Electrochemical and Raman-Scattering Characterizations of Defects in Polycrystalline Silicon Thin Films Formed by Excimer-Laser Annealing, Solid-Phase Crystallization, and Continuous-Wave Laser Lateral Crystallization

Abstract

We investigated the electronic activity of defects in polycrystalline silicon (poly-Si) thin films grown by excimer-laser annealing (ELA), solid-phase crystallization (SPC), and continuous-wave laser lateral crystallization (CLC). The activity of defects was deduced from the erosion by Secco etching, which is based on enhancement of etching due to electronically active states in the band gap. Hydrogenation protected grain boundaries (GBs) and sub-GBs from etching, which indicates that those defects are originally active and are inactivated by hydrogen. Ingrain defect density was characterized by variation of stress in films with etching, where stress was estimated using Raman spectroscopy. It is shown that ELA poly-Si contains a high density of active defects in grains, while SPC and CLC poly-Si films contain a lower density. That feature of ELA is attributed to freezing of defects in grains during rapid cooling after laser irradiation, which is consistent with the elimination of defects by post-annealing of the ELA film at 1000 °C. For CLC, we deduced that laterally directed growth is effective for decreasing defects.