This paper discusses the influence of deposition conditions on in-situ As doped amorphous silicon emitter films used in NPN RF bipolar transistors. In-situ As doped amorphous and/or polysilicon layers improve electrical performance in BiCMOS devices by reducing the number of process steps and eliminating issues associated with implanted polysilicon on high aspect ratio topographies (plug effect). This study was made using a vertical furnace configuration capable of 150 wafer loads. Because adsorbed AsH3 decomposition species tightly bind to the active surface sites and inhibit the deposition rate, the process recipe is complex. Predictable bipolar parametrics require control of the As diffusion profile within the base region after activation, so a thorough understanding of emitter film growth and dopant incorporation is necessary.

We describe the relationship between process conditions and recipe variants on transistor gain (Hfe), base current (Ib), and emitter resistance (Re). SIMS and in-line sheet resistivity measurements were used to monitor dopant incorporation into the emitter. This data was found to be predictive not only of the Hfe for a population, but also as an indicator of potential “renegade” Hfe behavior.