Smooth etching of epitaxially grown AlN film by Cl2/BCl3/Ar-based inductively coupled plasma

•The etch characteristics of epitaxial AlN with Cl2/BCl3/Ar mixtures are investigated.•High etch rate of AlN and high selectivity of AlN over Ni mask are demonstrated.•New method is proposed to suppress crystallographic orientation dependent etching.•Smooth etched surface with root-mean-square roughness of 0.77 nm is obtained.

Inductively coupled plasma dry etching of epitaxially grown aluminum nitride (AlN) film using Cl2/BCl3/Ar mixture has been investigated. The etch rate of AlN increases significantly with the addition of BCl3, and an etch rate as high as 258 nm/min has been demonstrated. High selectivity of AlN over Ni mask has been realized, and the etch rate of Ni is almost zero for lower bias voltage. By optimizing the etching parameters, grain formation due to crystallographic orientation dependent etching has been suppressed, and smooth etched surfaces and nearly vertical sidewalls are obtained. The root-mean-square roughness of the etched surface is measured to be 0.77 nm, which is almost the same as that of the as-grown surface. These results are suitable for the fabrication of low-loss AlN waveguides and optoelectronic devices.