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

摘要

A 900 MHz surface wave antenna was used for plasma-enhanced chemical vapor deposition (PECVD) of silicon thin films in an H-2 + SiH4 discharge, with an emphasis on photovoltaic applications. Gas mixtures of 0.7-10% SiH4 at medium pressure (similar to 100 mTorr) were tested with an optimal substrate temperature of 285 +/- 15 degrees 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 degrees C up to 15 +/- 3 nm at 400 degrees C. Electron spin resonance showed that a-Si:H films grown via SWP were of acceptable defect density (similar to 10(16) cm(-3)) and conductivity (similar to 10(-8) S/cm). Conversely, nc-Si:H films were poor quality (similar to 10(18) cm(-3) defect density, 10(-3)-10(-2) S/cm conductivity) due to low hydrogenation and small grain size. (c) 2017 Elsevier B.V. All rights reserved.