The effect of interlayer deformation on blister test for measuring adhesive strength was analyzed by modeling the interlayer as a Winkler foundation. Critical load for the initiation of debonding along the interface between the interlayer and an elastic thin film was obtained as a function of the adhesive strength, interlayer deformation, elastic modulus of Winkler foundation, and blister size. The critical pressure increases with increasing the elastic modulus of Winkler foundation. The propagation of debonding was discussed, and the arrest of debonding was observed for the condition of constant deflection. The results provide a rational for characterizing the effect of interlayer deformation on the measurement of adhesive strength from a blister test.
IntroductionTechnological demand for good adhesion of thin films on substrates has arisen in many applications, including reflective coatings on optical components, metallic coatings and conducting patterns on semiconductor chips, and their packaging substrates. Ideally, the bonding of a thin film to a substrate should be physically strong, and bonding strength should not be degraded with time and the normal usage of the structures. This suggests that the interface between the thin film and the substrate must be chemically and thermodynamically stable. In reality, depending on the application condition and environment, the bonding interface may be subjected to cyclic thermal stresses and surface forces. It is nevertheless possible that a strong bonding interface becomes weakened and degraded due to applied physical and chemical stresses. Interfacial defects will lead to the occurring of interfacial failure, such as the initiation and propagation of a crack in the interface.Characterization of interfacial strength becomes of importance in quantitative evaluation of the bonding quality between thin films and substrates. The blister test [1][2][3][4][5][6][7] is often used to measure the adhesive strength between a thin film and a substrate. The test is performed by etching a hole through the substrate, and the film is then left tented over the hole by applying hydrostatic pressure on the film from the substrate side until delamination or tearing of the film occurs. The energy needed to separate the film from the substrate and the adhesive strength can be calculated from the hydrostatic force and the work done on the back of the film as a function of geometry of the blister and