Pulse electrodeposited copper is known for its unique characteristics. Improvement of surface roughness [1] can be expected, since the deposit consists of finer sized grain compared to that made by using direct current [2] and the edge bead due to concentration distribution of plating solution can be suppressed. These advantages are available when nearly limiting current is applied, and it is difficult to make such optimal experimental condition steadily.

In this study, we used a micro fluidic device to control the concentration of cupric ion over the electrode. Pt electrode of 100 µm in diameter was used for the working electrode, and copper for the counter and reference electrode. We use transparent glass and photoresist for the micro channel, thereby, it is possible to observe the plating process with optical microscope, externally. Flow through micro channel forcibly becomes a laminar flow, so by controlling the flow velocity and ion concentration, we can calculate the ion distribution around the electrode. From the calculation and the pulse on-time, off-time, current density, we made a simulation to figure out the experimental condition that the cupric ion depletes at the vicinity of the electrode surface (Fig.1). Applying this, we can expect a fine nucleation, depositing randomly on the electrode every time the periodic current is applied, thus we can expect a smoother deposition surface compared to that obtained by direct current plating, since the surface roughness is suppressed. SEM (JEOL Carry Scope JCM-5100) was used to observe the surface morphology of the plating. Results indicates that pulse plating suppress the hump at the edge of the plating.

References

[1]M.J.Kim, T.Lim, K.J.Park, S.K.Cho, S.Kim, and J.J.Kim, J. Electrochem. Soc., 159(9) D538-D534 (2012)

[2]J.B.Marro, T.Darroudi, C.A.Okora, Y.S.Obeng, K.C.Richardson, Thin Solid Films 621 91-97 (2017)