Applications of Ion Beam Methods in Silicide/Si and Silicide/GaAs Nanometre Structures

University dissertation from Division of Nuclear Physics, PO Box 118, SE-221 00 Lund, Sweden

Abstract: Ion beam methods are used to analyse material (Ion Beam Analysis, IBA) and to modify the target (Ion Beam Modification of Materials, IBMM). In this thesis, ion beams have been used in various IBA techniques to investigate the surface nanometre structures, and also in an ion beam synthesis (IBS) technique to form thin films and to modify material properties. The work is divided into two main parts: the development of Time-of-Flight Energy Elastic Recoil Detection (ToF-E ERD) and Delta E-E ERD IBA-techniques, and the investigation of silicide formation in silicide/Si and silicide/GaAs-based systems. The first part of this thesis deals with the development of ToF-E ERD and Delta E-E ERD. The detection efficiency of recoils for ToF-E ERD systems with masses ranging from H up to Nb at energies from 0.05 - 1 MeV per nucleon has been investigated. It was observed that the detection efficiency for the ToF-E detector telescope was dependent on the electronic stopping power (Se) in the carbon foils, which in turn depended upon the recoil mass and energy. The detection efficiency of a single time detector could be expressed as a simple empirical formula as a function of Se. The response of thin self-supporting p-i-n Delta E Si detectors for light recoils has also been characterised using a conventional ERD set-up with a detector telescope that measured Time-of-Flight (ToF), the signal from the thin Delta E detector and the residual energy of each recoil. The correlation of the signals could be modelled with a near-constant energy loss per channel and a zero offset that corresponded to energy loss in inactive layers of the thin detector. The regression lines revealed that the standard errors of the estimate associated with DE and energy loss were very similar and were dominated by the resolution of the energy loss measurements. In order to obtain high-quality nanometre-sized thermodynamically and chemically stable electrical contacts, silicide phase formation and foreign atom incorporation have been investigated under pulsed keV metal-ion implantation. The metal ions were produced from a MEtal Vapour Vacuum Arc (MEVVA) ion source with high currents and high achievable doses. This new MEVVA IBS technique opens a promising low-temperature method of forming metallic silicide in vacuum. The approach to high-dose equilibrium during MEVVA bombardment has been studied through measurements of the partial sputtering yield. Implantation-induced surface topography development shows that defects and disorders from the initial surface could result in very different morphologies. Interfacial reactions between Si (75 nm), metal Pd (50 nm) and substrates, GaAs and AlxGa(1-x)As have also been studied to investigate the formation and thermal stability of silicides on GaAs and AlxGa(1-x)As.

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