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

THIN SOLID FILMS

卷:693

Article; Proceedings Paper

Powers, Max¹  Derby, Benjamin¹  Raeker, Evan¹  Champion, Nicholas¹  Misra, Amit¹ 

[1] Univ Michigan, Dept Mat Sci & Engn, Ann Arbor, MI 48109 USA

关键词: Copper tantalum;    Thin films;    Hillock formation;    Immiscible alloys;    Sputtering;   

DOI  :  10.1016/j.tsf.2019.137692

来源: Elsevier

【 摘 要 】

y 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 CuMo-Ag films were co-deposited with physical vapor deposition (PVD) magnetron sputtering at 25, 400, 600, and 800 degrees C. A significant number of homogeneously distributed surface hillocks were observed only in the 600 and 800 degrees 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. This indicates a phase separation driving force paired with the constituent elements' dissimilar mobilities at elevated deposition temperatures contribute to the presence of hillocks.

【 授权许可】

Free