Does SEM Have a Future?

摘要

CD-SEM's importance to metrology cannot be overrated. However, it seems that current tools are restricted to running at energies between 1 keV and a few hundred electron volts, because that is the energy range found to give the best beam interactions, while minimizing charging and limiting resist shrinkage. With structures hundreds of nanometers in size, this choice did not matter. However, now they are in the tens of nanometers and getting smaller, which is causing problems. For example, low-energy electron wavelengths are large at a few hundred volts; their wavelength is a significant fraction of an angstrom. Consequently, diffraction effects must be controlled or beam spot size is affected. Chromatic aberration resulting from the natural energy spread of the electron source is even more important. Here, electrons of different energies are focused to different planes. In the ＜ 3 keV range, chromatic aberration's effect on spot size is critical.