copper anneal

**Copper Anneal** is a **thermal treatment applied to electroplated copper** — to promote grain growth, reduce resistivity, stabilize the microstructure, and improve electromigration resistance before CMP planarization. **What Is Copper Anneal?** - **Conditions**: 100-400°C, 30 minutes to several hours, inert atmosphere (N₂ or forming gas). - **As-Plated Cu**: Fine-grained (10-50 nm grains), high resistivity, metastable. - **After Anneal**: Large grains (0.5-2 $mu m$), lower resistivity (~1.7 $muOmega$·cm), stable microstructure. - **Self-Annealing**: Some Cu films undergo partial grain growth at room temperature over days (but controlled anneal is faster and more uniform). **Why It Matters** - **Resistivity**: Grain boundaries scatter electrons. Fewer grain boundaries (larger grains) = lower resistance. - **CMP Uniformity**: Uniform grain structure improves CMP planarity and reduces dishing. - **Reliability**: Large-grain, bamboo-like structure resists electromigration (no continuous grain boundary path for atom transport). **Copper Anneal** is **crystal healing for copper wires** — growing the grains to reduce resistance and strengthen the metal against electromigration failure.