Hydrogen at compact sites in hot-wire chemical vapour deposited polycrystalline silicon films

Abstract

Polycrystalline silicon (poly-silicon) films made by hot-wire chemical vapour deposition (HWCVD) in a controlled range of deposition conditions show the Si–H stretching vibration at 2000 cm −1 in infrared absorption. This band is in contrast to commonly observed IR spectra in plasma enhanced chemical vapour deposition (PECVD) poly-silicon films in which the Si–H vibration is at 2100 cm −1. Raman spectra of the stretching vibration confirmed that the 2000 cm −1 mode is from the crystalline region (top) of the material. The thickness dependence of the single hydrogen effusion maximum (∼640°C) reveal a diffusion-limited effusion of hydrogen migration similar to the case of the high-temperature hydrogen effusion maximum of amorphous silicon deposited at 25°C. The diffusion profile of implanted deuterium confirms the diffusive property in a compact material. The diffusion is through isolated Si–H sites at a trap depth of ∼1.5 eV determined by the hydrogen chemical potential. These isolated Si–H bonds, being located at compact sites, have the vibrational mode at 2000 cm −1 in their infrared spectra.