JPH0740475B2 - X-ray generator - Google Patents

Description

TECHNICAL FIELD The present invention relates to an X-ray generator, and more particularly to an X-ray generator suitable for X-ray lithography.

[Conventional technology]

Recently, a lithographic apparatus using soft X-rays has been studied for manufacturing a large scale integrated circuit. Examples of the soft X-ray source include an anticathode X-ray tube, synchrotron radiation, and an X-ray generation tube by the pinch effect of high temperature plasma. The anticathode type has a drawback of low brightness, and the equipment cost of the synchrotron radiation is high. Therefore, a plasma X-ray source that is inexpensive and can obtain high brightness is considered promising for lithography. As a plasma X-ray source, for example, JP-A-SHO
There is a vacuum spark type proposed in Japanese Patent Laid-Open No. 58-188040. As shown in FIG. 3, this system is a vacuum container 1
A pair of electrodes 2 and 3 are provided inside to face each other. A capacitor 5 charged by a charging device 4 provided outside the vacuum container 1 is connected between both electrodes. To discharge between the electrodes 2 and 3, first, a voltage is applied to the third electrode 6 by an appropriate means to discharge between the electrodes 2 and 6, or between the electrodes 3 and 6, and this is used as a trigger for the electrodes 2 and 3. The space is discharged. Due to this discharge, a large pulsed current flows between the electrodes 2 and 3, a large amount of metal vapor is generated from both electrodes, and the magnetic field due to the large current conduction squeezes the plasma around the electrodes to generate a Z pinch. A characteristic X-ray generated by the Z pinch phenomenon is drawn into an exposure device provided in the direction of an arrow shown in the drawing to expose a silicon wafer or the like. By the way, in the case of the vacuum spark type, in order to facilitate generation of metal vapor due to electric discharge, a structure in which both electrodes have needle-like tips is preferable. However, in this case, the tips of both electrodes are worn out so much that both electrodes must be supplied, which complicates the apparatus. In the case of the vacuum spark type, it is generally said that it is desirable to use the anode side electrode as the X-ray generating substance. It has been considered that this is because electrons are ejected from the cathode side to the anode side due to the electric charge applied between the electrodes and collide with the anode side, whereby the anode surface is heated and metal vapor is easily generated. For this reason, a structure in which the anode-side electrode is needle-shaped is preferred (for example, Ando et al .: Spectroscopy of multiply charged ions by low-inductance vacuum spark: Applied Physics,
(Vol. 49, No. 1 (1980)) [Problems to be Solved by the Invention] The above-mentioned prior art does not consider electrode consumption and variations in discharge voltage accompanying it, and can withstand high frequency,
Moreover, it has been difficult to apply as an X-ray source for lithography, which requires stable and high-intensity X-rays.

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a stable and high-intensity X-ray generator with less electrode consumption and less variation in discharge voltage.

[Means for solving problems]

In order to achieve the above object, in the present invention, the tip of the anode electrode is formed into a spherical shape, and the cathode electrode is formed into a conical shape, and the radius of curvature or thickness of the cathode side electrode tip is the anode side electrode. It is characterized in that it is configured to be smaller than the radius of curvature of the tip of the.

[Action]

Conventionally, both the cathode and the anode have been formed as needle-shaped electrodes, but in this method, current concentrates at the tip of the electrodes and both electrodes are melted and damaged. In the present invention, since the radius of curvature of the anode is large, the effective area of incidence of electrons is increased, the current density is decreased, and the consumption of the anode is reduced first. As the electron collecting area of the anode portion increases, cathode spots are distributed over the entire surface of the cathode, and the surface of the cathode is evenly worn. As a result, only the tips of the cathode and the anode are not locally melted, and it is possible to provide an X-ray generator having a stable discharge voltage with little wear.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. Those having the same functions as those described in the prior art are designated by the same reference numerals. Opposing electrodes 7 and 8 are provided in the vacuum container 1, and an external switch 9 is provided instead of the third electrode described in the prior art. In this case, a high melting point X-ray generating substance such as tungsten molybdenum is used for both electrodes, the tip of the anode side electrode 7 is made spherical, and a conical electrode is used for the cathode side electrode 8. Is larger than the radius of curvature of. The capacitor 5 is charged by the charging device 4, the switch 9 is turned on at a desired voltage, and the opposing electrodes 7 and 8 are discharged.
Due to this discharge, characteristic X-rays peculiar to the material used for the counter electrode can be generated. This characteristic X-ray is introduced into an exposure device provided in the direction of the arrow to expose a silicon wafer or the like coated with an X-ray resist. By the way, in the conventional electrode consumption, as shown in FIG. 4 (a), the tip of the electrode is largely melted, whereas in the present invention, as shown in FIG. 4 (b), both the anode and cathode surfaces have a wide range. Will be slightly consumed. This is because the effective area of the anode that collects electrons is increased, so that the current density of the anode is reduced first and the consumption amount is reduced.
Correspondingly, the cathode spots are distributed over a wide range on the surface of the cathode on the cathode side, and the surface portion on the cathode side is uniformly consumed. As described above, according to the electrode configuration of FIG. 1, the position of the anode-side electrode 7 is kept constant and only the cathode-side electrode 8 is slightly changed every several tens to several hundreds of discharges, so that stable discharge is achieved. In addition, the position where the Z pinch is generated hardly changes, high-frequency discharge is possible, and high-frequency X-rays can be stably generated.

