The results of a comparative study of reactive ion etching in oxygen and oxygen ion beam etching of carbonaceous materials is presented. Scanning electron micrographs are shown of 1600 Å linewidth surface relief structures with vertical sidewalls etched into polyimide, and vitreous carbon. The directional nature of oxygen ion beam etching is demonstrated by the etching of a 3200 Å period grating structure into a polyimide substrate at 45°. It is proposed that the etching of carbonaceous materials in oxygen is an excellent model system for studying etching of materials in reactive gases because of its relative simplicity compared to the more commonly used processes employing fluorocarbon gases.