Influence of the interface width on the adhesion strength of copper films deposited on negatively biased carbon steel substrates

Abstract

In order to improve the adhesion of copper films deposited by DC magnetron sputtering on carbon steel substrates, a negative bias voltage was applied to the substrate during the film deposition process. The scratch test was used to evaluate the adhesion strength of the films on the substrates. Chemical element identification and interface width measurement were carried out by Auger electron spectroscopy. The experimental results show that a variation of the bias voltage causes a change in the behaviour of the interface width similar to that of the critical load. The size of the interface width is obtained from Auger elemental depth profiles by measuring the depth of the interface between the coating and the substrate. It had a value of 45 min for an unbiased substrate and increased to 310 min at a bias of 450 V. In the latter case, the interface is relatively wide and the effects of diffusion and physical mixing of materials at the interface become preponderant. Then, the interface width decreased to 130 min at 600 V in which case it gets narrower and the phenomenon of film densification becomes prominent. In all cases, the substrate temperature generated by the bias voltage also has an effect. Moreover, it was observed in this study that the critical load increases with the size of the interface width. As a result, the application of a bias voltage contributes positively to the enlargement of the interface and consequently enhances the adhesion strength.

Keywords:

• DC magnetron sputtering
• bias voltage
• adhesion
• scratch test
• Auger electron spectroscopy

Acknowledgements

The author is grateful to Dr. D. Roptin and Mr. J. P. Roche, Ecole Centrale de Nantes, University of Nantes, France, for the Auger electron spectroscopy analyses. The author would like to thank Prof. A. Hennache, Department of Physics, Al-Imam Muhammad Ibn Saud University, Riyadh, Kingdom of Saudi Arabia, for critical reading of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author.