Lattice Site Location of Group VII Impurities in Silicon
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LATTICE SITE LOCATION OF GROUP VII IMPURITIES IN SILICON
D.O. BOERMA, P.J.M. SMULDERS, AND T.S. WIERENGA L.A.N. and Materials Science Centre, University of Groningen, Westersingel 34, 9718 CM Groningen, The Netherlands
ABSTRACT Chlorine- and iodine-implanted silicon have been investigated using the channeling/RBS technique after laser and oven annealing. Both annealing methods result in good epitaxial recrystallization of the implanted layer. A large near-substitutional I fraction exceeding 90% was found after oven annealing at 875WC. The near-substitutional fractions found after laser annealing for Cl and I, and after thermal annealing at 9000C for Cl are in the order of 50% only. The precise lattice site for these Cl and I fractions are determined by fitting the angular scans with simulated results. The results are interpreted in terms of vacancy association.
INTRODUCTION Implantation of impurities is a widely used process in the semiconductor technology [i]. Implantation produces well-defined doped regions with steep profiles and has proved to be of great value for manufacturing a variety of semiconductor devices. Relatively little is known about implanted group VII impurities in silicon. The location of iodine in silicon was previously investigated by 129I Mdssbauer spectrocospy on 129mTe-implanted and laserannealed crystals. 2 It was found that the I-atoms introduced into silicon via the decay of 1 mTe are either part of a cubically symmetric or a (Jahn-Teller) distorted configuration, dependent on the charge state [2,31. Tellurium has been found to occupy mainly substitutional sites in silicon after laser annealing [4]. In previous channeling studies [4,5] on iodineimplanted silicon it was found that after laser annealing only 60% of the I-atoms are at near-substitutional sites, and a considerable redistribution and loss of impurities was observed. However, after thermal annealing, about 90% of the I-atoms were found to occupy near-substitutional sites. To our knowledge nothing is known about the site of other group VII impurities in silicon. It has been shown [61 that after thermal annealing to 0 1000 C chlorine-implanted silicon exhibits a donor character. In this work we report results of an analysis of channeling data on iodine and chlorine in Si. A preliminary account of the iodine experiment was published earlier [5]. EXPERIMENTAL DETAILS Single crystals of orientation of pure silicon were implanted 37 with 1271 ions or with C, ions. To circumvent ion channeling the implantations were done with the beam at an angle of 70 with the normal string. After implantation part of the samples were oven-annealed in a quartz tube, either in vacuum or in a flow of argon. Other samples were laser-annealed in air using a Q-switched ruby laser with a pulse width of about 30 ns and a power density of 1.5 Jcm . A surface layer of 'U 5 nm was removed from the iodine-implanted samples by anodic oxidation and subsequent etching in a dilute HF-solution. Further details on the sample preparation are given in table I. Mat.
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