Electrochemical Plating (ECP) is the standard method for depositing copper to fill damascene trenches and vias — using an electrochemical cell where Cu²⁺ ions from a copper sulfate solution are reduced onto the wafer surface (cathode) by an applied electrical current.

How Does ECP Work?

• Setup: Wafer (cathode) + Cu anode + CuSO₄/H₂SO₄ electrolyte + organic additives.
• Additives (Critical for superfill):
• Suppressor: Large polymer (PEG) that slows deposition at the top.
• Accelerator: Small molecule (SPS/MPSA) that speeds deposition at the bottom.
• Leveler: Selectively suppresses deposition on bumps -> planarizes.
• Superfill: Bottom-up filling that avoids voids by plating faster at the trench bottom than the top.

Why It Matters

• Industry Standard: Every copper interconnect since IBM's 1997 introduction has been filled by ECP.
• Void-Free Fill: The additive chemistry enables defect-free filling of features with aspect ratios > 10:1.
• Throughput: High deposition rate (~0.5-1 $mu m$/min) at low cost.

ECP is the electrochemistry that fills every wire in modern chips — using precisely tuned bath chemistry to grow copper from the bottom up.