Thermal Field Simulation Of SiC Crystal Based On PVT Method And P-type 4H-SiC Single Crystal Growth

Silicon carbide?SiC?is a new type wide bandgap semiconductor material,which can replace traditional semiconductor materials in the extreme environments of high temperature,high voltage and high frequency.Physical vapor transport?PVT?requires more than 2000?in a sealed crucible to grow a large sized SiC wafer.Because the high cost,long time and temperature distribution can not be measured directly,we must simulate the thermal field of SiC crystal growth.So we can master its growth rules and optimize the experimental device to obtain high quality crystals with low cost and high efficiency.Most electronic devices require the participation of n-type and p-type conductive SiC materials.Due to the limitation of doping technology,the resistivity of p-type substrates is 50 times higher than that of n-type substrates.The fabrication of p-type SiC wafers with high doping,low resistivity and low defects is still an urgent problem to be solved.Thermal field simulation was carried out for the growth of SiC single crystal by PVT.High doping and stable 4H-SiC crystals were prepared by adjusting the doping process of p-type SiC crystals.Specific are as follows:?1?The experimental device for the growth of SiC by PVT method was modeled.The thermal field of SiC crystal was simulated by using VR-PVT SiC6.5 simulation software of STR Company,it aims at the factors affecting the growth of SiC crystal,such as temperature,pressure,coil position,distance between powder and seed crystal and size of temperature measuring hole.The simulation results show that the growth temperature of the system is about2200?and the pressure is 400-500 Pa.When the distance between seed and powder is 79 mm and the radius of temperature measuring hole is 10-15 mm,the average growth rate can be maintained at 100-140 um/h,thus avoiding the decomposition of seed crystals at low rates and the uneven growth of high-rate crystals.The temperature field in the growth chamber can be fine-tuned by adjusting the coil height and the temperature measuring hole depth.?2?Simulation of crystal growth can give the crystal state after 50 hours of growth.The change of temperature field in the crystal after changing the structure of crucible was studied,and the influence of temperature field on thermal stress was analyzed.It is found that the temperature gradient distribution in the crucible can be effectively improved by changing the side and top structure of the crucible.The design of thin-walled crucible and hollow crucible cap can effectively reduce the thermal stress in SiC crystal and move the high dislocation area to the edge of the crystal.The optimized crucible structure can reduce the maximum thermal stress from 1.85 MPa to 1.58 MPa,and move the dislocation density region from 20 mm to 45 mm away from the crystal symmetry center.This crucible structure optimization concept can also be applied to other PVT growth devices.?3?The process of p-type SiC doped with Al element was investigated.The causes of micropipe in the first growth crystals were analyzed.It was found that the rapid sublimation of Al source at the initial stage resulted in the formation of carbon inclusions in the crystals,which led to the formation of micropipe.An efficient experimental method to obtain the optimum process was proposed.In one experiment,p-type SiC crystals were grown at three temperatures.Ar and N₂ were used as filling gases to reduce the stress in the crystals.A 4-inch4H-SiC single crystal substrate with a resistivity of 0.485?.cm was obtained.The half-width of Raman LOPC mode was fitted with the carrier concentration data measured by secondary ion mass spectrometer.The empirical formula of carrier concentration for p-type 4H-SiC was revised.The maximum carrier concentration was 9.62×10¹88 cm^-3,and the calculation error was within 3.87%.