JP4696478B2 - Plasma X-ray generator - Google Patents

Description

  The present invention relates to a plasma X-ray generator that includes a plasma X-ray source that emits extreme ultraviolet light (EUV) and is used in semiconductor lithography and the like.

  An X-ray generator equipped with a plasma X-ray source by discharge generation introduces a working gas such as Xe between plasma generation discharge electrodes, converts it into high density and high ionization plasma by high-speed pulse discharge, A device for taking out a wire. By repeating the process of taking out the X-rays at a high speed, the output of the X-rays is increased (high repetition operation).

  As a main plasma X-ray source, there is a discharge type X-ray source such as a capillary discharge type (for example, see Non-Patent Document 1).

  A capillary discharge type plasma X-ray source is a device that obtains a large current by flowing a current through a capillary (capillary) filled with a working gas and obtains a high-temperature plasma by Joule heating. It is performed in the capillary.

  In addition to the capillary discharge X-ray source, there is a Z-pinch plasma X-ray source. The Z-pinch plasma X-ray source uses a shaft current flowing in the plasma and an azimuthal magnetic field generated thereby to compress the plasma strongly and perform shock wave heating, as well as Joule heating, A plasma column of density is generated on the discharge tube axis and confined.

  In order to improve the X-ray emission efficiency, there is an X-ray generator that generates and discharges rotating plasma between pinch electrodes with improved nonuniformity and asymmetry of the density distribution of plasma (see, for example, Patent Document 1). .

JP 2001-155896 A JP 2003-22950 A Hotta, “Current Status and Future Prospects of EUV (Extreme Ultraviolet) Light Source Research for Lithography”, Plasma Fusion Society, 2003, 79, No. 3, p.245-251

  However, in the conventional X-ray generator, charged particles having a large mass number (excluding ions, fine particles, etc., excluding electrons) constituting residual plasma that emits X-rays and has passed the effective emission time are mirrors, lenses, etc. Diffusion of plasma after X-ray emission and incidence on the optical system were major problems such as damage to the optical system due to the sputtering effect caused by collision with the optical system.

  In addition, when a plasma X-ray source is operated at a high repetition rate in order to generate a high output of X-rays, the exhaust speed by the vacuum pump is limited, and the residual plasma is not sufficiently discharged until the next shot. For this reason, the concentration of residual plasma in the vicinity of the X-ray generation portion increases and the absorption loss of X-rays increases, which is a major obstacle to higher output.

  On the other hand, in an EUV light source using a laser, there is an exposure apparatus for the purpose of removing debris such as charged particles having a large mass number constituting plasma generated when EUV light is generated (for example, Patent Documents). 2).

  However, in the conventional X-ray generator using plasma generation discharge, there has been no device intended to solve the above-mentioned problems by positively removing residual plasma.

  Accordingly, an object of the present invention is to provide a plasma X-ray generator that solves the above-described problems and exhausts residual plasma in the vicinity of the plasma X-ray source to suppress damage to the optical system and X-ray absorption loss. .

In order to achieve the above object, the invention of claim 1 includes a vacuum vessel, an exhaust hole formed in a side wall of the vacuum vessel, an exhaust means connected to the exhaust hole, and an interior of the vacuum vessel near the exhaust hole. Capillary discharge type comprising a capillary with plasma generating electrodes provided at both ends and generating X-rays by converting the working gas supplied to the plasma generating part in the capillary formed between the plasma generating and discharging electrodes into plasma A plasma X-ray source; a magnetic field generating means provided in the vicinity of the exhaust hole on the side wall of the vacuum vessel; and generating a magnetic field in the vacuum vessel; a plasma generating pulse voltage applying means connected to the plasma generating discharge electrode; and the plasma An electron emission electrode formed away from a plasma generation discharge electrode of an X-ray source, and a plasma generation discharge electrode after a light emission effective time has elapsed in the plasma generation unit Ri low low voltage electric potential and a discharge pulse voltage applying means for applying to the electron-emitting electrode,
A low potential formed by emitting X-rays from the plasma generated in the plasma generation unit and emitting and supplying electrons from the electron emission electrode to the magnetic field generated by the magnetic field generation means after the effective emission time has elapsed. A plasma X-ray generator that accelerates by an electrostatic force generated by an electrode and exhausts the gas from the exhaust hole at a high speed.

