Brush scrubbing uses rotating brushes with chemicals or DI water to physically dislodge stubborn particles from wafer surfaces. Mechanism: PVA (polyvinyl alcohol) brushes rotate against wafer surface while chemicals flow. Mechanical force removes adhered particles. When needed: Particles too strongly attached for megasonic or chemistry alone. Post-CMP clean is major application. Brush material: PVA foam - soft enough not to scratch, effective for particle capture. Nodules or patterns for scrubbing action. Process: Wafer rotates while brushes contact surface. DI water, dilute ammonia, or other chemistries provide lubrication and particle removal. CMP post-clean: Critical to remove slurry particles and residues. Double-sided brush scrubbing common. Limitations: May cause scratches if particles are hard or brush is worn. Not for delicate structures. Double-sided: Clean both wafer surfaces simultaneously. Important for backside cleanliness. Integration: Part of post-CMP clean sequence with megasonic, chemicals, and spinning rinse/dry. Brush lifetime: Limited use cycles. Regular replacement required.