In Situ Wafer Emissivity Variation Measurement in a Rapid Thermal Processor

Wafer backside reflectivity measurements at room temperature have been performed in a rapid thermal processor equipped with two rows of heating lamps by measuring, with the process optical pyrometer, the light emitted by the lower row of the heating lamps and reflected by the wafer. The differences in reflectivity have been correlated with the process temperature variations induced by emissivity changes. Optical pyrometer recalibration procedures have then been established. It has been demonstrated that the reflectivity measurement, performed automatically for each wafer prior to the thermal cycle, may drastically improve the accuracy of temperature control.