electrochemical plating (ecp)

**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.