on-device overlay

**On-Device Overlay** is the **measurement of overlay directly on functional device structures** — rather than using dedicated overlay targets in the scribe line, on-device overlay extracts registration information from the actual product features, providing the truest representation of overlay at the device location. **On-Device Overlay Methods** - **e-Beam**: SEM-based measurement of overlay on actual device features — high resolution but slow. - **In-Die Targets**: Small overlay targets placed within the die area (near devices) — better than scribe-line targets. - **Computational**: Extract overlay from design features using pattern matching or machine learning. - **Hybrid**: Combine scribe-line target measurements with in-die corrections. **Why It Matters** - **Accuracy**: Scribe-line targets may not represent actual device overlay — target-to-device offset varies. - **Intrafield Variation**: On-device captures intrafield overlay variation that scribe-line targets cannot. - **Advanced Nodes**: At <5nm, overlay budgets are ~1-2nm — target-to-device differences can consume the entire budget. **On-Device Overlay** is **measuring what matters** — extracting overlay from actual device features instead of proxy targets for the most accurate registration measurement.