Anatomy of mc-Si thin films by plasma enhanced chemical vapor deposition: An investigation by spectroscopic ellipsometry

A detailed analysis of the anatomy of microcrystalline (mc-Si) films deposited by plasma enhanced chemical vapor deposition from both SiF4-H2 and SiH4-H2 mixtures is performed by spectroscopic ellipsometry (SE). Specifically, the mc-Si film anatomy consists of an interface layer at the substrate/mc-Si bulk layer, a bulk mc-Si layer, and a surface porous layer. All these layers have their own microstructures, which need to be highlighted, since it is this overall anatomy which determines the optical properties of mc-Si films. The ability of SE to discriminate the complex microstructure of mc-Si thin films is emphasized also by the comparison with the x-ray diffraction data which cannot provide unambiguous information regarding the distribution of the crystalline and the amorphous phases along the mc-Si film thickness. Through the description of the mc-Si film anatomy, information on the effect of the growth precursors (SiF4 or SiH4) and of the substrate (c-Si or Corning glass) on the growth dynamics can be obtained. The key role of the F-atoms density and, therefore, of the etching-to-deposition competition on the growth mechanism and film microstructure is highlighted.