Effect Of Ohmic Contact On The Electrical Properties Of SiC MOSFETs

Power electronic devices play an important role in many fields,such as:new energy access,FACTS high-voltage direct current transmission,smart grid construction,etc.,of which power semiconductor devices are the core elements of power electronic devices.In order to fundamentally improve the reliability and stability of power electronic equipment,the overall loss of the system needs to be reduced,and it is necessary to study new semiconductor devices with high withstand voltage,low power consumption and high temperature resistance.The ohmic contact between the electrode metal and the silicon carbide device plays an important role in the power semiconductor device and is part of the total resistance of the device,which directly affects the on-state loss of the device,which in turn affects the overall performance and efficiency of the device.With the increase of the nominal power of the power device,the current density of the electrode contacting the metal flowing through the device also increases accordingly,which requires a lower contact resistance between the metal and the semiconductor to reduce the contact power consumption at the contact point of the device electrode and improve the reliability of the contact.There is a close relationship between ohmic contact and electrical properties,because Ohm’s law describes the relationship between current and voltage and resistance,i.e.current equals voltage divided by resistance.and this relationship is based on the conductivity and resistivity of the material,which in turn are affected by the physical and chemical properties of the material itself.Therefore,it is of great practical significance to study the effect of SiC MOSFET ohmic contact on electrical properties.Firstly,in order to accurately measure the specific contact resistance of SiC MOSFETs,the process design of SiC MOSFET ohmic contact TLM samples was carried out.Through process pre-treatment,step isolation etching,sacrificial oxidation,metallization,and alloying,the corresponding transmission line model sample for ohmic contact resistance testing is finally obtained to produce a process assembly.Secondly,this paper studies the selection of different metal or alloy systems for n-type SiC MOSFET ohmic contact research,including Ni,Ti and Ni/Ti forming ohmic contact with n-type SiC,respectively,and obtaining the optimal n-type SiC MOSFET ohmic contact process formula and conditions by comparing different contact metal structures,deposition process methods,alloying rapid thermal annealing process conditions and the specific contact resistivity of the sample.Finally,by performing 400℃ aging experiments on the ohmic contact of n-type SiC MOSFETs of Ni,Ti and Ni/Ti metals,the thermal stability/reliability of n-type SiC MOSFETs based on Ni,Ti and Ni/Ti metals under these optimal ohmic contact process conditions was analyzed and evaluated,and the influence of ohmic contact and its reliability on electrical properties was analyzed.