THERMOREFLECTANCE MICROSCOPY: CALIBRATION OF TEMPERATURE MEASUREMENTS UPON MICROMETRIC METAL LINES APPLIED TO THERMAL CONDUCTIVITY IDENTIFICATION OF MICROMETRIC DIELECTRIC LAYER

The objective of this contribution is the determination of the thermal properties of micrometric polymer dielectric layers used in microelectronic. The increasing integration scale (more than one million transistors per square centimeter) leads to new fabrication processes. One of these processes consists in using Cu interconnects deposited on BCB polymer instead of A1 deposited on Si0₂. The mean time before failure of such devices is directly correlated to the failure mechanisms taking place in the interconnections. These mechanisms are thermally activated by the operating temperature of the Cu line. This temperature is strongly dependent on the thermal properties of the BCB layer. At microscopic scale, material properties can be quite different from the bulk value [1].
The aim of this work is to measure the temperature of such a Cu line under normal operating conditions and using a model of heat transfer in multilayer systems to identify the thermal properties of the micrometric layers. We have therefore developed a thermoreflectometric laser probe capable to measure the reflectance changes due to temperature variations. We propose an original methodology to calibrate the reflectance measurement in order to get absolute temperature measurements. This makes our laser probe to be an optical contactless thermometer with a sensitivity of about a few hundred microkelvins in the DC-1MHz range. The identification of thermal properties is obtained, by comparing the calculated temperature to the measured one. A semi analytical thermal quadrupole model is used.