Nature Of The Silicon And Silicon Dioxide Surfaces During Plasma Etching With Fluorocarbon Containing Discharges

Plasma etching of silicon dioxide using fluorocarbon gas containing discharges is an important process in integrated circuit manufacturing. Except for subtle differences, many gas mixtures that contain fluorocarbon gases such as CnFzn+2 (n>O) and CHF3 exhibit similar etching behavior.lT2 During etching with these gases, a thin steady state layer that contains fluorocarbon moieties forms on the ~urface."~ Even in presence of such a layer, thin films of silicon, silicon dioxide and silicon nitride can be etched with rates as large as several thousands of Ang~tromdmin.~.~ However, under conditions that favor fluorocarbon polymerization, such as low energy ion bombardment, a continuous layer of a fluorocarbon film can deposit on the surface and inhibit the etching of the underlying film.'-7 It has been suggested and widely adopted that the etch inhibition results when the thin steady-state fluorocarbon layer that forms during etching becomes too thick to allow the etchant and the etching products to diffuse through this layer.3'436,7 The nature of these steady-state and etch-inhibiting overlayers has been the subject of many studies and vigorous debate over the last two decades. The conditions that favor etch inhibition on various films have been discovered by trial and error. For example, it is well known that the addition of HZ to the etching gas tends to promote the formation of an etch inhibiting film whereas an increase in ion bombardment and ion flux to the surface decreases the tendency of these layers to grow. The formation of the etch inhibiting layer can also depend on the film being etched. For example, in the presence of ion bombardment, the etch-inhibiting layer forms easier on Si than on silicon dioxide and this fact has been exploited to etch silicon dioxide selectively over Si.*