The invention according to claim 2 is the plasma X-ray according to claim 1, wherein the electron emission electrode is a thermoelectron supply body formed of a material capable of emitting heat electrons at a low temperature such as LaB ₆ , tungsten, or a tungsten compound. Generator.

  According to the present invention, charged particles such as ions constituting the plasma remaining in the vicinity of the X-ray source are exhausted at high speed for each shot, and optical system damage and X-ray absorption loss due to these particles are greatly reduced. Exhibits excellent effects such as

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  The present invention is an apparatus for electrostatically accelerating and rapidly exhausting plasma that remains in the vicinity of a plasma X-ray source and causes X-ray absorption loss. The plasma X-ray generator according to the present invention includes the following: The present invention is not limited to the embodiment.

  FIG. 1 is a block diagram showing a preferred embodiment of a plasma X-ray generator according to the present invention.

  As shown in FIG. 1, a plasma X-ray generator 10 according to the present embodiment is provided with a vacuum vessel 11, an exhaust means 12 for exhausting the inside of the vacuum vessel 11, and generates X-rays. And a plasma X-ray source 13 to be operated.

The vacuum vessel 11 is connected to an exhaust means 12 for exhausting the gas in the vacuum vessel 11 and raising the degree of vacuum through an exhaust hole 24 formed in the side wall 23. In the drawing, the evacuation means 12 is provided on the upper side and the lower side of the plasma X-ray source 13, but the evacuation means 12 may be provided on either side of the vacuum vessel side wall 23. It may be provided on the side wall (in the direction perpendicular to the paper surface). The atmospheric pressure in the vacuum vessel 11 is approximately 1 Pa (10 ⁻² torr). As the exhaust means 12 at the time of supplying the working gas (Xe gas or the like), a conventional vacuum pump can be used, and a turbo molecular pump capable of high-speed exhaust is preferable.

The plasma X-ray source 13 is an X-ray source using generated discharge plasma. In this embodiment, a capillary discharge type plasma X-ray source is used. The plasma X-ray source 13 includes a capillary 14 and plasma generation discharge electrodes (hereinafter referred to as discharge electrodes) 15 and 16 provided at both ends of the capillary 14. The hollow portion in the capillary 14 is a plasma generation unit 17 that converts the working gas G supplied into the capillary 14 into plasma. The material for forming the capillary 14 is preferably an insulator such as alumina (Al ₂ O ₃ ) or ceramic, having a low sputtering coefficient and good thermal stability.

  The discharge electrodes 15 and 16 are connected to a pulse voltage applying means (not shown) for plasma generation so that the left discharge electrode 16 in the figure is GND and the right discharge electrode 15 in the figure is at a high potential. That is, the discharge electrode that generates X-rays on the right side is a positive discharge electrode (anode) 15 and the discharge electrode on the left side is a negative discharge electrode (cathode) 16. A working gas supply means (not shown) is provided so that the working gas G to be converted into plasma is supplied to the plasma generation unit 17 from the negative discharge electrode 16 side. In this embodiment, Xe gas is used as the working gas G in order to generate 13.5 nm X-rays used for lithography or the like, but the working gas G is not limited to this.

  As shown in FIG. 2, the pulse voltage applying means for plasma generation applies (shots) an extremely short pulse voltage 31 for discharge in order to turn the working gas G supplied to the plasma generation unit 17 into plasma. The voltage is several k to 10 kV, the voltage application time for one time is about 100 ns, and the pulse period is about 100 μs (10 k to 100 kHz).

  The feature of this embodiment is that a low voltage electrode is formed in the vicinity of the X-ray source 13 in the vacuum vessel 11 of the plasma X-ray generator 10.

  The low voltage electrode is formed by the action of the electron emission electrode 19 provided in the vacuum vessel 11 and the magnetic field generation means 21.

  The electron emission electrode 19 is provided apart from the plasma generation discharge electrodes 15 and 16, and an exhaust pulse voltage application unit 22 is connected to the positive discharge electrode 15 so as to be at a low potential (negative potential). More specifically, the electron emission electrode 19 is disposed behind the X-ray emission point 25 in order to avoid the plasma of the working gas G to be evacuated from colliding with the electron emission electrode 19 (in the figure, the positive emission electrode 19 is positive). Left side of the discharge electrode 15).

