JPH1197332A - Electron gun - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the electron discharging amount of an electron gun without giving the influence of a demagnetizing field on the convergence of an electron beam by reducing the size of the gun without using any coil and, at the same time, eliminating the need of a constant-current source. SOLUTION: An electron gun which converges an electron beam by impressing a magnetic field upon electrons discharged from an electron discharging source by means of heat or an electric field is provided with a permanent magnet 13 which generates the magnetic field and outer and inner pole pieces 11 and 12 which form a first gap Cg on the orbital axis of the electron beam and, at the same time, form a second gap Rg at a prescribed distance from the orbital axis of the electron beam, for example, on the rear side of the electron discharging source (emitter) and generate the magnetic field generated from the permanent magnet 13 between the first and second gaps Cg and Rg .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an observation apparatus using an electron beam, such as an SEM (scanning electron microscope) or TE.
The present invention relates to an M (transmission electron microscope), an electron gun used in an EB (electron beam) exposure apparatus used as a fine pattern exposure apparatus for semiconductors.

[0002]

2. Description of the Related Art As such an electron gun, LaB6
Thermionic emission gun (TEG) using (lanthanum hexaborite) as a material,
Field emission type electron gun (FEG; Fe) using W or ZrO / Wcrystal (tungsten ziroconium) as material
ild Emission Gun) or a type (TFE) obtained by adding a thermionic emission effect to this field emission.

[0003] Among them, the difference between TEG and FEG or TFE is mainly in current value (electron flow rate), for example, several hundred nA.
To obtain a current of the order or more, TEG is used. The electron emission size when using this TEG is several μm.
The energy width (corresponding to the chromatic aberration of the electron optical system) is generally 1 to 5 eV.

On the other hand, when the current is several hundred nA or less, FE
G or TFE is used. In this case, the electron emission size is about 0.1 μm to several μm, and the energy width is 0.1 to 1 e.
V is known.

In the field of EB exposure equipment, it is important to reduce aberrations, especially chromatic aberration proportional to the energy width.
In terms of performance, FEG has a preferable performance that is about one fifth of TEG.

However, the emitter (electron emission source) cathode, which is an electron emission source of FEG or TFE, emits an electron beam having a large opening angle to obtain a large current value in order to radiate electrons radially from the tip. Must converge.

[0007] For this reason, generally, there is a disadvantage that the diameter of the cross beam becomes large due to the spherical aberration of the anode lens, and the average luminance decreases. As such a countermeasure, for example, a magnetic field immersion electron gun that employs a method of converging an electron beam by superposing a magnetic field on a bipolar region including an emitter is employed. That is, in a magnetic field immersion electron gun, an electromagnet is formed by a coil and a pole piece to generate a magnetic field, which is applied to an electron beam to converge.

[0008]

However, in the method of applying a magnetic field using an electromagnet, the strength of the magnetic field can be adjusted by an electric current, but the coil needs to be wound, so that the coil diameter is several tens mm to several hundred mm. It becomes big. further,
Since it is necessary to drive the electromagnet with a current, a constant current source is required to supply a constant current.

Further, in order to cause a current to flow through the coil, heat is applied to the coil portion and an emitter disposed in the vicinity thereof, which adversely affects the mechanism portion such as temperature drift. That is, the distance between the emitter and the extraction electrode from which electrons are extracted is extremely narrow, for example, 600 μm. Actually, in this interval, the voltage / interval becomes the electric field strength, so that even if the interval changes by about several μm, the electron emission amount is affected.

Accordingly, the present invention provides an electron gun that can be reduced in size without using a coil, does not require a constant current source, and can increase the amount of electron emission without affecting the convergence of the electron beam due to a demagnetizing field. With the goal.

[0011]

According to the first aspect of the present invention, there is provided an electron gun for applying a magnetic field to electrons emitted from an electron emission source by heat or an electric field to converge an electron beam. A gap is formed at least on the orbit axis of the electron beam and a predetermined distance from the orbit axis of the electron beam, and a magnetic circuit structure that generates a magnetic field generated by a permanent magnet between the gaps, It is an electron gun provided with.

According to a second aspect of the present invention, in the electron gun according to the first aspect, the magnetic circuit structure is arranged such that one gap is overlapped with an extraction electrode for extracting an electron beam, and the other gap is configured to overlap the other gap of the electron beam. It was arranged behind the electron emission source on the orbit axis.

According to a third aspect of the present invention, in the electron gun according to the second aspect, the magnetic circuit structure generates a positive magnetic field in one of the gaps arranged so as to overlap with the extraction electrode, and is located behind the electron emission source. , A negative magnetic field is generated in the other gap.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. First, the electron gun of the present invention employs a method using a permanent magnet, and applying a magnetic field using this permanent magnet does not seem to be special at first glance. The magnet was not used for the following reason.

FIG. 1 shows a magnetic flux density distribution curve on the center axis of the electron beam orbit when an electromagnet is used, and FIG. 2 shows a magnetic flux density distribution curve on the center axis of the electron beam orbit when a permanent magnet is used. Is shown.

