Aluminium deposition on SF sub 6 plasma-treated polycarbonate: an AFM, XPS and mass spectroscopy study

• Published in: Surface and interface analysis 1998-04, Vol.26 (4), p.306-315
• Main Authors: Seidel, C, Gotsmann, B, Kopf, H, Reihs, K, Fuchs, H
• Format: Article
• Language: English
• ISSN: 0142-2421

A systematic investigation was made of the chemical and morphological influences of SF sub 6 plasma on polycarbonate and the influence of plasma treatment on Al metallization. Mass and ion spectroscopy were used for characterization of the plasma and the etching process. X-ray photoelectron spectroscopy (XPS) measurements were applied for the chemical characterization, while atomic force mciroscopy (AFM) (static and dynamic mode) served to inspect the surface morphology. All analytical techniques were performed in an ultrahigh vacuum system, in order to prevent the polycarbonate sample from being exposed to ambient air after the plasma treatment. During the etching process we used mass difference spectra to demonstrate the removal of masses 19, 28 and 32 corresponding to HF, CO (N sub 2 ) and CF. Additionally, the inclusion of fluorine was also observed by this technique. The XPS spectra of polycarbonate surfaces show a significant inclusion of fluorine (C-F, C-F sub 2 ) and a reduction of the oxygen content after the plasma treatment. Aluminium metallization leads to the formation of an Al-F interlayer; metallic growth of Al is only observed when the metallic layers become thicker than a few nanometers. The AFM investigations have shown that even a short plasma treatment causes changes in morphology (structures with an extension of 20-40 nm). After extended plasma exposure the surface becomes very rough, resulting in poor Al adhesion. On untreated polycarbonate, Al grows in the form of weakly bound clusters, which can only be imaged in the dynamic AFM mode. After plasma treatment, Al grows in the form of well-adhering flat layers without clustering.