Zeiss Axio Imager 2 - Page 191

Axio Imager 2 OPERATION ZEISS
Illumination and contrast methods
01/2016 430000-7544-001 191
Important:
• If the step and the environment are of different materials, the phase jumps inherent in the material
must be taken into account. The phase jump for all non-conductors is 180° and for semiconductors it
only deviates slightly from 180°, i.e. the measuring error is negligible, however the measured values
may be falsified for metals on glass for example. The phase jumps in table 2 calculated for vertically
incident light and compact material serve as recommended values because it can be assumed that the
phase jumps depend on the layer thickness and the angle of incidence of the light. Accurate
determination of the thickness is only possible by coating the entire object with a homogeneous layer
and then measuring the path difference.
• If the layers or steps are transparent (e.g. silicon dioxide on silicon), the interference fringes may
change their color. Determination of the interference order then becomes problematical. This can also
be remedied by coating the surface with an additional homogenous layer.
Material
Phase jump
φ
Half the difference of the phase jumps is included in the
determination of the thickness:
22
d
δφ
−
∆
=
Example: Extreme case: copper on glass
°=Φ 140
copper
,
°=Φ 180
glass
therefore part of the
phase jump
°=
δφ
20
2
or
nm30
18
=
λ
without taking the phase jump inherent in the material
into account the measured value would be 30 nm too
large.
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°
Chromium 165.0°
Carbon 160.0°
Graphite 165.0°
Silicon 177.0°
Glass 180.0°
Table 2:
Calculated phase jumps for
compact material and vertically
incident light