Effects of interfacial oxide on hot carrier reliability of polysilicon emitter npn transistors

The results of reverse emitter-base stress testing of polysilicon emitter bipolar transistors with various process options is described. Variations in interfacial oxide whether from pre-deposition cleans or controlled thin oxide growth have a major effect. Significant improvement to hot carrier stress is achieved by elimination of the interfacial oxide. Degradation rates increase with thicker interfacial oxide. Anneal conditions (RTA vs. furnace) appear to have less impact although the furnace results are generally better. Since interfacial oxide suppresses base current and increases hfe, selection of process options represents a tradeoff between performance and reliability