Research On Novel IGBT Structures Utilizing Germanium Silicon Material

As a stable part of the semiconductor industry,the development of power semiconductors is very important,and IGBT devices,which combine the advantages of gate control capability of power MOS and low forward conduction voltage drop of GTR,are attracting much attention because of their small on-resistance,easy driving,and high voltage capacity.However,two factors that limit IGBTs are the latch-up effect under excessive current and the delay in turn-off process due to the trailing hole current.The use of silicon germanium(SiGe),which is a semiconductor material with a narrower band width than silicon,as the anode of IGBTs can significantly reduce the turn-off delay by reducing the conductance modulation effect.In this context,this paper proposes a new idea of using SiGe in the source region of IGBTs to improve the latch-up free characteristic of IGBT devices.By replacing the material of the emitter region of the parasitic transistor from Si to SiGe,the band gap of the heterojunction which equals to E_GE-E_GBis made negative,thus lowering the current gain of transistor to exp((E_GE-E_GB)/KT)times of the original one.Therefore,the idea of using SiGe in the source region proposed in this thesis can reduce?_NPN,thus making the latch-up effect occurrence condition?_PNP+?_NPN=1 more difficult to satisfy,and therefore improving the latch-up free capability and expending the safe operating area of IGBT.Besides that,the decrease of?_NPNwill not bring any negative impact to the IGBT.In order to further solve the latch-up problem,this paper also proposes a LIGBT structure using Schottky barrier as the source region,which basically eliminates the NPN transistor by utilizing the Schottky contact which mainly transmits majority carrier,so that the IGBT device basically achieve latch-up free,and therefore it can work in more huge current mode at low voltage condition without latch-up occurring,and the safe operating area is greatly improved as well.Based on the theory of IGBT utilizing SiGe as source region,this paper also proposes a vertical SiGe source region trench gate-fully surrounded IGBT device structure that can eliminate the deep P-well doping and cathode shorting.The advantages of this structure are:the channel is fully surrounded by the trench gate,so the gate control capability and current density are higher;and by removing the cathode short and P+base region structure,the device cell area can be reduced,which further increases the operating current density and reduces the specific on-resistance;additionally the device process steps are reduced,the processes of ion implantation annealing and lithography is reduced,therefore the fabrication cost and time are reduced;at the same time,the device still maintains excellent latch-up free characteristic after eliminating the P-well.In this paper,we describe and characterize the operating principle of each of these device structures mentioned,and Synopsys'TCAD software Sentaurus is used for simulation verification.After analyzing and comparing the simulation results,it is confirmed that either SiGe or Schottky contact as the source region of IGBT can significantly improve the latch-up free characteristic of the device.