LPCVD of tungsten by selective deposition on silicon

Tungsten has been deposited in a low pressure chemical vapor deposition (LPCVD) system by silicon reduction of WF6. Hydrogen passivation of the silicon was found essential to inhibit native oxide formation on the silicon. A self-limiting W thickness of 100 nm was achieved at a deposition temperature of 440 degreesC. A typical layer sheet resistance of 2 Omega/square was obtained. Layers deposited at higher temperature yielded greater thickness, but showed the inclusion of higher resistivity beta phase W. WSi2 also observed, indicating solid phase reaction between the silicon and the deposited W. A reduced self-limiting thickness of W was observed when heavily doped single-crystal substrates were employed. This reduction in thickness was also observed when polycrystalline samples were employed. (C) 2001 Kluwer Academic Publishers.