wafer bow and warp

**Wafer Bow and Warp** are **metrology measurements that characterize the flatness deviation of semiconductor wafers** — bow measures the center-to-edge height deviation of the median surface, while warp measures the total range of surface height variation across the entire wafer. **Definitions** - **Bow**: The deviation of the center point of the median surface from a reference plane defined by three edge points. Reported as a single value (μm). - **Warp**: The total range (max - min) of the median surface deviation from the reference plane. Always positive, always ≥ |bow|. - **TTV (Total Thickness Variation)**: Max - min of wafer thickness across the surface. **Why It Matters** - **Lithography**: Excessive bow/warp causes defocus during lithographic exposure, limiting pattern fidelity. - **Film Stress**: Thin-film deposition introduces stress that causes wafer bowing (Stoney equation relates stress to curvature). - **Specifications**: SEMI standards specify bow < 40 μm and warp < 50 μm for 300 mm production wafers. **Wafer Bow and Warp** are **the flatness report card** — critical metrology parameters ensuring wafers are flat enough for nanometer-scale lithography.