5-6
5 Technical Specifications
Metrological Properties
Measured under vibration-damped conditions
INFORMATION
The sampling increment not only has a significant impact on the resolution,
but also on the measurement time. To obtain a short measurement time you
have to accept an inferior resolution. This means that sample rates < 50 nm
only slightly improve the resolution, but significantly increase the data rate
and the size of the measurement file. Apart from that, it can be said, the
shorter the increment, the smaller the largest possible AOI.
Measurement procedure
Coherence scanning,
analysis: "Smooth
Surfaces"
1
Coherence scanning,
analysis: "Rough Surfaces"
2
Phase-
shift
3
Specifications for the z performance
4
Measurement noise
individual measurement
(Sq-value according to
ISO 25178)
< 0.5 nm
< 15 nm
< 0.6 nm
Vertical resolution
5
< 1.45 nm
< 42.4 nm
< 1.7 nm
Typical flatness measurement
6
Flatness deviation
< 75 nm
< 125 nm
< 65 nm
Repeatability (without
averaging for individual
measurements)
5 nm
10 nm
< 1.5 nm
1
analysis of the correlogram phase
2
analysis of the correlogram envelope
3
In the phase-shift method, the interference phase is varied in an number of steps and from the individual interference
intensities the phase value of each measurement point is determined from which the height value is calculated.
4
Empirically determined typical specification parameters for z-performance of the sensor head when measuring on a plane
mirror (95% of maximum AOI, interference contrast
≈
1)
5
measurement noise x
6
Rounded values of the deviation of the measured flatness for various sensor heads with various sampling increments, object
filters and for the three measurement processes determined from the empirical measurement data and a statistical evaluation;
measurement on a plane mirror (95% of maximum AOI)
Typical step height measurements
1
Nominal step height
[µm]
5
50
450
1 000
2 000
5 000
Repeatability
2
(Standard deviation)
[µm]
0.008
0.06
0.05
0.05
0.05
0.05
Relative repeatability
[%]
0.160
0.120
0.011
0.005
0.003
0.001
Expanded uncertainty of measurement
3
[µm]
0.05
0.25
0.3
0.3
0.3
0.4
Relative expanded uncertainty of
measurement
[%]
1.000
0.500
0.067
0.030
0.015
0.008
1
Empirically determined typical performance when measuring on a calibrated PTB depth setting standard type A1 (ISO 5436-1)
2
Variation of measurement values for a series of measurements under repeat conditions, worst value when looking at several
measuring instruments
3
interval limit of a confidence range with 95.4% probability (2
σ
), determined from the standard deviation from the calibrated
value over all measurements at the respective step height
