Evaluation of poly-Si thin film crystallized by solid green laser annealing using UV/visible Raman spectroscopy

Depth and in-plane distributions of the crystal qualities in low-temperature polycrystalline Si (LTPS) films fabricated by green laser annealing with s and p-polarizations and commercial excimer laser annealing were evaluated by Raman spectroscopy with UV and visible excitation laser sources from the front and back surfaces. A quasi-line excitation source provides a one-dimensional profile with 200-nm spatial resolution and step-by-step scanning parallel to the quasi-line to obtain two-dimensional mapping images. The Raman peak shift corresponds to the residual stress in the film, and the full width at half-maximum (FWHM) indicates the crystallinity. Both were analyzed using the mapping images and one-dimensional profiles. Crystal quality and residual stress as measured by the Raman peak shift and crystallinity as indicated by FWHM significantly depended on the annealing conditions. The depth profile was also unique to each sample. These results show that Raman mapping using UV and visible excitation sources is very useful for evaluating the crystal quality of LTPS films.