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Study on Laser Cleaving Mechanism of Brittle Materials

This paper describes the investigation of the laser cleaving mechanism of brittle materials such as silicon wafer using experimental and computational methods. The applied laser energy produces a thermal stress that causes the wafer to split along the irradiation path. The wafer separation is similar to crack extension. In this study, the use of micro-groove was introduced, and the influences of groove length and depth were also examined. The temperature of the laser spot was measured using a two-colour pyrometer, while the fracture occurrences were observed by monitoring the acoustic emission signal. The relationships amongst laser power, temperature, fracture initiation, crack propagation, cleaved surface features and groove parameters are obtained from the experimental analysis. In order to understand the stress condition during laser irradiation, thermal stress distribution was analysed using the computational finite element method (FEM). The results indicate that the wafer separation occurred in two stages, fracture initiation and intermittent crack propagation. A higher temperature resulted in faster fracture initiation and higher repetition of the crack propagation signal. The wave mark on the cleaved surface was consistent with the AE signal. By using FEM, stress condition has been quantitatively determined by identifying the stress intensity factor K I . Fracture toughness K IC of the material has been determined experimentally using the Vickers indentation technique.