Closed-Loop Control of MBE Using an Integrated Multi-Sensor System

ABSTRACTThe use of in situ sensors to achieve real-time control of molecular beam epitaxy (MBE) 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. To achieve robust real-time control of MBE, we have constructed a multiple-sensor control system comprising in situ sensors for substrate temperature, for effusion cell fluxes, and for the epitaxial layer composition and thickness, along with advanced software to manage the sensor information and execute sensor-feedback control algorithms. This system has been used to grow a number of different III-V semiconductor materials and device structures, including heterojunction bipolar transistors, resonant tunneling devices, and mid-IR lasers. In the present paper, we present results demonstrating control and regulation of substrate temperature and epitaxial layer composition during the growth of lattice-matched InGaAs and InA1As on InP. The control algorithms and software used in the system are described, and we discuss how the synergistic application of multiple sensors allows the regime of composition control to be expanded beyond what would be possible with only a single composition sensor.