A method for etching an organic anti-reflective coating (ARC) layer on a substrate in a plasma processing system comprising: introducing a process gas comprising nitrogen (N), hydrogen (H), and oxygen (O); forming a plasma from the process gas; and exposing the substrate to the plasma. The process gas can, for example, constitute an NH.sub.3/O.sub.2, N.sub.2/H.sub.2/O.sub.2, N.sub.2/H.sub.2/CO, NH.sub.3/CO, or NH.sub.3/CO/O.sub.2 based chemistry. Additionally, the process chemistry can further comprise the addition of helium. The present invention further presents a method for forming a bilayer mask for etching a thin film on a substrate, wherein the method comprises: forming the thin film on the substrate; forming an ARC layer on the thin film; forming a photoresist pattern on the ARC layer; and transferring the photoresist pattern to the ARC layer with an etch process using a process gas comprising nitrogen (N), hydrogen (H), and oxygen (O).