For patterning during integrated circuit fabrication, an image layer is activated for forming a respective first type polymer block at each of two nearest activated areas. A layer of block copolymer is formed on the image layer, and a plurality of the first type polymer blocks and a plurality of second and third types of polymer blocks are formed on an area of the image layer between outer edges of the two nearest activated areas, from the block copolymer. At least one of the first, second, and third types of polymer blocks are removed to form a variety of mask structures.