A method for forming a semiconductor structure including forming a plurality of mandrel lines on a first dielectric layer and forming one or more groups of discontinuous mandrel line pairs with a first mask. The method further includes disposing a second dielectric layer, and forming dielectric spacers on sidewalls of the mandrel lines and the discontinuous mandrel line pairs. The method further includes removing the mandrel lines and the discontinuous mandrel line pairs to form spacer masks, forming one or more groups of blocked regions using a second mask, and forming openings extended through the first dielectric layer with a conjunction of the spacer masks and the second mask. The method also includes removing the spacer masks and the second mask, disposing an objective material in the openings, and forming objective lines with top surfaces coplanar with the top surfaces of the first dielectric layer.