Ultraviolet illumination thermoreflectance for the temperature mapping of integrated circuits

Noncontact optical methods such as thermoreflectance, which measure temperature-induced optical reflectivity changes, are particularly suitable for obtaining high-resolution temperature mappings on integrated circuits. Unfortunately, the coefficient linking the variations of temperature and reflectivity depends on the nature of the material and can be modified when optical interferences occur in the Si3N4-based encapsulation layers protecting the circuits. We show that taking advantage of the deep UV absorption of encapsulation layers yields temperature mapping that is independent of the underlying materials. A single calibration is therefore enough to yield the temperature on any point of the uniform and thermally thin encapsulation layer. This simplification and its potential for high resolution should make UV thermoreflectance more attractive to the semiconductor industry.