Analysis of the influence of structure on mechanical properties of multilayer Ni/Cu thin films for use in microelectronic technologies

Abstract

Multilayer Ni/Cu thin films were produced by dual-bath electrodeposition technique (DBT) on polycrystalline cold-rolled Cu substrate. Different Ni/Cu multilayer structures were realized by changing of process parameters such as total film thickness, sublayer thickness and Ni/Cu sublayer thickness ratio. The mechanical properties of Vickers microhardness and interfacial adhesion in the films were investigated. Decreasing of sublayer thickness down to 300 nm and increasing of Ni:Cu sublayer thickness ratio to 1:4, lead to higher values of Vickers microhardness compared to monolayer metal films. Thin films with sublayer thicknesses from 75 nm to 5 μm show strong interfacial adhesion. A weak adhesion and sublayer exfoliation for the films with sublayer thickness greater than 5μm were found. Three-dimensional Ni microstructures can be fabricated using multilayer Ni/Cu film by selective etching of Cu layers in an acidic thiourea solution ('surface micromachining' technique).

Keywords

• Ni/Cu electrochemical deposition
• multilayer thin films
• Vickers microhardnbess
• interfacial adhesion
• selective etching