Water-assisted pulsed Er:YAG laser interaction with silicon

Abstract

Silicon is virtually transparent to the Er:YAG laser with a wavelength of 2.94 mu m. In this study, we report that moderately doped silicon (1-10 Omega cm) can be processed by a pulsed Er:YAG laser with a pulse duration of 350 mu s and a peak laser intensity of 1.7 x 10(5) W/cm(2) by applying a thin water layer on top of silicon as a light absorbing medium. In this way, water is heated first by strongly absorbing the laser energy and then heats up the silicon wafer indirectly. As the silicon temperature rises, the free carrier concentration and therefore the absorption coefficient of silicon will increase significantly, which may enable the silicon to get directly processed by the Er:YAG laser when the water is vaporized completely. We also believe that the change in surface morphology after melting could contribute to the increase in the laser beam absorptance. It was observed that 525 nm-thick p-type wafer specimens were fully penetrated after 15 laser pulses were irradiated. Bright yellow flames were observed during the process, which indicates that the silicon surface reached the melting point. (C) 2015 AIP Publishing LLC.