The Diffusivity and Solubility of Oxygen in Silicon
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THE DIFFUSIVITY AND SOLUBILITY OF OXYGEN INSILICON J. C. MIKKELSEN, JR. Xerox Research, 3333 Coyote Hill Road, Palo Alto, CA 94304
Abstract The diffusivity and solubility are two key parameters required for understanding and modeling the behavior of oxygen in silicon. This paper gives an up to date review of experimental determinations of these parameters, including some recent unpublished data. There is very good agreement within the long-range diffusivity results determined by secondary ion mass spectrometry (SIMS), charged particle analysis (CPA), and x-ray diffraction. The oxygen diffusivity is independent of [0], orientation, ambient, or crystal doping. The data also extrapolate well to the diffusivities obtained by the intrinsic oxygen atomic hop frequency at low temperature to give a combined expression of D = 0.13 exp(-2.53eV/kT) cm2s- 1 . There is somewhat poorer agreement on the solubility measurements, in part due to inconsistent calibration factors and the observation of a processing-dependent extrinsic oxygen solubility. The intrinsic solubility derived from SIMS, CPA, and infrared absorption is described by [0] = 9E22 exp (-1.52 eV/kT) cm- 3 . Finally, the above diffusivity and solubility parameters are compared to modeling of oxygen related phenomena in silicon, such as thermal donor and precipitate formation kinetics, and interaction with point defects during the relaxation of stress-aligned dichroism.
Introduction Oxygen is perhaps the most important of the light element, non-doping impurities in si icon(1, 2 ) due to the technological importance of Czochralski (CZ) Si substrates used in the manufacture of integrated circuits. The high [0] of 1E18 cm- 3 arises from the incorporation of 0 into the growing crystal from the slow dissolution of the silica (Si0 2 ) crucible by the molten Si. Although the equilibrium oxygen solubility decreases rapidly with decreasing temperature, the excess oxygen can remain in a metastable solid solution during the cooling of the as-grown Si ingot. However, oxygen complexing and precipitation typically occur during subsequent thermal treatments of the Si crystal. In the case of Si wafer processing to produce integrated circuits, electrically active oxygen-complexes may adversely affect doping profiles, and precipitation causes secondary defects, such as dislocation loops, which may affect the performance and yield of circuits. It is also the complex nature of oxygen behavior in Si at low and intermediate temperatures which makes it such a scientifically interesting materials system to study. Since large, dislocation-free single crystals of Si are readily available, which are free from other foreign components but have modest concentrations of oxygen, the Si-O system should be viewed as a prototypical solid state materials system for the study of fundamental solid state reactions, such as precipitation and impurity interactions with point and extended defects. These reactions are introduced in a preceding overview and are discussed in some detail in these Proceedings.
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