Determination of the Coefficient of Piezoresistivity in Aluminum Alloy Interconnect Structures

AbstractThe resistance of Al thin film metallization interconnects has been measured during temperature cycling where thermal expansion mismatch between the Al and the substrate and passivation is used to induce interconnect strain. Both passivated and unpassivated interconnects were thermally cycled between 80K and 373K. The coefficient of piezoresistivity, defined as dp/dE, where ρ= resistivity and εv = volumetric strain, is measured to be 2.0 10−5Ω-cm in tension, consistent with previous results determined in bulk Al under hydrostatic pressure. We describe a model which incorporates the thermal, geometrical, and piezoresistance effects on the measured interconnect resistance during temperature changes. Thermal expansion mismatch strains and the degree of interconnect constraint by the rigid surrounding materials, which vary with interconnect aspect ratio, are considered. The application of piezoresistance analysis to measurement of local stresses and stress relaxation in advanced interconnects will be described.