A reflectometer can measure thin film layer.
A reflectometer utilizes a mirror based objective, a laser plasma light source, a filter wheel or shutter and a spectrometer with wavelength regions from ultraviolet to near infrared.
Reflectometry means measurement of the reflectance of a sample, which is measurement of intensity with subtracted dark noise (light off) in relation to a reference measurement of a calibration standard, weighted with simulated spectra of the calibration standard.
The simulated spectra is calculated with the transfer matrix method. Thousands of simulated spectra will be calculated for a sample using the Fresnel equations. Comparison between measured and simulated spectra identifies the spectrum that fits the most with the measured spectrum by searching for the minimum of the Error Function.
The thickness value that belongs to the best matched simulated spectrum results the thickness of the sample.
With this technique multilayer thickness of thin material down to 5 nm can be measured with sub-nanometer resolution.
Measuring instrument StraDex t is used for this technology.