Noise and Its Effects on the Low-Voltage SEM

Noise is the single most important limiting factor in scanning electron microscopy. Because of the presence of noise, we are forced to operate the SEM to maximize the available beam current and the beam dose (current × time) at the expense of degraded image resolution, increased charging, and more sample damage. Recent developments in high-performance electron guns, aberration correctors, and lenses are all part of an attempt to attain control of the noise while still achieving ever higher levels of resolution. In this chapter, we will examine noise in the SEM, its origin and properties, its measurement, and how the properties of the detectors used for the collection of secondary emission (SE) electrons and backscatter electrons (BSE) signals affect the noise.