Laser-Induced Backside Wet Etching of Sapphire

Sapphire plates were etched with the approach of laser-induced backside wet etching (LIBWE) using neat toluene or saturated pyrene/acetone solutions as the etching medium. Using this approach, flexible patterns on the scale of 4-µm can be fabricated on the surface of the plates. The etching process was observed in situ by a CCD camera, which revealed the deposition of black particles and the formation thereafter of a laser-absorbing film in the etched area. By Raman spectroscopic analysis, the film was characterized to be amorphous carbon resulting from the decomposition of toluene or pyrene upon laser irradiation, which is an essential factor contributing to the etching process.