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Title:
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The effect of argon dilution on deposition of microcrystalline silicon by microwave plasma enhanced chemical vapor deposition
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Author(s):
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Published by:
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Publication date:
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ECN
Solar Energy
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1-6-2006
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ECN report number:
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Document type:
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ECN-RX--06-015
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Conference Paper
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Number of pages:
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Full text:
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20
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Download PDF
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Presented at: E-MRS, European Materials Research Society, Nice, France, 29 mei 2006-2 juni 2006.
Abstract:
Microwave PECVD is a very promising method for industrial scale fabricationof microcrystalline silicon solar cells since the technique is well
applicable for large areas, and high deposition rates can be obtained.
We have investigated the effect of Ar dilution on the growth process
and the material properties of microcrystalline silicon. The major benefit
of Ar addition in the MWPECVD process, using H2 and SiH4 as reactant
gases, is an improved stabilization of the plasma, in particular at
low pressure and MW power. We show, however, that material properties
of the microcrystalline silicon layers deteriorate if we partly substitute
H2 by Ar during the deposition. The density of the layers ? as expressed
by the refractive index ? decreases, and the defect density (measured
by FTPS) increases with increasing Ar flow. Investigation of the plasma
by optical emission study shows that Ar atoms play a very active role
in the dissociation processes of H2 and SiH4. Substitution of H2 by
Ar decreases the SiH* emission and increases the Si* emission. On the
other hand, the Ha/Hb ratio increases upon substitution of H2 by Ar.
The latter effect shows that Ar addition does not lead to higher electron
temperatures and we conclude that the changes of SiH* and Si* emissions
are due to dissociation of SiH4 by Ar* (quenching reactions). The precise
role of Ar in MWPECVD of microcrystalline silicon needs further investigation,
but we conclude that the usage of this gas should be minimized in order
to maximize the quality of the silicon layers.
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