The Study On 4H-SiC Homoepitaxial And High-voltage Schottky Barrier Diode Devices

4H-Silicon carbide (SiC) material and its High Voltage SBD devices have shown the attractive prospects for wide range applications to the various field of social economy because of their excellent physical and electrical properties, one of which is the application in power electronic engineering. The high quality 4H-SiC single crystal material is the base for achieving 4H-SiC SBD devices with high performance. Needless to say, both 4H-SiC epitaxial material growth or manufacture of high-voltage SBD devices still exist many problems and difficulties,Seriously restricted the development of high-voltage SBD device.It led still the Significant difference between our country's overall level and international advanced level to lack the in-depth, detailed and systematic study on 4H-SiC wide bandgap semiconductor and 4H-SiC SBD devices key theoretical problems because domestic 4H-SiC single crystal epitaxial material preparation and 4H-SiC SBD device development started late. There are following problems: (1) high-quality 4H-SiC epitaxial film growth mechanism and key technologies have not yet been clearly understood; (2) the lack of a series of test and characterization methods for characteristics of 4H-SiC homoepitaxial layers; (3) there are the lacks of the accurate junction terminal data for high voltage SiC SBD device; (4) the SiC SBD device key technologies are yet unresolved.In this dissertation, the main problem mentioned above is studied systematicly. The main studies and contributions of this dissertation are as follows.1. The key processes of growth are studied by experiments based on the theoretical analyse, and the major factors to affect the key processes are obtained. The trend of parameters and process are achieved.2. 4H-SiC homoepitaxial layers are tested. The quality of 4H-SiC homoepitaxial layers is evaluated and the depth is calculated using the intensity and frequency of interference fringes in FTIR spectrum. The surface topography and element of 4H-SiC homoepitaxial layers are qualitatively and quantitatively analysed by SEM, AFM.3. The quantitative relationship between high-voltage 4H-SiC SBD reverse breakdown voltage with the SiC semiconductor material critical electric field, the doping concentration and the thickness of epitaxial layer is proposed. The Schottky barrier height, series resistance and ohmic contacts under room temperature are analyzed, and their relative formulas are obtained. Then it is demonstrated that the current conduction mechanism follows the thermionic emission theory at the temperature range from 300K to 500K under forward biased conditions. A theoretical model used in calculating reverse current density is proposed considering several current transport mechanisms. The comparison of theoretical results with experimental data indicates that tunneling effect is the dominant mechanism under room temperature, but the thermionic emission current and the generation current in the depletion region will increase greatly when temperature becomes high so that they are no longer negligible.4. The necessity of junction termination technique for high-voltage 4H-SiC SBD is described because of the premature breakdown voltage occuring with electrical field crowding at the device edge. Some common plane termination extension techniques are put forward including field plate, guard ring, etch contour, field limiting ring and, junction termination extension technique, etc.. The digital simulation software ISE-TCAD characteristics and simulation operation process are introduced. The breakdown voltage characteristics of high-voltage 4H-SiC SBDs with field limiting rings and junction termination extension techniques are simulated respectively. The influence relations on the high voltage 4H-SiC SBD breakdown voltage obtained by the simulation substration doping concentration, thickness and junction termination structure will contribute to the design and development for high voltage 4H-SiC SBD.5. The ohmic contact and Schottky contact are studied because they are basis and key process of the farbrication for high-voltage 4H-SiC SBD device. According to the simulations results and our actual process conditions, the high-voltage Mo/4H-SiC SBD with field limiting ring and the high-voltage Ni/4H-SiC SBD with junction termination extension are farbricated respectively. The experimental results show that the protections of the two planar junction termination structures are very effective. This will provide for the experiment foundation for high-performance 4H-SiC SBD farbrication in the future.Finally, the ideas for future improvement are presented according to the preliminary experimental results.