Abstract: The SEM according to the invention is arranged to detect scattered electrons transmitted by the specimen (22). The detector is constructed so as to have a flat detector surface (26) for a large angular range. In order to select a given angular range, a mask (24) with an eccentric opening (40) is arranged between the specimen and the detector surface and it is also arranged so as to be rotatable. An optimum angle relative to a given direction in the specimen can thus be selected for a given type of contrast. The mask is preferably displaceable in the specimen direction, the detector surface being subdivided into a plurality of parts (26a, 26b) and the assembly formed by the specimen and the detector surface is tiltable through an angle relative to the optical axis (4). A high degree of flexibility is thus achieved for the selection of the electrons to be detected which are scattered by the specimen, so that adjustments can be made so as to achieve an optimum contrast situation.

Abstract: The current of secondary electrons emanating from the specimen 14 in an ESEM is amplified by an avalanche-like ionization of the molecules 41 of the gas atmosphere. However, in order to achieve an adequate number of successive ionizations, a comparatively high voltage is required at the detector electrode 30 and, because of the risk of electric breakdowns, the distance between the specimen and the detector may not be smaller than a comparatively large minimum distance. Consequently, the number of successive ionizations is limited and hence also the current amplification. In order to achieve a higher amplification, the invention proposes the application of an additional magnetic field B in the ionization space. The path length of the secondary electrons is thus substantially increased so that a significantly larger number of ionizations takes place and hence a higher amplification is achieved.

Abstract: Electron-optical rotationally symmetrical lenses inevitably suffer from spherical and chromatic aberration which often impose a limit on the resolution. These lens defects cannot be eliminated by compensation by means of rotationally symmetrical fields. In order to enhance the resolution nevertheless, it has already been proposed to correct the spherical aberration by means of a correction device provided with two hexapoles (24, 26) and two rotationally symmetrical transmission lens systems (28, 30). Each transmission lens system in the known correction device consists of two lenses. According to the invention, one or both transmission lens systems can be replaced by a respective system (46) of four quadrupoles (48, 50, 52, 54), without the correction capability being reduced or only hardly so.

Abstract: Objects such as semiconductor wafers to be studied in a scanning electron microscope (SEM) are subject to vibrations which are intensified by vibration resonance of the (thin) wafer, so that the resolution of the SEM is severely degraded. In prior art it is known to support the wafer by means of elastic support members. However, such support members do not counteract the detrimental vibrations. According to the invention there are provided elastic support elements 28 that can accommodate to the inevitable shape errors of the wafer 18 and hence remain in contact with the wafer surface 32. Moreover, the support elements are embodied in such a manner that frictional contact exists between the moving part 38 of the support element and the body 34 of the object carrier 20. The support elements thus provide support which is elastic for macroscopic support but hard for the vibrational movements in the nanometer range, thus inhibiting such vibrational movements.

Abstract: particle-optical apparatus at a comparatively low acceleration voltage (from 0.5 kV to 5 kV). This lens defect cannot be eliminated by means of rotationally-symmetrical fields. In order to enhance the resolution nevertheless, it has already been proposed to mitigate said lens defect by means of a corrector of the Wien type. This known configuration consists of a number of electrical and magnetic multipoles. In order to adapt the corrective capacity of the corrector 28 to the strength of the objective 8 to be corrected and to achieve less severe requirements in respect of mechanical tolerances, according to the invention the corrector 28 is excited in such a manner that the trajectory of the electrons constitutes a sinusoid of a length which does not deviate more than 10% from a full sine period, upstream and downstream from the correction device there being arranged an n-pole, where n=4, 6, . . . (27, 29), at a distance which is less than ¼ of the length of the corrector.

Abstract: Electron-optical rotationally symmetrical lenses inevitably suffer from spherical aberration which often imposes a limit on the resolution. This lens defect cannot be eliminated by compensation by means of rotationally symmetrical fields. In order to enhance the resolution nevertheless, it has already been proposed to correct the spherical aberration by means of a correction device provided with two hexapoles (24, 26) and two rotationally symmetrical transmission lens systems (28, 30). Each transmission lens system in the known correction device consists of two lenses. According to the invention, one or both transmission lens systems can be replaced by a single lens without reducing the corrective capacity (when only one system 30 is replaced) or while reducing it only slightly (when both systems 28, 30 are replaced).

Abstract: Electron-optical rotationally symmetrical lenses inevitably suffer from chromatic aberration which often determines the resolution limit at low acceleration voltages. This lens defect cannot be eliminated by compensation by means of rotationally symmetrical fields. In order to improve the resolution nevertheless, it has already been proposed to correct the chromatic aberration by means of a corrector (28) provided with two correction elements (34, 40). Each correction element consists of a number of quadrupole fields. Using the known corrector, it has been found that the chromatic magnification error is inadmissibly high. In order to solve this problem, the correction elements in the corrector according to the invention are provided with at least five layers of electrodes (60-a, 60-b, 60-c, 60-d) which produce quadrupole fields.

Abstract: Amplification of the current of secondary electrons emanating from the specimen 14 is realized in an ESEM by avalanche-like ionization of the molecules 41 of the gas atmosphere. However, in order to achieve an adequate number of successive ionizations, a comparatively high value of the electric field at the detector electrode 46 is required and, because of the risk of electric breakdowns, the distance between the specimen and the detector electrode may not be smaller than a comparatively large minimum distance. The number of successive ionizations, and hence the current amplification, is thus limited. The invention proposes to configure the electric field of the detector 46, 50, co-operating with the magnetic field 52 of the immersion lens 8 already present in the ionization space, as an electric multipole field. In the case of electric multipoles, at a given field strength on the optical axis the electric field strength outside the optical axis may be substantially higher.