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Increase in mechanical strength of As-Cut mono-crystalline silicon wafers by alkaline etching process

: Orellana Peres, T.; Mayer, K.; Schumann, M.; Granek, F.


Sinke, W. ; WIP - Renewable Energies, München; European Commission; UNESCO; World Council for Renewable Energy; International Photovoltaic Equipment Association:
24th European Photovoltaic Solar Energy Conference 2009. CD-ROM : The compiled State-of-the-Art of PV Solar Technology and Deployment. Proceedings of the International Conference held in Hamburg, 21-25 September 2009
München, 2009
ISBN: 3-936338-25-6
European Photovoltaic Solar Energy Conference and Exhibition (EU PVSEC) <24, 2009, Hamburg>
Fraunhofer ISE ()

The mechanical strength of silicon wafers is a very important parameter to assure the processing of the wafers throughout the whole solar cell production chain without breaking. Micro-cracks at the edges and on the surface of the wafers are well known to limit their mechanical strength. In the present work, the micro-cracks removal capability of an industrial standard etching solution and its impact on the mechanical strength of monocrystalline silicon wafers have been investigated. After 5 min etch, micro-cracks were removed or partially rounded and therefore the mechanical strength of the wafers increased by 39% in comparison with the mechanical strength of as-cut and only cleaned wafers. Longer etching times did not increase the mechanical strength of the wafers significantly. The breaking micro-mechanism of silicon under the four-line bending test has been identified by the analysis of fracture surfaces by SEM microscopy. Micro-crack propagation is detected at fracture origins leading to the cleaving of the {111} and {110} crystallographic planes. Micro-cracks and surface irregularities where crack propagation starts, seem to show the tendency to be oriented through the {111} and {100} crystallographic planes.