Ocean Optics ElliCalc - Manual (Page 53)

Ocean Optics Germany GmbH Thin Film Metrology
52
10 Experimental setups and problems
10.1 General
10.1.1 Experimental setup
Ellipsometer setup:
•
carefully adjust the height of your stage to get maximized in intensity
• if your samples are not really perfectly plane thin about installing an autocollimator
• try to avoid stray light in the lab
• as your spot size is so small: pay attention on dust particles which may give wrong results
10.1.2 Maximum intensity
This value describes the maximum intensity in the spectrum of your lamp (can be easily checked in “auto
intensity” mode).
If you use a double spectrometer there are TWO wavelengths corresponding to the sensitivities of the two
spectrometers and your light source.
10.1.3 Polarization
In case of oblique incidence polarization plays an important role. In a vertical arrangement (like NanoCalc)
the polarization does not play any role. “angle of incidence” is defined as the angle between the direction of
incoming light and an axis vertical to the surface.
10.1.4 Signal to noise ratio
The intensity of your acquired signal depends on:
the adjustment of the lamp (see light source or ElliCalc-2000 manual)
the integration time (see menu options)
the number of averages (see samples to average in menu options)
the diameter of the fiber
the distance between fiber and wafer
the sample itself
Do not extend the extraction limits into regions with a high signal-to-noise-ratio !
10.1.5 Stray light
There is a slight risk to catch stray light from your laboratory lamps. Try to avoid this as much as. External
light sources usually change and will produce errors.
10.1.6 Fiber
Your ellipsometer may be equipped with different fibers with core diameters between 50 and 600
micrometers.
The spot size is directly proportional to the fiber diameter, of course the signal intensity decraeses
quadratically.
Consult your hardware supplier.
10.1.7 Absorbing media
It is not too easy to measure absorbing media like polycrystalline silicon as their refractive and absorption
indices usually depend strongly on preparation conditions.
Try to find good optical models for n(λ) and k(λ).