Large-Scale Deposition and Growth Mechanism of Silver Nanoparticles by Plasma-Enhanced Atomic Layer Deposition

The control of nanometer-scale metallic silver particles morphology and their functional properties on a large scale represent a key factor for applications such as plasmonics, sensors, catalysts, or antimicrobial surfaces. The present work investigates in detail the growth of Ag nanoparticles deposited by plasma-enhanced atomic layer deposition (PE-ALD), from triethylphosphine(6,6,7,7,8,8,8-heptafluoro-2,2-dimethy1-3,5-octanedionate)silver(I) [Ag(fod)(PEt3)-C16H25AgF7O2P] as the Ag precursor and H-2 as the reducing agent. The uniformity of the deposition in terms of nanoparticle morphology and chemical composition over a large surface area (8 in.) is analyzed using an original method. For all morphological, crystallographic, and chemical quantities, we report both the value at the center position and more originally, the gradient over a 10 cm distance on the substrate. The evolution of the gradient provides significant information on the growth mechanism. An effective growth rate of 0.020 +/- 0.003 nm/cycle at 130 degrees C determined by energy-dispersive X-ray spectroscopy is found uniformly over the whole 8-inch area of the sample. According to X-ray diffraction and X-ray photoemission spectroscopy performed on the whole silicon wafer, the deposited material is made of polycrystalline pure metallic Ag, with a low amount of impurities emanating from the precursor, showing the completeness of the reduction reaction. Under self-limiting conditions, the effects of the chamber temperature and cycle number on the morphology of Ag nanoparticles deposited on silicon are analyzed. The results suggests that the Ag thin films mainly evolve following a material transfer. Two potential mechanisms are in competition: the migration of the particles and their further coalescence through the Volmer-Weber growth mode or a "surface Ostwald ripening"-like process. Under certain conditions, this last mechanism could explain the nonuniformity of the deposition.