Micro three-dimensional removal processing inside sapphire substrate

Femtosecond laser-assisted etching is a promising technique as micro three-dimensional removal processing. This technique consists of two-steps: the first step is irradiation of focused femtosecond (fs) laser pulses along the pre-designed pattern, and next step is wet etching. Provided the modified region is etched faster than the un-modified host material, the modified region is selectively removed. However, when this technique was applied to volume etching of sapphire, there was a problem of incomplete removal (residues remain after etching). In the present report, we propose and demonstrate a new strategy of two-cycle process, i.e., repeating {irradiation-etching} cycle two-times. The region that should be removed was divided into two. Outer layer was etched at the first cycle and inner volume was etched at the second cycle. In this way, the etching capability was improved as well as suppressing undesirable side effects of cracks and surface pits.