Laser Micromachining for Gallium Nitride Based Light-Emitting Diodes

Abstract

Micromachining with nanosecond laser pulses is a powerful tool that is suitable for replacing or complementing traditional wafer processes, such as dicing and etching, as well as advanced process developments, such as laser lift-off [1], laser-assisted machining [2] and medical and biotechnology research [3]. Tightly-focused nano-second laser pulses can enable microma‐ chining with much higher precision and dimensions down to several micrometers [4]. For more advanced applications, micromachining parameters, such as laser wavelength, pulse energy, repetition rate and pulse duration, should be considered seriously. Drilling and cutting with nanosecond, or even femtosecond ultraviolet (UV) laser pulses has been reported to produce very small heat-affected zones (HAZ) [5]. Recently, laser micromachining is being adopted gradually for gallium nitride (GaN)-based light-emitting diodes (LEDs). Because epitaxial GaN layers are typically grown on sapphire, the separation of fabricated LED dies is commonly achieved by wafer sawing, which is slow and expensive. The use of high energy laser pulses increases the process efficiency and enables a high packing density of chips through the reduced dimensions of the scribe lanes.