Laser-Assisted Wet Etching of Quartz Crystal Resonators

This paper reports on the development of a laser-assisted wet etching process for quartz crystal resonators. The quartz crystals are in contact with hydrofluoric acid on the backside while the laser is irradiating the front side of the crystal. The quartz crystal has a chromium thin film deposited with thicknesses varying from 5 to 20 nm to absorb the energy from the laser during processing. The laser used has a wavelength of 808 nm ±3 nm with a power output of 5 W. By increasing the power density, the etch rate with the laser setup can be adjusted from 3.8 to 278 μm/hr. This can be done through beam shaping with focusing lenses. Current wet etching processes require quartz crystals to be frequency trimmed after each step with multiple steps required for processing. With the laser assisted wet etching process quartz resonators can have their frequency tuned by varying the etch rate through adjust the laser's power density.