JPH0517652B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an electron gun for an electron microscope, and particularly to an electron gun suitable for a field emission type electron source.

[Background of the invention]

The structure of a conventional field emission type electron gun is shown in FIG. An electron source for field emission, that is, a cathode 1 is supported by a cathode potential introduction terminal 2 . The cathode potential introduction terminal 2 is fixed to the flange 11 and fixed to the electron gun barrel 10 via vacuum packing. A first anode 3 is arranged at a position facing the field emission cathode 1. The first anode 3 is the bottom surface 18 of the electron gun barrel 10.
It is supported by a cylindrical insulator 4 placed above. An extraction voltage 14 is applied to the first anode 3 and the field emission cathode 1 through an anode potential introduction terminal 12 and a contact ring 19 . Field emission cathode 1 and the first
When a voltage of 3 to 5 kV is applied between the anode 3 and the field emission cathode 1, electrons 23 are emitted.

In field emission, it is necessary to heat the field emission cathode 1 to a high temperature and clean the cathode. Heating power source 15
is provided for this cleaning, and is carried out by passing electricity through the two terminals of the cathode potential introduction terminal 2. Of the emitted electrons 23, those that have passed through the aperture 22 of the first anode 3 are emitted from the field emission cathode 1.
The electron beam is accelerated or decelerated to the acceleration voltage 13 applied between the electron gun barrel and the electron gun barrel (ground potential) 10. A magnetic field type electron lens 25 consisting of an upper magnetic pole 6, a lower magnetic pole 7, a magnetic path 5, a coil 8, and a nonmagnetic spacer 16 is arranged below the electron gun barrel 10.

The electron beam passing through the aperture 24 of the bottom surface (second electrode) 18 of the electron gun barrel 10 is focused by a magnetic field type lens 25, and further guided to a magnetic field type electron lens or the like (not shown) located below. As can be seen from this figure, in this configuration, the distance between the magnetic field type electron lens 25 and the field emission cathode 1 becomes long. For this reason, the magnetic field type electron lens 25 operates as a long focal length lens, and has the drawback of large aberrations.

The reasons for this structure were as follows. The coil 8 of the magnetic field type electron lens 25 moves the inside of the electron gun barrel 10 under an ultra-high vacuum (10 ^-8 Pa).
This was because it could not withstand baking (200° to 300° C.) using the heater 20 to achieve the desired temperature. Therefore, the magnetic field type electron lens 25 is placed downwardly and away from the electron gun lens barrel 10 to prevent the temperature from reaching high temperatures during the above-mentioned baking. Vacuum exhaust is
Vacuum exhaust hole 9 provided in the side wall of the electron gun barrel 10
Start from

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a field emission type electron gun in which a magnetic field type electron lens can be operated at a short focus, and an electron gun barrel can also be baked.

[Summary of the invention]

Among magnetic field type electron lenses, it is the coil portion that poses a problem during baking. Therefore, in the present invention, this coil section is arranged at the end of the lens barrel behind the electron source, and is configured to be detachable during baking.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. Coil section 2 consisting of coil magnetic path 5 and coil 8
6 is attached to the top end of the electron gun lens barrel 10 outside the vacuum. Since the uppermost end of the electron gun barrel 10 is vacuum sealed with a spacer 29, there is no vacuum problem even if the coil section 26 is removed. During normal use, the coil section 26 is mechanically connected to the electron gun barrel section 10. Therefore, during baking, this coil portion 26 can be removed to prevent damage to the coil 8 due to baking.
Baking is performed by using a heater 2 wrapped around the outer periphery of the electron gun barrel 10 while evacuating the inside of the electron gun barrel 10.
0 (e.g., a sheathed heater), the entire electron gun chamber is heated to, for example, 250°C to 300°C. This is done for about 5 hours, for example. After baking is completed and the inside of the lens barrel 10 is in an ultra-high vacuum state, the coil portion 26 is attached.

Magnetic flux is generated when the coil 8 is energized, and this magnetic flux is transmitted through the coil magnetic path 5, the inner magnetic path 27, and the first anode 1.
7. Flows through the bottom surface 18 of the electron gun barrel and the electron gun barrel 10. An insulating ring 2 is placed in the middle of the inner magnetic path 10.
1 is inserted. This is to float the first anode 17 from the ground potential. Although magnetic resistance occurs in this portion, since the insulating ring 21 has a thickness of about 2 to 3 mm, it does not change the amount of magnetic flux.

In this embodiment, the first anode 17 and the bottom surface 18 of the electron gun barrel serve as the upper and lower magnetic poles of the magnetic field type electron lens, respectively. In this structure, the lens action of the magnetic field type electron lens is mostly based on the upper magnetic pole (first anode 1).
7) and the lower magnetic pole (electron gun lens barrel bottom surface 18), the magnetic field type electron lens can be operated with a short focus. The upper end of the inner magnetic path 27 and the upper end of the electronic lens barrel 10 are connected via a nonmagnetic spacer 29. The field emission cathode 1 is supported by a cathode potential introducing terminal 2 fixed to a flange 11. The electron gun is evacuated through the vacuum exhaust hole 9, and an inner magnetic path exhaust hole 28 is further provided in a part of the inner magnetic path 27.
The area around the field emission cathode 1 is evacuated.

FIG. 3 shows another embodiment of the present invention, in which a coil portion 26 consisting of a magnetic path 5 and a coil 8 is attached to the upper end portion of the lens barrel 10. A feature of this embodiment is that the lens barrel can be shortened, which is particularly effective for devices that do not like vibrations, such as scanning electron microscopes. Needless to say, the coil portion 26 is configured to be detachable from the lens barrel 10.

〔Effect of the invention〕

As detailed above, according to the present invention, it is possible to combine a field emission type electron gun and a short focus magnetic field type electron lens. It is possible to reduce the aberration of the shaped electron lens. For example, the focal length of a magnetic field type electron lens conventionally used in the next stage of a field emission type electron gun was about 5 cm, but according to the present invention, this can be reduced to 1 cm. As a result, spherical aberration is reduced to about 1/100, and chromatic aberration is reduced to about 1/5. Furthermore, when the focal length is 5 cm, the brightness of the electron beam after passing through the magnetic field type electron lens decreases to about one-tenth of the brightness of the electron source itself, while at a focal length of 1 cm, the brightness decreases. The reduction is about 2 times. That is, by implementing the present invention, it is possible to extract an electron beam that is five times brighter.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a combination of a conventional field emission type electron gun and a magnetic field type electron lens, FIG. 2 is a diagram showing one embodiment of the present invention, and FIG. 3 is a diagram showing another embodiment of the present invention. FIG. 1... Cathode, 5... Coil magnetic path, 8... Coil, 10... Lens barrel, 11... Flange, 13...
Accelerating voltage, 14... Extraction voltage, 17... First anode, 18... Electron gun barrel bottom surface, 20... Heater,
26...Coil part, 27...Inner magnetic path.

Claims (1)

[Claims] 1. An electron source for field emission, a first anode for extracting electrons from the electron source for field emission, a second anode for accelerating or decelerating the electrons that have passed through the aperture of the first anode, and A field emission type electron gun comprising a magnetic field type electron lens for focusing an electron beam emitted from a source, wherein the first anode and the second anode are shared with the magnetic pole of the magnetic field type electron lens, and A field emission type electron gun, characterized in that the excitation coil of the magnetic field type electron lens is disposed at an end portion of the lens barrel behind the electron source and configured to be removable.