Abstract: The Czochralski growth of a crystal may be automatically controlled to provide uniform crystal cross-sectional area by weighing the crucible containing the melt from which the crystal is grown and deriving a weight signal which is compared with its expected value to produce a feedback loop control signal to control the melt heater power. However a magnetic field will be associated with the melt heater current and the interaction of this field on the crucible can produce a levitation force which is recorded erroneously as part of the weight signal. This unwanted force can make the closed-loop control unstable. The error component in the weight signal is cancelled in the invention by deriving an equal and opposite component by monitoring the current supplied to the melt heater and adding the derived component to the weight signal in the feedback loop.

Abstract: Apparatus for the closed-loop controlled growth of crystalline material by the Czochralski technique includes means for establishing a melt of a given crystallisable material, means for pulling a crystal from said melt when established, said means for pulling incorporating a rigid elongated pulling member defining a crystal pulling axis, means for rotating said pulling member about said crystal pulling axis and a weighing cell located at the end of said pulling member distant from said means for establishing a melt and capable of providing, for the purpose of closed-loop control of said crystal pulled, a signal related to the force along said crystal pulling axis on the pulling member.The weighing cell is preferably one of the kind having a spring and a transducer arranged to produce an electrical output related to the tension of the spring. The pulling member is preferably freely suspended from the weighing cell by a coupling which allows the pulling member to be rotated without rotating the weighing cell.