| Electron beam lithography can delineate features 10 nm and smaller. However the throughput is slow, limited by space charge blurring when writing with large currents. One way to overcome this limit is to employ multiple beamlets distributed over a large area. The approach described here employs a uniform axial magnetic field to focus thousands of electron beams simultaneously.; The source must be at least as small as the beam at the wafer. Fabrication and operation of an aperture source with a diameter of 50nm or less was demonstrated. To prevent contamination, the beam heats the aperture to 200°C. Successful operation was demonstrated by building a test-bed featuring a region of uniform magnetic field and building, inside this region, a miniature scanning electron microscope. We observed resolution between 30nm and 50nm at 10kV and better than 75nm at 1kV. This SEM can image at landing energies as low as 260 Volts.; The detection and separation of the secondary electrons generated by adjacent beamlets is achieved by spacing the beamlets by more than the cyclotron diameter of the secondary electrons (250 microns is sufficient). Detection was demonstrated with a custom-designed and built, monolithic, PIN detector with 40 detector elements.; The system requires a sparse array of matched electron sources with current densities exceeding 10A/cm2, and electron energy spread less than 0.5 eV. Two new configurations were investigated to meet this requirement. The first, the electron bombardment source features a thin semiconductor membrane with a negative electron affinity emission surface. Free carriers are generated by high-energy electrons impinging on the back surface. We demonstrated the first scanning electron microscope images employing this cathode.; The other configuration, the plasmon enhanced photocathode, couples the incident light to surface plasmons on a metallic film. This yields quantum efficiencies 100 times larger than conventional photoemission from a metallic film. A conservative estimate of a magnesium-coated, edge-polished, single-mode fiber yields a current density of 25 A/(cm2 mw) when surface plasmons are excited with a HeCd (325 nm) laser.; While the initial motivation for our approach was lithography, it is also extendible to high-speed inspection of wafers and masks. |
