Metal-polymer interfaces

Summary form only given, as follows. The increasing application of polymers in microelectronics has aroused much interest in metal-polymer interfaces. In this talk it is reviewed how structure and formation of metal-polymer interfaces are controlled by the preparation process and the nature of the materials involved. Emphasis is put on noble metal deposition onto fully cured polyimides and polycarbonates. Valuable information originates from radiotracer measurements of metal diffusion at the interface, structural investigations by means of cross-sectional electron microscopy, and computer simulations on the interplay of atomic metal diffusion and aggregation. Moreover, X-ray photoemission spectroscopy has largely contributed to our present understanding of the interfacial chemistry and the early stages of interface formation. Reactive metals always form relatively sharp interfaces with polymers, although the initial growth of Cr on polyimide recently proved to be different from the layer by layer mode. Metals of lower reactivity, on the other hand, diffuse into polymers at elevated temperatures and have a very strong tendency to agglomerate. The extent of diffusion appears to be determined by the initial stage of the deposition process. Here sticking coefficients recently measured for metals on virgin polymer surfaces deviate markedly from unity. Diffusion into the polymer increases strongly at low deposition rates, where a large fraction of isolated metal atoms is able to diffuse into the polymer before being trapped by other atoms at or near the surface. No significant diffusion is expected from a continuous metal film as a consequence of the high cohesive energy of the metal. The model emerging from these observations allows us to predict the salient features of interface formation between metal and polymers in general and particularly with respect to the new low k polymers. The correlation between interfacial structure and adhesion is addressed.