Stable titanium silicide formation on field oxide after BF 2 ion implantation

The use of titanium silicide for low resistivity interconnects in a complementary metal–oxide–semiconductor process is investigated. After a source-drain processing, a wet oxide strip, and a 600 Å Ti deposition, a two-step anneal forms stable TiSi 2 in the diffused regions and amorphous silicon gate. Extraneous regions or islands of TiSi 2 were found to form on BF 2 implanted thick field oxide, and were not present on 11 B , n-type (N+), or nonimplanted field areas. The growth and nucleation of TiSi in the presence of oxygen is discussed, and an oxygen solubility model is used to explain the nucleation of TiSi 2 from a Ti 5 Si 3 interlayer. Two models are presented to explain the availability of Si to form stable TiSi in field oxide regions. In the first, B is shown to promote the formation of oxygen vacancies resulting in a Si rich oxide, while the second involves oxide network strain from the incorporation of F in the oxide, facilitating Si segregation to the surface and subsequent availability of Si atoms.