High-temperature wet chemical etching of Ta2O5 in NaOH-based solutions for fabricating antiresonant reflecting optical waveguides

In this paper, a high temperature wet chemical etching technique to pattern tantalum pentoxide (Ta2O5) antiresonant reflecting optical ridge waveguides (ARROW) in sodium hydroxide based systems was developed. The Ta2O5 dielectric films were formed by a magnetron RF sputtering technique on a Si substrate. After deposition, the films were etched in hot NaOH and NaOH/H2O2 solutions. The NaOH etchants etched the deposited Ta2O5 at a relatively high rate (similar to 1 mu m/min, 100 degrees C, 40 % NaOH solution), but they left an insoluble residue on the substrate. The residue can be reduced either by raising the etchant temperature or by adding hydrogen peroxide to the NaOH solutions. Using the NaOH/H2O2 etchants, we successfully fabricated the ARROW-type ridge waveguides with an undercut of less than 1 mu m for an etching depth of 5 mu m. An etching rate of 5 mu m/min was achieved at 130 degrees C with a mixture containing 50 % NaOH solution and 35 % H2O2.