Organic additives have been often used in electrodeposition to modulate the deposition kinetics, film morphology and material property. One particular example is the well-known super conformal deposition of copper in trenches and other fine structures used in interconnects^1-3. Additives that suppress and accelerate copper deposition are used together to achieve a high deposition rate at the bottom of trenches while maintaining little deposition at the top⁴. Electrochemical 3D printing has recently gained more and more interest in research as an approach to make free standing arbitrary shaped structures for micro-devices. 3D growth of microstructures with local counter electrode in a vicinity of deposition substrate^5-7, meniscus droplet depositio^{8, 9} and local injection of metal cation electrolyte¹⁰ have all been demonstrated. This paper presents a new method of fabricating 3D structures with a local injection of organic additives that controls the growth rate of metals.

Figure 1 shows the diagram of the deposition system including an additive injection pump, an electrochemistry workstation, an electrochemical cell fixed on a 3D moving stage, and an optical monitoring system. Figure 2 shows the optical images of the evolution of a copper pillar structure. In this particular case, the background electrolyte contains both polyethylene glycol as a suppressor and chloride ion as the suppression promoter, whilst the injected electrolyte does not have the suppression promoter. Therefore, the growth rate of copper in the injected electrolyte is faster than in the background electrolyte. On the other hand, the fast diffusion of chloride results in a confined region where the chloride is absent and therefore a confined growth region. Both experimental observations and numerical simulation results will be discussed in the talk.

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