Electromigration Reliability Of Cu Interconnects Research Articles

Reinforcement in electromigration reliability of Cu interconnects by alloying of extremely dilute MnO

Nonconformal high-aspect-ratio trenches/vias filling has limited the use of conventional sputtered Ta/TaN liner/barrier for Cu metallization on nanoscaled technology nodes. The self-forming alloyed metallization could offer an alternative barrier-layer/capping-layer thinning scheme for the downsizing Cu interconnects. This study reports an entire-wet process involving trench-filling of electroless plating Cu interconnects alloyed with and without an extremely dilute MnO content of 0.10%. The electromigration (EM) reliability and thermal stability of the Cu(MnO) metallization were evaluated for interconnect applications in integrated circuits. Incorporating the diluted MnO can significantly enhance the EM reliability by a factor of nine by shifting the failure mechanism towards void growth. The failure mode is thoroughly evaluated through analysis of the activation energies and current-density scale factors obtained from Black’s equation. The proposed scheme has promised the application for the nanoscaled technology nodes. The reinforcement in EM reliability by self-forming Cu(MnO) will be elucidated.

Electromigration in Dual-Damascene CuMn Alloy IC Interconnects

Electromigration reliability of Cu interconnects is an important issue for continued performance improvement of IC technologies. In this paper, we investigate the impact of Mn impurities on the electromigration drift velocity of Cu conductors. Under accelerated test conditions, the drift velocity in CuMn alloys is reduced by an order of magnitude compared with pure Cu with polycrystalline microstructure. Dilute CuMn alloys exhibit a large activation energy for drift of 1.05 eV, which is significantly increased above that for pure Cu as a result of a 0.2 eV impurity(Mn)-vacancy binding energy. There is no measurable impact of the presence of the Mn dopant on diffusion along the Cu/dielectric cap interface in the samples studied here.

Grain structure effect on electromigration reliability of Cu interconnects with CoWP capping

Abstract

Electromigration in damascene copper interconnects of line width down to 100 nm

The electromigration reliability of Cu interconnects of line width down to 100 nm is investigated. The activation energy for the electromigration failure of the line width of 150 nm is found to be 1.2 eV, and the Cu/Ta interface is found to be the fast diffusion path for the line widths of 100 nm and 150 nm without any catastrophic void formation in the lines. An atomic flux divergence-based finite element model is used to explain the observed failure sites. Both the resistivity and electromigration reliability of the fabricated interconnects are found to be promising for future technology nodes.

Isothermal stress relaxation in electroplated Cu films. II. Kinetic modeling

In Part I we reported experimental results obtained from isothermal stress relaxation tests of electroplated Cu thin films with and without a passivation layer and deduced grain-boundary and interface diffusivities based on a kinetic model. Here in Part II we describe the detail of the model, which is based on coupling of grain-boundary diffusion with surface diffusion for unpassivated films and with interface diffusion for passivated films. Numerical solutions are obtained for the coupled diffusion problems and analytical solutions are obtained for several limiting cases. The effects of surface diffusivity and interface diffusivity on stress relaxation of polycrystalline thin films are analyzed and compared with experiments. The model predicts a transient behavior of stress relaxation and provides a quantitative correlation between stress relaxation and the kinetics of mass transport. In particular, the models can be used together with isothermal stress relaxation tests to characterize interface diffusion and to evaluate selected cap layers for improving electromigration reliability of Cu interconnects.

Isothermal stress relaxation in electroplated Cu films. I. Mass transport measurements

Recent studies on Cu interconnects have shown that interface diffusion between Cu and the cap layer dominates mass transport for electromigration. The kinetics of mass transport by interface diffusion strongly depends on the material and processing of the cap layer. In this series of two papers, we report in Part I the interface and grain-boundary mass transport measured from isothermal stress relaxation in electroplated Cu thin films with and without a passivation layer and in Part II a kinetic model developed to analyze the stress relaxation based on the coupling of grain boundary and interface diffusion. We show that a set of isothermal stress relaxation experiments together with appropriate modeling analysis can be used to evaluate the kinetics of interface and grain-boundary diffusion that correlate to electromigration reliability of Cu interconnects. Thermal stresses in electroplated Cu films with and without passivation, subjected to thermal cycling and isothermal annealing at selected temperatures, were measured using a bending-beam technique. Thermal cycling experiments showed the effect of passivation and provided information to select the initial stresses and temperatures for isothermal stress measurements. Isothermal experiments at moderate temperatures showed a significant transient behavior of stress relaxation. Based on the kinetic model developed in Part II, grain boundary and interface diffusivities were deduced. While the deduced grain boundary diffusivity reasonably agrees with other studies, the diffusivity at the Cu∕SiN cap layer interface was found to be generally lower than the grain-boundary diffusivity at the temperature range of the present study.

Electromigration performance of electroless plated copper/Pd-silicide metallization

The electromigration reliability of Cu interconnects has been studied under DC, pulse-DC, and bipolar current stressing conditions. Electroless plating was used to selectively deposit Cu in oxide trenches by using Pd silicide as a catalytic layer at the bottom of the trenches to initiate copper deposition. The DC and pulse-DC lifetimes of Cu are found to be about two orders of magnitude longer than that of Al-2%Si at 275 degrees C, and about four orders of magnitude longer than that of Al-2%Si when extrapolated to room temperature. On the other hand, Cu AC lifetimes are found to be comparable to the AC lifetimes of Al-2%Si. The pulse-DC lifetime of copper interconnects follows the similar frequency and duty factor dependence as aluminium and the prediction of the vacancy relaxation model.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>