Increasing the accuracy of the contact method of measuring the current square of crystals grown by the way of the Czohralsky

For crystals grown from a liquid melt by the Czochralski method, when monitoring and controlling the current crystal area, based on the contact method of measurement, the basic requirements for ensuring the accuracy of measuring the area of the crystal on the cylindrical part of the growing are determined. In the control system with respect to the coordinates of the movement of the crystal and the crucible, it is necessary to use photo-reading optical rulers, with a sampling resolution of 0.1 µm, to determine the amount of movement during the control signal evaluation cycle. To eliminate the error due to the accuracy of stabilization of the melt level in the crucible, the following algorithm for the operation of the crystal growing apparatus is proposed. During the evaluation of the control signal on the cylindrical part of the growing crystal, the sampling time of the predetermined number of pulses of the crucible movement is adopted. Calculation of the evaluation time of the control signal begins at the moment of closure of the melt sensor and ends when the melt sensor closes, provided that a predetermined number of pulses of the crucible transfer is sampled. The evaluation time of the control signal in the previous control cycle is used in the current cycle to calculate the closure pause as part of the calculated evaluation cycle time. In the control system, at the moment of closing the contact sensor, a pause of the closed sensor is maintained, followed by a similar pause of the open state of the level sensor. During the moments of pauses, the state of the contact sensor by the control system is not analyzed and the control of the crucible lift occurs with a slowed and accelerated rate of the crucible lift during the moments of the “conditionally” closed and “conditionally” open states of the level sensor. All this ensures in this control system the accuracy of measuring the current area of the crystal, on the cylindrical part, by a value not worse than 1 %.