Factors Influencing Adhesion of Submicrometer Thin Metal Films: A Critical Review
Résumé
The scratch test was used to determine the coating-substrate adhesion of d.c. magnetron-sputtered films on substrates. Several systems are discussed, including Cu, Al, AlN/XC70 steel; Cu, Au/Al2O3; and Cu/Ni. Furthermore, the following effects of deposition conditions on adhesion are also discussed: the effect of heating the sample during or after deposition; the effect of applying a bias voltage on the substrate during deposition; the effect of ion bombardment etching of the substrate surface; the effect of ageing treatment after deposition; the effect of chemical etching treatment before deposition.
The scratch track was observed by scanning electron microscopy (SEM), and some energy-dispersive X-ray spectra were recorded to reveal whether the coating was completely removed from its substrate or not. The adhesion failure probability was estimated for each load (Q) by optically inspecting the channels. A correlation between the thermal contact resistance and the adhesion, as determined by the scratch test, is found. To understand the origin of the mean critical load and interface evolution, observations were made using SEM, Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The results show that the structural change of the film and formation of a complex interface appear to be the main reasons for interface evolution. In most cases, the widening of the interfacial region offers a better film anchorage to its substrate, which requires a notably high stylus load to produce an adhesion failure.