Study On Growth Of Silicon Carbide Crystal By Flux Method

Silicon carbide(SiC),as an important third generation semiconductor material,has excellent properties such as high thermal conductivity,high power,high temperature resistance,radiation resistance and so on.It has been used in the fields of smart grid,electric vehicles,high-speed trains and advanced radar.Developing the SiC industry has important implications for many countries.The new emerging method,SiC single crystal grown by liquid phase growth technology shows lower concentration defect density compared with the SiC wafer obtained by previous physical vapor transport method(PVT method).That is to say,it can grow high quality SiC single crystal by solution growth method.Using SiC substrate material with low defect density is the fundamental way to effectively improve the device operating voltage,sharply reduce the device switching loss and improve the working frequency.However,compared with PVT method,the technology maturity of growing SiC by liquid phase method is lower,and the research progress is lagged behind.The main problems are as follows:(1)The selection and proportion of flux system need to be further explored and improved;(2)Controllable dissolution of carbon and directional growth of silicon carbide in the growth process are also needed to be concerned.In this thesis,the selection and proportion of flux for liquid phase growth of SiC crystal are preliminarily studied.By optimizing the growth structure and the process of top seed solution method,the growth rate and the process of liquid phase growth of SiC crystal are studied.The main research contents are as follows:1.The growth conditions of SiC crystal,such as the flux,the seed suspender structure and thermal fields distribution,and the seed crystal bonding have been preliminarily explored.The flux systems,Cr-Si and Fe-Si,have been initially selected.The thermal field distributions of three different suspender structures have been simulated and analysed.Meanwhile,the bonding problem of the seed wafer has also been solved.2.The growth experiments in Cr-Si and Fe-Si systems have been carried out.In the Fe rich system,the surface of the seed crystal is covered by flux,without crystal formation.In the Cr rich system,the surface of the seed crystal has been grown by polycrystal and wrapped by the flux.The graphite crucible has been cracked after growth.Due to the large temperature gradient,the growth rate of polycrystal on the seed surface can reach 417 μm/h in the flux system with less Cr.3.The growth experiments in Cr-Si-Al system have been carried out and optimized the technological process.We have selected the appropriate temperature of falling the seed crystal according to the etching condition of the seed crystal.We have studied the effect of growth temperature on the morphology and Raman spectrum of SiC single crystal,by improving the growth structure and reducing the temperature gradient inside the crucible.The growth mode has been discussed.