Patent Number: 046510036
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 schematically shows an electron beam apparatus. In the cathode chamber, an electrode beam B is emitted by the cathode K and is shaped by a Wehnelt electrode. The electron beam B is accelerated in the direction toward an electron-beam accelerating anode A of the invention. The electron beam B first passes through a bore in the anode A which is optimally designed for an acceleration voltage of 2.5 kV. At the end of this bore, the electron beam B passes through a diaphragm which seals the vacuum V1 of the cathode chamber off from the remaining vacuums of the electron beam apparatus. The vacuum V1 of the cathode chamber is generated via a pump P1. After passage through the first diaphragm of the anode A, the electron beam B passes two plates of a blanking system, passes through a further diaphragm, and then proceeds into the first part V2 of a vacuum tube. After passing a first sliding diaphragm B1 having an aperture dimension of less than 500 .mu.m and preferably about 300 .mu.m, the electron beam B passes the second portion V3 of the vacuum tube and then passes through a further sliding diaphragm B2. Finally, the electron beam B impinges on a measuring location on the specimen PR. This specimen PR is situated in a vacuum V4. This vacuum V4 is generated via a pump P2. In the vacuum tube formed of the parts V2, V3, the electron beam B is influenced by the condenser lenses K1, K2 and by further deflector means that are not shown in the drawing. FIG. 2 schematically shows an electron-accelerating anode A of the invention. The electron beam B emitted by the cathode K is shaped by the Wehnelt electrode W. The electron beam B then passes a first part 8 at the input of the anode A as viewed in the beam direction. This part 8 comprises a bore which provides an optimum beam value or brightness and an optimum centering. At the end of this bore of the part 8 a diaphragm 9 is positioned for the vacuum seal between the vacuum V1 of the cathode chamber and the portion V2 of the vacuum tube following thereupon. The diaphragm 9 has a diameter of 300 .mu.m. This enables a vacuum V1 in the cathode chamber of 10.sup.-7 bar. After passage through the diaphragm 9, the electron beam B passes the two deflector plates 7, 11 of the blanking system integrated into the Faraday cage of the anode A. In order for the pulse generator which supplies the blanking pulses for the blanking system to be designed as simply as possible, the plate 7 as well as the part 8 and the diaphragm 9 advantageously lie at anode potential. In such a case, blanking pulses from a pulse generator need only be communicated to the plate 11. This plate 11 must therefore be electrically insulated from all parts that lie at anode potential. A carrier 4 to which the plate 11 is secured via a part 3 by screws is therefore advantageously designed as an insulator. An electrical line for the blanking pulses for the plate 11 can be channeled in the carrier 4 and then through a bore through a part or through a plurality of parts of the anode A. Finally, the electron beam B impinges an output diaphragm 10 at the electron beam output of the anode A. This diaphragm 10 has a diameter of less than 2 mm and preferably from 500 .mu.m to 1 mm. The diameter of the diaphragm 10 represents a compromise because, on the one hand, it should be as small as possible in order to permit a best possible vacuum in the portion V2 of the vacuum tube and, on the other hand, it should permit a certain divergence of the electron beam B so that the electron beam B can be shaped in a beneficial fashion by the condenser lenses K1, K2. The anode A finally comprises a connecting piece 2 which serves for centering and adjusting the anode A in the opening of a vacuum wall and simultaneously serves for vacuum sealing. A ring 1 can be positioned on this connecting piece 2, the dimensions of this ring being capable of being flexibly adapted to various dimensions of openings in vacuum walls of various commercially available electron beam apparatus. The connecting piece 2 and the diaphragm 10 again advantageously lie at anode potential, just as do the parts of the anode A which are not referenced with numerals, these to be at least partially placed at anode potential so that a Faraday cage can be formed. Given employment of a somewhat more expensive pulse generator, both deflector plates 7, 11 can also be controlled with blanking pulses. Methods for the control of a plate or of two mutually opposite plates for blanking a particle beam are disclosed in U.S. Pat. No. 4,413,181, incorporated herein by reference. The vacuum in the portion V2 of the vacuum tube amounts to about 10.sup.-3 through 10.sup.-5 bar V4 amounts to 10.sup.-5 through 10.sup.-6 bar. The height of the anode A amounts to about 3 cm. The invention enables improved particle beam properties with respect to the focussing thereof. Although various minor changes and modifications might be proposed by those skilled in the art, it will be understood that I wish to include within the claims of the patent warranted hereon all such changes and modifications as reasonably come within my contribution to the art.