Electrochemical Formation of Free-Standing 3D Structures Using Injection of Additives

Abstract

A new method of electrochemical formation of free-standing 3D structures based on the injection of additives that controls the deposition rate was demonstrated using copper-chloride-polyethylene glycol as an example. A densely-packed defect-free pillar was formed upon the injection of chloride-free electrolyte into a chloride-containing electrolyte, where copper deposition was fully suppressed. The effects of diffusion coefficient, injection rate and the distance between injection nozzle and pillar top were evaluated with numerical simulation. A fast diffusion species, a moderate injection rate and a small gap between injection and pillar were found beneficial to obtaining the best contrast in the growth rates between pillar and background. The demonstration of free-standing copper structure in this paper provides an alternative path for electrochemical 3D printing of various metallic materials. Free-standing metallic structures are of interest for various devices. The recently developed additive manufacturing enables the direct formation of such structures without the need of expensive lithography processes.1 Among them, the metal wire feed process 2 was directly adapted from the original extrusion version of polymer 3D printing. 3-5 Extrusion and sintering of metal paste 6 also allow the formation of metal structures. Selective laser melting or sintering [7][8][9] of metal particles can create free-standing or non-attached metallic structures embedded in metal powders.While most of the above processes were heat-based physical processes, chemical reaction based 3D printing processes have been developed typically for direct formation of smaller structures. Tip based electrochemical machining has been widely used in the past to subtractively machine metallic or non-metallic structures for microdevices.10,11 However, electrochemical deposition processes have not been used until more recently for additive formation of 3D metal [12][13][14][15] and conductive polymer [16][17][18] micro-structures. Metal electrodeposition typically involves the reduction of metal ions into metal atoms on a conductive substrate. Therefore, 3D electrodeposition methods taking advantage of a local electrical field, local metal ion or local conductive substrate have been developed. The traditional lithography based electroforming, for example, the through-mask plating and LIGA process are based on the local exposure of conductive substrate. 19 This through mask concept has also been extended to achieve direct formation of nanostructures through local deposition. [20][21][22] Another so-called local electrochemical deposition was invented relying on a locally positioned anode.12-14 Such an anode is typically surrounded by a large insulating material and is closely positioned in a vicinity of the cathode substrate, 23-26 creating a highly local electrical field that enables the deposition to occur only at the location closest to the anode. Recently, Hirt et al. 27 used a modified atomic force microscope tip with fluidic channel to introduc...

Filament Growth and Related Instabilities during Adsorbate Suppressed Electrodeposition

“…Beyond through-mask or template electrodeposition, the engineered growth of individual fine scale filament-like structures has been demonstrated by directing current or reactant transport by the positioning of submicrometer sized counter electrodes and/or microfluidic devices, e.g., scanned pipettes. − In contrast, the present work uses microelectrodes to examine spontaneous filament growth in the presence of suppressor additives to gain insight into growth instabilities and to unify our understanding of electrolyte additives in the engineering of surface profiles and related manufacturing processes. Herein controlled filament growth is elicited from the same additive suppressor chemistry used to fill trenches and vias in the fabrication of Cu microelectronic interconnects and printed circuit boards. ,,, For CuSO 4 –H 2 SO 4 electrolytes, inhibition derives from a polyether-Cl – adlayer where polymer coadsorption depends upon interface hydrophobicity induced by halide adsorption .…”