PLASMA-ETCHING - DISCUSSION OF MECHANISMS

The purpose of the present paper is to review the salient features of our understanding of phenomena which occur in plasma etching situations. The etching process is discussed in terms of three basic steps: adsorption, product formation, and product desorption. Experiments performed in well-defined (nonplasma) environments are discussed with the goal of clarifying the relative importance of these three steps in the etching process. An attempt is made to relate the resulting concepts to several phenomena generally observed in plasma situations (e. g. etching anisotropy, selective etching, the loading effect, and the role of additive gases). Moreover, the glow discharge, in addition to generating active species which initiate the chemical reactions, also causes the etched surface to be subjected to energetic particle (ions, electrons) bombardment. The role of this radiation in the etching process is emphasized. Speculative comments relating to plasma etching parameters and apparatus are also given.