metal cmp

Metal CMP removes excess metal deposited during damascene metallization, planarizing the surface to leave metal only in patterned trenches and vias. **Materials**: Copper (most common), tungsten (for contacts/local interconnect), cobalt, ruthenium (emerging). **Copper CMP**: Multi-step process. Step 1: Bulk Cu removal at high rate. Step 2: Barrier removal (TaN/Ta) with selectivity to oxide and Cu. Step 3: Buff polish for surface quality. **Tungsten CMP**: Remove excess W from contact/via fill. H2O2 oxidizes W surface, abrasive removes oxide. Stops on underlying dielectric. **Chemistry mechanism**: Oxidizer creates soft metal oxide surface layer. Mechanical abrasion removes oxide. Fresh metal exposed, re-oxidized, removed again. **Slurry components**: Oxidizer (H2O2, ferric nitrate), abrasive (silica, alumina), complexing agents, inhibitors (BTA for Cu), pH buffers, surfactants. **Challenges**: Dishing of wide lines, erosion of dense areas, scratches, corrosion, residual contamination. **Endpoint**: Motor current, optical, or eddy current sensors detect when metal clears from field areas. **Over-polish**: Some over-polish ensures complete field clearing but worsens dishing and erosion. Minimize with good endpoint. **Process control**: Removal rate, uniformity, selectivity, defectivity all monitored.