Effects of substrate bias voltage on adhesion of DC magnetron-sputtered copper films on E24 carbon steel: investigations by Auger electron spectroscopy

Abstract

The adhesion strength of copper thin films on E24 carbon steel substrates was studied using the scratch test via the critical load. Coatings were deposited by a DC magnetron sputtering system. All substrates were mechanically polished; some of them were directly coated and others were ion-etched by argon ions prior to deposition process. The effects of substrate negative bias voltage during the film growth were investigated. Experimental results showed that the critical load depended on the bias voltage and that the higher bias voltage, the better adhesion. It was also observed that the deposition rate of deposited films gradually decreased with the increase of the substrate bias voltage. Furthermore, the working pressure during the substrate ion bombardment etching greatly affected the critical load. Scanning electron microscopy was used to observe the scratch tracks to accurately evaluate the critical load. Substrate surface profiles obtained by a mechanical profilometer showed that the critical load increased with the increase of the surface roughness. The analysis by Auger electron spectroscopy revealed that the interface, in case of an unbiased substrate, was relatively narrow and abrupt. However, in case of a bias voltage application, the interface was wider and more diffuse. These results suggest that the mechanisms involved in critical load enhancement are due firstly to the substrate surface roughness and the substrate temperature generated by the ion bombardment, secondly to the physical mixing in the interfacial domain and the densification of the deposited material created by the bias voltage.

Correlation between the Interface Width and the Adhesion Strength of Copper Films Deposited on Ion-Etched Carbon Steel Substrates by Varying the Bias Voltage

“…So, three series of specimens were produced and analyzed with negative bias voltages of 0, 300 and 600 V. Nevertheless, all the samples received before deposition process an in situ ion bombardment etching treatment with argon ions. The experimental conditions of ion bombardment etching that were obtained in a previous study [9] represent the optimal conditions giving the higher critical load in the adhesion scratch test namely argon pressure of 10 Pa, cathodic voltage of 600 V and ion etching time of 10 min. When the ion etching was performed, the pressure in the vacuum chamber was adjusted to the desired pressure, the bias voltage was immediately applied to the substrate and the film deposition process started.…”