overlay fingerprint

**Overlay Fingerprint** is the **systematic, repeatable pattern of overlay errors across a wafer or across fields** — decomposing the overlay error map into systematic components (translation, rotation, magnification, distortion) and residual random errors for targeted correction and process optimization. **Fingerprint Components** - **Interfield**: Wafer-level systematic errors — translation ($T_x, T_y$), rotation ($R$), magnification ($M_x, M_y$), trapezoidal, higher-order terms. - **Intrafield**: Within-field lens distortion — third-order, fifth-order, and higher-order polynomial terms. - **Per-Exposure**: Corrections applied by the scanner for each exposure field — correctables. - **Non-Correctable**: Residual errors after all systematic corrections — the irreducible floor. **Why It Matters** - **APC**: Overlay fingerprints are the basis for advanced process control — systematic errors are corrected, reducing total overlay. - **Lot-to-Lot**: Fingerprints vary by lot, wafer position in cassette, and process conditions — real-time correction needed. - **Tool Matching**: Different scanners have different fingerprints — matching scanners requires fingerprint alignment. **Overlay Fingerprint** is **the signature of misalignment** — the systematic, repeatable error pattern that can be characterized and corrected.