Modeling the Tensile Strength and Crack Length of Wire-Sawn Silicon Wafers

Abstract

Solar silicon wafers are mainly produced through multiwire-sawing. This sawing implies microcracks on the wafer surface, which are responsible for brittle fracture. In order to reduce the sawing-induced cracks, the wafers are damage etched after sawing. This paper develops a model for the impact of crack length manipulation on fracture stress distribution. It investigates the effect of damage-etching on the mechanical properties of solar silicon wafers. The main idea is to transform the fracture stress distribution into a crack length intensity function and to model the effect of etching in terms of crack lengths. The fracture stress distribution is determined statistically by fracture tests of wire-sawn and sawn and etched wafers. The Griffith criterion then enables the transition to crack lengths and crack length intensity functions. Two numerical parameters, called truncation parameter and scaling parameter, determine this relationship and enable a quantitative description of the effect of etching. They turn out to be dependent on etchant and geometry of load and thus tested crack population.