Current status and future trends of SiGe BiCMOS technology

The silicon germanium (SiGe) heterojunction bipolar transistor (HBT) marketplace covers a wide range of products and product requirements, particularly when combined with CMOS in a BiCMOS technology. A new base integration approach is presented which decouples the structural and thermal features of the HBT from the CMOS. The trend is to use this approach for future SiGe technologies for easier migration to advanced CMOS technology generations. Lateral and vertical scaling are used to achieve smaller and faster SiGe HBT devices with greatly increased current densities. Improving both the f_T and f_MAX will be a significant challenge as the collector and base dopant concentrations are increased. The increasing current densities of the SiGe HBT will put more emphasis on interconnects as a key factor in limiting transistor layout. Capacitors and inductors are two very important passives that must improve with each generation. The trend toward increasing capacitance in polysilicon-insulator-silicon (MOSCAP), polysilicon-insulator-polysilicon (Poly-Poly), and metal-insulator-metal (MIM) capacitors is discussed. The trend in VLSI interconnections toward thinner interlevel dielectrics and metallization layers is counter to the requirements of high Q inductors, potentially requiring a custom last metallization layer