Precursors for the deposition of amorphous silicon–hydrogen alloys by remote plasma enhanced chemical vapor deposition

Abstract

We have grown thin films of intrinsic and doped a-Si:H alloys by remote plasma enhanced chemical vapor deposition (remote PECVD) and studied their optical, electrical, and infrared vibrational properties. The electronic properties of remote PECVD films deposited at Ts =240 °C are similar to glow discharge (GD) films produced at the same Ts . Remote PECVD a-Si:H films deposited at Ts =100 °C show predominantly monohydride bonding in the infrared absorbance spectrum, and have electrical properties that are markedly improved over GD films deposited at this same relatively low Ts. We have studied the deposition process by mass spectrometry and optical emission spectroscopy and find that the concentration of silane fragments (SiHx, x=0–3) and higher silanes (e.g., disilane, Si2H6) in the gas phase is below our detection limit of 1%. Bias experiments and a comparison of the a-Si:H deposition rate with the known concentration of silane in the gas phase suggest that in remote PECVD, electrons from the He plasma produce vibrationally excited silane molecules (as opposed to silane fragments) in the gas phase or on the deposition surface which then act as the precursors for the a-Si:H thin-film deposition reactions.