OXIDATION OF SI-RICH CHEMICAL-VAPOR-DEPOSITED FILMS OF TUNGSTEN SILICIDE

We have studied dry oxidation characteristics of Si-rich WSi//x thin films prepared by LPCVD directly on SiO//2, with x equals 2. 7 for as-deposited films. It has been reported previously that thin (less than 100 nm) CVD tungsten silicide adheres well to SiO//2. Using Auger depth profiling and Rutherford backscattering spectroscopies, we find that silicon in excess of stoichiometric WSi//2 diffuses through the silicide toward the surface to form a SiO//2 passivating overlayer. The extracted activation energy for this oxidation process is E//a equals 1. 2 ev, consistent with oxygen diffusion in SiO//2. A similar value of E//a is found for WSi//x deposited on polysilicon. During the anneal, the stoichiometry x of WSi//x decreases monotonically with the annealing temperature, reaching x equals 2 after 30 min at 900 degree C or 20 min at 950 degree C. Longer times or higher temperatures result in silicon depletion, with x equals 1. 7 after 30 min at 1000 degree C.