Phase change analysis of crystalline silicon thin film grown by very high frequency - plasma enhanced chemical vapour deposition and radio frequency - magnetron sputtering

Abstract

In this study, silicon thin films had been successfully produced by using Very High Frequency-Plasma Enhanced Chemical Vapour Deposition (VHF-PECVD) technique. The phase transition from amorphous to crystalline silicon along with crystallite types remains unknown, especially at VHF region up to 200 MHz. In this work, very high frequencies ranging from 35 MHz until 200 MHz were investigated. The deposition time were fixed for 3 minutes and 15 minutes, while Radio Frequency (RF) power were fixed at 20 W and 30 W. For comparison purpose, RF-Magnetron Sputtering technique was used to deposit silicon thin films with the same RF power at 20 W and 30 W. Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy and Raman spectroscopy were used to determine the phase transition of film structure from amorphous to crystal, while X-Ray Diffraction (XRD) technique was used to determine the crystallites in the samples for both deposition techniques. Morphology study was carried out using Field Emission Scanning Electron Microscope (FESEM) and Atomic Force Microscope (AFM). The transition from hydrogenated amorphous silicon (a-Si:H) to hydrogenated crystalline silicon (c-Si:H) in the thin film samples was observed as deposition frequency increased from 35 MHz to 200 MHz. Typical Si (111) and Si (311) crystalline were formed in VHF-PECVD samples while only Si (311) was formed in RF-Magnetron Sputtering. VHF-PECVD produced 248 nm and 250 nm film thicknesses compared to RF-Magnetron Sputtering at only 34 nm. Rougher films were produced by VHF-PECVD with maximum average surface roughness of 3.64 nm compared to RF-Magnetron sputtering at 0.38 nm. Therefore, it can be concluded that the transition of silicon film from amorphous to crystal occurred at high deposition frequency using VHF-PECVD technique, but were hardly seen for RF-Magnetron Sputtering samples as the deposited thin films were too thin.