Selective Laser Etching of Crystalline Sapphire for 3D Structure Fabrication

Selective laser etching (SLE) is unique technology which enables to fabricate high quality 3D structure out of various transparent materials such as glass and crystals [1] . SLE of glass like fused silica is studied in detail and have been already demonstrated lots of possible glass 3D structure applications such as microfluidics [2] , micromechanics [3] and optics or photonics [4] . Crystals like sapphire could be even more attractive material in various applications due to its optical and mechanical properties. However, SLE processing of crystals is even more complicated and not widely studied. SLE is a few step process when material is modified by focused ultrashort laser beam and later is etched in aggressive etchant. Modified material is etched many times faster than unmodified one. Ratio between modified and unmodified material etching rate called selectivity describes the highest possible aspect ratio of the particular feature of the 3D structure. Sapphire shows very high selectivity value which can be up to 10000 [4] . However, process difficulties hides in material lattice with tends to crack during fabrication. Moreover, very high selectivity value comes not from high etching rate of modified material, but rather from low etching rate of unmodified material. Nonetheless, further investigations need to be done to improve SLE process of the crystals towards true 3D structures formation.