Adhesion studies of magnetron sputtered copper films on steel substrates: Effects of heat treatments

Abstract

The scratch test was applied to determine the coating-substrate adhesion of d.c. magnetron-sputtered copper films on steel substrates. The effect of heating the sample during or after deposition was investigated. It was found that the critical load was small at lower deposition temperatures and increased rapidly with increasing deposition temperature. Above 400 °C, no clear evidence of loss of adhesion was observed along the scratch track, whatever the applied load was. The effect of a post-deposition heating treatment on the coating-substrate adhesion of copper coatings deposited at room temperature was also studied. Above 300 °C, the heating treatment led to a rapid increase in the critical load, as a function of the heating time. The scratch track was observed by scanning electron microscopy, and some energy-dispersive X-ray spectra were recorded in order to reveal whether the coating was completely removed from its substrate or not. Elemental depth profiles were acquired by Auger electron spectroscopy. They showed that the increase in the critical load values was correlated with an increase in the width of the interfacial layer between the coating and its substrate, whether the sample was heated during or after deposition. They showed also that carbon and oxygen were eliminated from the interfacial region by heating. This elimination can contribute to the coating-substrate adhesion enhancement, but it is thought that the major part of the increase in the critical load comes from an improved anchoring of the coating to its substrate, because of an enhanced interpenetration of the film material and the substrate. However, an eventual influence of a decrease in the substrate hardness and the coating total stress cannot be ruled out, so that the mechanism might be complex.