Dual atom beam studies of etching and related surface chemistries
Most surface science studies relating to plasma-assisted etching proc- esses have been carried out using model systems in which clean surfaces in ultrahigh vacuum environments are subjected to controlled fluxes of reactive neutral species and energetic ions chosen so as to be representative of a plasma-assisted etching environment. This approach allows both control over the particle fluxes and in-situ surface characterization which are not easily achieved in a reactive gas plasma environment. Most of these studies have involved stable reactive molecules such as XeF, or CI,. However in a plasma process the key species are belleved to be atomic or molecular radic,als, often involving more than one halogen, halogen-hydrogen or other gas mixtures. Whereas there have been some studies in which atom beams are directed onto surfaces, very little work has been reported involving two separate beams of reactive species. Recently studies have been carried out in which various binary combinations of fluorine, chlorine and hydrogen atoms andlor molecules have been directed onto Si(ll1) and other surfaces with and without energetic ion bombardment. The gaseous species evolved from or reflected from the surface under study are monitored with modulated beam mass spectrometry. Some interesting synergistic effects are observed on Si(ll1) and some catalytic reactions have been noted on other surfaces.