| High resolution electron beam systems are used in lithography to create masks for patterning integrated circuits, and in microscopy for imaging materials. Traditionally, such systems use energies from 10 keV up to 100 keV to generate fine beams. However, electrons at these energies scatter over a large area upon entering the sample, leading to a loss in resolution and pattern fidelity. The interaction volume can be dramatically reduced by decreasing the landing energy of the beam below 1 keV. The challenge is then to design optics which maintains high resolution in the beam at these very low energies.;For energies below 100 eV, the solution is to use a scanning tunneling microscope (STM) operating in the field emission mode. Because the gap between the STM tip and the sample is only several hundred Angstroms, the beam has a diameter comparable to the size of the tip, and the beam diameter decreases as the energy is reduced. The STM has been used to expose ultrathin polymer resist films at energies between 5 and 100 eV and with linewidths down to 30 nm. The films have also successfully been used as etch masks to transfer the patterns into underlying metal layers.;At energies above 100 eV, the optimal approach is a scaled-down focusing system. By employing magnetic or electrostatic fields with maximum possible strengths, lenses may be designed with minimized aberrations. These systems may take the form of a microlens where the electron source and target are in close proximity (... |
