Physical Principles of Electron Microscopy: An Introduction to TEM ...

The Scanning Electron Microscope 153
For microelectronics and nanotechnology applications, patterns must be
generated on a very fine scale, and the spatial resolution of the pattern is of
prime concern. Electrons can be focused into a probe of very small diameter,
but when they penetrate a thick solid, the beam spreads laterally (Fig. 5-3),
and so the backscattered electrons (which affect a resist coating the surface)
cause a loss in resolution, just as in secondary-electron imaging. One
solution is to use a thin substrate in which backscattering is minimal,
allowing line widths as small as 10 nm; see Fig. 5-22. Another option is to
use electrons of low incident energy, where the penetration and lateral
spreading of the beam in the substrate are small. In addition to electronics
applications, a recent use of electron-beam lithography has been to fabricate
zone plates for focusing x-rays; see Fig. 5-23.