A method of forming a doped portion of a semiconductor substrate includes: defining a plurality of protruding portions on the substrate surface, the protruding portions having a minimum height; providing a pattern layer above the substrate surface; removing portions of the pattern layer from predetermined substrate portions; performing an ion implantation procedure such that an angle of the ions with respect to the substrate surface is less than 90°, wherein the ions are stopped by the pattern layer and by the protruding portions, the predetermined substrate portions thereby being doped with the ions; and removing the pattern layer.