Impact of back end stress on SiGe bipolar transistors

The impact of back end stress on the electrical characteristics of SiGe HBTs was investigated experimentally and theoretically. It was found that collector currents depend strongly on the layout of metal interconnects in the vicinity of the transistor. This effect is caused by uniaxial stress perpendicular to the surface due to different thermal expansion coefficients of metal lines and interlayer dielectrics. The layout dependence of the collector current can be simulated based on known mechanical properties and deformation potential theory.