Hyperspectral thermoreflectance imaging for power devices

This paper presents a novel method for obtaining optimized, accurate, and fully calibrated images of the thermal behavior of complex semiconductor devices with submicron features. To thermally analyze the growing number of high power devices, such as microwave amplifiers for wireless mobile applications, a technique is required for high speed transient and high spatial resolution thermal characterization. Thermoreflectance imaging has been shown to have an advantage in measuring the time-dependent thermal response. A challenge, however, has been a noisy spatial response due to an optical artifact and/or the complex reflection of the layers of thin-films and geometries which comprise the transistor features. To intuitively understand the thermal profile, which is a great advantage of imaging, this nonphysical response can sometimes result in confusion. Wavelength dependent reflectance is a property of the material and the material's surface characteristics. A multiple wavelength or a full spectrum (hyperspectral) illumination, rather than a single wavelength, can be employed to achieve much greater accuracy and a clearer thermal image for all regions on a complex integrated circuit. A single heating wire deposited on a substrate is used to experimentally demonstrate how this technique works. The results show a very good hyperspectral thermoreflectance fitting for all materials on the test structure.