| The expensive SiC substrate is a key factor restricting the cost of the device.The development of large-diameter,thick ingot SiC growth technology is expected to reduce the cost of SiC substrates.At present,although the preparation of SiC crystals has achieved the replacement of 4 inches to 6 inches,the growth of 6-inch SiC crystals still has problems such as insufficient thickness of the growing ingot,high thermal stress and high defect density.To this end,this article uses finite element analysis to carry out PVT method 6-inch SiC crystal growth system modeling,to study the influence of process parameters,insulation layer,crucible,and induction coil on the thermal field and growth rate,and analyze the main factors affecting the growth of thick ingots.Explore the growth process to reduce crystal thermal stress and dislocation methods.The main work and conclusions of the thesis are as follows:1.The effects of process parameters,insulation layer,thermal component structure and size on thermal field and growth rate are studied.The high temperature area of the traditional crucible moves down due to the movement of the coil,and the heat generation rate at the edge of the crucible lid decreases,resulting in a lower temperature at the edge of the seed crystal.The high temperature area on the surface of the seed crystal moves away from the edge to the center position,resulting in an "M"-shaped temperature field distribution."W" type crystal growth rate.Increasing the number of coil turns can improve the "W"-shaped growth rate distribution.2.A crucible lid structure with groove structure is proposed.The structure is provided with a heat dissipation groove on the top of the crucible cover,which effectively improves the "M"-shaped temperature field distribution on the surface of the seed crystal,and the radial temperature gradient is reduced by 33.3%.The main factors affecting the growth of thick ingots are studied.·As the thickness of the crystal ingot increases,the heat dissipation efficiency at the top of the crucible lid decreases,leading to an increase in the surface temperature of the crystal growth,making the growth rate appear to be fast and then slow down,and the temperature gradient between the axial direction of the cavity and the radial direction of the seed crystal decreases,and the surface of the powder source Recrystallization occurs,causing the particle size of the powder source to increase and the porosity to decrease.3.The growth process of secondary feeding and its low thermal stress seed crystal bonding method are studied.A crucible structure with graphite rings is proposed to reduce the radial temperature gradient of the ingot,and the axial temperature gradient can be reduced at the same time by increasing the thickness of the top carbon felt.The center thickness of the ingot grown by the improved component structure is 31.2mm,and the edge thickness is 27.1mm,which is more uniform than the crystal thickness without ring structure,the maximum shear stress is reduced by 21.6%,and the maximum dislocation density is reduced by 51.3%.The improvement of the thermal stress of the ingot by the seed crystal fixing method was studied.The study found that the use of the slip fixing method reduces the maximum shear stress to 18MPa between seed and crucible lid,which was reduced by 57.4%,and the maximum dislocation density was 6.5×106/cm2.Reduced by 82.8%,using free fixation between seed and crucible lid,the shear stress is less than the critical value of 1MPa,resulting in zero dislocation density. |
