Improved adhesion of Cu on pre-etched polytetrafluoroethylene by PECVD deposited thin metallic layers

Abstract

The adhesion of copper to PTFE has been studied with regard to the influence of a pretreatment in discharges of reactive gases, such as O₂ and CF₄/O₂, and a subsequent deposition of thin metallic interlayers of Pd, Pt, Au, and Cu by PECVD methods. Adhesion forces could be enhanced by about the factor of 10 compared with merely pretreated surfaces up to 5 N/mm, which, as scanning electron micrographs prove, corresponds to the tensile strength of the bulk material. SIMS spectra of the back surface of a peeled copper stripe show the typical signals of PTFE. The thermal stability of the layers was established by dip** the samples into a tin bath of 540 K. The enhanced adhesion is not only due to the changes in surface morphology by etching. It can be attributed to chemical effects, i. e. chemical bonds between substrate atoms and the interlayer, and physical effects, caused by implantation of metal ions into the upper surface layers accompanied by a probable electron transfer from PTFE to metal.