Optical Disk

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. 1a-b. The smallest features are pits about 400nm long, 320nm wide, 120nm deep, with a track pitch of 740nm. 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 <7nm) that can be checked using AFM imaging.

While standard AFM probes (e.g. HQ:NSC14 series) have a geometry compatible with the reliable imaging of CD and DVD patterns, an AFM operator should use high feedback gains and relatively slow scan rates (0.3-0.5Hz) 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).

Fig. 1. Topography and error images of structures on a DVD. Scan size 6µm.
(a) Height image. Z-scale 120nm.	(b) Amplitude image of the same area. Z-scale 1V.