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Title: Hillock formation in co-deposited thin films of immiscible metal alloy systems

Abstract

Hillocks are protruding sections of a surface that can influence the electronic and mechanical properties of a thin film. In monolithic films, these hillocks are formed due to thermally induced stress gradients during deposition. In this study, the surface morphology of co-sputtered immiscible Cu-X (X is a body centered cubic (BCC) group V or VI metal) thin films is characterized to elucidate the conditions that lead to hillock formation. Cu-Ta and Cu-Mo-Ag films were co-deposited with physical vapor deposition (PVD) magnetron sputtering at 25, 400, 600, and 800°C. A significant number of homogeneously distributed surface hillocks were observed only in the 600 and 800°C films. High-angle annular dark field (HAADF) cross-sectional imaging revealed significant Cu agglomerations underneath the protruding features. For the Cu-Ta films, the Cu was enveloped in a Cu-Ta nanocrystalline matrix. For Cu-Mo-Ag, the Cu was surrounded by Mo-Ag concentration modulations. While thermal stress gradients arise during deposition of immiscible metal films, biaxial stress calculations and literature cases reveal that they are not solely responsible for hillock formation. The observed morphologies align with a surface diffusion kinetic model that evaluates diffusion length of adatoms during deposition as a function of deposition temperature. Finally, this indicates a phase separationmore » driving force paired with the constituent elements’ dissimilar mobilities at elevated deposition temperatures contribute to the presence of hillocks.« less

Authors:
 [1];  [1];  [1];  [1];  [1]
  1. Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Materials Science and Engineering
Publication Date:
Research Org.:
Univ. of Michigan, Ann Arbor, MI (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1574372
Grant/Contract Number:  
NA0003857
Resource Type:
Accepted Manuscript
Journal Name:
Thin Solid Films
Additional Journal Information:
Journal Volume: 693; Journal Issue: C; Journal ID: ISSN 0040-6090
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; copper tantalum; thin films; hillock formation; immiscible alloys; sputtering

Citation Formats

Powers, Max, Derby, Benjamin, Raeker, Evan, Champion, Nicholas, and Misra, Amit. Hillock formation in co-deposited thin films of immiscible metal alloy systems. United States: N. p., 2019. Web. doi:10.1016/j.tsf.2019.137692.
Powers, Max, Derby, Benjamin, Raeker, Evan, Champion, Nicholas, & Misra, Amit. Hillock formation in co-deposited thin films of immiscible metal alloy systems. United States. doi:10.1016/j.tsf.2019.137692.
Powers, Max, Derby, Benjamin, Raeker, Evan, Champion, Nicholas, and Misra, Amit. Fri . "Hillock formation in co-deposited thin films of immiscible metal alloy systems". United States. doi:10.1016/j.tsf.2019.137692. https://www.osti.gov/servlets/purl/1574372.
@article{osti_1574372,
title = {Hillock formation in co-deposited thin films of immiscible metal alloy systems},
author = {Powers, Max and Derby, Benjamin and Raeker, Evan and Champion, Nicholas and Misra, Amit},
abstractNote = {Hillocks are protruding sections of a surface that can influence the electronic and mechanical properties of a thin film. In monolithic films, these hillocks are formed due to thermally induced stress gradients during deposition. In this study, the surface morphology of co-sputtered immiscible Cu-X (X is a body centered cubic (BCC) group V or VI metal) thin films is characterized to elucidate the conditions that lead to hillock formation. Cu-Ta and Cu-Mo-Ag films were co-deposited with physical vapor deposition (PVD) magnetron sputtering at 25, 400, 600, and 800°C. A significant number of homogeneously distributed surface hillocks were observed only in the 600 and 800°C films. High-angle annular dark field (HAADF) cross-sectional imaging revealed significant Cu agglomerations underneath the protruding features. For the Cu-Ta films, the Cu was enveloped in a Cu-Ta nanocrystalline matrix. For Cu-Mo-Ag, the Cu was surrounded by Mo-Ag concentration modulations. While thermal stress gradients arise during deposition of immiscible metal films, biaxial stress calculations and literature cases reveal that they are not solely responsible for hillock formation. The observed morphologies align with a surface diffusion kinetic model that evaluates diffusion length of adatoms during deposition as a function of deposition temperature. Finally, this indicates a phase separation driving force paired with the constituent elements’ dissimilar mobilities at elevated deposition temperatures contribute to the presence of hillocks.},
doi = {10.1016/j.tsf.2019.137692},
journal = {Thin Solid Films},
number = C,
volume = 693,
place = {United States},
year = {2019},
month = {11}
}

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