A method for forming small dimension openings in the organic masking layer of tri-layer lithography. The method includes forming an organic polymer layer over a semiconductor substrate; forming a silicon containing antireflective coating on the organic polymer layer; forming a patterned photoresist layer on the antireflective coating, the patterned photoresist layer having an opening therein; performing a first reactive ion etch to transfer the pattern of the opening into the antireflective coating to form a trench in the antireflective coating, the organic polymer layer exposed in a bottom of the trench; and performing a second reactive ion etch to extend the trench into the organic polymer layer, the second reactive ion etch forming a polymer layer on sidewalls of the trench, the second reactive ion etch containing a species derived from a gaseous hydrocarbon.