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Competition between dislocation nucleation and void formation as the stress relaxation mechanism in passivated Cu interconnects
J. Zhanga, J.Y. Zhanga, G. Liua, Y. Zhaoa and J. Suna
aState Key Laboratory for Mechanical Behavior of Materials and School of Materials Science and Engineering, Xi'an Jiaotong University, Xi'an 710049, China
Received 6 March 2008; revised 26 November 2008; accepted 10 December 2008. Available online 24 December 2008.
Abstract
We perform systematic calculations to study the competition between the dislocation nucleation and void formation as stress relaxation mechanism in Cu interconnects under thermal stress, which is related to the aspect ratio (ratio of the film thickness to width) of the Cu lines. It is quantitatively found from both elastic-perfectly plastic model and kinematic strain hardening model that there exists a critical aspect ratio, below and above which the stress relaxation is dominated by the dislocation nucleation and void formation, respectively. The critical aspect ratio is revealed to modulate by both the length scale of the interconnects and the interfacial strength between the Cu lines and surroundings, suggesting potential application to achieve artificial controlling on stress relaxation mechanism in Cu lines. Calculations are in good agreement with available experiments.
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Unusual thermal fatigue behaviors in 60 nm thick Cu interconnects
J. Zhanga, J.Y. Zhanga, G. Liua, Y. Zhaoa, X.D. Dinga, G.P. Zhangb and J. Suna
aState Key Laboratory for Mechanical Behavior of Materials and School of Materials Science and Engineering, Xi’an Jiaotong University, Xi’an, 710049, ChinabShenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
Received 21 June 2008; revised 16 September 2008; accepted 9 October 2008. Available online 21 October 2008. -
Thickness dependent fatigue life at microcrack nucleation for metal thin films on flexible substrates
X J Sun1, C C Wang1, J Zhang1, G Liu1, G J Zhang1, X D Ding1, G P Zhang2 and J Sun1,3
1 State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China
2 Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, People's Republic of China
3 Author to whom any correspondence should be addressed.
E-mail: junsun@mail.xjtu.edu.cnAbstract. For polymer-supported metal thin films used in flexible electronics, the definition of the fatigue lifetime at microcrack nucleation (FLMN) should be more physically meaningful than all the previous definitions at structural instability. In this paper, the FLMN of Cu films (with thickness from 100 nm to 3.75 µm) as well as Al thin films (from 80 to 800 nm) was experimentally characterized at different strain ranges and different thicknesses by using a simple electrical resistance measurement (ERM). A significant thickness dependence was revealed for the FLMN and a similar Coffin–Manson fatigue relationship observed commonly in bulk materials was found to be still operative in both the films. Microstructural analyses were carried out to verify the feasibility of ERM correspondingly.
Print publication: Issue 19 (7 October 2008)
Received 8 July 2008, in final form 5 August 2008
Published 11 September 2008
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