Control and design of crystal growth furnace

We present the control and design of a vertical transparent multizone furna ce which can operate in the temperature range of 25-750 degrees C and deliv er thermal gradients of 2-45 degrees C/cm for the commercial applications t o crystal growth. A multivariable projective control algorithm is used for the temperature control. The controller accounts for the inevitable zone to zone thermal interactions. In addition, the control system operates such t hat the thermal profile is maintained under the thermal load of crystal, th us boundary conditions on crystal growth ampoules can be predetermined prio r to crystal growth. Temperature profiles for the growth of crystals via di rectional solidification, vapor transport techniques, and multiple gradient applications can be easily implemented. The unique feature of its transpar ency and stable thermal profiles make the furnace useful for the determinat ion of process parameters that optimize crystal growth conditions. (C) 1999 Elsevier Science Ltd. All rights reserved.