Adhesion enhancement of Ni films on polyimide using ion processing. III. Si intermediate layers and 84Kr+ implantation

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Abstract
The influence of 10 nm Si intermediate layers and 84Kr+ implantation on the adhesion of 30 nm Ni films on poly [N,N-(p,p′-oxydiphenylene) pyromellitimide] (PI) substrates was examined. The Ni/Si/PI specimens were implanted with either 5×1015, 1×1016, or 5×1016 Kr/cm2 at a specimen temperature of less than 100 °C. Surface topography remained smooth after the 5×1015 and 1×1016 Kr/cm2 implants. In contrast, the 5×1016 Kr/cm2 implant resulted in extensive island formation, which destroyed the integrity of the Ni films. Auger electron spectroscopy (AES) depth profiles of the as-deposited films showed graded Ni distributions throughout the Si intermediate layers, which form abrupt interfaces with the PI substrates. After implantation with 5×1015 or 1×1016 Kr/cm2 implants, the Si intermediate layers become highly oxidized. Significant quantities (15 to 20 at. % in the Ni film) of carbon were transferred into the Ni films from the PI substrates, but the interface to the PI substrates remained sharp. The Ni that was present in the as-deposited Si layers appears to segregate out of these layers after the ion-induced oxidation. X-ray photoelectron spectroscopy (XPS) analysis showed that the chemistry of the Si interfacial layers changed from a mixture of SiO and Ni2Si in the as-deposited specimens to almost entirely SiO2 in the implanted specimens. The adhesion of the Ni films was examined using a scratch test. The as-deposited Ni films were removed at a force of 4 N with failure at the Si/PI interface. After ion implantation, the films were removed at a force of only 2 N, and the failure occurred at the Ni/SiO2 interface. This reduction in adhesion, which was in startling contrast to the adhesion enhancement obtained by implanting Ni/PI specimens with 28Si+, was attributed to the preferential formation of SiO2 during the 84Kr+ ion bombardment. It was concluded that the Si must be implanted into both the Ni films and the PI (or other oxygenated polymers) in order to maximize the adhesion enhancement of Ni films.

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