Electronic device fabrication from thin film diamond: Surface preparation, patterning, metallisation and characterisation

The unique combination of the material properties of diamond as predicted by theory suggests that numerous fields of applications may benefit from its development. Natural and synthetic crystals grown within the extreme conditions required for crystallisation in the thermodynamically stable regime results in material where the size, shape and expense has proved to be prohibitive for many applications. The synthesis of diamond by the technique of chemical vapour deposition in the metastable phase permits thin films of this material to be deposited over sufficient substrate areas and geometries for new applications to be considered. Of particular interest in this thesis is the electronic properties of semiconducting thin films of diamond, and the development of elements essential towards the routine fabrication of reliable devices based on standard integrated circuit fabrication techniques. With this aim, the theoretical properties of diamond pertaining to electronic applications are summarised; investigations within the literature considering the superiority over present semiconducting materials are also discussed. Such levels of performance are compared to the current status of semiconducting thin film diamond. Characterisation of thin film diamond with particular emphasis on the electronic properties of current state-of-the-art material has been carried out via the surface and bulk analytical techniques of Auger electron spectroscopy. Raman scattering spectroscopy, scanning electron microscopy and Hall-effect measurements; the limitations of this material are identified. Surface investigations undertaken show that the as-deposited state of such films may he graphitic in nature; proper material preparation prior to the fabrication of electronic devices is considered a pre-requisite in order to achieve reliable device behaviour. Contact metallisations on properly prepared material display a bulk dependence; the requirements for rectification are demonstrated and discussed. Both rectifying and non-rectifying electrical contacts have been developed to a state where stable operation at room and elevated temperatures prevail. In view of the present lack of a routine patterning method, the excimer-laser based technique of projection patterning has been studied in terms of operational parameters, and both surface features and hulk microstructures have been created. The nature of the material after laser processing is fully characterised. Thin film diamond field-effect transistors capable of operation under high temperature ambients have been designed and fabricated based on the principles derived here; the performance of future electronic device structures is discussed in view of required improvements in fabrication technique and material requirements