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

The impact of thin TaN layers $(0.5–10nm)$ 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 $0.5nm$⁠, 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 $TaxSiyNz$ 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 $(4.2–4.3eV)$⁠.