Selective etching of ultrafast laser modified sapphire

Due to its hardness and scratch resistance sapphire is a favorite material for various high-quality applications e.g. in consumer electronics. Because of those excellent properties sapphire is a demanding material regarding processing. Using ultrashort pulses in combination with beam shaping offers the possibility to deposit energy precisely into the material and modify in a controlled manner reducing thermally induced stress and avoiding microcracks. Separation along modified paths especially for inner contours is still an open task. Selective etching of laser modified sapphire is a promising technology to release outer contours as well as inner contours and even smallest through holes. By using Bessel-like beam profiles an amorphized elongated modification in the monocrystalline bulk along the whole material thickness can be achieved by a single pulse. The amorphous phase in contrast to the monocrystalline sapphire is etchable in 30 wt.-% KOH solution. For a successful process development, a fundamental comparison of different types of modification and its etching behavior depending on pulse duration, pulse energy, number of pulses, spatial and temporal distances of modifications at a wavelength of 1030 nm is carried out. The etching rate depends on the processing and etch solution parameters and is optimized to 10 μm/min. Besides the contours a nanosieve consisting of two-dimensional arranged crack free nanoholes (200 nm in diameter, 5 μm in distance) is realized with an aspect ratio of 1:1500.