Tungsten gate technology using wet hydrogen oxidation

This report describes two key techniques for using tungsten (W) in place of poly-silicon (Si) or polycide in highly reliable metal gate technology for VLSIs: a new oxidation method, Wet Hydrogen Oxidation (WHO), to allow Si oxidation without oxidizing W, and W gate formation by sputtering using a high-purity W target. The effects of these new techniques on characteristics of MOSFET´s were investigated. Gate breakdown voltage was improved after WHO with no unfavorable effects on other device characteristics. Flatband voltage shift due to mobile-ion contamination was greatly reduced using a high-purity W target. Compared with poly-Si gates, the W gate MOS capacitors have higher gate breakdown voltage. W gate technology was applied to NMOS VLSIs, showing potential for megabit level VLSIs because of its low resistance ( < 0.5 Ω/□) and improved compatibility with poly-Si gate technology.