Subcritical debonding of polymer/silica interfaces under monotonic and cyclic loading Original Research Article

The effects of interface chemistry and alternating mechanical loads on subcritical debonding of thin polymer layers from inorganic dielectrics are of significant interest for the integrity of devices used in a range of modern technologies. However, the mechanisms of subcritical debond growth at polymer interfaces, particularly under cyclic loads, are not well understood. Such subcritical debonding of a representative polymer dielectric (benzocyclobutene) to a silica-passivated silicon substrate was studied under cyclic and monotonic loading in moist environments. The effect of interface chemistry on subcritical debonding was evaluated using selected amino- and vinyl-functional silane adhesion promoters. Debond growth rates over the range of 10−3–10−9 m/s were characterized under Mode I and mixed Mode I/Mode II loading. AFM and XPS results suggest that the failure mode of the BCB was cohesive in a region very close to the interface. Fatigue loading was found to significantly accelerate subcritical debond growth rates, producing fatigue striations with a striation height of ~1–2 nm and a spacing that was correlated with the debond growth rate. A model is presented for the mechanism of striation formation.