The Influence of Implantation-Induced Non-Stoichiometry on the Epitaxial Recrystallization of CoSi 2
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M.C. RIDGWAY*, A. VANTOMME**, A.-M. VAN BAVEL** AND G. LANGOUCHE ** *Department of Electronic Materials Engineering, Australian National University, Canberra, Australia ** Instituut voor Kernen Stralingsfysika, Katholieke Universiteit Leuven, Leuven, Belgium ABSTRACT Epitaxial CoSi 2 layers on Si substrates have been amorphized with Co and/or Si ion implantation. The influence of nonstoichiometry on the rate of solid-phase epitaxial growth (SPEG) of amorphized CoSi 2 has been investigated with time-resolved reflectivity, Rutherford backscattering spectrometry and Mossbauer spectrometry, the latter with radioactive 5 7 Co probes. A decrease in SPEG rate was apparent with an increase in nonstoichiometry. For a given ion dose, the decrease was greater following Co implantation. The means by which non-stoichiometry is accommodated in a crystalline CoSi 2 lattice - either through phase separation or defect formation - has been considered. SPEG rate retardation was also evident in samples implanted with both Si and Co ions with a Si:Co dose ratio of 2:1. Additional mechanisms may thus also contribute to the observed SPEG rate reduction. INTRODUCTION Metal silicide applications in integrated circuit fabrication include inter-connections, gate and contact metallization. Epitaxial metal silicides (such as CoSi 2 ) also have potential usage in future, three-dimensional devices and thus, a study of the recrystallization of an amorphized metal silicide is of technological significance. The implantationinduced amorphization and subsequent thermally-induced epitaxial recrystallization of CoSi 2 has been investigated previously [131. The recrystallization of an amorphized CoSi 2 layer proceeds by solid-phase epitaxial growth (SPEG) from the original amorphous/crystalline (a/c) interface with an activation energy of 1.17 +/- 0.03 eV [2,3]. Implanted impurities retard the SPEG rate and these effects were attributed to combinations of size, structural and/or chemical factors [4,51. Co and/or Si implantation can negate such effects and thus, for the present report, the influence of non-stoichiometry on the SPEG rate of amorphized CoSi 2 was studied. Also, the means by which limited non-stoichiometry is accommodated in a post-anneal, crystalline CoSi 2 lattice has been considered. EXPERIMENTAL Co films of thickness -30 nm were deposited on Si substrates of (111) orientation by electron-beam evaporation at a pressure of IX10- 6 torr. Prior to Co deposition, the native oxide was removed from the substrates with a 10:1 H 2 0:HF solution. After Co deposition, selected samples were implanted with 5 7 Co ions at 203 Mat. Res. Soc. Symp. Proc. Vol. 320. ý1994 Materials Research Society
The an energy and dose of 30 keV and 1X10 1 4 /cm- 2 , respectively. projected range and range straggle of 5 7 Co ions (10.4 nm and 5.7 nm, respectively [6]) are such that greater than 99.95% of the All implanted atoms are confined to the evaporated Co layer. samples were annealed for 10 min at 1100 0 C in an Ar ambient to form an epitaxial CoSi
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