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    Modeling Anomalous Junction Formation in Silicon by the Codiffusion of Implanted Arsenic with Phosphorus

    Published: 01 January 1983

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    Cross-contamination of phosphorus in arsenic-implanted layers has been found to occur in mechanically scanned ion implantation systems. Phosphorus introduced at low levels exhibits a diffusivity that depends upon n2, where n is the free electron concentration of the highly doped arsenic background layer. If the arsenic layer is shallow and the phosphorus diffuses through the arsenic junction, an enhanced phosphorus tail region is formed. Tail diffusion coefficients at 900°C were ∼20 times greater than the intrinsic phosphorus diffusion coefficient. Also, when a phosphorus tail is formed, the mechanism that enhances the tail diffusion also enhances the high concentration arsenic diffusion. These results are remarkable, since arsenic by itself will not produce an enhanced tail during diffusion in silicon, nor will it cause any emitter push effect.

    These results have been modeled and provide strong support for a Fermi-level-controlled point-defect model of phosphorus diffusion with impurity-point-defect pair dissociation creating the tail region. We have essentially duplicated high-concentration phosphorus diffusion results by replacing the highly doped portion of the profile with arsenic. The fact that arsenic diffusion is also predictably enhanced when a phosphorus tail is formed strongly implies that the point-defects involved are vacancies.


    vacanices, emitter push effect, ion implantation, diffusion

    Author Information:

    Fair, RB
    Microelectronics Center of North Carolina, Research Triangle Park, N.C.

    Meyer, WG
    Microelectronics Center of North Carolina, Research Triangle Park, N.C.

    Committee/Subcommittee: F01.06

    DOI: 10.1520/STP36175S