Patent Number: 
Section: claims

1. A beam apparatus in which backscattered electrons are detected comprising:a beam source for producing a primary beam;an objective lens for focusing the primary beam produced from the beam source onto a sample;at least one condenser lens disposed between the beam source and the objective lens and operating such that the primary beam forms one crossover point between the condenser lens and the objective lens;an aperture plate positioned on the optical axis of the primary beam to block the orbit of secondary electrons emitted from the sample, the aperture plate having an opening through which the primary beam passes and being mounted at the crossover point or a position between the crossover point and the objective lens; anda charged-particle detector positioned to detect backscattered electrons emitted from the sample and passed through the opening of the aperture plate, the charged-particle detector being mounted at a position closer to the beam source than the crossover point. 2. A beam apparatus in which backscattered electrons are detected comprising:a beam source for producing a primary beam;an objective lens for focusing the primary beam produced from the beam source onto a sample;at least one condenser lens disposed between the beam source and the objective lens and operating such that the primary beam forms one crossover point between the condenser lens and the objective lens;a first charged-particle detector positioned on the optical axis of the primary beam to block the orbit of secondary electrons emitted from the sample for detecting the secondary electrons, the first charged-particle detector having an opening through which the primary beam passes and being mounted at the crossover point or at a position between the crossover point and the objective lens; anda second charged-particle detector positioned on the optical axis of the primary beam to detect backscattered electrons emitted from the sample and passed through the opening of the first charged-particle detector, the second charged-particle detector being mounted at a position closer to the beam source than the crossover point. 3. A beam apparatus in which backscattered electrons are detected comprising:a beam source for producing a primary beam;an objective lens for focusing the primary beam produced from the beam source onto a sample;at least one condenser lens disposed between the beam source and the objective lens and operating such that the primary beam forms one crossover point between the condenser lens and the objective lens; anda charged-particle detector positioned on the optical axis of the primary beam to detect secondary electrons emitted from the sample, the charged-particle detector having an opening through which backscattered electrons from the sample pass as well as the primary beam passes and being mounted at the crossover point or at a position between the crossover point and the objective lens. 4. A beam apparatus as set forth in any one of claims 1 to 3, wherein said objective lens is a magnetic objective lens. 5. A beam apparatus as set forth in any one of claims 1 to 3, wherein said objective lens is a cathode lens, and wherein a potential difference is produced between an outer wall of an electron optical column and a sample holder. 6. A beam apparatus as set forth in any one of claims 1 to 3, wherein said objective lens is a combined magnetic objective lens-cathode lens, and wherein a potential difference is produced between an outer wall of the objective lens and a sample holder. 7. A beam apparatus as set forth in any one of claims 1 to 3, wherein said objective lens is a combined magnetic objective lens-decelerating electrostatic objective lens, and wherein a potential is produced between an outer wall of the objective lens and the inside of the objective lens. 8. A beam apparatus as set forth in any one of claims 1 to 3, wherein said objective lens is a combined magnetic objective lens-cathode lens, and wherein the objective lens is at ground potential and a high voltage is applied to a sample holder. 9. A beam apparatus as set forth in any one of claims 1 to 3, wherein a beam-shaping aperture is mounted between said beam source and said condenser lens.