Plasma etching a "pseudo-black-box" approach

A framework for understanding plasma etching has been developed (using the CF4 plasma etching of silicon and silicon compounds as an example) which treats the discharge as a "pseudo-black-box" which is characterized by a dissociation rate G of the CF4 molecules and a recombination rate R at which CF4 and other inert molecules are re-formed by recombination of the active fragments. Expressions based on the conservation of fluorine and carbon in the system have been derived which relate the concentration of the various species in the effluent gas to the etch rate. This approach provides a semiquantitative understanding of several aspects of plasma etching such as the effects of additive gases and the presence of a much larger "loading" effect for Si than for SiO2.