Showing papers by "Hans Norström published in 2016"

Electromigration behavior of Cu metallization interfacing with Ta versus TaN at high temperatures

Abstract: High-temperature stability of Cu-based interconnects is of technological importance for electronic circuits based on wide band gap semiconductors. In this study, different metal stack combinations ...

High-temperature Ta diffusion in the grain boundary of thin Cu films

Abstract: In order to ascertain the applicability of the technologically well-established Cu metallization in high-temperature circuits, the authors have investigated layered metal stacks having one Ta/Cu interface at temperatures from 400 to 700 °C. The authors have found that Ta releases from the Ta layer and moves through the Cu film to the opposite interface via the grain boundaries. In the simplest bilayer stack with Cu on top of Ta, the up-diffused Ta on the surface spreads out over the Cu grains so as to cover the Cu grains completely at 650 °C. The activation energy for the grain boundary diffusion is found to be 1.0 ± 0.3 eV. The Ta diffusion in the grain boundaries leads to stabilization of the Cu grain size at 360 nm and an increase in sheet resistance of the metal stack. The latter is in fact observed for all metal stacks having Cu in contact with Ta on one side and TaN or nothing at all on the other. The implication is that the Cu metallization with one Ta/Cu interface has to be stabilized by a preanne...

Massive Ta diffusion observed in Cu thin films but not in Ag counterparts

Abstract: This letter presents an extensive investigation by means of microscopic and chemical analyses finding Ta diffusion in Cu films but not in Ag films. This difference in Ta diffusion persists in all samples containing either Cu/Ta or Ag/Ta interfaces, wherein both a driving force for diffusion and point defects for mediation of atomic movement are present. By referring to atomistic simulation results in the literature, it is plausible that the subtle difference between the Cu/Ta and Ag/Ta interfaces plays a crucial role in differentiating them in making Ta available for diffusion. The energetically favored binding between Cu and Ta assists in liberating Ta atoms from being strongly bound by surrounding Ta atoms, as the bond strength of Cu-Ta is about one third that of Ta-Ta. Hence, the formation of the much weaker Cu–Ta bonds acts as an important intermediate step. Such a mechanism does not exist for the Ag/Ta interface.