JP2004134417A - Insulating transformer for heating electron gun cathode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an insulating transformer for heating an electron gun cathode which can inexpensively prevent a directing accuracy of an electron beam from decreasing by removing an influence of a leakage magnetic flux. <P>SOLUTION: The insulating transformer 10 for heating includes a primary coil connected to an AC power source, and a secondary coil connected to a cathode of an electron gun. The transformer is used to heat the cathode by an electric energy supplied from the AC power source to radiate heating electron. The transformer 10 includes a pair of first and second insulating transformers 10a, 10b of the same constitutions. The transformers 10a and 10b are disposed at an axial symmetry to the emitting axis O of the beam as a center. The primary coils of the transformers 10a and 10b are connected so that currents of reverse phases always flow, and the secondary coils are connected in series with each other in the same phase. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an insulating transformer for heating a cathode of an electron gun, and more particularly to a technique for preventing deflection such as deflection and oscillation of an emission direction of an electron beam.
[0002]
[Prior art]
In an electron beam type exposure apparatus that performs microfabrication using an accelerated electron beam or an electron beam type electron microscope, a vacuum atmosphere is used to accelerate the electron beam emitted from the electron gun and irradiate the target with the electron beam. It has an electron gun column installed below.
[0003]
In the electron gun used in such an electron column, it is necessary to heat the cathode to emit electrons. FIG. 6 shows an example of a cathode heating device for emitting electrons in this type of electron gun.
[0004]
In FIG. 1, an electron gun 1 includes a cathode 2, a Wehnelt 3 (extraction electrode) and an acceleration electrode 4 disposed in front of the cathode 2. A secondary coil of an insulating transformer 5 is connected to the cathode 2, and an AC power supply 6 is connected to the primary coil of the insulating transformer 5 so that the cathode 2 is heated by the AC power supply 6. I have.
[0005]
A high-voltage potential from a DC high-voltage power supply 7 is applied to the Wehnelt 3, and the thermoelectrons generated from the cathode 2 are beamed and emitted toward the acceleration electrode 4. However, the conventional cathode heating apparatus having such a structure, particularly the insulating transformer 5, has the following technical problems.
[0006]
[Problems to be solved by the invention]
That is, in the conventional cathode heating device shown in FIG. 6, the heating insulating transformer 5 includes, for example, a core wire arranged at the center and a sheath wire provided around the core wire via an insulating layer. A cable is used, and the coaxial cable having such a structure is bent in a U-shape and arranged near the cathode 2.
[0007]
However, in the insulating transformer 5 having such a structure, a leakage magnetic flux is generated, and a leakage magnetic field is formed around the transformer 5. In this case, particularly, since the transformer 5 is disposed near the cathode 2, such a leakage magnetic field is applied to the low energy electron beam immediately after the electron beam is emitted from the cathode 2, and the electron beam is deflected and oscillated. There is a problem that this has an adverse effect and lowers the accuracy of the electron beam irradiation position.
[0008]
In order to eliminate the leakage magnetic field from the insulating transformer 5 against such a problem, for example, it is conceivable that the insulating transformer itself is magnetically shielded with a material having a high magnetic permeability such as permalloy. Such a measure would be too costly for countermeasures.
[0009]
The present invention has been made in view of such conventional problems, and an object of the present invention is to eliminate the influence of leakage magnetic flux, thereby preventing a decrease in the pointing accuracy of an electron beam at low cost. To provide an insulating transformer for heating an electron gun.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, an AC power supply is connected to a primary coil, an electron gun cathode provided with a high DC potential is connected to a secondary coil, and electric energy supplied from the AC power supply is connected. In the insulating transformer for heating the electron gun cathode for heating the electron gun cathode, the insulating transformer includes at least a pair having the same configuration, and leakage magnetic fluxes generated in each of the insulating transformers are mutually canceled. Then, the primary coil and the secondary coil of each insulating transformer are connected to each other.
[0011]
According to the insulating transformer for heating the electron gun cathode configured in this way, the insulating transformers are formed of at least a pair of the same configuration, and the leakage magnetic fluxes generated in each of the insulating transformers are canceled each other. Since the primary coil and the secondary coil of the insulating transformer are connected to each other, when the cathode is heated by an AC source via the insulating transformer, deflection and oscillation of the electron beam emitted from the cathode of the electron gun are caused by leakage magnetic flux. As a result, it is possible to avoid a decrease in the pointing accuracy of the electron beam.
[0012]
In this case, even if the insulating transformer is installed near the electron gun cathode, the electron beam loses the effect of the stray magnetic field affecting its directivity at the beginning of the low energy state, and the directivity is maintained with high accuracy. can do.
[0013]
The insulating transformer is constituted by a coaxial cable having a core wire arranged at the center and a sheath wire provided on the outer periphery of the core wire via an insulating layer, and bending the coaxial cable into a U-shape. The sheath wire may be the primary coil, and the core wire may be the secondary coil.
[0014]
The insulating transformer is disposed opposite to an axially symmetric position with respect to an axis of an electron beam emitted from the electron gun, and connected so that the primary coils are in opposite phases, and the secondary coils are in phase. Can be connected.
