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Spectroscopic reflectometry (spectroscopic interferometry) is a technique used to measure the thickness of transparent and semi-transparent thin films.

Spectroscopic reflectometry
Technology Details
Technology Metrology
Equipment NanoSpec 6100



Reflectometer KLA Filmetrics F54 (main cleanroom)

The Reflectometer KLA Filmetrics F54 analyzes normal incident reflected light from 190 to 1700nm wavelength in order to extract thickness of thin films.

NanoSpec 6100 (ROBIN lab)

Main article: NanoSpec 6100

The NanoSpec 6100 analyzes normal incident reflected light from 400 to 800nm wavelength in order to extract thickness of thin films.

Method of operation

  • Spectroscopic reflectometry analyzes the intensity versus wavelength of light reflected from a sample to extract thickness of thin films on the sample.

Illustration of Spectroscopic Reflectometry[1]

  • The graphic above shows the incident and reflected light at an angle for illustration purposes. Our spectroscopic reflectometer (the NanoSpec 6100) uses light that is at normal incidence with the sample surface.
  • Some light is reflected from the top surface of the thin film and some transmits into the film. There is another reflection when the transmitted light reaches the bottom interface of the film. The light from each of these reflections recombines to generate varying levels of constructive or destructive interference depending on the wavelength of light and the optical distance the light travels.
  • A model is fit to the reflected intensity versus wavelength data to extract thin film thickness.
    • The thin film layer thickness is varied in the model to minimize the error between the model fit and the measured data.
    • Optical constants for the substrate and thin film materials are fixed values that are stored in material files. The material type is specified for each layer in the fitting model.
  • Spectroscopic reflectometry can only solve for layer thicknesses for one layer or up to a stack of three layers.
  • If the optical properties of a material need to be measured, spectroscopic ellipsometry is the measurement technology that is needed.


  • Spectroscopic reflectometry provides a quick and easy method for measuring thin film thicknesses. Coupled with an automated mapping stage, this technology is the preferred method for collecting multi-site maps of film thickness on samples to analyze within sample thickness variation.


  1. 1.0 1.1 [1] Hamamatsu Spectroscopic Light interferometry technology

Further reading