critical dimension small angle x-ray scattering

**CD-SAXS** (Critical Dimension Small-Angle X-Ray Scattering) is a **X-ray metrology technique that measures the critical dimensions and cross-sectional profiles of periodic nanostructures** — using the angular distribution of scattered X-rays from gratings to reconstruct 3D feature shapes. **How Does CD-SAXS Work?** - **X-Ray Beam**: Monochromatic X-ray beam incident on a periodic grating structure. - **Scattering**: The periodic structure produces diffraction peaks at angles determined by the pitch and shape. - **Modeling**: Fit the measured scattering pattern to a parameterized model of the feature cross-section. - **3D Profile**: Extract CD, height, sidewall angle, corner rounding, and line edge roughness. **Why It Matters** - **Model-Independent**: X-ray scattering provides model-independent measurements (unlike OCD/scatterometry). - **Sub-nm Sensitivity**: Sensitive to sub-nanometer changes in line profile. - **Reference Metrology**: NIST is developing CD-SAXS as a reference metrology for advanced node calibration. **CD-SAXS** is **X-ray rulers for nanoscale features** — using X-ray scattering to measure the shapes of transistor features with sub-nanometer precision.