Studies of the Effect of Rapid Thermal Annealing on the Structural and Electrical Properties of Heteroepitaxial CaF 2 /C
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STUDIES OF THE EFFECT OF RAPID THERMAL ANNEALING ON THE STRUCTURAL AND ELECTRICAL PROPERTIES OF HETEROEPITAXIAL CaF 2 /CoSi 2 /Si(111) STRUCTURES Julia M. Phillips, J. C. Hensel, D. C. Joy, and W. M. Augustyniak AT&T Bell Laboratories Murray Hill, NJ 07974
ABSTRACT 'We have used electron channeling and scanning electron microscopy to study the crystallinity and morphology of epitaxial CaF 2 layers on CoSi 2 /Si(111) substrates before and after a rapid thermal anneal. The channeling patterns from the layers after a rapid thermal anneal are nearly indistinguishable from patterns from bulk crystals, indicating high crystalline quality. The annealing procedure also improves the film morphology substantially. We have studied the effect of the rapid thermal anneal on the electrical resistivity of the underlying CoSi 2 layer. The room temperature resistivity is unaffected by the anneal, but the low temperature behavior of the resistivity indicates a high degree of diffuse surface scattering, in contrast to as-grown films. There has recently been considerable effort by several groups on the growth and characterization of epitaxial insulators1 or metals 2 on semiconductors. One motivation for both lines of research is the possible application of such heteroepitaxial layers to three-dimensional integration. There is also considerable interest in gaining insight into the epitaxial growth process itself. Most of the work dealing with epitaxial insulators has centered around the alkaline earth fluoride compounds such as CaF9 , in light of their cubic fluorite crystal structure, close lattice matches to common semiconductors, and excellent insulating properties at room temperature. CaF 2 grown on Si has been a particularly popular system for study in light of the simplicity of the system (one alkaline earth fluoride and one elemental semiconductor) and small (0.6%) lattice Study of the growth of epitaxial metals on Si has silicides, CoSi, and NiSi 2 . CoSi 2 is particularly resistivity at room temperature (-15 p02-cm). Its than that of Si at room temperature.
mismatch at room temperature. centered around the two cubic interesting because of its low lattice constant is 1.2% smaller
With the success of the epitaxial growth of both of these classes of materials on Si, it is natural to think in terms of combining both an epitaxial silicide and a fluoride sequentially on Si as a possible completely epitaxial approach to three-dimensional integration. \Ve recently reported the first successful growth of an epitaxial insulator-metal-semiconductor structure using CaF 2 as the insulating layer, CoSi 2 as the metal, and Si(111) as the semiconductor substrate. 3 Using Xmi , the ratio of backscattered high energy ions in a channeling direction to random Arection, as a measure of epitaxial quality, we found the epitaxial quality of the CoSi layers to be generally very good (y 20%) over a ie range of growth conditions. We also found a rapid
Mat. Res. Soc. Symp. Proc. Vol. 74. 1987 Materials Research Society
610
thermal anneal (RTA) to
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