Abstract
The present study investigated the influence of nanoscale residual stress depth gradients on the nano-mechanical behavior and adhesion energy of aluminium nitride (AlN) and Al/AlN sputtered thin films on a (100) silicon substrate. By using a focused ion beam (FIB) incremental ring-core method, the residual stress depth gradient was assessed in the films in comparison with standard curvature residual stress measurements. The adhesion energy was then quantified by using a nanoindentation-based model. Results showed that the addition of an aluminum layer gave rise to additional tensile stress at the coating/substrate interface, which can be explained in terms of the differences of thermal expansion coefficients with the silicon substrate. Therefore, the coatings without the Al layer showed better adhesion because of a more homogeneous compressive residual stress in comparison with the coating having the Al layer, even though both groups of coatings were produced under the same bias voltage. Results are discussed, and some general suggestions are made on the correlation between coating/substrate property combinations and the adhesion energy of multilayer stacks. The results suggested that the Al bond layer and inhomogeneous residual stresses negatively affected the adhesion of AlN to a substrate such as silicon.
Highlights
High-quality thin coatings of aluminium nitride (AlN) have been extensively used in electronics for heat dissipation applications [1]
The present study investigated the influence of nanoscale residual stress depth gradients on the nano-mechanical behavior and adhesion energy of aluminium nitride (AlN) and Al/AlN sputtered thin films on a (100) silicon substrate
This paper reports the work that aimed to clarify the role of interfacial residual stresses in the adhesion of thin films, as measured by nanoindentation coupled with scanning electron microscopy (SEM) investigations of indentation-induced failure modes
Summary
High-quality thin coatings of aluminium nitride (AlN) have been extensively used in electronics for heat dissipation applications [1]. This paper reports the work that aimed to clarify the role of interfacial residual stresses in the adhesion of thin films, as measured by nanoindentation coupled with scanning electron microscopy (SEM) investigations of indentation-induced failure modes. To this purpose, four different coating systems were produced: a simple AlN single layer on a Si substrate, where the film was expected to be in compression; the same AlN layer with the addition of an aluminum bond layer that was designed to have tensile residual stress in the aluminum layer (as it usually happens for Al metallic sputtered layers), to investigate the effect of an inhomogeneous state of stress (tensile–compressive) on the adhesion of the coating. By combining the results from the four different samples, a discussion was made on how the residual stress distribution in Al/AlN sputtered coatings would affect adhesion and crack propagation modes
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