CMP
Planarizing the surface between layers.
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At a glance
Inputs
- Wafer with surface topography
- CMP slurry
- Polishing pad
Outputs
- Planarized (flat) wafer ready for the next layer
What is it?
Chemical-mechanical planarization: polishing the wafer flat between build-up steps using a combination of chemical slurry and mechanical abrasion.
Why is it needed?
Each added layer creates topography. Lithography needs a flat surface to keep features in focus, so the wafer must be re-planarized many times as layers stack up — CMP is what makes multilayer wiring possible.
How does it work?
The wafer is pressed face-down against a rotating polishing pad flooded with an abrasive, chemically active slurry. Chemistry softens the surface while abrasives remove the high spots.
CMP is used both to remove excess material (e.g. copper overburden in damascene wiring) and to level dielectric layers.
Critical parameters
- Removal rate
- Within-wafer uniformity
- Dishing and erosion
- Endpoint control
Typical defects
- Dishing
- Erosion
- Micro-scratches
- Residual slurry particles
Equipment involved
- CMP polisher
- Post-CMP cleaning stations
Materials involved
- Abrasive slurry
- Polishing pads
- Ultra-pure water
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