Abstract
Sapphire has been widely used for a substrate of high brightness LED because of its excellent physical and chemical properties. In the manufacturing process of LED device, there are some problems such as chipping and low throughput in singulation of sapphire substrate because of its high hardness and brittleness. The laser dicing technology is expected to overcome this problem. However, this laser dicing method normally requires a high N.A. objective lens to achieve the space-selective absorption of laser beam inside material, and the standoff distance between a processing head and a target material becomes narrow. Since it is required to control the distance between focusing point and target material plane precisely in this method, alternative technique with high flexibility of focusing control would be useful in industrial application. Therefore, the high flexile processing to create the modified layer inside the sapphire substrate was experimentally investigated by using a sub-nanosecond pulsed fiber laser with a wide emission bandwidth and a normal achromatic lens, which can keep the sufficient wide standoff distance. The control of N.A. and irradiation condition made it possible to create a modified layer with high aspect ratio without any damage the epitaxial layer of sapphire substrate.
