The formation of thin-film tungsten silicide annealed in ultrahigh vacuum

Abstract
Thin films of tungsten silicide have been formed by sputter depositing 710 Å of W metal onto (100)-oriented, 3–7 Ω cm, p-type silicon wafers. The samples were annealed in an ultrahigh vacuum ambient (pressure≤1.0×10−9 Torr) at temperatures ranging from 845 to 1100 °C for 30 s. The lack of oxygen contamination in the ambient allows the W-Si interaction to proceed, first producing both the W-rich W5 Si3 phase and the tetragonal WSi2 phase near 900 °C, followed by only the tetragonal, low-resistivity (30–40 μΩ cm) WSi2 phase above 1000 °C. This result is in contrast to previous work where films formed by rapid thermal processing in vacuum showed no significant W-Si interaction for temperatures below 1100 °C due to the formation of an interfacial oxide diffusion barrier gettered into the films from the 10−6 Torr ambient.