The Structural Evolution of A-SI:H Films Prepared by Pulse Rf Power Modulation with Hydrogen and Helium Dilution

Abstract

ABSTRACTA-Si:H films were deposited in a PECVD system using 5k to 5 Hz and 25 to 75% duty cycle square-wave pulse modulation RF power and with 80% hydrogen or 80% helium dilution. The transmission and the microstructure of the hydrogen bonding configuration were measured using NIR-VIS-UV and FTIR spectrometers. The powder formation in the reactor chamber was low for a deposition rate less than 5.87 nm/min and was completely suppressed by the 500 Hz pulse RF power with a duty cycle less than 33.3%. The low microstructure R ratio is the result of the reduction of the polymization reaction in the plasma for a low deposition process. A R ratio less than 14% could be obtained using 500 Hz with a duty cycle less than 33.3% for helium dilution or using 5k to 50 Hz with a duty cycle less than 50% for hydrogen dilution. The refractive index of the films is high for the films with low R ratio. The more compact and higher quality films exhibit greater SiH bonding configurations in the a-Si:H films.