Development of electromagnetic lenses for multielectron beam lithography system

High-throughput electron-beam (EB) lithography systems require high current. However, beam blur increases because of the individual Coulomb interaction among the electron beams. Isolating the electron beam into 4–16 perfectly independent beamlets is effective. As for the electromagnetic lens, many openings in the parallel flat plates can form the compound eye lens. This lens is called the lotus root lens (LRL). Simulations and experiments with the LRL were carried out. In the case of LRL of 4×4 openings with a 22 mm pitch, the uniformity of magnetic field along the axis was within 0.2%. The basic lens function between two openings separated by 44 mm in the LRL with 21 openings in the conventional column qualitatively evaluated. The LRL should be a potential platform for a multicolumn cell system that provides a multibeam direct-writing system that utilizes variable-shaped beam or character projection as unit-column optics.