Anisotropic etching for dry development of thick resist layers in oxygen-based plasmas has been developed for two particular applications : trilayer resist for planarization of steep binary optics structures, and top surface imaged (silylated) resists for deep submicron lithography. To reduce linewidth degradation during etching of high-aspect-ratio resist structures, lateral etching and bow are minimized in two different reactors, a conventional parallel-plate reactive ion etching (RIE) system and a low-pressure, high-ion-density helicon etcher. In the conventional RIE system, C5H8, a polymer-forming gas is added to the O-2 feed gas to form a sidewall inhibition layer. In the helicon reactor, very low temperatures (-100 degrees C) are used to suppress sidewall etching. Different optimization conditions are found for trilayer resist etching and pattern transfer of silylated resist in the helicon reactor.