The EBES4 electron-beam column.

The electron-beam column for AT&T Bell Laboratories' EBES4 electron lithographic system forms a writing spot less than 125 nm in diameter (FWHM) with a current in excess of 250 nA at a fixed beam energy of 20 keV. A thermal-field-emission gun uses a long life zirconium-tungsten cathode operated at 1750-1800K. The optical system contains three magnetic lenses and produces one intermediate crossover adjacent to a knife- edge. The beam can be blanked in less than 500 ps by deflecting it so that it is interrupted by the knife edge. The beam current is changed by varying the strengths of the first and second lenses. Fast, accurate deflections are provided by three deflection systems: A telecentric magnetic deflection system covers a 0.28-mm-square field and settles in 5 microseconds. Two electrostatic deflection systems cover 32micron and 4micron square fields with settling times of 100 ns and 1 ns respectively. The electron- beam column has excellent mechanical stability and reliability, and requires very little maintenance.