RESEARCH AND DESIGN ON THE COMBINED OBJECTIVE LENSES FOR ELECTRON BEAM LITHOGRAPHY SYSTEMS

Based on the synthetic study of the previous magnetic combined objective lenses, such as MOL (moving objective lens), VAL (variable axis lens), SOL (swinging objective lens) etc; the general theory of combined objective lenses is approached, and a set of general formulas is presented. A new combined objective lens called Bent Objective Len (BOL) is proposed for improving the optical properties in electron beam systems. Using the analytical functions of the magnetic lens field and electron ray, the aberration analysis of the BOL system is performed, and a practical BOL system is also designed. The numerically computational results indicate that this system offers extremely small coma and transverse chromatic aberrations. At the corner of a 5 X 5mm2 deflection field with a 5 mrad aperture angle and 0.0001 beam voltage ripple, the beam blur caused by coma is 0.00.5 m nad the transverse chromatic aberration is 0.001 m.