Analysis of Defects in Polycrystalline Silicon Thin Films Using Raman Scattering Spectroscopy

We investigated defects in polycrystalline silicon (poly-Si) for thin-film transistors using Raman-scattering spectroscopy, where poly-Si films were fabricated by solid-phase crystallization (SPC) and excimer-laser annealing (ELA). Defects were characterized by the optical-phonon mode at ∼520 cm -1 and local-vibration modes (LVMs). LVMs were induced by termination of dangling bonds at defects with hydrogen atoms using a catalytic-hydrogenation technique. Two dominant LVMs of Si-H bond stretching modes were detected for poly-Si films at 2000 and 2100 cm-1. The 2000 cm-1 band was attributed to dangling bonds at grain boundaries. The dangling bonds are identical to those observed by electron spin resonance. The 2100 cm-1 band was detected only for ELA and related to atomic vacancies left by rapid cooling after laser irradiation. It was shown that the width of the optical-phonon mode is enlarged by the presence of intragrain defects and correlates with the 2100 cm-1 band intensity in some cases. The relationship between dangling bonds and ordering of amorphous Si at the initial stage of SPC was also shown.