Fabrication of Copper Film on Aluminum Nitride by Novel Electroless Plating

A detailed study aimed at investigating the interfacial structure of Cu films deposited on high purity aluminum nitride (AlN) substrate, which controls the adhesive strength of the deposited Cu film, is described. In this system, the Cu films are deposited by uniform coating of nanosized particles onto the substrate, oxidation of to CuO by heat-treatment in air, and subsequent reduction to metallic Cu followed by electroless Cu plating. Effect of the treatment condition on the structure of composite layer formed on the AlN substrate was investigated by means of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, which show that the interfacial structure depends significantly on the annealing conditions. Upon heat-treatment above 800°C in air, an and/or phase is formed on the AlN surface. The adhesive strength of the deposited Cu film increased with increasing the annealing temperature, and maximum strength observed is ca. 4 kg per 2 × 2 mm 2 (kg/4 mm 2 ), much greater than that obtained by conventional electroless plating process. The formation of an interfacial oxide layer is suggested to be responsible for high adhesive strength through chemical interaction. The use of particles as deposition seeds having chemical bonding with AlN substrate can be crucial in this methodology, which has important implications for practical manufacture of Cu-based electronic devices fabricated on AlN substrate.