This invention provides a method for reducing tip-to-tip spacing between lines using a combination of photolithographic and copolymer self-assembling lithographic techniques. A mask layer is first formed over a substrate with a line structure. A trench opening of a width d is created in the mask layer. A layer of a self-assembling block copolymer is then applied over the mask layer. The block copolymer layer is annealed to form a single unit polymer block of a width or a diameter w which is smaller than d inside the trench opening. The single unit polymer block is selectively removed to form a single opening of a width or a diameter w inside the trench opening. An etch transfer process is performed using the single opening as a mask to form an opening in the line structure in the substrate.