Barrier & Liner Layers

Why Barriers Are Critical

Copper is a fast diffuser in silicon and SiO₂. Without barriers, copper atoms would migrate into the dielectric and silicon, causing:

• Dielectric leakage: Copper in the insulator creates conductive paths between wires (shorts)
• Transistor degradation: Copper in silicon creates deep-level traps that destroy device performance
• Reliability failures: Copper migration under voltage stress causes time-dependent failures

The standard barrier stack is TaN/Ta:

• TaN (tantalum nitride): Amorphous barrier that blocks copper diffusion. Deposited by PVD or ALD.
• Ta (tantalum): Promotes adhesion between the barrier and copper. Its BCC crystal structure helps copper nucleate in the preferred (111) orientation for better reliability.

As wires shrink, the barrier takes up a larger fraction of the trench width, reducing the effective copper area and increasing resistance. This is the "barrier scaling challenge" — a major driver of research into alternative materials.