In the present invention, strong X-rays can be generated when the radius of curvature or thickness of the tip portion on the cathode side is as small as possible, and it is particularly effective if this radius of curvature or thickness is 5 mm or less. In terms of electrode consumption, it is very effective to make the radius of curvature of the tip end on the anode side twice or more the radius of curvature or thickness of the tip end on the cathode side.

FIG. 2 shows another embodiment. A hole 9 is formed in the center of the anode-side electrode 7 in FIG. 1 so as to communicate with each other in the vacuum container above the electrode. In the case of this electrode, the discharge is generated around the hole 9 provided at the tip of the anode electrode 7, and the spread of the arc can be regulated by the size of the hole diameter. In order to generate a strong Z-pinch, it is effective to make the arc wide and capture a large amount of plasma, and it is effective in generating high-intensity X-rays. Also, since the holes 9 communicate with each other in the same container,
There is no need to worry about vacuum leaks, and since the metal vapor generated by the discharge is sucked up by the chimney effect through this communicating hole,
There is also an effect that the metal vapor is easily collected in the central portion and the variation in the Z pinch occurrence position is small. Further, since the unnecessary metal vapor after the Z pinch is generated can be quickly discharged through the hole 9, the insulation recovery between the electrodes is quick, and continuous repeated discharge is possible.

〔The invention's effect〕

According to the X-ray generator of the present invention described above, the tip of the anode-side electrode is formed into a spherical shape, and the cathode-side electrode is formed into a conical shape, and the radius of curvature or thickness of the cathode-side electrode tip is set to the above-mentioned value. Since the radius of curvature of the tip of the anode is smaller than that of the tip of the anode, the current density of the anode is reduced first and the consumption is reduced due to the increase of the active area of the anode that collects electrons. The cathode spots will be distributed over a wide range on the surface of the cathode, and the surface of the cathode will be evenly consumed, so that stable discharge with less electrode wear can be obtained, and it can withstand high frequency, and The effect is that high-intensity X-rays can be generated stably.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an embodiment according to the present invention, FIG. 2 is a schematic diagram showing another embodiment according to the present invention, FIG. 3 is a schematic diagram showing a prior art, and FIG. 4 is a detailed explanation of the present invention. It is a figure. 1 ... Vacuum container, 7 ... Anode side electrode, 8 ... Cathode side electrode, 9 ... Hole.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kunio Hirasawa 4026 Kujicho, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Ltd. Central Research Laboratory (56) References JP-A-58-188040 (JP, A) JP-A-59-198645 (JP, A)

Claims (4)

[Claims] 1. An X-ray generator comprising a vacuum container, a pair of electrodes formed of an anode and a cathode provided in the vacuum container, and a pulsed large current source connected to the electrodes, wherein the anode side is provided. The tip of the electrode is formed in a spherical shape, and the cathode side electrode is formed in a conical shape, and the radius of curvature of the tip of the cathode side electrode,
Alternatively, an X-ray generator having a thickness smaller than a radius of curvature of the tip of the anode electrode. 2. The X-ray generator according to claim 1, wherein a radius of curvature or a thickness of the tip of the cathode side electrode is set to 5 mm or less. 3. The X according to claim 1, wherein the radius of curvature of the tip of the anode-side electrode is twice or more the radius of curvature of the tip of the cathode-side electrode or the thickness thereof. Line generator. 4. An opening portion is provided in a central portion of an axis of the anode electrode, and the opening portion communicates with the inside of the vacuum container at an upper portion of the electrode. The described X-ray generator.