The Art of Molecular Dynamics Simulation
The Art of Molecular Dynamics Simulation
Interpretation of texture changes during self-annealing of electroplated copper
Microelectronic Engineering
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This paper presents two new experimental observations on electrodeposited copper: unusual morphology as seen in the scanning electron microscope at high magnification, and mechanical properties, as measured by tensile testing. We report detailed characterization of a 2.6 µm thick copper electrodeposit, made on silicon using laboratory procedures and similar to materials now widely used in advanced electronic interconnect structures. The microstructure was characterized by X-ray diffraction, electron backscattered diffraction, imaging in a field emission scanning electron microscope (FESEM), and microtensile testing. Initial observations indicated microstructural dimensions and mechanical properties in the expected ranges. However, using high-magnification, high resolution imaging in the FESEM, we found a surprising result: the morphology of this electrodeposit resembled an agglomeration of round balls or spheres approximately 30-50 nm in diameter. Both X-ray and electron diffraction results showed grain and subgrain sizes much larger than the individual spheres. Molecular dynamics (MD) simulations of spheres of copper atoms were carried out to interpret the observations, and produced a degree of interpenetration of the spheres that was consistent with the observations. However, in MD simulations of two initially misoriented spheres of up to a thousand atoms, with diameters up to 3 nm and for durations up to 30 ps, the spheres readily agglomerated but remained misoriented. So, the mechanism and rate of crystallographic grain growth within the agglomeration of spheroids remains unknown. This unusual spheroidal morphology may be related to the unusual room-temperature grain growth observed in electrodeposited copper.