Thermal stress cleaving of brittle materials by laser beam

Thermal stress cleaving is a prospective technique for separating a wafer or thin plate from brittle materials such as glasses and ceramics. In this paper, the cleaving mechanism of a silicon wafer irradiated with Nd:YAG laser is investigated. A pulsed laser is used for the purpose of investigating the mechanism of crack propagation more precisely. The temperature at the area irradiated with the laser is measured using a two-color pyrometer with an optical fiber. The AE signal is also measured to examine the mechanism of the crack propagation, The AE signal makes it possible to monitor the crack behaviour. During one pulse of the laser, crack propagation begins some milliseconds after laser heating and ceases at about the end of irradiation. The temperature at the area irradiated with the laser is an important factor in the control of the propagation of the crack to achieve high cleaving accuracy and low thermal damage.