An X-ray diffraction (XRD) study of vapor deposited gold thin films on aluminum nitride (AlN) substrates

The promise of aluminum nitride (AlN) as a substrate material for highly thermally-conductive electronics packages has fostered a number of efforts to develop adherent metallization systems for AlN. In this study, thin films of Au have been thermally evaporated onto polycrystalline AlN substrates under a variety of conditions, and studied using X-ray diffraction (XRD), in conjunction with transmission electron microscopy (TEM). It has been shown that the root mean squared strain obtained from the Warren-Averbach method based on X-ray peak broadening offers a qualitative non-destructive measure of interfacial adhesion between the Au film and the AIN substrate. Interfacial adhesion between Au and AlN has been shown to improve with increasing substrate surface roughness, improving deposition vacuum, increased substrate surface cleanliness, and when a Cr or Al2O3 inter-layer is present between the film and the substrate. A method based on X-ray line shift data was utilized to calculate stacking fault probabilities in the Au films. It was found that the density of stacking faults increased with improving interfacial adhesion for a given substrate surface roughness. TEM revealed numerous twins steeply inclined to the film/foil surface, although the twinning probability calculated via XRD based on peak asymmetry was small, suggesting a low twin density parallel to the film surface. All the films studied had similar grain sizes (similar to 50-70 nm), and possessed a weak {111} fiber texture with the fiber axis normal to the substrate surface. The in-plane grain size and film texture were found to have little dependence on the substrate surface preparation, although Variations in the crystallite sizes measured by XRD suggested that the through-thickness grain size may depend on interfacial adhesion. (C) 1997 Elsevier Science S.A.