Work Function and Effective Oxide Thickness Engineering via Alloying of Metal Gate Electrodes

Dielectric capping layer and electrode alloying approaches for tuning the effective work function and effective oxide thickness of metal oxide semiconductor transistors are compared. TaMgC and MoAlN electrodes are compared to MgO and Al2O3 capping layers for n-type and p-type transistors respectively. Results indicate that by incorporating the Mg or Al into the gate electrode instead of into the dielectric capping layer reductions in threshold voltage can be achieved, but with the added benefit of an effective oxide thickness reduction. SIMS results suggest that the threshold voltage shift is likely caused by the inward diffusion of Mg or Al though the gate dielectric towards the bottom interface layer. The limitations of each approach for work function engineering are discussed.