Plasma Chemistry

The chemical processes that can take place in a plasma are exceptionally complicated and little understood. A treatment of all the possible chemistries of interest for semiconductor fabrication would be an enormous undertaking. Here we establish some guidelines for thinking about plasma chemistry, rather than attempting to describe all the possibilities. A number of texts on plasma chemistry are available, although the emphasis in many is more on plasma polymerization than on silicon processing [83–91].

The term plasma chemistry is usually not appropriate to describe the important effects. The hot electrons from the plasma are responsible for driving unusual chemistry – mostly neutral chemistry. (The main exception to the electrons driving the chemistry is activation of surfaces by ions.) Perhaps only the first step in a chain of reactions even involves the electrons, however. The energy an electron needs to ionize a neutral is much higher than the energy needed to dissociate most neutrals. There are usually vastly more electrons with enough energy to dissociate neutrals than there are electrons that have enough energy to ionize neutrals.