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

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.     

Adhesion studies of radio-frequency sputtered SiO2 films on Ti,stainless steel,Ni and Inconel substrates. Effects of substrate surface ion bombardment etching

The scratch test was applied to determine the adhesion strength of radio-frequency (RF) sputtered SiO₂ films to Ti, stainless steel, Ni and Inconel substrates. The effect of substrate ion bombardment etching was investigated by using a mean critical load derived from a Weibull-like statistical analysis. It was found that the mean critical load values obtained on substrates etched by ion bombardment for a sufficiently long time were two to three times those obtained on mechanically polished substrates. Scratch tracks were observed by scanning electron microscopy and some X-ray spectra were measured after the electron beam of the scanning electron microscope was focused inside the scratch channel. Depth composition profiles were also recorded by Auger electron spectroscopy. No important presence of contamination was observed in the interfacial domain even after mechanical polishing, but the width of this interfacial domain was higher after ion bombardment than after mechanical polishing. This difference in width could result from the formation of microcavities and vacancies at the substrate surface during ion bombardment. In such a case, the significant adhesion improvement should principally occur from an enhanced interlocking of the coating to its substrate.     

The effect of thermal annealing on the adherence of Al2O3 films deposited by LP-MOCVD on several high alloy steels

Thin alumina films, deposited at 280°C on several high alloy steels by low-pressure metal-organic chemical vapor deposition (LP-MOCVD), were annealed at 0.17 kPa in a nitrogen atmosphere for 2, 4, and 17 h at 600 and 800°C. Film adhesion was studied by scanning scratch testing (SST) and Auger electron spectroscopy (AES). The best adhesion properties were obtained with commercial oxide dispersion-strengthened (ODS) high-temperature alloys, especially PM 3030. Among the 'normally' high alloy stainless steels, type AISI-321 showed the best adhesion. The other stainless steel-alumina combinations exhibited a reduced critical load, L_c, after thermal treatment. Alumina on ODS alloys exhibited an increased adhesion. AES studies revealed that this increase could be explained by: (1) the presence of sulfur-trapping elements, preventing segregation of sulfur at the interface; and (2) titanium and carbon enrichment at the interface, resulting in an anchoring effect between the oxide and the substrate.