A Novel Method for Measuring Nonuniformities in Metallization Temperatures of an Operating Integrated Circuit

A nonuniform temperature distribution was observed along the metallization and on the top surface of an integrated circuit. Very small latex SEM calibration spheres were distributed over the circuit, and their changes of shape and contrast, due to melting, allowed us to discern hotter and cooler regions on the chip. Much of what was observed seemed to indicate that electromigration can take place at a relatively low temperature, around 113°C or less. Further discussion of the thermal calibration of the spheres, effects of the surface, and the effects of the vacuum is also given. Various difficulties involved with the technique and some proposals to overcome them are given as well.