JP2004095496A - Insulation protector for coaxial cable used for electron gun - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an insulation protector for a coaxial cable used for an electron gun capable of effectively preventing dielectric breakdown by eliminating the attenuation pulsation in discharge. <P>SOLUTION: This electron gun 10 is provided with a cathode 12, an accelerating electrode 14 and a target electrode 16. In an isolation transformer 18A, a coaxial cable is used, a core wire is a secondary-coil 18a, and a sheath line is used as a primary-coil 18b. In the electron gun 10, an insulation protector 32a comprising a diode group 34 of a plurality of diodes connected in series is provided. The protector 32a is for protecting the insulation of the isolation transformer 18 comprising the coaxial cable, one end of the diode group 34 is grounded and the other end is connected with a connection node of the coaxial cable 26 and the cathode 12. If arc discharge occurs and the potential of the core wire of the coaxial cable 26 is high to exceed a specified value, the one end of the diode group 34 of the protective device 32a is higher than the grounding potential and part of a surge current in discharge flows into the grounding side through the diode group 34. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a coaxial cable insulation protection device used for an electron gun, and more particularly, to a technique for preventing insulation breakdown of a coaxial cable used for an electron gun at the time of discharge.
[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 for accelerating an electron beam emitted from an electron gun and irradiating a target electrode with the electron beam is used. It has an electron gun column installed in the atmosphere.
In the electron gun used in such an electron column, it is necessary to heat the cathode to emit electrons. FIG. 5 shows an example of a cathode heating device for emitting electrons in this type of electron gun.
[0003]
In FIG. 1, the electron gun 1 includes a cathode 1a, an acceleration electrode 1b disposed in front of the cathode 1a, and a grounded target electrode 1c. A secondary coil of an insulating transformer 2 is connected to the cathode 1a, and an AC power supply 3 is connected to a primary coil of the insulating transformer 2 so that the cathode 1a is heated by the AC power supply 3. I have.
[0004]
A high voltage potential is applied to the cathode 1 a from a DC high voltage power supply 4 via a coaxial cable 5. A high voltage potential is applied to the accelerating electrode 1b from a DC high voltage power supply 6 via a coaxial cable 7, and the thermoelectrons generated from the cathode 1a are beamed and emitted toward the target electrode 1c. .
[0005]
For example, 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 is used as the heating insulating transformer 2. It was arranged in the shape of a letter and arranged near the cathode 1a. The member indicated by reference numeral 8 in FIG. 5 is a rectifier for converting alternating current to direct current, and the sheath wires of the coaxial cables 5 and 7 are grounded.
[0006]
However, in the conventional electron gun having such a configuration, the coaxial cables 5 and 7 including the insulating transformer 2 have the following technical problems.
[0007]
[Problems to be solved by the invention]
That is, in the conventional electron gun 1 shown in FIG. 5, since the inside of the electron column in which the electron gun is built is in a vacuum atmosphere and a high DC voltage of 160 kV is applied, the high voltage is applied inside the electron gun. Arc discharge is likely to occur in the application section, and when arc discharge occurs, the surge current attenuates and pulsates because the insulating transformer 2 composed of a coaxial cable has a capacitance with respect to the earth (ground). And it was found that the insulation transformer 2 was broken down.
[0008]
In this case, the coaxial cable used for the insulating transformer 2 has no problem in using it as a high-voltage DC cable, but it is weak to pulsation. It is considered to cause destruction, and such a defect was inherent in the coaxial cables 5 and 7 of the electron gun 1 shown in FIG.
[0009]
The present invention has been made in view of such a conventional problem, and an object of the present invention is to eliminate a damping pulsation at the time of discharge, thereby effectively preventing dielectric breakdown. An object of the present invention is to provide an insulation protection device for a coaxial cable used in an electron gun.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention includes an insulating transformer having a primary and a secondary coil formed of a coaxial cable, an AC power supply is connected to the primary coil, and a DC high potential is applied to the secondary coil. Is connected to the cathode of the electron gun to which the cathode is connected and the cathode is heated by electric energy supplied from the AC power source. A plurality of diodes are connected in series between the application section and ground, and a diode group having a withstand voltage corresponding to the high potential is provided. Through to the ground side.
According to the insulation protection device for the coaxial cable used in the electron gun configured as described above, a part of the surge current at the time of discharging is caused to flow to the ground side via the diode group, so that surge current pulsation is eliminated, and the coaxial cable The dielectric breakdown of the insulating transformer constituted by the above is prevented.
[0011]
Further, according to the present invention, an AC power supply is connected to a primary coil, a cathode of an electron gun to which a high DC potential is applied is connected to a secondary coil, and the cathode is electrically powered by the AC power supply. In a coaxial cable insulation protection device used for an electron gun to be heated, the electron gun has an electrode portion disposed in front of the cathode,
A coaxial cable that transmits a high potential to the electrode unit via a core wire arranged at the center is connected between the electrode unit and the DC power supply, and the insulation protection device is connected between the core wire and ground. A plurality of diodes connected in series, a diode group having a withstand voltage corresponding to the high potential, and a part of a surge current at the time of discharging is caused to flow to the ground side through the diode group. I made it.
