Temperature measurements of metal lines under current stress by high-resolution laser probing

Accelerated reliability tests of aluminum interconnections with respect to electromigration are often performed by high current density stressing of particular structures designed to promote failures of this kind, In order to derive predictions of the interconnect lifetime under normal operating conditions, it is essential to know the temperature of the test structure when high current-density stressing conditions are applied. In this paper, we present the first experimental temperature measurements with two high spatial resolution laser probes of metal lines. The two optical probes provide an indirect access to the temperature of the metal line, The calibration of the probes for temperature measurements is performed by comparison to electrical temperature measurements. The probes have a lateral resolution of 1 mu m. Two types of test structures, used in accelerated electromigration analysis, are studied. The measurements are compared with two theoretical simulations, Good agreement is obtained only when a particular value of the thermal conductivity of the submicrometer oxide insulation layer of the metal line is used. This is not surprising, since the thermal properties of submicrometer layers are size dependant. Our experimental method provides an elegant way to determine these parameters.