Effect of uniaxial strain on characteristic frequency of scaled SiGe HBT with embedded stress raiser

Abstract

In order to further improve the performance of scaled silicon-germanium (SiGe) heterojunction bipolar transistor (HBT) and consider the compatibility with mature CMOS process, a novel SiGe HBT is designed by introducing the embedded Si1−yGey stress raiser into the collector. In the proposed HBT structure, the collector region is subjected to additional uniaxial stress, to enhance the characteristic frequency. The effect of embedded Si1−yGey stress raiser on the frequency performance with different Ge mole fractions is simulated and analyzed by employing SILVACO TCAD tools. The simulation results show that the high frequency performance of the device can be significantly improved by applying additional uniaxial stress in the collector. At y = 0.3, the current gain of the device is increased by approximately 6% compared to the case where no stress is applied to the collector region (y = 0). Taking the uniform SiGe base case with the Ge fraction of 0.25 as an example, by adjusting the Ge fraction of the stress raiser, the peak values of f T and f max reach about 507.7 GHz and 730.7 GHz, respectively. Compared with the traditional SiGe HBT without any additional stress in the collector region, f T and f max are respectively increased by 29.1% and 71.5%. When y = 0.1, the proposed device has the best frequency characteristics due to the peak value of the f T×f max product.