scatterometry ocd

**Scatterometry OCD** (Optical Critical Dimension) is an **inline metrology technique that measures the dimensions and profile of periodic structures by analyzing the diffraction of light** — comparing measured spectral signatures (reflectance vs. wavelength/angle) with simulated libraries to extract CD, height, sidewall angle, and other geometric parameters. **OCD Measurement** - **Illumination**: Broadband light (UV to NIR, ~190-1000nm) or single wavelength at multiple angles. - **Measurement**: Measure reflectance, ellipsometric parameters ($Psi, Delta$), and/or Mueller matrix elements. - **Library**: Pre-compute a library of spectra for many geometric parameter combinations using RCWA (rigorous coupled-wave analysis). - **Fitting**: Match the measured spectrum to the library — extract the best-fit profile parameters. **Why It Matters** - **Speed**: OCD measurements take seconds — fast enough for 100% inline monitoring. - **Non-Contact**: Optical measurement — no tip wear, sample damage, or contamination. - **Multi-Parameter**: Simultaneously extracts CD, height, sidewall angle, film thicknesses from a single measurement. **Scatterometry OCD** is **measuring shapes with light** — using diffraction signature analysis for fast, inline critical dimension metrology.