GOALI: Diamond Wire Slicing of Crystalline Silicon Materials with Application to Manufacturing of High Quality Solar Cell Substrates

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In fixed abrasive diamond wire slicing, very hard and brittle materials such as crystalline silicon and sapphire are cut into thin wafers utilizing a moving wire web consisting of thin steel wires coated with diamond abrasives. These wafers are used as substrates for photovoltaic solar cells and energy efficient lighting devices such as light emitting diodes. Although the fixed abrasive diamond wire slicing process can potentially offer higher production rates than existing semiconductor wafer slicing methods, scientific knowledge required for its cost-effective application and optimization is lacking. This Grant Opportunity for Academic Liaision with Industry (GOALI) award supports fundamental research that will yield the scientific knowledge needed to produce high quality photovoltaic solar silicon substrates with minimal mechanical damage. Since higher quality wafers are less prone to breakage during solar cell manufacture, the knowledge derived from this research will lead to lower solar cell production costs, which in turn will lead to lower solar energy costs. This will directly benefit the United States economy and the society at large. Knowledge derived from this research will also benefit other industries such as micro and optoelectronics where the diamond wire slicing process is used to cut other semiconductor and optical materials. The research involves the disciplines of advanced manufacturing, materials science, and mechanics. The project will engage students from diverse backgrounds including underrepresented groups, and will thereby contribute to educating the next generation of engineers in advanced manufacturing.The research team will focus on understanding and minimizing the surface and sub-surface damage generated in diamond wire slicing of microstructurally-complex crystalline silicon materials used as substrates in photovoltaic solar cells. The specific objectives of the project are to understand and quantify the effects of diamond grit geometry, crystal orientation and defects (such as grain/twin boundaries, dislocation density variations), and diamond grit wear on the cutting mode (ductile vs. brittle), surface morphology, and sub-surface damage produced in diamond wire slicing of mono- and multi-crystalline solar silicon materials. Single grit diamond scribing experiments using diamond indenters with idealized shapes, crystal defect characterization as a function of crystal orientation, numerical modeling using the extended finite element modeling method, and lab-scale diamond wire slicing experiments will be used to investigate these effects. The findings from these investigations can be used to synthesize diamond wires with optimized grit shapes and wear behavior for use in the manufacture of high quality thin semiconductor wafers.