Research On Pressure Control System Of SiC Growth Furnace

As an excellent representative of the third generation semiconductor materials,SiC not only has high temperature resistance,stable chemical performance,good conductivity and thermal conductivity,but also has strong radiation resistance.These advantages determine its broad development prospects.At present,the PVT method is widely used to grow SiC crystals.It is grown in a fully enclosed crucible.Corresponding pressure changes are needed at different stages to ensure the growth speed and quality of crystals.Reliable pressure control in SiC growth furnace is particularly important.With the rapid development of semiconductor industry,the domestic demand for SiC crystal is increasing year by year.However,most of the equipment for SiC growth in China still need to be imported from abroad,and the accuracy of the matching equipment is limited.All these have resulted in the inconvenience of equipment maintenance,the inadequacy of the accuracy of sensors and other equipment,and the high cost,which has seriously restricted the development of SiC growth and application in China.According to the requirement of the project"Development of 6-inch SiC single crystal furnace"of the National Natural Science Foundation of China,the pressure control system of SiC growth furnace is studied,which provides a reference for the pressure control in the chamber during the growth of SiC.single crystalIn this paper,the current demand form of semiconductor is briefly introduced,and the advantages and application fields of the third generation semiconductor material SiC crystal are described first.Then the current status and research progress of SiC growth at home and abroad are introduced,and the specific equipment defects are put forward.Secondly.the growth method of SiC and the composition of growth furnace are briefly described.On this basis,we designed and realized the hardware module of pressure control system.researched the characteristics of growth furnace equipment and parameter setting,tested and analyzed the PID algorithm control parameters.The specific work of this paper is as follows:(1)According to the current situation of supply and demand for SiC in semiconductor industry,in this paper,the restrictive factors of affecting the growth and application of SiC and the deficiencies of pressure control equipment of SiC growth furnace at present are pointed out,and the design goal of pressure control system of SiC single crystal growth furnace is put forward.The composition and main technology of growth furnace for PVT method,which is the most commonly used method for growing SiC at present,are described and analyzed.(2)Aiming at the pressure control system of SiC single crystal growth furnace proposed in this paper,a high precision and high reliability pressure control circuit is designed and implemented.The selection of devices and the design of circuit board in the hardware part of the control circuit are completed,and the design and implementation of the software part of the control system are also carried out.(3)We introduced the corresponding relationship between the feedback value of the serial port and the actual voltage and current,and the conversion relationship between the voltage and the voltage of the capacitive diaphragm vacuum gauge.Through many experiments,the pressure curves of SiC growth furnace in the process of pure air intake and air extraction are obtained,and the stable pressure values of furnace chamber under different valve opening values are tested and sorted out,we completed the corresponding curves of pressure and opening.(4)In the process of system debugging,many experiments were carried out to tune the parameters of the PID algorithm.Through comparative analysis,the most suitable curve was found and the corresponding coefficients were determined.In the research results of this paper,the most suitable PID control parameters were finally determined as Kp=2,K1=0.02,Kd=0.01·The pressure control system of SiC growth furnace designed and implemented in this paper has greatly reduced the cost of the system compared with the imported equipment abroad.At the same time,it has improved the reliability of hardware circuit design and the accuracy of algorithm control,shortened the response time to pressure,and realized the precise control of system pressure.