Patent Number: 
Section: claims

1. A mechanism for supporting an apertured plate, comprising:a plate holder for holding the apertured plate provided with an aperture through which a beam of charged particle passes;a holder support for supporting the plate holder;grooves extending radially in plural directions about the center axis of said aperture and formed in a supported surface of the plate holder or a supporting surface of the holder support; andconvex portions engaged in the grooves and formed on the other of the supported surface or the supporting surface. 2. A mechanism for supporting an apertured plate as set forth in claim 1, wherein said grooves extend in three directions about the center axis of said aperture. 3. A mechanism for supporting an apertured plate as set forth in claim 1, wherein each of said grooves has a V-shaped cross section. 4. A mechanism for supporting an apertured plate as set forth in claim 1, wherein each of said convex portions is made of a spherical member. 5. A mechanism for supporting an apertured plate as set forth in claim 1, wherein said grooves are formed in the supported surface of the plate holder, while said convex portions are formed on the supporting surface of the holder support. 6. A charged-particle beam instrument having a charged-particle beam source for emitting a beam of charged particles, an apertured plate provided with an aperture through which the beam passes, a plate support mechanism for supporting the apertured plate, and an illumination system for directing the beam passed through the aperture at a substrate,wherein said plate support mechanism has a plate holder for holding the apertured plate and a holder support for supporting the plate holder,wherein grooves extending radially in plural directions about the center axis of said aperture are formed in a supported surface of the plate holder or a supporting surface of the holder support, andwherein convex portions engaged in the grooves are formed on the other of the supported surface or the supporting surface. 7. A charged-particle beam instrument as set forth in claim 6, wherein said grooves in said plate support mechanism extend in three directions about the center axis of said aperture. 8. A charged-particle beam instrument as set forth in claim 6, wherein each of said grooves in said plate support mechanism has a V-shaped cross section. 9. A charged-particle beam instrument as set forth in claim 6, wherein each of said convex portions of said plate support mechanism is made of a spherical member. 10. A charged-particle beam instrument as set forth in claim 6, wherein said grooves in said plate support mechanism are formed in the supported surface of the plate holder, while said convex portions of said plate support mechanism are formed on the supporting surface of the holder support.