Polycrystalline silicon (poly-Si) films were deposited on glass substrates (corning 7059) at 300 degrees C by a plasma enhanced chemical vapor deposition (PECVD) from a SIH4/SiF4 mixture. All poly-Si films were prepared under the same deposition conditions on the substrates subjected to nitrogen, hydrogen and/or CF4 plasma with different gas pressures, just before deposition of the poly-Si films. Effects of such pretreatments for substrates on the structural properties of the resultant poly-Si films have been investigated. The Si film deposited on the substrates without any pretreatments was amorphous. However, formation of a strong [110] preferentially oriented poly-Si with improved crystallinity was obtained for the films deposited on the glass substrate after plasma pretreatments, which exhibit smoother surfaces. This result was interpreted in terms of a removal of weak Si-Si bonds during nucleation and the subsequent grain growth.