Modeling B clustering in Si and SiGe
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Modeling B clustering in Si and SiGe Ljubo Radic, Aaron D. Lilak1, and Mark E. Law Department of Electrical and Computer Engineering, University of Florida, Gainesville, FL 32611-6130, USA 1 Technology CAD Department, Intel Corporation, Hillsboro, OR 97124, USA Abstract Our experiments show boron-interstitial cluster dissolution is reduced during oxidation, a behavior not predicted by the current models. Both our experiments and others on the time dependence indicate the reactivation is coming from more than one cluster. Since oxidation induced interstitial injection reduces reactivation, one of the significant clusters has to release an interstitial release during dissolution. Recent ab-initio calculations provide a qualitatively different B clustering model, with two significant cluster species. Based on these energetics, we have developed a new physically based model that for the first time accounts for the experimentally observed cluster dissolution time and ambient dependence. Anomalous B diffusion behavior is also observed in an investigation of Ge influence on B diffusion. Silicon wafers were subjected to a Si preamorphization implant (PAI), followed by Ge and B implants contained within the existing amorphous layer. The control sample received only Si PAI and B implant. Upon annealing, the peak of the B profile shifts towards the surface and increases in magnitude, exhibiting uphill diffusion. The control samples subjected to the same thermal processing exhibit TED, but no uphill diffusion behavior. This is consistent with the model of B diffusion in Si1-xGex, accounting for trapping of B at Ge sites through formation of GeB complex. Introduction Boron has historically been the acceptor of choice for silicon based integrated circuits. Point defects formed during implantation recombine during the anneal following the implant. At the same time, excess interstitials may form extended defects and dislocation loops, which control enhanced diffusion [1,2]. Besides the TED effects, formation of immobile and inactive boron occurs in high interstitial concentrations, through formation of BICs [3]. Other influences on B diffusion include diffusion retardation in the presence of Ge. Lever et al. [4] suggested a model of Ge reacting with B, forming immobile GeB complex. The idea of a GeB complex was based on the possibility of microscopic strain relaxation. These phenomena were also observed macroscopically through Ge effect on activation energy of B diffusion at concentrations ~5e20 cm-3 [5], further supporting the notion of clustering. Modeling of boron clustering and cluster dissolution processes is necessary for the implant and anneal optimization. Experiment In an effort to verify the model described in Pelaz et al. [6], an experiment was performed. The boron cluster evolution paths, as shown in Fig 1, suggest that boron activation could be increased by a low interstitial supersaturation. Therefore, an oxidation experiment was performed, as oxidation is known to inject silicon interstitials [7]. B implante
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