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Heterostructure  Thickness Measurement

Heterostructure thickness measurement


Heterostructure filmstack sample : (2.0 nm ZnO/2.1nm Alumina) x 60 on Si. Fit of the model to measured data to determine thicknesses of ZnO and Alumina and optical constants of the ZnO  

Heterostructure thickness measurement is an important quality control step after deposition. It can work together with the in-situ real -time thickness control  or instead of it.  Heterosctructure filmstack ,typically, consists of repeated alternating layers of low and high reflective index material, e.g. Al oxide  and Zn oxide. Double layer can be repeated 10s or 100s of times – typically from 60x to 200x. They are widely used for filters, anti-reflection coatings and other applications. One of these applications is LED and semiconductor laser: heterostructure filmstack, in this case, is used to concentrate light radiation in the narrow wavelength range.  Frequently, optical constants of the constituent materials are measured separately and only thickness is measured in the actual heterosctucture. Unfortunately, it is not always possible because materials in heterostructure may have different optical properties. It is possible , however, to measure both thickness and optical constants assuming that all the same material layers have identical properties.   

Heterostucture thickness Measurement
How to measure heterostructure?
  • Heterostructure, typically, includes thin layers of the metal oxides. In this case, it is best to use MProbe 20 UVVis measurement system
  •  Use of the linked layers helps reduce the number of independent layers for the first step in the data analysis
  • If the fit to the measured data is not good – one can try to add optical constants of one of the materials to measured parameters. It is likely that they are different from the previously measured data
  • If the fit improves but still not perfect – one can fix the optical constant at the latest results and let thickneses of the individual layers flow independently 
Heterostructure thickness measurement, ZnO


Optical dispersion of the ZnO determined from the measurement of heterostructure. It shows that thin ZnO  is more amorphous than expected from thick ZnO layer measurement 

Heterostructure thickness measurement ZnO


Optical dispersion of the ZnO is used in the measurement of thin ZnO layer to check the optical constants determined from the heterosctructure measurement are correct

MProbe 20 UVVis thin-film measurement system

MProbe UVVis 20  system basic specification:

  • Wavelength range: 200-1000nm
  • Wavelength resolution: < 1nm  (optional: 2nm or 4 nm:depends on the entrance spit)
  • Thickness range: 1nm -75 um 
  • Measurement precision: 0.01nm or 0.01% (whichever is greater)
  • Light source: 30W Deuterium short-arc lamp and 20W TH lamp (lamps lifetime 2000hrs)
  • Spectrometer: astigmatism corrected  Ariel spectrometer 
  • Measurement spot size < 1mm
  • Typical measurement time(on Si): 20ms
  • Integration time range: 10us – 1000ms
  • Communication interface: USB2 and 1 Gb LAN 
Read more about MProbe 20 UVVis
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