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TRANSIENT ENHANCED DIFFUSION IN B+ AND P+ IMPLANTED SILICON* S. J. PENNYCOOK and R. J. CULBERTSON Solid State Division, Oak Ridge National Laboratory, Oak Ridge,

TN 37831

ABSTRACT We report the transient enhanced diffusion of supersaturated phosphorus in ion-implanted SPE grown Si. Precipitation proceeds rapidly to a metastable SiP phase, which can be converted to an orthorhombic form or redissolved by subsequent heat treatment. The effects are strongly temperature dependent, and consistent with the trapped interstitial model. The behavior of different dopants follows their relative interstitialcy diffusion coefficients. The results suggest that ion implantation induced point defects dominate over thermally activated point defects during low temperature and certain rapid thermal processing, controlling dopant deactivation and diffusion in crystalline or amorphous silicon, and can also affect the SPE growth rate. INTRODUCTION Transient enhanced diffusion in ion-implanted silicon is an important and challenging phenomenon to understand. Besides giving new insights into diffusion mechanisms, it has important practical consequences including enhanced dopant deactivation or enhanced dopant profile broadening, while the point defects responsible for the transient can condense into extended defect arrays. As device dimensions continue to shrink such effects will become an increasingly severe limitation to future technology. A number of reports of transient enhanced diffusion in boron [1-5] and phosphorus [6-7] implanted silicon have appeared previously. By transmission electron microscopy (TEM) techniques we have been able to identify two separate causes of transient enhanced diffusion. The first, which is well known, is damaged crystal which arises for example from a B÷ or low dose P+ implantation into crystalline Si, and below the amorphous surface layer caused by higher dose P+ implantation. The second source exists within the amorphous layer itself. Stable dopant interstitials formed during implantation may decay during subsequent thermal processing releasing high concentrations of self-interstitials [8]. This process appears to be independent of the SPE growth process, at least to first order, and besides causing transient enhanced diffusion in the recrystallized material, we believe it affects the SPE growth rate and may cause transient enhanced diffusion in the amorphous phase. We first briefly review the behavior of the Sb implanted Si, which behaves in many ways as a model system from which the behavior of the other dopants can be understood and seen to follow a clear trend. We discuss the reasons for this trend and the implications. EXPERIMENTAL DETAILS Samples were prepared by ion implantation followed by SPE growth in a furnace under flowing dry nitrogen gas to create supersaturated alloys [9]. Additional annealing induces precipitation of excess dopant, and diffusion coefficients can be determined directly from the precipitate size distribution observed by TEM [10]. High sensitivity to the initial diffusion