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Automatic separation of large and thin wafers

Automatische Vereinzelung von großen und dünnen Wafern
: Reddig, K.; Fickert, K.; Jäger, F.

Poortmans, J. ; European Commission, Joint Research Centre -JRC-:
21st European Photovoltaic Solar Energy Conference 2006. Proceedings. CD-ROM : Proceedings of the international conference held in Dresden, Germany, 4 - 8 September 2006
München: WIP-Renewable Energies, 2006
ISBN: 3-936338-20-5
1 S.
European Photovoltaic Solar Energy Conference <21, 2006, Dresden>
Fraunhofer IPA ()
Photovoltaik; Separierung; Vereinzeln; wafer; wafer fabrication

Purpose of the work and approach:
Photovoltaic wafer manufacturing faces serious challenges with the increase in manufacturing quantity and the increase in wafer size (156mm edge length in common use). At the same time the wafer thickness is decreasing with 210µm in commercial use and the aim to further decrease the wafer thickness down to 150µm. The actual most used method for cutting wafers is based on wire saws. Manual separation is still widely in use, but is now at its limits. The hand span cannot cover these large wafers and yield cannot be maintained with the manual separation of very thin and large wafers Therefore a solution for automated separation is highly desirable to increase yield and throughput. This paper presents a solution for a high throughput, automatic separation of wet wafers which will have been tested in a manufacturing environment at the time of the conference.
The idea to this solution is based on experiences made in electronic and paper industry. It is based on rolls and a separator, separating a stack of wafers one by one. To achieve this, the stack of wafers is conveyed to a separator which allows only one wafer to pass. With this new principle concept an industrial partner approached Fraunhofer IPA to jointly build up a prototype. To proof the method in principle, a prototype was built by Fraunhofer IPA. Based on this prototype, the method was evaluated as practicable and a industry suitable design was jointly developed by ACI-ecotec and Fraunhofer IPA. The current version of the separation equipment has been tested with multi- and monocrystalline wafers of all available sizes and thicknesses including 156mm-wafers with a thickness of 150µm.
Scientific innovation and relevance & results: Wafer separation and cleaning was a discrete process in the past. This approach needed a large quantity of carriers, space and resources. The required number of handling operations is always influencing wafer breakage and therefore additional costs. With the availability of inline cleaning (single wafer cleaning) the need for more continuous processing steps increased. The proposed solution implements the continuous wafer flow by separating the whole ingot from the workpiece holder with a fully automated separation afterwards, feeding the wafers directly to the cleaning, testing and classification equipments. The approach addresses significantly the quality issues, by introducing minimal stress to the wafers. This is achieved by the absence of vacuum grippers as well as the use of only lateral force on the wafer, avoiding bending and twisting the wafer. Further work will be invested to increase the reliability and the fault tolerance of the method. The wafering is a very hazardous environment using different chemicals and producing a considerable amount of contamination (silicon, slurry, etc.) To deal with this environment, studies have been conducted, to improve the equipment into a state of high reliability as well as easy and fast maintenance.
The experiments and studies have been transformed into a working equipment. With this the wafering can deal with the upcoming generations of large and thin wafers.
An innovation was introduced for affordable and reliable automatic separation. This innovation was filed for a patent. Based on this further studies and experiments will be conducted to further improve the method and maybe extend the application to cell and module manufacturing.