Relative Stability of Silicon Self-Interstitial Defects
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Relative Stability of Silicon Self-Interstitial Defects G.Subramanian*, K.S. Jones*, M.E.Law**, M.J.Caturla***, S.Theiss***, T.Diaz de la Rubia*** *Department of Materials Science & Engineering, 525 Engineering Bldg. **Department of Electrical and Computer Engineering, 525 Engineering Bldg. SWAMP Center, University of Florida, P.O.Box 116400, Gainesville, FL 32611 ***Lawrence Livermore National Laboratory, Livermore, CA 94550
ABSTRACT {311) defects and dislocation loops are formed after ion-implantation and annealing of a silicon wafer. Recent Transmission Electron Microscopy studies by Li and Jones have shown that sub-threshold dislocation loops nucleate from {311} defects. In our study, the conjugate gradient method with the Stillinger Weber potential is used to relax different configurations such as {311} defects with a maximum of five chains and perfect dislocation loops. From the formation energies thus obtained we find that there is an optimal width for each length of the {311} defects. Moreover the relative stability of {311}s and loops is studied as a function of defect size. We observe that at very small sizes the perfect loops are more stable than the {311}s. This may provide an explanation for the experimental observation by Robertson et al that, in an annealing study of end of range damage of amorphized samples, 45% of the loops had nucleated in the first 10 minutes of anneal. Out of these 25% of the loops could not have nucleated by unfaulting of {311}s. We propose that homogeneous nucleation, as against unfaulting of the {311}s, could be the source of these sub-microscopic loops.
INTRODUCTION Shallow junctions , produced by ion-implantation, are a necessity if microelectronic devices of smaller dimensions are to be realized. It is well known that {311} defects and dislocation loops are formed upon annealing subsequent to ion-implantation. It is also known that {311} defects, as a source of interstitials , contribute significantly to the phenomenon of transient enhanced diffusion (TED) of dopants such as boron in ion implanted silicon during post-implant annealing [1]. Transient enhanced diffusion has a deleterious effect on the formation of shallow junctions The formation and evolution of these {311} defects is of great interest to researchers. On the other hand, the source of dislocation loops has been a subject of conjecture for a number of years. It has been observed by
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transmission electron microscopy (TEM) that concomitant with the dissolution of {311} defects, some small loops grow in size [2]. Similar connection between the dissolution of {311} defects and the growth of loops has been observed by other groups [3]. Recently, Li and Jones have shown through TEM studies that subthreshold dislocation loops nucleate from {311} defects by unfaulting of the latter [4]. Robertson et al have reported that in the case of end-of-range damage of ion implanted silicon 45% of the dislocation loops were formed in the first 10 minutes of anneal [5]. In this work, we report, for the first time, thr
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