Coupling effect of the electric and temperature fields on the growth of nanocrystalline copper films

Abstract

The effect of an external static electric field on the grain growth in nanocrystalline Cu films was studied at different annealing temperatures. Transmission electron microscopy and x-ray diffraction indicate that the grain growth in Cu films is accelerated with various rates by an external electric field at different annealing temperatures. It is found that there is a coupling effect from the external electric and temperature fields on grain growth in Cu films during annealing. The growth rate is accelerated proportional to a factor f͑E͒ · T/100°C , which is determined from the theoretical derivation. The analysis indicates that the enhanced grain growth is achieved by the effect of the electric field on the vacancies migration and dislocation climb along grain boundaries.With the continuous down scaling of the size of integrated circuits ͑ICs͒, guaranteeing the reliability of microelectronic devices becomes a major challenge for semiconductor technology in the future. 1,2 Copper has a lower electrical resistivity and less electromigration than aluminum and has therefore become the dominant on-chip interconnect material in IC. 3,4 The use of copper enhances the working speed and reduces the interconnect resistance-capacitance delay. 5 The microstructure of Cu films, such as grain size and texture, can impact on the resistance to stress-induced migration and electromigration in Cu interconnects remarkably. 6,7 Generally, Cu lines with a bamboolike grain structure offer the significant advantage of antielectromigration and those with ͑100͒ texture have a higher resistance to stress-induced migration compared to those with ͑111͒ texture. 8 Especially in fast IC, the working temperatures can be quite elevated and similar holds for the electric fields that accompany small distances close to sharp features inside modern IC. 9,10 Moreover, special applications, as, for example, in certain sensors, often lead to high temperatures and high electric fields. These can change the microstructure of Cu lines 11 and will finally lead to the degeneration of the microelectronic devices. Thus, it is important to know how the microstructure of Cu films evolves in different conditions.It is well known that the growth of the grain size of nanoscale Cu films increases rapidly along with the annealing temperature. In addition to the temperature, it is also found that the electric field can influence the grain growth of metals. 12,13 However, it is still under debate whether external electric fields can accelerate grain growth or not. Jung and Conrad 14 found that the electric field could retard grain growth of electrodeposited Cu foil during annealing. However, Liu et al. 15 reported that the grain growth rate of Cu was accelerated by the field. Accelerated growth of the texture of cold-rolled steel under an applied electric field was also observed by He et al. 16 Consequently, the effect of the electric field on grain growth of Cu at different temperatures needs to be studied further. Especially interesting is the interdependence bet...

Molecular Dynamics Simulation of the Cu3Sn/Cu Interfacial Diffusion Mechanism under Electrothermal Coupling

“…Therefore, it eventually accelerates the diffusion of the interfacial atoms. Similar tendencies are also observed in the literature [12,25,26]. Based on the electron theory, vacancies in a pure metal possess a negative charge, and a lattice defect represents a form of static electrical energy resulting from a thin layer of negative charge that screens positive charges.…”

Thermal stability of the nanostructure of mechanically milled Cu–5 vol% Al2O3 nanocomposite powder particles

“…10, the value of the activation energy of grain growth of the nanocrystalline Cu matrix of the Cu-5 vol% Al 2 O 3 nanocomposite powder particles has been determined to be 63.4 kJ/mol. For comparison, the values of the apparent activation energy of grain growth of monolithic nanocrystalline Cu collected from the published literature 35,[39][40][41][42][43] along with the value obtained in this study are summarized in Table I. It can be seen that the reported values of the apparent activation energy of grain growth of monolithic nanocrystalline Cu are in the range of 30-83 kJ/mol, which is much smaller than that of the grain growth of microcrystalline Cu (211 kJ/mol).…”

Critical Assessment 39: Effects of applied fields during annealing of metals – a review

“…It is possible that structural heterogeneities existed within this material and the rather coarse grain structure was not well suited for the EBSD method that was used. Grain growth in nanocrystalline copper was studied by Cao et al [36] at several temperatures with and without a field of 300 V mm −1 . The grains grew larger and more rapidly when the field was applied, in contrast to the behaviour of bulk material [28] but consistent with the single crystal findings.…”