High quality stealth dicing of sapphire with a picosecond Bessel beam by controlling the polarization direction

Sapphire is an important substrate material in optoelectronic devices, and it is also widely used as a touch screen panel. In order to achieve high quality cutting of sapphire, the stealth dicing of 500 µm thick sapphire by a picosecond Bessel beam is studied in this paper. The influences of laser polarization direction and process parameters on cutting section roughness were studied. By controlling the laser polarization direction, different crack propagation morphologies were obtained. When the polarization direction was vertical to the cutting path, the crack propagation path was straighter, and the sapphire had better cutting quality. The laser processing parameters, including burst mode, hole spacing, and pulse energy, had a significant impact on the cutting section roughness. When the polarization direction was vertical to the cutting path under the optimal process parameters, the cutting section was uniform and flat, with no recondensable particles, no ripples, and no chamfer, and an 89.7 nm average roughness of the cutting section could be obtained.