Influence of the interfacial oxide layer on the gain of polycrystalline silicon emitter bipolar transistors processed in VLSI BiCMOS technology

The effect of the process thermal steps on the transistor properties in BiCMOS technology was investigated. The analysis of the device performances shows that changes in both emitter/base dopant profiles and polysilicon/monosilicon interface structure must be taken into account in order to explain the current gain variations according to the thermal budget. The transistor gain/base sheet resistance/emitter sheet resistance ratio gives a good representation of the interface related gain enhancement factor.