Variable axis lens of mixed electrostatic and magnetic fields and its application in electron-beam lithography systems

Existing variable axis lens (VAL) concepts are based upon the power series expansion of the lens field, which theoretically limits them to situations where the focusing and in-lens deflection fields are of the same type, usually magnetic. In this article, a general VAL condition is derived from the paraxial trajectory equation that is applicable to any combined focusing and in-lens deflection system with mixed magnetic and electrostatic fields. Two basic configurations of mixed-field VALs are predicated. The feasibility of a magnetic VAL using in-lens electrostatic deflectors for e-beam lithography applications is analyzed. Deflection aberration simulations show that this mixed-field VAL is comparable to its pure-field counterpart.