The effects of dopant and impurity redistributions on WSi2 formation by rapid thermal processing

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Abstract
Thin‐film samples of WSi2 were formed by sputter depositing tungsten metal directly onto chemically etched, p‐type, B‐doped, 5 Ω cm Si(100) wafers, followed by rapid thermal processing (RTP) in high vacuum at temperatures over 1100 °C. The resulting dopant and impurity elemental redistributions are studied by secondary ion mass spectroscopy. Boron, initially present both at the W/Si(100) interface as an impurity and in low concentration in the Si substrate, diffuses into the growing WSi2 film, eventually escaping into the vacuum. It is shown that RTP can be used to form high‐quality, low‐resistivity (∼30 μΩ cm) WSi2 films without total dopant out‐diffusion. Oxygen is the major impurity in these samples and is gettered at the metal/Si(100) interface during RTP from the vacuum ambient. Removal of this interfacial oxide is needed for the growth of uniform, low‐resistivity silicide films and can be done with RTP. Trace quantities of F, Cl, Na, K, C, and Cr have also been detected. Their origin and movement through the growing silicide films are also monitored as a function of RTP conditions.

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