It has long been recognized that a molecular gas glow discharge is a prolific source of chemically active radicals. However, it was not until the last twenty years or so that glow discharges were used to provide active radicals for the etching of solid materials. The first major application of this type was the use of oxygen glow discharges to volatilize carbonaceous materials such as photoresists (1). In the mid-1960s this approach was extended to the etching of silicon and its compounds using glow discharges of fluorineand chlorine-containing gases (2). Beginning in the mid-1970s and continuing up to the present time (mid-1982), there has been an explosive growth in the use of reactive gas glow discharges for etching of solids. The driving force behind this growth has been the need for anisotropic or directional etching processes in microfabrication technologies-most notably in the elec­ tronics industry. Many lithographic patterns now have minimum feature sizes in the 1-3-J.Lm range and isotropic etching processes, either wet or dry, cannot maintain the dimensional control necessary to replicate these small features with acceptable yield. Associated with this rapid growth has been a proliferation of etching equipment, accompanied by a sometimes confusing terminology. Early work was performed with "plasma ashing" or "plasma stripping" equip­ ment originally intended for oxidative volatilization of carbonaceous layers. In these systems, the surface to be etched is immersed in the glow discharge without an applied electrical bias (i.e. the surface resides at the floating potential in the plasma). These so-called barrel systems usually etch isotropically; and hence, are unsatisfactory for most high resolution etching tasks. Recognition of the importance of energetic ion bombardment in obtaining etching directionality led to the use of "planar systems" (3, 4) in which energetic ion bombardment of the surface to be etched can be easily