Modulation of the work function of silicon gate electrode using thin TaN interlayers

The impact of thin TaN layers (0.5-10 nm) on the effective work function of polycrystalline silicon (poly-Si)/TaN stacks has been investigated. It is found that when the TaN layer is as thin as 0.5 nm, it can have a significant effect on the effective work function of poly-Si, and that n-type and p-type poly-Si behave differently. The observed results are explained by reactions between poly-Si and the TaN layer leading to the formation of Ta _xSi _yN _z at the poly-Si-gate dielectric interface. Electrical tests show minimal poly-Si depletion with the TaN layers, and gate leakage current and fixed charges that are comparable to conventional poly-Si electrodes. The results show that these stacked electrodes can be useful for nearly n-type effective work functions (4.2-4.3 eV).