Two deposition methods, using chemical reactions between liquid sources will be discussed:

• electroplating
• electroless plating

ELECTROLESS PLATING

• Purpose: plating (depositing) different materials with metals such as copper

• How it is done?
  • By immersing a metal such as Zn in a solution of Cu₂SO₄
    • Zn is eroded and dissolves in solution
    • Cu2+ ions from solution accept electrons and deposit on the substrate

• Chemical reactions:

  • Zn → 2e- + Zn2+ oxidation (dissolution) of Zn

  • Cu2+ + 2e- → Cu reduction of Cu ions to neutral metal

• Advantages:
  • inexpensive: does not require expensive equipment or cleanroom
  • no applied bias required
  • copper deposits uniformly on the present structures, therfore stuctures with high aspect ratio can be plated

• Applications: MEMS, ICs, masks, packaging