B Diffusion in Low Energy B/BF2 Implants with Pre-Amorphization of Different Species
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B Diffusion in Low Energy B/BF2 Implants with Pre-Amorphization of Different Species Hong-Jyh Li, Todd Rhoad, Peter Zeitzoff, Robin Tichy, Larry Larson and Sanjay Banerjee* International SEMATECH, 2706 Montopolis Drive, Austin, TX 78741 *Microelectronics Research Center, 10100 Burnet Road, MER 1.108, R9900, University of Texas at Austin, TX 78712 ABSTRACT The formation of an amorphous layer is needed to prevent channeling effect of B in the subsequent implant and hence, shallower as-implanted and annealed profiles could be expected. B diffusion in the pre-amorphization (PAI) Si has been studied extensively by many research groups and the diffusion has been explained by the interaction of B and defects generated by the PAI and B implant processes. In our previous study, we found that B diffusion can also be affected by the immobile B clustering caused by the incorporated species and therefore, B diffusion in the PAI Si should be expected to be different with different PAI species due to their different effect on the B clustering. In this paper, we reported different B diffusion behavior in bulk Si with respective to different PAI species. The species include GeF2, Ge, F, BF2, and In and the immobile B clustering plays an important role in the B diffusion reduction. INTRODUCTION It is expected that B transient enhanced diffusion (TED) can be reduced by reducing the implantation energy, thus placing the dopant and the implantation-induced excess interstitials closer to the surface which is a sink for interstitials. At the beginning of the annealing process, Si interstitials are quickly recombined with vacancies and hence, there will be less interstitials remaining to enhance dopant diffusion [1]. On the other hand, the formation of an amorphous layer prior to B implant has the merit of preventing channeling effect of B in the subsequent implant and in addition, a large number of Frenkel pairs created during ion implantation quickly recombines in the amorphous region and do not contribute significantly to TED. Therefore, preamorphization implant (PAI) has been normally practiced in achieving shallower junction. Recent studies showed that the effect of PAI on B diffusion could not be solely explained by the de-channeling and fast annihilation of Si interstitials through recombination with vacancies. Downey et al [2] showed that, in BF2 implant, the reduction in boron TED is a chemical effect. Robertson et al [3] reported that the fluorine interacts with boron to reduce TED. It was also observed that there is an optimal ratio of the energies of the fluorine and boron (12:1) to produce the shallowest junction in their experiment. The interaction between B and F is consistent with our previous simulation results [4], which show that, in the presence of fluorine, the migration of boron in silicon could be hindered by the electronic bonding between fluorine and boron. However, the observation for the energy ratio was puzzling because that using F:B energy ratio 12:1 (12keV F and 1.12keV B), the projected ranges of F a
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