Patent Number: 046510036
Section: summary

BACKGROUND OF THE INVENTION The invention relates to a particle-accelerating electrode designed as a Faraday cage structure and inside of which a blanking system is provided for blanking a particle beam. It is standard in electron beam measuring technology to register high-frequency events at a measuring location with the assistance of stroboscopic measuring methods. Given a stroboscopic measuring method, an electron beam or, in more general terms a particle beam, is gated synchronously with the high-frequency event at a measuring location such that the particle beam senses the measuring location and thus triggers measured signals only during a fraction or during a plurality of fractions of a period duration of the high-frequency event at the measuring location. This occurs during each and every period of the high-frequency event at the measuring location. Stroboscopic measuring methods are preferably executed in scanning electron microscopes. Since the particle beam must be keyed in and blanked out given stroboscopic measuring methods, a particle beam blanking system is required in a stroboscopic measuring apparatus. Such a particle beam blanking system is usually provided as part of a beam generating system. A blanking system for a particle beam is known from U.S. Letters Pat. No. 4,169,229, incorporated herein by reference, wherein the particle beam is shaped after its emission with the assistance of a Wehnelt electrode and then passes an accelerating electrode designed as an apertured disk. After passage through this accelerating electrode, the particle beam impinges a first pin diaphragm, passes through the actual deflection system which comprises two symmetrical deflector plates, passes through a further pin diaphragm, and finally enters a vacuum tube through a third apertured disk secured to the vacuum tube. Since this known apparatus for blanking a particle beam is extended in the direction of the particle beam, the incorporation of such a blanking system in a particle beam apparatus requires a lengthening of the particle-optical column by introducing an additional ring into the particle-optical column. Such an apparatus, moreover, is difficult to manipulate, since many different piece parts must themselves be respectively dismantled when replacing such an arrangement or when merely removing such an arrangement from the particle-optical column. As a consequence of the many different piece parts, involved adjustment systems are required, these making the overall apparatus relatively expensive. The overall arrangement, moreover, requires many individual pin diaphragms or apertured disks in order, on the one hand, to meet particle-optical requirements and, on the other hand, in order to enable a good vacuum seal. Given this known apparatus, the entire blanking system is accommodated in a vacuum-tight housing together with the beam generator. A particle beam generating system is known from German patent application No. P 32 04 897.1, incorporated herein by reference, which comprises a particle-accelerating electrode designed as a Faraday cage and in whose interior a blanking system is attached for blanking a particle beam. This known particle beam generating system is designed such that it permits an optimum beam value or brightness and an optimum centering for a specific accelerating voltage. Since the patent application states nothing with respect to a required vacuum seal of the particle beam generating system, it is assumed that this particle-accelerating electrode is also integrated into the particle-optical beam path together with the blanking system in a fashion that is standard according to the prior art. Since, due to the blanking system, the particle-emitting electrode has a considerable extent in the direction of the particle beam, the particle-optical column must be lengthened in comparison to a particle beam system without the blanking system. This usually occurs by means of an additional introduction of a ring into the particle-optical column. As in the aforementioned apparatus, moreover, additional apertured disks or pin diaphragms are required for the vacuum seal, these resulting in a considerable expenditure for additional adjustment systems. SUMMARY OF THE INVENTION An object of the present invention is to specify a particle-accelerating electrode of the type initially cited which solves the problem of the vacuum seal in a simple way, wherein the particle-optical column need not be lengthened, is easy to manipulate, and can be relatively inexpensively manufactured. This object is achieved by providing a particle-accelerating electrode according to the invention wherein at least one sealing means for vacuum sealing is provided in a beam path as a part of the particle-accelerating electrode. A particle-accelerating electrode of the invention permits a simple adjustment of this electrode in the particle beam optical beam path. A connection piece of a particle-accelerating electrode of the invention can be designed such that it can be fitted in vacuum-tight fashion into an opening of a vacuum wall as a flange. When this opening in the vacuum wall is disposed in defined fashion with respect to the particle-optical axis, then this particle-accelerating electrode is also disposed in defined fashion relative to the particle-optical axis via a defined arrangement of the connecting piece at the particle-accelerating electrode. The connecting piece of the particle-accelerating electrode can be designed such that an additional flange ring can be disposed on it, said flange ring being flexibly adaptable to various openings of vacuum walls of various commercially available particle beam devices. As an apparatus for the vacuum seal, a pin diaphragm or an apertured disk can, in particular, be integrated into the particle-accelerating electrode. Advantageously, the bore of the particle-accelerating electrode at the particle beam input of this particle-accelerating electrode should be designed such that it permits an optimum beam and an optimum centering of the particle beam. It is beneficial for this purpose when the appliance provided for the vacuum seal is not provided until the end of this bore immediately in front of the blanking system. This appliance for the vacuum seal need not be designed as a separate part. The bore at the particle beam input of the particle-accelerating electrode can also be designed such that it is gradually or discontinuously or abruptly tapered to dimensions which are required for the vacuum seal. An appliance for the vacuum seal can also be disposed at the particle beam output of the particle-accelerating electrode. It is fundamentally sufficient when a single appliance for the vacuum seal is integrated into the particle-accelerating electrode. This single appliance for the vacuum seal can be disposed at an arbitrary location of the particle-accelerating electrode insofar as it fulfills the purpose of the vacuum seal. In electron beam measuring technology, an acceleration voltage of 2.5 kV is usually used in the quantitative potential measurement at LSI electronic components. Since the potential resolution is particularly favorable given a high-current source, high-current cathodes such as, for example, lanthanum hexaboride cathodes, are advantageously employed. Such high-current cathodes, however, require a particularly good vacuum in the cathode chamber because the performance capability of these high-current cathodes otherwise suffers. It is beneficial in such a case when a structure for the vacuum seal having a particularly small opening is provided at the particle beam input of the particle-accelerating electrode. In such a case, it is particularly beneficial for the vacuum seal and for the beam shaping when a further structure, for example a pin diaphragm having a small opening, is provided at the particle beam output of the particle-accelerating electrode. Since the vacuum in the particle-optical column need not be particularly good at the level of the imaging structure or deflector structure, the opening of the structure for the vacuum seal and beam shaping at the particle-beam output of the particle-accelerating electrode can be somewhat larger than the opening of the structure for the vacuum seal at the particle beam input of the particle-accelerating electrode. Given an apparatus of the invention, the particle-accelerating electrode together with the blanking system and together with at least one structure for vacuum sealing is compactly replaceable. The invention enables a particle-optical column of a particle beam apparatus to be employed without an extension ring. The invention facilitates the adjustment of the particle-accelerating electrode. The invention solves the vacuum problem better--viewed overall--than is possible with the prior art because not as many parts have to be adjusted in the beam path, and thus tighter tolerances are possible for the applicances for the vacuum seal. When switching between various acceleration voltages, a particle-accelerating electrode of the invention can be interchanged rather comfortably for a different particle-accelerating electrode without a cathode or an anode having to be modified. The electrode is held in position by screws or in some other fashion.