Emissivity of silicon: a mystery to some but not to all!

The variation of emissivity and absorption between different parts of a production wafer results in nonuniform wafer temperature. The formula for the reflection and emissivity of electromagnetic radiation of a semitransparent semiconductor wafer is presented. It is shown that changes in the absorption coefficient due to different levels of semiconductor doping result in different reflectivity, and consequently, in different emissivity. It is also shown that undoped regions of the wafer must be considered as a semitransparent material where absorption of incident radiation is a volumetric process and the blackbody radiant energy flux within an absorbing medium and reflectivity depends on the complex index of refraction.