angle-resolved scatterometry

**Angle-Resolved Scatterometry** is a **variant of optical scatterometry that measures the diffraction signature as a function of incidence angle** — varying the angle of the incoming light beam and measuring the reflected/diffracted intensity at each angle to extract structural parameters of periodic features. **Angle-Resolved Approach** - **Fixed Wavelength**: Typically uses a single wavelength (e.g., 633nm HeNe laser) at multiple incidence angles. - **θ-2θ Scan**: Vary both incidence and detection angles — measure the angular distribution of scattered light. - **Signature**: The angular reflectance curve is the "fingerprint" of the structure's geometry. - **Measurement Types**: Specular reflectance vs. angle, or specific diffraction order intensity vs. angle. **Why It Matters** - **Complementary**: Angle-resolved data provides different sensitivity than spectroscopic (wavelength-varying) data. - **Robust**: Combining angle and wavelength variation (hybrid approach) improves parameter extraction accuracy. - **Overlay**: Critical for diffraction-based overlay (DBO) measurement — first diffraction order intensity vs. angle. **Angle-Resolved Scatterometry** is **reading the angular fingerprint** — extracting structural dimensions from the angle-dependent diffraction signature of periodic features.