Nanoporous hard etch masks with various pore sizes were fabricated using a new type of silicon-containing block copolymers, polystyrene-block-poly(4-(tert-butyldimethylsilyl)oxystyrene) with different molecular weights. Since organic-inorganic block copolymers have a large difference in etch resistance between the organic and inorganic blocks, a hard etch mask of silicon oxide can be directly produced upon oxygen plasma treatment. Orientation and hexagonal arrays of cylindrical nanodomains were manipulated simply by adjusting the relative composition of selective and non-selective solvents in the annealing solvent. When the cylindrical nanostructures aligned perpendicular to the substrate surface were exposed to an oxygen plasma, hexagonally arranged nanopore arrays of silicon oxide with controlled pore sizes were fabricated. These nanoporous hard etch masks can be applied to the nanopatterning processes that require high aspect ratio structures. (C) 2010 Elsevier Ltd. All rights reserved.