Application of low-temperature N/sub 2/O-annealed oxide and chemical oxide for both boron penetration and gate depletion reductions for thin p/sup +/ tungsten polycide gate

Abstract

Boron behavior in p/sup +/ W-polycide gate used for high performance surface-channel pMOSFET was investigated. The poly structure and poly-WSi/sub 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 /spl Aring/ amorphous Si layer. In addition, boron out-diffusion into the WSi/sub 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/sub x/ layer. A surface channel pMOSFET using N/sub 2/O-annealed oxide and chemical oxide shows excellent characteristics of high saturation current, low leakage and gate depletion.