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Spectral Ellipsometry (SE)

Spectral Ellipsometry Main Image
Thickness map of a resist coating on silicon wafer substrate

Spectral ellipsometry (SE) – also called “spectroscopic ellipsometry” – is a non-contact, non-destructive optical characterization technique that can be used to assay numerous physical, optical, and topographical properties simultaneously and indirectly.

With the development of appropriate analysis models, examples of material properties that can be measured by ellipsometry include:

  • Layer thickness and optical properties (n, k)
  • Surface and interface properties
  • Film density and porosity
  • Material quality and homogeneity
  • Layer composition
  • Birefringence
  • Bandgap energy in semiconductors
  • Depth gradients
  • Monolayer coverage


  • Data collection is generally quick and straightforward
  • Precise and reproducible
  • Very sensitive to ultra-thin films (single angstroms thick)


  • Measured region on the sample must be smooth and flat
  • Complex modeling required to access most indirect properties – often requires extensive expertise to avoid analytical pitfalls
  • Analysis of multi-layered samples sometimes requires fabrication of intermediate test samples with fewer layers to uniquely determine the properties of all layers present

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Spectral Ellipsometry Methods

Traditional Ellipsometry

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Covalent is a leading provider of cutting-edge ellipsometry measurement services, and we excel in providing customized modeling solutions that are fine-tuned to the characteristics of your samples and overall project goals. We have deep experience in projects ranging from routine film thickness measurements to complex, application-specific model development for novel materials or multilayer structures.

Batch Inspection Ellipsometry

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Our batch inspection service offers a cost-efficient solution for quality control and qualification of a large volume of sample replicates (10+).

This service leverages the excellent precision of ellipsometry to provide a statistical understanding of variation in sample batches.  Typically, this is used to qualify a set of coatings or substrates from a vendor or to check for variation and/or uniformity in thin film deposition, etch, or other processes.

Sample Requirements

Example Outputs

1000 nm SiO2 on Si spectroscopic ellipsometry raw data and model fit

Index of refraction mapped across nitride-rich SiNx film on a silicon wafer substrate

Thickness map of a resist coating on silicon wafer substrate

Example optical properties for partially transparent (< 30 nm) Pt thin films

Instruments Used

J.A. Woollam RC2-DI

J.A. Woollam RC2-DI

  • Spectral Range: 193 to 1690 nm (0.73 to 6.42 eV; 1075 total wavelength bands)
  • Dual-rotating compensator configuration (PCSCRA configuration)
  • Automated mapping up to 300 mm substrates w/ fully customizable X-Y resolution and scan pattern
  • Measurement Beam Diameter: 5 mm (standard); or 300 µm (focused)
  • Full Muller matrix measurement capability
  • Variable-angle transmission stage (45° – 90° angle-of-incidence range)
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How SE Works

In an SE system, a beam of set wavelength and known initial polarization state is either reflected by (or transmitted through) the sample to be measured.

A detector measures the changes to the beam’s polarization state vectors induced by interactions with the sample. This produces a raw data set capturing polarization at each measured wavelength; however, this is almost always the starting point of analysis.

In order to determine many properties of interest, Advanced Modeling is required. This involves computationally fitting thickness and optical properties of layers in the sample to the raw spectra, enabling indirect determination of these material attributes, and numerous other more abstract characteristics (such as: surface roughness, interfacial layers, diffusion profiles, composition, crystallinity, and more).