Structural, Mechanical and Electrical Characteristics of Copper Coatings Obtained by Various Electrodeposition Processes

Abstract

Mechanical (hardness and adhesion) and electrical (sheet resistance) characteristics of electrolytically produced copper coatings have been investigated. Morphologies of Cu coatings produced galvanostatically at two current densities from the basic sulfate electrolyte and from an electrolyte containing levelling/brightening additives without and with application of ultrasound for the electrolyte stirring were characterized by SEM and AFM techniques. Mechanical characteristics were examined by Vickers microindentation using the Chen–Gao (C–G) composite hardness model, while electrical characteristics were examined by the four-point probe method. Application of ultrasound achieved benefits on both hardness and adhesion of the Cu coatings, thereby the use of both the larger current density and additive-free electrolyte improved these mechanical characteristics. The hardness of Cu coatings calculated according to the C–G model was in the 1.1844–1.2303 GPa range for fine-grained Cu coatings obtained from the sulfate electrolyte and in the 0.8572–1.1507 GPa range for smooth Cu coatings obtained from the electrolyte with additives. Analysis of the electrical characteristics of Cu coatings after an aging period of 4 years showed differences in the sheet resistance between the top and the bottom sides of the coating, which is attributed to the formation of a thin oxide layer on the coating surface area.

Influence of Parameters and Regimes of the Electrodeposition on Hardness of Copper Coatings

“…In the DC regime, it is necessary to apply an electrolyte stirring to obtain compact and uniform coatings suitable for application in industrial purposes. The most often used methods of an electrolyte mixing are magnetic stirring (MS), ultrasound assistance (US) and barboting [12,[17][18][19]. A stirring of electrolyte during electrodeposition process achieves a strong influence on mass transfer, nucleation and growth, and as a result of it, on morphological, structural and mechanical features of electrodeposited coatings [19].…”

“…The pile-u effect affecting the coating hardness value can be the easiest looked at through analysis the Cu coatings electrodeposited from electrolyte I and electrolyte II, as seen from Figure 2 showing Vickers indents. In the Cu coating electrodeposited from electrolyte I, the main mechanism is a plastic deformation of the coating under the indenter (Figure 28a) [18]. The plastic deformation of fine-grained coatings produced from electrolyte I occurs throughout the grain with the slip of dislocations mostly in the grain interior (intragranular slip) [77].…”