What is current efficiency?
In wafer electroplating, current efficiency refers to the proportion of the electric current that is used for depositing the target metal during the electroplating process, as opposed to being consumed by side reactions (such as hydrogen evolution, additive reduction, etc.).
Definition formula of current efficiency:
η = (Actual mass of deposited metal / Theoretical mass of deposited metal) × 100%
Based on Faraday’s law, the theoretical mass of deposited metal is calculated as:
Theoretical mass:
mtheoretical=I⋅t⋅M / n⋅F
Where:
I = current (A)
t = plating time (s)
M = molar mass of the metal (g/mol)
n = number of electrons transferred per metal atom (e.g., Cu²⁺ = 2)
F = Faraday constant (96485 C/mol)
Measurement of actual deposited mass:
Weighing method: Measure the change in wafer mass before and after plating:
m_actual = m_after − m_before
Thickness-area method:
If the density ρ, surface area A, and thickness h of the deposited metal are known, it can be calculated as:
m_actual = ρ × A × h
Finally, substitute into the formula to calculate current efficiency.
Example of current efficiency (taking copper as an example)
Assume the following copper electroplating conditions for a wafer:
Current: 2 A
Plating time: 10 minutes = 600 seconds
Copper molar mass: 63.55 g/mol
Copper valence: +2 (n = 2)
Copper density: 8.96 g/cm³
Measured thickness after plating: 1 μm, 8-inch wafer
m_theoretical = 2 × 600 × 63.5 / (2 × 96485) = 0.395 g
m_actual = 3.14 × 100 × 1 × 10⁻⁴ × 8.96 = 0.28 g
Current efficiency = 0.28 / 0.395 = 70.89%
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