Abstract
The residual stress of thin films during the deposition process can cause the components to have unpredictable deformation and damage, which could affect the service life and reliability of the microsystems. Developing an accurate and reliable method for measuring the residual stress of thin films at the micrometer and nanometer scale is a great challenge. To analyze the residual stress regarding factors such as the mechanical anisotropy and preferred orientation of the materials, information related to the in-depth lattice strain function is required when calculating the depth profiles of the residual strain. For depth-resolved measurements of residual stress, it is strategically advantageous to develop a measurement procedure that is microstructurally independent. Here, by performing an incremental focused ion beam (FIB) ring-core drilling experiment with various depth steps, the digital image correlation (DIC) of the specimen images was obtained. The feasibility of DIC to FIB images was evaluated after the translation test, and an appropriate procedure for reliable results was established. Furthermore, the condition of the film in the function of residual stress was assessed and compared to elucidate the applicability of this technology.
Highlights
For modern microsystem technologies, it is important to understand the residual stress of thin films, as they might cause some unforeseeable damages or deformation to the components because of the residual stress accumulated during the deposition
The focused ion beam (FIB) combined with scanning electron microscopy (SEM) image
Full-field measurements of the surface deformation of each sample on each milling step were performed by digital image correlation (DIC)
Summary
It is important to understand the residual stress of thin films, as they might cause some unforeseeable damages or deformation to the components because of the residual stress accumulated during the deposition. It is a great challenge to conduct a reliable modeling and measurement for the residual stress of micro and nanostructured thin films. In order to realize the residual stress in a manner that considers the mechanical anisotropy and the preferred orientation of the materials, the detailed understanding of strain function corresponding to the depth lattice is required when analyzing depth profiles of residual strain [1]. There are several ways to measure residual stress, which can be divided into non-destructive, semi-destructive, and destructive. The most commonly used is the non-destructive measurement method, the X-ray diffraction (XRD). The lattice function of the material must be considered, and it cannot measure amorphous materials. Developing a Materials 2020, 13, 1291; doi:10.3390/ma13061291 www.mdpi.com/journal/materials
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