JPS62229643A - Electron ray generating device - Google Patents

Abstract

PURPOSE:To reduce the opening angle of electron beams and make the cross over image small, by furnishing an electron lens magnetic field rotary- systemmetrically close to a filament, and at the same time, making two magnetic poles at a potential same as the filament. CONSTITUTION:The electron lens 9 is composed of a pair of magnetic poles 10a and 10b connected magnetically each other and an exciting coil 11. And the electron lens 9 is made to form a rotady-systemmetric lens magnetic field around the electron beam apertures optical axis Z close to the tip of a firament 1 by forming the electron beam apertures ofthe two magnetic poles 10a and 10b small and by positioning them close to the tip of the filament 1. Moreover, the two magnetic poles 10a and 10b are connected with the filament 1 electrically to keep at the same potential. Therefore, after the electrons are focused, they are focused further by an electrostatic of the Wehenelt electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improvements in electron beam generators used in electron microscopes, electron beam lithography devices, and the like.

[Prior Art] Such an electron beam generator uses a filament made of a thin tungsten wire bent into a hairpin shape, and emits thermoelectrons by applying an appropriate negative potential to Wehnelt electrodes arranged so as to surround the filament. At the same time, the electron beam is focused by the action of an electrostatic lens, and the high voltage applied to the anode accelerates and extracts the electron beam.

[Problems to be Solved by the Invention] However, the electron beam obtained by such an apparatus has a large aperture angle, making it impossible to obtain a sufficiently small loss-over image, and there are limits to the improvement of resolution.

In view of the above, an object of the present invention is to provide an apparatus capable of obtaining an electron beam having a small aperture angle and a sufficiently small crossover image.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a filament that emits electrons, a filament arranged so as to surround the filament,
and an apparatus comprising a Wehnelt electrode that controls electrons taken out from the filament and an anode that accelerates the electron beam from the filament, wherein two magnetic poles are provided near the filament in the Wehnelt electrode so that the optical axis of the electron beam is centered on the Wehnelt electrode. The present invention is characterized in that an electron lens is provided for forming a rotationally symmetrical lens magnetic field, and the two magnetic poles are kept at the same potential as the filament.

Hereinafter, embodiments of the present invention will be explained in detail based on the drawings.

[Example 1] Fig. 1 is a schematic diagram showing an embodiment of the present invention, and 1 is a filament. This filament is supported by two electrode rods 3a and 3b fixed to the support plate 2, and this filament is heated by a heating element 14 connected between the two electrode rods and emits thermoelectrons. Furthermore, a negative high voltage is applied to this filament 1 by accelerating NrA5. A Wehnelt electrode 6 is arranged so as to surround the filament 1, and a negative voltage is applied to the filament 1 by a bias power supply 7 to control electrons emitted from the filament. Reference numeral 8 denotes an anode for accelerating the electron beam emitted from the filament 1, and is maintained at ground potential.

Reference numeral 9 denotes an electron lens provided within the Wehnelt electrode 6, and the electron lens is composed of two magnetic poles 10a, 10b and an excitation coil 11 that are magnetically connected to each other. Moreover, this electronic lens has two magnetic poles 10a and 10b.
By forming most of the electron beam passing portions to be thin and disposing them near the tip of the filament 1, a lens magnetic field rotationally symmetrical about the electron beam optical axis Z is formed near the tip of the filament 1. ing. Further, the two magnetic poles 10a and 10b are electrically connected to the filament 1 and kept at the same potential.

In this way, the electrons emitted from the filament 1 are focused by the rotationally symmetrical lens magnetic field formed by the two magnetic poles 10a and 10b at their generation portion, and then further focused by the bias voltage applied to the Wehnelt electrode 6. It is focused by the action of the electrostatic lens that is formed, is accelerated by the anode 8, and is taken out. As a result, the aperture angle of the electron beam becomes small, and the crossover image can also be made very small, so that resolution can be improved.

Here, the two 11 poles 10a and 10b are the filament 1
The electric field distribution of the electrostatic lens formed between the filament 1 and the Wehnelt electrode 6 is not changed by the two magnetic poles, and is no different from the case where no magnetic poles are provided. .

FIG. 2 is a schematic structural diagram showing another embodiment of the present invention, and the same numbers as in FIG. 1 indicate the same components.

That is, in this embodiment, of the two magnetic poles 10a and 10b constituting the electron lens 9 shown in FIG.
This is characterized in that the Wehnelt electrode 6 is used for both.

In this case, the upper magnetic pole 10a and the excitation coil 11 side of the Wehnelt electrode 6 are separated without being connected, and the upper magnetic pole 10a
It is necessary to maintain the Wehnelt electrode 6 at a negative bias potential with respect to the filament at the same time as keeping it at the potential of the filament 1. Even if the upper magnetic pole and Wehnelt electrode are separated in this way, the magnetic field will not be affected in any way (
, a lens magnetic field can be formed in the electron beam optical axis 7 portion.

[Effects of the Invention] In the present invention as described in detail above, after focusing the electrons at the part where electrons are generated from the filament by forming a rotationally symmetrical lens magnetic field near the tip of the filament, the Wehnelt electrode is further focused. Since the electron beam can be focused by an electrostatic lens, the aperture angle of the electron beam becomes very small. Therefore, since it is possible to extract an electron beam with high brightness and a very small crossover image, it is possible to improve the resolution.

Further, if the Wehnelt NwA is used also as the lower magnetic pole constituting the electron lens as in the embodiment shown in FIG. 2, it is possible to simplify the device and reduce costs.

[Brief explanation of drawings]

FIG. 1 is a schematic structural diagram showing one embodiment of the present invention, and FIG. 2 is a schematic structural diagram showing another embodiment of the present invention. 1: Filament 2: Support plate 3a, 3b: Electrode rod 4: Heating power source 5: Acceleration power source 6: Wehnelt electrode

Claims (2)

[Claims] (1) A device comprising a filament that emits electrons, a Wehnelt electrode that is arranged to surround the filament and controls electrons extracted from the filament, and an anode that accelerates the electron beam from the filament. An electron lens is provided near the filament in the electrode to form a lens magnetic field rotationally symmetrical about the optical axis of the electron beam by two magnetic poles, and the two magnetic poles are kept at the same potential as the filament. An electron beam generator. (2) The electron beam generating device according to claim 1, wherein the Wehnelt electrode also serves as a lower magnetic pole forming the electron lens.