LPCVD of tungsten by selective deposition on silicon

Abstract

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 °C. A typical layer sheet resistance of 2 Ω/□ was obtained. Layers deposited at higher temperature yielded greater thickness, but showed the inclusion of higher resistivity β 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.