Room-temperature epitaxy of Cu on Si(111) using partially ionized beam deposition
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D. B. Knorr Center for Integrated Electronics and Materials Engineering Department, Rensselaer Polytechnic Institute, Troy, New York 12180 (Received 6 September 1989; accepted 8 February 1990) The epitaxial growth of Cu on Si(lll) substrate at room temperature was achieved using the Partially Ionized Beam (PIB) deposition technique in a conventional (10~4 Pa) vacuum without prior in situ cleaning of the substrate or post-annealing of the film. The beam contained —2% of Cu self-ions, and a bias of 0 to 4.2 kV was applied to the substrate during deposition. X-ray diffraction studies showed the existence of a twin structure in the epitaxial Cu layer deposited at 1 kV. A mechanism of epitaxial growth of Cu(lll) on Si(lll) substrate via an i7"-Cu3Si intermediate phase is proposed. Based on the crystal structure of i7"-Cu3Si, it is demonstrated that the geometrical lattice matching concept provides a simple picture of lattice continuity at the interface in this epitaxial system.
I. INTRODUCTION
The ion-assisted deposition techniques have received considerable attention because ion bombardment during deposition can modify the structure and electronic properties of the films.1 By properly controlling the ion bombardment parameters one can obtain films of desired properties. Both foreign ions such as argon ions1 or ions derived from the depositing material2"7 have been used in ion-assisted deposition. The Partially Ionized Beam (PIB) deposition technique belongs to the latter category in which a controlled percentage of self-ions are used.7 Recently, a PIB ion source which yields up to 5% of self-ions in the beam has been designed. With this high ion/atom ratio PIB source we showed that Al can be grown epitaxially on Si(lll) substrate at room temperature under conventional vacuum condition.9 Also, the PIB technique can be used to reduce spike formation at the Al/Si interface,8 to control the morphology of the Al films,1011 to form crystallographically oriented films on SiO2,23 and to produce thick (4-5 /im) Al films without the usual columnar structure.39 In this paper, we report our study on the orientation effects of Cu films deposited at room temperature on Si(lll) substrate using the PIB deposition technique. An epitaxial growth of Cu(lll)/Si(lll) was achieved under conventional vacuum condition (10~4 Pa) without in situ cleaning prior to deposition using the PIB technique. The Cu(lll)/Si(lll) epitaxial system, with about 33% lattice mismatch, represents one of the largest lattice mismatches where epitaxy has been achieved.1618"20 J. Mater. Res., Vol. 5, No. 5, May 1990
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Based on the reported reaction between Cu and Si at the interface, we shall discuss the mechanism of epitaxial growth of Cu(lll) via an intermediate silicide phase on the Si(lll) substrate, and the application of geometrical lattice matching to this epitaxial system. II. EXPERIMENTAL SETUP AND FILM DEPOSITION
Figure 1 is a schematic diagram of the PIB experimental setup.710 High purity Cu is vap
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