Surface Interactions of Radicals During Plasma Processing of Polymers

Surface interactions of radical species were investigated using the imaging of radicals interacting with surfaces (IRIS) technique during plasma surface modification of polymers. Three plasma systems were investigated by spatially probing the laser induced fluorescence of individual radical species and determining their surface scattering coefficients, S. The behavior of CF₂ moieties on polymer surfaces was studied using the fluorocarbon plasmas C₂F₆ and hexafluoropropylene oxide (HFPO). Three types of surface interactions were observed, surface generation of CF₂ (S > 1), surface loss of CF₂ (S < 1), and unit scattering (S = 1). Surface loss of CF₂ was seen in HFPO plasmas, while CF₂ was generated in C₂F₆ systems. The differences between these systems is believed to be the result of different overall surface interactions, specifically film deposition in the HFPO system and etching in the C₂F₆ system. Using NH₃ plasmas, the surface interactions of NH₂ radicals with polymers was also investigated. Here, NH₂ is generated at the surface of polyethylene and polytetrafluoroethylene substrates, but is consumed on polyimide substrates. Ion effects were also investigated by placing a grounded mesh in the path of the molecular beam to remove charged species.