Adhesion Mechanisms of Silane Adhesion Promoters in Microelectronic Packaging
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Adhesion Mechanisms of Silane Adhesion Promoters in Microelectronic Packaging
Maura Jenkins, Jeffrey Snodgrass, Aaron Chesterman, Gretchen DeVries, Reinhold H. Dauskardt, and John C. Bravman Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, U.S.A. ABSTRACT Silane adhesion promoters are seeing increasing use in microelectronic packaging applications. For example, they are currently used to adhere the passivating polymer overlayer to oxide. In this paper, we present detailed studies of silane adhesion promoters on the silicon oxide surface. Two common promoters (aminopropyltriethoxysilane and vinyltriethoxysilane) as well as non-functional silanes are investigated. It was found that without a functional end group, long carbon chain silanes can severely degrade adhesion, resulting in interfaces weaker than if no silane is used. Several spin coat solution formulations are used in depositing these films. The resulting surface coverage is examined and quantified using XPS, and the adhesion behavior of various promoter films is tested in sandwich structures using a fracture mechanics approach. Finally, spin-coat solution concentration, surface coverage, and interface fracture energy are compared for the amine functional promoter. INTRODUCTION The mechanical strength of oxide/polymer interfaces in microelectronic packaging is of utmost importance, as delamination degrades the performance and reliability of the entire package. The effectiveness of these interfaces can be greatly increased through the use of adhesion-promoting organic films. The silane family of adhesion promoters is designed with functional groups at each of the two ends: one which bonds with an OH-terminated substrate and the other chosen to bond to a passivating polymer. Previous work [1] has shown that the use of either γ-aminotriethoxysilane adhesion promoter or vinyltriethoxysilane significantly improves the adhesion of benzocyclobutene (BCB) to silicon oxide. These adhesion promoters include silane groups which crosslink with one another while forming strong bonds with the substrate, as well as a functional group that bonds with the polymer overlayer. For these promoters, the functional group is either an amine group (–NH2) or a vinyl group (–C=C). The mechanism by which these molecules augment adhesion is thought to be a combination of chemical bonds, which form between the functional group and the polymer, and physical bonds, or chain entanglement, between the adhesion promoter and the polymer [2]. In this work, we attempt to isolate the effects of chemical and physical bonding to determine the respective contribution of each using the adhesion promoters discussed above as well as several “non-functional” silanes (–CH3 terminated). Also, prior work correlating surface coverage of the aminosilane to interface adhesion strength is continued. Adhesion at the interface is evaluated using a fracture mechanics approach with four-point bend test geometry. Angleresolved x-ray photoelectron spectroscopy (XPS) was used
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