T. Phan

Laser beam thermography of circuits in the particular case of passivated semiconductors

Abstract Surface temperature changes upon integrated circuits can be observed by measuring the corresponding reflectance variation. We presented this method for temperature measurement in earlier work [1, 2] for Si integrated circuits with no passivation layer. We show in this presentation how the passivation oxide layer upon integrated circuits increases, with a factor depending upon the oxide thickness, the reflectance response resulting from a temperature change. Absolute temperature changes are derived from reflectance measurements through a temperature coefficient. This coefficient, known for silicon, is calculated for different oxide thickness.s. We have built a laser probe for reflectance measurements upon integrated circuits. The probe, which includes a visualisation set-up, has a lateral resolution of 1 μm, the size of the laser spot. Absolute temperature changes from 0.05 to 500 K can be determined and followed as a function of time as the detection system covers the DC-125 MHz range. The laser probe allows also the precise measurement of the oxide thickness upon the semiconductor component. This is performed through the measurement of the reflectance at two different angles of incidence.

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 /spl 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.

Thermoreflectance measurements of transient temperature upon integrated circuits : application to thermal conductivity identification

An analytical 2D study, based on the method of integral transform, for transient heat transfer in a multilayered structure, and an optical technique for transient temperature measurement have been developed. Their application to the case of Joule heating of micrometric interconnections on submicron insulation layers permits one to identify thermophysical properties of the materials involved.

Modelling and experimental study of heat deposition and transport in a semiconductor laser diode

Abstract An analytical model of heat transport in a laser diode is presented together with measurements of the temperature distribution by photothermal microscopy. Comparison between model and measurements shows the temperature distribution to be issued from a cylindrical heat source diffusing in the surrounding bulk material. Laser output facet heating by stimulated photon absorption is shown to be of negligible importance.

Sondes laser et méthodologies pour l'analyse thermique à l'échelle micrométrique. Application à la microélectronique

Abstract We have developed optical techniques for thermal characterisation at micrometric scale based upon the detection and the analysis of the modifications of a reflected laser beam. The modifications are induced by a well controlled thermal excitation originating from electric heating. According to this principle we have developed a very compact, high sensitivity and high resolution optical bench. It includes a homodyne stabilised Michelson interferometer, a reflectometer and a differential interferometer. It is capable of detecting a temperature variation as small as 10−3 K and a thermal dilatation as small as 10−15 m. It has a large bandwidth ranging from DC to 125 MHz. The optical bench also includes a microscope and a visualisation system allowing analysis at micrometric scale. In the field of thermal studies in microelectronics, we have been able to determine the temperature of running microelectronic components in order to estimate their quality and reliability, to study the temperature distribution and to detect hot spots in integrated circuits and to study thermooptical and thermophysical properties of materials used in microelectronics.

Thermomechanical effects in metal lines on integrated circuits analysed with a differential polarimetric interferometer

Abstract We present a new laser probe, a differential polarimetric interferometer, which is dedicated to the study of common failure mechanisms in microelectronic interconnects. Our investigation is mainly concentrated on the study of thermomechanical stress build-up and electromigration in metal lines. In the differential interferometer, two laser beams, separated by a few microns, are reflected from the surface of the device under test. Reflectance, phase and polarization changes between the two beams can be observed, this allows surface temperature and surface bending measurements together with the observation of stress induced in the silicon dioxide layer by Joule thermal expansion. The laser probe provides unique and useful information about local thermal effects due to electromigration. It also shows, for the first time to our knowledge, induced local stress effects due to the mismatch of thermal expansion coefficients of the metal, Si and SiO 2 involved in running interconnect lines.

High sensitivity and high resolution differential interferometer: Micrometric polariscope for thermomechanical studies in microelectronics

Abstract A high sensitivity and high resolution laser probe devoted to the thermomechanical studies of microelectronic interconnects has been developed. Surface displacements as low as 0.1 picometer (10 −13 m) can be observed, this allows the laser probe to investigate the edge effect in interconnects. The stress field induced by the edge forces in the underlying silicon dioxide layers has been observed. All measurements are performed with a micrometric lateral resolution.

Laser probe measurements of quality evolution of solder joints during thermal cycling ageing tests

We present the results of a non-destructive measuring method allowing us to characterize the evolution of solder joints during thermal cycling ageing tests. The method uses a high resolution optical probe to detect selectively pure Joule and Peltier thermal responses of the solder joint subject to a given current pulse. The results show the Peltier and Joule responses to be good indicators for the evaluation of the age and the degradation of solder joints.