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1049-AA03-05

Microstructure and Mechanical Properties Characterisation of Nanocrystalline Copper Films Nursiani Indah Tjahyono, and Yu Lung Chiu Department of Chemical and Materials Engineering, University of Auckland, 20 Symonds Street, Auckland, 1142, New Zealand ABSTRACT The microstructure and mechanical properties of nanocrystalline copper with grain size ranging from 50 nm to 80 nm have been investigated. Nanocrystalline copper films were electrodeposited from an additive-free acidified copper sulphate solution at room temperature by employing constant current at different current density magnitudes between 20 and 80 mA/cm2. Both austenitic and ferritic steel substrates with the same surface finishing conditions have been used for the deposition. The microstructure of the films has been further studied using electron microscopy techniques, and the mechanical properties using nanoindentation technique. The nanoindentation study was carried out on both the plan view and cross-sectional directions to study the isotropy characteristic of the copper film. It has been noted that both the modulus and hardness measured following the Oliver-Pharr scheme show an apparent indentation size effect tested on the cross-sectional sample. INTRODUCTION Over the years, there has been an increasing interest in the development of thin film systems. Understanding of the mechanical properties and deformation mechanism of these materials is crucial to the development of reliable devices. Nanoindentation technique has been developed to provide an easier approach to evaluate the mechanical properties of thin films without complicated sample preparation and significantly reduced the sample size requested for testing and is considered as a non-destructive method [1]. Thin films often contain very small sized grains (e.g. nanocrystalline films) and many studies have shown that they exhibit very different microstructure and mechanical behaviours in comparison to their conventional coarse-grained counterparts [2]. This is because nanocrystalline materials contain a relatively high grain boundary volume fraction which in turn influenced their mechanical properties, such as the yield strength, hardness and ductility, considerably [2, 3]. Furthermore, the film/substrate interface in the thin film system plays a role in restraining the dislocation motion thus increases the film hardness with decreasing film thickness [4]. Thin film copper has been widely used as an interconnect material in microelectronic devices as well as in the integrated circuit manufacturing industry [2, 5]. Many studies have been conducted to characterise the mechanical properties of the copper thin film including the effect of different substrates by Fang and Chang [6] and Beegan et al [7], the effect of copper film thickness by Volinsky et al [8] and the

tribological properties of nanocrystalline copper by Tao and Li [5]. Nevertheless, most of these studies have focused on the plan view samples and studies on the cross section samples are rare, despite the fact that t