A fracture model for exfoliation of thin silicon films
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The direct exfoliation of thin films from silicon wafers has the potential to significantly lower the cost of flexible electronics while leveraging the performance benefits and established infrastructure of traditional wafer-based fabrication processes. However, controlling the thickness and uniformity of exfoliated silicon thin films has proven difficult due to a lack of understanding and control over the exfoliation process. This paper presents a new silicon exfoliation process and model which enables accurate prediction of the thickness and quality of the exfoliated thin-film based on the exfoliation process parameters. This model uses a parametric, finite element, linear elastic fracture mechanics study with nonlinear loading to determine how each process parameter affects the crack propagation depth. A metamodel is then constructed from the results of numerous simulations to inform the design and operation of a novel exfoliation tool and predict thickness of produced films. In order to manufacture uniform, high-quality films, the tool creates a controlled peeling load that is able to propagate a crack through the silicon in a controlled manner. Finally, exfoliated silicon samples produced with the prototype tool are evaluated and compared to metamodel projections, confirming the ability of the tool to steer crack trajectory within ± 3 microns of the crack depth predictions.
KeywordsExfoliation Single crystal silicon Finite element analysis Spalling
The authors acknowledge and thank Miaomiao Yang for her experience, effort, insight, and support in accomplishing this work. The authors thank Kirsten Cole Christopherson for her effort in completing these experiments. The authors would also like to thank Liam Conolly, Dipankar Behera, and Cheng Zhao for the informative discussions and technical expertise. This work is based upon work supported primarily by the National Science Foundation under Cooperative Agreement No. EEC-1160494. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
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