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Inorganic Capping Layers in RDL Technologies: Process Advantages and Reliability

  • Advanced Functional and Structural Thin Films and Coatings
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Abstract

Atomic layer-deposited (ALD) inorganic films were processed on top of copper metal lines in a polymer-based redistribution layer (RDL). The primary objective was to develop capping layers thinner than 15 nm to prevent copper oxidation. Due to their uniformity and high density, ALD layers are established permeation barriers. Nonetheless, owing to the presence of polymers in the final product, a low deposition temperature is required, resulting in an increased defect density and a greater susceptibility to degradation by moisture. In this study, various inorganic cappings, based on Al\(_2\)O\(_3\), HfO\(_2\) and TiO\(_2\), deposited at 100 °C were integrated in an RDL stack. It is demonstrated that they impede the reaction of the polymer photo acid generator with copper, improving the lithography process, and ultimately allowing to print smaller critical dimensions. Additionally, capping layers built upon Al\(_2\)O\(_3\) or HfO\(_2\) are shown to fully block copper oxidation after reliability stress tests.

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Acknowledgements

The authors would like to express their gratitude to the different imec teams involved in this study. Contributions from imec’s 3D IIAP program are deeply acknowledged. Special thanks for the numerous FIB cross-section requests handled by Dr. Olivier Richard and Ms. Chris Drijbooms. Sincere thanks should go to JSR Corporation and JSR Micro N.V. for providing the photosensitive polymer used in this study. The support of A. Hiro and H. Noda is deeply recognized.

Funding

The research leading to these results received partial funding from European Union’s Horizon 2020 research and innovation programme Marie Sklodowska-Curie under the under Grant Agreement No. 888163.

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Authors and Affiliations

  1. IMEC, Kapeldreef 75, 3001, Leuven, Belgium

    Emmanuel Chery, Nelson Pinho, John Slabbekoorn, Silvia Armini & Eric Beyne

  2. Aberystwyth University, Department of Physics, Aberystwyth, Ceredigion, SY23 3BZ, Wales

    Anita Brady-Boyd

  3. Veeco Instruments Inc., 130 Turner Street, Ste 110, Waltham, MA, 02453, USA

    Ritwik Bhatia & Ganesh Sundaram

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  1. Emmanuel Chery
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Contributions

EC, AB-B, RB, SA, JS and GS conceived and planned the experiments. EC, AB-B and RB carried out the experiments. AB-B, RB, NP and JS contributed to sample preparation. EC took the lead in writing the manuscript. All authors provided critical feedback and helped shape the research, analysis and manuscript.

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Correspondence to Emmanuel Chery.

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Chery, E., Brady-Boyd, A., Bhatia, R. et al. Inorganic Capping Layers in RDL Technologies: Process Advantages and Reliability. JOM 75, 5096–5102 (2023). https://doi.org/10.1007/s11837-023-06015-x

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