Scanning charged beam particle beam microscope

Abstract

For dark-field imaging of the specimen, a scanning corpuscular-beam micrope is equipped with multiple annular apertures located between the beam source and the specimen on the one hand and between the specimen and the detector on the other hand. The areas of the multiple annular apertures conjointly i.e. complementarily cover the ray path. The aperture situated in front of the detector is surrounded by a wide, radiation-transmitting region. The invention affords utilizing for the generation of the image not only the rays scattered outside of the aperture cone but also a large part of the rays scattered within this cone.

I claim: 
     
       1. A scanning charged particle beam microscope comprising a charged particle beam generator for generating a beam having a radiation cone having a primary longitudinal beam axis extending between said generator and a specimen, as system adjacent said generator for deflecting said beam perpendicular to the axis in accordance with a set of raster coordinates, a charged particle beam optical condenser lens disposed about said axis for focusing the beam into a small spot in the plane of said specimen for scanning thereof, said lens being disposed between said .[.deflecting system.]. .Iadd.beam generator .Iaddend.and said specimen, a detector arrangement for providing a signal of those portions of the beam which are scattered when the specimen is irradiated, said detector being disposed about the axis under said specimen, and an aperture combination arrangement having dimension independent of the size of the radiation cone through said condenser lens, said aperture combination comprising a first, input aperture disposed about the beam axis between said .[.deflecting system.]. .Iadd.beam generator .Iaddend.and said .[.condenser lens.]. .Iadd.specimen, .Iaddend.and a second output aperture between said specimen and said detector complementary to said first aperture and having a first inner portion which is radiation opaque with respect to the unscattered portions of the beam complementary to said input aperture and permeable to the scattered portions of the beam and a second outer portion having a portion totally permeable in respect to scattered charged particles, the areas of said first aperture and the complementary areas of the first portion of said second aperture being ring-shaped and concentric, the outer portion of the output aperture having a radial width at least equal to one half of the radius of the inner portion whereby the ratio between primary radiation intensity and detected scattered radiation is improved for the wide primary radiation cone required for high resolution and least possible radiation loading of the specimen. 
     
     
       2. In a scanning microscope according to claim 1, said first aperture being a phase-correcting zone plate having closed areas which lets only such partial beams reach the specimen locality which after passing through said condenser lens have phases of the same polarity. 
     
     
       3. In a scanning microscope according to claim 2, the closed areas of said first aperture having a width larger that the minimum width required for shielding off all partial beams with phases of one polarity. 
     
     
       4. Scanning microscope according to claim 1, comprising a further deflection system between the specimen locality and said second aperture, said further deflection system being arranged for compensating the beam deflection caused by said first deflection system. 
     
     
       5. In a scanning microscope according to claim 1, said deflection system comprising two partial systems following each other in the direction of the beam, of which the first deflects the beam away from the optical axis of the microscope and the second redirects the deflected beam so that the axis of the redirected beam intersects the optical axis substantially in the plane of said first aperture. 
     
     
       6. In a scanning microscope according to claim 5, said first aperture and said second aperture being located in coordinated optical planes of said condenser lens. 
     
     
       7. In a scanning microscope according to claim 5, said first aperture being located in the focal plane of said condenser lens. 
     
     
       8. Scanning microscope according to claim 1, comprising concentric ring-shaped radiation detectors having open areas therebetween, the open areas of said second aperture being formed by said open areas of said detectors. 
     
     
       9. Scanning microscope according to claim 1, comprising a velocity analyzer arranged after said second aperture.