Comparing these magnetic flux density distribution curves, it can be seen that in the case of a permanent magnet, a reversal magnetic field (minus magnetic field) R exists. For this reason, the point C
_{When c} and _Cp are matched, even in the case of a permanent magnet, even the reversal magnetic field that is not originally desired to be applied is added to the electron beam trajectory and affects it, and it is difficult to control the trajectory and convergence of the electron beam. For this reason, permanent magnets have not been used.

Therefore, in the electron gun of the present invention, a steep and strong magnetic field is generated near the electron emission source, and the location of the reversal magnetic field is separated from the electron emission source and the electron beam orbit to reduce the influence of the reversal magnetic field. It is something to do.

Hereinafter, the configuration of the electron gun of the present invention will be described. FIG. 3 is a sectional view of the electron gun. The vacuum lens barrel 1 to which the electron beam is applied is provided with a vacuum pump 2 for evacuating the inside of the vacuum lens barrel 1. The vacuum pump 2 is, for example, an ion pump, a turbo pump, or the like.

Further, an electron gun assembling section 3 of a magnetic field immersion type is provided in the vacuum lens barrel 1. This electron gun assembly part 3
Is composed of a suppressor electrode 4 and a TFE chip 5 as shown in FIG.

The suppressor electrode 4 is, for example, about φ17 m
The TFE tip 5 is disposed at the tip of the suppressor electrode 4 and its tip is formed sharply by ZrO / W. The radius R is formed to be 0.1 to several μm.

A few hundred μm ahead of the TFE chip 5,
A lead electrode 6 is arranged. This extraction electrode 6
Is formed of a thin metal plate with a diameter of about several hundred μ at the center.
m is a member with holes.

Further, in front of the extraction electrode 6,
Lens electrode 7, anode electrode 8, blanking electrode 9,
A blanking aperture 10 is provided. On the other hand, the permanent magnet 13 is held between the outer pole piece 11 and the inner pole piece 12.

The permanent magnet 13 is made of, for example, samarium cobalt, and generates a magnetic field. As described above, the outer and inner pole pieces 11 and 12 are used as a pair, sandwich the permanent magnet 13, and have a predetermined distance from the orbit axis of the electron beam emitted from the TFE chip 5 and from the orbit axis of the electron beam. The first and second gaps C _g and R _g are formed at a distance from each other, and these first and second gaps C _g and R _g are formed.
And the second gaps C _g and R _g have a function as a magnetic circuit structure for generating a magnetic field generated by the permanent magnet 13.

Outer and inner pole pieces 11, 1
Second gap R _g formed between the 2 is formed in the rear than the position of the suppressor electrode 4 and TFE chip 5 as the electron emission source in the direction of the electron beam trajectory axis.

The outer and inner pole pieces 11, 1
Numeral 2 is formed of a material having a high magnetic permeability such as soft magnetic iron or ferrite, and a gap between the permanent magnet 13 and the magnetic material is filled with a non-magnetic material such as copper.

The extraction electrode 6 is arranged so as to overlap the first gap C _g of the outer pole piece 11. As described above, the lens electrode 7, the anode electrode 8, the blanking electrode 9, and the blanking aperture 10 are disposed in front of the extraction electrode 6.

FIG. 5 shows the magnetic field data on the electron beam axis in the magnetic field generating section by the permanent magnet 13, and shows the electron beam between the first gap C _g and the second gap R _{g at} the tip of the outer pole piece 11. The magnetic field at the on-axis position is shown.

It can be seen that a positive magnetic field exists in the first gap C _g and a negative magnetic field exists in the second gap R _g . This shows that the influence of the demagnetizing field is extremely small in the region F from which electrons are emitted.

Next, the operation of the electron gun configured as described above will be described. FIG. 6 is a graph showing the result of a simulation calculation in which electrons are emitted from the tip of the TFE chip 5, in which the electrodes of the electron gun and the tip of the outer pole piece for applying a magnetic field are enlarged.

The TFE chip 5 is set at a potential of 0 V. Behind the emitter, a suppressor electrode 4 is connected to, for example, -V.
_s (= 500 V), the extraction electrode 6 is set to V _ex (= + 3 kV), for example, and the anode electrode 8 is set to V _ad (= + 4 kV to +100 kV), for example.

Further, the blanking electrode 9 and the blanking aperture 10 are set to a potential close to the potential V _ad of the anode electrode 8. Under such a setting, the potential of the lens electrode 7 is set to, for example, about 300 V to 3 kV,
After adjustment, the leading electrode 6 is pulled out from the tip of the TFE chip 5.
The electrons extracted by diverge.

However, the outer and inner pole pieces 1
Electrons are focused by the magnetic field applied at 1 and 12, ie, the equipotential lines B shown in FIG.
And the lens electrode 7, and the equipotential line P generated by the electrostatic lens that forms the lens electrode 7 and the anode electrode 8, and converges so as to form the smallest crossover at the blanking aperture 10.

