Profile Parameters of Implanted‐Diffused Arsenic Layers in Silicon

Abstract

In a previous paper, the diffusion of ion-implanted As in <100> Si was discussed as well as the electrical quality of implanted-diffused layers. It is the purpose of this paper to derive equations that describe the important characteristic profile parameters, and to support these equations with experimental data. A discussion of total As surface concentration, junction depth, and profile gradient will be presented, which will be followed by an analysis of the sheet resistance of implanted-diffused As layers and the surface concentration of the electrically active As. AnalysisTotal As surface concentration, CTO, and junction depth, xj.--It was shown previously (1) that the implanted-diffused total As profile shape is approximately described by the equationt is the diffusion time (sec), Di is the intrinsic As diffusivity (cm2/sec), n1 is the intrinsic electron concentration, and CTO is the As surface concentration (atom/cm 8) assumed to be greater than ,~1 X 1019 cm-~ Equation [1] is a Chebyshev polynomial approximation to the solution of the diffusion equation with a linear concentration-dependent diffusion coefficient and constant surface concentration, CT0. It is probable that the polynomial coefficients are time-dependent for the case of nonconstant CTO, such as the case of a redistributing impurity distribution. For the case of implanted As in St, CT0 decreases as t -~/~, and the con-

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