Errors Associated With Light-Pipe Radiation Thermometer Temperature Measurements

Accurate measurement of surface temperature distribution is of concern in the semiconductor industries, particularly in rapid thermal processing. The International Technology Roadmap for Semiconductors 2004 has established requirements of uncertainties of plusmn1.5 degC at a temperature of 1000 degC, with temperature calibration traceable to ITS-90 (International Temperature Scale-1990). Light-pipe radiation thermometers (LPRTs) are becoming increasingly important as an industrial tool for temperature measurement, especially in the semiconductor industry. However, achieving improved accuracy will be difficult without fully understanding several issues associated with LPRTs. In this paper, the "drawdown effect," the "shadow effect," and the "environmental effect" are investigated. The drawdown effect is caused by the physical mass of the light-pipe probe acting as a radiation heat sink for the measured object. The shadow effect is caused by distortion of the wafer radiosity distribution due to the presence of the light-pipe probe. The environmental effect is caused by nonspecular reflection due to surface imperfection or impurity of the light-pipe material. Monte Carlo simulation was conducted to better understand the underlying physics, and the simulation results are compared to the experiment results. The latter two effects were found to be very important in the present study