Research On Growth Equipment And Temperature Control Method Of Large Size Silicon Carbide Single Crystal

The preparation of silicon carbide single crystal substrate material is the upstream link of silicon carbide industry chain.At present,the mainstream silicon carbide substrate products in the world are mainly 4-6 inches,but some advanced enterprises have successfully grown silicon carbide single crystals with a diameter of 8 inches.In recent years,China is also vigorously developing the silicon carbide industry.However,due to the late start and the serious technical blockade abroad,there is still a certain gap between China and foreign countries in terms of crystal growth technology and equipment.This thesis studies the silicon carbide single crystal growth equipment and its temperature field control technology,in order to break through the foreign neck technology and provide reference for the independent development of a new generation of large-size silicon carbide single crystal growth equipment.Firstly,this thesis studies the growth method of silicon carbide crystal,takes the physical vapor transport method(PVT method)as the main research object,determines its growth process and process,analyzes the growth kinetics in the growth process of this method,and obtains the crystal growth rate curve at the seed crystal.The growth of silicon carbide crystal needs a very suitable temperature field environment,but because the crystal growth is carried out in a closed graphite crucible,it is impossible to directly observe the crystal growth process.Therefore,this thesis simulates the temperature field and gas-phase flow field in the crystal growth process by means of numerical simulation.Firstly,the mathematical model of heat and mass transfer in the crystal growth process is established,Then the finite element modeling is carried out by using COMSOL simulation software to determine the characteristic parameters of each component,analyze the influence of current size,frequency,coil structure and other factors on the temperature field distribution,and study the influence of natural convection on mass transfer effect.Then,this thesis designs the equipment structure of silicon carbide crystal growth by PVT method.Firstly,the structural configuration of the crystal growth furnace is determined,and then combined with the heat transfer theory,the structural parameters of each component are determined.The subsystems such as induction heating system,gas supply and vacuum air circuit system,crucible motion system and cooling system are designed,and the three-dimensional model diagram of the equipment structure is displayed.Finally,the temperature control system of the crystal growth furnace is modeled.According to the characteristics of nonlinearity,large lag and instability of the temperature control system of the crystal growth furnace,the traditional temperature control algorithm is improved,and a new temperature control strategy is designed by combining Smith prediction compensation and fuzzy control,which is verified by Simulink.The results show that Smith fuzzy PID control mode has the advantages of small overshoot,less vibration times and strong anti-interference ability,and has better control accuracy and dynamic characteristics.To sum up,this thesis studies the large-size silicon carbide single crystal growth system,analyzes the temperature field and flow field environment in the furnace through simulation,optimizes the system structure,and improves the temperature control algorithm,which provides a certain research basis for the development of a new generation of silicon carbide crystal growth equipment.