Multiple reflection effects during the in-situ calibration of an emissivity independent radiation thermometer

We present an improved in-situ calibration procedure for the reflectometer channel of an integrated radiometer/reflectometer used for emissivity independent wafer temperature measurement in semiconductor production lines in RTP and other single-wafer processes (HDP-CVD, PVD, etc.). The improved calibration procedure, which has been implemented in our NTM line of radiation thermometers, allows for more accurate wafer temperature measurement, particularly for very low emissivity wafers. The calibration procedure is improved by explicitly accounting for the localized drop in reflectivity of a calibration standard used for the reflectometer calibration, when this standard is brought in close proximity to the radiometer/reflectometer probe tip. The reflectivity of the standard decreases near the probe tip due to a small "cavity effect" interaction between the probe tip and the reflectivity standard. Failure to account for the decreased reflectivity of the calibration standard results in a small reflectometer calibration error, which causes the combined radiometer/reflectometer to exhibit a small residual emissivity dependence in the temperature measurement. The improved calibration procedure eliminates this small emissivity dependence, thus allowing improved temperature measurement accuracy, particularly for high reflectivity (low emissivity) wafers