Zeiss Axio Observer 5 - Page 168

OPERATION
ZEISS Illumination and contrast techniques Axio Observer
168 431004-7244-001 12/2016
Attention:
• If the step and the environment are of different materials, the phase jumps inherent to 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 are to 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 such as silicon dioxide on silicon, the interference fringes may
change their color. Determination of the interference order then become problematical. This can also
be remedied by additionally coating the surface with a 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 of 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°
Aluminium 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