Hydrogen passivation is essential for improving the properties of polycrystalline silicon thin films, We have observed that remote plasma hydrogenation with duration up to 30 min effectively passivated the defects and improved the Hall mobility. trap density and photoluminescence intensity. Over 60 min of hydrogenation caused the photoluminescence intensity to decrease, It seems that excessive hydrogenation not only passivated defects but also created new defects (Si H-2 bonds and hydrogen molecule,.,) in the grains. Raman spectroscopy detected that hydrogen formed Si-H-2 bonds in the poly-Si up to 100 nm from surface, Creation of these defects corresponded to a decrease of the photoluminescence intensity. These defects might be harmful to poly-Si-based devices, (C) 2005 Elsevier B.V. All rights reserved.