Adhesion enhancement of Ni films on polyimide using ion processing. I. 28Si+ implantation

Abstract

The influence of 28Si+ ion implantation on the interfacial chemistry and adhesion of 30 nm Ni films on po1y[N,N-(p,p′-oxydiphenylene) pyromellitimide] (PI) substrates was examined. The Ni/PI specimens were held at temperatures below 100 °C, and implanted with 55 keV 28Si+ at doses of either 1×1016 , 5×1016 or 1×1017 Si/cm2 . The 1×1016 Si/cm2 implants had no influence on the surface topography, but the higher dose implants introduced some submicron void formation. Cross-sectional transmission electron microscopy and Auger electron spectroscopy depth profile analyses showed that the as-deposited Ni films formed very sharp interfaces with the polyimide substrates. However, after implantation the interfaces became graded by up to a factor of 2 compared to the as-deposited specimens. Large quantities of C were transferred into the Ni films, resulting in the formation of a C overlayer. The concentration of implanted Si reached a maximum (at approximately 16 at. % for the 1×1017 Si/cm2 implant) in the Ni films and extended deeply into the PI substrates. X-ray photoelectron spectroscopy analysis of the interfaces of the specimens implanted with 1×1017 Si/cm2 showed a mixture of Ni–Si, Si–O, and C–O chemical bonding, consistent with Ni–Si–O–C complex formation. Adhesion testing showed substantial adhesion increases (up to a factor of 20) with 28Si+ dose. The Ni films implanted with 1×1017 Si/cm2 were only removed upon substrate failure. The adhesion increases induced by 28 Si+ implantation are attributed to a combination of substrate toughening, mechanical interlocking, interfacial grading, and chemical bonding across the interfaces.