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Laboratory of Nuclear Analytical Methods
Research topics

  Diffusion of Ag and Cu atoms in poly-ethylene-terephtalate (PET) and poly-imide (PI) was studied using Rutherford Backscattering Spectroscopy (RBS) and Elastic Recoil Detection Analysis (ERDA). The samples were prepared by deposition of Ag and Cu thin layers on polymer surface using CVD and diode sputtering techniques. Samples were annealed at temperatures up to 240C. X-ray Photoelectron Spectroscopy (XPS) was used for determination of metal-polymer interaction and chemical state of atoms on metal- polymer interface. Faster diffusion of Ag atoms was observed from non-compact Ag layers prepared by diode sputtering than from those prepared by CVD technique. Ag atoms show higher mobility in PET in comparison with PI. XPS measurement gives an evidence of Ag clustering in Ag-PET samples prepared by cathode sputtering. In PI the Cu atoms exhibit higher diffusivity than Ag atoms due to their lower atomic radius.
  Wide range of applications of metallized polymers in microelectronics has stimulated research of metal-polymer interaction. Polyimide encompassing low dielectric constant, high temperature and radiation stability is one of the best candidates for fabrication of multilayer metallization structures on the chip level and for packaging. In these structures, comprising alternate metal and insulating layers, high-temperature polymers are increasingly used and aluminum is replaced by the lower resistance copper. It has been observed that the microstructure and hence the mechanical and dielectric properties of the metal- polymer interface is strongly affected by the degree of metal-polymer diffusion and intermixing. Thus there is a basic need to understand the mechanism of metal diffusion in polymers and its effects on the structure and formation of metal-polymer interface. The diffusion depends on the physical and chemical properties of metal and the structure of the polymer as well. Cu and Ag for example exhibit higher mobility in polymers in comparison with that of more reactive metals such as Cr or Ti. In this study the diffusion of Cu and Ag in polyethyleneterephtalate (PET) and polyimide (PI) is examined using different methods with the aim to shed more light onto the diffusion mechanism.

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