MEBES IV THERMAL-FIELD EMISSION TANDEM OPTICS FOR ELECTRON-BEAM LITHOGRAPHY

The MEBES(R) IV column design and test results are presented. A new thermal-field emission (TFE) electron gun comprised of a Zr/O/W <100> cathode and a low-aberration, large-aperture electrostatic lens operates as part of a variable-magnification, four-lens "tandem-optics" column. A 10 kV beam with brightness up to 5 x 10(6) A/cm2 sr at the mask is produced. The resulting advantage in electron optical performance is divided between a maximum current density of 400 A/cm2 and a convergence angle reduced to 5 mrad at 0.1-mu-m beam size. System accuracy is enhanced by the improved depth of focus, reduced aberrations, and the ability to reduce address size while maintaining present throughput levels set by the writing time of the serial-exposure, raster-scan machine. Doubling the blanking rate to 160 MHz improves throughput and enables the use of resists having 2.5-mu-C/cm2 sensitivity. The use of a dual-stigmator column setup and a 7.5 V/ns double-deflection beam blanker maintains beam jitter below 0.01-mu-m. The four-lens optics can expose masks with a continuously variable beam size over a 0.05-0.30-mu-m range while maintaining constant current density without adjusting the gun extraction voltage. GHOST(TM) proximity correction of 0.25-0.50-mu-m features is possible with a fast defocus optic, which forms 0.50-1.0-mu-m beams and also reduces the exposure current to required values. A beam component analysis provides a measure of the Boersch and radial beam broadening effects.