Thermal Stability and Substitutional Carbon Incorporation far above Solid-Solubility in Si 1-x C x and Si 1-x-y Ge x C y
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Thermal Stability and Substitutional Carbon Incorporation far above SolidSolubility in Si1-xCx and Si1-x-yGexCy Layers Grown by Chemical Vapor Deposition using Disilane M. S. Carroll*, J. C. Sturm, Dept. of Electrical Engineering, Princeton University, Princeton NJ; E. Napolitani, D. De Salvador, and M. Berti INFM and Dept. of Physics, University of Padova, Padova, Italy *Present address: Agere Systems, Murray Hill NJ Abstract Growth conditions for epitaxy of Si1-x-yGexCx and Si1-xCx alloy layers on (100) silicon substrates by rapid thermal chemical vapor deposition (RTCVD) with disilane as the silicon source gas are described and the Si1-xCx conditions are compared to previously reported RTCVD growth conditions for epitaxy of Si1-xCx using silane as the source gas. The thermal stability of the layers at 850˚C in nitrogen is examined using x-ray diffraction as a measure of the average substitutional carbon concentration in the layers after annealing. A characteristic time constant to describe the reduction of average substitutional carbon concentration in the layer is extracted from the XRD measurements. The characteristic time constants are found to agree within a factor of 3 with that observed in previous reports. However, the time constants are found to depend more strongly on the as-grown substitutional carbon concentration than what is predicted by simple precipitation kinetics, assuming carbon diffusion to a constant number of nucleation centers. Introduction The incorporation of high concentrations (> 0.1%) of carbon in silicon and SiGe is of wide technological interest for its potential use to engineer dopant diffusion [1], engineer the conduction band in silicon based materials [2, 3], and strain compensation [4]. However, because the solid solubility of substitutional carbon in silicon is ~1017 cm-3 and carbon at concentrations above this can incorporate on interstitial sites or precipitate as β-SiC, special non-equilibrium epitaxial growth conditions are required to grow metastable films with substitutional carbon concentrations greater than 0.1 atomic percent. It is has been shown that the incorporation of substitutional carbon incorporation increases with reduced growth temperature and higher growth rates [5, 6]. Because the growth rate of silicon and SiGe by rapid thermal chemical vapor deposition is strongly dependent on the choice of silicon source gas and disilane is known to produce higher silicon epitaxial growth rates for similar partial pressures and temperatures as silane and dichlorosilane, disilane is a promising candidate for expanding the available parameter space of growth conditions that produce 100% substitutional carbon alloys with silicon and SiGe, which in turn could allow for increased throughput and an extension of the maximum total carbon concentration that can be incorporated entirely as substitutional carbon grown by RTCVD. This paper characterizes the growth of Si1-x-yGexCx and Si1-xCx layers using a mixture of 10% disilane in hydrogen as the silicon source gas. Growth condition
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