Study On The Process Parameter And Thermal Field Structure Of 4H-SiC Crystals Grown By TSSG Method With Different Crystal Sizes

The current method for the industrial growth of SiC crystals is mainly physical vapor transport（PVT）method.However,the SiC single crystal still faces challenges,such as high dislocation density and high cost.The top-seeded solution growth（TSSG）method can grow SiC crystals in near thermodynamic equilibrium with the low latent heat of crystallization and relatively low growth temperature,which is conducive to reducing the dislocation density in crystals and is one of the ideal methods for growing high quality and low cost SiC crystals.But the main problems of growing SiC crystals by TSSG method are the easy volatilization of Si in solution at high temperature,which makes auxiliary solution system deviate from the initial design working condition.Meanwhile,the formation of large steps during the growth of SiC crystals causes surface roughening and leads to inclusions defects（auxiliary solution inclusions）.In this study,we first explore the process of growing 32 mm diameter SiC crystals by TSSG method,focusing on the effects of crystal growth surface,growth temperature,crystal rotation rate and aluminum（Al）content on crystal growth.The results show that the crystals grown on the C surface are 4H-SiC,while the crystals grown on the Si surface have polymorphic transition.When the growth temperature increases from1700℃ to 1800℃,the full width at half maximum of the rocking curve increases from71.7 arcsec to 79.6 arcsec,and the surface morphology of crystal also changes from smooth to rough.When crystal rotation rate was increased from 0 rpm to 10 rpm and the Al content was 4 at%,the FTO peak width decreased from 3.90 cm^-1 to 3.82 cm^-1.Based on the above process exploration,4H-SiC crystals with 1 mm thickness and 44.8mm diameter（1.4 times of expansion）were obtained using the C surface,growth temperature of 1700℃,crystal rotation rate of 10 rpm,and 4 at%Al content,and the half-peak width value of rocking curve was 71.7 arcsec.Second,the thermal field structure of 2-inch diameter SiC crystals grown by the TSSG method is explored to compare the effects of the crucible cover,crystal holder structure and the height of auxiliary solution on crystal growth.Compared without crucible cover,spontaneous nucleation inside the auxiliary solution was obvious after the addition of the crucible cover.When the crystal holder structure was adjusted from a 45 mm diameter hollow rod to a 25 mm diameter solid rod,crystal type changed from4H-SiC to 6H-and 15R-SiC,resulting in polycrystalline inclusions.When the auxiliary solution height was increased from 35 mm to 60 mm,the volatilization of Si in the auxiliary solution was significantly reduced,and the half-peak width value of FTO peak decreased from 3.97 cm^-1 to 3.78 cm^-1.In summary,for the 2-inch thermal field structure,a hollow rod with a diameter of 45 mm and an auxiliary solution height of 60mm can improve the surface step morphology and enhance the stability of the crystal type.Finally,a two-dimensional global heat and mass transfer calculation model is developed for the 4H-SiC crystal growth process by TSSG method.The effects of crystal rotation rate on the thermal field,flow field,C concentration distribution and growth rate are investigated.The numerical results show that crystal rotation rate makes the solution move upward,which improves the distribution uniformity of radial temperature and carbon supersaturation at the growth interface.As the crystal rotation rate increases,the thickness of the diffusion boundary layer at the growth interface decreases and the maximum value of the C concentration gradient becomes larger,leading to an increase in the maximum growth rate.However,with the increase of crystal rotation rate,the radial distribution uniformity of growth rate shows a trend of first getting better and then getting worse.When the crystal rotation rate reaches 45 rpm,the radial distribution uniformity of growth rate is the best.In this study,the effects of different process parameters and thermal field structures on the growth of 4H-SiC crystals with different crystal sizes by TSSG method were studied by combining experimental and numerical simulation methods.It provides a scientific theoretical basis for improving the surface morphology and quality of SiC crystals.