Design And Simulation Of Novel SOI SiGe HBTs Based On Uniaxial/Biaxial Strain Technology

As the working frequencies of modern communications systems move from GHz to terahertz?THz?bands,there is a higher demand for the high-speed transmission of signals in communications systems and the high frequency characteristics of core semiconductor devices.In this work,based on strain engineering and Silicon-on-Insulator?SOI?process,a novel architecture of SOI SiGe HBT is disigned.The Uniaxial compressive stress is introduced by embedded SiGe source/drain stress raiser in the collector region.Process simulation and device simulation are carried out by using SILV_ACO? TCAD tools.The effects of Ge component distribution in the base and the stress in the collector on device performance are then discussed.The key performance,such as current gain???,Early voltage?V_A?,cut-off frequency?f_T?,maximum oscillation frequency(f_max)are simulated.The simulation results show that when the base Ge component is divided into trapezoidal distribution,?_max,V_A,f_T,f_max are: 1062,186 V,419GHz,485 GHz respectively.Compared with the conventional SOI SiGe HBTs without any stress raiser in the collector region,the cut-off frequency f_T increased by 1.1 times and the maximum oscillation frequency f_max increased by 42.2%.Secondly,the effect of different stress raisers?SiO₂,Si₃N₄,SiGe?in the collector region and the stress introduction technology on the device performance is analyzed.It is concluded by TCAD simulation that under the condition of the same process parameters and geometrical size of the device,the value of additional uniaxial stress,i.e.?,introduced by the different stress raisers mentioned above is ??Si₃N₄?> ??SiO₂?> ??SiGe?.The simulation results of cut-off frequencies show that f_T?SiGe?> f_T?Si₃N₄?> f_T?SiO₂?with the values of 419 GHz,392GHz and 379 GHz,respectively.As a stress raiser,SiGe is more beneficial to realize high frequency characteristics,and this is in line with the architecture of uniaxial strained-silicon PMOS transistors using SiGe source/drain,which is beneficial to the integration of the Si/SiGe BiCMOS process.Finally,considering the possibility of integration with strained Si/SiGe heterojunction CMOS transistors,an improved SGOI SiGe HBT architecture is designed and simulated.The simulation results exhibit that the change of Ge component in relaxed Si_1-yGe_y substrate has little effect on the frequency characteristics of the device.The higher the concentration of epitaxial layer in the collector,the larger the peak current gain ?_max and the larger the cut-off frequency f_T.When the epitaxial layer concentration is 7.5×10¹⁷cm^-3,the peak current gain is about 2341,and the cut-off frequency f_T is 419 GHz;when the epitaxial layer thickness is smaller,the cut-off frequency is larger,and when the thickness is 80 nm,the characteristic frequency f_T is 438 GHz.The research work carried out in this paper has some reference value and engineering significance for the development of silicon-based high speed/high frequency semiconductor devices and circuits.