Atomistic Analysis of the Role of Silicon Interstitials in Boron Cluster Dissolution
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Atomistic Analysis of the Role of Silicon Interstitials in Boron Cluster Dissolution Maria Aboy1, Lourdes Pelaz, Luis A. Marqués, Pedro López, and Juan Barbolla Dpto. de Electrónica, Universidad de Valladolid, Campus Miguel Delibes, 47011 Valladolid, Spain. ABSTRACT Boron implantation into preamorphized Si, followed by low temperature solid phase epitaxial (SPE) regrowth produces high activation combined with low diffusion. However, in the presence of high B concentrations, the activation obtained after the SPE regrowth only can reach concentrations in the order of a few times 1020 cm-3, and even more deactivation occurs during additional annealing. We have analyzed the role of the Si interstitials injected from the end of range (EOR) damage in B deactivation and reactivation by atomistic simulations. We have shown that the B cluster evolution can be clearly correlated to the evolution of Si interstitial defects at EOR. This is also compatible with B cluster stabilization in the presence of excess Si interstitials, observed in oxidation experiments.
INTRODUCTION Ion implantation is currently the preferred method for introducing dopants such as boron into silicon for the fabrication of integrated circuits. This process produces a large amount of defects in the lattice, which can degrade the device performance. Moreover, after implantation, dopants generally reside in non-substitutional lattice positions, and they are electrically inactive. Annealing following the implant is used to remove the implant damage, and to electrically activate the dopant atoms. However, during the annealing, two undesired processes take place: transient enhanced diffusion (TED) of the implanted B [1], and formation of stable boroninterstitial clusters (B clusters) [2,3] which immobilize and deactivate a fraction of B atoms. Non-amorphizing implants produce a highly damaged region overlapping with the B profile, causing B clustering [3, 4]. It has been observed experimentally that preamorphizing implants (PAI) enhance dopant activation during low temperature solid-phase-epitaxial (SPE) regrowth of the amorphous layer, with a minimal amount of dopant diffusion [5-6]. It is generally assumed that B is incorporated into substitutional positions and becomes electrically active, and defects within the amorphous layer are swept towards the surface during the regrowth. Only defects beyond the a/c (amorphous/crystalline) interface remain from the PAI. Therefore, PAI combined with low temperature regrowth processes have been proposed for ultrashallow junction formation. However, it has been observed that the activation achieved after SPE regrowth only can reach concentrations in the order of a few times 1020 cm-3 [5]. Moreover, in the presence of high B concentrations, subsequent thermal treatments results in additional boron deactivation [68]. Si interstitials have been probed to have a key role in B clustering and dissolution during the annealing [3,9]. In this work we analyze the influence of the end of range (EOR) defects on the
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