Design, development, and testing of real-time feedback controllers for semiconductor etching processes using in situ spectroscopic ellipsometry sensing

Real-time feedback controllers for two semiconductor etching processes are developed. Both controllers rely upon in situ spectroscopic ellipsometry measurements of sample thickness for their feedback variables. Spectroscopic ellipsometry (SE) is a commonly used nondestructive, noninvasive in situ sensor for dry etching. The first etching process we consider is the thermal chlorine etching of gallium arsenide. An empirical/first principles physics-based model for the etching process is developed. A linear-quadratic controller based on the model is designed and tested. The second etching process is the electron cyclotron resonance freon-14/oxygen (CF₄O₂) plasma etching of silicon nitride thin films. An adaptive etch rate controller for the fluorocarbon plasma etching process is designed, implemented, and tested