System and method for optically determining the temperature of a test object

Abstract

A system and method are disclosed for optically measuring the temperature of a packaged integrated circuit (IC). A light beam is focused inside the IC package onto a region of the integrated circuit whose temperature is to be measured. The through-substrate reflectivity of the IC, which is a function of temperature and material characteristics (e.g., doping) of the region, determines how much of the incident light is reflected to a photo-detector. The photo-detector measures the intensity of the reflected light and generates a corresponding through-substrate reflectivity signal R. The reflectivity signal R is correlated with transmission curves for that region or materials with similar characteristics and the temperature of the region determined therefrom. Confocal techniques can be applied to substantially reduce measurement signal noise due to light reflected from the IC package which interferes with the light reflected from the IC. Measurements can be made at one specific position within the IC or a temperature map can be produced for the entire IC. Because different IC layers with different material characteristics have different transmission properties at the same temperature, the temperature measurement of a multi-layer region can be localized to a particular layer by selecting a measurement wavelength at which that region's transmission properties are most sensitive to temperature variations.