JPH0654643B2 - Lens for field emission electron gun - Google Patents

Description

TECHNICAL FIELD The present invention relates to a lens for a field emission type electron gun using a permanent magnet.

[Conventional technology]

FIG. 3 is a diagram showing a conventional example of an electrostatic lens type field emission electron gun, and FIG. 4 is a diagram showing a conventional example of a magnetic lens type field emission electron gun. In the figure, 1 is a field emission chip, 2 is an extraction electrode, 3 is an electrode, 4 is an anode, 5 is a crossover point, 6 is a coil yoke, and 7 is a coil.

The field emission type electron gun is equipped with a field emission chip having a thin tip and is used for an EB tester for irradiating an electron beam to test a printed circuit board, an LSI or the like. The feature is that the electron beam emission point by the field emission chip is particularly small,
If the electron beam emitted from a small point is focused, the electron beam can be easily narrowed down and the measurement accuracy can be improved by using the electron beam tester. Generally, an electrostatic lens or a magnetic lens is used in a field emission electron gun.

In the electrostatic lens, as shown in FIG. 3, the extraction electrode 2, the electrode 3, and the anode 4 are arranged on the lower optical axis so as to face the field emission chip 1, and the voltage of the electrode 3 and the voltage of the electrode 4 are The ratio of 1 gives the electrostatic lens effect, and the crossover point 5 is formed between the electrode 3 and the anode 4. In the case of this electrostatic lens, the structure is simple, but there is a drawback that the aberration is large.

On the other hand, in the latter magnetic lens, the extraction electrode 2, the coil yoke 6 having the coil 7 therein, and the electrode 3 are arranged below the field emission chip 1 as shown in FIG.
A crossover point 5 is formed between the electrode 3 and the electrode 3. This magnetic field lens has a slightly more complicated structure than the electrostatic lens, but has the feature that the aberration is one order of magnitude smaller, and therefore the reduction in brightness is small when a large amount of current is applied. This conventional magnetic field lens has a fourth
As shown in the figure, a current is passed through the coil 7 in the coil yoke 6 to generate a magnetic field.

[Problems to be solved by the invention]

However, as described above, the magnetic lens has a feature that the aberration is smaller by one digit than the electrostatic lens.
Since a current is passed through the coil 7 to generate a magnetic field, there is a problem that this coil generates heat and gas is generated from the coil yoke 6 and the extraction electrode 2. The field emission type electron gun lens is placed in a high vacuum to obtain stable performance. Therefore, when gas is generated as described above, the degree of vacuum in the vicinity of the field emission tip 1 is deteriorated,
It makes the emission unstable.

The present invention solves the above-mentioned problems, and provides a lens for a field emission electron gun in which heat generation of a coil is reduced, deterioration of vacuum degree is prevented, and emission is stabilized. It is intended.

[Means for solving problems]

To this end, the present invention provides a field emission electron gun lens in which an extraction electrode is arranged on the optical axis so as to face the field emission chip and is provided below the extraction electrode. A coil provided inside, and an upper yoke and a lower yoke provided at the upper and lower ends of the permanent magnet and the coil, respectively, and the magnetomotive force of the permanent magnet is within a variable range of the magnetomotive force required by the lens magnetic field. And the lens magnetic field is adjusted by controlling the direction and magnitude of the current flowing through the coil.

[Action]

In the field emission electron gun lens of the present invention, the permanent magnet, the upper and lower pole yokes, the lens gap formed by the upper and lower pole yokes, and the coil provided therein form the lens magnetic field. It is possible to finely adjust so as to obtain a desired lens magnetic field depending on the direction and magnitude of the current flowing through the coil without applying most of the magnetomotive force. Therefore, the current flowing through the coil can be reduced, and the amount of heat generated by the coil can be reduced.

〔Example〕

 Hereinafter, embodiments will be described with reference to the drawings.

FIG. 1 is a diagram showing a configuration of one embodiment of a lens for a field emission type electron gun according to the present invention, and FIG. 2 is a diagram showing a relation between an extraction voltage for keeping a crossover point constant and an ampere turn of the lens. Is.

In FIG. 1, 1 is a field emission chip, 2 is an extraction electrode, 3 is an electrode, 6 is a coil yoke, 7 is a coil, 8 is a permanent magnet, and 9 is a lens gap.

