Fabrication of an AlN ridge structure using inductively coupled Cl 2 /BCl 3 plasma and a TMAH solution

We fabricated an AlN ridge structure using a chlorine-based inductive-coupled plasma reactive-ion etching (ICP-RIE) and a tetramethylammonium hydroxide (TMAH) solution. The ICP etching of single-crystal AlN was systematically investigated by varying ICP power, chamber pressure, and Cl 2 /BCl 3 /Ar mixture gas composition. The selectivity and anisotropy for all samples with a Ni mask were more than 20 and ∼1, respectively. Etching of AlN in a Cl 2 /BCl 3 mixture gas yields a higher etch rate compared with a Cl 2 /Ar mixture gas. The etch rate of AlN increases with increasing ICP power, reaching 286 nm min −1 for 400 W. The TMAH solution has an anisotropic characteristic for an AlN etch. A ridge structure with smooth { 1 1 ¯ 00 } sidewalls was achieved by dipping AlN in the TMAH solution after ICP-RIE.