The Variation of Crystalline Structure Induced by Gas Dilution and Thermal Annealing in Silicon Layers Deposited by PECVD Technique

We prepared hydrogenated thick silicon film by plasma enhanced chemical vapor deposition (PECVD) method using SiH4 and H-2 gas mixture and we investigated the effect of the hydrogen dilution ratio defined as R=H2SiH4 on the as-deposited and annealed films. With increase in hydrogen dilution ratio, amorphous to microcrystalline transition has been observed. The crystallization has been confirmed from Raman spectroscopy, UV reflectance, low angle X-ray diffraction (XRD), spectroscopic ellipsometry and atomic force microscopy (AFM) analysis. Tauc band gap shows a decreasing trend with increasing H-2 dilution of silane. It decreases from 1.8 to 1.57 eV. It has been concluded that H-2 dilution of silane in PECVD enhances the crystallinity of the film and affects its optical and structural properties.