Study by real time ellipsometry of the growth of amorphous and microcrystalline silicon thin films combining glow discharge decomposition and UV light irradiation

Abstract

We present here the application of spectroscopic phase modulated ellipsometry (SPME) to the study of the growth of amorphous and microcrystalline silicon thin films combining plasma-enhanced chemical vapor deposition (PECVD) and excimer laser irradiation. Our results show that laser fluence is a critical parameter in UV-assisted deposition. When we increase the laser fluence we observe a gradual transition from hydrogenated amorphous silicon ( a− Si: H) to an a− Si: H with greater roughness and porosity, then to a very dense a− Si: H, after that to a dense microcrystalline silicon (μc−Si) material, and finally to a porous microcrystalline material. The crystallization, after and during plasma deposition, is characterized by the evolution of the imaginary part of the pseudo-dielectric function which allows us to identify the threshold of crystallization in the two cases. Moreover, the substrate temperature is found to activate the crystallization process in UV-assisted PECVD.