Residual stresses in polycrystalline Cu/Cr multilayered thin films

Abstract

Residual stresses in sputter-deposited Cu/Cr multilayers and Cu and Cr single-layered polycrystalline thin films were evaluated by the substrate curvature method. The stresses in the multilayers were found to be tensile and to increase in magnitude with increasing layer thickness (h) to a peak value of ∼1 GPa for h ‫ס‬ 50 nm. For h > 50 nm, the residual stress decreased with increasing h but remained tensile. The same trends were observed in single-layered Cu and Cr thin films, except that the maximum stress in Cu films is 1 order of magnitude lower than that in Cr. Transmission electron microscopy was used to study the microstructural evolution as a function of layer thickness. The evolution of tensile growth stresses in Cr films is explained by island coalescence and subsequent growth with increasing thickness. Estimates of the Cr film yield strength indicated that, for h ജ 50 nm, the residual stress may be limited by the yield strength. Substrate curvature measurements on bilayer films of different thicknesses were used to demonstrate that a non-negligible contribution to the total stress in the multilayers arises from the interface stress.

Tensile stress in hard metal films

“…Here phenomenological Hall-Petch type models, 4 based on film thickness and plastic deformation erroneously predicted square root dependence of stress on thickness. [5][6][7] By combining the 30 year old grain boundary shrinkage model, modern grain growth models for nonrecrystallizing films and accurate stress gradient measurents we show that stress and grainsize codevelop in hard polycrystalline metal films.…”

“…It was, however, noted that both for bcc metals as well as for fcc metals the stress in thicker films is less than the stress in thinner films, all other things being equal. 7 For bcc polycrystalline films we assume that at each height in the film stress is generated at the moment of deposition and that the stress at that height in the film is preserved during further growth of the film. In order to test this hypothesis we deposited a 1.1 m Cr film on a Si wafer and etched the Cr film back in a number of steps.…”

“…Misra et al 7 presented data on stress and grain growth in Cr films deposited in a parallel plate reactor. We can describe both the stress and the grainsize development in their experiments with a power pϭ0.39 and a grain boundary shrinkage ⌬ϭ0.006 nm.…”

Mechanical Properties of Nanostructured Metals

“…Interfacial stress can be obtained by combining these techniques (Ag-Ni [192], Au-Ni [193], Ag-Cu [194], Ni-Mo [195], Cu-W [196]) or by monitoring s f during deposition using in situ substrate curvature techniques (Ag-Cu [197]; Pd-Pt, Cu-Pd, Cu-Pt [198]). Another option is to combine measurements of s f for the multilayer film with s A and s B measurements based on tests of single A and B films (Cu-Cr [199], Cu/330 stainless steel [200]). An implicit assumption is that s A and s B values from single films approximate those in the multilayer.…”

Optimum Design of Ultrahigh Strength Nanolayered Composites

“…The changes in the residual stress during ion irradiation are explained by considering the manner in which the interatomic distances and forces change during irradiation, and the generation of defects during irradiation. A detailed account of the work has been published in (14,18,(20)(21)31).…”