408 Prakt. Met. Sonderband 38 (2006) 
adc 
n i tre 
Scansdize: 900.03 300.0nm 256x256 
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: 
d 
nN