The present disclosure relates to semiconductor processing, and to the plasma etching of organic layers, and in particular antireflective coating layers. We have discovered a particular combination of gases useful in producing chemically reactive plasma species, which provides unexpected control over etched feature critical dimension, etch profile, and uniformity of etch across a substrate surface, despite a difference in the spacing of etched features over the substrate surface. The combination of gases which produces chemically reactive plasma species consists essentially of C.sub.x H.sub.y F.sub.z, a bromine-comprising compound (which is typically HBr), and O.sub.2, where x ranges from 1 to 4, y ranges from 0 to 3, and z ranges from 1 to 10. Oxygen atoms may be substituted for hydrogen atoms in the C.sub.x H.sub.y F.sub.z compound to a limited extent Essentially inert gases which do not produce chemically reactive species may be added to the combination of etchant-species producing gases. A combination of CF.sub.4 /HBr/O.sub.2 has been demonstrated to work well. With this combination of plasma source gases, critical Dimension (CD) uniformity control across the surface of the substrate is generally improved by using a volumetric ratio of C.sub.x H.sub.y F.sub.z :HBr ranging from about 2:1 to about 5:1, with a range of about 3:1 to about 4:1 being preferred. An increased plasma density also helps improve CD uniformity control. The volumetric ratio of (C.sub.x H.sub.y F.sub.z +HBr):O.sub.2 should range between about 1:1 to 5:1, with a range of about 2:1 to about 3:1 being preferred.