scatterometry overlay

**Scatterometry Overlay** is the **general term for using optical scatterometry (OCD) principles to measure overlay** — encompassing both DBO (diffraction-based) and spectroscopic overlay methods that extract layer-to-layer registration from the spectral signature of overlay targets. **Scatterometry Overlay Methods** - **DBO**: Measure +1st/-1st diffraction order intensity difference — proportional to overlay. - **Spectroscopic**: Measure full spectral response of overlay targets — fit overlay from spectrum shape changes. - **µDBO**: Miniaturized targets for in-die measurement — multiple pads per target for X/Y overlay. - **2D Targets**: Measure X and Y overlay simultaneously from 2D grating targets. **Why It Matters** - **Speed**: Scatterometry-based overlay is faster than image-based — higher throughput for high-volume manufacturing. - **Accuracy**: Achieves <0.5nm accuracy — competitive with or better than IBO for advanced nodes. - **In-Die**: Small targets enable in-die overlay measurement — captures local variations that scribe-only targets miss. **Scatterometry Overlay** is **registration measurement through diffraction** — using the spectral response of grating targets for high-throughput overlay metrology.