A porous anodic aluminum oxide (AAO) template was fabricated selectively on a patterned substrate from a sputter-deposited Al film. The pattern size was varied from 2 to 500 mu m with a depth of 1.5 mu m. The overall surface undulation of Al resulting from the underlying patterns was planarized by chemical mechanical polishing. During the anodization of the confined Al, the anodization rate was significantly retarded at the vertical sidewall of the pattern. This suggests that the stress should be carefully controlled for the successful integration of a porous AAO structure on a patterned substrate. (c) 2006 The Electrochemical Society.