The electron emission electrode 19 is a thermoelectron supplier formed of LaB ₆ or a tungsten compound such as W (pure tungsten), BaW (barium tungsten), or ThW (thorium tungsten) in order to emit thermoelectrons at a low temperature. Was used.

  The exhaust pulse voltage application means 22 applies the exhaust pulse voltage 32 (FIG. 2) in order to emit the thermoelectrons from the thermoelectron supply body 19. The applied voltage was 1 kV or less.

  The magnetic field generating means 21 is provided in the vicinity of the exhaust hole 24 of the side wall 23 of the vacuum vessel 11, and the magnetic field generating means 21 constantly generates a magnetic field H in the vacuum vessel 11. The magnetic field H is generated in a direction that prevents the movement of thermoelectrons between the discharge electrode 15 and the electron emission electrode 19, that is, substantially parallel to the X-ray irradiation direction. In the present embodiment, the magnetic field generating means 21 is formed of a conventional coil.

  Next, the operation of the plasma X-ray generator 10 of the present embodiment will be described.

  First, an operation for generating X-rays from the plasma X-ray source 13 will be described.

  The working gas G is supplied to the plasma generation unit 17 of the plasma X-ray source 13. The working gas G is enclosed at a high density in the plasma generation unit 17, and a high voltage ultrashort pulse voltage 31 is applied between the plasma generation discharge electrodes 15 and 16, so that the working gas G in the plasma generation unit 17 is changed. It is turned into plasma and X-rays are emitted from the plasma. At this time, since it is difficult to hold high-temperature and high-density plasma for a long time in the plasma generation unit 17, it is difficult to continuously excite ultrashort ultraviolet light such as X-rays. It is customary to apply light to emit light. Therefore, in order to increase the output of X-rays, X-rays are generated by repeatedly performing shots (high repetition operation).

  In the high repetition operation, the X-ray emission effective time is about 100 ns from the start of discharge, and the plasma (residual plasma) D that has passed the light emission time exists in the vicinity of the plasma generation unit 17 and the light emission point 25.

  Here, the effect | action which exhausts the residual plasma D is demonstrated using FIG.

  With the end of the effective light emission time, an exhaust pulse voltage is applied to the electron emission electrode 19 to emit thermoelectrons E. Since the magnetic field H is always generated by the magnetic field generating means 21 in the vacuum vessel 11, the thermoelectrons E move along the magnetic field H1 passing through the electron emission electrode 19, and a large number supplied on the magnetic field H1. The thermoelectrons E are fixed so as to float around the magnetic field H1, so that they are equivalent to those formed with parallel electrodes having a negative potential. The low voltage electrode formed by the thermoelectron group held in the magnetic field H1 is referred to as a virtual electrode 18.

  The residual plasma D existing in the vicinity of the plasma generation unit 17 is several to dozens of positive ions, and is accelerated in the direction of the virtual electrode 18 by an electrostatic force with the virtual electrode 18. However, the thermoelectrons E of the virtual electrode 18 are substantially fixed on the magnetic field H1. The residual plasma D electrostatically accelerated in the direction of the virtual electrode 18 is exhausted from the exhaust hole 24 to the outside of the vacuum vessel 11 by the exhaust means 12. As described above, since the residual plasma D can be exhausted by the next shot by electrostatic acceleration, the degree of vacuum in the vicinity of the plasma generation unit 17 can be increased (atmospheric pressure), and the X-ray absorption loss can be greatly reduced. can do.

  Furthermore, since the plasma X-ray generator 10 can exhaust the residual plasma D at a high speed in a direction different from a direction in which the optical system such as an X-ray mirror (X-ray irradiation direction) is present, damage to the optical system is prevented. be able to.

  In addition, since the thermoelectron supply body that is the electron emission electrode 19 is formed of a material that can emit the thermoelectrons E at a low temperature, the discharge pulse voltage 32 can be reduced and the plasma X-ray source can be reduced. 13 is not affected by heat.

