PURPOSE: To obtain a charged-particle-beam irradiation apparatus whose resolution can be increased without making the aberration coefficient of an optical system extremely small and without lowering a beam current by a method wherein the aperture half-angle of the optical system is set in a region in which the blur amount of a charged-particle beam due to a space-charge effect becomes the increasing function of the aperture half-angle.

CONSTITUTION: Solid lines Δd10, Δd20 respectively indicate blur amounts of a beam due to the aberration of an optical system and due to a space-charge effect. As computation conditions, the main field-of-view size of the optical is set at 20×1mm, its subfield-of-view size is set at 250μm square, an accelerating voltage is set at 100kV, and a beam current is set at 10μA. In the case of the conditions, in a region in which an aperture half-angle α is at nearly 3mrad or lower, the blur amount Δd20 becomes the increasing function of the aperture half-angle α. Consequently, when the aperture half-angle α is set at 3mrad or lower, the effect of this invention can be obtained. A solid line Δd30 indicates a computation example of a blur amount due to diffraction. The blur amount Δd30 becomes a decreasing function with reference to the aperture half-angle α, and the aperture half-angle α is set in such a way that the composed blur amount Δdol of the blur amounts Δd20, Δd30 becomes a minimum value.