12098 | J. Mater. Chem. C, 2015, 3, 12098--12106 This journal is © The Royal Society of Chemistry 2015 Cite this: J. Mater. Chem. C, 2015, 3, 12098 Direct-liquid-evaporation chemical vapor deposition of smooth, highly conformal cobalt and cobalt nitride thin films† Jing Yang, a Kecheng Li, a Jun Feng b and Roy G. Gordon* ab By a direct-liquid-evaporation chemical vapor deposition (DLE-CVD) method, we deposited smooth low- resistance cobalt (Co) and cobalt nitride (Co x N) thin films with excellent conformality at low temperatures down to 200 1C. In the DLE process, a cobalt amidinate precursor solution, bis(N,N 0 -diisopropylacet- amidinato)cobalt(II) dissolved in tetradecane, was vaporized as it flowed smoothly, without boiling, inside heated tubing. This DLE process avoids creating unwanted particles that are generated when droplets from a nebulizer evaporate in a conventional direct-liquid-injection (DLI) process. The vapor then mixed with ammonia (NH 3 ) and hydrogen (H 2 ) and flowed over substrates in a tubular CVD reactor, resulting in metallic Co or Co x N films by tuning the NH 3 /H 2 co-reactant ratio. This process deposited pure and highly conformal Co or Co x N films in trenches with 60 : 1 or 45 : 1 aspect ratio respectively. The good conformality is crucial towards realizing potential applications, such as in 3D contacts and interconnects in microelectronics. Introduction Thin films of cobalt (Co) and cobalt nitride (Co x N) have attracted considerable attention for their applications in giant magnetoresistance (GMR) devices, 1–3 spintronics, 4 and micro- electronics technology. 5,6 For example, Co, 5 Co x N, 7 or Co-based alloy 8,9 have proven to be effective adhesion layers in copper interconnects as they demonstrated enhanced bonding between copper and barrier layers. Co has also been used as a wetting layer to induce void-free filling of narrow copper lines by reflow of non- conformal PVD copper for sub-20 nm nanostructures. 10 CoSi 2 , fabricated by the reaction of Co with silicon, is a useful material for contacts due to its thermal and chemical stability. 11,12 Cobalt and cobalt nitride have been previously deposited by various means, including physical vapor deposition (PVD), 2,4 chemical vapor deposition (CVD) 7–9,12–18 and atomic layer deposition (ALD) 5,6,8,9,19–21 methods. As microelectronics and magnetic-storage devices continue to shrink in dimensions, 22 highly conformal metal deposition is required for further downsizing and for the construction of ultra large scale integration (ULSI) with three dimensional structures. In these applications, the poor step coverage of PVD methods causes severe limitations, while CVD 8 and ALD 5 are favored as they are able to produce high-quality and conformal thin films. By thermal ALD using Co( i Pr-MeAMD) 2 (bis(N,N 0 -diisopropyl- acetamidinato)cobalt(II)) precursor and H 2 5 or NH 3 20 co-reactants, successful deposition of high quality cobalt films has been realized at temperatures between 260 1C and 350 1C. The films exhibited resistivity ranging from 46 to 200 mO cm and excellent step coverage, 5 coating holes with a 40 : 1 aspect ratio conformally. However, the growth rate of the ALD-Co 5 is less than 0.1 nm min 1 , which is slow compared to CVD methods. In contrast, direct-liquid-injection (DLI)-CVD 17,23 provides much faster growth rates. It has the advantage of effective prevention of precursors’ early decomposition as compared to the traditional bubbler delivery since the precursor is typically stored at room temperature. 24 Furthermore, this technique can be applied to a wide range of precursors, even those having low vapor pressure and/or limited thermal stability. DLI-CVD can deliver high vapor concentrations of precursors that are hard to achieve by conventional bubbler delivery, which is favorable for growing highly conformal films with high growth rates. DLI-CVD has been employed to deposit Ni, 16,23,25 Co, 16 cobalt oxide, 26 Ag, 16,27 Ru, 28 Cu, 16,29 and metal oxides (high-k). 30 The DLI-CVD method typically employs a nebulizer to break up the liquid solution into tiny droplets, which then generate vapor when the droplets contact a hot carrier gas. 16 However this method is limited a School of Engineering, Applied Sciences, Harvard University, Cambridge, MA 02138, USA b Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA. E-mail: gordon@chemistry.harvard.edu † Electronic supplementary information (ESI) available: Electron Diffraction (ED) images and results for DLE-CVD Co and Co x N films, Arrhenius plot of the Co growth rate, deposition rate and sheet resistance as a function of the cobalt precursor delivery rate, and an X-ray Reflection (XRR) measurement of film thickness. See DOI: 10.1039/c5tc03221k Received 8th October 2015, Accepted 2nd November 2015 DOI: 10.1039/c5tc03221k www.rsc.org/MaterialsC Journal of Materials Chemistry C PAPER Published on 03 November 2015. Downloaded by Harvard University on 19/11/2015 15:08:36. View Article Online View Journal | View Issue