a method includes providing a substrate with a patterned second layer over a first layer . the second layer includes a second layer opening having a first cd equal to the cd produced by a lithographic system . cd l is larger than a desired cd . a third layer is formed to fill the opening , leaving a top surface of the second layer exposed . the second layer is removed to produce a mesa formed by the third layer . the cd of the mesa is equal to about the first cd . the mesa is trimmed to produce a mesa with a second cd equal to about cd d . a fourth layer is formed to cover the first layer , leaving a top of the mesa exposed . the substrate is etched to remove the mesa and a portion of the first layer below the mesa to form an opening in the first layer with cd d .