Application of low-temperature N2O-annealed oxide and chemical oxide for both boron penetration and gate depletion reductions for thin p+ tungsten polycide gate

Boron behavior in p⁺ W-polycide gate used for high performance surface-channel pMOSFET was investigated. The poly structure and poly-WSi_x interface play an important role in the characteristics of the MOSFET. It was found that large-grain poly showed severe boron penetration compared to an 800 Å amorphous Si layer. In addition, boron out-diffusion into the WSi_x layer causes severe gate depletion which gives rise to low saturation current. Application of chemical oxide between poly and tungsten silicide turns out to be good barrier to block fluorine diffusion into the gate oxide as well as boron out-diffusion into the WSi_x layer. A surface channel pMOSFET using N₂O-annealed oxide and chemical oxide shows excellent characteristics of high saturation current, low leakage and gate depletion