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Strength of thin silicon wafers with via holes

: Schoenfelder, S.; Kaule, F.; Oswald, M.; Bagdahn, J.; Petzold, M.

Fraunhofer-Einrichtung für Modulare Festkörper-Technologien -EMFT-, München:
13th International Workshop on Thin Semiconductor Devices. Proceedings : Held during the Forum "be-flexible" 2012, 21st November 2012, Munich, Germany
München: Fraunhofer EMFT, 2012
International Workshop on Thin Semiconductor Devices <13, 2012, Munich>
Forum "be-flexible" <2012, Munich>
Fraunhofer IWM ()
strength; Weibull; silicon; through silicon via; metal wrap through; solar cells

A Metal-Wrap-Through (MWT) solar cell is able to reduce shading losses by changing the contact structure on the cell front side. By using silicon via holes the front side contacts are placed on the back side.
These via holes are laser drilled into as-cut silicon wafers before cell processing. In order to maintain a high yield manufacturing the influence of silicon via holes needs to be investigated in detail.
In this work the strength of monocrystalline silicon wafers with different number of via holes was investigated in detail using experimental and theoretical methods. A statistical failure model was developed, which can predict the influence of the holes on the strength of the wafers. As a result, holes in silicon material showed a significant but rather small reduction in strength of silicon wafers.
This can be explained by the size effect of strength, where the strength of a device is governed by the statistical occurance of single critical defects. Thus, besides the maximum stress also the size of the stress field and the probability of existing critical defect are important. With respect to the stress concentration of a hole this means that the strength of the wafers with holes is not only governed by the factor of stress concentration, but also the defect distribution and the size as well as the number of holes.
Though, the model was developed for MWT solar cells, it can also be used for other applications as TSV in semiconductor industry.