AbstractPolycrystalline silicon has found numerous applications in silicon integrated circuits, initially as a MOS gate material, and later for advanced isolation, capacitor electrodes, resistors, interconnect, bipolar emitters and bases, trench refill, doping sources, and the active material in thin film transistors. Integration of these techniques in a BiCMOS technology requires knowledge of the interactions between the processing steps, and their cumulative effect on the final device and circuit operation. New process techniques also present opportunities for process simplification, added functionality, or improved performance. Examples of polysilicon applications that interact with other process steps and influence device performance are P+ and N+ poly gates and silicidation of gate poly. Silicidation improves circuit speed and provides additional integration opportunities in the form of faster local interconnect, but it may create a problem for older designs with synchronous timing circuitry. More innovative integration of polysilicon includes improved deposition techniques, such as the use of amorphous silicon, “Lo-Hi” poly, in sinat doping, and deposition from disilane sources enable more flexible process design. Other innovations include polysilicon emitters, bases, and buried sinkers in bipolar design, polysilicon sidewall spacers in CMOS, and polysilicon based active transistors for display applications and three dimensional integration.