Cobalt Silicide (CoSi₂) is a low-resistivity silicide phase — that was the industry standard contact material at the 130nm-65nm nodes, offering better narrow-line behavior than TiSi₂ but later replaced by NiSi at 45nm and below.

What Is CoSi₂?

• Resistivity: ~15-18 $muOmega$·cm.
• Formation: Two-step anneal. Co + Si -> CoSi (high-$ ho$, first anneal) -> CoSi₂ (low-$ ho$, second anneal at ~700°C).
• Si Consumption: Consumes 3.6 nm of Si per nm of Co deposited (consumes more Si than NiSi).
• Advantage over TiSi₂: No narrow-line effect (sheet resistance doesn't increase on narrow gates).

Why It Matters

• Historical: Enabled scaling from 250nm to 65nm where TiSi₂ failed at narrow gate widths.
• Replaced by NiSi: NiSi consumes less silicon (critical for ultra-shallow junctions) and forms at lower temperature.
• Thermal Budget: CoSi₂ requires higher anneal temperatures (~700°C) than NiSi (~450°C).

CoSi₂ is the second-generation contact silicide — bridging the gap between early TiSi₂ and modern NiSi for reliable low-resistance contacts.