Effects of curing processes on material properties of porous copper

Abstract

In the course of this project, methods for the application and processing of porous copper pastes in semiconductor industry were developed and refined. Three different copper pastes consisting of copper micro- and nano-particles as well as organic particle coatings and solvents were applied on Si-Wafer substrate using the stencil- and screen-printing technique, a straight forward, fast and cost-efficient way of applying metal layers in the size range of a few to a few hundred micro meters to a substrate. After solidification of the fluid copper pastes in a furnace in reducing atmosphere, an interconnected porous copper network is formed showing interesting material properties, primarily a porosity around 30% and relatively low electrical resistivity of 4:51 μΩ cm (bulk copper: 1:68μΩcm), thus qualifying for various applications in semiconductor technology. Further, experiments were designed during this project in order to systematically investigate various influencing parameters during sintering and curing of the pastes. Factor-effect correlations between input and output parameters were quantified. It could clearly be shown that, when adequately controlling the process parameters, the design of porous copper layers with made-to measure material behavior can be realized. Microstructural characteristics such as porosity, layer thickness and surface roughness were analyzed and linked to the electrical, thermal and mechanical performance of the material. Analysis methods included optical microscopy, scanning electron microscopy, energy-dispersive X-ray, thermo-gravimetric analysis, differential scanning calorimetry, X-ray computed tomography, profilometry, four-point probing, thermo-mechanical analysis, dynamical mechanical analysis, electron backscatter diffraction and wafer bow measurements.