[0015]
The insulating transformers may be vertically stacked and connected such that the primary coils are in opposite phases and connected such that the secondary coils are in phase.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. 1 to 3 show a first embodiment of an insulating transformer for heating an electron gun cathode according to the present invention.
[0017]
As shown in the circuit diagram of the electric system in FIG. 3, the heating insulation transformer 10 shown in FIG. 3 has an AC power supply 12 connected to a primary coil and an electronic power supply connected to a secondary coil, similarly to the above-described conventional insulation transformer. The cathode 16 of the gun 14 is connected, and is used for heating the cathode 16 with electric energy supplied from the AC power supply 12 to emit heat-generating electrons.
[0018]
The heating insulating transformer 10 according to the present embodiment includes a pair of first and second insulating transformers 10a and 10b having the same configuration. Each of the insulating transformers 10a and 10b includes core wires 100a and 100b disposed at the center, and sheath wires 102a and 102b made of mesh metal formed on the outer periphery of the core wires 100a and 100b with the insulating layers 101a and 101b interposed therebetween. , A coaxial cable having outer sheath layers 103a and 103b formed on the outer circumference of the sheath wires 102a and 102b.
[0019]
In the coaxial cable having such a configuration, a plurality of ring cores 104a and 104b for varying the mutual inductance are inserted into the outer periphery, the U-shaped curve is formed, the heating transformer 10 is used, and the sheath wires 102a and 102b are insulated. It is used as a primary coil of the transformer 10, and the core wires 100 a and 100 b are similarly used as secondary coils of the transformer 10.
[0020]
The insulating transformers 10a and 10b having such a configuration are installed at an upper end of a container 18 in which an electron gun column for accelerating an electron beam emitted from the electron gun 14 and irradiating the target with a target is accelerated.
[0021]
Details of this installation state are shown in FIGS. In the figure, an electron beam emitted from an electron gun 14 built in a container 18 is accelerated in a vertical direction on the central axis of the container 18 from above to below.
[0022]
In the case of the present embodiment, the first and second insulating transformers 10a and 10b are arranged facing each other at an axially symmetric position with respect to the axis O of the electron beam, and the primary coils are connected so as to be in opposite phases. The next coils are connected so that they have the same phase.
[0023]
FIG. 3 shows an electrical connection state at this time. In the case of the present embodiment, an AC power supply 12 is connected to one end of the sheath wire 102a (primary coil) of the first insulating transformer 10a, and the other end of the sheath wire 102a (primary coil) is grounded.
[0024]
One end of the sheath wire 102b (primary coil) of the second insulating transformer 10b is grounded, and the AC power supply 12 is connected to the other end of the sheath wire 102b (primary coil).
[0025]
On the other hand, the core wires 100a and 100b (secondary coils) of the first and second insulating transformers 10a and 10b are connected in series. When the first and second insulating transformers 10a and 10b connected in this manner are installed such that the U-shaped openings of the transformers 10a and 10b face each other and are symmetric with respect to the axis O of the electron beam. When an AC power is supplied from the AC power supply 12 to each of the insulating transformers 10a and 10b, current always flows in the primary coils of the first and second insulating transformers 10a and 10b in opposite phases.
[0026]
When the primary coils (sheath wires 102a, 102b) of the pair of insulating transformers 10a, 10b are connected in such a manner, the following operational effects can be obtained. That is, in this type of transformer, most of the leakage magnetic flux is generated from the primary coil arranged on the outer peripheral side.
[0027]
However, since currents always flow in opposite phases in the primary coils (sheath wires 102a, 10bb) arranged on the outer peripheral side of the transformer, the leakage magnetic flux generated from one transformer 10a is generated in the other transformer 10b. The magnetic flux is offset by the magnetic flux leakage and disappears. As a result, no magnetic field is formed due to the magnetic flux leakage.
[0028]
On the other hand, in the secondary coil, the core wires 100a and 100b are directly connected and have the same phase. As a result, a double voltage is output. In the case of the present embodiment, the output side (secondary coil side) of such insulating transformers 10a and 10b is connected to the cathode 16 of the electron gun 14 via the rectifier 20, as shown in FIG.
[0029]
In the case of this embodiment, the connection point of the secondary coil is connected to the midpoint of the rectified DC output of the bridge rectifier 20, and this potential is used as a virtual cathode potential. A high-voltage DC power supply 24 is connected to an acceleration electrode 22 provided in front of the cathode 16.
[0030]
By the way, in the insulating transformer for heating 10 configured as described above, when the electron gun 14 emits an electron beam, the AC power supply 12 is applied to the primary coil, and the electric energy at this time is rectified by the rectifier 20. The heat is applied to the cathode 16 later, and the cathode 16 emits thermionic electrons to form an electron beam.
[0031]
At this time, according to the insulating transformer for heating the cathode of the electron gun of the present embodiment, the insulating transformer 10 is composed of a pair of the same configuration 10a, 10b, and the leakage magnetic flux generated in each of the insulating transformers 10a, 10b causes mutual leakage magnetic flux. The primary and secondary coils of each of the insulating transformers 10a and 10b are connected to each other so that the cathode 16 is heated by the AC power supply 12 via the insulating transformers 10a and 10b. Deflection and swing of the electron beam emitted from the cathode 16 of the electron gun 14 are eliminated, and a decrease in the directivity of the electron beam can be avoided.
