(536c) The Degradation of Additives during the Electrodeposition of Copper for Metamaterial Fabrication

Metamaterials, a class of artificial optically-active materials with exceptional properties based on their patterned structures, typically use metallic and dielectric repeating features to provide a negative index of refraction. In the fabrication of metamaterials utilized in this study, copper is selected for the metallic part of metamaterial due to its high thermal and electrical conductivity, excellent mechanical properties and relative ease of acquisition.

Electrodeposition from a highly-acidic copper electrolyte is the most attractive approach for fabricating the conductive component of the metamaterial in this study due to its ease of control and high deposition rate. However, since the presence of special high-aspect ratio patterns in the metamaterial requires bottom-up super-filling and leveling of micron and sub-micron scale volumes; additives such as chloride ions, 3-mercapto-1-propanesulfonate (MPSA), polyethylene glycol (PEG), and polyvinylpyrrolidone (PVP) are introduced into the electrodeposition process in order to provide excellent conformality and adhesion. Most of the present study focuses on investigating the optimal parameters of electrodeposition of copper such as the effects of additive aging, the degradation of MPSA and the electrodeposition parameters of deposition voltage and its corresponding current density.

Electrochemical methods such as cyclic voltammetry, chronopotentiometry and controlled potential coulometry probe the mechanism of both the specific effects of additives and the interplay between additives. In parallel, COMSOL finite element modeling (FEM) software is used to simulate the 2D electrodeposition of copper to investigate the copper super-filling, mass transfer and the electrochemical behavior of the electrodeposition system.

Atomic force microscopy (AFM), four-point probe sheet-resistivity measurements, optical microscopy, optical profilometry and X-ray diffraction (XRD) are used as characterization tools to map the surface topography, sheet resistances, surface roughness and crystal structure of the deposited films obtained under different experimental conditions. Nuclear magnetic resonance (NMR) is conducted to analyze the degradation of the additives during the electrodeposition process. Combined with the electrochemical methods, optimized parameters for electrodeposition of copper are obtained and desired fabrication methods for metamaterials are achieved in this study.