White-light Interference

White-light interference is an optical phenomenon resulting from two broadband light rays [e.g. from a halogen lamp] interfering with one another. The interference pattern varies with respect to the phase difference of the 2 [or more] waves where parts of the light are periodically attenuated or amplified.  
This phenomenon can be utilized to measure the thickness of transparent layers. The interference occurs at the optical boundaries of the transparent layers where a certain amount of light is reflected. Different layer thicknesses induce varying phase differences of the back-scattered light. This can be used to evaluate the layer thickness by analyzing the interference spectrum. Depending on the spectral sensor, a layer thickness of 0.1 to 150 µm can be detected with high reproducibility using a special Fourier analysis.
For thinner layers or layers stacks with more than two layers, the interference signal becomes very complex, and more sophisticated fitting algorithms are used. These algorithms fit to an optical model as close as possible to the measured spectrum. Depending on the quality of the signal, it is possible to measure layers down to the nanometer regime in a stack with up to ten layers.

tec5 spectrometer technology offers the perfect platform for contactless layer thickness measurements for lab and process environment. The product are used worldwide in different applications such as:
  • Semiconductor industry
  • Solar industry
  • Glass and optical industry
  • Plastic and foil production