Abstract
Copper wiring formation on a resin material with a low dielectric constant, a low dielectric loss and a smooth surface is indispensable to realize high-frequency signal propagation with fine wiring patterns. Cycloolefin polymer (COP) resin is a promising material to meet these requirements. We propose adhesive copper seed layer formation on the COP by magnetron sputtering as an alternative to the electroless deposition which usually requires an intentional roughness-induced process to obtain practical adhesion between the resin and the metal. The proposed process steps include plasma nitridation of the COP surface, thin CuN film deposition and Cu film deposition before the electroplating. Excellent adhesion strength between the COP and the metal, greater than 1 kN/m, can be obtained while maintaining a smooth surface, which is attributed to the strong chemical bond generated between the nitrided COP surface and the CuN film. The coplanar transmission line was fabricated using the proposed process steps with semi-additive processes, and we found that the introduction of relatively high-resistive CuN film does not cause degradation of the propagation characteristics.