At this time, for example, since a positive magnetic field exists in the first gap C _g and a negative magnetic field exists in the second gap R _g , a negative magnetic field exists in the region F from which electrons are emitted. No magnetic field exists, and there is no influence of the demagnetizing field.

As described above, in one embodiment,
A first gap _Cg is formed on the trajectory axis of the electron beam emitted from the tip of the TFE chip 5 by heat or an electric field, and at a predetermined distance from the trajectory axis of the electron beam, for example, behind the TFE chip 5 A second gap R _g is formed on the side, outer and inner pole pieces 11 and 12 for generating a positive magnetic field in the first gap C _g and generating a negative magnetic field in the second gap R _g are provided. Therefore, the amount of emitted electrons can be increased without affecting the convergence of the electron beam due to the demagnetizing field.

Usually, when no magnetic field is used, several m
Only electrons having an electron emission angle of about rad to several tens mrad can converge on the blanking aperture 9. However, in the case of the electron gun of the present invention, electrons having an electron emission angle of about several tens to hundred mrad are obtained. Can also be converged.

As a result, the number of electrons that can be used after passing through the blanking aperture 9 can be increased from the normal several nA order to several hundred nA or several μA order. In addition, since the permanent magnet 13 is used, a current control circuit and the like are not required, and a low-cost and stable electron gun can be obtained.

The shape of the pole piece to which a magnetic field is applied is formed by forming two gaps, a first gap C _g and a second gap R _g, of which the first gap C _g is overlapped with the extraction electrode 6. And set the second gap R _g to TF
Since it was formed behind the E chip 5 in the electron beam orbit axis direction, the demagnetizing field did not affect the convergence of the electron beam.
The magnetic field design, that is, the design of the permanent magnet 13 can be simplified.

The present invention is not limited to the above-described embodiment, but may be modified as follows. For example, the position of the second gap R _g is formed by the outer and inner pole pieces 11 and 12, if the rear-side in the electron beam trajectory axis than TFE chip 5, contrary to the region F where electrons are emitted The shape of the outer and inner pole pieces 11, 12 without generating a magnetic field is not limited to the above-described embodiment.

The electron gun of the present invention may be a thermionic electron gun (TEG), a field emission electron gun (FEG), or a type obtained by adding a thermionic emission effect to this field emission (TFE). Can be applied.

[0040]

As described in detail above, claims 1 to 5 of the present invention.
According to 3, an electron gun that can be reduced in size without using a coil, does not require a constant current source, and can increase the amount of emitted electrons without affecting the convergence of the electron beam due to a demagnetizing field can be provided. According to the second and third aspects of the present invention, it is possible to provide an electron gun in which the demagnetizing field does not affect the convergence of the electron beam and the design of the permanent magnet can be simplified.

[Brief description of the drawings]

FIG. 1 is a diagram showing a magnetic flux density distribution curve on a central axis of an electron beam trajectory when an electromagnet is used.

FIG. 2 is a diagram showing a magnetic flux density distribution curve on a central axis of an electron beam trajectory when a permanent magnet is used.

FIG. 3 is a configuration diagram showing one embodiment of an electron gun according to the present invention.

FIG. 4 is a configuration diagram of a suppressor electrode in the electron gun.

FIG. 5 is a diagram showing data of a magnetic field on an electron beam axis in a magnetic field generation unit using a permanent magnet.

FIG. 6 is a graph showing a result of a simulation calculation for emitting electrons from the tip of the TFE emitter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Vacuum lens barrel, 2 ... Vacuum pump, 3 ... Electron gun assembly part, 4 ... Suppressor electrode, 5 ... TFE chip, 6 ... Leader electrode, 7 ... Lens electrode, 8 ... Anode electrode, 9 ... Blanking electrode, 10 ... Blanking aperture, 11 ... Outer pole piece, 12 ... Inner pole piece, 13 ... Permanent magnet, _Cg ... First gap, _Rg ... Second gap.

Claims (3)

[Claims] 1. An electron gun for applying a magnetic field to electrons emitted from an electron emission source by heat or an electric field to converge an electron beam, comprising: a permanent magnet for generating the magnetic field; A gap is formed at a predetermined distance from the orbital axis of the electron beam, and a magnetic circuit structure that generates the magnetic field generated by the permanent magnet between the gaps,
An electron gun comprising: 2. The magnetic circuit structure according to claim 1, wherein one of the gaps is disposed so as to overlap with an extraction electrode for extracting the electron beam, and the other gap is located on the orbit axis of the electron beam, more than the electron emission source. 2. The electron gun according to claim 1, wherein the electron gun is disposed rearward. 3. The magnetic circuit structure according to claim 1, wherein a positive magnetic field is generated in one of the gaps superposed on the extraction electrode, and a negative magnetic field is generated in the other of the gaps disposed behind the electron emission source. 3. The electron gun according to claim 2, wherein: