In situ Simultaneous Measurement of Temperature and Thin Film Thickness with Ultrasonic Techniques

A novel technique to measure in situ, simultaneously, temperature and thin film thickness during semiconductor processing is described in this paper. The measurement technique is based on the principle propagating in a silicon wafer is a function of both the that the velocity of an ultrasonic Lamb wave wafer temperature and the thin film coating on the wafer surface. We are able to btain the processing sets of sensors operating at two distinct frequencies, temperature and film thickness simultaneously with two OSMHz and 1.5MHz. This technique is demonstrated in an aluminum sputtering system. We have achieved a temperature measurement accuracy of C0.lS’C and an aluminum film thickness resolution of +170A. The measurement does not depend on the optical or the electrical properties of either the wafer or the film material, and is insensitive to the processing environment. With its high measurement accuracy and setup simplicity, this sensor system carries great potential i n semiconductor process monitoring and control. INTRODUCTION Feature sizes in integrated circuits (IC) continues to shrink which makes close-looped process control of situ temperature and film thickness ensors are processing parameters increasingly important, thus in necessary in many stages of IC manufacturing. Ultrasonic sensors utilizing Lamb wave propagation in silicon wafers have been used to measure temperature’,2, and film thickness’, both in a wide range and with high accuracy. In this paper, we further advance this technology to perform in situ measurement of temperature and thin film thickness simultaneously. We demonstrate the ability of achieving an accuracy of fo .15’C in temperature and t170.& i n film thickness. 0-7803-3615-1/96/$5.00