Adhesion Mechanism of Electroless Copper Film Formed on Ceramic Substrates Using ZnO Thin Film as an Intermediate Layer

Electroless Cu layers with pull strengths of greater then 2.5 kg/mm² were fabricated on smooth ceramic substrates (glass, , AlN) without surface etching . High adherence was achieved using ZnO thin films (ca. 1 μm thickness), prepared by spray pyrolysis as an intermediate layer between the ceramic substrates and the Cu layers. It was shown from the interfacial analysis that the high adherence was due to both strong van der Waals forces acting at the Cu/ZnO interface and a chemical‐type bond acting at the ZnO/ceramic interface. The adhesive forces at the Cu/ZnO interface were enhanced by numerous small pores (<0.5 μm diam) formed on the ZnO thin film during catalyzation. In contrast, the ZnO/ceramic adhesion was due to the thermal diffusion of Zn into the substrate during the preparation of the ZnO thin film, which involves chemical bonding forces. As a result, the ZnO thin film acts as a highly effective adhesive layer between the electroless Cu layer and the ceramic substrate.