Gas-phase reactions of WF6with SiH4for deposition of WSinfilms free from powder formation

We elucidate the comprehensive mechanism of gas-phase reactions of WF6 with SiH4 for deposition of high-density W silicide (WSin, 0 < n ≤ 12) films, while avoiding powder formation. It is shown that the most important parameter is the partial pressure ratio of SiH4 to WF6, RS/W. As RS/W increases ≥1, the gas-phase reaction becomes dominant compared to the surface reaction and powder formation starts owing to the high reactivity of WF6 with SiH4 in the gas-phase, resulting in granular films with rough surfaces. Under the condition of RS/W > ∼10, less reactive fluorine-deficient molecules are formed by the reduction reaction, inhibiting the powder formation. Only when the gas-phase reaction with SiH4 is sufficiently promoted under the condition of an extremely high RS/W > 103, the W-atom-encapsulated Sin cage clusters are formed without fluorine content, leading to the powder-free deposition of the dense WSin film of n ≥ 6 with a homogeneously smooth surface.