Electron beam lithography system with new correction techniques

Abstract

In our electron exposure system, the focal length of the final projection lens is designed to be very short. To decrease aberrations due to beam deflections, which cannot be corrected by a dynamic focus coil or a stigmator, deflection coil parameters are determined by a simulation, which used the conditions: coma length=0, transverse chromatic aberration coefficient=0, and beam incidence is normal to the sample surface. Patterns of the size under 0.2 μm are well resolved inside the whole deflection field of 1.6×1.6 mm. Current density of the system is more than 40 A/cm2. Refocusing and refocus–flyback are necessary to utilize the high current density for spot size between 0.1 and 3.0 μm. Large spot defocusing is refocused by small refocus coils, and refocused beam position shifts are corrected by a refocus–flyback method. Beam-settling retardation caused by an eddy current occurs after an electromagnetic jump. A differentiated electromagnetic signal is added to electrostatic deflectors to compensate for the transitional beam positions between the jump. The beam-settling time is less than 100 μs for a 1 mm jump, about a tenth of that without the compensation.