The VLSI route for highly reliable ESDs

We present the control and design of a vertical transparent multizone furnace which can operate in the temperature range of 25-750° C and deliver thermal gradients of 2-45° C/cm for the commercial applications to 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 that the thermal profile is maintained under the thermal load of crystal, thus boundary conditions on crystal growth ampoules can be predetermined prior to crystal growth. Temperature profiles for the growth of crystals via directional solidification, vapor transport techniques, and multiple gradient applications can be easily implemented. The unique feature of its transparency and stable thermal profiles make the furnace useful for the determination of process parameters that optimize crystal growth conditions. © 1999 Elsevier Science Ltd. All rights reserved.