JPS62122034A - X-ray source unit for x-ray exposure - Google Patents

Abstract

PURPOSE:To realize a long service life and stabilize the radiation of X-rays, by applying a tungsten alloy for an electrode material in a plasma generating chamber. CONSTITUTION:A plasma generating chamber 3 is composed by furnishing a high voltage electrode 4 and a low voltage electrode 5 with the electrode end applying a high melting point material. On both conditions when a hole is not made at the center of the high voltage electrode in an ordinary case (A), and when a hole is made there (B), a metal plate of a high melting point, such as a copper-tungsten alloy or a silver-tungsten alloy, is fixed to the end 4a of the high voltage electrode 4 and the opposite low voltage electrode 5 at the discharge generating electrode ends, in soldering, shrinkage fit, or bolting. Although it is most favorable to form the whole bodies of the high voltage electrode 4 and the low voltage electrode 5 with unitary tungsten alloys, such an alloy may be used only for the ends for the purpose of economy because it is expensive.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to stable operation of soft X-ray generation by applying the pinch effect of high-temperature, high-density plasma. This relates to the source device.

Conventional technology A conventional radiation source device for X-ray exposure generates arc plasma by passing a large pulsed current between two electrodes by discharging a capacitor, and then pinching the plasma using a self-magnetic field to generate soft X-rays. was occurring.

This type of device usually supplies the energy stored in a capacitor to the discharge electrode in the plasma generation chamber through a low impedance circuit, so the current reaches several hundred kA, and the arc plasma has an extremely high temperature of less than 2 φ. Showing the pinch effect.

Problems to be Solved by the Invention However, high-temperature, high-density plasma extremely melts the discharge electrode and exhibits a consumption phenomenon that creates holes locally, resulting in unstable plasma generation, which makes reproducibility difficult. It has the drawbacks of poor quality and the inability to produce a stable spot X'4iA source, and is currently hardly used for industrial porcelain.

Means for Solving the Problems The present invention seeks to provide a source device for X-ray exposure that eliminates the above-mentioned drawbacks.

In an X-ray exposure source device that generates X-rays by plasma generated by passing a large current between a pair of high-voltage electrodes and a low-voltage electrode, the high-voltage electrode and low-voltage electrode or a part thereof in the plasma generation chamber have a high melting point. Tungsten or a tungsten alloy that is a combination of tungsten and silver or copper is used.

Wear of the electrode surfaces of the working high-voltage electrode and the low-voltage electrode can be reduced, and as a result, X-rays can be generated with good reproducibility over a long period of time.

Embodiment FIG. 1 shows an embodiment of a plasma generation chamber used in the X-ray exposure source device of the present invention.

■ is a capacitor, 2 is a switch, 3 is a plasma generation chamber,
4 is a high voltage electrode, 5 is a low voltage electrode, 6 is an insulator, 7 is a container airtightly equipped with an X-ray extraction window 8, 9 is an electric current, 10 is a pinch plasma, and 11 is an X-ray.

Although not shown, the high voltage electrode 4, the low voltage electrode 5, the insulator 6, and the container 7 are each held airtight through a backing by tightening bolts to form the plasma generation chamber 3. Further, the capacitor is connected via a switch 2 to a high voltage electrode 4 and a low voltage electrode 5 which are insulated by an insulator 6.

Next, the operation will be explained.

Charge is supplied to the capacitor 1 from a DC power source (not shown) to charge it to a predetermined voltage.

When the switch 2 is closed by an external factor (not shown) and a voltage is applied to the high-voltage electrode 4 and low-voltage electrode 5 of the plasma generation chamber 3 to cause arc discharge, the current 9 gradually increases to 1
It reaches several hundred kA in less than 0 μs. When such a large impact current flows, the arc plasma rapidly causes a pinch effect (self-convergence) due to its self-magnetic field, generating a pinch plasma 10 of less than 2 flφ, with a temperature of 1 keV and a density of 10
It reaches more than 18CI11-3 and emits strong X-rays due to plasma interaction. Thereafter, the current 9 gradually begins to attenuate, and the pinched plasma collapses as the self-magnetic field pressure is overcome by the plasma pressure.

Now, the X-rays 11 obtained in this way are taken out to the outside through the X-ray extraction window 8 made of a material with good transparency, and although not shown, is used for X-ray exposure of the VLSI. Next, exposure (transfer) is performed by irradiating the wafer coated with resist (polymer film) through an X-ray mask.

In the conventional X-ray exposure source device, the discharge in the plasma generation chamber 3 initially occurs in a relatively stable state, but as the number of discharges increases, local damage due to the pinch effect of the plasma occurs and the high voltage of the high voltage electrode 4 increases. This occurs at the center of the electrode end 4a. In an attempt to obtain strong X-rays, when a pulse current reaching several hundred kA is passed in a few μs, the plasma becomes thinner than the pinched 2 φ, and the high-temperature, high-density plasma passes through the high-voltage electrode 4.
However, it has the disadvantage that the low voltage electrode 5 is easily melted.

