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 high ly thermally-conductive electronics packages has fostered a number of efforts to develop adherent metallization systems for AlN. In this stu dy, thin films of Au have been thermally evaporated onto polycrystalli ne AlN substrates under a variety of conditions, and studied using X-r ay diffraction (XRD), in conjunction with transmission electron micros copy (TEM). It has been shown that the root mean squared strain obtain ed from the Warren-Averbach method based on X-ray peak broadening offe rs a qualitative non-destructive measure of interfacial adhesion betwe en the Au film and the AIN substrate. Interfacial adhesion between Au and AlN has been shown to improve with increasing substrate surface ro ughness, improving deposition vacuum, increased substrate surface clea nliness, and when a Cr or Al2O3 inter-layer is present between the fil m and the substrate. A method based on X-ray line shift data was utili zed to calculate stacking fault probabilities in the Au films. It was found that the density of stacking faults increased with improving int erfacial adhesion for a given substrate surface roughness. TEM reveale d numerous twins steeply inclined to the film/foil surface, although t he twinning probability calculated via XRD based on peak asymmetry was small, suggesting a low twin density parallel to the film surface. Al l 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 th e substrate surface. The in-plane grain size and film texture were fou nd to have little dependence on the substrate surface preparation, alt hough Variations in the crystallite sizes measured by XRD suggested th at the through-thickness grain size may depend on interfacial adhesion . (C) 1997 Elsevier Science S.A.