AVS 53rd International Symposium
    Thin Film Wednesday Sessions
       Session TF-WeM

Paper TF-WeM6
Microcrystalline Silicon Deposition Efficiency Optimization

Wednesday, November 15, 2006, 9:40 am, Room 2022

Session: Thin Films for Photovoltaics and Energy Applications
Presenter: B. Strahm, Ecole Polytechnique Fédérale de Lausanne, Switzerland
Authors: B. Strahm, Ecole Polytechnique Fédérale de Lausanne, Switzerland
A.A. Howling, Ecole Polytechnique Fédérale de Lausanne, Switzerland
L. Sansonnens, Ecole Polytechnique Fédérale de Lausanne, Switzerland
Ch. Hollenstein, Ecole Polytechnique Fédérale de Lausanne, Switzerland
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Microcrystalline silicon is widely used in solar cells, because of its better performances and stability compared to the standard amorphous silicon. However, the low light absorption of microcrystalline silicon implies that thick layers have to be deposited. Therefore high deposition rates (> 1 nm/s) have to be achieved in order to allow a cost-effective mass production of solar cells. An analytical plasma chemistry model has been used to determine the amorphous/microcrystalline silicon microstructure transition and the gas utilization efficiency as a function of plasma parameters. Modeling results show that high gas utilization efficiency is not incompatible with microcrystalline silicon deposition. In situ deposition rate and infra-red absorption measurements in a large area RF-PECVD capacitive reactor have been used to determine the gas utilization efficiency and the silane depletion. Ex situ Raman spectroscopy was used to measure the crystallinity of the deposited layers. Experimental data have validated the analytical plasma chemistry model and the results were used to build up a new experimental approach to optimize microcrystalline silicon deposition efficiency. Starting with appropriate plasma parameters (RF input power, excitation frequency and silane flow rate and concentration) and by varying only hydrogen flow rate and pressure, the gas utilization efficiency can be increased to values higher than 80 %. This high efficiency has not only the advantage of high deposition rate, but also reduces raw material consumption and powder formation.