FIGURE 2-24 Illustration of the three viewing positions of an optical microscope in an AFM.

2.2.7 Mechanical Loop

The greatest factor that effects the vertical resolution, or noise floor of an AFM is the rigidity of the mechanical loop. The mechanical loop is comprised of all the mechanical elements between the sample surface and the probe, as illustrated in Figure 2-25. If this loop is not rigid, then the probe can vibrate out of phase from the sample, and noise is introduced into images. It is typically easier to make the mechanical loop very rigid by making the microscope very small. Because of this, in practice the highest resolution AFMs are very small. It is also very difficult to make AFM stages for larger samples such as wafers and discs that have very high vertical resolutions.

FIGURE 2-25 The mechanical loop in an AFM includes all of the structural elements that are required to hold the probe at a fixed distance from the sample. This includes: xyz Scanner X-Y Stage Z Motor AFM Sensor

2.3 Electronics

Most of the electronics in an AFM are resident in a separate cabinet from the stage and the computer. The functions in the electronic controller may be constructed with a DSP chip or analog electronics. This section does not discuss the implementation, but describes the block functions in the controller. The primary function of the electronics in an AFM are to: