Patent Number: 06207962&
Section: claims

1. A charged-particle-beam projection-exposure apparatus, comprising: (a) an illumination optical system situated and configured to direct a charged-particle illumination beam along an optical axis from a source to a selected region on a reticle, the reticle being situated at a reticle plane orthogonal to the optical axis;  (b) a projection-optical system situated and configured to direct a charged-particle imaging beam from the reticle to a sensitized substrate so as to transfer the pattern portion defined by the selected exposure unit to the substrate;  (c) at least one upstream mark situated on the reticle plane so as to be selectively irradiated by the illumination beam; and  (d) a shield situated between the source and the upstream mark, the shield defining an aperture that transmits a portion of the illumination beam to the upstream mark while blocking other portions of the illumination beam.  the reticle comprises multiple upstream marks distributed over the reticle; and  the shield defines multiple apertures each corresponding to a respective individual upstream mark on the reticle. 2. The apparatus of claim 1, wherein the upstream mark is situated on the reticle. 3. The apparatus of claim 2, wherein: 4. The apparatus of claim 1, further comprising a mark member separate from the reticle, wherein at least one upstream mark is situated on the mark member. 5. The apparatus of claim 4, wherein the shield extends over the mark member. 6. The apparatus of claim 1, wherein the upstream mark comprises multiple mark portions. 7. The apparatus of claim 6, wherein the aperture defined by the shield is sized, whenever the aperture is registered axially with the upstream mark, to circumscribe all the mark portions collectively. 8. The apparatus of claim 6, wherein the shield defines multiple apertures each corresponding to a respective individual mark portion. 9. The apparatus of claim 1, wherein the shield is situated between the illumination-optical system and the upstream mark.