GROWTH-CHARACTERISTICS OF COPPER ON TUNGSTEN GROWN THROUGH CEMENTATION, VAPOR-DEPOSITION AND ELECTROPLATING

The growth characteristics of thin copper deposits grown through cementation, electrodeposition and vapor deposition were evaluated through imaging the coated samples in the field ion microscope at 78 K utilizing a 90% He-10% Ne gas mixture. Although the thicknesses of overgrowths were found to be varied with the method and time of deposition, copper in thin overgrowths (less than approximately 50 atom layers) was observed to grow epitaxially on the tungsten substrate surface. In thicker layer growths the epitaxial growth was found to change to a misfit zone with excessive defect structures followed by a polycrystalline copper arrangement. A prominent feature of these thick overgrowths was observed to be their instability under field-induced stresses of the field ion microscope imaging, thus rendering a layer-by-layer evaluation through the three-zone arrangement quite difficult. The initial tungsten surface was recovered upon controlled field evaporation only in the vapor deposition experiments while in the electroplating and cementation experiments the tungsten surface recovered was quite different from the original substrate imaged, thus indicating that an initial dissolution followed by deposition of copper had taken place in the electroplating and cementation processes. In spite of this initial surface reaction, the copper overgrowths were found to be deposited epitaxially. The observed epitaxy of the face-centered cubic copper on body-centered cubic tungsten substrate end forms at thin coverages was consistent with earlier studies of vapor deposition utilizing the copper overgrowth- tungsten substrate system. © 1979.