Research On Liquid Level Detection Technology Of Single Crystal Furnace Based On Binocular Vision

Silicon is the main functional material of the electronic information industry and the photovoltaic industry.The CZ silicon Crystal Furnace is the main production equipment of single-crystal silicon.The measurement accuracy of the surface position of the molten silicon in the CZ silicon Crystal Furnace directly affects the quality of the crystal.If the measurement of the liquid surface position is inaccurate,it will lead to an increase in silicon crystal impurities,and may also cause defects in the crystal.The research on the liquid level measurement of the CZ silicon Crystal Furnace has theoretical significance and practical application value.Based on the comprehensive analysis of domestic and foreign data,this dissertation has completed the following work:The Gaussian curve model is used to fit the edge gray gradient of the single-crystal silicon meniscus halo,and the sub-pixel edge points of the halo are extracted as the feature points of the stereo matching;the matching algorithm based on the epipolar line search is used to match the halo edges of the two cameras' images,and the sub-pixel refinement of the matching points is achieved by the curve fitting of the matching cost,and the three-dimensional position of the meniscus halo is accurately detected.The positional change of the halo in the vertical direction is also the change of the liquid surface position of the molten silicon;The liquid level measurement software based on binocular vision for CZ silicon Crystal Furnace is programmed.The binocular vision measurement experiment platform is designed and built to verify the measurement accuracy of the software.The results show that the software system meets the accuracy requirements for crystal growth.The liquid level measurement system based on binocular vision does not require a large field of view,avoids asymmetry of the thermal field structure,and can reduce the difficulty of adjustment process during the crystal growing period.The main contents of the article are as follows:The first chapter expounds the importance of single-crystal silicon and what the influence of liquid level will cause during the crystal growing period,and concretely analyzes the shortcomings of existing CZ silicon Crystal Furnace liquid level measurement scheme.At the same time,it summarizes the field of visual measurement,especially the research results in the field of binocular vision,and points out the key points of binocular vision application in the field of liquid level measurement in CZ silicon Crystal Furnace.In the second chapter,the composition of the binocular vision liquid level measurement system of the CZ silicon Crystal Furnace is discussed.The meniscus halo is used as a substitute for the molten silicon liquid level.The main hardware of the system is selected,the mathematical model of the camera is described,and the overall design of the binocular vision measurement software is carried out.In the third chapter,the edge of the halo generated in the growth process of single-crystal silicon is used as the feature of the halo.The reason why the halo edge is fuzzy is analyzed.The Gaussian curve model is used to fit the edge gray gradient of the meniscus halo,and the coordinate points of the halo edge are extracted as the feature points of the stereo matching.In the fourth chapter,the gray-scale template matching algorithm based on epipolar search is used to match the halo edges of the two cameras' images,and the sub-pixel refinement of the matching points is achieved by the curve fitting of the matching cost,which reduces the least squares error of the triangulation.The three-dimensional position of the edge point of the meniscus halo is accurately detected,which represents the position of the molten silicon liquid level.In the fifth chapter,the system of binocular vision liquid level measurement for CZ silicon Crystal Furnace is implemented.Binocular vision measurement software is developed,including binocular calibration module and measurement module.A binocular vision measurement experimental platform is built.and the accuracy verification test of the binocular vision measurement system is completed.The influence of different sampling methods on the measurement accuracy is compared.The experimental results show that the single-crystal silicon liquid level measurement system of CZ silicon Crystal Furnace meets the precision requirements for crystal growth.The sixth chapter summarizes the full text,discusses the main research contents and looks forward to the research work in the future.