[0012]
According to the insulation protection device for the coaxial cable used in the electron gun configured as described above, a part of the surge current at the time of discharging is caused to flow to the ground side via the diode group, so that surge current pulsation is eliminated, and the coaxial cable Is prevented from dielectric breakdown.
In the insulation protection device, the diode group may be arranged on an input / output side of the coaxial cable.
[0013]
In the insulation protection device, the diode group may be disposed between the high-potential application unit and ground, and between the center conductor and ground.
[0014]
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. FIG. 1 shows an embodiment of a coaxial cable insulation protection device used in an electron gun according to the present invention.
[0015]
The electron gun 10 shown in FIG. 1 includes a cathode 12, an acceleration electrode 14 disposed in front of the cathode 12, and a grounded target electrode 16. A secondary coil 18a of an insulation transformer 18 is connected to the cathode 2 via a rectifier 20. An AC power supply 22 is connected to the primary coil 18b of the insulation transformer 18, and the cathode 12 is connected to an AC power supply. Heating is performed with the energy supplied from 22.
[0016]
Specifically, a coaxial cable having a core wire disposed at the center and a sheath wire provided on the outer periphery of the core wire with an insulating layer interposed therebetween is used as the insulation transformer 18. The coil 18a is used, and a sheath wire is used as the primary coil 18b, and the primary coil 18b is grounded.
[0017]
A high-voltage potential (3 kV) is applied to the cathode 12 from the first DC high-voltage power supply 24 via the core of the first coaxial cable 26. Also, a high voltage potential (120 kV) is applied to the accelerating electrode 14 from the DC second high voltage power supply 28 via the core wire of the second coaxial cable 30, and the thermoelectrons generated from the cathode 12 are converted into a beam. The light is emitted toward the target electrode 16 side. The sheath wires of the first and second coaxial cables 26 and 30 are grounded.
[0018]
The basic configuration of the electron gun 10 as described above is substantially the same as this type of conventional electron gun. However, the electron gun 10 of the present embodiment has remarkable features in the points described below. is there.
[0019]
That is, in the electron gun 10 shown in FIG. 1, three first to third insulation protection devices 32a to 32c are provided. Each of the protection devices 32a to 32c includes a diode group 34 in which a plurality of diodes are connected in series.
[0020]
The diode group 34 includes a plurality of diodes having a high peak voltage connected in series in order to provide a withstand voltage corresponding to a high potential. In the case of the present embodiment, the diode group 34 has a withstand voltage of 22 kV by itself. A total of ten diodes are connected in series and have a withstand voltage of 220 kV.
[0021]
The first protection device 32a is for protecting the insulation of the insulating transformer 18 formed of a coaxial cable, and one end of the diode group 34 is grounded and the other end of the diode group 34 applies a high DC potential to the cathode 12. Portion, that is, a connection node between the output side of the core wire of the first coaxial cable 26 and the cathode 12. In this case, the diode group 34 is arranged such that the ground side is forward in each diode connected in series.
[0022]
The second and third protection devices 32b are for protecting the insulation of the second coaxial cable 30. At the input / output end of the second coaxial cable 30, one end of each diode group 34 is connected to a core wire. The other end of each diode group 34 is grounded. In this case, similarly to the first protection device 32a, the diode group 34 is arranged such that the ground side is forward in each diode connected in series.
[0023]
In the first protection device 32a configured as described above, in a steady state, −3 kV of the first DC power supply 24 is applied to one end of the diode group 34 (actually, (−120 kV when viewed from the ground). + (− 3 kV) = − 123 kV), a reverse voltage is applied to the diode group 34, and no current flows to the ground side via the diode group 34, whereby the potential of the cathode 12 becomes −123 kV. Is kept.
[0024]
On the other hand, when an arc discharge occurs and the potential of the core wire of the coaxial cable 26 increases and exceeds a predetermined value, one end of the diode group 34 of the first protection device 32a becomes higher than the ground potential, causing Part of the current flows through the diode group 34 to the ground side.
[0025]
Since the surge current at the time of discharge pulsates in the forward and reverse directions, in the first protection device 32a configured as described above, when a forward discharge voltage exceeding the ground potential occurs, the surge current flows to the ground side. That is, at least a surge current in the positive direction of the pulsation can be eliminated.
[0026]
However, according to the experimental results described later, it was confirmed that no pulsation occurred when a discharge occurred when the protection devices 32a to 32c having the configuration shown in the present embodiment were used.
[0027]
In this manner, when the pulsation at the time of arc discharge is eliminated, it is possible to effectively eliminate the insulation breakdown of the insulating transformer 18 made of a coaxial cable, which is apt to cause insulation breakdown due to the pulsation.
Further, since the first protection device 32a of the present embodiment is connected to the output-side core wire of the first coaxial cable 26, the dielectric breakdown of the first coaxial cable 26 can also be prevented.
[0028]
On the other hand, in the second and third protection devices 32b and 32c configured as described above, in the steady state, -120 kV of the second DC power supply 28 is applied to one end of the diode group 34. Since a voltage is applied and no current flows to the ground side via the diode group 34, the acceleration electrode 14 is kept at a potential of -120 kV.
