Gas-phase reactions of WF6 with SiH4 for deposition of WSin films free from powder formation

We elucidate the comprehensive mechanism of gas-phase reactions of WF6 with Si-4 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, R-S/W. As R-S/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 R-S/W > similar to 10, less reactive fluorinedeficient 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 R-S/W > 10(3), the W-atom-encapsulated Si-n 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. (C) 2019 The Japan Society of Applied Physics