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Silicon wafers account for half of the total cost of a solar cell. So, thinning wafers after slicing has garnered substantial interest as a way to reduce manufacturing costs. Knowing more about what makes wafers weaker—and, specifically, the influence of wafer thickness on mechanical resistance—is vital.
Researchers at Liten, a CEA Tech institute, sliced wafers of different thicknesses (180, 160, 140, and down to 100 microns) from silicon ingots of different qualities (monolike, monocrystalline, and polycrystalline). They used a diamond-wire cutting technique with the same configuration for each silicon type and wafer thickness. The resulting wafers’ bend resistance was tested along and perpendicular to the cutting axis. They discovered that, for a given material, the maximum stress a wafer can withstand does not vary according to the thickness of the wafer; this was true for bend testing in either direction. However, they also noted that monocrystalline silicon is more resistant to bending than monolike and polycrystalline silicon, which appear to undergo degradation during cutting.
The researchers’ findings suggest that reduced wafer thickness does not alter a wafer’s mechanical resistance. The researchers are conducting further investigations, including impact resistance and fatigue testing, to identify other cutting-related mechanisms that could weaken wafers.
CEA is a French government-funded technological research organisation in four main areas: low-carbon energies, defense and security, information technologies and health technologies. A prominent player in the European Research Area, it is involved in setting up collaborative projects with many partners around the world.