Prakt. Met. Sonderband 38 (2006) 407 
leave 2.3 TIP CHARACTERIZATION USING AFM 
Scanning probe microscopy (SPM) is a technique for high resolution surface 
characterization. The quality of surface measurements depends on many factors like non- 
linearity of piezoactuators, tilt of a sample or feedback settings. However, the geometry of 
a scanning probe is one of the most significant factors for surface investigation. Main 
parameters describing this geometry are given by the angle of the tip’s cone, and by the 
radius of curvature. A high radius of curvature causes edges of surface to be gentler (Fig. 
6a), whereas a conical or pyramidal shape of the tip causes steep slopes to be more 
slanted (Fig. 6b). 
Fig. 6. Imaging errors resulting from the radius of curvature (a) and the cone 
ı the angle (b). 
These effects show that data obtained with the atomic force microscope result from a 
| convolution of the tip and sample geometries. As an example, Fig. 7 represents the 
ching topography of a DVD obtained with a destroyed and a new probe. As the real tip geometry 
This leads to distortion of the AFM data, it is crucial for high accuracy measurements to know 
SPM the parameters of the scanning probe. 
wire 
h nm 
Fig. 7. Topography of a DVD obtained with destroyed (a) and new (b) scanning 
probe. 
Scanning probes, even when produced in the same technological process and with the 
same silicon substrate, may have different parameters. Specifications usually included in 
AFM probe datasheets give only rough data. 
The analysis of tip parameters can be carried out using every sample of known geometry 
and dimensions. Several investigations have been performed on various calibration 
structures as nano-width lines formed in silicon dioxide [9, 10], circular depressions [11, 
12], nanospheres or pyramids. Among the possible shapes, laterally isotropic test 
structures give best results as they enable three-dimensional visualization of scanning 
probes. 
a, 
3) b)