High deposition rate nanocrystalline and amorphous silicon thin film production via surface wave plasma source

Abstract

A 900 MHz surface wave antenna was used for plasma-enhanced chemical vapor deposition (PECVD) of silicon thin films in an H₂ + SiH₄ discharge, with an emphasis on photovoltaic applications. Gas mixtures of 0.7–10% SiH₄ at medium pressure (~ 100 mTorr) were tested with an optimal substrate temperature of 285 ± 15 °C, producing nanocrystalline hydrogenated silicon (nc-Si:H) at rates up to 3 nm/s, while amorphous films were grown in excess of 10 nm/s. A sharp transition from crystalline to amorphous growth was seen as SiH₄ flowrate increased, as is characteristic of silane PECVD. Increasing both substrate temperature and source power served to move this transition to higher flowrates, and by extension, higher deposition rates for the crystalline phase. Grain size also increased with substrate temperature, ranging from 10 ± 2 nm at 200 °C up to 15 ± 3 nm at 400 °C. Electron spin resonance showed that a-Si:H films grown via SWP were of acceptable defect density (~ 10¹⁶ cm^− 3) and conductivity (~ 10^− 8 S/cm). Conversely, nc-Si:H films were poor quality (~ 10¹⁸ cm^− 3 defect density, 10^− 3–10^− 2 S/cm conductivity) due to low hydrogenation and small grain size.