Hybrid Micromachining of Transparent Sapphire Substrate by Pulsed Green Laser Irradiation

Abstract

Sapphire is an important material for LED substrates and optical windows. Technical challenges of green laser micromachining sapphire include low absorption coefficient and easily to crack as sapphire is transparent from UV to IR light. In this paper, we develop a hybrid laser micromachining technique with the green laser irradiation to enhance the energy absorption to avoid micro-cracks. Firstly, the surface is grooved at a low laser fluence but a higher overlap ratio. At this stage, the surface structure is modified from crystallite to amorphous state, so that its green light absorption increases greatly. Secondly, a subsequent high laser fluence is applied at the same position, and a higher groove depth and narrower groove width can be achieved. Effects of laser fluence on groove depth and width are analyzed. In order to reduce redeposited debris and microcracks, a hybrid laser micromachining at a low laser fluence and multiple scans is conducted. Results indicate that the ablation quality by the hybrid laser micromachining is much better than the direct laser micromachining.