ELECTROPLATING

• Definition: an electrochemical process in which a metal is deposited on a substrate by passing a current through the bath solution.

• Differences between electroplating and electrodeless plating: 2 electrodes, a bias is applied betwwen the two electrodes

• How is it done?
  • Cathode (-) provides the electrons necessary for the ions Ni2+ to be neutralised and deposited (plated)
    • Ni2+ + 2e- → Ni reduction
  • Anode (+) Ni is etched
    • Ni - 2e- → Ni2+ oxidation
  • Formation of H₂ is undesirable

• Metal source: (there are two possible sources for the deposited metal)
  • metal anode with desired material (as in the previous example - see animation)
  • solution, which is the salt of the metal (for example NiCl₂ is used to deposit Ni)
    • a bias is still aplied, but the anode is not etched
    • the chemical reactions in this case are:
      • Cathode (-) Ni2+ + 2e- → Ni reduction
      • Anode (+) 2Cl- + 2e- → Cl₂ oxidation

• Deposition rate =
  • proportional with the applied current and the mass of atom
  • inverse proprtional with the number of electrons required for the ion to be neutralised (2 in the cas of Ni)

• Step coverage: Smaller features are plated first (for smaller structures, the current is higher, therefore the deposition rate is higher)