cmp slurry

**CMP Slurry** is the **chemically active abrasive suspension used in chemical mechanical planarization** — combining abrasive particles with chemical etchants to remove material planarly through both mechanical abrasion and chemical dissolution. **Slurry Components** - **Abrasive Particles**: SiO2 (silica, 50–200 nm), CeO2 (ceria, for oxide), Al2O3 (alumina, for metal). - Harder particles = faster removal, more scratching risk. - Ceria: orders of magnitude faster SiO2 removal than silica at same concentration. - **Chemical Additives**: Oxidizers (H2O2, KIO3), pH buffers, complexing agents, surfactants. - **Deionized Water**: Base carrier. - **pH**: Critical — oxide slurries typically pH 10–11; copper slurries pH 2–4. **Material-Specific Slurry Chemistry** **Oxide (STI, ILD) CMP**: - Silica or ceria abrasives in basic solution. - Ceria slurry: KrF litho-grade selectivity SiO2 vs. Si3N4 > 100:1 — stops on nitride automatically. **Tungsten (Contact/Via) CMP**: - Silica abrasive + H2O2 oxidizer. - H2O2 oxidizes W → WO3 → removed by mechanical abrasion. - Selectivity: W removal >> SiO2 removal. **Copper (Cu Interconnect) CMP**: - BTA (benzotriazole) inhibitor: Forms Cu-BTA passivation layer — prevents corrosion between abrasion events. - H2O2 or iodate oxidizer. - Two-step: Bulk Cu removal → barrier (TaN) removal. **Polishing Pad** - IC1000 (Dow/DuPont): Polyurethane, hard, provides planarity. - Suba-series: Soft pad for global planarity. - Grooves and micro-texture: Slurry distribution and transport. - Pad conditioning: Diamond conditioner continuously refreshes pad texture (glazing prevention). **Key Metrics** - **Removal Rate (RR)**: Angstroms per minute — target 1,000–5,000 Å/min. - **Within-Wafer Uniformity (WIWNU)**: < 3% σ/mean target. - **Defect Density**: Scratches, particles counted by KLA Surfscan after CMP. CMP slurry chemistry is **the heart of the planarization process** — slurry selection and optimization directly determines the yield and reliability of every interconnect layer.