Defect Formation by Ion Implantation in Cz-Si Studied by a Monoenergetic Positron Beam
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DEFECT FORMATION BY ION IMPLANTATION IN Cz-Si STUDIED BY A MONOENERGETIC POSITRON BEAM A.
UEDONO*,
Y. UJIHIRA*, L. WEI', Y. TABUKI**, S. TANIGAWA**, J. SUGIURAt , M. OGASAWARA' AND M. TAMURA* *Department of Industrial Chemistry, Faculty of Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan **Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 305, Japan tDevice Development Center, Hitachi Ltd. 2326, Imai, Ome-shi, Tokyo 198, Japan tCentral Research Laboratory, Hitachi Ltd. 1-280, Kokubunji 185, Japan ABSTRACT Vacancy-type defects in ion implanted Si were studied by a monoenergetic positron beam. The depth-distributions of the defects were obtained from measurements of Doppler broadening profiles of the positron annihilation as a function of incident positron energy. The results showed that a size of vacanyclusters introduced by 150-keY P+-ion implantation was found to be smaller than that introduced by 2-MeV P+-ion implantation. This was attributed to an overlap of collision cascades in lowenergy (150 keV) ion implanted specimens. From isochronal annealing experiments for 80-key B+and 150-keV P+-ion implanted specimens, the defected region was removed by 1200 0 C annealing, however, for 2-MeV P+-implanted specimen, two-types of oxygen-vacancy complexes were found to coexist even after 1200 *C annealing. INTRODUCTION The most widespread application of ion implantation technique is the localized doping of selected impurity species into semiconductors during the planar device fabrication process [I]. In order to ensure the high reliability of semiconductor devices on an increasing miniaturized scale, many fundamental studies have been carried out on the interaction between implanted ions and the bulk lattice. A major side effect of the ion implantation is radiation damage. The use of a monoenergetic positron beam has emerged as a nondestructive and sensitive tool for studying vacancy-type defects in the subsurface region and multilayer systems. Details of this technique can be found in ref. 2. In the present paper, we report the application of the monoenergetic positron beam technique to the study of defects in Si introduced by the ion implantation. When positrons implanted into a condensed material, they rapidly slow down to thermal energies. After this thermalization process, a positron annihilates with an electron from the surrounding medium into two 511-keV y-quanta. The motion of the positron-electron pair causes a Doppler shift on the energy of the annihilation photons measured in the laboratory system. In a material containing defects, a freely diffusing positron may localize in open-volume defects by a Coulomb interaction from ion cores. The positrons trapped by open-volume defects annihilate with electrons in such region. The change of the Doppler broadening spectrum due to the Mat. Res. Soc. Symp. Proc. Vol. 262. @1992 Materlals Research Society
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annihilation of positrons from trapped states is characterized by the lineshape parameter S, which is the ratio
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