CMP Dishing and Erosion are planarization non-uniformity effects in chemical mechanical polishing — where metal or dielectric material is selectively over-polished, causing topography that degrades device performance and subsequent process steps.

Dishing

• Definition: Depression of metal fill below the surrounding dielectric surface after CMP.
• Cause: Soft metal (Cu, W) polishes faster than hard dielectric (SiO2) — metal recesses.
• Pattern Dependency: Wider metal lines dish more (deeper concave center).
• Impact: Increases Cu line resistance; downstream litho sees non-flat surface.
• Typical Cu Dishing: 20–100nm for 10–100μm wide Cu lines after bulk CMP.

Erosion

• Definition: Loss of dielectric material in densely patterned areas.
• Cause: High pattern density areas have more metal exposed to slurry → dielectric overpolished.
• Pattern Dependency: Dense arrays (50% metal density) erode most; isolated lines erode least.
• Impact: Reduces interlayer dielectric (ILD) thickness → increases coupling capacitance.

Dishing and Erosion Interaction

• In dense arrays: Both dishing and erosion occur simultaneously.
• Net topography = erosion depth + dishing depth.
• For 5nm node Cu lines: Total step height must be < 5nm — extremely demanding.

Root Causes

• Pad compliance: Soft pad → more dishing in wide features.
• Slurry selectivity: High metal:oxide selectivity → less dishing but non-uniform erosion.
• Polish pressure: Higher pressure → faster removal, more dishing.

Mitigation Strategies

• Dummy Fill: Add dummy metal tiles in sparse areas → equalize density → reduce erosion variation.
• Two-Step CMP: Bulk removal (high rate) + clearing step (low rate, better control).
• Low-Selectivity Slurry: Oxide and metal remove at similar rates → less dishing.
• Endpoint Detection: Stop exactly at barrier layer, don't over-polish.

Controlling dishing and erosion is critical for achieving tight CD and resistance uniformity — especially at sub-10nm nodes where topography budgets are measured in single nanometers.