Ehlers, F.J.H.; (2008) Modelling of the interactions of Cu and rare earth metal with Si(001). Doctoral thesis , University of London.

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Abstract

Cu is one of the most detrimental impurities to the Si devices. A theoretical investigation into diffusing interstitial Cu (Cuj) in Si and the interactions of Cu with other impurities and defects of the host lattice is strongly desired in order to understand and control the reaction paths of this impurity. We have performed ab initio modelling of the interactions of isolated Cu with bulk Si and the Si(OOl) surface, presenting explanations to a previously unsolved phenomena for the interactions of Cu with Si: according to our studies, Cu is a shallow donor with a closed 3d shell, strongly affected by inherent distortions of the Si environment The attraction of Cu to Si(OOl) is explained by surface reconstruction induced distortions of the Si environment with Cu-Si bond formation (leading to trapping of the impurity) only occurring within three layers of the surface. Our results provide promising results for gettering of Cu and Cu nanowire formation on the Si(OOl) surface. Rare earth (RE) disilicide nanowires on the Si(OOl) surface have been intensely studied by experiment as a candidate for next generation interconnects in devices. Our investigations of these systems represent the first theoretical studies of the interacting wire and substrate. We have focussed on the importance of treating the wire growth as a ID phenomenon, presenting a new candidate structure for the epitaxially grown wire on the basis of these considerations. Our studies, involving Y (not a RE metal but displaying the same behaviour with regards to wire growth) for simplicity, have verified the stability of the wire relative to the RE metal and Si atom reservoirs on the substrate. Finally, initial studies of atomic strings observed in very recent experiments upon deposition of Y on Si(OOl) have been carried out.

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