Transient and Steady‐State Response of the Dopant System of a Silicon Epitaxial Reactor: Transfer‐Function Approach

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Abstract
The transient response of the dopant system of a horizontal, silicon epitaxial reactor has been studied in order to obtain a “transfer function” relating the time variation of the dopant gas flow and the spatial variation of the dopant concentration in the epitaxial film. This transfer function should be useful in fabricating nonuniform dopant concentrations needed for desired device characteristics. The transfer function was obtained from the response of the system to both increasing and decreasing step changes in the dopant gas flow with time. The transfer‐function approach was verified by experiments in which the input was an increasing step followed by a decreasing step (approximating a pulse). Pulse widths both longer than and comparable to the decay time of the system were used, and the measured profiles agreed very well with calculated profiles in all cases. The transient and steady‐state responses of the dopant system were studied at different growth rates to determine the effect of growth rate on the parameters entering into the transfer function. These experiments showed the presence of two regions of operation and provide insight leading to a better understanding of the doping process.

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