RTP Calibration Wafer Using Thin-Film Thermocouples
Kenneth G. Kreider, D P. DeWitt, Benjamin K. Tsai, Francis J. Lovas, David W. Allen
Rapid thermal processing (RTP) is a key technology for the cluster tool, single wafer manufacturing approach that is used to produce integrated circuits at lower cost with reduced line widths and thermal budgets. However, various problems associated with wafer temperature measurements and dynamic temperature uniformity have hindered the widespread use of RTP in semiconductor device manufacturing. The current technology for calibrating the radiometers employs a thermocouple instrumented wafer. We have accomplished improvements in the accuracy of these measurements through the use of thin-film thermocouples had the new Pt/Pd thermocouple system. These new calibration wafers can reduce the uncertainty in wafer temperature measurement technology by (1) reducing the perturbation due to heat transfer at the thermocouple juctions and (2) replacing conventional thermocouples with the superior Pt/Pd system. The thin-film thermocouples were calibrated suing proof specimens fabircated with the Si 200 mm wafers and evaluated in the NIST RTP sensor test bed. The commercial type K thermocouples yielded temperature measurements within 4 C of the thin-film Rh/Pt and Pt/Pd thermocouples on the 200 mm calibration wafer between 725 C and 875 C. The Pt/Pd thin-film thermocouples proved less durable than the Rh/Pt thin films and the limitations of these systems are discussed. We also present a comparison of the radiometric measurements with the thermements with the thermocouple measurements using a model estimating the wafer temperature from its spectral radiance temperature.