| 摘要 |
Charged-particle-beam projection optical systems are disclosed including a symmetric magnetic doublet comprising first and second magnetic lenses arranged along a system axis between a reticle position and a sample position. The lenses have point symmetry about a crossover point and a centrally located mutual focal point located between the two lenses. The dimensions on the sample-side of the cross-over point are reduced, in both the axial direction measured from the axis and the radial direction measured from the crossover point, by a demagnification ratio. The magnetic fields of each lens are opposite, the electrical excitation current applied to each lens coil is equal, and the lenses are preferably energized by the same power supply. A first beam deflector is located near the reticle inside the first lens; a second and third beam deflector are located inside the first lens and the second lens, respectively; and a fourth beam deflector is located near the sample inside the second lens. When an off-axis position on the reticle is projected, the beam deflectors deflect the beam so that the principal ray of the beam travels along the system axis between the second and third def lectors. Axis deflectors deflect the optical axis of the lenses to coincide with the path of the principal ray.
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