A Comparative Study of Dose Loss and Diffusion for B 11 and BF 2 Implants
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A Comparative Study of Dose Loss and Diffusion for B11 and BF2 Implants Reza Kasnavi, Peter B. Griffin, and James D. Plummer Center for Integrated Systems, Stanford University, Stanford, CA 95025-4077, U.S.A. ABSTRACT We have studied dose loss for B11 and BF2 implants with energies ranging from 10 keV to 1keV for B11 and 45 keV to 2keV for BF2. We found that B11 implants during a 1050C-10s RTA anneal segregate mainly to the bulk of the oxide. High dose BF2 implants on the other hand, show significantly larger amounts of dose loss after stripping the oxide, due to a pile-up of boron at the Si/SiO2 interface. In order to simulate B11 diffusion we have introduced a simple average cluster size model to simulate Boron-Interstitial-Cluster (BIC) evolution. For BF2 implants, we have simulated the effect of F by reducing the damage and we have used interface traps to account for the dose loss observed experimentally. Using these models, we have been able to fit the SIMS profiles across the whole matrix of implant conditions for both B11 and BF2 implants.
INTRODUCTION B11 and BF2 implants behave differently upon annealing. There are reports that channel BF2 implants show up to 20% dose loss, resulting in a shift in the threshold voltage, whereas B11 implants with similar as-implanted profiles retain most of the implanted dose [1]. The dose loss observed in BF2 implants was attributed to formation of a pile-up at the Si/SiO2 interface, which was removed by stripping of the oxide in HF. Also in forming shallow junctions, B11 and BF2 implants with similar asimplanted profiles behave quite differently. It has been shown that BF2 implants result in a shallower junction, significant dose loss and very high activation levels. B11 implants on the other hand, resulted in deeper junctions, retained most of the implanted dose but showed strong deactivation [2, 3]. A careful experimental study revealed that the presence of F is the cause of this difference and not the damage from implanting the larger BF2 molecules [3]. In this work, we have investigated dose loss and diffusion for a large matrix of B11 and BF2 implant conditions. We have implanted B11 at energies ranging from 10 keV down to 1 keV, with a high dose of 1x1015 cm-2 and a low dose of 2x1013 cm-2 at each energy. We have chosen BF2 implant energies to result in similar as-implanted boron profiles as B11 implants. We found that for a 1050C10s RTA anneal, B11 implants only show segregation to the bulk of the oxide, while at high implant doses BF2 implants show significant dose loss due to pile-up of boron at the Si/SiO2 interface. In order to simplify the modeling of Boron-Interstitial-Cluster (BIC) evolution, we have used an average BIC size model. For BF2 implants, we have shown that the effect of fluorine can be simulated by removing most of the initial damage from the implant region, resulting in a much less than +1 damage factor.
EXPERIMENTAL SETUP p-type Czochralzki silicon wafers were oxidized in a dry O2 ambient at 800C to grow 45A of oxide. B11 and BF2 were implante
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