Here we show a method for patterning a thin metal film using self-assembled block-copolymer micelles monolayers as a template. The obtained metallic mask is transferred by reactive ion etching in silicon oxide, silicon and silicon nitride substrates, thus fabricating arrays of hexagonally packed nanopores with tunable diameters, interspacing and aspect ratios. This technology is compatible with integration into a standard microtechnology sequence for wafer-scale fabrication of ultrathin silicon nitride nanoporous membranes with 80 nm mean pore diameter.