408 Prakt. Met. Sonderband 38 (2006)
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Fig. 8. SEM (a) and AFM (b) image of calibration test structures.
Fig. 8a represents a SEM image of a test structure, which was used for AFM tip
characterization. The diameter determined straightforward based on the AFM data (Fig. In
8b) is smaller than in reality due to the tip geometry. To obtain a realistic image from the whi
AFM data, a deconvolution process as shown schematically in Fig. 9 for a two-dimensional we
model of circular depression is applied boi
e me
Mo
fee
Fig. 9. Method of a tip characterization: recording information about tip shape during
scanning process (a), analysis of AFM data (b), reconstruction of the scanning probe
profile (c).
At first it is assumed that the tip moves along the surface, and that interactions between
the probe and the sample occur only at the apex. When the tip approaches the brink, the
contact begins to shift towards the probe side area. In case of a tip with low aspect ratio or
a depression with high aspect ratio, the probe might fail to reach the bottom of the hole.
The AFM image indicates that the left profile of the probe is mirrored in the left-hand part
of the convoluted image, and the right profile in the right-hand part (Fig. 9b).
Reconstruction of the probe profile is possible only if the real diameter of the circular
depression is known, as this parameter defines the area where information is recorded. To
obtain a three-dimensional probe characterization, it is necessary to calculate the cross-
section of the tip in many directions.
In our experiments we developed a software routine for the scanning probe visualization, Fig
which was created in Visual C++ environment using the graphical language OpenGL.
Applying the defined model (mask) of the calibration depression structure, it was possible An
to calculate from the recorded AFM image the three-dimensional tip geometry. In order to rec
achieve the best accuracy it is required to adjust the middle of the trench model (mask) del
with the center of the hole image measured by AFM. For that purpose we utilized tip:
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