Symmetric self-aligned processing
A method of manufacturing a semiconductor device using simplified processing and eliminating and/or minimizing the extrinsic parasitic elements of the device. The method is particularly suited for manufacturing heterojunction bipolar transistors where the extrinsic parasitic base resistance and the extrinsic parasitic base-collector and base-emitter capacitances can be virtually eliminated and the base contact resistance can be greatly reduced. The method includes formming symmetric emitter and collector portions using front and backside processing of the wafer, respectively. The symmetric emitter and collector virtually eliminates the extrinsic collector and emitter regions of the device thereby virtually eliminating the extrinsic base-collector and base-emitter capacitance. The extrinsic base contact region may also be increased to minimize the base contact resistance without increasing parasitic capacitive elements of the device. Self-aligned processing features are also included to form self-aligned contacts to the base layer thereby virtually eliminating the extrinsic base resistance. The method may include building up the collector and emitter contacts to separate the emitter and collector interconnections from the base layer to avoid increasing the emitter-base and collector-base extrinsic parasitic capacitances and to minimize associated resistances and inductances. The method may further include forming etch stop layers to facilitate removing of the substrate to perform the backside processing and to accurately etch through the collector layer without etching the base layer.