Adhesion of copper to polytetrafluoroethylene surfaces modified with vacuum UV radiation downstream from He and Ar microwave plasmas

Poly(tetrafluoroethylene) (PTFE) is an attractive material for insulating layers between conductors, such as copper, in the packaging of high-performance electronic devices because of its excellent thermal and chemical properties and its low dielectric constant. Strong adhesion between copper and PTFE is difficult to develop because perfluorinated materials are hydrophobic, relatively inert chemically and possess low surface energies, thus accounting for their non-stick behavior. Since vacuum UV radiation (VUV) is of current interest in the production of small feature sizes on polymer surfaces using photolithography, investigations were conducted to study the ability of plasma generated VUV radiation to control the adhesion of Cu to PTFE. PTFE surfaces were modified with VUV radiation from low-pressure He and Ar microwave plasma both in the presence and absence of oxygen gas flowing over the surface. Copper deposition by sputtering was done and a peel test was employed to check for adhesion improvement on the treated PTFE. Peel test resulted in about 90% adhesion of copper to PTFE in the case of He plasma and 85% of the adhesion in the case of an Ar plasma. X-ray photoelectron spectroscopy was employed to characterize the surface of PTFE and determine the composition of different components on the PTFE surface. Oxidation of the surface was found for modification of PTFE treated with He and Ar plasma. Scanning electron microscopy was carried out to acquire images of the surface and determine if there is any change in the surface topography. The surface was found rough when treated with Ar plasma in presence of oxygen environment. Contact angle for treated and untreated PTFE was studied to check the change in hydrophilic nature of PTFE. Weight loss measurements were made to determine the photo-etching rate of PTFE. Similar experiments have been done with He and Ar plasma with a LiF window placed between the plasma and the sample surface