Sensors for In-Situ Process Monitoring and Process Control

This report presents the results of the development of an ultrasonic sensor for in-situ monitoring of silicon wafer temperature. The sensor is based on the measurement of the velocity of ultrasonic Lamb waves in the wafer, and relating this velocity to temperature. We present a method for efficient excitation and detection of Lamb waves in the wafer, a theoretical model for relating the variation of velocity as a function of temperature, and an electronic implementation for the sensor. Our results indicate the ability to measure the temperature with an accuracy of 10C in most integrated circuit processing environments. The sensor has also been used in a tomographic configuration to allow the measurement of spatial distribution of temperature. Finally, we highlight the potential for simultaneous measurement of temperature and film thickness in-situ.