| 摘要 |
PROBLEM TO BE SOLVED: To facilitate focus adjustment and to keep the magnification ratio or magnification of an image constant by varying a focus position in the X-axis direction and the Y-axis direction, according to the variation of an image surface position so as to set it to that of the new image surface. SOLUTION: An optical axis takes an X-Y-Z orthogonal coordinate system of the Z-axis. It is assumed that the magnetic permeability of vacuum isμ0, the absolute value of the charge of charged particles is (q), its sign is (s), the mass of the charged particles is (m), the axial potential isϕ[Z], an object surface is Z0, an image surface is Z1, two paraxial trajectories in the X-direction are expressed by the expression I and the equation II on the object surface Z0, and two paraxial trajectories in the Y direction are expressed by the equation III and the equation IV on the object surface X0. The astigmatic field P2j [Z] of the j-th Q lens is expressed by the product of the axial astigmatic field distribution D2j [Z] per unit current multiplied by the expression V when the j-th Q lens is an electromagnetic Q lens, and by the quotient of the axial astigmatic field distribution D2j [Z] divided byϕZ, when the j-th Q lens is an electrostatic Q lens. A height deviationΔZ of the image surface when the equation VI and the equation VII are satisfied is detected, and variations Ij, Ik of excitation currents or voltages of the j-th and k-th Q lenses are set in the equations VIII and IX, respectively.
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