Full Paper Plasma-Assisted Atomic Layer Deposition of Palladium By Gregory A. Ten Eyck,* Jay J. Senkevich, Fu Tang, Deli Liu, Samuk Pimanpang, Tansel Karaback, Gwo-Ching Wang, Toh-Ming Lu, Christopher Jezewski, and William A. Lanford A method is presented for the atomic layer deposition (ALD) of palladium using remote hydrogen plasma as the reducing source and agent. Palladium was deposited on iridium, tungsten and silicon at 80 C using a remote inductively coupled hydrogen plasma with palladium(II) hexafluoroacetylacetonate as the precursor. In the case of the Pd film grown on Ir, the carbon and fluorine content were significantly reduced compared to previous thermal ALD results. Use of remote plasma eliminated the noble metal substrate requirement needed for thermal ALD, enabling films to be grown on W and Si. Ultra-thin Pd films grown on W and Si possessed a nearly random texture from reflection high-energy electron diffraction (RHEED) measurements. Atomic force microscopy (AFM) images showed very different surface morphologies for the different substrates suggesting very different substrate film interactions. X-ray photoelectron spectroscopy (XPS) measurements indicate high quality Pd films for all substrates, suggesting the substrate temperature was low enough to prevent dissociation of the hfac ligand and adequate C and F scavenging by the atomic hydrogen. The remote hydrogen plasma source results in the loss of selectivity but growth is evident on every surface used including surfaces that do not react strongly with the Pd precursor and are not catalytic towards the dissociation of molecular hydrogen. Keywords: ALD, H 2 plasma, Metal±organic, Palladium, Plasma-assisted 1. Introduction Self-limiting chemistries that result in atomic layer control of deposited films are becoming popular due to their conformality with thickness control and control of interface chemistry. Coordination-compound-based precursors for ALD are attractive because their chemical bonding can be tailored to yield stable ALD precursors with controlled vapor pressure, condensation temperature, and precursor- substrate interaction. [1] ALD is a viable deposition technique for future ultra-large scale integrated devices since sputter- ing techniques have limited deposition conformality for high aspect ratio trench/via structures. Palladium and its alloys are potential replacements for gold electrical contacts, [2,3] in gas sensors, [3] and as seed' layers for electroless plating. [4] ALD is defined by its utilization of self-limiting chemistry via the alternating pulses of source materials to generate layer-by-layer growth on a substrate that favors the chemisorption of the precursors. [5] There are many coordina- tion compounds based on the b-diketonate chemistries that are suitable for metal ALD. [6] Further, b-diketonates are known to have a high vapor pressure, [7] and have been utilized for the CVD of metals. [4,8±10] However, for ALD these precursors often require high substrate temperatures or specific surface compositions for metal reduction and organic ligand removal. [2,4,11] Metal±organic compounds based on acetylacetonato and dipivaloylmethanato chemis- tries can exist in the solid state at room temperature and have been shown to be suitable for plasma CVD, [7] however each of these has a volatility at temperatures high enough that alternative chemistries were investigated. Of the various b-diketonate derivatives of Pd available, Pd(hfac) 2 has been shown to have the highest vapor pressure, and can therefore be implemented at the lowest process temperature. [6] To date, Pd ALD has not achieved success on oxide- terminated surfaces primarily due to the lack of chemisorp- tion of palladium(II) hexafluoroacetylacetonate, Pd II - (hfac) 2 . [12,13] Additionally, there has been a lack of suitable reducing agents. Senkevich et al. [12] successfully demonstrat- ed the use of thermally cleaved glyoxylic acid as a reducing agent for Pd ALD, but this technique required substrate temperatures in excess of 200C, which only yielded a monolayer seed' layer whereupon hydrogen could be used at 80 C. Hydrogen can only be utilized with thermal ALD when a catalytic surface is present for the dissociation of molecular hydrogen to atomic hydrogen. Other methods of substrate-independent Pd ALD have been explored, includ- ing the use of sulfur to enhance the chemisorption of the Pd coordination compound. [1] 60  2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/cvde.200306312 Chem. Vap. Deposition 2005, 11, No. 1 ± [*] G A. Ten Eyck Dept. of Electrical, Computer, and Systems Engineering Rensselaer Polytechnic Institute Troy, NY 12180-3590 (USA) E-mail: teneyg@rpi.edu Dr. J. J. Senkevich, F. Tang, Dr. D. Liu, S. Pimanpang, Dr. T. Karaback, Dr. G.-C. Wang, Dr. T.-M. Lu Dept. of Physics, Rensselaer Polytechnic Institute Troy, NY 12180-3590 (USA) Dr. C. Jezewski, Dr. W. A. Lanford Dept. of Physics, University at Albany 1400 Washington Ave., Albany, NY 12222 (USA)