Zeiss Axio Scope.A1, Operating Manual

Page: 90 / 123

OPERATION
Carl Zeiss Illumination and Contrasting Method Axio Scope.A1
90
M60-2-0007 e 05/08
Attention:
•
If the step and its surrounding are made from different materials, the phase jumps characteristic for
the material have to 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
only possible when the complete object is covered with a homogeneous layer and the path differences
are measured.
•
If the layers, respectively the steps are transparent, as e.g. in silicon dioxide on silicon, the interference
stripes can change their color and consequently 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
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°
For a thickness measurement, half the difference of the phase
jump at the respective interface has to be considered:
2 2
d
δφ
−
Δ
=
Example: extreme case copper on glass
° = Φ
140
copper
,
° = Φ
180
glass
, consequently we
obtain for the additional thickness due to the phase jump
° =
δφ
20
2
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.
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