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Structural Stability of Diffusion Barriers in Cu/Ru/MgO/Ta/Si

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Department of Materials Science and Engineering, National Formosa University, 64 Wunhua Road, Huwei, Yunlin 632, Taiwan
2
Graduate School of Materials Science, National Yunlin University of Science and Technology, 123 University Road, Section 3, Douliou, Yunlin 640, Taiwan
*
Author to whom correspondence should be addressed.
Academic Editor: Thomas Nann
Nanomaterials 2015, 5(4), 1840-1852; https://doi.org/10.3390/nano5041840
Received: 30 August 2015 / Revised: 18 October 2015 / Accepted: 26 October 2015 / Published: 3 November 2015
Various structures of Cu (50 nm)/Ru (2 nm)/MgO (0.5–3 nm)/Ta (2 nm)/Si were prepared by sputtering and electroplating techniques, in which the ultra-thin trilayer of Ru (2 nm)/MgO (0.5–3 nm)/Ta (2 nm) is used as the diffusion barrier against the interdiffusion between Cu film and Si substrate. The various structures of Cu/Ru/MgO/Ta/Si were characterized by four-point probes for their sheet resistances, by X-ray diffractometers for their crystal structures, by scanning electron microscopes for their surface morphologies, and by transmission electron microscopes for their cross-section and high resolution views. The results showed that the ultra-thin tri-layer of Ru (2 nm)/MgO (0.5–3 nm)/Ta (2 nm) is an effective diffusion barrier against the interdiffusion between Cu film and Si substrate. The MgO, and Ta layers as deposited are amorphous. The mechanism for the failure of the diffusion barrier is that the Ru layer first became discontinuous at a high temperature and the Ta layer sequentially become discontinuous at a higher temperature, the Cu atoms then diffuse through the MgO layer and to the substrate at the discontinuities, and the Cu3Si phases finally form. The maximum temperature at which the structures of Cu (50 nm)/Ru (2 nm)/MgO (0.5–3 nm)/Ta (2 nm)/Si are annealed and still have low sheet resistance is from 550 to 750 °C for the annealing time of 5 min and from 500 to 700 °C for the annealing time of 30 min. View Full-Text
Keywords: diffusion barrier; ultra-thin film; Cu metallization; Cu3Si; Ru/MgO/Ta diffusion barrier; ultra-thin film; Cu metallization; Cu3Si; Ru/MgO/Ta
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Hsieh, S.-H.; Chen, W.J.; Chien, C.-M. Structural Stability of Diffusion Barriers in Cu/Ru/MgO/Ta/Si. Nanomaterials 2015, 5, 1840-1852.

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