FIGURE 6-9 A test pattern with squares, A, will appear severely distorted if the piezoelectric scanner in the AFM is not linear as in B.

Once the scanner is properly linearized, it is also critical that the scanner be calibrated. For example, it is possible for the scanner to be linear but not calibrated. If the calibration is incorrect, then the X-Y values measured from line profiles will be incorrect.

FIGURE 6-10 This AFM image of a test pattern is very linear. The spacing of the squares at the top, bottom, left and right sides are all the same distance apart. It appears as it should. A common method for correcting the problems of X-Y non-linearity and calibration is to add calibration sensors to the X-Y piezoelectric scanners. These sensors can be used to correct the linearity and the calibration in real time.

6.2.3 Z Calibration / Linearity

Height measurements in an AFM require that the piezoelectric ceramics in the Z axis of the microscope be both linear and calibrated. Often the microscope is calibrated at only one height. However, if the relationship between the measured Z height and the actual Z height is not linear, then the height measurements will not be correct.