Polycrystalline Silicon Thin Films at Low Temperature using SiF$_{4}$ / SiH$_{4}$ mixture

Polycrystalline silicon films with a strong (110) texture were prepared at 400$^{\circ}$C by a plasma-enhanced chemical vapor deposition using different SiF$_{4}$~flow rates ([SiF$_{4}$] $=$ 0--0.5 sccm) under a fixed SiH$_{4}$~flow rate ( [SiH$_{4}$] $=$ 1 or 0.15 sccm). The effects of the addition of SiF$_{4}$ to SiH$_{4}$ on the structural properties of the films were studied by Raman scattering, X-ray diffraction (XRD), Atomic force microscopy and stress measurements. For [SiH$_{4}$] $=$ 1 sccm, the crystallinity and the (110) XRD grain size monotonically increased with increasing [SiF$_{4}$] and their respective maxima reach 90{\%} and 900 {\AA}. However, for [SiH$_{4}$] $=$ 0.15 sccm, both the crystallinity and the grain size decreased with [SiF$_{4}$]. Mechanisms causing the change in crystallinity are discussed, and it was suggested that an improvement in the crystallinity, due to the addition of SiF$_{4}$, is likely to be caused by the effect of a change in the surface morphology of the substrates along with the effect of \textit{in situ} chemical cleaning.