**1. Introduction**

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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.

One of the typical configurations of laser micromachining relies on the laser scanner head, which steers the beam into the incident direction. Although it is relatively fast, mechanical vibrations tend to be magnified, resulting in a loss of pattern resolution. Alternatively, the sample to be micro-machined can be mounted onto a precision motorized translation module while the optical beam remains static, which is more suitable for processing the optical microstructures. In a conventional laser micro-machining setup for wafer dicing, the focused laser beam is incident perpendicular to the sample to be processed, so that only two dimen‐ sional patterns can be generated and vertical cuts can be obtained. Projecting the beam at an oblique angle to the sample enables three-dimensional micromachining. Nevertheless, it

© 2013 Hui and Hui; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Hui and Hui; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

cannot mount the translation module at a tilted angle because it will result in severe beam distortion. In the proposed approach, a laser beam turning mirror was introduced to the optical path to achieve a continuously-tunable range of tilting angles for beam projection, while retaining the beam quality. Laser micromachining is a potential simple, inexpensive and highthroughput alternative method for creating geometrically-shaped GaN LEDs compared to other available technologies [6,7,8]. K.N. Hui et al. reported the effectiveness of laser micro‐ machining incorporated with GaN semiconductors to achieve high light extraction GaN LEDs [7,9] and color tunable vertically-stacked LEDs in solid-state lighting applications [7,10].

This chapter examines the experimental process of laser micromachining, and the structural and optical properties of laser micromachining LED chips with a range of geometries. The optical characterization of LED, particularly the light extraction efficiency of geometricallyshaped LEDs, is discussed because the light extraction efficiency plays an important role in achieving high luminous efficacy LEDs. Finally, several applications derived from the utilization of laser micromachining, e.g. geometrically-shaped LED, angularly uniform white LEDs, and vertically-stacked polychromatic LEDs are presented.
