Characterization of Orientation-Dependent Etching Properties and Surface Morphology of Sapphire Crystal in Wet Etching

Sapphire crystal is extensively used in fabrication of advanced micro/nano devices. Due to its crystalline structure, sapphire shows more complicated properties in wet etching process. This paper for the first time investigates the measurement of the overall orientation dependence of the etch rate for sapphire under different etchant. The experiment shows that sapphire crystal has six high etch rate regions in etch rate distribution, which is quite different from other trigonal crystal materials. The change in surface morphology also strongly depends on the crystallographic orientation. We demonstrate etch rate distribution and texture of morphology as a function of orientation. The overall etch rate distribution successfully explains the transient and stable structural facets appearing on the sidewalls of trenches, cavities, mesas and complex structures during anisotropic etching, which is essential for the applications such as patterned sapphire substrates (PPS).