cobalt silicide (cosi2)

**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.