Relationship between Substrate Surface Chemistry and Adhesion of Thin Films

Abstract

The surface chemical compositions of high purity Al2O3 substrates have been characterized by Auger electron spectroscopy. It was found that when a ground ceramic surface, essentially free of inorganic impurities, is annealed at a high temperature, the bulk impurities Ca and Si tend to segregate at the surface. With extended annealing, however, the surfaces become depleted of impurities, possibly due to evaporation. The adhesion of Ta2N–TiPdAu films on the same surfaces were characterized by the results of 90 ° peel tests performed on leads which were thermocompression-bonded to the films. These results demonstrate that the poor adhesion observed on ground surfaces is significantly improved when Ca and/or Si appear at the surface in significant quantities. A subsequent etching treatment, which was found to remove the Ca and Si from the surface, also degraded adhesion, while a post-etch anneal again led to the recovery of both the impurities and adhesion. It was concluded that a necessary requirement for good adherence of Ta2N–TiPdAu films to alumina substrates is the presence of a minimum amount of Ca and/or Si at the surface.