Thin film and emissivity effects on radiometric temperature measurement accuracy

Abstract

This work addresses issues that affect the traceability and accuracy of radiometric temperature measurements applicable to the metrology and rapid thermal processing of semiconductor materials. The difficulty of accurately measuring the surface temperature in real-time of thin semiconductors layers that are deposited on substrates of a different emissivity is not well understood. A theoretical understanding of the source of these errors and possible techniques for minimizing them is developed. Absolute measures of surface emissivity are required when making precision pyrometric measurements. Emissivity measurement is important in estimating the actual surface temperature. Furthermore, emissivity measurement uncertainty is important m estimating temperature measurement uncertainty. It will be shown that for emissivities approaching zero the temperature measurement uncertainty diverges. Thin films can profoundly affect the emissivity of semiconductor wafers due to optical interference fringes. The surface emissivity can change dramatically as the film thickness changes. Therefore, it is necessary to compensate for a changing surface emissivity during pyrometric temperature measurements. This can be achieved by emissivity compensated pyrometry where a reflectometer is integrated into the pyrometer to allow real-time emissivity measurement. This technique and its limitations will be addressed.