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STEM tomography study on structural features induced by MTJ processing

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Abstract

The structure of a magnetic tunnel junction (MTJ) patterned by reactive ion etching is investigated in detail. Using a scanning transmission electron microscope (STEM) and energy-dispersive X-ray spectroscopy (EDX) combined with electron beam tomography, the unknown 3D interface roughness of CoFeB/MgO/CoFeB was successfully observed. From the orthoslice image, the interface morphology revealed characteristic features influenced by the roughness of the underlying layer. In contrast, a uniform morphology was observed for the metal layers except for the oxidized outer periphery of the MTJ. Additionally, we demonstrate that redeposited material at every turn of the MTJ side wall during the MTJ etching can be observed three-dimensionally by identifying the constituent elements using an electron tomographic technique combined with EDX. This analysis demonstrates a promising method to clarify the cause of electrical shorting of the ultra-thin tunnel barrier in MTJs, the location of which is challenging to determine using conventional cross-sectional transmission electron microscopy (TEM).

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Funding

This work was supported by the industrial affiliation of CIES’s Industrial Affiliation on STT MRAM program, by JST OPERA, and by JST ACCEL Grant number JPMJAC1301, Japan.

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Authors and Affiliations

  1. Center for Innovative Integrated Electronic Systems, Tohoku University, 468-1 Aza-aoba, Aramaki, Aoba-ku, Sendai, 980-8572, Japan

    Masaaki Niwa, Toshinari Watanabe, Hiroaki Honjo, Shoji Ikeda & Tetsuo Endoh

  2. Morphological Research Laboratory, Toray Research Center, Inc., 3-7 Sonoyama 3-chome, Otsu, 520-8567, Japan

    Kosuke Kimura & Takanori Naijou

  3. Graduate School of Engineering, Tohoku University, 6-6 Aza-aoba, Aramaki, Aoba-ku, Sendai, 980-8579, Japan

    Tetsuo Endoh

  4. Center for Spintronics Integrated Systems (CSIS), Tohoku University, 2-1-1 Katahira, Aoa, Sendai, Miyagi, Japan

    Shoji Ikeda & Tetsuo Endoh

  5. Center for Spintronics Research Network (CSRN), Tohoku University, 2-1-1 Katahira, Aoba, Sendai, Miyagi, Japan

    Shoji Ikeda & Tetsuo Endoh

  6. JST-ACCEL, 468-1 Aza-aoba, Aramaki, Aoba-ku, Sendai, 980-8572, Japan

    Masaaki Niwa, Toshinari Watanabe, Hiroaki Honjo, Shoji Ikeda & Tetsuo Endoh

Authors
  1. Masaaki Niwa
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  2. Kosuke Kimura
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  3. Toshinari Watanabe
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  4. Takanori Naijou
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  5. Hiroaki Honjo
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  6. Shoji Ikeda
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  7. Tetsuo Endoh
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Correspondence to Masaaki Niwa.

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Niwa, M., Kimura, K., Watanabe, T. et al. STEM tomography study on structural features induced by MTJ processing. Appl. Phys. A 124, 724 (2018). https://doi.org/10.1007/s00339-018-2144-x

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  • DOI: https://doi.org/10.1007/s00339-018-2144-x

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