Design of an electron-optical system with a ball-tip emission source through a numerical optimization method for high-throughput electron-beam–direct-write lithography

To improve the throughput of electron-beam–direct-write lithography (EBDWL), we propose a new electron-optical system (EOS) design method with the capability of systematically optimizing EOSs with various types of emission source. A ball-tip emission source initially proposed by another group is further discussed. A numerical optimization method is utilized in the design method to maximize EOS emission current while satisfying constraints including the size of the electron beam spot and the amount of induced electric field on electrodes and insulators inside EOSs. For performance comparison, two EOSs, one with a generic emission source and the other with a ball-tip emission source, are designed using the proposed method. Preliminary results indicate that a sixfold emission current is obtained from the EOS with the ball-tip emission source. Furthermore, patterning fidelity investigations are conducted using the obtained design results. It is shown that the higher emission current from the ball-tip emission source is achieved without compromising patterning quality.