Phosphorus Activation and Diffusion in Germanium

Declaration This thesis is a presentation of my original research work. Wherever contributions of others are involved, every effort is made to indicate this clearly, with due reference to the literature, and acknowledgement of collaborative research and discussions.Abstract Currently, the International Technology Roadmap for Semiconductors (ITRS) is targeting the 22nm technology node in accordance with Moore's Law. The low mobility of silicon makes it inherently unsuitable as a channel material for devices at this scale, and therefore a significant amount of research is being focused at re-evaluating germanium as an alternative substrate. Germanium offers a higher mobility than that of silicon and is compatible with existing silicon device manufacturing techniques. P-type ultra shallow junction (USJ) implemented in germanium exhibit low leakage currents and low sheet resistivity, satisfying the ITRS demands. However, N-type USJ formed using phosphorus as the dopant species do not yet satisfy these requirements due to a high diffusivity and low levels of electrical activation. This is due to the fact that at high phosphorus concentrations , the difference between the equilibrium solid solubility limit and the effective solid solubility is related to the formation of phosphorus-vacancy complexes. These evolve into electrically inactive clusters, by capturing the additional phosphorus resulting in an overall reduction of the electrical activity of the phosphorus population. Another problem is phosphorus out-diffusion during annealing process. In order to overcome these problems, novel techniques are currently being research. This thesis investigates the phosphorus activation and diffusion characteristics as a function of implant temperature and co-implantation of low dose germanium. The samples were subsequently subjected to an isochronal annealing before Hall Effect and SIMS analyses were performed to characterize the electrical activation and diffusion respectively. The results from the studies indicate that it is a non trivial process for germanium to replace silicon in order to become the next dominant substrate.Acknowledgements Firstly, I would like to thank my supervisor, Professor Russell Gwilliam for his patience, support and guidance during my PhD journey. Next, I would like to give a special mention to Dr Andy Smith, my ex co-supervisor, for setting up a foundation for this research. Trento, Italy for advice and help with SIMS measurements. I would like to give appreciation and thanks the staffs in the ATI, Kostis, Vj and John Under-wood for their help with the equipment in the cleanroom. Thanks also to other staff in the IBC, Karen Arthur for all the …