Characterization of Epitaxial CoSi 2 Film Growth on Si(100) by Slow Positron Beam
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BINGZONG LI**,
*Ion Beam Laboratory, Shanghai Institute of Metallurgy, Chinese Academy of Sciences, Shanghai 200050, China "~Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China `Department of Electronic Engineering, Fudan University, Shanghai 200433, China ABSTRACT
A slow positron beam was used to investigate the solid state reaction of Co/Si and Co/Ti/Si. Variable-energy (0-20 keV) positrons were implanted into samples at different depths. The Doppler broadening of the annihilation -y-ray energy spectra, measured at a number of different incident positron energies were characterized a line-shape parameter "5". It was found that the measured S parameters were sensitive to thin film reaction and crystalline characteristics. In particular, the S parameter of epitaxial CoSi 2 formed by the ternary reaction was quit different from that of the polycrystalline CoSi2 formed by direct reaction of Co with Si. L. INTRODUCTIO0N
Epitaxial silicide films have received growing attention because of their promising application in fabricating new structural and high-performance microelectronics devices(1]. A new approach to solid phase epitaxy Of CoSi2 on Si substrate through a reaction of the ternary Co/Ti/Si system has been investigated[2-6]. Slow positron annihilation technique (SPAT) has developed as an effective way to study near-surface defects in solids and the phase transition of materials[7-l0]. A positron implanted into a material annihilates with an electron, producing two antiparallel annihilation y photons with energy of 511 keV. A Doppler-broadened profile of these y)photons can provide information about the existence of defects. In particular, positron are very sensitive to vacancy-like defects. As the density of defects increases the width of the spectrum becomes narrow due to the positron trapping and annihilation at these defects. A slow positron beam consists of monoenergetic positrons which the energy can be varied by adjusting the accelerating voltage. In this way positrons can be implanted into the films at different depths. By detecting the annihilation photons, one can obtain information about defects, structure and phase-transition 233 Mat. Res. Soc. Symp. Proc. Vol. 320. @1994 Materials Research Society
of the films at different depths.
We have reported the epitaxial growth
Of CoSi 2
films with minimum channeling
backscattering: yields of 10- 14 %on both (100) and (111) oriented Si substrates by a multi-step annealing of ternary Co/Ti/Si system[5,6]. In this work the slow positron annihilation technique was used to characterize the epitaxial COSi 2 growth during the thin film reaction of Co/Ti/Si. LI.EXPERIMENTAL
A set of 5-8 (1cm, p-type (100) Si wafers with ion beam sputtering deposited thin films of 20 nmi Ti followed by 36 nm Co were multi-step annealed from 550 to 900*C in a nitrogen ambient to grow epitaxial CoSi 2. The details of reaction process are described in our earlier publication[5]. Six samples, as listed in Table 1, were prepared for th
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