electroless plating

**Electroless Plating** is a **chemical deposition method that deposits metal without an external electrical current** — using a chemical reducing agent in solution to drive the metal reduction reaction autocatalytically on a catalytic surface, enabling selective deposition on specific materials. **How Does Electroless Plating Work?** - **Reaction**: $M^{n+} + Red ightarrow M^0 + Ox$ (Metal ions reduced by chemical agent). - **Catalyst**: Deposition only occurs on catalytic surfaces (e.g., Pd-activated or existing metal surfaces). - **Materials**: CoWP, CoB, NiP are common for semiconductor capping layers. - **Selectivity**: Deposits only on metal (Cu) surfaces, not on dielectric — no lithography needed. **Why It Matters** - **Selective Cu Capping**: CoWP electroless cap on Cu lines improves electromigration lifetime by 10x vs. dielectric cap. - **No Lithography**: Self-selective deposition reduces process steps and cost. - **Barrier Application**: Potential for selective barrier deposition on Cu without blanket PVD/ALD. **Electroless Plating** is **self-directed metal deposition** — a chemistry-driven process that puts metal exactly where it's needed without masks or electrical connections.