International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B5. Istanbul 2004 
  
  
feedback loop 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
Controller 
Laser 
Signal WE 
electronics | 
Scanner 
Xyz 
m Lb I 
Split Photodiode Duo 
Detector Cantilever & Tip 
Sample 
  
Figure 1. AFM contact and non-contact mode. In contact 
mode, the change of the cantilever deflection is monitored 
with the split photodiode detector. A feedback loop tries to 
keep the cantilever deflection constant by moving the z- 
scanner in order to maintain a constant photodetector 
difference signal. The topographic information is related to 
this movement of the z-scanner. When in non-contact mode, 
the scanning tip oscillates close to the sample surface. Here 
the oscillation amplitude is kept constant and used for 
topographic information. 
The probe head is a tip mounted on the top of a flexible 
cantilever (Figure 1), which scans across the sample surface. 
For high resolution, the tip has to be very sharp, usually 
between 2nm to 20nm. A piezoelectric tube scanner performs 
the scan. Thereby, either the tip is moved or the sample 
itself, depending on the device used. The tip surface 
interaction is monitored by the reflection of a laser beam at 
the cantilever. The laser is detected by a split photodetector, 
where the difference in the photodetector output voltage is 
related to either the cantilever deflection or the oscillation 
amplitude. 
In order to use scanning probe methods for the spatial 
measurement of surfaces, the measured values (Current) have 
to be transformed into metric measures. This involves 
special complications, because of the non-linearity of the 
scanning motion and the measurement errors due to the 
complex probe and sample geometry, which are hard to 
determine. A solution of this problem is provided by the 
development of metrological AFM (MAFM). These combine 
a high vertical measuring accuracy of AFM with the exact 
lateral measuring, for instance by controlling the motion of 
the AFM with interferometric methods. Because of the 
combination of several sophisticated instruments, these 
devices are custom-made and therefore very expensive. They 
are used mainly for calibration purposes. 
2.3 Volumetric measurement 
Confocal Laser Scanning Microscopy 
Confocal Laser Scanning Microscopy (CLSM) is a 3D light 
microscopy technique. The CLSM is based on conventional 
microscopes, but the light source is a laser. The laser beam is 
focused on a sample in a way, that only one object point is 
illuminated. A detector pinhole discriminates against 
scattered light that is not emitted in the plane of focus. The 
resulting signal information from every object point 
represents a data cube. The CLSM can be used in reflection 
mode to characterize topographies. In order to achieve 
higher resolutions, a laser beam is applied in combination 
with a 3D scanner. The resolution of a CLSM is then 
restricted by the wavelength of the used laser and the 
resolution of the scanning system. CLSM images can be 
acquired of a wide range of samples, if only the minimum 
requirements concerning reflection are fulfilled. But, since 
most objects do not behave as perfect mirrors, data from 
reflection mode have to be carefully interpreted. The use of 
CLSM in life science is well established for a broad range of 
research activities {sce Pawley, 1990], whereas the 
application in technical and material science is rather new 
[Wendt, 1995, Tiziani et al., 2000]. 
3. A VERSATILE CALIBRATION OBJECT 
In the first place, it has been our aim to create a method for 
the quantitative 3D reconstruction of SEM data. This task 
could be achieved by using an appropriate tilting stage and 
a suitable calibration object [Sinram et al., 2002b]. But, more 
and more it became clear that there is a general wish to 
combine existing data with additional specific information 
provided only by other micro-range measurement methods. 
The correlation of complementary information from samples 
of interest offers new characteristics and a more precise 
analysis of surface features, e.g. if scanning electron 
microscopy and confocal laser scanning microscopy are 
combined [Al Nawas et al., 2001, Wessel et al., 2003]. Yet, in 
order to be able to correlate additional data with existing 3D 
datasets, the accuracy of all methods involved has to be 
determined. To us, the easiest and most accurate way to 
accomplish this task is the calibration of all the micro- 
measurement methods involved with one calibration object. 
Since every sensor used for analytic purposes has its 
specific optical and mechanical peculiarities, the calibration 
object has to be carefully designed in order to cope with a 
variety of requirements. Most important was the decision to 
use gas assisted focused ion beam (FIB) metal deposition to 
produce the 3D micro-object. This method allowed the 
fabrication of 3D objects of various shape and structure. 
However, the precision to be achieved with this kind of 
technique has its limits and up to now, can only be roughly 
estimated. Considering all of the above facts, we found a 
possibility, which is not simply a compromise but a new 
methodological approach. It allows correlative 3D 
microscopy by using a flexible calibration technique. 
3.1 Fabrication by gas assisted ion beam deposition 
The most suitable way for the fabrication of the calibration 
object was found in the technique of gas assisted focused 
ion beam deposition [see Steckl et al., 1988]. Focused ion 
beam (FIB) systems operate similar to scanning electron 
microscopes, though a focused beam of gallium ions (Ga) 
instead of an electron beam is used. The FIB technique 
allows imaging or patterning of structures. Patterning in this 
case either means the process of specific removal of material 
as the beam scans along the sample surface, or the process of 
specific deposition of metal (by gas assisted deposition) 
onto the surface (Figure 3). 
When the gallium ions of the primary beam hit the sample 
surface, a small amount of material is sputtered, leaving the 
surface as either ions or neutral atoms. This process is called 
milling. Additionally, the primary beam produces secondary 
electrons (SE). The secondary electrons can be used for 
imaging or for gas assisted deposition. If an organometallic 
gas, e.g. W(CO)s is introduced into the sample chamber of 
the microscope, it interacts with the secondary electrons of 
the ion beam as well as the beam itself and forms a nof- 
volatile product that adsorbs on the surface. Lateral 
deposition and structure formation can be controlled by 
    
  
  
  
  
  
  
  
     
  
  
   
   
   
   
   
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
   
  
  
  
  
  
  
   
  
  
  
  
  
  
  
  
  
  
  
   
  
  
  
  
   
  
  
   
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
   
  
  
     
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