Control of the workfunction in bilayer metal gate stacks by varying the first layer thickness

Ni/TiN and Al/TiN bilayer stacks were investigated to determine the influence of the thin metals on the total effective workfunction. The workfunctions of the bilayer stacks were measured using CV (capacitance-voltage) curves. The effective workfunctions of both bilayer stacks were controlled by changing the TiN layer thickness. The workfunctions of both bilayer stacks shift toward the workfunction of the upper layer, and the absolute effective workfunction of the Ni/TiN bilayer stack was higher than that of the Al/TiN bilayer stack. The workfunction of the TiN layer itself decreased with the decreasing thickness.