Silane and hydrogen discharges are widely used for the deposition of silicon thin film solar cells in large area plasma-enhanced
chemical vapor deposition reactors. In the case of microcrystalline silicon thin film solar cells, it is of crucial
importance to increase the deposition rate in order to reduce the manufacturing costs. This can be performed by using
high silane concentration, and usually high RF power and high pressure, all favorable to powder formation in the
discharge that generally reduces the deposition rate as well as the deposited material quality. This work presents a study
of powder formation using time-resolved optical emission spectroscopy. It is shown that this technique is suitable to
detect different regimes in powder formation ranging from powder free discharge to discharge producing large dust
particles. Intermediate powder formation regimes include the formation of small silicon clusters at plasma ignition as
well as cycle of powder growth and ejection out of the discharge, and both are observable by this low-cost and
experimentally simple technique.
Amorphous and microcrystalline silicon have been proven to be very interesting for low cost thin film photovoltaic
devices. Usually these two materials are deposited using the same large area plasma-enhanced chemical vapor deposition
reactors from silane and hydrogen gases. The transition from amorphous deposition regime to microcrystalline
deposition regime is generally done by reducing the silane concentration in the input gas flow and the optimum
deposition parameters to achieve high performance device stands just at the transition between the two microstructures.
In the present work, a study of the transition width from amorphous to microcrystalline silicon is presented as a function
of the input silane concentration. It is shown that the higher the input silane concentration, the wider is the microstructure
transition. As a consequence, the process is less sensitive to fluctuations of the silane concentration when silane
concentrations higher than 10 % are used and better uniformity and reproducibility can be then achieved.
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