CoSi 2 Precipitate Coarsening During Formation of Buried Epitaxial Cosi 2 Layers By Ion Beam Synthesis
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CoSi 2 PRECIPITATE COARSENING DURING FORMATION OF BURIED EPITAXIAL CoSi2 LAYERS BY ION BEAM SYNTHESIS R.Jebasinski, S.Mantl, K. Radermacher, P. Fichtner 2 , W. Jager' and Ch. Buchal Institut fUr Schicht-und Ionentechnik, 'Institut fUr Festkbrperforschung, Forschungszentrum JUlich, D-5170 JUlich, Germany 2 Escola de Engenharia UFRGS, 90000 Porto Alegre, Brazil
ABSTRACT The coarsening of CoSi2 precipitates and the microstructural evolution 6 im-2 2 of (111) 1Si 6 0 planted with 200 keV Co' ions at 350 C and fluences of Ix101 cm- and 6xl0 cm" were investigated as a function of depth, annealing temperature and annealing time using Rutherford Backscattering Spectroscopy (RBS) and Transmission Electron Microscopy (TEM). After annealing cross-section TEM micrographs show a layered array of platelet-shaped precipitates with preferred facets on 1111) planes. The fraction of Coatoms, that were redistributed during the different annealing temperatures and times, has been used to determine an activation energy for the precipitate coarsening. By applying the Meechan-Brinkman and the change-of-slope methods, we obtained activation energies in the range of 3.2 - 3.6 eV.
Introduction The formation of precipitates and their coarsening during annealing are precursory mechanisms for the growth of buried epitaxial CoSi2 layers by ion beam synthesis [1-3]. This contrasts to the case of the formation of silicide layers by vacuum deposition or solid phase epitaxy where layer growth occurs by different mechanisms [5]. Buried silicide layers are of growing interest because of their use in microelectronic devices [6]. In this contribution we present investigations of the precipitate coarsening and redistribution of implanted Co in (111) Si during annealing. In particular low dose implanted samples have been studied, where only isolated precipitates are produced during annealing, in contrast to high dose implantations (e.g. 2x10' 7 cm 2 ), where continuous CoSi2 layers are formed after high temperature annealing [3,41.
Experimental For the 59Co implantations, a medium current ion accelerator (EATON NV-3204) was used. Doses of 1 or 6x10 16 Co+/cm 2 were implanted at 200 keV into (111) Si. The substrates were tilted by 70 to minimize channeling of the implanted ions and were heated to 350 0 C to prevent amorphization. The first annealing step was performed in an evacuated tube furnace at 10"7 torr and 6000 C for 1 hour. The second annealing procedure was performed in a rapid thermal processor (AET RV-1002) at temperatures ranging from 700Q C to 11500 C with annealing times from 5 s up to 600 s in flowing high purity Ar. The first annealing step was frequently omitted because no influence on the Co depth distribution was observed. Microstructural characterizations were made by Mat. Res. Soc. Symp. Proc. Vol. 201.
1991 Materials Research Society
412
cross-section transmission electron microscopy (XTEM). Co concentration depth profiles were measured by Rutherford backscattering spectroscopy (RBS) using a He beam of 1.4 MeV energy.
Results
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