A time-resolved optical emission spectroscopic study identified transient behavior of the excited SiH emission in a parallel plate SiH 4 /H 2 plasma. The transient behavior could be prevented by filling the background gas with H 2 prior to plasma ignition. Applying this condition, state-of-the-art microcrystalline silicon ͑ c-Si: H͒ could be deposited irrespective of the applied H 2 flow, ultimately demonstrated by a 9.5% efficient solar cell deposited from pure SiH 4 . The results are discussed in terms of SiH 4 back diffusion: an initial diffusion flux of SiH 4 from the reactor's dead volume back into the plasma.

The H flux to Si growth flux ratio is experimentally determined under state-of-the-art silicon thin-film deposition conditions by employing the recently introduced etch product detection technique. Under the technologically relevant high-pressure depletion conditions and for different process parameter settings such as pressure, SiH4 concentration, rf power, and excitation frequency, it was demonstrated that the microcrystalline to amorphous silicon phase transition is uniquely and reactor independently determined by the flux ratio of H and Si growth species.

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Exploiting the higher etch probability for amorphous silicon relative to crystalline silicon, the transiently evolving phase composition of silicon films in the microcrystalline growth regime was probed in situ by monitoring the etch product (SiH4) gas density during a short H2 plasma treatment step. Etch product detection took place by the easy-to-implement techniques of optical emission spectroscopy and infrared absorption spectroscopy. The phase composition of the films was probed as a function of the SiH4 concentration during deposition and as a function of the film thickness. The in situ results were corroborated by Raman spectroscopy and solar cell analysis.