High Energy Ion Beam Annealing in Implanted CdTe
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HIGH ENERGY ION BEAM ANNEALING IN IMPLANTED CdTe S. P. Withrow Oak Ridge National Laboratory, Oak Ridge, TN 37831 A. Lusnikov1 , H. J. Jim6nez-Gonz£lez, G. Dresselhaus Massachusetts Institute of Technology, Cambridge, MA 02139
Abstract The annealing effects of a high energy beam of Cu ions on implanted CdTe crystals are studied. Single crystals of CdTe have been implanted with Eu (energy 60 keV, fluence 1 X 1016 cm-2) at substrate temperatures of 25 0C, and 400°C. Lattice damage introduced by the implantation process was measured by Rutherford backscattering. The samples were then implanted with high energy Cu ions (energy 3.5 MeV, fluence 0.5 x 1016 cm- 2) at substrate temperatures of 25°C and 200°C. Channeling spectra from these samples indicate a reduction in the near-surface lattice damage as a result of the Cu implantation that can be unambiguously separated from the external heating of the substrate.
Introduction The field of ion implantation has gained a prominent place in the semiconductor industry because it offers a degree of control over the doping process that cannot be matched by more conventional diffusion techniques. Among the principal advantages of ion implantation are the wide range of dopants that can be introduced and the fact that the doping process is not dominated by the solubility limits of the impurities. However, this technique has the side effect of creating a large number of defects in the near-surface region. This damage has to be removed by annealing in such a way as to maximize the incorporation of dopants into substitutional sites and minimize their diffusion out of the region of interest. The number of lattice defects introduced by the ion beam depends on the implant conditions, including fluence and energy of the beam, and substrate temperature. The idea of using a high energy ion beam to anneal damage introduced by a previous implantation has been explored fairly recently by several authors [1,2,3,4,5,6]. The underlying physical mechanisms of ion beam annealing (IBA) are not well understood at the present time. It has been suggested [2,6] that this annealing effect is due to the creation of point defects in the crystalline regions of the substrate; these defects subsequently interact at the crystalline-amorphous interface where vacancies and interstitials recombine causing a propagation of the crystalline interface. Other authors [3] suggest that the important interactions may occur inside the disordered layer. In particular, it was proposed that a large number of sub-threshold collisions (i.e. where the nuclear energy transfer to the target atom is insufficient to cause its displacement) are needed in 1Present Address: University of Nebraska at Omaha, Department of Physics, Omaha, NE 68182-0266
Mat. Res. Soc. Symp. Proc. Vol. 100. C1988 Materials Research Society
306
order to induce crystallization. The relatively low ion currents used in these experiments 2 (". ltA/cm ) rule out the possibility of macroscopic beam heating of the target. The previous IBA results were obtain
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