Investigation of Vibrational Bonding Modes in Hydrogenated Silicon Thin Films Near the Amorphous-to-Nanocrystalline Transition via Argon-Diluted Silane PECVD

Abstract

This study investigates the structural properties and hydrogen bonding configurations in hydrogenated silicon (Si:H) thin films deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) using argon-diluted silane. The films were characterized near the amorphous-to-nanocrystalline transition zone using a combination of Fourier Transform Infrared (FTIR) and Raman spectroscopy. Results show that increasing RF power and pressure induces a transition from amorphous to nanocrystalline films, accompanied by an increase in crystalline fraction and crystallite size. The infrared analysis reveals the evolution of different hydrogen bonds (SiH, SiH₂, and (SiH₂)n), with the bending mode (840–900 cm⁻¹) and stretching mode (1850–2200 cm⁻¹) providing insights into the bonding environment. Our findings show that increasing RF power promotes monohydride bond formation while pressure variations mainly affect polyhydride concentrations, providing insights into controlling material properties. A correlation between the crystalline fraction and the relative concentrations of SiH, SiH₂, and (SiH₂)_n bonds was observed. Hydrogen content was found to decrease with higher RF power and increase with pressure, while oxygen contamination was more significant at higher RF power and lower at increased pressure. These findings emphasize the importance of deposition conditions in tailoring the microstructure and chemical properties of Si:H films for optimized performance in various technological applications.