Dual near-zero-thickness sealing for the strengthening of cobalt thin films and nanolines for future interconnect applications

• Published in: Applied surface science Vol. 609; p. 155387
• Main Authors: Chen, Giin-Shan, Pan, Yen-Chang, Chen, Wei-Chun, Hsiao, Chien-Nan, Chang, Chin-Chia, Cheng, Yi-Lung, Fang, Jau-Shiung
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 30.01.2023
• Subjects: Cobalt film; Electroless plating; Interconnect; Reliability; Self-assembled monolayer; Self-forming barrier; Interconnect; Self-assembled monolayer; Self-forming barrier; Cobalt film; Reliability; Electroless plating
• ISSN: 0169-4332
• DOI: 10.1016/j.apsusc.2022.155387

Graphical abstract showing the samples of thin Co and Co(MnO) films and nano-lines (left column), the STEM images of the samples of thin Co and Co(MnO) films after annealing (middle column), and the schematics of their microstructure changes (bottom, right column), along with electromigration testing curves of Co and Co(MnO) nano-lines (top, right column). [Display omitted] •Self-assembled monolayers (SAMs) and self-forming barriers are surface-functional coatings.•An all-wet electroless process is used to seal Co films and nanolines with a 1-nm-thin SAM and 0.1% of MnO.•The dual-sealing enhances thermal stability of the Co films on NiSi/Si substrates.•The dual-sealing enhances electromigration reliability of Co nanolines.•Mechanism of the enhancements is elucidated by electron microscopy and analysis. Self-assembled monolayers (SAMs) and self-forming barriers are molecularly thin surface functional coatings and could be a viable option for enhancing the reliability of thin Co films and Co nanolines. Here, we present an all-wet metallization process which enables electroless-plated Co films to be protected by an amino-based SAM coating and self-forming manganese monoxide (MnO) alloy. Co or lightly alloyed (0.1 % MnO) Co was deposited on the SAM barrier on NiSi/Si, denoted Co [or Co(MnO)]/SAM/NiSi/Si. The two types of samples were annealed to some extent for the evaluation of their thermal stability, primarily using (scanning) transmission electron microscopy [S(TEM)]. For the Co/SAM/NiSi/Si after annealing, the SAM barrier retains its integrity, but it alone is insufficient to prevent interface diffusion and chemical reactions of Co and Si. A three-nanolayered structure, CoSi2(CoSi2−x)/CoSi2/Co2Si, is formed beneath the SAM; faceted CoSi precipitates with a three-domain structure are found above the SAM. By contrast, the Co(MnO)/SAM/NiSI/Si is stable under identical annealing without interface diffusion and chemical reactions. Significant enhancement of electromigration reliability of Co nanolines by the tiny MnO alloying is confirmed by activation energy measurements, and the mechanism for the enhancement is thoroughly elucidated by S(TEM).