| Silicon Carbide (SiC) has received a substantial increase in research interest due toits wide band gap, high critical field strength, high radiation tolerance and excellentthermal conductivity. SiC-based devices are deemed as a candidate to replace Si-baseddevices in applications of high temperature, high power, and high radiation hardness. Ina power system, a well-built rectifier shall have low conduct resistance, low reverseleakage current, high breakdown voltage and fast switching speed, making SiC acandidate for high-performance Schottky barrier (SBD) and junction barrier Schottky(JBS) diodes. SiC SBDs have been studied and reported worldwide, but the nationalreports, especially those about fabrication, are relatively limited. Though the materialquality and techniques have been improved enormously, there are still many problemsleft to be studied and improved. In this work,4H-SiC SBD and JBS diodes have beenthus designed, fabricated and characterized, the main work including:1. The characteristics of4H-SiC SBD and JBS diode were simulated and analyzed.Suitable models were built based on the performance of the devices, and the simulationusing ISE-TCAD was carried out to understand the influence of the structure on thecharacteristics of devices.2. The key techniques in manufacturing SiC devices were analyzed. N-epilayerswere grown on the4H-SiC substrate by LPCVD and characterized using FTIR, SIMS,and AFM. Furthermore, Trim was used for the simulation to determine the dosage andenergy for selective doping with ion-implantation, and the simulated results werecompared with the empirical findings. Finally, a study on active annealing was carriedout; and results showed that masking by carbon film effectively protects the surface ofthe wafer during annealing.3. A JBS diode terminated by field guarding ring (FGR) was simulated, and bothSBD and JBS diode using FGR were fabricated. Two different techniques wereemployed in fabricating the P-type Ohmic contact: independent metal deposition andannealing, and simultaneous fabrication of the Schottky contact and ohmic contact. TheDC characteristics of devices produced by these two methods were compared tounderstand the difference between those two techniques.4. Directed towards the sensitivity of the devices on the charges in the oxidationlayer, the offset field-plate (offset-FP) was employed as the edge termination of SBD and JBS diode. With stimulation and theoretical analyses, effects of the charges in oxidelayer were studied, and the structure were determined thereby. The devices werecharacterized by DC and switching tests; all these tests were also carried out in a variedtemperature to show the temperature dependence of the devices’ performances. Thereverse recovery characteristics show that with B and Al ion co-implantation, therecovery time of a4H-SiC JBS is remarkably reduced to44ns at room temperature.5. A Floating metal ring (FMR) was fabricated as the edge termination for4H-SiCSBD to avoid ion-implantation and activating annealing. Ti and Ni were employed toform the Schottky contact. Using Ti contacts, SBD reached a forward current density of1600A/cm~2when forward voltage is4.4V. Meanwhile, Ni contacts formed a higherSchottky barrier height, yielding SBDs with lower reverse current density, which islower then10-7A/cm~2within200V, and4H-SiC SBD breakdown voltages of850V wereachieved. Furthermore, junction termination extension (JTE) was also simulated instudy of SBD to find suitable parameters of structure. In the experiment, a4H-SiC SBDterminated by JTE with breakdown votage of950V is achieved; the forward currentdensity of which is803A/cm~2at5V. |
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