Date of Award


Degree Type


Degree Name

Master of Engineering Science


Mechanical and Materials Engineering


Professor Robert J. Klassen

Second Advisor

Professor Andy Sun


The objective of this thesis was to study the creep behavior at 298 K of two types of cantilever microbeams: 1) free-standing beams made from sputter deposited Cu of 200 nm, 748 nm, and 13 3 5 nm thickness and 2) bilayer beams made of sputter deposited Cu of 200 nm, 300 nm and 450 nm thicknesses, deposited upon 100 nm of Si3N4. The second objective of this research was to express the measured creep rate in terms of a physically-based model of creep deformation occurring by the combined mechanisms of interfacial diffusional creep and obstacle-limited dislocation glide. The microstructure of the Cu thin films was investigated with electron microscopy and showed clearly that the grain structure was columnar, with equiaxed grain shape normal to the columns, and that the width of the columnar grains increases with increasing Cu film thickness. Equations describing the elastic bending of a cantilever beams were applied to determine the stress exponent C2 and time dependence C3 of the creep rate upon Cu film thickness. Nanoindentation bending creep tests were performed at various cantilever beam location for each microbeam thickness. Finite Element models of the cantilever microbeams were developed and were found to predict well the experimentally measured beam deflection versus time trends. The dependence of the thermal activation energy ΔF and athermal flow stress τ of the deformation rate limiting obstacles upon Cu film thickness was determined by curve fitting. ΔF and τ decreased with increasing Cu thickness while the slopes of the resulting Haasen plots increased with increasing Cu thickness. Both ΔF and î increased in magnitude for the bilayer Cu/Si3N4 microbeam compared to a freestanding Cu microbeam of the same thickness. This is probably due to the effect of the passivated layer in reducing the amount of creep resulting from surface diffusion and producing a layer of high dislocation density near passive layer interface.



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