Feedback control of substrate temperature and film composition during MBE growth of lattice-matched InGaAs on InP

The use of in situ sensors to achieve real-time control of MBE growth is a rapidly evolving technology that promises to revolutionize MBE in terms of process repeatability and first-pass success, and consequently, to improve the overall yield and reduce the cost of the process. For the growth of InGaAs and related materials on InP, the most critical process variables to control are the substrate temperature and the epitaxial layer composition, insofar as both of these parameters can have dramatic effects on the performance of heterojunction bipolar transistors and other electronic and opto-electronic devices grown on InP. To achieve robust real-time control of the MBE growth process, we have constructed a multiple-sensor control system comprising in situ sensors for substrate temperature, effusion cell fluxes, and epitaxial layer composition and thickness, along with advanced software to manage the sensor information and execute sensor-feedback control algorithms. The design and operation of this system is described and its performance is illustrated through examples of real-time sensor-feedback control of substrate temperature and layer composition during the growth of InGaAs on InP.