Direct Observations of Rapid Diffusion of Cu in Au Thin Films using In-Situ X-ray Diffraction Page: 4 of 35
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Copper and gold are high conductivity metals used widely in the semiconductor industry
and elsewhere . Thin Au coatings are sometimes used on Cu substrates to prevent oxidation
of the Cu and to enhance electrical conductivity, but these thin coatings can diffuse into the
copper substrate over periods of time, even at moderately low temperatures. Numerous studies
have investigated the diffusion of Au in Cu using different techniques such as tracer diffusion
, high resolution electron microscopy , x-ray diffraction , and Rutherford back-scattering
[5, 6]. The effects of grain boundaries and other defects have been investigated and are of
particular importance since they accelerate the diffusion rate [7-9].
At elevated temperatures, Cu and Au are mutually soluble and form a melting point
minimum at 910 C , which makes this alloy combination useful to join the materials together
through a eutectic-type bonding method. However, due to the high diffusivity of Au in Cu at
elevated temperatures, thin-films of gold may diffuse into the copper during heating to the
bonding temperature, thus altering both the temperatures at which the liquid first forms and the
widths of the joints produced . This study was undertaken to further investigate the diffusion
of Au into Cu using a synchrotron based x-ray diffraction technique in order to determine the
temperature dependence of the interdiffusion that occurs at elevated temperatures in Au-Cu thin
films. The in-situ synchrotron studies presented here are particularly useful in that they directly
track the initial rapid diffusion that takes place as the thin films intermix, as well as follow the
interdiffusion that takes place at longer times. The real-time information gathered from these
experiments reveals information about the kinetics and the mechanisms responsible for the
interfusion that takes place.
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Elmer, J W; Palmer, T A & Specht, E D. Direct Observations of Rapid Diffusion of Cu in Au Thin Films using In-Situ X-ray Diffraction, article, November 28, 2005; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc879360/m1/4/: accessed November 25, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.