Such contrast is not possible with any other type of microscope. It is critical that the viewing area of the image is on the same length scale as the features giving rise to the surface texture. As an example, the image shown here is of a 1 X 1 micron region of a silicon wafer. The surface roughness of this area is 0.1 nm. If there are larger scale surface features, such as waviness or bow in the wafer, then the AFM will not measure this surface topography.

FIGURE 7-4 Polished Quartz 10 x 10 u.

7.1.4 Defects

Defects in many types of materials such as metals, crystals, and ceramics are easily measured with an AFM. Because the AFM measures three dimensional surface structure, it is possible to measure not only the area of the defect but also the volume of a defect at a surface. A drawback of using an AFM for imaging defects is that the field of view of an AFM is fairly small, so the density of the defects must be such that at least one defect is in the FOV. This problem is sometimes dealt with by using another microscope or instrument for locating the defect. The AFM is then used to fully characterize the defect.