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A shielded rotating disk setup with improved current distribution

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Abstract

In contrast to wafer-scale experiments that can employ a sophisticated and well-optimized plating tool, coupon-scale studies of electrodeposition can be hindered by poor current distribution. The impact on primary current distribution and mass transfer of an insulating shield that can readily be used in a rotating disk setup is presented. Numerical simulations were employed to design an insulating shield assuming mass-transfer resistances were negligible. Several designs were fabricated and characterized using copper electrodeposition as the electrochemical reaction. Numerical and experimental results are consistent, and the shield is a convenient and effective way to achieve more uniform current distribution. However, the shield disturbs the uniform mass-transfer rates to the substrate surface that are achieved with a rotating disk. Rates are characterized experimentally, and design tradeoffs are discussed.

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Abbreviations

r s :

Outer radius of the shield in unit mm

r ho :

Inner radius of the shield in unit mm

r o :

Radius of the working electrode in unit mm

i :

Local current density in unit mA/cm2

κ :

Electrolyte conductivity in unit S/m

\( \phi \) :

Electrical field in the electrolyte

N :

Normal unit vector

i c :

Applied current density in unit mA/cm2

A c :

Surface area of the working electrode in unit cm2

A a :

Surface area of the counter electrode in unit cm2

Z :

Axial coordinate

i o :

Exchange current density in unit mA/cm2

α c :

Cathodic charge transfer coefficient

F :

Faraday constant, 96,485 C/mol

V :

Potential on the working electrode in unit V

T :

Temperature in unit K

R :

Gas constant, 8.314 J/(K mol)

Wa :

Wagner number

H :

Distance between the anode and the cathode in unit mm

λavg :

Linear average of thickness profile of copper deposit in unit nm

N :

Number of data points of each thickness profile

λ i :

Thickness of the copper deposit at ith data point in unit nm

S :

Standard deviation of normalized thickness

i avg :

Linear average of current–density profile

R :

Radial position away from the center in unit mm

K :

Slope of Levich plot

N :

Number of electrons exchanged in reduction reaction in measuring Levich plots

D :

Diffusion coefficient in unit cm2/s

ω :

Rotation speed of RDE in unit rpm

ν :

Kinematic viscosity in unit cm2/s

c ∞ :

Bulk concentration of the Fe(III) complex, 1 mM

i L :

Limiting current density in unit mA/cm2

t :

Thickness of the shield in unit mm

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Acknowledgments

The authors are very grateful to Atotech Inc. for their financial support. We also thank Qian Zhang for her experimental contributions to this study.

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Authors and Affiliations

  1. Department of Chemical Engineering, Columbia University, New York, NY, 10027, USA

    Feng Qiao, Xiaoxuan Sun & Alan C. West

Authors
  1. Feng Qiao
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  2. Xiaoxuan Sun
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  3. Alan C. West
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Corresponding author

Correspondence to Feng Qiao.

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Qiao, F., Sun, X. & West, A.C. A shielded rotating disk setup with improved current distribution. J Appl Electrochem 44, 945–952 (2014). https://doi.org/10.1007/s10800-014-0701-3

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  • DOI: https://doi.org/10.1007/s10800-014-0701-3

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