Adhesion studies in integrated circuit interconnect structures

Abstract The thermo-mechanical robustness of interconnect structures is a key reliability concern for integrated circuits. The miniaturization process and the package/silicon interaction result in an increase of the thermal stresses whilst the use of new low- k materials, with degraded mechanical properties, makes it more and more difficult to predict their in-service behavior. A new testing technique for the characterization of the mechanical behavior of the interconnect structures is introduced in this paper. The technique is called modified cross-sectional nanoindentation (MCSN) and it is the result of extending cross-sectional nanoindentation (CSN) to patterned structures. As in the conventional CSN, a Berkovich indenter is used to initiate fracture in the silicon substrate of the interconnect structure. The cracks propagate through this structure, preferentially along the weakest interfaces in the system. In this novel technique, focused ion beam (FIB) is used for the sample preparation, machining a trench parallel to the indentation surface. In this way, the crack growth can be better controlled, and the problem may be modelled in two dimensions. The results obtained with this technique correlate well with those obtained by four-point bending (4 PB) for the interfacial adhesion in blanket films. The MCSN technique proposed in this paper is better suited to study local adhesion in patterned structures and has also proven useful for the study of crack propagation through the interconnect structure.