Particle-optical instrument comprising a deflection unit for secondary electrons
AssigneeU.S. Philips Corporation
InventorsKars Z. Troost, Alexander Henstra
Life of this patent
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Abstract
A primary beam in a scanning electron microscope (SEM) releases secondary electrons in the specimen to be studied. These electrons move back to the focusing lens against the direction of the primary beam, detection of these electrons taking place in the vicinity of said lens. A known detector comprises a Wien filter for deflecting the electrons from the optical axis to the actual detector. In accordance with the invention a SEM detector is provided with a double electric dipole. The latter leaves the primary beam undisturbed to a high degree, but very efficiently deflects the secondary electrons to the actual detector.
Claims6
A particle-optical instrument which comprises a particle source for producing a beam (34) of electrically charged particles which propagate along an optical axis (4) of the instrument, is arranged to scan a specimen (14) to be examined by means of the particle beam (34), and comprises a focusing lens (6) for forming a beam focus in the vicinity of the area in which the specimen is to be arranged, which instrument also comprises a detection device (24, 26) for detecting electrically charged particles (32) originating from the specimen, which detection device (24, 26) comprises an electric dipole 24) whose electric field intersects the optical axis and extends transversely thereof, thus defining a field integral of the electric field over the optical axis,
- characterized
- in that the detection device 24, 26) comprises at least one further electric dipole (30) which has been shifted in the direction of the optical axis relative to the first dipole and whose electric field at the area of the optical axis opposes that of the first dipole and has a strength such that the algebraic sum of the field integrals along the optical axis of all dipoles of the detection device is substantially zero.
Dependencies are inferred from the claim text.