Integrated circuit tester using interferometric imaging

Summary form only given. An interferometric imaging technique can provide time-resolved diagnostics of semiconductor integrated circuits. The semiconductor device is placed in one arm of an interferometer and illuminated with a picosecond pulse from a sub-bandgap infrared laser. As the laser passes through the semiconductor, it samples local variations in the index of refraction. These variations are caused by a number of physical phenomena including dopants in the material such as those used to form device structures, heating due to the flow of electrical currents, and changes in carrier concentration due to injection. These variations have both static and dynamic components. The dynamic components are associated with the normal device operation and are the most interesting. To separate the two components, the device is first imaged in a quiescent state (no external voltage applied), and then a second image is taken after the device enters a known voltage state. Differences between the two images determine where the local index of refraction has changed and by how much. A third image taken with the reference arm of the interferometer blocked, allows device structures to be associated with particular changes in the index of refraction. Activation of the voltage state is synchronized with the pulsed illumination source, and the time delay between the application of the voltage and the laser probe pulse allows us to take a series of images that map the time evolution of the interferogram.