Diameter Feedback Control Sub-system as On-line State Estimator for Growth Control in Czochralski Process

The state variables in the Czochralski crystal growth process have an important influence on crystal structure and properties. In this paper, in order to enhance the accuracy of state estimation, a diameter feedback control subsystem is designed, and Unscented Kalman Filter(UKF) is used for online state estimation. The system is a nonlinear system with pulling speed and power as input and diameter as output, two feedforward curves of growth rate and power are added in this paper. Since the controlling time of pulling speed on the diameter is shorter than the time of power on the diameter, the closed-loop control subsystem composed of pulling speed-diameter, which is used as the measurement subsystem of the power-growth rate closed-loop control subsystem, the two subsystems together constitute the diameter feedback subsystem to estimate the state variables online. Based on the crystal growth model, the relationship between various state variables in the system is given, and the UKF is designed to estimate the true radius of the crystal and the height of the meniscus. The experimental results show that UKF has a good filtering effect and higher state estimation accuracy under this control system.