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Research Papers

Effect of Crystallographic Quality of Grain Boundaries on Both Mechanical and Electrical Properties of Electroplated Copper Thin Film Interconnections

[+] Author and Article Information
Naokazu Murata

Department of Nanomechanics,
Graduate School of Engineering,
Tohoku University,
6-6-11-716, Aoba Aramaki, Aobaku,
Sendai, Miyagi 980-8579, Japan
e-mail: naokazu.murata@rift.mech.tohoku.ac.jp

Naoki Saito

Department of Nanomechanics,
Graduate School of Engineering,
Tohoku University,
6-6-11-716, Aoba Aramaki, Aobaku,
Sendai, Miyagi 980-8579, Japan

Kinji Tamakawa, Ken Suzuki, Hideo Miura

Fracture and Reliability Research Institute,
Graduate School of Engineering,
Tohoku University,
6-6-11-716, Aoba Aramaki, Aobaku,
Sendai, Miyagi 980-8579, Japan

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received July 31, 2011; final manuscript received February 25, 2015; published online March 18, 2015. Assoc. Editor: Madhusudan Iyengar.

J. Electron. Packag 137(3), 031001 (Sep 01, 2015) (8 pages) Paper No: EP-11-1060; doi: 10.1115/1.4029931 History: Received July 31, 2011; Revised February 25, 2015; Online March 18, 2015

Effects of crystallographic quality of grain boundaries on mechanical and electrical properties were investigated experimentally. A novel method using two parameters of image quality (IQ) and confidence index (CI) values based on electron back-scattering diffraction (EBSD) analysis was proposed in order to evaluate crystallographic quality of grain boundaries. IQ value was defined as an index to evaluate crystallinity in region irradiated with electron beam. CI value determined existence of grain boundaries in the region. It was found that brittle intergranular fatigue fracture occurred in the film without annealing and the film annealed at 200 °C because network of grain boundaries with low crystallinity remained in these films. On the other hand, the film annealed at 400 °C caused only ductile transgranular fatigue fracture because grain boundaries with low crystallinity almost disappeared. From results of measurement of electrical properties, electrical resistivity of copper interconnection annealed at 400 °C with high crystallinity (2.09 × 10−8 Ωm) was low and electron migration (EM) resistance was high compared with an copper interconnection without annealing with low crystallinity (3.33 × 10−8 Ωm). It was clarified that the interconnection with high crystallinity had superior electrical properties. Thus, it was clarified that the crystallographic quality of grain boundaries has a strong correlation of mechanical and electrical reliability.

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References

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Figures

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Fig. 1

Scanning electron microscope (SEM) photographs of the cross section of the film: (a) without annealing, (b) annealed at 100 °C, (c) annealed at 200 °C, and (d) annealed at 400 °C

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Fig. 2

Outlook of a test sample attached on a test jig

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Fig. 3

Change of the stress–strain curve of the electroplated copper thin films

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Fig. 4

Change of the S–N curves of electroplated copper thin films depending on the annealing temperature

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Fig. 5

Cross-sectional SEM photographs of the fracture surface of the electroplated copper thin films after their fatigue test: (a) as electroplated, (b) annealed at 200 °C and fractured in low cycle region, (c) annealed at 200 °C and fractured in high cycle region, and (d) annealed at 400 °C

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Fig. 6

GAM map of the each films measured by EBSD: (a) as electroplating, (b) anneal at 200 °C, and (c) anneal at 400 °C

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Fig. 7

Relationship between yield stress and average grain size

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Fig. 8

Schematic crystallographic structure of the area measured by EBSD categorized by the combination of the IQ and CI values. (a) CI: high, IQ: high, (b) CI: high, IQ: low, (c) CI: low, IQ: high, and (d) CI: low, IQ: low.

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Fig. 9

Change of the IQ distribution as a function of annealing temperature

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Fig. 10

Change of the CI value distribution of the films as a function of annealing temperature

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Fig. 11

Change of the crystallinity of the electroplated copper thin films evaluated by the combination of the IQ and CI values: (a) as electroplated, (b) annealed at 200 °C, and (c) anneal at 400 °C. The area marked by light blue color is the area with low IQ value and high CI value. Red marked area is the area with high IQ value and low CI value. Dark blue area corresponds to the area with low IQ value and low CI value, and thus, grain boundary with low crystallinity.

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Fig. 12

Schematic structure of copper thin film interconnections for measurement of electrical properties of: (a) cross section and (b) overview

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Fig. 13

Change of the crystallinity of the electroplated copper thin film interconnections evaluated by the combination of the IQ and CI values: (a) without annealing and (b) annealed at 400 °C

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Fig. 14

Example changes of resistance of the electroplated copper thin film interconnections during EM test

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Fig. 15

Current density dependence of the abrupt failure rate of the electroplated copper thin film interconnection without annealing

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Fig. 16

SEM photographs of the surface of the film after EM test: (a) without annealing and (b) annealed at 400 °C

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