Tyrrell, Glenn Clive; (1992) Surface reactions of halogens and hydrocarbons on Si and GaAs: Application to ion-assisted device processing. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The current trend in microelectronic processing is towards the reduction of device dimensions, thus allowing a higher density of active components per chip, reduced unit costs, increased performance and reduced power consumption. It is, therefore, necessary to develop processes and materials that conform to these requirements. The transformation of semiconducting material into active devices requires a number of processing steps to be performed. Current methods are based on an empirical approach to change rather than a complete understanding of the chemical or physical nature of the mechanisms. Two prime examples are, firstly, the way in which semiconductor material is etched to delineate a pattern and create the correct device geometry. Secondly, the means by which overlayers are deposited onto the semiconductor for dielectric properties leading to device isolation. The first of these examples often involves the thermal and ion-assisted etching reactions of semiconductor surfaces (e.g. silicon, gallium arsenide) with halogens such as chlorine and bromine. The second may, in the future, require an understanding of the mechanisms of deposition of diamond, diamond-like carbon and silicon carbide films. Mechanistic control in both of these critically rely upon reactions occurring at the surface-gas phase interface; characterisation of this region during such reactions using a variety of surface spectroscopic probes is thus of significant interest. This thesis examines the underlying surface reactions which occur at a molecular level in these systems using the techniques of Thermal Desorption Spectroscopy (TDS) and other surface sensitive probes e.g. AES, LEED and considers the future direction of aspects of semiconductor processing in the light of the results obtained. The initial surveys the use of surface science techniques as important tools in obtaining in situ information on both deposition onto, and etching of semiconductors. A description of experimental methods employed is then presented, with particular emphasis on the technique of Thermal Desorption Spectroscopy. The interaction of energetic particle beams with surfaces and adsorbate covered regions, which is fundamental to many processing steps, is also discussed at this stage. Then follows a detailed study of the reaction of bromine with silicon (100) surfaces. A mechanism for thermal etching is put forward and the interaction of energetic particle beams with adsorbed states on the semiconductor surface is discussed. A study of the etching reactions of halogens with gallium arsenide, a compound semiconductor is then presented. The mechanism for thermal and ion-assisted etching reactions are evaluated and implications for GaAs etching are discussed, the final results section considers the surface growth processes of silicon carbide, and the novel hard diamond-like carbon (DLC) and diamond film materials, results are presented for adsorption of ethene and methane on silicon. Activation of the hydrocarbon molecules by a hot tungsten filament are also studied. Perturbation of the surface states by energetic hydrogen and argon neutral beams are also considered. Implications for the growth of device quality diamond, or DLC, layers are then discussed.

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