Research And Realization Of Single Crystal Silicon Diameter Measurement Technology

With the rapid development of solar photovoltaic cells,the demand of single crystal silicon wafers in the domestic and foreign markets is daily increasing.Especially large diameter monocrystalline silicon will be in short supply for a long time in the future.There are still some gaps between the mature monocrystalline silicon production process and advanced technology,which need to be further studied and improved.The monocrystalline silicon diameter measuring system uses CMOS camera to photograph the single crystal silicon Czochralski stage.Because the melting point of silicon crystal is as high as 1 450 degrees Celsius and the CMOS camera can only withstand 60 degrees Celsius,it can only be taken by thermal insulation equipment.The edge of the image is elliptical semi-circular arc.In order to provide diameter data for automatic monocrystalline silicon control equipment,non-contact image measurement is needed.Traditional image processing architecture captures images by front-end and processes images by back-end.This method need large bandwidth to communication a nd it also need a large consume to central processing unit so that it is difficult to achieve the algorithm.In order to improve the manufacturing level of large diameter silicon single crystal and meet the market demand for silicon,the paper studies the analysis and improvement of the measurement algorithm.The best solution is distributing more work to front-end,processing the captured images in real time.Only in this way we can reduce the cost of bandwidth.High speed FPGA can process the images concurrent,so it can marked raise the processing ability.Images processing system often be divided two categories according to different levels.Different categories needs different processing system.Low-medium level algorithms have many repeated calculation if using the concurrent nature of FPGA can optimize the performance.In the other side,high-medium level algorithms have many judgements and jumps so it usually processed by central processing unit.In this paper,according to the feature of the image,the region of interest can be automatically selected without user participation.The region of interest can be selected quickly and can reduce the computational complexity of the latter algorithm.In view of the noise interference in the process of image acquisition,this paper adopt an adaptive median filter,which can not only remove salt and pepper noise,but also retain the edge information of the image.In order to provide the diameter data of single crystal,the diameter of the extracted aperture edge should be measured.In this paper,under the prior condition of camera tilt angle,the ellipse fitting of traditional least square method is improved,and the diameter of monocrystalline silicon is finally calculated.