The optical diagnostic o
f spectroscopic ellipsometry is shown to be an e
ffective tool to investigate the mechanism o
f excimer laser crystallization (ELC) o
f silicon thin
films. A detailed spectroscopic ellipsometric investigation o
f the microstructures o
f polycrystalline Si
films obtained on SiO
2/Si wa
fers by ELC o
f a-Si:H and nc-Si
films deposited, respectively, by SiH
4 plasma enhanced chemical vapor deposition (PECVD) and SiF
4-PECVD is presented. It is shown that ellipsometric spectra o
f the pseudodielectric
function o
f polysilicon thin
films allows to discern the three di
fferent ELC regimes o
f partial melting, super lateral growth and complete melting. Exploiting ellipsometry and atomic
force microscopy, it is shown that ELC o
f nc-Si has very low energy density threshold o
f 95 mJ/cm
2 for complete melting, and that re-crystallization to large grains o
f ![](http://www.sciencedirect.com/scidirimg/entities/223c.gi<font color=)
f" alt="not, vert, similar" border=0> 2 μm can be achieved by multi-shot irradiation at an energy density as low as 260 mJ/cm
2 when using nc-Si when compared to 340 mJ/cm
2 for the ELC o
f a-Si
films.