[0032]
In this case, if the insulating transformers 10a and 10b are installed in the vicinity of the electron gun cathode 16, the electron beam in the low energy state is largely deflected and oscillated even with a small disturbance of the magnetic field, and becomes directional in the initial state. Although disturbance may occur, if the leakage magnetic flux is eliminated as in the present embodiment, the directivity of the electron beam can be maintained with high accuracy.
[0033]
Such an operation and effect can be obtained only by connecting the primary coils of the insulating transformers 10a and 10b formed of a pair of coaxial cables having the same configuration so as to have opposite phases, so that the configuration is simple and expensive. Since no high permeability member is required, it is very advantageous in terms of economy.
[0034]
In the first embodiment, the case where the pair of insulating transformers 10a and 10b having the same configuration are arranged axially symmetric with respect to the axis O of the electron beam is exemplified. However, the present invention is applied to this configuration. There is no limitation, and for example, the same effect can be obtained by arranging four insulating transformers at 90 ° intervals.
[0035]
FIGS. 4 and 5 show a second embodiment of an insulating transformer for heating an electron gun cathode according to the present invention, in which the same or corresponding parts as those in the above embodiment are denoted by the same reference numerals and the description thereof will be omitted. A description thereof will be omitted, and only the characteristic points will be described below.
[0036]
The insulating transformer 10 shown in the figure includes a pair of first and second insulating transformers 10a and 10b having the same configuration as in the above embodiment.
[0037]
Each of the insulating transformers 10a and 10b is formed of a coaxial cable and is formed in a U-shape as in the first embodiment. In the case of the present embodiment, the insulating transformers 10a, 10b are vertically stacked.
[0038]
Further, the first and second insulating transformers 10a and 10b are connected so that the primary coils (sheath wires) are in opposite phases, and the secondary coils (core wires) are in phase, as in the above embodiment. Connected so that
[0039]
Also in the heating insulating transformer configured as described above, the leakage magnetic flux generated in each of the insulating transformers 10a and 10b is canceled by each other, so that the same operation and effect as in the above embodiment can be obtained. In the case of the present embodiment, the insulating transformers 10a and 10b are vertically stacked and adjacent to each other, so that the leakage magnetic flux can be directly canceled.
[0040]
In the above embodiment, the case where the secondary coils of the pair of insulating transformers 10a and 10b are connected in series in the same phase is illustrated. However, the embodiment of the present invention is not limited to this. The secondary coil may be connected in the opposite phase as the primary coil.
[0041]
【The invention's effect】
As described above in detail, according to the insulating transformer for heating the electron gun cathode according to the present invention, it is possible to inexpensively prevent a decrease in the directivity of the electron beam by eliminating the influence of the leakage magnetic flux. .
[Brief description of the drawings]
FIG. 1 is a top view of an installed state showing a first embodiment of an insulating transformer for heating an electron gun cathode according to the present invention.
FIG. 2 is a side view of FIG.
FIG. 3 is a connection diagram of the electric system of the first embodiment shown in FIG.
FIG. 4 is a top view of an installed state showing a second embodiment of an insulating transformer for heating an electron gun cathode according to the present invention.
FIG. 5 is a side view of FIG. 4;
FIG. 6 is an explanatory diagram showing an example of an insulating transformer for heating an electron gun cathode.
[Explanation of symbols]
Reference Signs List 10 heating insulating transformer 10a first insulating transformer 10b second insulating transformer 12 AC power supply 14 electron gun 16 cathode 18 container

Claims (4)

An AC power supply is connected to the primary coil, an electron gun cathode to which a high DC potential is applied is connected to the secondary coil, and an electron gun cathode for heating the electron gun cathode with electric energy supplied from the AC power supply. In a heating insulation transformer,
The insulating transformer is composed of at least a pair of the same configuration,
An insulation transformer for heating an electron gun cathode, wherein the primary coil and the secondary coil of each insulation transformer are connected to each other so that leakage magnetic flux generated in each of the insulation transformers is mutually canceled. The insulating transformer is constituted by a coaxial cable including a core wire arranged at the center and a sheath wire provided on the outer periphery of the core wire via an insulating layer,
2. The insulating transformer for heating an electron gun cathode according to claim 1, wherein the coaxial cable is bent into a U shape, the sheath wire is used as the primary coil, and the core wire is used as the secondary coil. The insulating transformer is opposed to an axially symmetric position with respect to an electron beam axis emitted from the electron gun,
3. The insulating transformer for heating an electron gun cathode according to claim 2, wherein the primary coils are connected so as to be in opposite phases, and the secondary coils are connected so as to be in phase. The insulating transformer is stacked and arranged in a vertical direction,
3. The insulating transformer for heating an electron gun cathode according to claim 2, wherein the primary coils are connected so as to be in opposite phases, and the secondary coils are connected so as to be in phase.

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