optical critical dimension library matching

**OCD Library Matching** is a **scatterometry-based metrology approach that compares measured optical spectra to a pre-computed library of simulated spectra** — finding the best-matching simulated spectrum to determine the CD, height, sidewall angle, and other profile parameters of nanostructures. **How Does Library Matching Work?** - **Library Generation**: Pre-compute optical spectra (reflectance or ellipsometric) for a grid of profile parameter combinations using RCWA. - **Measurement**: Measure the optical spectrum of the actual structure. - **Match**: Find the library entry that best matches the measured spectrum (least-squares or correlation). - **Result**: The profile parameters of the best-matching entry are the measured CD, height, SWA, etc. **Why It Matters** - **Speed**: Pre-computed library enables microsecond measurement time (no real-time simulation). - **Production**: The standard metrology method for inline CD monitoring at all major nodes. - **Limitation**: Requires library regeneration when the structure type changes. **OCD Library Matching** is **finding the needle in the simulated haystack** — comparing measurements to millions of pre-computed spectra to determine nanoscale dimensions.