Evolution of in situ growth stresses and interfacial structure in phase changing Cu/V multilayered thin films

Abstract

As the layer thickness is reduced in a Cu/V multilayered thin film, a change in phase from face centered cubic (fcc)-to-body centered cubic (bcc) can result for Cu. A series of Cu/V multilayered films with equal layer thicknesses that spanned bilayer spacing values from 40 nm to 0.6 nm have been sputtered deposited with their in situ growth stress monitored during the deposition. When the bilayer spacing was reduced, and the layers maintained their bulk phase stability, the tensile stress in the multilayer film reduced. This has been contributed to compressive strain generated at the interfaces even with Cu forming stacking faults in response to the strain. When the bilayer was at 2 nm, the Cu layer phase transformed to bcc and adopted its own lattice parameter separate from that of bcc V. Further reductions in bilayer spacing retained a crystalline bcc phase but with a matching lattice spacing between the layers. Significant intermixing was quantified by atom probe tomography even though the elements are immiscible in the bulk state. The change in phase also resulted in an increase in the film's overall tensile growth stress.