Song, Xiaoning (2011)
M.Phil. thesis, University of Birmingham.
Nanostructured materials have assumed increasing scientific and technological interest due to the significant improvement of mechanical properties compared to their coarse-grained counterparts. Nanostructured electrodeposited copper film, for example, is of interest for applications in ultra large-scale integrated (ULSI) devices. However, the microstructure evolution of the copper film at room temperature, which is termed self annealing, can cause reliability problems. The understanding of the microstructure, in particular the stability of the electrodeposited Cu film, relative to its mechanical properties, is essential to the further development of the performance and reliability of the resulting devices. In this work, the microstructure and mechanical properties of electrodeposited copper films have been investigated. These copper films were electrodeposited in an additive free acidified copper sulphate solution by employing either direct current (DC) or pulsed current (PC) of different current densities. The microstructure of the films has been studied using electron microscopy and the mechanical properties have been examined using nanoindentation. It has been noted that the microstructure of the thicker electrodeposited copper films was controlled by deposition parameters. It has been found that the substrate has no significant effect on the texture of the thick copper films formed where the growth direction is parallel to <110>. The twin density in the deposited copper film seems varying with the off-time of the deposition and the highest twin density was observed in the sample deposited with 0.02 s on time and 2 s 3 off-time. Self-annealing (grain growth at ambient condition) of the deposited copper film has been confirmed using focused ion beam imaging and back-scattered electron imaging. Grains with <110> parallel to the film normal direction have a large propensity to grow than those with other orientations. The nanoindentation results show that the high hardness over elastic modulus ratio measured is associated with the high twin density.
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