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Research Papers

Evaluation of the Dominant Factor for Electromigration in Sputtered High Purity Al Films

[+] Author and Article Information
X. Zhao

Department of Nanomechanics, Tohoku University, Aoba 6-6-01, Aramaki, Aoba-ku, Sendai 980-8579, Japanzhao@ism.mech.tohoku.ac.jp

M. Saka

Department of Nanomechanics, Tohoku University, Aoba 6-6-01, Aramaki, Aoba-ku, Sendai 980-8579, Japan

M. Yamashita, F. Togoh

 Fuji Electric Advanced Technology Co. Ltd., Hino, Tokyo 191-8502, Japan

J. Electron. Packag 132(2), 021003 (Jun 11, 2010) (9 pages) doi:10.1115/1.4001687 History: Received August 20, 2009; Revised April 14, 2010; Published June 11, 2010; Online June 11, 2010

This paper is focused on evaluating the dominant factor for electromigration (EM) in sputtered high purity Al films. A closed-form equation of atomic flux divergence by treating grain boundary diffusion and hillock formation in a polycrystalline structure without passivation layer was derived to construct the theoretical model. According to the developed equation, it is available to see the effect of various parameters on the EM resistance. Moreover, based on the proposed model, we compared the EM resistance of different sputtered high purity Al films. These films differ in purity and features, which are realized as affecting factors for the EM resistance. Finally, according to the analysis by the synthesis of the obtained EM resistance, the evaluation of the dominant factor for EM in sputtered high purity Al films was approached. Although the effects of the average grain size and the effective valence cannot be ignored, the difference in diffusion coefficient was believed to have a dominant influence in determining the EM resistance. Thus, increasing the activation energy for grain boundary diffusion can significantly reduce the damage during EM in such sputtered polycrystalline Al films.

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Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 5

Comparison of the surface morphology of the samples in group 2: (a) 4N sample and (b) 6N sample

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Figure 6

SIM images of the cross-sectional observation of the samples in group 1: (a) 4N sample and (b) 6N sample

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Figure 7

SIM images of the cross-sectional observation of the samples in group 2: (a) 4N sample and (b) 6N sample

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Figure 8

EBSD analysis and GBCD of 6N material (15 min grinding) in group 2 before experiment

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Figure 9

The experimental setup

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Figure 3

The geometry of the Al strip with a narrow section

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Figure 4

Comparison of the surface morphology of the samples in group 1: (a) 4N sample and (b) 6N sample

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Figure 10

FESEM image of 4N sample in group 1: (a) the local anode end of the narrow section before current supply, (b) the local anode end subjected to current supply for 18 h, (c) magnified view of the appeared hillocks due to EM, (d) the local cathode end before current supply, (e) the local cathode end subjected to current supply for 18 h, and (f) magnified view of the appeared voids due to EM

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Figure 11

FESEM image of 6N sample in group 1: (a) the local anode end of the narrow section before current supply, (b) the local anode end subjected to current supply for 18 h, (c) magnified view of the appeared hillocks due to EM, (d) the local cathode end before current supply, (e) the local cathode end subjected to current supply for 18 h, and (f) magnified view of the location without significant change

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Figure 12

Comparison of 4N and 6N samples in group 2 subjected to current supply for 18 h: (a) 4N sample and (b) 6N sample

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Figure 1

Modeling of polycrystalline structure

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Figure 2

A metal strip with polycrystalline structure

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