Study On4H-SiC Schottky Diode

High-voltage Silicon Carbide Schottky Diode has the advantages of highbreakdown voltage, low on-resistance, fast switching speed and can work under hightemperature. It has been applied in many areas of the national economy and military,one of which is power electronics.There are still a lot of problems in the research of silicon carbide device nowadays.For example, the junction termination still need optimization, and the oxide layergrowth, the ohmic contact and annealing, the Schottky contact and other processconditions need to further be improved.In this paper, the different structure of the silicon carbide Schottky were simulatedand analyzed to solve above problems. Manufacturing process was focused on in4H-SiC Schottky diode.1. We study the effect of junction terminal on breakdown voltage. First, simulationof field plate structure of the Schottky diode was done to find the effect of the oxidethickness and the length of the field plate on breakdown voltage. The results ofsimulation show that breakdown voltage is largest, when oxide thickness is0.4μm, andthe breakdown voltage of the device is no longer increasing with the increases of thelength of the field plate, when the field plate length reached at8μm. Second, a siliconcarbide Schottky diode with a field limiting ring and field plate was simulated tooptimize the doping of field limiting ring and the length of the field plate. The resultsshow that Schottky diode under the different doping in the field limiting rings needsdifferent length of field plate. Finally, a trench structure of the schottky diode wassimulated to get the best schottky diode whose breakdown voltage is953V and forwardvoltage is0.98V when the forward current is100A/cm².2. In order to obtain high performance of the silicon carbide Schottky diode, theohmic contact and annealing, oxidation and Schottky contacts annealing were studied.First, the different surface treatment and annealing after the ohmic contact is researched.It was found that SiC under RCA cleaning also didn’t form an ohmic contact after theannealing at550℃in5minutes. The characteristic of ohmic contact is preferable after annealing under875℃in30seconds; Silicon carbide after dry oxidation and BOEetching treatment formed ohmic contact after annealing at350℃in5minutes. Ohmiccontact characteristics reached the best after annealing under900°C. Second, study theinfluence of the annealing temperature on the oxide layer of silicon carbide in an argonatmosphere,the result is that the quality of the SiC thermal oxide layer is best after theannealing at600℃. Finally, after studying ohmic contact, annealing temperature andthe dielectric layer of the Schottky diode were studied.4H-SiC Schottky diode with thedielectric layer grown by dry oxidation and PECVD had the best performance afterannealing at400℃, whose ideal factor was1.447and the Schottky barrier height is1.029eV and the breakdown voltage is220V. Compared characteristics of4H-SiCSchottky diode with the dielectric layer grown by wet oxidation and PECVD tocharacteristics of4H-SiC Schottky diode with the dielectric layer grown only byPECVD, it is found that4H-SiC Schottky diode with the dielectric layer grown by wetoxidation and PECVD has the best performance, whose ideality factor of1.114andSchottky barrier height is1.020eV and the breakdown voltage is345V and the reversesaturation current isJ_S=.2×10^-10A/cm².