liner

A liner is a thin conformal layer deposited inside etched features to provide adhesion, nucleation, or wetting between the dielectric and the main fill material. **Distinction from barrier**: Barrier prevents diffusion; liner promotes adhesion and proper nucleation. Often combined in bilayer structures. **TaN/Ta example**: TaN serves as barrier, Ta serves as liner for Cu adhesion and promotes (111) Cu grain texture for better electromigration resistance. **Thickness**: 1-5nm. Must be minimal to maximize conductor cross-section. **Requirements**: Good adhesion to dielectric sidewalls. Good adhesion and wetting to fill material. Must not add excessive resistance. **Conformality**: Must coat all surfaces uniformly, especially challenging in high-AR features. **Deposition methods**: PVD for thicker liners, ALD for thinnest and most conformal, CVD as intermediate option. **Cobalt liner**: Co liners explored as Cu wetting and adhesion layer. Also investigated as Cu replacement for narrow lines. **Ruthenium liner**: Ru liners for direct Cu plating (no seed needed). Good Cu wetting properties. **Integration**: Liner deposited after etch clean, before seed layer or direct metal fill. **Scaling challenge**: At sub-10nm line widths, even 1-2nm liner takes significant fraction of line cross-section. Driving research into barrierless or linerless metallization.