Do SEII Electrons Really Degrade SEM Image Quality?

Generally, in scanning electron microscopy (SEM) imaging, it is desirable that a high-resolution image be composed mainly of those secondary electrons (SEs) generated by the primary electron beam, denoted SEI. However, in conventional SEM imaging, other, often unwanted, signal components consisting of backscattered electrons (BSEs), and their associated SEs, denoted SEII, are present; these signal components contribute a random background signal that degrades contrast, and therefore signal-to-noise ratio and resolution. Ideally, the highest resolution SEM image would consist only of the SEI component. In SEMs that use conventional pinhole lenses and their associated EverhartThornley detectors, the image is composed of several components, including SEI, SEII, and some BSE, depending on the geometry of the detector. Modern snorkel lens systems eliminate the BSEs, but not the SEIIs. We present a microfabricated diaphragm for minimizing the unwanted SEII signal components. We present evidence of improved imaging using a microlithographically generated pattern of Au, about 500 nm thick, that blocks most of the undesired signal components, leaving an image composed mostly of SEIs. We refer to this structure as a spatial backscatter diaphragm. SCANNING 35:1-6, 2013. (c) 2012 Wiley Periodicals, Inc.