Liquid-immersion laser micromachining of GaN trenches and its application in device fabrication

Abstract

Trench formation for device isolation on GaN light-emitting diode (LED) wafer via nanosecond pulsed laser micromachining in deionized (DI) water is demonstrated. The basis of this technique relies on the large difference between the ablation thresholds of GaN and sapphire, so that the ablation can automatically terminate at the GaN/sapphire interface to produce a smooth and tapered trench. Compared with micromachining in ambient air, re-deposition and re-solidification of ablated material on the sidewalls are found to be greatly reduced in DI water. In addition, liquid immersion admits a larger focus offset tolerance and a better control of the trench width through adjustment of pulse energy. As an application in rapid device prototyping, a 5 × 7 dot-matrix microdisplay with laser-micromachined trenches for pixel separation is demonstrated, illustrating the effectiveness of this processing technique. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.