/wetting layer comprises tantalum aluminum carbon nitride (TaAlCN); a work function layer disposed over the multi-function blocking/wetting layer; and a conductive layer disposed over the work function layer.