Flow cell design for metal deposition at recessed circular electrodes and wafers

In this study we have designed and tested a vertical flow channel which can be used to electrodeposit microelectronic devices, where industry standard s demands require good uniformity and low roughness of deposited structures . At first, a theoretical analysis was carried out to determine when mass t ransfer to the electrode was controlled by forced convection. The analysis revealed that a forced convection How velocity of 0.12 m s(-1). a channel g ap (or inter-electrode distance) of 0.1 m, and an entry length of 0.44 m we re sufficient to ensure that mass transfer was fully governed by forced con vection. Based on the analysis, a design for a rectangular flow channel was proposed. The performance of the flow cell was assessed by electrodepositi ng copper and gold. The cathodes used in these experiments were either rect angular, placed flush against the channel wall or circular, located in a sl ight recess. A series of limiting current experiments with CuSO4, H2SO4 ele ctrolyte and Reynolds number ranging between 450 and 4500 was carried Out t o obtain a Sherwood-Schmidt-Reynolds number correlation. It was found that mass transfer at electrodes that were flush with the channel wall was gover ned by laminar forced convection. Mass transfer at electrodes placed in a r ecess was controlled by turbulent forced convection. Copper and gold deposi ts obtained in the flow cell were found to have thickness variation of < 12 % and roughness of < 1.6%. (C) 2001 Elsevier Science Ltd. All rights reserv ed.