In-situ Monitoring and Control during Epitaxial Growth

摘要

Real-time monitoring and control of epitaxial growht is vital to volume manufacturing of epitaxial-based compound semiconductor optoelectronic and electronic devices. Recent progress in optical-based monitoring instrumentation and ever declining computational cost has made this approach both technologically feasible and economically desirable. To date, in situ non-invasive pyrometric interferometry (PI) and normal incidence laser reflectance (LR) are increasingly being used for in situ growth monitoring for both molecular beam epitaxy (MBE) and metal-organic vapor phase epitaxy (MOVPE). In this talk, we will focus on physical modeling and control methodologies for various in situ monitoring sensors (for thickness, growth rate, temperature measurements etc.), including pyrometric interferometry, laser reflectometry, and diffused reflectance spectroscopy under MBE growth conditions. Accurate modeling of the sensor process is the first step toward the development of effective control strategy. It also enables the user to develop realistic control simulator where the performance and limitation of various control methods can be tested before the experiments are carried out. On the control side, we will discuss a signal processing technique based on the extraction of the oscillating phase of the monitoring signal for thickness measurement. In contrast to earlier direct calculation method (such as virtual interface), this method does not require absolute measurement of the sensor data and the results are relatively immune to the slow-varying background signal commonly encountered in MBE growth. Based on this 'signal phase' technique, we will present the experimental results on close-loop control growth of periodic AlAs/GaAs Distributed Bragg Reflector (DBR) structures and growth rate estimation of short AlAs/GaAs layers. Although the experimental results are discussed in the context of MBE, many of these monitoring techniques and control methodologies are applicable to MOVPE as well. The prospect of an integrate4d monitoring system and actuation mechanism in MBE will also be discussed.