Abstract
Compressive residual stresses generated during thin film deposition may lead to undesirable film damage, such as delamination, buckling, and flaking, ultimately leading to the failure of the device employing the film. Understanding the residual stress generation and role in these damage mechanisms is necessary to preserve thin film integrity and optimize its functional properties. Thin shell theory has been used for decades to predict buckling but the results have not yet been correlated with experimental data since the techniques used to measure stress in metallic films were not able to do so at the required micron scale until recently. Micro scanning X-ray diffraction now enables the direct mapping of the local stress of metallic films. In this paper, finite element method based on thin shell theory and synchrotron X-ray micro diffraction have been used to determine stress maps of thin film buckling patterns. Calculations of the stress distribution in the metallic films have been performed taking into account the buckling geometry determined from optical measurements. Stress distributions over gold blisters and tungsten wrinkles obtained with the two techniques are in fair agreement and allow for the accurate determination of the stress relaxation profile from the bottom to the top of the buckling, validating the thin shell theory model.
Highlights
The phenomenon of stress buildup during film deposition on substrates has been known for many years
Compressive residual stresses generated during thin film deposition may lead to undesirable film damage, such as delamination, buckling, and flaking, leading to the failure of the device employing the film
Determination of residual stresses in thin films is often performed experimentally over the global film surface, mapping of the local stress distribution being rarely performed for metallic films [13]
Summary
The phenomenon of stress buildup during film deposition on substrates has been known for many years. The micro-Raman technique may be applied for stress mapping at a micron scale and recent works have illustrated its potential for thin film wrinkles [11,20] This technique may only be considered for specific materials, such as ceramics, oxides and semiconductors with well-defined microstructure, and does not work for metals [20]. Stress mapping of buckling patterns of thin film deposited on silicon substrates is investigated by micro-scanning monochromatic X-ray diffraction and finite element analysis. Use of μSXRD to measure the distribution of stresses is classical and was performed for the first time in gold and tungsten films using the sin2Ψ method [13] This characterization technique is very useful to study systems developing mechanical instability such as film/substrate systems [4,10], especially when buckling occurs.
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