Interactions of Point Defects and Impurities With Open Volume Defects in Silicon
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Interactions of Point Defects and Impurities With Open Volume Defects in Silicon J.S. Williams1, M.C. Ridgway1, M.J. Conway1, J. Wong-Leung1, B.C. Williams1 , M. Petravic1, F. Fortuna2, M.-O. Ruault2 and H. Bernas2 1 Department of Electronic Materials Engineering, RSPhysSE, Australian National University, Canberra, 0200, Australia, 2 Centre de Spectrometrie Nucleaire et Spectrometrie de Masse, CNRS-IN2P3, Batiment 108-F91405 Orsay, France ABSTRACT Ion implantation can produce open volume defects in silicon by one of two methods, either by H or He implantation followed by annealing to create a band of nanocavities and also by direct implantation to reasonably high doses, which results in a vacancy excess region at depths less than about half the projected ion range. This paper reviews three interesting aspects of open volume defects. In the first case, the very efficient gettering of fast diffusing metals to nanocavities formed by H-implantation is illustrated. In addition, the non-equilibrium behaviour of Cu3Si precipitation and dissolution at cavities is examined. The second example treats the interaction of irradiation-induced defects with nanocavities, particularly preferential amorphisation at open volume defects and subsequent cavity shrinkage. The final example illustrates the coalescence of excess vacancies into small voids on annealing and the use of gettering of Au to detect such open volume defects.
INTRODUCTION Nanocavities in silicon are formed by first implanting H or He to high doses (> 1016 cm-2) to form gas bubbles and then annealing at temperatures greater than about 750oC to drive out the gas [1-8]. It is interesting that the cavity band forms close to the ion projected range and also that the silicon surrounding the cavities is essentially defect-free. The silicon released from the cavity volume is thought to be removed to the surface on annealing by way of mobile silicon interstitials [8]. Fast diffusing metals have interesting interactions with cavities in which they can be strongly trapped. Many metals have been observed to exhibit such behaviour including Cu [1,3], Au [4], Fe [9], Ni [10], Pt and Ag [11]. At low concentrations, metals decorate cavity walls and this strong trapping can be used to remove extremely small metal concentrations [12] from a silicon wafer, as is illustrated in the following section. As the metal concentration increases, precipitation of a second phase can occur within the cavity volume [3,4]. We also demonstrate below that this process can exhibit decidedly non-equilibrium behaviour, with precipitation and dissolution controlled by the availability or removal of silicon interstitials [6]. Nanocavities are also found to be excellent sinks for silicon interstitials [13]. Indeed, if silicon that contains cavities is re-irradiated with silicon ions, then intriguing interactions of defects with cavities can occur both during irradiation and also subsequent annealing. For example, nanocavities can act as preferential nucleation sites for amorphisation [14] under appropriat
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