The present invention is an X-ray exposure source device that eliminates such conventional drawbacks and is equipped with a high voltage electrode and a low voltage electrode using a material with a high melting point at the end of the electrode. The main parts of high-voltage electrodes and low-voltage electrodes are shown. (A) shows the general case where no hole is provided in the center of the high-voltage electrode, and (II) shows the case where a hole is provided in the center of the high-voltage electrode. A metal plate such as a copper-tungsten alloy or a silver-tungsten alloy with a high melting point is attached to the high voltage electrode end 4a and the low voltage electrode 5 facing it by brazing, blind fitting, or bolting. Fix it using the following method.

It would be best if both the high-voltage electrode and the low-voltage electrode were made of a single piece of tungsten alloy, but considering the cost and economy, it is better to use it only at the end of the electrode.

In the structure shown in Fig. 2 (A), as the current 9 increases, the plasma gradually begins to converge toward the center of the high-voltage electrode end 4a due to the pressure of the self-magnetic field caused by the self-current. A dense pinch plasma 10 is generated. This pinch plasma 10 melts the electrode, but in the case of the above-mentioned copper electrode, a wedge-shaped hole with a diameter of about 5 fins reaches about 10 holes in the center of the high voltage electrode end 4a after 100 discharges, and the low voltage electrode In contrast, in the present invention, the electrode surface was only slightly roughened under the same conditions, and there was no adverse effect on the stability of the plasma. Even when the discharge was performed 10,000 times intermittently, the wear of the electrodes was slight, and the emission of X-rays was stable and effective in practice.

Various electrode shapes are possible; for example, in the case of the structure shown in FIG. 2(b), a hole is provided from the beginning in the part of the high-voltage electrode end 4a where plasma is generated. Plasma is generated in a concentrated manner, but some of the plasma migrates to the inner surface of the cylindrical shape, and the current density on the electrode surface becomes warmer and smaller than that without holes, which is beneficial for extending the life of the electrode. By taking this into account, even longer life can be achieved.

FIG. 3 shows another embodiment of the plasma generation chamber used in the X-ray exposure source device of the present invention.

The configuration is the same as that in FIG. 1 except for the shape of the tip of the low-voltage electrode 5, and the same reference numerals are given to corresponding parts, so a description thereof will be omitted.

The operating principle is almost the same as that in FIG. 1, but the plasma generation process is different. When a voltage is applied between the high voltage electrode 4 and the low voltage electrode 5, an initial discharge or plasma is generated on the creeping surface 6a of the insulator 6, and an initial current 9a flows. As the current increases, the plasma gradually moves outward (toward the bottom in Figure 3) due to electromagnetic force due to the interaction between the self-magnetic field created by this current and the plasma, and the current 9 moves in the same way, eventually forming a strong self-magnetic field. Pinch plasma 10 is generated outside the high-voltage electrode 4 by the magnetic field, and strong XwA is emitted.

Even in this type of X-ray generator, the electrodes are subject to severe wear, so use of the tungsten alloy of the present invention significantly reduces the wear.

As for the high melting point tungsten alloy, a sintered material which is a combination of high conductivity silver or copper as the main component is good, and a combination of tungsten carbide and silver is also good. These exhibit excellent arc resistance and melting resistance in a large current range, and can be used as electrode materials with low wear and high reliability. However, if the ratio of silver or copper to tungsten is too high, wear will be severe, and if the ratio is too low, cracks will occur. (2:8)~(5
:5) were effective.

Since electrode wear is due to polarity effects and the structure of both electrodes,
It is not necessarily necessary to use tungsten alloy for both electrodes, and it is effective to use it for one electrode, which is subject to severe wear.

Effects of the Invention As described above, the X-ray exposure source device of the present invention uses a tungsten alloy as the electrode material in the plasma generation chamber, so it has a lifespan more than 100 times longer than conventional copper or brass electrodes. The present invention is capable of achieving a high degree of stability, and the emission of X-rays is extremely stable, making it a great contribution to industrial practical application.

[Brief explanation of drawings]

FIG. 1 is an explanatory cross-sectional view of one embodiment of a plasma generation chamber used in the X-ray exposure source device of the present invention, and FIG. 2 is a cross-sectional view of a high-voltage electrode and a low-voltage electrode forming the plasma generation chamber according to the present invention. These are explanatory cross-sectional views of the main parts, (A) shows the case where no hole is provided in the center of the high voltage electrode, (B) shows the case where the hole is provided in the center of the high voltage electrode, and FIG. 3 shows the case where the hole is provided in the center of the high voltage electrode. FIG. 7 is an explanatory cross-sectional view of another embodiment of a plasma generation chamber used in an exposure radiation source device. l: Capacitor 2: Switch

Claims (2)

[Claims] (1) In an X-ray exposure source device that generates X-rays by plasma generated by passing a large current between a pair of high-voltage electrodes and a low-voltage electrode, a tungsten alloy is used for some or all of the electrodes. A radiation source device for X-ray exposure characterized by the following. (2) The combination of tungsten alloy is silver or copper, and the component ratio is (silver or copper: tungsten) = (2:
8) to (5:5), the radiation source device for X-ray exposure according to claim 1.