OPERATION
Axioscope 5/7/Vario
Illumination and contrast methods in reflected light …
ZEISS
03/2018
430035-7344-001
119
Attention:
•
If the step and its surroundings are made from different materials, the phase jumps characteristic for
the material must be considered. For all non-conducting materials, the phase jump is 180°, and for all
semi-conductors only slightly different from 180°. Consequently, errors in the step-height
determination may be neglected. However, if metals on top of glass are investigated, the results may
become erroneous. The phase jumps given in table 2 were calculated for vertical light incidence and
compact materials. They can serve as approximate values, since the phase jumps depend on the layer-
thickness and the angle of incidence of the light. An accurate determination of the layer thickness is
possible only when the complete specimen is covered with a homogeneous layer and the path
differences are measured.
•
If the layers and the steps are transparent, as with silicon dioxide on silicon, for example, the
interference stripes can change their colors, so that the determination of the order of the interference
may become problematic. This complication can be avoided if the sample is covered with a
homogeneous layer.
Material
Phase jump
φ
For a thickness measurement (step height), half the difference
of the phase jump at the respective interface must be
considered:
2
2
δφ
−
∆
=
SH
Example: extreme case of copper on glass
°
=
Φ
140
copper
,
°
=
Φ
180
glass
, consequently, for the
additional thickness due to the phase jump we obtain
°
=
20
2
δφ
or
nm
30
18
=
λ
Without consideration of the phase jump at the respective
interfaces, the thickness value would be too large by 30 nm.
Copper
140.0°
Gold
142.5°
Silver
151.0°
Bismuth
151.0°
Nickel
157.0°
Iron
157.5°
Zinc
159.0°
Platinum
160.0°
Aluminum
160.0°
Tin
160.5°
Chrome
165.0°
Coal
160.0°
Graphite
165.0°
Silicon
177.0°
Glass
180.0°
Table 2:
Calculated phase jumps for
compact material and
vertical incidence of light