Chemical and Structural Characterization of Silane Adhesion Promoting Films for Use in Microelectronic Packaging

We investigate the mechanism by which an aminosilane adhesion promoter strengthens the interface between benzocyclobutene (BCB) and an oxidized silicon wafer. The adhesion promoter film is characterized using AFM and angle-resolved XPS to identify surface bond density, morphology, and chemistry for a range of adhesion promoter spin-coat solution concentrations. The adhesion strength of the SiO2 / adhesion promoter / BCB interface was also evaluated. The 0.0083% solution produces what appears to be a single monolayer on the surface, while the 0.014% concentration yields two monolayers. In both cases, the directionality of the films is preserved. That is, the amine functional group is oriented toward the BCB, and the silane groups are oriented toward the silicon oxide substrate. Finally, this solution concentration is optimized with respect to the mechanical strength of the interface, and 0.01% concentration is found to perform best. When the adhesion data is plotted versus the calculated surface bond density, a nearly linear relationship is seen, supporting a direct correlation.