Mixed phase silicon thin films grown at high rate using 60Â MHz assisted VHF-PECVD technique

Mixed phase amorphous and nanocrystalline silicon (a-Si:H and nc-Si:H) thin films were deposited by VHF-PECVD (60 MHz) using Argon (Ar) as the diluent of silane. These amorphous and crystalline silicon thin films were deposited by varying the argon dilution (fAr) from 10-97.5% while keeping other process parameters constant. The effects of argon dilution on deposition rate, structural and optical properties of micro/nanocrystalline silicon thin films are studied. It has been observed that the films deposited from fAr 10-70% showed the deposition rate >20 Å/s with the highest deposition rate achieved of ~25 Å/s. Structural characterization has been performed by micro-Raman analysis and Atomic force microscopy. Raman shift towards higher wave number (515 cm−1) with increase of fAr indicates variation in crystallinity of silicon films. HRTEM studies revealed the distribution of grain size and the degree of crystallinity. Optical absorption spectroscopy confirmed the increase in band gap of the materials from 1.5 to 2.1 eV.