The barrier layer of anodic aluminum oxide (AAO) formed on the silicon substrate was etched with Cl-2/BCl3 gas mixtures by a neutral beam and the results were compared with the AAO etched by an ion beam. The etch rate of AAO itself was increased with the increase of BCl3 in Cl-2/BCl3 up to 60% in the gas mixture. And, the etching of AAO itself was related to the Cl radical density in the plasma and the formation of volatile BOxCly on the AAO surface for both the neutral beam etching and the ion beam etching. The AAO itself could be etched by both the neutral beam and the ion beam in all Cl-2/BCl3 gas mixtures. However, the barrier layer of the AAO located near the bottom of the AAO pore could not be etched using the ion beam etching due to the charging of the nanometer size AAO pore similar to the case of conventional reactive ion etching. Using the neutral beam etching, the barrier layer of AAO pore could be successfully etched with BCl3-rich BCl3/Cl-2 gas mixtures by removing the barrier layer without charging the AAO pore and by the forming volatile BOxCly. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3561421] All rights reserved.