Singulation of sapphire substrate with high aspect ratio internal modification by sub-nanosecond pulsed fiber laser

Sapphire has been widely used for a substrate of high brightness LED, and it is important to reduce the edge damage in the singulation process of sapphire substrate for the high quality product and the cost reduction. In this study, the internal modification technique of sapphire substrate by a sub-nanosecond pulsed fiber laser of 180ps was experimentally investigated with a normal achromatic focusing lens of 20mm in focal length, and the possibility of singulation method with this internal modification technique was discussed. The laser beam of 180ps and 1060nm was focused in sapphire substrate of 0.4mm thickness by passing through the epitaxial layer grown on the top side, and the internal modification zone was generated from the satin-finished surface as the bottom side of sapphire substrate. A high aspect ratio modified line such as 5-10μm width and 200μm height was successfully performed by the laser irradiation from the epitaxial layer side. A sapphire wafer of 0.4mm thickness could be broken from the internal modified line with less damage of the epitaxial layer by sufficient smaller stress compared with the tensile strength of sapphire. The breaking strength and its dispersion became smaller with increasing the number of laser scanning.