A method for evaluating aberration in the crossover image in mask irradiation optics of electron beam

Abstract

Comparative study of resolution limiting factors in electron beam lithography using the edge roughness evaluation method Electron optical image correction subsystem in electron beam projection lithography Low energy electron-beam proximity projection lithography: Discovery of a missing link Lie algebraic aberration theory and calculation method for combined electron beam focusing-deflection systems A method for evaluating aberration in the crossover image in a cell projection lithography system has been developed. In an electron-beam lithography system of projection-type such as a cell projection lithography system, the aberration in the crossover image causes the electron beam to pass off-axis in the electron optics. Optical simulation has quantitatively shown that the aberration in the crossover image causes an electron-beam blur and a positioning error on a writing sample. The evaluating method consists of four square apertures and a mark-detection function in a cell projection system. By measuring each position of the images of the four square apertures on the writing sample at difference focuses, the aberration can be calculated. The field curvature and the astigmatism in a cell projection system were evaluated by using this method. The field curvature agrees with the simulation. In addition, the measurement of the effect of beam alignment is also demonstrated. It is thus concluded that the method can effectively evaluate the aberration in the crossover image. This method is also useful for other projection-type lithographies of charged particles-like ion and electron beams.