Ocean Optics NanoCalc - Manual (Page 65)

Ocean Optics Germany GmbH Thin Film Metrology
64
10 Experimental setups and problems
10.1 General
10.1.1 Experimental setup
microscope setup:
•
if you use a microscope you have the advantage of a high spatial resolution (depending on your lens
system), but you should keep in mind:
• the angle of incidence is not well defined and you should repeat your measurement with different lenses to
control your results (usually the results are slightly dependent on the magnification factor)
• you have a good chance to measure lots of stray light from your laboratory. Control your measured lamp
spectra !
• If you use a fiber for illumination: turn off the usual microscope lamp
• as your spot size is so small: pay attention on particles which may give wrong results
• if film thickness is high: such samples often are inhomogeneous. Try a different spot to measure
• use reference wafers and device under test of the same height
fiber setup:
if you use a simple fiber setup you should keep in mind:
•
the spot size corresponds to the area of your fiber core (e.g. 200 micrometers or less)
• try to avoid stray light
• use a distance of at least 3-30 mm (otherwise the results are sensitive to different heights of your reference
wafer and the device under test)
10.1.2 Reference spectrum
To measure the thickness of any thin film you have to measure a reference spectrum first. This is necessary
to get information about the incoming amount of light as a function of wavelength.
Insert a blank (silicon?) wafer or your blank substrate in the measuring arrangement and press “reference”.
You should get a typical spectrum of a halogen lamp (see chapter 5.1) (or a warning to increase or decrease
the intensity of the lamp)
If you want to continue with measuring your thin films:
Do not forget to tell NanoCalc which substrate you used in this step (by pressing EditStructure and adjusting
the correct catalogue)
10.1.3 Maximum intensity
This value describes the maximum intensity in the spectrum of your amp (could be easily checked in
Reference mode). This value helps NanoCalc to achieve an automatic adjustment of the reference spectrum
within the limits of the screen (=without saturation)
If you use a double spectrometer there are TWO wavelengths corresponding to the sensitivities of the two
spectrometers and your light source.
10.1.4 Polarization
In case of oblique incidence polarization plays an important role. In a vertical arrangement (like NanoCalc)
the polarization does not play any role.
Attention: in microscope arrangements this condition of vertical incidence may no longer be fulfilled. You
should test your results with different magnifications.