Research On The Process And Kink Effect Of SiGe HBT With EBL Structure

The double-polysilicon self-aligned(DPSA)structure has higher extrinsic base connection resistance,which has become an important limiting factor for increasing the frequency of SiGe devices.The current research hotspot is the improvement of the extrinsic base connection process.It can improve the frequency characteristics of the device.In this paper,the resistance and frequency characteristics of the epitaxial base link(EBL)structure SiGe HBT are studied.The mechanism and influencing factors of the device base kink effect are analyzed.The shallow trench isolation field plate EBL structure is proposed to improve the kink effect.SiGe BiCMOS process with improved structure is designed.First,the three kinds of process structures for improving the extrinsic base connection:EBL(Epitaxial base link)structure,EEB(Epitaxial elevated base)structure,EXBIC(Epitaxial eXtrinsic Base Isolated from the Collector)structure are compared and analyzed.In contrast,EBL structure is more conducive to improving the Maximum oscillation frequency.The base resistance of EBL and DPSA is studied.The extrinsic base connection interface resistance Rlink and the resistance Rsp under the side wall is reduced,and the low doping SiGe layer resistance RLDB under the connection in the DPSA is removed by the lateral epitaxial silicon base connection of the EBL.Therefore the device base resistance is significantly reduced.The input resistance is extracted through the Y parameter.Compared with DPSA,the input resistance of EBL is reduced from 485? to 360.5?,which prove EBL is effective to improve the extrinsic base connection resistance.The EBL structure process is studied,and the complete process flow is given.Secondly,the base kink effect of EBL is studied.Heterojunction barrier effect leads to the recombination of the base and the voltage drop in the neutral region are the two main factors that cause the kink effect.Under high injection conditions,it will reduce the maximum stable gain of the device.The jump of the kink effect can be reduced by decreasing the Ge component concentration,the extrinsic base doping concentration,the emitter doping concentration,and increasing the height of the emitter region.The occurrence of the jump in the kink effect current can be delayed by penetrating the Ge component into the collector.To increase the device frequency through size scaling,it is necessary to reduce the size of each area and increase the doping concentration of each area.It is impossible to relieves the base kink effect through parameter optimization.This paper improve the kink effect by introduced shallow trench isolation field plates into the EBL structure.By adjusting the potential of the field plate,the device's current transmission ability is enhanced,the collector electron current density is increased,the critical current where the kirk effect occurs is increased,and the generation of the kirk effect and the heterojunction barrier effect is delayed.This reduces the accumulation and recombination of holes in the base and improves the base kink effect.Finally,the shallow trench isolation field plate EBL structure SiGe HBT process is studied,and the two kinds of field plate process schemes are compared and analyzed.Considering the process cost and the device integration compatibility,the shallow trench isolation field plate EBL is embedded into SiGe BiCMOS process,a complete shallow trench isolation field plate EBL SiGe BiCMOS process is designed.