Copper Nanofilm Formation by Electrochemical ALD

Abstract

This paper describes the formation of Cu nanofilms using atomic layer deposition (ALD) via surface-limited redox replacement, also referred to as monolayer-restricted galvanic displacement. An automated flow-cell electrodeposition system was employed to make Cu nanofilms using 100, 200, and 500 ALD cycles. The cycle was composed of a sequence of steps: Pb underpotential deposition (UPD), rinsing with blank, introduction of Cu2+ at open circuit, and exchange of the Pb atoms for Cu, rinsing with a blank. The open-circuit potential was used to follow the replacement, exchange, of Pb for Cu, which shifted from that used to deposit Pb UPD (−0.44 V) up to the equilibrium potential for Cu2+/Cu or −0.013 V upon a complete exchange. The resulting Cu films appeared homogeneous from inspection, optical microscopy, and scanning electron microscopy. Electron probe microanalysis showed no Pb in deposits formed using −0.44 V for Pb UPD. However, for deposits formed with Pb deposition at potentials more negative than −0.44 V, Pb was evident in the deposit. A prominent Cu(111) peak was displayed in the X-ray diffraction pattern for the Cu nanofilms. Morphology studies of the Cu films were performed using ex situ scanning tunneling microscopy and attested to the layer-by-layer growth of the Cu film. The 250 nm flat terraces suggested that a surface may have become smoother during growth rather than roughened as normally experienced during the electrodeposition or growth of thin films in general. A decrease in coulometry for Pb UPD during the first 30 cycles could also be interpreted as a decrease in surface roughness, or surface repair during ALD.

Recent Advances in the Growth of Metals, Alloys, and Multilayers by Surface Limited Redox Replacement (SLRR) Based Approaches

“…The use of flow a cell was also extended to the growth of thicker Cu deposits by up to 500 SLRR cycles on Au films on glass. Interestingly enough, while the thicker films were displaying expected homogeneity and overall appearance at the end of the growth process, a flattening of the surface was reported in these experiments during the first 30 cycles [76]. The flow-cell deposition approach was also extended by Stickney et al to the growth of thinner [77] and thicker [75] Cu films on Ru substrates.…”

“…Studies on the SLRR deposition of Cu on Au (111) were reported in flow-cell [36,[74][75][76][77] and in one-cell configuration [31]. In a flow-cell Stickney et al used Cu UPD to deposit the first Cu atomic layer on a Au (111) substrate, modified with an atomic layer of I atoms [36].…”

Electrodeposition of Metals in Catalyst Synthesis: The Case of Platinum Monolayer Electrocatalysts

“…This procedure can be extended into the area of thin film metal electrodeposition. 19,[21][22][23][47][48][49] Scale-up of this synthesis method is possible and successfully tested up to 50 grams per batch. 43 The method facilitates growing various nanoparticles architectures with controllable thickness of components in stratified structures.…”

Atom Probe Tomography Characterization of Thin Copper Layers on Aluminum Deposited by Galvanic Displacement

“…1,2 Galvanic displacement, a type of electroless deposition in which the substrate or an adsorbed species acts as the reducing agent, can produce nanometer-thickness films on semiconductors and noble metals. 3,4 Galvanic deposition of copper layers has been reported on oxide-covered materials such as aluminum, tantalum, as well as TiN and TaN diffusion barriers. 5−7 However, it seems that electroless deposition and galvanic deposition have not yet been used to fabricate ultrathin films on oxidized substrates.…”