Research And Design Of Novel Device Structures For SOI SiGe HBT With Strained-silicon Emitter

Compared with traditional Si-based bipolar transistors,SiGe heterojunction bipolar transistors have high-speed and high-frequency performance.Compared with III-V compound semiconductor devices,SiGe heterojunction bipolar transistors have the advantages of low cost,good thermal conductivity and easy compatibility with CMOS process.The introduction of strained Si technology and SOI technology can further improve performance of devices.Strained Si technology and SOI technology are combined to design device structures of SOI SiGe HBT with strained-silicon emitter.This device structures are simulated and analyzed in this paper.Based on the working principle of SiGe HBT and the principle of silicon-based strain technology,the structure of SOI SiGe HBT that covered with nitride stress film is designed.Depositing a layer of Si₃N₄ on the surface of the device structure introduces uniaxial compressive stress in the base to enhance the carrier mobility and improve frequency performance.The effects of different buried oxide thicknesses and the presence or absence of nitride film on the performance of SOI SiGe HBT device are discussed.The simulation results show that when the Ge composition in the base is 17%to 30%stepped distribution and the thickness of the buried oxide layer increases from 90 nm to 190 nm,the cut-off frequency f _T of the device increases by 56 GHz,and the maximum oscillation frequency f_max increases by 68 GHz.When the thickness of the buried oxide layer is set to 190 nm,compared with the device structure without the nitride film,the current gain?decreases slightly,the early voltage increases V_A by 1.4 V,the figure of merit of?×V_Aincreases by 0.02×10⁵ V,the breakdown voltage BV_CEO increases very little and it is basically unchanged,the cut-off frequency f _T increases by 38 GHz,and the maximum oscillation frequency f_max increases by 44 GHz.Furthermore,considering the compatibility with CMOS process and frequency characteristics,the device structure of strained silicon folded collector SOI SiGe HBT is designed.The influence of different thicknesses of nitride film on device performance is discussed.The simulation results show that when the Ge composition of the base is stepped distribution,the thickness of the buried oxide layer is set to 190 nm,and the nitride film thickness increases from 20 nm to 60 nm,the current gain?of the SOI SiGe HBT device decreases by 10,the early voltage V_A increases by 14.8 V,the figure of merit of?×V_A increases by 0.23×10⁵ V,the breakdown voltage BV_CEO slightly increases,the cut-off frequency f _T increases by 134 GHz,and the maximum oscillation frequency f_maxincreases by 179 GHz.In general,by introducing the Si₃N₄ stress film on the device surface,the SOI SiGe HBT device that designed in this paper is better compatible with the strained Si CMOS process at the 45?65 nm process node than the conventional SOI SiGe HBT.The circuit design and process integration of Si/SiGe Bi CMOS have a certain reference.