Preparation Research On Growth Of SiC Single Crystal Utilizing Fe-Si Melt As Cosolvent

At present,SiC single crystal used in conmerce were mainly prepared by physical vapor transport（PVT）technique.However,SiC crystal prepared by PVT normally forms micropipe and dislocation which will deteriorate the property of device.Solution growth,is another technology to grow SiC single crystal.As the growth interface is in thermodynamic equilibrium,the bulk SiC single crystals have no microtubules and few dislocations.However,there have been few studies on the growth of bulk SiC single crystals using the technology of solution growth.The main reason is that the growth rate of SiC is too slow to prepare bulk SiC single crystals.As the addition of Fe into Si can increase the solubility of C and thus increase the growth speed of SiC,Fe was employed additive to form Fe-Si solvent in this study.Three methods of liquid phase epitaxial growth such as the top seed crystal solution method,the slow cooling method and the top seed crystal pulling method were employed.The graphite crucible was employed as the solvent container and source of carbon,and the 4H-SiC single crystal was employed as the seed crystal.The thickness of growth layer,crystal type,surface morphology and crystal quality of the prepared SiC single crystal were determined SEM,Raman,UV,AFM and EPMA.The growth parameters of SiC single crystals were optimized to obtain larger growth speed and better quality of the SiC single crystal.The main research contents and conclusions are given as follows:1.The best composition of the Fe-Si solvent for the growth of 4H-SiC crystals were determined:using Fe-xmol%Si as the solvent,x were 30,36,40,50,60,70 and 80,respectively.The Fe-xmol%Si solvent were charged into a graphite crucible and kept in an resistance furnace at 1500℃.In addition,using Fe-ymol%Si as a solvent,y were 0,10,20,30,40,50,60 and 70,respectively,which were charged into an Al₂O₃ crucible and kept at 1450,1500,and 1570℃,respectively,to determine the solubility of SiC.According to the thermodynamic analysis based on the solubility of C and SiC,it was determined that Fe-40mol%Si was the best solvent for growth of 4H-SiC single crystal.2.Using as the solvent,The crystal growth were carried out in the Fe-40mol%Si solvent at1500℃using the Si and C surfaces of the 4H-SiC seed.The results show that the growth speeds using Si and C face were 53μm/h and 57μm/h,respectively.high orientation analysis using EBSD were employed to analyze the crystal growth layer and seed interface of SiC and the results showed that the growth of SiC single crystal in the Fe-Si solvent was homogenous epitaxial growth.3.The rotation speed（seed/crucible）for growing SiC crystal using the top seed crystal solution were 10/3.3 rpm,13/4.3 rpm,16/5.3 rpm,19/6.3 rpm and 22/7.3 rpm,respectively.The corresponding growth rates were 20μm/h,34.4μm/h,40μm/h,35.2μm/h and 26μm/h,respectively.The rotation speed（seed/crucible）for growing SiC crystal using the slow cooling method were 12/4 rpm,15/5 rpm,18/6 rpm,21/7 rpm and 24/8 rpm,respectively.The corresponding growth rates were 15μm/h,28μm/h,47μm/h,42μm/h and 38.4μm/h,respectively.Rotation speed for growing SiC crystal using the top seed crystal drawing method（seed/crucible）were 12/4 rpm,15/5 rpm,18/6 rpm,21/7 rpm and 24/8 rpm,respectively,and corresponding the growth rates were 27.4μm/h,55.1μm/h,79.4μm/h,60.2μm/h and 38.8μm/h,respectively.The tendence of SiC growth rates in the three methods is first increase and then decrease with the increase of the rotation speeds.4.The temperature gradients for SiC growth using the top seeded solution growth method were 30℃/cm,35℃/cm,38℃/cm and 48℃/cm,respectively,and the corresponding the growth rates were 50μm/h,60μm/h,53μm/h and 34μm/h,respectively.The temperature gradients for SiC growth using the slow cooling method were 25℃/cm,30℃/cm,35℃/cm,38℃/cm and 48℃/cm,respectively,and corresponding growth rates were 60μm/h,68.2μm/h,58.2μm/h,54μm/h and 30μm/h respectively.The temperature gradients for Si C growth using the TSSG were 30℃/cm,35℃/cm,38℃/cm and 48℃/cm,respectively,and the corresponding growth rates were 27.4μm/h,55.1μm/h,79.4μm/h,60.2μm/h and 38.8μm/h,respectively.The tendence of SiC growth rates in the three preparation methods is all firstly increase and then decrease with the increase of the temperature gradients.5.The preparation parameters were optimized by the above three preparation methods.The SiC single crystal prepared by the top seed solution method,the main crystal polytype were4H-SiC and a small amount of 6H-SiC.The impurities were analyzed by EPMA and mainly impurities Fe were found.The Fe content is only 0.023-0.114 mol%.The SiC single crystals prepared by the slow cooling method,the crystal polytype were 4H-SiC and 15R-SiC.The crystal polytype of SiC single crystal prepared by top seeded pulling growth method was all4H-SiC.6.According to-EDS analysis,the molar percentage of C in the SiC crystals prepared by the three methods were all higher than that of the SiC standard sample（29.75%）.High-crystallinity SiC single crystal were obtained using the three methods.However,the gro owth rate of the SiC single crystals prepared by the top seed crystal pulling method were higher than those prepared by other methods,and the crystal was more single,which can avoid the occurrence of multi-type defects.In general,the top seed solution method,the slow cooling method and the top seed crystal pulling method were used to enhance the growth rate and crystal quality for growth of SiC single crystalin this study.The research results were important for increasing the growth rate and improving the crystal quality of SiC for SiC growth in the Fe-Si solvent.