Technology for Fundamental Improvement of an Extremely Low-Quality Video Signal for Use in Fine Focusing and Astigmatism Correction in Scanning Electron Microscopy

Figure 5

Performance confirmation of the SEM image acquisition method when priority is placed on the SNR. To determine a suitable magnification condition for this method and for our SEM instrument, three magnifications ((a) 300,000x, (b) 60,000x, and (c) 12,000x) were selected for the experiments. The images were processed using the procedure described in Figure 4, and the changes in their SNRs with repetition of the averaging operations for pixels are plotted in (d). (a)–(c) show the processed results for the SEM images acquired at each magnification. Next, an evaluation index of the scattering of the signal for focusing operations from Equation (1) was obtained as shown in (e), and the maximum value (as identified by a small circle) of all the calculated values was selected for our purpose. See the main text for details. The bars represent 0.14 μm (a and a), 0.7 μm (b and b), and 3.5 μm (c and c).