This example of an AFM metrological application is related to the
profiling of surface patterns of CDs and DVDs. The height and amplitude
(error) images of DVD structures are shown in Fig. 2a-b. The smallest
features are pits about 400 nm long, 320 nm wide, 120 nm deep, with
a track pitch of 740 nm. The size, shape and position of the pits
seen in the images must be controlled on the nanometer scale. Quality
control of DVD manufacturing includes a number of stringent specifications
(e.g. a feature placement in the radial direction with 1 standard
deviation < 7 nm) that can be checked using AFM imaging.
Height image of DVD structure. Scan size 6 µm.
Z-scale 120 nm.
Amplitude image of the same area. Z-scale equals
to 1V.
While regular probes (e.g. 14 series) have a geometry compatible
with the reliable imaging of CD and DVD patterns, an AFM operator
should use high gains of feedback and relatively slow scanning rates
(0.3-0.5 Hz) for precise profiling of the pits and high accuracy
of the measurements. The minimization of the imaging error can be
judged from amplitude variations, which are presented in the amplitude
image (b).
