Measurement of collector and emitter resistances in bipolar transistors

New DC methods to measure the collector resistance R/sub C/ and emitter resistance R/sub E/ are presented. These methods are based on monitoring the substrate current of the parasitic vertical p-n-p transistor linked with the n-p-n intrinsic transistor. The p-n-p transistor is operated with either the bottom substrate-collector or the top base-collector p-n junction forward-biased. This allows for a separation of the various components of R/sub C/. R/sub E/ is obtained from the measured lateral portion of R/sub C/ and the collector-emitter saturation voltage. Examples of measurements on advanced self-aligned transistors with polysilicon contacts are shown. The results show a very strong dependence of R/sub C/ on the base-emitter and base-collector voltages of the n-p-n transistor. The bias dependence of R/sub C/ is due to the conductivity modulation of the epitaxial collector. From the measured emitter resistance R/sub E/ a value for the specific contact resistance for the polysilicon emitter contact of rho /sub c/ equivalent to 50 Omega - mu m/sup 2/ is obtained.<
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