The Study Of N-type 4H SiC Ohmic Contact Prepared By Pulsed Laser Annealing

SiC（Silicon Carbide）,one of the representatives of the third-generation semiconductor materials,has been discovered for about 200 years.It has been attracting attention because of its wide band gap,high breakdown field and extremely high thermal conductivity.SiC has great potential in the application of advanced power devices.The preparation of low-resistance and high-reliability ohmic contacts has always been one of the important prerequisites for obtaining high-performance power devices.In this thesis,the effect of different laser energy on ohmic contact of Ti metal with thickness of 80nm on n-type 4H SiC is studied.Ti（80 nm）was deposited on 4H SiC substrate by electron beam evaporation method as ohmic contact metal.The samples were annealed by pulsed laser.The energy intensity of the laser was changed to obtain 9 groups of samples including non annealed samples.The contact surface and interface of these samples were analyzed and characterized by optical microscope,AFM（Atomic Force Microscope）,SEM（Scanning Electron Microscope）,and EDS（Energy Dispersive Spectroscopy）.It was found that as the laser pulse energy increased,the surface roughness of the samples decrease first and then increase.When the laser pulse energy is 1.8-1.9 Jcm^-2,the surface roughness of the sample is the smallest,and the surface is relatively flat without obvious grooves.When the laser energy reaches 2.3 Jcm^-2,the temperature of the irradiated area is too high due to the high laser intensity,and the surface of the sample is completely melted due to excessive burning,which leads to obvious wavy shape and contact failure.It is concluded that when the laser energy is 1.9 Jcm^-2,the surface morphology is the best and the contact cross section is clear.A small amount of Ti enters into SiC,and Si is distributed at all depths.A small amount of C escapes to the electrode surface,leaving C vacancy at the interface,which reduces the potential barrier and helps the carrier transport.Then TLM pattern was used to test the contact resistance.I-V test showed that the as deposited samples,low laser energy samples and high laser energy samples emerged schottky characteristics,and the rest samples emerged ohmic characteristics.The specific contact resistance of the samples with laser energy intensity of 1.9 Jcm^-2 was 6.14×10^-4Ω·cm².Based on the results of ohmic contact experiment,the process flow of SiC JBS（Junction Barrier Schottky diode）is changed from the traditional"back first"scheme to the ideal process sequence of"front first".The front Schottky contact can be completed first,and then the back ohmic contact can be prepared by laser annealing.The process flow including pulse laser annealing for ohmic contact on the back side was drew up,and then made the650V JBS.The results show that the on voltage drop is 1.2 V,the breakdown voltage is 1170V,the reverse leakage current is 25n A,the barrier height is 1.2 e V,and the ideal factor is1.03.