a-Si: H was deposited in a VHF-plasma in a wide frequency range up to 250MHz. The deposition rate was found to increase with excitation frequency up to 180MHz, where values of 35Å are achieved maintaining good film properties
The onset of this increase occurs near 60MHz, when the excitation frequency exceeds the inelastic electron-neutral collision rate. From optical emission of hydrogen and a He/Ar line pair the high energy tail of EEDF was probed. It is found, that the rise in deposition rate is solely due to the increased plasma density and not to an enhancement of the high energy tail of the EEDF, as postulated previously.