Analysis of surface cracks in multi-crystalline thin silicon wafers

Surface cracks are the most common defects in solar silicon wafers. The stress intensity factors (SIFs) calculated by the semi-analytical equation derived by Newman and Raju have been compared with results of 3D finite element analysis for a wide range of semi-elliptical surface crack configurations in thin silicon wafer subjected to bending. It has been shown that the geometrical nonlinearity of silicon wafers significantly influences the SIF values. The discrepancy between nonlinear and linear models is 19% for a surface crack with 20 μm depth and 1 mm length, while it is 74% for a surface crack with 160 μm depth and 100 mm length. Furthermore, the results show that for long surface cracks ( a / c ⩽ 0.01 ) finite element models should be used to calculate the SIF and the existing semi-analytical solution is not reliable.