Highly reliable tungsten gate technology

In this paper, the reliability of W gate process is discussed from three aspects; thermal stability of gate/SiO/sub 2//Si structure, oxidation resistance of W and high-purity film formation. In terms of thermal stability of refractory metals/SiO/sub 2//Si structure, it is shown that Si/SiO/sub 2/ reaction can be a key problem, rather than metal (W or Mo)/SiO/sub 2/ reaction in the case of (W or Mo)/SiO/sub 2//Si structure. A new oxidation method, wet hydrogen oxidation, can overcome the oxidation problem of W gate process, in which Si can be oxidized without oxidizing W. W gate technology using CVD method has been developed to reduce mobile ion contamination and is shown to be very promising for use in VLSIs