Comparative analysis of mechanical strength of diamond-sawn silicon wafers depending on saw mark orientation, crystalline nature and thickness

Abstract

Reducing the as-cut thickness of silicon wafers is one of the key issues to significantly lower the manufacturing costs of the photovoltaic industry. The pursuit of this objective is encouraged by the outstanding development of diamond wire sawing technology, which in addition to being twice more productive, also has great potential for further kerf reduction. However, in order to avoid higher breakage rates, it is crucial to understand how the sawing process affects the mechanical resistance of wafers as their thickness decreases. In this study, wafers of 180, 160 and 140 μm thickness were cut out of monocrystalline and multicrystalline silicon bricks. Their mechanical strength was evaluated by performing 4-line bending tests coupled with finite element simulations. The specimens were loaded in the parallel and perpendicular direction with respect to the saw marks. Because of the particular shape and orientation of the sawing-induced defects, all tested wafers are significantly weaker in parallel loading. While monocrystalline and multicrystalline wafers exhibit similar mechanical strength when bent perpendicular to the sawing marks, multicrystalline wafers are 30% less resistant in parallel loading. Finally, it is shown that the fracture stress of a wafer of a given silicon quality is independent of its thickness.