JPS5823164Y2 - Denkai Houshiyutsugata Denshijiyu - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a field emission type electron generation source equipped with a thermionic emission source for purifying an anode.

Field emission electron guns have the advantage of being able to obtain electron beams with a much higher electron current density than normal thermionic emission electron guns, but they do not produce ions that are generated when the electron beam collides with the anode. It has the disadvantage that the emitter is often damaged by vacuum arc discharge between the emitter and the anode.

In order to prevent such damage to the emitter, a filament for emitting thermionic electrons is installed near the emitter, and by colliding the thermionic beam with the anode, gases and impurities that are occluded or attached are repelled, and the anode is heated. Recently, devices have been proposed that evaporate impurities and clean the anode surface facing the emitter.

However, in such a device, the convergence of the thermionic beam generated from the filament is poor, and since a wide area of the anode surface is irradiated, the electron flow density is low. It has the disadvantage that it is not possible to raise the electron beam, therefore it is not possible to perform a sufficient cleaning treatment, and it is not possible to obtain a stable electron beam due to field emission.

The present invention aims to eliminate such drawbacks and will be explained in detail below with reference to the embodiments shown in FIGS. 1 and 2.

In the figure, 1 is an emitter made of a material suitable for field emission, which is held by a holder 2, and an accelerating power source 1.
3, a more negative high voltage is applied.

The holder 2 is supported by a cathode support plate 4 via stems 3 a and 3 b.

Reference numeral 5 denotes a thermionic emission filament placed near the emitter 1 so as not to come into contact with the emitter and its holder 2, and is supported by the support plate 4 via stems 6 a and 6 b. 6a and 6b are connected to a heating power source 7.

8 is a Wehnelt electrode placed on the outer periphery of the filament 5, which is kept at the same potential as the filament 5 or at a lower potential than the filament, and is used for the purpose of converging the thermoelectron beam generated from the filament 5; It is attached to the support plate 4.

Further, the lower end 8a of the Wehnelt electrode is set back several mm from the tip of the emitter 1 so as not to cause a drop in the electric field applied to the tip of the emitter 1.

Reference numeral 9 denotes an anode for generating the electric field strength necessary for emitting a field at the tip of the emitter 1, and has an opening 9a in the center. High voltage is applied.

A thin plate 11 having a thickness of, for example, about 50 μm is installed near the central opening 9a of the anode (this part is irradiated with most of the electron beam EB emitted from the emitter 1). is made of a material with little storage gas, such as tantalum.

The thin plate has a hole 11a near the optical axis through which the electron beam EB emitted from the emitter 1 passes, and is fixed to the anode 9 by a holding plate 12.

Furthermore, a space 14 is formed between the thin plate and the anode 9.

After the electron gun is evacuated to a predetermined high vacuum, the thermionic emission filament 5 is heated while the vacuum is continued, and the power source 10 is adjusted so that an appropriate voltage (for example, 2KV) is applied to the anode 9. When a certain amount of heat is applied, the thermoelectrons from the filament 5 are accelerated and are converged by the Wehnelt electrode 8 without being diverged radially and impinge on the thin plate 11.

As a result, gases and impurities occluded or attached to the thin plate are repelled by the electron beam, and the thin film is heated.

At this time, since a space 13 is formed between the thin plate and the anode 9, heat conduction to the anode can be extremely reduced, so that the thin plate is heated to a high temperature.

Therefore, impurities are evaporated and the surface of the thin plate is cleaned.

Thereafter, when the heating power source 7 for the thermionic emission filament 5 is turned off and a high voltage is applied to the anode 9, an electron beam EB is emitted from the emitter 1.

As described above, in the present invention, the region to which most of the electron beams emitted from the anode emitter is irradiated is formed of a thin plate, and the thin plate is formed in a state in which the hot electrons are focused by the Wehnelt electrode (a state in which the electron current density is high). Because of the irradiation, the temperature of the part irradiated by the electron beam from the emitter of the anode can be increased.

Therefore, sufficient cleaning treatment can be performed, and damage caused by vacuum discharge to the emitter can be minimized.
An electron beam can be obtained by stable field emission.

As a result, a field emission scanning electron microscope has practical effects such as eliminating the need for a device (noise canceller) for removing electron beam noise, which was always required in the past.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing one embodiment of the present invention, and Fig. 2 is a schematic diagram showing an embodiment of the present invention.
It is a figure seen from the AA direction of a figure. In the figure, 1 is an emitter, 4 is a support plate, 5 is a filament for thermionic emission, 7 is a heating power source, 8 is a Wehnelt electrode, 9 is an anode, 10 is a power source for applying high voltage to the anode, 11 is a thin plate, and 14 is a It is space.

Claims (1)

[Scope of utility model registration request] In the apparatus, a thermionic emission source is installed near the emitter, and the anode surface is degassed and surface dirt is evaporated by irradiating thermionic electrons from the thermionic emission source to the surface of the anode facing the emitter. A field emission type electron field emission type electron source in which an end of a Wehnelt electrode for converging thermoelectrons placed around a thermionic emission source is recessed from the tip of the emitter, and at least the vicinity of the central opening of the anode is formed into a thin plate shape. gun.