A 100-kV, 100-A/cm2 Electron Optical System for the EB-X3 X-Ray Mask Writer
In order to increase the throughput of the EB-X3 variably shaped electron beam writing system, a method of increasing the current density with a zoom lens was introduced into the electron optical system. The electron optical characteristics were measured at current densities of 50 and 100 A/cm2 under various zoom-lens conditions, and the results show that this method can increase the current density to 100 A/cm2 without any change in the major electron optical characteristics. At this current density, the patterning resolution was estimated to be 55 nm, and no melting of the first shaping aperture and no microdischarges in the 100-kV electron gun were observed. This confirms that the current density of the EB-X3 can in fact be extended to 100 A/cm2 for the fabrication of X-ray masks with a minimum feature size of 100 nm and below.
Electron optical system for the x-ray mask writer EB-X3
An electron optical system that yields a calculated beam edge resolution of 21 nm at a beam voltage of 100 kV and a current density of 50 A/cm2 was developed for the EB-X3 x-ray mask writer. Based on the system, we investigated a way to increase the current density. The introduction of a zoom lens into the system provided a calculated beam edge resolution of 35 nm at 100 A/cm2. Problems arising from the high beam voltage and high current density, such as the melting of the first shaping aperture and microdischarges in the electron gun, were also examined. Optimization of the aperture and its holder through thermal simulations reduced the temperature of the first shaping aperture to 753 °C at 100 A/cm2. Through electron trajectory calculations, an electron gun was designed in which reflected electrons are prevented from charging the insulators; and this enabled us to completely eliminate microdischarges.
Accurate electron ray tracing for analysis of electron guns immersed in a magnetic-lens field
Abstract This paper describes an electron ray tracing method for calculating the electron trajectories and aberrations of electron guns immersed in a magnetic-lens field. Computation accuracy is improved by (1) solving the modified ray equation that the aberrations satisfy, (2) using the finite element method with third-order isoparametric elements for calculation of the electrostatic and magnetic fields, and (3) introducing the mesh subdivision method into the finite element method to treat the electron gun structure. Calculations of the aberrations, brightness, and emittance of a magnetic-lens-field-immersed gun demonstrate that the method is effective for analyzing and designing such guns.