The Effect of Rapid Thermal Annealing on Heteroepitaxial Structures
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THE EFFECT OF RAPID THERMAL ANNEALING ON HETEROEPITAXIAL STRUCTURES Julia M. Phillips, J. L. Batstone, and L. Pfeiffer AT&T Bell Laboratories, Murray Hill, NJ 07974
ABSTRACT We present evidence on the types of structural changes caused by the rapid thermal annealing of two types of heteroepitaxial layers: CaF 2 /CoSi 2 /Si(111) and Si(100) on A12 0 3 (1102). We find that grains in a film can be merged into a single crystal and that the microtwin density can be dramatically lowered. We also find a number of changes in the structure of the heteroepitaxial interfaces.
The application of rapid thermal annealing (RTA) to the improvement of heteroepitaxial structures was first demonstrated in the CaF 2 /Si system 1 . Early in the work on this pair of materials, it was found that the optimum' substrate temperature for the growth of epitaxial CaF 2 on Si(100) substrates was very narrowly defined. Deviation from this optimum temperature by as little as 250C resulted in a dramatic decrease in the crystallinity of the overlayer. Even films which were grown under optimum conditions were found to be somewhat inferior to bulk single-crystal CaF as measured by Rutherford backscattering/channeling. On the other land, after these samples underwent an RTA with a peak temperature near the CaF 2 sublimation temperature, we found that the crystallinity improved dramatically, so that films superior to even the best as-grown films were readily obtained. In fact, when an RTA was used, the initial growth conditions for the CaF2 layer became quite unimportant, and high quality epitaxial films were obtained after RTA even for films deposited as much as 3000C below the "optimum" substrate temperature. RTA also improved a variety of other properties of the films, including surface morphology, electrical properties, and chemical stability. Since the initial report of the remarkable success of applying RTA to the improvement of CaF 2 films on Si, it has been shown to be useful in other heteroepitaxial systems as well. Chand and co-workers demonstrated that the crystallinity and photoluminescence of GaAs films grown on Si(100) could be improved by an RTA, though the defect density in these layers was not observed to decrease2. Tu and co-workers have made similar observations in GaAs films grown on (Ca,Sr)F 2 /Ge substrates . Finally, we recently showed the utility of an RTA for dramatically decreasing the microtwin density in commercially available Si on A12 0 3 (Silicon on Sapphire or SOS)4. In this paper, we present results on the structural changes induced in two particular epitaxial heterostructures by RTA: CaF 2 /CoSi 2 /Si(111) and Si(100) on A12 0 3 (1102). We conclude by making some comments regarding the possible mechanisms underlying the success of the RTA process. All of the heterostructures described were rapidly thermally annealed in a commercially available RTA furnace. The maximum temperature was slightly Mat. Res. Soc. Symp. Proc. Vol. 91. '1987 Materials Research Society
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less than the melting or sublimation temperature o
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