JPS63216255A - Electron gun - Google Patents

Abstract

PURPOSE:To simplify the structure and improve the reliability and profitability by supporting heating bodies with the restoring force of support electrodes when no force is applied from the outside. CONSTITUTION:When a cathode 1 and heating bodies 2a, 2b are to be fitted to support electrodes 3a, 3b, first the distance between the electrodes is expanded by such a means as to insert a spacer between the electrodes. Next, the cathode 1 and the heating bodies 2a, 2b are installed between the electrodes, finally the spacer is removed, then tips of the support electrodes 3a, 3b approach to each other by the restoring force of springs, the heating bodies 2a, 2b are pressed, and the cathode 1 is supported. When the heating bodies are thus fitted, the good conductivity and mechanical support can be invariably obtained by the fixed pressing force, and no pressing screw is required. Accordingly, the structure is simplified, and the reliability and profitability can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to an electron gun that generates an electron beam in an electron microscope, an electron exposure apparatus, or the like.

Conventionally, an electron gun is a two-pole electron gun consisting of a cathode made of a material that emits electrons when heated, a Wehnelt electrode with a through hole located at its tip, and an anode that accelerates electrons. is widely used. In addition to tungsten and oxides, lanthanum hexaboride (L
aB6) has been widely used because it has a low work function, easily emits electrons, has high brightness, and has a long life.

FIG. 1 is a diagram showing the structure of a conventional LaB6 electron gun. The LaB6 cathode 1 is supported by supporting electrodes 3a and 3b via a heating element 2a s 2 b, and power is supplied to the heating element via this electrode, and the cathode is heated by the Joule heat generated in the heating element. be done. Thermion electrons are emitted from the heated cathode tip and are taken out to the outside through a through hole provided in the Wehnelt electrode 10. Heating element 2a
, 2b is generally carbon such as pyrolytic graphite or amorphous carbon. This is because the above-mentioned boride cathode becomes active at high temperatures and reacts with metals, and carbon is suitable for avoiding this. Terminals 5a and 5b are screwed at their tips to fix the support electrodes 3a and 3b to the insulator 5. These terminals 6a and 6b are connected to a heating power source 1 (not shown), and the cathode 1 is connected to the heating power source 1.
Power is supplied to heat the

4a and 4b are screws for pressing the support electrodes 3a and 3b. In the natural state where the support electrode is not pressed by a spring, the distance between its tips is equal to that between the cathode 1 and the heating element 2a,
2b is configured to be wider than the total width. Therefore, by loosening the screws and installing the cathode and the heating element with the tips of the electrodes open, and then tightening the screws, the supporting electrodes come close to each other and press and support the heating element and the cathode.

In such conventional support methods, it was necessary to pay close attention to the force with which the screws were tightened. In other words, if the pressing force is weak, the conductivity between the supporting electrode, the heating element, and the cathode is insufficient and no heating current will flow; if the pressing force is too strong, the heating element,
This is because the cathode may be damaged or the supporting electrode may be plastically deformed. Furthermore, the balance between the left and right tightening forces is delicate, and if this balance is not maintained, distortion will occur when the cathode is heated, causing the cathode to move and making the electron beam unstable. For these reasons, the current situation is to strictly control the tightening force using a torque gauge or the like. Furthermore, the method of tightening the screws necessitates a mechanically complex structure. On the other hand, the supporting electrode becomes high in temperature due to heat conduction from the heating element, so it needs to be made of highly heat-resistant materials such as tungsten and molybdenum, but these are difficult-to-process materials and are difficult to process into complex structures. be. Therefore, manufacturing requires a large amount of time and cost. Furthermore, there were other drawbacks such as the screws loosening during use. In the above points, the conventional technology has many difficulties and poses practical problems.

OBJECT OF THE INVENTION The present invention aims to eliminate the drawbacks of the prior art as described above, and to provide an electron gun with a simple structure, high reliability, and high economic efficiency.

21 Structure of the Invention The present invention comprises a cathode that emits electrons, a heating element that holds and heats the cathode, and a supporting electrode that supports the heating element, and when the supporting electrode is not subjected to external force. The present invention relates to an electron gun characterized in that a heating element is supported by a force that returns to its natural state.

E. Embodiment FIG. 2 is a sectional view showing an embodiment of the present invention. In the figure,
The same numbers as in FIG. 1 indicate the same components. However, the electrodes 3a and 3b are not pressed by screws as in the conventional example. FIG. 2(b) is a diagram showing the state before the cathode and the heating element are attached in this embodiment.

