Enhanced Adhesion of Direct Sputtered Copper Seed Layer on Cycloolefin Polymer through Vacuum Ultraviolet Irradiation and Oxygen Plasma Treatment

This study introduces a novel surface modification process involving vacuum ultraviolet (VUV) irradiation followed by oxygen plasma treatment to enhance the adhesion between a cycloolefin polymer (COP) film, known for its excellent dielectric properties, and a copper plating layer with a direct sputtered copper seed layer, intended for use in antenna circuits for 6 G communications. Various surface analyses revealed that oxygen plasma treatment after VUV irradiation increased the quantity of functional groups in the extreme surface layer (∼10 nm) of the COP film more than oxygen plasma treatment alone and removed the brittle modified layer formed by VUV irradiation. This dual effect resulted in a peel strength of 1 kN m −1 , exceeding the 0.8 kN m −1 achieved with oxygen plasma treatment alone, confirming the synergistic effect of VUV irradiation and oxygen plasma treatment. Based on the surface analysis results, a process model was constructed explaining how oxygen plasma treatment etched away part of the modified layer containing the functional groups formed by VUV irradiation while simultaneously introducing additional functional groups to the newly exposed surface layer.