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.