Wafer Temperature Control Using Helium Pressure and Observer-Based Model Predictive Control

Abstract

Stabilizing a wafer's temperature during plasma etching is a critical issue in semiconductor manufacturing. In this study, we propose feedback control of the wafer temperature using the pressure of helium gas (He) that is fed into the gap between the wafer and an electrostatic chuck (ESC) and an algorithm of the model predictive control (MPC) combined with an observer. The temperatures are measured only at the wafer edge zone and the ESC ceramic plate that are accessible during the process. The observer estimates wafer temperatures of center and edge zones and the injected heat power with the help of the measured edge zone temperature. The MPC determines the optimal He pressures based on the estimated temperatures to control both zone temperatures. The algorithm of the feedback control was formulated, and its validity was experimentally confirmed. Results showed that the observer worked well to estimate both zone wafer temperatures and the injected heat power. Results also showed that the temperatures were successfully controlled.