ITS-90 calibration of radiation thermometers for RTP using wire/thin-film thermocouples on a wafer

Abstract

Light-pipe radiation thermometers (LPRTs) are the sensor system of choice in RTP tools. They can be calibrated against blackbodies with an uncertainty (k=1) less than 0.3 °C. In an RTP tool, however, account must be made for wafer emissivity and wafer-chamber interreflections, or else temperature measurement uncertainties will be orders of magnitude higher. We have used two complementary approaches for accomplishing this: 1) in situ calibration using high-accuracy wire/thin-film thermocouples calibrated on the International Temperature Scale of 1990 (ITS-90) and 2) developing optical models to estimate the effective emissivity of the wafer eeff when used in the radiation environment of the RTP tool. The temperature measurement uncertainty of LPRTs using either technique is 2.1 °C or less.