Optical profilometry

Optical profilometry, based on the reflection of a luminous signal on a surface, allows to observe the topography of that same surface on different measurement ranges going from a few dozens of µm² to a few mm², with an optical lateral resolution.

Confocal microscopy allows imaging for all types of samples (sharp or rough, slopes going up to 70 %) with a nanometric vertical precision. Interferometry allows on  less disturbed samples to reach sub-nanometric vertical resolutions.

 

Applications

  • All types of materials : polymers, biological samples, powders, metals, glasses
  • Tridimensional morphologic analysis (fabrication studies, corrosion studies, nano and micro particles structures, following of morphology through time…)
  • Roughness parameters measurement
  • Observable area is of a few mm². To observe smaller areas or requiring a nanometric resolution, we will prefer an atomic force microscope.
 

Other modes

A reflectometry module also allows to measure thin layers thickness (optical fibre).

Operational principles

Confocal microscopy realise images of low field depth or « optical sections ».
Putting the lens focal plan at different levels of depth in the sample and suppressing the light coming from out of focus points, it is possible to realise series of images from which a tridimensional representation of the item can be done.

Interferometry is based on the spliting of a luminous beam in two, one brought on the surface and the other on a miror of reference ; the recombinaison of beams reflected when the sample is at a focal distance gives an interference fringe pattern.
When the interference pattern is at the focal point,
–        In PSI (Phase Shift Interferometry), a few moves in z matches with known phase cancellations are applied ; it allows to rebuild the surface (smooth surfaces, lightly rough samples with steps < 120 nm).
–        In VSI (Vertical Scanning Interferometry), a vertical sweeping is made and the fringe envelops is observed in order to find the maximum of correlation between the waves and the focalisation points (samples of roughness going from 50 nm to 1 µm, steps height > to 120 nm).
In reflectometry, an optical fibre capture the light reflected by the sample.

 
Optical profilometry
Metal deposit, height measurement, interferometric lens DI x10, height 41.5 nm