M.R. Elizalde

Cross-sectional nanoindentation: a new technique for thin film interfacial adhesion characterization

Abstract Interfacial adhesion is becoming a critical material property for improving the reliability of multilayer thin film structures used in microelectronics. Cross-sectional nanoindentation (CSN) is a new mechanical test especially designed for measuring the fracture toughness of thin film interfaces. Interfacial fracture is achieved by nanoindentation in the structure cross-section. A model based on the elastic plate theory has been developed to calculate numerically the interfacial critical energy release rate (Gci) for ceramic–ceramic systems from CSN test results. The model inputs are the thin film elastic properties, thin film thickness, interfacial crack area and maximum thin film deflection during the test. Closed form analytical solutions, obtained for two limiting cases, are consistent with the numerical approach. This technique has been successfully applied to silicon nitride–silicon oxide thin films, commonly used as electrical isolators in microelectronic devices.

Interfacial fracture induced by cross-sectional nanoindentation in metal–ceramic thin film structures

Abstract The cross-sectional nanoindentation (CSN) technique is extended to examine the fracture properties of thin film metal–ceramic interfaces. The methodology includes the selection of appropriate indentation parameters to achieve controlled interfacial delamination together with finite element modelling to estimate the contribution of plasticity of the metallic film to the overall interfacial fracture process. The results show good agreement with four-point bending, a method commonly used to measure thin film interfacial toughness, provided that mode mixities are similar. In addition, CSN allows observation of the interfacial crack by scanning electron microscopy and a local measurement of adhesion, with debonded areas in the range of 100–1000 μm2. The numerical modelling of the test provides an estimate of the intrinsic interfacial adhesion energy, separating the effects of metal plasticity.

Adhesion Studies in Low‐k Interconnects Using Cross Sectional Nanoindentation

The thermo‐mechanical robustness of interconnect structures is a key reliability concern for integrated circuits. Cross‐sectional nanoindentation (CSN) was developed to characterize the interfacial adhesion in blanket films deposited on silicon substrates. Recently, this technique has been adapted to the study of adhesion failure in real interconnect structures. The method has been applied to test chips simulating a portion of the interconnect structure and it has proven useful to study local adhesion effects in patterned structures. The test has been modelled using an FE code and cohesive elements developed in house to improve the understanding of the crack path and its interaction with the different structures present in the interconnect stack.

Damage Induced in Interconnect Structures Mimicking Stresses During Flip Chip Packaging

Flip‐chip packages are produced by an interconnection technique in which the active area of a chip is mounted by various interconnecting materials on a multilayer substrate [1]. While flip‐chip technologies have progressed rapidly and are now widely used, they present special reliability concerns [2–4]. A large thermal expansion mismatch between the chip and the substrate increases the likelihood of fatigue failure in solder joints under cyclic thermal loading [2, 3]. In addition, the thermal mismatch often results in the delamination of interfaces between two materials, which eventually leads to mechanical and/or electrical failure [4]. In this paper piezo actuators are used to mimic stresses during packaging assembly and in operation. The test has been modeled using finite elements and the results show that the level of stresses reached during packaging can be attained. Electronic speckle‐pattern interferometry (ESPI) was applied for noncontact, real‐time evaluation of the deformation. Failure analysis ...