Melt level measurement for the CZ crystal growth using an improved laser triangulation system

An improved image-based laser-triangulation measurement system is proposed in this paper to measure the melt level in CZ crystal pullers. The system uses a line laser to overcome the deficiency of the traditional laser-triangulation system caused by the heat shield. The laser line projected to the melt surface and the bottom of the heat shield generates two scattered bars, which are captured by the camera. The relationship between the pixel distance of the two bars and the melt level is studied. An optimized adaptive laser bar detection approach is applied to measure the melt level quickly and accurately. Three experiments have been made to demonstrate the advantages of the system. The calibration experiment shows the system has a measurement resolution of 0.0755 mm. The accuracy experiment proves the system has a precise measurement performance and the robustness experiment demonstrates the system using a truncated mean filter is reliable and robust.