Insight into excimer laser crystallization exploiting ellipsometry: Effect of silicon film precursor

The optical diagnostic of spectroscopic ellipsometry is shown to be an effective tool to investigate the mechanism of excimer laser crystallization (ELC) of silicon thin films. A detailed spectroscopic ellipsometric investigation of the microstructures of polycrystalline Si films obtained on SiO2/Si wafers by ELC of a-Si:H and nc-Si films deposited, respectively, by SiH4 plasma enhanced chemical vapor deposition (PECVD) and SiF4-PECVD is presented. It is shown that ellipsometric spectra of the pseudodielectric function of polysilicon thin films allows to discern the three different ELC regimes of partial melting, super lateral growth and complete melting. Exploiting ellipsometry and atomic force microscopy, it is shown that ELC of nc-Si has very low energy density threshold of 95 mJ/cm2 for complete melting, and that re-crystallization to large grains of ∼ 2 μm can be achieved by multi-shot irradiation at an energy density as low as 260 mJ/cm2 when using nc-Si when compared to 340 mJ/cm2 for the ELC of a-Si films.