In the field emission type electron gun lens of the present invention, FIG.
As shown in FIG. 3, the coil yoke 6 including an upper yoke and a lower yoke is provided on the upper and lower ends of the cylindrical permanent magnet 8. The permanent magnet 8 originally forms a magnetic field as shown in FIG. 1B, but the magnetic flux generated by the permanent magnet 8 is guided to the lens gap by the coil yoke 6 including an upper yoke and a lower yoke which are not connected to each other. Create a magnetic field. further,
A coil 7 is provided between the permanent magnet 8 and the lens gap 9 inside the permanent magnet 8, that is, at a position shown by A in FIG. Then, by changing the direction and magnitude of the current flowing through the coil 7, the magnitude of the lens magnetic field is changed to keep the crossover point at a constant position.

In the field emission electron gun lens, a high voltage of about 3 to 10 kV is applied to the field emission chip 1 to extract electrons, but when the field emission chip 1 deteriorates, the extraction voltage is further increased. Will be required. On the other hand, in order to keep the crossover point at a constant position, it is necessary to make the lens magnetic field stronger for the electrons extracted at a higher voltage. Therefore, generally, as shown in FIG. 2, the magnetomotive force (ampere turn) has a predetermined variable width A ₁ -A.
_{It has 2} (AT). This ampere turn (A
When the central value of the variable width A _{1 to} A ₂ (AT) of T) is generated by the permanent magnet, Is generated by the coil 7 of the lens. That is, when only the magnetomotive force of the permanent magnet is insufficient, the current of the coil 7 is set so that the magnetomotive force is further added. Conversely, when the magnetomotive force of the permanent magnet is too large, the magnetomotive force is reduced. Thus, the current of the coil 7 is set in the opposite direction. On the other hand, according to the conventional magnetic lens shown in FIG. 4, the coil 7 needs the ability to generate up to A ₂ (AT). It is possible to greatly reduce the amount of current flowing.

The present invention is not limited to the above embodiment, and various modifications can be made. For example, in the above embodiment, the magnetomotive force generated by the permanent magnet is set to the center value of the variable width, but it may be set to the lower side or the upper side instead of the center value.

〔The invention's effect〕

As is apparent from the above description, the conventional lens coil has a minimum A ₁ (AT) to a maximum A ₂ corresponding to the lens magnetic field.
The magnetomotive force of (AT) is required, and the heat generated by the current flowing to secure this magnetomotive force increases the amount of gas released from the electrodes and the lens outer cylinder, deteriorating the degree of vacuum and making the emission unstable. According to the present invention, most of the required magnetomotive force is Can be covered with a permanent magnet, and the magnetomotive force required by the coil is It's done. As a result, the amount of heat generated is low and the amount of gas released is small, so that the degree of vacuum can be prevented from deteriorating and the emission can be stabilized.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of one embodiment of a lens for a field emission type electron gun according to the present invention, and FIG. 2 is a diagram showing a relation between an extraction voltage for keeping a crossover point constant and an ampere turn of the lens. FIG. 3 is a view showing a conventional example of an electrostatic lens type field emission electron gun, and FIG. 4 is a view showing a conventional example of a magnetic field lens type field emission electron gun. 1 ... Field emission chip, 2 ... Extraction electrode, 3 ... Electrode, 6 ... Coil yoke, 7 ... Coil, 8 ... Permanent magnet, 9 ... Lens gap.

Claims (2)

[Claims] 1. A lens for a field emission electron gun, wherein a lead-out electrode is arranged on the optical axis so as to face the field emission chip, and is provided below the lead-out electrode, the permanent magnet and the inside of the permanent magnet. And a permanent magnet and an upper yoke and a lower yoke provided on the upper and lower ends of the permanent magnet and the coil, respectively, and the magnetomotive force of the permanent magnet is within a variable width of the magnetomotive force required by the lens magnetic field. A lens for a field emission electron gun, characterized in that the lens magnetic field is adjusted by selecting and controlling the direction and magnitude of the current flowing through the coil. 2. The field emission type electron gun lens according to claim 1, wherein the magnetomotive force of the permanent magnet is an average value of the magnetomotive force required for the lens magnetic field.