Engineer's Office for Applied Spectroscopy

Bischof-Fischer-Str. 108
73430 Aalen - Germany
Fon +49 7361 97 53 28 0
Fax +49 7361 97 53 28 5

Film Thickness Measurement

Our TranSpec Lite film thickness instruments use the white-light interference phenomenon in order to determine the thickness of thin transparent layers. These gauges distinguish from all others because of:

  • Non-contact and non-destructive measurement with no calibration!
  • Non-radiation optical method using white light
  • Fast measurement and evaluation - within milliseconds!
  • Wide thickness range: ~ 0.1 - 150 µm ( 0.004 to 6 mil )
  • High accuracy - typically better ± 0.005 µm
  • Simultaneous determination of double-layers possible
  • Motion bridge controlled measurement on webcoaters possible

Download Application Note: Film Thickness Measurement right click to save - left click to open

A commonly well-known effect, which occurs for example with soap bubbles or on a thin oil film on water, is used here for the determination of the film thickness. You can see many colors which change according to the layer thickness, e.g. when the soap bubble is blown up. Also check out this Soap Bubble Web site for some really nice pictures and detailed explanation of this effect!
These "colors at thin layers" are based on the interference phenomenon, which is the superposition of light waves reflected at the front and back side of the layer (or say: at two boundaries with different optical densities). The interference model
The undisturbed superposition of the two reflected light rays 1 and 2 leads to periodical amplifications and extinction in the spectrum of a (pseudo) white continuum light source, such as a halogen spectral lamp.

Since the superposition of the two light rays is not purely additive, a so-called interference occurs. The figure righ beside shows the interference spectrum of a 1 micron and 2 micron thick layer.
Example of interference spectra