OPTIMAL-CONTROL OF THE WAFER TEMPERATURES IN DIFFUSION LPCVD REACTORS

In this paper it is shown that controllers currently used to control the temperature in batch type diffusion/(low pressure) chemical vapour deposition reactors are highly inefficient for VLSI applications. An alternative temperature controller of the LQG type is proposed which features direct wafer temperature control. This controller is based on a model of the heat transfer inside a cylindrical resistance diffusion/LPCVD reactor. The derived model covers the important class of furnaces equipped with semitransparent quartz process tubes and takes into account the thermal behaviour of the thermocouples. Simulation results and results of application of the proposed controller on a real furnace are given.