In this paper, we report in-situ spectroscopic ellipsometry of Cu deposition from supercritical carbon dioxide fluids. The motivations of this work were 1) to perform a detailed observation of Cu growth with precision optical metrology, 2) to study substrate dependence on Cu growth, particularly for Ru and TiN substrates in the present case, and 3) to demonstrate the possibility and usefulness of ellipsometry for diagnosing supercritical fluid processing. The Cu deposition was carried out through hydrogen reduction of a Cu-diketonate precursor at 160-180 C. During growth, a very large deviation of ellipsometric parameters (É and Á) from a single-layer model prediction was observed; this deviation was much larger than that expected from island formation which has been frequently reported in in-situ ellipsometric observation of the vapor growth of thin films. From model analyses, it was found that an abnormal dielectric layer having a high refractive index and a thickness of 10-50 nm is present on the growing Cu surface. The refractive index of this layer was ð1:5{2Þ þ ð0:2{0:3Þi; and from this, we concluded that this layer is the condensed precursor. The condensed layer develops prior to Cu nucleation. As for the substrate dependence on Cu growth, both layers develop faster on Ru than on TiN. This corresponds to the fact that chemisorption occurs more easily on Ru. The deposition kinetics under the presence of the condensed layer are also discussed.
Supercritical fluid chemical deposition is known for its superior capability of filling metals into nanofeatures. The mechanism behind this filling capability has not been well understood and can be very different from those of other deposition techniques such as chemical vapor deposition. We have proposed a filling mechanism where the precursor condenses preferentially in narrow concave features and then converts into a metal deposit. In accordance with these two sequential phenomena, the narrower the feature is, the better the filling will be achieved. In this article, selective Cu deposition into nanopores of a silica-based porous thin film is described. When the conventional supercritical fluid deposition method was employed, a significant amount of Cu penetrated into the nanopores along with the continuous film formation on the substrate surface. By illuminating UV light before the start of Cu nucleation, Cu deposited selectively only inside the nanopores. During the selective deposition, optical changes in the porous film were investigated by in situ ellipsometry. These results indicate that the precursor condenses preferentially only in the nanopores and converts into a metal deposit.
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