OPERATION
Axio Imager
Illumination and contrast methods
Carl Zeiss
M70-2-0020 e 06/2009
430000-7344-001
175
Caution:
•
If the step and the environment are of different materials, the phase jumps inherent to the material
must be taken into account. Whilst the phase jump for all non-conductors is 180° and for
semiconductors only deviates slightly from 180°, i.e. the measuring error is negligible, 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 and the 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
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°
Half the difference of the phase jumps is included in the
determination of the thickness:
2
2
d
δφ
−
Δ
=
Example: Extreme case of copper on glass
°
=
Φ
140
copper
,
°
=
Φ
180
glass
therefore part of the
phase jump
°
=
δφ
20
2
or
nm
30
18
=
λ
without taking the phase jump inherent in the material
into account the measured value would be 30 nm too
great.
Carbon 160.0°
Graphite 165.0°
Silicon 177.0°
Glass 180.0°
Table 2:
Calculated phase jumps for
compact material and
vertically incident light
