seed layer

A seed layer is an initial thin metal film deposited by PVD that provides a conductive surface for subsequent electrochemical plating of the bulk conductor. **Primary use**: PVD copper seed for copper electroplating in damascene interconnect fabrication. **Function**: Provides electrical conductivity for electroplating current flow. Nucleation surface for uniform copper grain growth. **Thickness**: Typically 20-100nm. Must be thin to leave volume for plated Cu but thick enough for continuous coverage. **Deposition**: PVD (IPVD) for directionality into features. Must cover sidewalls and bottom of trenches/vias. **Continuity**: Seed must be continuous - any gaps cause plating voids. Critical challenge for high-AR features at advanced nodes. **Overhang**: PVD seed tends to be thicker at feature top than bottom. Overhang can cause premature closure during plating. **IPVD enhancement**: Ionized PVD improves bottom and sidewall coverage by directing ionized Cu atoms into features. **Seed on barrier**: Cu seed deposited directly on Ta or TaN barrier layer. Adhesion and crystal orientation of seed affect plated Cu grain structure. **Agglomeration**: Very thin seed layers can agglomerate during subsequent processing. Minimum thickness required for stability. **Alternatives**: Direct plating on barrier (seedless) being researched. CVD/ALD Cu seed for extreme AR features.