  Here, as shown in FIG. 2, the plasma generation discharge pulse voltage 31 and the exhaust pulse voltage 32 are alternately applied, and the X-ray generator 10 is operated at a high repetition rate. Since the thermoelectron group electrostatically accelerating the residual plasma D is gradually diffused, when performing a high repetition operation, an exhaust pulse voltage is applied every time the discharge pulse voltage 31 is applied, and a new virtual electrode 18 is formed. Then, X-ray emission and residual plasma D exhaust are repeated. Therefore, the residual plasma D can be exhausted whenever X-rays are generated and the plasma emission effective time elapses, and the degree of vacuum in the vicinity of the plasma generation unit 17 can always be kept high.

  Further, since the direction in which the residual plasma D is accelerated depends on the position and shape of the virtual electrode 18, the electrostatic acceleration direction of the residual plasma D can be adjusted by changing the shape of the virtual electrode 18. The position and shape of the virtual electrode 18 can be adjusted by the direction of the magnetic field H generated in the vacuum vessel 11 and the position of the electron emission electrode 19.

  In the plasma X-ray generator 10 of the present embodiment, the virtual electrode is formed as the low potential electrode, but the low potential electrode of the plasma X-ray generator according to the present invention is not limited to the virtual electrode 18.

  For example, the low potential electrode may be a metal electrode made of metal formed in a flat plate shape or an arc shape. However, if a metal electrode is used, the residual plasma D may collide with the metal electrode, causing the residual plasma D to remain in the vacuum vessel 11 and reducing exhaust efficiency, or the residual plasma D may sputter the metal electrode. Flying objects may be generated. Therefore, the low potential electrode is preferably a fine mesh (mesh) metal electrode so that the electrostatically accelerated residual plasma D can be transmitted without colliding with the electrode. The virtual electrode 18 is most preferable.

  The plasma X-ray source 13 used in the X-ray generation apparatus 10 of the present embodiment is a capillary discharge type plasma X-ray source. However, the plasma X-ray source according to the present invention is not limited to the capillary discharge type, and Z A plasma X-ray source generated by discharge using a pinch or a plasma focus may be used, and has the same effect as this embodiment regardless of the discharge method of the X-ray source.

It is a block diagram which shows the plasma X-ray generator which is one Embodiment of this invention. It is a figure which shows the characteristic of a plasma generation discharge pulse voltage and the pulse voltage for exhaust. It is a figure explaining the virtual electrode of the plasma X-ray generator of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Plasma X-ray generator 11 Vacuum vessel 12 Exhaust means 13 Plasma X-ray source 15,16 Plasma generation discharge electrode 17 Plasma generation part 18 Virtual electrode 19 Electron emission electrode 21 Magnetic field generation means 22 Exhaust pulse voltage application means G Working gas D Residual plasma H magnetic field

Claims (2)

A vacuum vessel, an exhaust hole formed in the side wall of the vacuum vessel, an exhaust means connected to the exhaust hole, and a capillary installed in a vacuum vessel near the exhaust hole and provided with plasma generating electrodes at both ends. A capillary discharge type plasma X-ray source that generates X-rays by converting the working gas supplied to the plasma generation part in the capillary formed between the plasma generation discharge electrodes into plasma, and in the vicinity of the exhaust hole on the side wall of the vacuum vessel A magnetic field generating means for generating a magnetic field in the vacuum vessel, a plasma generating pulse voltage applying means connected to the plasma generating discharge electrode, and electrons formed away from the plasma generating discharge electrode of the plasma X-ray source A low voltage having a lower potential than the plasma generation discharge electrode is applied to the electron emission electrode after the emission effective time has elapsed in the emission electrode and the plasma generation unit. And a pulse voltage applying means for output,
A low potential formed by emitting X-rays from the plasma generated in the plasma generation unit and emitting and supplying electrons from the electron emission electrode to the magnetic field generated by the magnetic field generation means after the effective emission time has elapsed. A plasma X-ray generator characterized in that it is accelerated by electrostatic force by an electrode and exhausted at a high speed from the exhaust hole . The electron emission electrode, LaB _6, tungsten or tungsten compounds, the plasma X-ray generating apparatus of claim 1, wherein the thermal electron supply body formed thermionic by heat releasable material at low temperature.

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