6-inch N-type 4H-SiC Single Crystal Substrate Material Research

The wide bandgap SiC semiconductor is a new generation of power semiconductor developed after the silicon semiconductor.It is mainly used in power electronics,microwave electronics,optoelectronics and other fields,and can significantly reduce system power consumption,improve energy conversion efficiency,and reduce system volume.It involves national defense,aerospace,microwave communication,high-end equipment manufacturing,new energy,semiconductor lighting and many other strategic industries which are encouraged by the country.And it has great significance for the protection of national defense security,the development of high-end equipment manufacturing industry,and the industrial upgrading.With the continuous development of SiC industry chain,the demand for SiC substrates has been increasing,as well as the quality requirements.In order to realize the industrialization of 6-inch N-type 4H-SiC single crystal substrates,we researched how to control the defects in crystal growth process by using self-developed crystal growth equipment.And we successfully achieved the wafer process of 6-inch crystal and got high quality 4H-SiC single crystal wafers.Then high voltage and high power Schottky diodes were fabricated on the wafers,to verify the practicability of the SiC materials.Following is the main research work of this paper:1.The thermal field distribution of SiC single crystal growth was analyzed by numerical simulation method.Based on the ideal thermal field for crystal growth,the influence of power frequency,furnace dimensions,insulation thickness,and crucible size on the thermal field was investigated,and the structure of heating system was optimized.According to the optimized thermal field,the integrated design of growth equipment was carried out to improve the automation level and safety level,thus forming a stable and reliable operation of the equipment.2.The formation mechanisms and the influencing factors for polytype inclusions,micropipes and dislocations were investigated,based on which the growth temperature,the growth rate,the temperature gradient and the quality of seed were optimized.100%4H polytype,micropipe density below 0.1/cm2,TSD density below 1000/cm2,BPD density below 2000/cm2 were achieved.3.The wafer processing technology of 6 inch was studied.The influence of string tension,string velocity,feed rate on the slicing quality during consolidated diamond multi wire cutting,and the influence of oxidants and additives on the surface roughness and flatness during chemical mechanical polishing were investigated.Accordingly,the process parameters of slicing and polishing were improved and warpage less than 20 microns were achieved.4.Based on our 6 inch N-type silicon carbide substrates,1200V/12A and 1200V/35A Schottky diodes were fabricated.According to device simulation,DOE experiments and process precision,the dimension ratio,linewidth ratio,and configuration of the junction barrier region and Schottky region for JBS were improved.The epitaxy,dielectric deposition and high temperature ion implantation processes were also investigated and improved.The test results show that the performance of the devices is comparable to that of the world-class products.