Electromigration: A review

Investigation of the effect of temperature and stress gradients on accelerated EM test for Cu narrow interconnects

Electromigration reliability of different metallization systems (Al-2%Si, Al-Cu/TiW, Cu, and TiN/Al-2%Si/TiN) and structures (Al-via and W-plug) under bidirectional current stress has been studied in a wide frequency range (from mHz to 200 MHz). The experimental results show that at low frequency, the damage healing factor and lifetime under ac stress increases with frequency. At very high-frequency regions, the pure ac lifetime was found to be determined by the thermal process (caused by asymmetrical geometry, etc.) instead of electromigration. All the observations are in agreement with an average current model.

Modeling and characterization of electromigration failures under bidirectional current stress

An a-SiC:H deposited by CVD system is the most promising dielectric diffusion barrier to replace silicon nitride in the Cu-interconnect structure due to its low dielectric constant, good Cu barrier ability, and low moisture uptake. In this paper, electrical instabilities of a-SiC:H film under electric field were reported for the first time. At electric field higher than 1.8 MV/cm and independent of the polarity, charges will be built up in the SiC film even at room temperature. A dielectric polarization model was proposed to explain this high field instability. The formation of molecular dipole is attributed to the incorporated nitrogen atoms, which distort the symmetric tetrahedral SiC molecule. The dielectric polarization is further verified by the increase of dielectric constant at high temperature and low frequency. At elevated temperature, film instability can be observed at electric field as low as 0.4 MV/cm. A carrier injection model combined with the polarization was proposed to explain the low-field instability. It is assumed that slight polarization occurs at such a low electric field because of high temperature. The dominant mechanism is electron injection from metal gate into SiC film via the Schottky emission process. It is thus recommended that the incorporation of nitrogen must be minimized and the film stability must be carefully evaluated at real circuit level.

Electrical instability of low-dielectric constant diffusion barrier film (a-SiC:H) for copper interconnect

A key element for future silicon IC technology development is the containment of electromigration – induced failure of Cu / low-k interconnects. Continued progress in meeting electromigration reliability requirements for future technology nodes will require a multi-faceted approach to the problem: first the development of effective process solutions to limit the impact of technology scaling on electromigration life-time reduction; and second, the provision of models of failure that are representative of circuit operation to determine realistic current-limiting design rules. We will show that process solutions involve limiting the rate of transport along interfaces and grain boundaries in the damascene trench architecture using metal capping layers and Cu alloys. Most models of electromigration failure have been developed using DC stress conditions, while circuits predominantly operate with non-DC (pulsed DC or AC) signals. Understanding the relationship between failure under DC and non-DC conditions is a necessary aspect of realistic reliability characterization. In this paper we review: our recent studies that establish the relationship between Cu microstructure, metallic capping and dilute Cu alloy additions and thereby identify effective scenarios for mitigation with technology scaling; and experimental studies of electromigration failure under non-DC stress that explore the physical mechanisms involved. © The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. [DOI: 10.1149/2.0171501jss] All rights reserved.

K. Konrad Young

Papers

and Aluminum Vias and Improvements Under AC Current Stress