Effects of the addition of SiF4 to the SiH4 feed gas for depositing polycrystalline silicon films at low temperature

Polycrystalline silicon films with a strong (110) texture were prepared on a coming 7059 glass substrate at 400 degrees C by a plasma-enhanced chemical vapor deposition method using a mixture of gases with different SiF4 flow rates ([SiF4] = 0-0.5sccm) under a fixed SiH4 flow rate ([SiH4] = 1 or 0.15sccm). The effects of the addition of SiF4 to SiH4 on the structural properties of the films were studied by Raman scattering, X-ray diffraction (XRD), atomic force microscopy and stress measurements. For [SiH4] = 1 sccm, the crystallinity and the (110) XRD grain size monotonically increased with increasing [SiF4]; and their respective maxima reach 90% and 900 PI. In contrast, for [SiH4] = 0.15 seem, both the crystallinity and the grain size decreased with [SiF4]. Mechanisms causing the change in crystallinity are discussed, and it was suggested that an improvement in the crystallinity, due to the addition of SiF4, is likely to be caused by the effect of a change in the surface morphology of the substrates along with the effect of in situ chemical cleaning. On the other hand, both the effect of in situ chemical etching on the growing surface and the effect of a change in the capability for surface migration of adsorbates may provide a minor contribution in determining the crystallinity.