Cleaving Process of Brittle Materials with Pulsed YAG Laser. Thermal Stress Analysis in Cleaving Process of Silicon Wafer.

Abstract

Laser cleaving process is a prospective technique to divide a thin plate of brittle materials into small pieces, because of its high yield ratio and controllability. In addition, the process is carried out without coolant which causes the environmental pollution and the contamination of the electrical devices etched on the wafer. In this paper, laser cleaving of silicon wafer is conducted with pulsed Nd: YAG laser. The temperature of laser spot is measured by means of the two-color pyrometer with optical fiber and the acoustic emission caused by crack propagation is also observed. When the laser spot is scanned at the appropriate interval and velocity, the crack propagates in sequence by the corresponding laser irradiation. As a result, both high linearity of cleaved edge and fine fractured surface roughness are obtained. The thermal stress distribution induced by laser irradiation is analysed with FEM model, in which the stress intensity factor is calculated at the vicinity of the crack tip in order to clarify the criterion of crack propagation. The analysis and experiments reveal that the maximum tensile stress at the crack tip increases with temperature and the crack propagates when the stress intensity factor reaches the fracture toughness of the material.