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Scribing of GaN wafer for white LED by water-jet-guided laser

In 1993, a laser light guiding water jet was successfully developed at the Institute of Applied Optics (EPFL, Lausanne, Switzerland) and patented as Laser Microjet. The laser beam is focused into a nozzle from which a thin low-pressure water jet is emitted. The laser beam is injected in the water jet and guided in it by total internal reflection at the water/air interface similarly to a standard optical fiber. Normally a pulsed laser is used, so the continuous water jet is able to immediately cool the cut, reducing efficiently the heat-affected zone. The result is a very narrow, parallel, burr-free, clean cut, without detectable thermal damage. LED manufacturing is one example where thin layers need to be removed from well-defined regions on a wafer without damaging the neighboring structures. Compared with diamond saw cutting for which chipping and delaminating of the wafer cannot be avoided due to the strong shear forces; or compared with conventional laser cutting where low power irradiation of nearby functional structures occurs, the laser Microjet offers better edge quality and high precision. Compared to the main competitor, etching techniques combined with subsequent sawing of the substrate, the water jet guided laser is faster at similar edge quality.