Stress and strain in thin films

It is well known that intrinsic residual stress generated during film growth in physical vapor deposited (PVD) coatings may have deleterious effects such as film cracking due to tensile residual stress or film delamination due to compressive residual stress. Therefore, it is crucial to study the stress generated in films during the growth process.

In multilayered films, as the thickness of individual layers approaches a few nanometers, the stress associated with interfaces may contribute much more to the overall stress than at layer thickness of a few mm. Interface stress in solids arises from the reversible work per unit area to elastically deform the interface, different from interface energy that represents the work done to create an interface. For a given multilayered system, it is useful to separate the effects of growth stresses in the layers and the interface contribution to residual stress.

Evolution of tensile residual stress in single layer Cu, 330 SS vs. total film thickness and in multilayer Cu/330 SS (with 3 bilayers) as a function of individual layer thickness. The average stress of single layer Cu and 330 SS is depicted as a dashed line.

Plot of Ds, the difference between the residual stress in multilayers and the arithmetic average of the residual stress in single layer Cu and 330 SS films, vs. 1/h that gives the interfacial stress, -1.3 ± 0.2N/m, for Cu/330 SS multilayers.

References

“Residual Stresses in Sputter-deposited Copper / 330 Stainless Steel Multilayers”, Journal of Applied Physics, 96 (2004) 7173. (PDF)

“Effects of Deposition Parameters on Residual Stresses, Hardness and Electrical Resistivity of Nanoscale Twinned 330 Stainless Steel Thin Films”, Journal of Applied Physics, in press.