Calibration of Radiation Thermometers in Rapid Thermal Processing Tools Using Si Wafers with Thin-film Thermocouples

Abstract

Rapid thermal processing (RTP) tools are currently monitored and controlled with lightpipe radiation thermometers (LPRTs) which have been calibrated with thermocouple instrumented wafers. We have developed a thin‐film thermocouple wafer that enables more accurate calibration of the LPRTs. The NIST thin‐film thermocouple calibration wafer uses Pt/Pd wire thermocouples welded to thin‐film Rh/Pt thermocouples to reduce the uncertainty of the wafer temperature measurement in situ. We present the results of testing these thin‐film thermocouple calibration wafers in the NIST RTP test bed at temperatures ranging from 650 °C to 830 °C together with a discussion of the materials limitations and capabilities. The difference between the thermocouple junction temperatures and the radiance temperatures indicated by the blackbody‐calibrated LPRT can be attributed to the effective emissivity of the wafer, the parameter that accounts for the geometry and radiative properties of the wafer‐chamber configuration. An analysis of the uncertainty, u = 1.3 K (k =1), of the wafer surface temperature measurements in the NIST RTP test bed is presented. Confirmation of this value was partially hampered by thermal gradients in the chamber and some problems with the weld pads at high temperature. In addition, we discuss the determination of the Seebeck coefficient of the thin‐film thermocouples used on the wafers.