The emissivity of silicon wafers in a rapid thermal processing chamber has been measured as a function of the wafer temperature. Wafers with different surface roughness and layers have been studied. For transparent wafers, both sides of the wafer affect the emissivity. This emissivity is not only affected by surface roughness, but also by the layers deposited on the wafer. It has also been observed that while the emissivity increases rapidly as the temperature increases from its room value to 600 °C, the emissivity decreases with a slope of −8.89×10−5 °C−1 for temperatures larger than 600 °C.
The emissivity effects and compensation schemes encountered in pyrometric temperature measurements in RTP systems are described in this paper. The emissivity effects include substrate roughness, layered films, substrate temperature, and chamber reflectivity. Compensation techniques are derived based on the emissivity effects, and include reference thermocouples and reflectance-based measurements. Compensated emissivity results in wafer-to-wafer temperature variations of less than ± 6 C, compared to as much as ± 100 C for uncompensated emissivity. A new model for emissivity analysis at temperatures larger than 700 C is also described.
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