Surface Chemical Probes and their Application to the Study of in Situ Semiconductor Processing

Abstract

Reactions at semiconductor-vapour interfaces as stimulated thermally and by incident photon, electron and ion radiation permit a wide range of thin film transformations in the semiconductor surface to be carried out (1). The processes involved include: (i) dry etching of semiconductors, metals and dielectrics (ii) epitaxial growth of elemental and compound layers (iii) growth of dielectrics (iv) deposition of metals and metal alloys. Since photon, electron and ion beams can also be spatially defined, either through the use of physical masks or highly focussed beams, in theory it should therefore be possible to achieve in situ the complete fabrication of electronic devices and integrated circuits or their repair and modification. The chemistry underlying the processing methods involved is extremely complex. Even in the most chemically simple reaction, MBE of semiconducting materials from elemental beams under ultra-high vacuum, a number of surface processes must be taken into account in order to achieve a full description of the phenomena (2). When other processing techniques are examined, very many more factors must be looked at. Thus if complex compounds as opposed to the elements are employed, the chemical conversions demanded become more sophisticated and the fate of a variety of species generated in the reaction must be controlled. At higher pressures (MOVPE etc) the fluid dynamics in the reaction cell has an important influence. When photon, electron or ion beams are used elementary steps as excited electronically and by momentum transfer are brought into play; such steps can occur in the gaseous, adsorbed or substrate phases present. Nevertheless, the optimisation of particular processing methods must rest on achieving a good description of the underlying reactions. Since a significant (if not dominating) number of such reactions actually take place at the substrate-vapour interface, understanding the surface chemistry must be one of the major aims. In this article we therefore survey and illustrate some of the ways which might permit this to be achieved.