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A VERSATILE 3D CALIBRATION OBJECT FOR VARIOUS MICRO-RANGE MEASUREMENT METHODS
A VERSATILE 3D CALIBRATION OBJECT FOR VARIOUS MICRO-RANGE
MEASUREMENT METHODS
M. Ritter
a
*, M. Hemmleb
b
, O. Sinram
b
, J. Albertz
b
and H. Hohenberg
a
a
HPI, Electron Microscopy and Micro Technology Group, D-20251 Hamburg, Germany -
(ritter, hohenberg)@hpi.uni-hamburg.de
b
TU Berlin, Photogrammetry and Cartography, D-10623 Berlin, Germany -
(hemmleb, sinram, albertz)@fpk.tu-berlin.de
Commission V, WG 1
KEY WORDS: Accuracy, Calibration, Close Range, Comparison, Correction, Microscopy, Orientation, Photogrammetry
ABSTRACT:
We present a new micrometer-sized 3D calibration structure containing nanomarkers that serve as well distinguishable
reference points for the calibration of various 3D micro-range measurement methods, e.g. scanning electron microscopy (SEM)
and environmental SEM (ESEM). The 3D calibration object was fabricated using gas-assisted focused ion beam (FIB) metal
deposition. This technique proved to be a valuable tool, as it principally allows the construction of variously shaped
microstructures that can be perfectly adapted to the special specifications of the sensor to be calibrated. The spatial data of
the 38 non-symmetrically distributed nanomarkers were obtained by high-precision atomic force microscopy (AFM). The
accuracy of the nanomarker measurement is shown and the efficiency of the calibration is demonstrated by triangulation and
spatial intersection. Additionally, alternative micro-range measurement methods, e.g. confocal laser scanning microscopy
(CLSM) and scanning profilometry were tested for possible application of the calibration structure.

* Corresponding author.
1. INTRODUCTION
The importance and number of micro- and nano-
technological applications in material science and in life
science is rapidly increasing. The 3D analysis of
microstructures generated by micro-fabrication as well as the
spatial characterization of surface details requires adequate
sensors and micro-range measurement methods. In general,
all measurement processes are subdivided into contact and
non-contact methods. Whereas most close range
measurements work with tactile mechanisms or use light
waves as information carriers, a variety of methods have
been developed for non-contact micro-range measurements.
An overview of relevant 3D micro-range measurement
methods will be given in chapter 2.
A most suitable sensor is the electron microscope. Modern
techniques in scanning electron microscopy like ESEM-
technology offer the possibility of imaging even hydrated
microstructures while maintaining their original 3D
topography. The application of photogrammetric methods
for the analysis of electron microscopic data has a long
tradition and has become the method of choice for the
quantitative 3D-reconstruction of SEM or (ESEM) images:
SEM data provide a large depth of focus, a high signal t o
noise ratio and images can be captured over a wide range of
magnification. The efficiency of the photogrammetric
method has been proved in numerous applications e.g. the
characterization of microstructures, the topographic analysis
of frictions and the reconstruction of biological surfaces
[König et al., 1987, Scherrer et al., 1999, Hemmleb et al.,
2000, Hemmleb, 2001, Ritter et al., 2003].
However, quantitative photogrammetric reconstruction of
electron microscopic data requires a set of basic
components. We recently presented a micrometer-sized 3D
calibration structure that allows the calibration of SEM
[Sinram et al., 2002a]. Yet, also optical errors of alternative
micro-range measurement methods, e.g. ESEM or confocal
laser scanning microscopy (CLSM) and scanning
profilometry can be detected. The 3D microstructure was
fabricated using gas-assisted focused ion (FIB) beam
technique. Based on this technique, an optimally designed
3D micro-object was created. The subsequent high precision
spatial measuring with atomic force microscopy (AFM) made
a calibration object out of the fabricated structure.
Here, we describe a method which makes it possible to build
3D structures of various size with a flexible design in order
to fit specific applications. Multiple sensors could be
calibrated and thus a comparative analysis of the
quantitative microscopic data and their significance can be
accomplished. Thus, we will give a short overview of 3D
micro-range measurement methods connected to this work.
2. SENSORS AND METHODS FOR 3D MICRO RANGE
MEASUREMENTS
2.1 Overview Micro-Range Measurement Methods
Non-destructive 3D micro-range measurement methods exist
in a great variety. For the determination of material
parameters, typically tactile methods are chosen. Optical
measurement methods are used for 3D surface or volumetric
measurements. Various optical measurement techniques were
adapted to micro-range requirements. For higher resolutions,
methods are needed, which overcome the borders of light
microscopy. Using electrons for imaging, the determination
of 3D information results from image processing methods,
e.g. photogrammetric or tomographic algorithms. Electron
beam imaging in combination with 3D image processing offers the possibility to bridge optical 3D measurement
methods and scanning probe microscopy. For a better
understanding, 3D measurement methods in micro-range are
divided into surface und volumetric methods. An overview
of important techniques is given in Table 1. The next two
chapters will deal with an overview of relevant micro-range
measurement methods.
Surface measurement
methods
Volumetric
measurement
methods
Profilometry (optical
or mechanical)
Light Microscopy and
shape from focus
Micro-optical
triangulation methods
(structured light)
Confocal Laser
Scanning Microscopy
(CLSM)
(Environmental)
Scanning Electron
Microscopy ([E] SEM)
combined with
photogrammetry
Transmission
Electron Microscopy
(TEM) and
tomographical
methods
Atomic Force
Microscopy (AFM)
Micro-Tomography
(Micro CT)
(Laser-) Interferometry
Table 1. 3D micro-measurement methods
2.2 Surface measurement
Scanning Electron Microscope and Photogrammetry
The electron microscope uses electrons instead of light for
imaging. In scanning electron microscopy, the signal of a
sample surface is generated by an accelerated electron beam
that is scanned over a sample surface line by line. Thereby,
electrons of the primary beam interact with the atoms of the
surface. In elastic and inelastic scattering processes,
electrons of a broad energy spectrum are emitted from the
sample surface. Two different types of emitted electrons are
commonly used for imaging: Secondary (SE) and
Backscattered (BSE) electrons. SE are created in the sample
itself and only capable to leave it, if generated in the first
few nanometres. Therefore, SE carry the high-resolution
information. SE emitted from the sample are detected by a
photomultiplier system. The signal is then converted to a
digital grey-scale image with an analogue-digital-adapter.
What makes the SEM so valuable for micro-range
measurements are the topographic details of the scanned
images and the large depth of focus. Also, SEM provides a
fairly high resolution due to the properties of the electron
optical system. Although the wavelength of the electrons
could be in the picometer range, due to lens aberration the
aperture of the magnetic lenses of electron microscopes must
not exceed values of about 10-2 rad (0.7 - 1.3 rad in light
optics). This limitation results in a maximum resolution in
the nanometer range. The depth of focus is also affected by
the electron-probe aperture and is quite large i n
correspondence to the small aperture. The depth of focus of