Interfacial adhesion and its degradation in selected metal/oxide and dielectric/oxide interfaces in multi-layer devices

Abstract

A previously-developed laser spallation technique for measuring the intrinsic tensile strength of single thin film interfaces was modified to test adhesion among multilayers deposited on planar substrates. A laser-generated compressive stress wave on the backside of the substrate pries off the weakest of the interface after reflecting from the surface of the outermost layer in the multilayer assembly, which is deposited on the substrate's front surface. The test procedure was demonstrated on (a) polyimide/SiO 2/Si 3N 4/Si, (b) W/SiO 2/Si, and (c) Cu/SiO 2/Si multilayer systems that have importance in device fabrication. The measured strengths were found to be rather sensitive to the coating deposition parameters and surface backsputter treatment prior to film deposition. Additionally, the polyimide/nitride interface showed a dramatic decrement in its strength when exposed to varying relative humidity levels for different durations. Beside showing the basic nature of the measurements, these latter results now afford implementation of a novel device reliability strategy which, in addition to being more rational, reliable, and robust, will result in significant time and cost savings compared with the exhaustive set of accelerated time/temperature/humidity tests that are presently employed by the industry. This new device reliability strategy is also discussed in the paper.