ellipsometry

**Ellipsometry and Spectroscopic Film Measurement** is **optical technique measuring changes in polarization state of reflected light to determine film thickness, refractive index, and composition — enabling non-destructive in-situ characterization of thin film deposition and processing**. Ellipsometry measures the change in polarization of light reflected from a surface. Incident linearly polarized light reflects from the sample and typically becomes elliptically polarized. The magnitude and phase shift between s-polarized (perpendicular) and p-polarized (parallel) components depend on optical properties and film structure. Two parameters (Ψ and Δ) completely characterize the polarization change. For single-film systems on substrates, the optical model relates measured Ψ and Δ to film thickness and refractive index. Solving the inverse problem determines unknowns from measured ellipsometric angles. Spectroscopic ellipsometry (SE) measures Ψ and Δ across a range of wavelengths, enabling measurement of dispersive optical properties — how refractive index varies with wavelength. The wavelength dependence provides additional information enabling simultaneous determination of thickness and composition. In-situ spectroscopic ellipsometry monitors film deposition in real time. As atoms deposit, thickness increases and refractive index may change (due to density variation or composition evolution). Real-time feedback enables process control — stopping deposition when target thickness is reached or adjusting precursor flow to maintain stoichiometry. Multi-layer systems require more complex models accounting for interference in intermediate layers. Rough interfaces are modeled through effective medium approximation or rigorous coupled-wave analysis. Temperature-dependent measurements reveal thermal expansion and phase transitions. Polarized light at oblique angles provides additional information — variable angle ellipsometry enhances sensitivity to specific layers. Depolarization effects indicate inhomogeneous layers or surface roughness. Ellipsometry is complementary to other techniques. Compared to X-ray reflectivity, ellipsometry is faster and provides less surface-damaging operation but may have lower resolution for very thin films. Compared to conventional thickness measurement techniques, ellipsometry is non-destructive and provides optical property information. Null ellipsometry uses rotating polarizers to find specific conditions where reflected light is circularly polarized, determining ellipsometric angles through mechanical means. Imaging ellipsometry maps spatial variations in thickness and properties across wafers. Recent advances include near-infrared extension enabling analysis of opaque conductors, and phase-sensitive detection improving signal-to-noise. **Ellipsometry provides non-destructive in-situ characterization of thin film properties, enabling real-time process control and process optimization during semiconductor processing.**