Selective electrochemical etching of epitaxial aluminum nitride thin film

Aluminum nitride (AlN) has an ultra-wide bandgap energy of 6.2 eV and is resistant to chemical etching owing to its high chemical stability, making it intractable in the device fabrication process. We developed a facile method of electrochemical (EC) etching of a high-quality AlN epitaxial layer, where both spatial selectivity and a controllable etch rate were achieved. Underneath porous metal electrodes, the lateral etch rate increased with the increasing external anodic bias, from 400 nm/min at 5 V to 700 nm/min at 15 V. Nonporous metal electrodes protected the AlN from etching in hot H₃PO₄, enabling the spatial selectivity. The high EC etch rate is attributed to the enhanced hole-assisted oxidation at the interface between the AlN and the etchant. The etch pit formed by EC etching exhibited an inverse hexagonal pyramid structure with {1 0 –1 −1} face. As an alternative to dry etching, our method can be applied to the low-damage patterning of AlN with a controllable etch rate.