Advanced nanotechnology applications are requires copper plating and epitaxial control by electrochemical method, which is used for various electronic devices such as a micro machine technology (MEMS). To control the surface structure of the plating film with high precision at the nanometer size, it is indispensable to clarify the mechanism of electrodeposition. However, since the electrochemical reaction process in nucleation and growth occurs rapidly in a small area, it is extremely difficult to capture the dynamic behavior at the nanoscale. In this study, we investigate the nucleation and growth process at the initial stage of copper electrodeposition by using Video-AFM.
A three-electrode electrochemical AFM cell was used for in-situ observation. In the cell, the working electrode was single crystal Au(100) substrate (φ= 3 mm). The reference electrode was a copper wire and the counter electrode was a platinum wire. Potentiostatic electrodeposition was carried out in an aqueous electrolyte containing 3 mM CuSO4 and 50 mM H2SO4 at room temperature. The Video-AFM measurement was performed during potentiostatic electrodeposition. The image area (500×375 nm2) was recorded at 2 flame s-1
3. Results and discussion
When the experiment was carried out at -0.09 V, the initial stage of the deposition on Au substrate was shown in Fig.1(a)~(d). Before electrodeposition, a smooth substrate without any irregularities was observed. Immediately after the start of electrodeposition, copper deposited with about 100 nm in x-axis direction instantaneously (Fig.1 (a)), and it was confirmed that growth of the deposited copper in the planar direction (Fig.1 (b) ~ (d)). From these images, the local deposition rate in the planar direction was calculated as 45 nm s-1. From the height profile, the thickness of the deposit was about 1 nm, which was corresponding to 4 or 5 atomic layers.