A plasma etch process for etching high aspect ratio openings in a dielectric film on a workpiece is carried out in a reactor having a ceiling electrode overlying the workpiece and an electrostatic chuck supporting the workpiece. The process includes injecting a first polymerizing etch process gas through a radially inward one of plural concentric gas injection zones in the ceiling electrode and injecting a second polymerizing etch process gas through a radially outward one of the plural concentric gas injection zones in the ceiling electrode, the compositions of the first and second process gases having first and second carbon-to-fluorine ratios that differ from one another. The process further includes evacuating gas from the reactor through a pumping annulus surrounding an edge of the workpiece, and etching the high aspect ratio openings in the dielectric film with etch species derived from the etch process gas while depositing a polymer derived from the etch process gas onto the workpiece, by generating a plasma in the reactor.