Adaptive Temperature Profile Control of a Multizone Crystal Growth Furnace

This paper presents an intelligent adaptive control system for the control of a solid-liquid interface of a crystal while it is growing via directional solidification inside a multizone transparent furnace. The task of the process controller is to establish a user specified axial temperature profile and to maintain a desirable interface shape. Both single input single output and multi input multi output adaptive pole placement algorithms have been used to control the temperature. We also describe an intelligent measurement system to assess the shape of the crystal while it is growing inside a multizone transparent furnace. A color video imaging system observes the crystal in real time, and determines the position and the shape of the interface. This information is used to evaluate the crystal growth rate, and to analyze the effects of translational velocity and temperature profiles on the shape of the interface. Creation of this knowledge base is the first step to incorporate image processing into furnace control.