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

Abstract

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 TiSi2 in the diffused regions and amorphous silicon gate. Extraneous regions or islands of TiSi2 were found to form on BF2 implanted thick field oxide, and were not present on 11B, 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 TiSi2 from a Ti5Si3 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.