Real-time, heuristic-based controlof molecular beam epitaxy

Abstract

Real-time, heuristic-based control is appropriate for materials processes where accurate numerical models are not available. Frequently,bdthe scientists working with a process base their decisions when controlling the process on a set of heuristics.This article describes the use of a rule base for real-time control of molecular beam epitaxy MBE,a semiconductor thin-film growth process. As is often true in applying real-time control to materials processes,the most difficult task is to develop sensor technology capable of monitoring the material properties of interest.The use of ellipsometry,an optical technique,is described for the MBE process.The requirement to extract the material parameters from the ellipsometry data is computationally complex and time consuming. Development of algorithms to compress this manipulation into an acceptably short period for real-time control is discussed. Given these data,a rule base has been implemented to control the thickness and composition of thin films grown using MBE in real time. This research demonstrates that a rule base need not be complex to be effective.