Localized electrochemical deposition of micrometer copper columns as affected by adding sulfuric acid

Abstract

Localized electrochemical deposition (LECD) is a metallic microfeature manufacture technology that uses tiny simple electrode to plate in the cathode. Compared with other conventional lithography employed in the semiconductor industry, LECD has the advantage of simple operation and low cost, and it is particularly suitable for manufacturing some precise metal components that have high aspect ratio microstructures. To study about deposition of copper microcolumns, the effect and mechanism of sulfuric acid in LECD were mainly investigated in this study. The micro-anode was made by a Pt-wire with a diameter of 100 µm, the cathode was made of a copper piece (6 mm×4 mm×1 mm) coated with silver thickness of 10 µm, and an electroplating solution containing CuSO4·5H 2 O and H 2 SO 4 was used as electrolyte. The effect of adding sulfuric acid on the morphology of deposited copper microcolumns under different voltages and different concentrations of sulfuric acid were respectively observed using scanning electron microscopy (SEM) images. Results show that compared with no sulfuric acid, added sulfuric acid can make the deposited Cu microcolumns become cylinder structure under different voltages. In no sulfuric acid concentration, the microcolumns had fast deposition rate and smooth surface, but they had the branches under high voltage. In high sulfuric acid concentration, the microcolumns had cylinder structure, but they had slow deposition rate and rough surface. When sulfuric acid concentration was 0.6 mol/L, the microcolumns had relatively fast deposition rate and smooth surface, and they did not develop the branches. Thus only adding appropriate amount of sulfuric acid can improve the morphology of the deposited copper microcolumns and increase the deposition rate of the copper microcolumns under high voltage.