Microstructures and Mechanical Properties of Sputtered Cu/Cr Multilayers

Abstract

The microstructures and mechanical properties of Cu/Cr multilayers prepared by sputtering onto (100) Si substrates at room temperature are presented. The films exhibit columnar grain microstructures with nanoscale grain sizes. The interfaces are planar and abrupt with no intermixing, as expected from the phase diagram. The multilayers tend to adopt a KurdjumovSachs (KS) orientation relationship: ( 110)Cr // ( 11 1 )Cu, 4 1 b C r // <1 lO>Cu. The hardness of the multilayered structures, as measured by nanoindentation, increase with decreasing layer thickness for layer thicknesses ranging from 200 nm to 50 nm, whereas for lower thicknesses the hardness of the multilayers is independent of the layer thickness. Dislocation-based models are used to interpret the variation of hardness with layer periodicity. The possible effects of factors such as grain size within the layers, density and composition of films and residual stress in the multilayers are highlighted. Comparisons are made to the mechanical properties of sputtered polycrystalline Cu/Nb multilayers which, like Cu/Cr, exhibit sharp f c c h c interfaces with no intermixing and a KS orientation relationship, but have a small shear modulus mismatch.

Electrical resistivity of sputtered Cu/Cr multilayered thin films

“…8,13 No significant oxygen in the Cr film was detected by ionbackscattering spectroscopy. 8 The observed SADP pattern is ring-type ͓Fig. 1͑b͔͒, consistent with the nanoscale grain size.…”

“…The residual stress in Cu films was on the order of 50 MPa. 8 Most of the grains in Cu show twins. Presumably, twinning is a mode of stress relaxation during growth of Cu films.…”

“…The residual stresses and mechanical properties of these multilayers have been published elsewhere. 8,9 At any given temperature, the effect of layer thickness on the electrical resistivity is explained using a model that accounts for interface scattering and the resistivities of single-layered films as a function of film thickness.…”