spectroscopic ellipsometry

Spectroscopic ellipsometry measures over a range of wavelengths, providing much richer data for characterizing multi-layer film stacks and complex materials. **Wavelength range**: Typically 190-1700nm (DUV to NIR). Broader range provides more independent data points for fitting. **Advantage over single-wavelength**: Multiple wavelengths enable simultaneous measurement of thickness and optical constants for each layer. Resolves ambiguities in multi-layer stacks. **Multi-layer capability**: Can measure 5-10+ layer film stacks simultaneously when optical contrast exists between layers. **Dispersion models**: Optical constants vary with wavelength (dispersion). Models include Cauchy, Sellmeier, Tauc-Lorentz, Drude for metals. Material-specific dispersion models improve accuracy. **Variable angle**: Combining multiple wavelengths with multiple angles of incidence provides even more data. Improves sensitivity to thin layers. **In-situ**: Real-time SE during deposition (CVD, ALD, epitaxy) monitors film growth in real-time. Growth rate, composition changes tracked live. **Applications**: Film thickness mapping, composition measurement (SiGe Ge fraction, SiON nitrogen content), crystallinity assessment, stress-related birefringence. **Semiconductor production**: Inline tools map thickness across wafer at 49+ sites. Feed-forward and feedback process control. **Mueller matrix**: Advanced SE measures full Mueller matrix for anisotropic or depolarizing samples. **Vendors**: KLA (Aleris), Nova, Onto Innovation, J.A. Woollam.