The support electrodes 3a, 3b are connected to the insulator 5 with terminals 6a,
6b. In this way, in the natural state where no external force is applied to the supporting electrodes, the electrodes are shaped so that their tips are close to each other and the distance between them is narrower than the sum of the widths of the cathode and the heating element. ing.

To attach a cathode and a heating element to this supporting electrode, first widen the distance between the electrodes by inserting a spacer between the electrodes, then install the cathode and heating element between the electrodes, and finally remove the spacer. For example, the tips of the supporting electrodes approach each other due to the restoring force of the spring, the heating element is pressed, and the cathode is supported.

FIG. 2(a) thus shows Yin 4:f! 1 and heating elements 2a and 2b are attached.As is clear from this example, the heating element is pressed by the force of the supporting electrode returning to its natural state, and this force is due to the shape of the electrode. and depends on the material. Therefore, if the shape and material of the electrode are always made constant, a constant pressing force can always be obtained after assembly, and there is no need to strictly control the force when tightening screws as in the prior art. Naturally, troubles due to loosening of screws do not occur, and there is no imbalance between left and right pressing forces. A further advantage is that no pressing screws are required, which simplifies the construction and significantly reduces manufacturing time and costs. This advantage will be more apparent in the next example.

FIG. 3 is a diagram showing another embodiment. In the figure, the same numbers as in FIG. 2 indicate the same components. In this embodiment, the support electrodes 3a, 3b are formed by cutting out a shape as shown in FIG. 3(b) from a plate material and then bending it along the dotted line in the figure. This supporting electrode is the third (
a) As shown in the perspective view, it is fixed to the terminals 6a and 6b by a method such as a slot 7) welding. Also, the terminal 6a.

6b is glass-sealed to the insulator 5. In this embodiment, as in the embodiment of FIG. 2, the supporting electrodes 3a,
3b presses and supports the heating elements 2a, 2b and the cathode 1 by the force that returns to the natural state when no external force is applied. If these terminals do not have sufficient mechanical strength, the number of terminals may be set to four, for example, and the support electrode 3a is fixed to two terminals, and the support electrode 3b is fixed to the other two terminals. The mechanical strength can be increased by doing something like this.

In this embodiment, the supporting electrodes 3a and 3b have a simple shape and are cut out from a plate material.
Material costs and processing costs are further reduced significantly, and even difficult-to-process materials such as tungsten and molybdenum can be easily manufactured. Furthermore, since the overall shape can be made compact, it is also possible to make it compatible with conventional tungsten hairpin cathodes.

When this electron gun was attached to an electron microscope and tested, the results were as follows.
The electron emission characteristics were good and the stability of the electron beam was extremely excellent.

In the above embodiments, the cathode may be a boride such as LaB6, or may be a so-called oxide cathode. Further, the emitted electrons are not limited to thermoelectrons, and may be emitted by field emission or the like. This is because even in the case of electric field emission, it is necessary to temporarily heat the cathode (flushing) or constantly heat it (in the case of thermal field emission), and the configuration of the present invention is effectively applied.

As described in detail in Section 1, the present invention is configured such that the support electrode presses and supports the heating element by the force that returns to its natural state when no external force is applied, so that the heating element cannot be attached. Good electrical conductivity and mechanical support can always be obtained with a constant pressing force, and there is no need to strictly control the force when tightening screws as in the prior art. In addition, since there is no need for a screw to press, the structure can be made thinner, and troubles due to loosening of screws naturally do not occur, and there is no imbalance between the left and right pressing forces.

Furthermore, since the support electrode can be manufactured by cutting it out of a plate material, material costs and processing costs can be significantly reduced, and even difficult-to-process materials such as tungsten and molybdenum can be easily manufactured, resulting in many effects.

[Brief explanation of the drawing]

FIG. 1 is a sectional view for explaining the prior art, FIG. 2 is a sectional view for explaining one embodiment of the present invention, and FIG. 3 is a sectional view for explaining another embodiment of the present invention. ) is a perspective view, (b
) is a plan view. In addition, in the reference numerals shown in the drawings, 1: cathode, 2a, 2b: heating element, 3a: H3b r supporting electrode.

Claims (1)

[Claims] 1. A cathode that emits electrons, a heating element that holds and heats the cathode, and a support electrode that supports the heating element, and that supports the electrode when no external force is applied to it. An electron gun characterized in that the heating element is supported by a force that returns it to its original state. 2. The electron gun according to claim 1, wherein the supporting electrode is constituted by a plate having a uniform thickness.