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Current induced organization in thin nanocrystalline gold films during deposition P. Chaoguang, J. Ederth, L. B. Kish, and C. G. Granqvist Department of Materials Science, The Angstrom Laboratory, Uppsala University, P.O. Box 534, SE-75121, Uppsala, Sweden

ABSTRACT Nanocrystalline gold films were prepared by advanced gas deposition. Electric field induced effects on the film structure during and after deposition was investigated. A dc electric field in the range 2 ≤ Ua ≤ 8 V/cm, was applied parallel to the substrate surface and led to changes of film microstructure and resistivity. In another set of experiments, films deposited at Ua = 0 were exposed to electric fields of similar strength after deposition. Film degradation could be understood from a mechanism consistent with a biased-percolation effect. Our results show that it is possible to control the film structure by varying the strength of an applied electric field.

INTRODUCTION Nanocrystalline (nc) materials with grain sizes of the order of 10 nm attract much interest because of their unusual properties[1-7]. Nanocrystalline materials have opened new perspectives in many areas [8], for example regarding, microelectronics, sensor technology, catalysts, medical technology, etc. Many investigations [2-4,9-11] have been done recently on nc-Au films. Electrical degradation of such films due to high current densities crucially influences the performance and lifetime of nanostructured thin film devices. One example is the process of electromigration damage in metallic interconnections. From an applied point of view, the investigations with reference to the understanding of film degradation are of great importance. This paper reports on electrical degradation phenomena of nc-Au films prepared by advanced gas deposition. The results show that the degradation mechanism can be attributed to a biased percolation model [1214].

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EXPERIMENTAL The gas deposition mode of an UFP (Ultra Fine Particle) unit (ULVAC/VMC, Japan) was used to produce nc-Au films [8,9]. Two chambers are used in the film formation process: an evaporation chamber and a deposition chamber. Evaporation, nucleation, and particle growth of gold (99.99% pure) takes place in the presence of a He gas flow in the evaporation chamber, where the pressure was set to 500 mbar. Substrates are positioned in the deposition chamber where the pressure was set to 10-1 mbar. Nanoparticles are then transferred, due to the pressure difference between the two chambers, from the evaporation chamber to the deposition chamber through a transfer pipe. In the deposition chamber the particle stream passes through a 0.5 mm diameter jet nozzle (mounted on the top of the transfer pipe), which accelerates the particles to a speed as high as ~500 m/s before impinging on the substrate. The distance between the nozzle and the substrate was 12 mm. Films produced by this method consist of high quality nanoparticles with narrow size distribution [9,15] and high packing density. Figure1 shows a schematic view of the in situ film r