Does wafer electroplating need to follow any theorems?
To perform wafer electroplating properly, two fundamental laws must be introduced: Faraday’s First Law of Electrolysis and Faraday’s Second Law of Electrolysis. These laws were derived by Michael Faraday in the early 19th century through extensive experimentation and were published in 1834. Faraday’s laws apply to all electrode reactions involving redox processes and are fundamental quantitative laws in electrochemical reactions.
Faraday’s First Law of Electrolysis states that the mass of a substance deposited at an electrode during electrolysis is proportional to the total electric charge passed through the electrolyte. Mathematically:
m=k·Q=k·I·t
m: mass of the deposited or dissolved substance (g)
k: electrochemical equivalent (g/C)
Q: electric charge (Coulombs, C)
I: current (Amperes, A)
t: time of electrolysis (seconds, s)
In simple terms:
The thicker the plating, the greater the amount of electricity required; if the current is constant, the longer the plating time, the thicker the deposit. This can be used to control plating thickness and deposition rate.
Faraday’s Second Law of Electrolysis
For the same amount of electric charge, the mass of different substances deposited is proportional to their chemical equivalent.
Mathematical expression:
m1/m2=E1/E2
m1, m2: masses of different substances
E1, E2: their respective chemical equivalents (i.e., molar mass / number of charges)
From the two laws, we get:
n=Q/zF
n = amount of substance produced [mol]
Q = total electric charge [C]
z = number of electrons transferred per ion
F = Faraday constant = 96,485 [C mol⁻¹]
What are the uses of Faraday’s Laws of Electrolysis?
- Calculate the mass of material deposited or dissolved at the electrodes
- Predict the plating thickness
- Design the plating time and current
- Calculate plating efficiency, etc.
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