On the fracture of multi-crystalline silicon wafer

This work focuses on the fracture behavior of multi-crystalline silicon in 4-point bending tests. The objective is to investigate the crack path as well as the effect of the grain boundary on the crack propagation. Thin specimens that contain the same grains have been tested under identical loading in order to assess the consistency of the fracture process. Fractography analysis has been carried out with a confocal microscope to describe the crack propagation within grains and at grain boundaries. The fracture paths have been also compared to X-FEM numerical simulations, and a very good agreement was found. Fractographies have been used to identify the cleavage planes in locations where surface instabilities are observed, and to reveal how grain boundaries are crossed. Laue x-ray diffraction analysis has been carried out to measure the grain orientations and further identify the cleavage planes in the areas far from instabilities and grain boundaries. It is observed that the fracture of multi-crystalline silicon is completely determinist, i.e. the same crack path for twin silicon plates, with the crack propagating mainly on the crystallographic plane $(1\,1\,1)$ and eventually on $(1\,1\,0)$ . The misorientation across the grain boundary can drive the crack away from the lowest surface energy plane. Another interesting observation is that the grain boundary slows down or stops shortly the crack propagation.