Copper Damascene Process

Dual damascene, electroplating, and CMP — how copper wires are made

The Damascene Process

Copper can't be plasma-etched like aluminum (copper halides aren't volatile). Instead, the industry uses the damascene process — named after the ancient art of inlaying metal into grooves:

1. Dielectric deposition: Deposit and planarize the insulating layer (low-k SiOCH or SiO₂)
2. Pattern & etch trenches: Lithography and etch to create trenches (for wires) and vias (for vertical connections)
3. Barrier/liner deposition: PVD TaN/Ta to prevent copper diffusion into the dielectric
4. Copper seed layer: PVD thin copper film as the electrode for electroplating
5. Copper electroplating: Fill trenches and vias with copper from a plating bath
6. CMP: Chemical-mechanical polishing removes excess copper, leaving copper only in the trenches

In dual damascene, the trench and via are etched and filled simultaneously, reducing the number of process steps.

Key Concept: Why Copper Replaced Aluminum

Copper has 40% lower resistivity than aluminum (1.7 vs 2.8 µΩ·cm), enabling faster signal propagation and lower power consumption. The switch from Al to Cu at the 130nm node was a major industry milestone.

Why Interconnects Matter

Barrier & Liner Layers

Knowledge Check

1 / 1

Why is the damascene process used for copper instead of etching?

Copper halides aren't volatile, so copper can't be plasma-etched effectivelyDamascene is cheaper than etchingCopper is too hard to etchEtching would damage the transistors