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

A previously-developed laser spallation technique for measuring the intrins ic tensile strength of single thin film interfaces was modified to test adh esion among multilayers deposited on planar substrates. A laser-generated c ompressive stress wave on the backside of the substrate pries off the weake st of the interface after reflecting from the surface of the outermost laye r in the multilayer assembly, which is deposited on the substrate's front s urface. The test procedure was demonstrated on (a) polyimide/SiO2/Si3N4/Si (b) W/SiO2/Si, and (c) Cu/SiO2/Si multilayer systems that have importance i n device fabrication. The measured strengths were found to be rather sensit ive to the coating deposition parameters and surface backsputter treatment prior to film deposition. Additionally, the polyimide/nitride interface sho wed a dramatic decrement in its strength when exposed to varying relative h umidity 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, rel iable, and robust, will result in significant time and cost savings compare d with the exhaustive set of accelerated time/temperature/humidity tests th at are presently employed by the industry. This new device reliability stra tegy is also discussed in the paper. (C) 2000 Elsevier Science Ltd. All rig hts reserved.