Formation of Al dot hexagonal array on Si using anodic oxidation and selective etching

A simple method of forming a nanometer-scale two-dimensional Al dot hexagonal array was developed by the combination of Al anodic oxidation and selective wet chemical etching. Porous alumina films formed by anodic oxidation of Al have been intensively studied as molds to form nanometer-scale wires or dots by depositing various metals or semiconductors in them. We formed a self-organized trianguler lattice of alumina nanoholes on a semiconductor substrate by depositing thick Al film with an excellent surface flatness. When there was a sufficiently thick (> 20 nin) SiO2 layer between the Al film and Si substrate and the electrode was formed at the top of the Al film, most of the Al film was changed in porous aluminum film with a sufficiently long anodic,oxidation time. We found that an Al nanodot hexagonal array remained after selective wet chemical etching of the porous alumina film using a mixture of phosphoric acid and chromic acid. When a typical self-organization condition of 40 V anodic voltage was used with oxalic acid solution, the nearest-neighbor distance of Al dots was 65 nm. We also found that Al dots shrunk with increasing anodization time after the break-up of Al film to dots. This phenomenon is ascribed to electrical conduction through the porous alumina film.