Characterization of defects in polycrystalline silicon thin films using chemical etching, hydrogenation, and Raman spectroscopy

The electrochemical and electronic activities of defects were investigated for excimer-laser-annealed polycrystalline silicon (poly-Si) thin films. Variations in surface geometry and Raman spectra with Secco-etching time were compared between ascrystallized and hydrogenated poly-Si films. For ascrystallized films, etching preferentially attacks defects at the grain boundary (GB). Furthermore, defects in grains were attacked by etching, which was deduced from etching rate and variation in the stress in films. Hydrogenation prior to etching effectively protects defects at GB and in grains from etching. The effects of hydrogenation were interpreted in terms of diminishing localized electronic states related to defects. Hydrogenation followed by Secco etching revealed submicron-size defects that were attributed to the segregation of oxide lying deep in films. The variation in the Raman spectra with etching time indicated that the local-vibration mode at 2000cm(-1) was related to electrochemically active defects terminated by hydrogen predominantly at GB. It was also shown that Raman scattering intensity is strongly modulated by interference in thinned films and the roughness of the etched surface.