Influence of random noise on the contrast-to-gradient image resolution in scanning electron microscopy

The contrast-to-gradient (CG) method has been proposed previously for the evaluation of image resolution in scanning electron microscopy (SEM). The CG resolution is based on the local resolution, which is defined as the distance to recognize the object's local surface at each pixel position. Then, the CG resolution R is inherently influenced by random noise contained in the image. The present study demonstrates the influence of random noise on the R-values using both personal computer-made dot patterns in various sizes and densities and SEM test micrographs. It is found that the R-values increase with increasing random noise intensity N and their increases are smaller for higher-density patterns, but the R-values are independent of their image sizes under constant pattern density. In addition, the standard CG algorithm is modified especially for straightly fabricated patterns along the x- (or y-) axis, resulting in an improvement in the measurement accuracy of y- (or x-) directional resolutions. The straightness as known information is utilized fully to recognize the local pattern in the random noise.