Strength of Si wafers with microcracks: A theoretical model

Wafer breakage is a major problem in the photovoltaic industry and becomes more serious as the industry attempts to use thinner wafers. It is well established that the poor strength of PV wafers is primarily due to the presence of residual microcracks, which are generated by cutting and wafering procedures and are not removed by subsequent etching of the wafers. This paper addresses fracture mechanics modeling of the strength of silicon PV wafers. We are showing that the surface damage, which includes the subsurface microcracks, determines the ultimate strength of the PV wafers. The modeling of PV wafers consists of Monte Carlo simulations and finiteelement analysis that is supported by the fracture energy theory for curved cracks. As an example, a virtual experiment on a statistical set of 100 wafers subjected to uniaxial tension is performed. The predicted strength distribution is shown to match well with the experimental results available in the literature.