Fast Fourier Transform Techniques for Measuring SEM Resolution

Abstract

Precise knowledge of a particular SEM's resolution is important for at least two reasons to the microscopist operating the instrument. First, accurate interpretation of micrographs obtained in the course of daily operation depends on knowing the performance limits of the instrument. Second, it is important for the microscopist to be able to verify instrumental performance.Spatial resolution is typically determined using micrographs of materials containing structures having a “known” spacing. By showing that two objects in the micrograph are separated by some distance, it is claimed that the instrument is capable of resolving this spacing. This method is passable for instruments whose maximum resolution resolves only features of known spacing. However, for High Resolution SEM's (HRSEM) this method is not adequate. It is difficult to identify specimens with surface structure that can be verified to exist at the ultimate limits of today's HRSEM resolution. The fact that verifying resolution by this method depends on being able to verify the spacing of surface structure on a particular specimen leads to an interesting paradox - the resolution of a given instrument can be verified only after a better instrument is available to characterize the structure spacing.