Laser lift off systems and methods are used to separate layers of material. One application in which laser lift off has been used advantageously is the separation of GaN layers from sapphire substrates when manufacturing light emitting diodes (LEDs). In spite of the advantages from UV-laser lift-off, GaN LED manufacturing has been limited due to poor productivity caused by low process yield. The low yield is due in part to high residual stresses in a GaN-sapphire wafer, resulting from a Metal-Organic Chemical Vapor Deposit (MOCVD) process.
Various laser lift off techniques have been developed in an attempt to separate layers, such as GaN and sapphire, more effectively. Examples of these laser lift off systems are disclosed, for example, in U.S. Pat. No. 7,202,141 and U.S. Patent Application Publication No. 2011/0132549, which are fully incorporated herein by reference. Despite the advantages of these techniques for many applications, challenges still exist when using laser lift off techniques because of localized problems, such as cracking, enhanced epi ablation, and local deviation in quality, which may impact overall yield. In some lift off processes, for example, higher exposures in certain areas may cause more material removal and higher pressures, which leads to epi cracking and eventually leads to degradation in the optical and/or electrical device.
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