[0029]
On the other hand, when an arc discharge occurs, the potential of the core wire of the coaxial cable 30 increases, and when this exceeds a predetermined value, one end of the diode group 34 of the second or third protection device 32b, 32c becomes higher than the ground potential. That is, a part of the surge current at the time of discharge flows to the ground side via the diode group 34, and by the same operation as the first protection device 32a, the dielectric breakdown of the second coaxial cable 30 can be avoided.
[0030]
FIG. 2 shows a test circuit performed to confirm the operation and effect of the protection devices 32a to 32c according to the present invention. In the test circuit shown in the drawing, a coaxial cable A having a length of 7 m is prepared, a resistor R1 is connected in series to one end of a core wire B of the cable A, and a -30V power supply C is connected to the other end of the resistor R1. Connected. The sheath wire D of the cable A was grounded.
[0031]
A resistor R2 was connected in series to the other end of the cable A, and a capacitor C1 having one end grounded and a diode D1 having one end grounded were connected in parallel to the other end of the resistor R2. The diode D1 corresponds to the protection devices 32a to 32c in the above embodiment, and the ground side is forward.
[0032]
A coil L1 and an FET were connected in series to the other end of the resistor R2, and the end of the FET was grounded. In the pseudo discharge, a pulse-like voltage as shown in FIG. 2 was applied to the FET, and this was applied to the coil L1.
[0033]
FIG. 3 shows an OSC point (a voltage observation point, in the above-described embodiment, a high-voltage part) in the test circuit shown in FIG. (Corresponding to.) Is shown.
[0034]
In FIGS. 3 and 4, output waveform diagrams at the gate of the FET are simultaneously shown on the upper side. As can be seen from the test results shown in FIG. 3, if the diode D1 is not installed, the voltage of the core wire B of the coaxial cable A rises from −30 V to +22 V during the pseudo discharge, and then causes a damped pulsation that moves up and down a plurality of times. It was confirmed that such a pulsation would cause dielectric breakdown of the coaxial cable A.
[0035]
However, when the diode D1 is installed in the test circuit shown in FIG. 2, it is found that almost no damping pulsation occurs at the time of pseudo discharge as shown in FIG. 4, and the protection devices 32a to 32c shown in FIG. 1 are used. It was also confirmed that dielectric breakdown of the insulating transformer 18 made of a coaxial cable could be avoided.
[0036]
【The invention's effect】
As described above in detail, according to the coaxial cable protection device used for the electron gun according to the present invention, it is possible to effectively prevent the dielectric breakdown of the coaxial cable due to the damping pulsation.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an embodiment of a coaxial cable protection device used for an electron gun according to the present invention.
FIG. 2 is a test circuit manufactured to confirm the operation and effect of the protection device shown in FIG.
FIG. 3 is an output waveform diagram of a high voltage portion at the time of pseudo discharge in a case where a protection device is not installed in the test circuit shown in FIG. 2;
FIG. 4 is an output waveform diagram of a high voltage portion at the time of pseudo discharge in the case where a protection device is installed in the test circuit shown in FIG. 2;
FIG. 5 is an explanatory view showing an example of a conventional heating device for an electron gun.
[Explanation of symbols]
Reference Signs List 10 electron gun 12 cathode 14 accelerating electrode 16 target electrode 18 insulating transformer 26 first coaxial cable 30 second coaxial cable 32 protective devices 32a to 32c first to third protective devices 34 diode group

Claims (4)

An insulating transformer having primary and secondary coils formed of a coaxial cable is provided, an AC power supply is connected to the primary coil, and a cathode of an electron gun to which a high DC potential is applied is connected to the secondary coil. In an insulation protection device for a coaxial cable used for an electron gun that heats the cathode with electric energy supplied from the AC power supply,
The insulation protection device includes a diode group having a plurality of diodes connected in series between the high-potential application unit and the ground, and having a withstand voltage corresponding to the high potential.
A part of a surge current at the time of discharge is caused to flow to the ground side via the diode group, thereby providing an insulation protection device for a coaxial cable used for an electron gun. An AC power supply is connected to the primary coil, a cathode of an electron gun to which a high DC potential is applied is connected to the secondary coil, and the cathode is used for heating the cathode with electric energy supplied from the AC power supply. In the insulation protection device of the coaxial cable,
The electron gun has an electrode unit disposed in front of the cathode,
A coaxial cable that transmits a high potential to the electrode unit via a core wire disposed at the center is connected between the electrode unit and the DC power supply,
The insulation protection device includes a diode group having a withstand voltage corresponding to the high potential by connecting a plurality of diodes in series between the core wire and the ground,
A part of a surge current at the time of discharge is caused to flow to the ground side via the diode group, thereby providing an insulation protection device for a coaxial cable used for an electron gun. The insulation protection device for a coaxial cable used in an electron gun according to claim 2, wherein the insulation protection device arranges the diode groups on the input and output sides of the coaxial cable. The insulation protection device is characterized in that the diode group is disposed between the high-potential application unit and ground, and between the center conductor and ground, respectively. Protection device.

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