Structure Optimization And Experimental Investigation Of High Voltage 4H-SiC PiN Diodes

Silicon Carbide(SiC) has shown great promise for high-temperature, high-voltage, high-power and high-frequency applications due to its superior electrical and physical properties such as wide bandgap, high critical electric field, high thermal conductivity and high electron saturated velocity. Compared to Silicon(Si) counterparts, 4H-SiC PiN diodes own 2 to 3 orders of magnitude switching speed, higher temperature tolerance, higher current density and higher power density, bringing Si C Pi N power rectifers a very promising development potential and research value in the field of power electronics. For the present, the study in SiC PiN diodes is still at primary research stage which is far behind the foreign countries. Based on the domestic research and process conditions, this thesis aims at the design and optimization of high voltage 4H-SiC PiN diodes in the hope of providing theoretical and experimental reference.Through the Silvaco Athena and Atlas semiconductor process and device two-dimensional numerical simulation platform, the conduction and blocking characteristics of high voltage 4H-SiC PiN diodes are studied and optimized. With the basic cell parameters, the effects of carrier lifetime and temperature on the forward characteristics of the PiN diodes are studied. The anisotropic impact ionization model of silicon carbide is investigated, and the influence of mesa height, mesa angle and micro trench on the breakdown characteristics of high voltage 4H-Si C PiN diode is analyzed. Then the Junction Termination Extension( JTE) termination structure is designed. Through the breakdown voltage and electric field analysis, the Two-SM-JTE terminal structure with a wide dose window is proposed, which can reach the target breakdown voltage of 3300 V in the dose range of 1.0-2.6×1013cm-2.The high voltage 4H-SiC PiN diodes are experimentally studied. The ion implantation process is firstly investigated. Then based on the domestic research conditions, the process flow is determined and the layout is designed, following with tapeout experiments. The forward conduction, reverse blocking and reverse recovery characteristics of the 4H-Si C PiN diodes are tested and analyzed. Measurement results demonstrate that the on-state voltage drop of the single-zone JTE 4H-SiC PiN diode is 3.2V. When the temperature is increased from 25 oC to 155 oC, there is an insignificant 0.2V change for the fabricated 4H-Si C PiN rectifiers, showing good temperature stability. When the JTE dose is 1.1×1013cm-2, A maximum reverse blocking voltage of 3.8kV is obtained with a mesa height of 2.1 μm and a mesa angle of 22°, corresponding to about 80% of a parallel plane breakdown voltage. The breakdown voltage of the fabricated 4H-SiC PiN diodes improves with the increase of the JTE length, and becomes saturated at a JTE length of 50μm. But the saturated breakdown voltage is 200 V lower than the simulated value. The reverse recovery time decreases with the increasing of reverse voltage, the rising of current slew rate and the reduced forward current.