Effect of laser beam intensity distribution in removal processing of ZnO film by nano-second pulsed laser with square section fiber

Removal characteristics of zinc oxide film used as a transparent conductive oxide were experimentally investigated using a square fiber and nano-second pulsed laser. Effects of the intensity distribution of the laser beam on removal phenomena were discussed with a combination of an achromatic lens and a single lens. An achromatic lens achieved better groove shapes with a narrow damaged region, but the electrical insulation state was unstable, in which scribed groove could not achieve insulation state even at a higher overlap rale around 80 %. High-speed observation revealed a possibility of zinc oxide film remaining on the glass substrate, since dominant removal of zinc oxide film progressed uniformly inside the spot area in thickness direction of film. On the other hand, a single lens resulted in a wide damaged region, but the electric insulation was obtained stably at more than a certain overlap rate. Because zinc oxide film was removed from center to outer side inside the laser spot with pushing material in width direction, and zinc oxide film was almost completely removed at the center area of laser spot. Therefore, the combination of a singlet lens and a slit mask was proposed to attempt different intensity distribution in parallel and perpendicular direction to scanning line. This optical setup could achieve both stable electric insulation state and better groove shapes with a narrow damaged region at more than overlap rate of 60 %.