Uniform Thermionic Cathode for High Emittance SCALPEL Electron Beam Source

The SCALPEL electron beam lithography exposure tool column consists of the two electron optics devices, illumination system and projection system, working in concert to expose wafer features as small as 0.1 micron and below. In the SCALPEL, a 1x1 mm wide high energy (100 kV) electron beam illuminates a thin membrane mask. After penetrating through the mask, electrons are focussed by means of projection doublet at the silicon wafer with 4X demagnification. This illumination system possesses unusually high depth of focus (at least 10") rendering the cathode emission surface nonuniformity at the mask plane. As a consequence, the projection system renders said nonuniformity at the wafer plane, thus downgrading the exposure quality.