JP3433151B2 - Laser plasma X-ray source - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser plasma X-ray source for generating vacuum ultraviolet rays and X-rays from a high temperature and high density laser plasma.

[0002]

2. Description of the Related Art A laser plasma X-ray source converges high-power laser light and irradiates it on a target to generate high-temperature and high-density laser plasma, which generates vacuum ultraviolet rays and X-rays. An exposure apparatus in semiconductor manufacturing is one of the apparatuses expected to utilize the laser plasma X-ray source. The laser plasma X-ray source used is required to have high brightness, although it is used in this exposure apparatus and the same as in other apparatuses.

Further, when this high-temperature and high-density laser plasma is generated, scattered substances such as atomic substances, ionic substances, and particulate substances (hereinafter, collectively referred to as debris) unless otherwise specified. Is released. Since this debris damages the X-ray mirror and the vacuum partition wall, it is necessary to suppress their generation or remove them.

As a conventional technique intended to solve these two different problems, there is a target in which a pressurized gas is injected into a vacuum container as described in US Pat. No. 5,570,709. Also, Japanese Patent Laid-Open No. 10-2214
As described in Japanese Patent Publication No. 99, there is one in which a target in which fine particles are mixed with gas is jetted into a vacuum. Further, as an aim to increase the intensity of generated X-rays, Japanese Patent Application Laid-Open No. H8-78
As described in Japanese Patent Application Laid-Open No. 195533, there is one in which a strong magnetic field is applied in the vicinity of a solid target to confine plasma. Further, as a method for removing debris, there is a method in which the generated debris is ionized with ultraviolet rays and removed with an electric field and a magnetic field, as described in JP-A-8-17371.

[0005]

In the prior art, a target in which a pressurized gas is injected into a vacuum container and a target or a target in which fine particles are mixed with gas are injected into a vacuum is a target. Although less debris is generated compared to the case where solid is only solid, ion components in plasma are always present and scatter as debris, so it is not possible to install an optical element such as an X-ray optical mirror near plasma. It was difficult.

Further, the one in which a strong magnetic field is applied in the vicinity of a solid target to confine plasma is not considered for suppressing debris, and further, in order to confine laser plasma and increase X-ray intensity. As will be described later, an extremely strong magnetic field of the order of 10 ² T is required, and its realization is not easy.

Further, the method of ionizing debris with ultraviolet rays has a problem that the ionization efficiency varies depending on the type of debris and the efficiency is not sufficiently high.

It is an object of the present invention to provide a laser plasma X-ray source which prevents damage to an optical mirror due to generated debris and improves X-ray collection efficiency.

[0009]

In order to achieve the above object, the laser plasm X-ray source of the present invention is a device for injecting a fluid into a vacuum, and a laser beam is applied to the target with the ejected fluid as a target. In a laser plasm X-ray source that emits X-rays from the plasma by irradiating
Then, with respect to the plane formed by the magnetic field application direction and the fluid ejection direction
Deflection of the ion debris in the vertical direction
It is characterized in that an optical mirror is arranged on the X line in the direction opposite to the deflection direction .

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to FIGS.

1 and 2 show the structure of a laser plasma X-ray source device according to an embodiment of the present invention. In this figure, support fittings 13A and 13B are attached to the support base 10, and the converging lens 2 is supported by the support fitting 13A on one side. The pulsed laser light 1 passes through the converging lens 2. The vacuum valve 4 and the magnetic circuit 6 are provided on the support metal fitting 13B on the other side.
Is attached. The target supply pipe 3 on one side of the vacuum valve 4 is inserted into the through hole 10A of the support base 10 and is connected to an external gas source. The supply nozzle 5 on the other side of the vacuum valve 4 passes through the through hole 5A of the magnetic circuit 6 and extends into the magnetic circuit. The pulsed laser light 1 from the converging lens 2 passes through the through holes 5B and 5C of the magnetic circuit.

The pulsed laser beam 1 is a laser beam having an output sufficient to generate the laser plasma 7. As the pulsed laser beam 1, such a pulsed laser beam 1 is usually used. As the type of laser, for example, a YAG laser, an excimer laser, or the like having an output per pulse of several 10 mJ to several 10 J is applied. The pulse width is a few tens of ns or less, and the converging lens 2 has a number 1
It is converged to 0 to several 100 μm, and the energy density at that time is about 10 ¹⁵ to 10 ²² W / m ² . In this embodiment, a YAG laser is used, and pulse laser light is emitted from the YAG laser.

As the target, a fluid is used as a target, and more specifically, a gas or a fine particle mixed gas is used. Although not shown in this figure, this gas, or a mixed gas of fine particles, is supplied from a gas source from a gas cylinder or a fine particle tank and is driven in a pulsed manner by a vacuum valve 4
Thus, the target is jetted into the vacuum from the supply nozzle 5 in synchronization with the irradiation timing of the pulsed laser light 1.

[0014] At this time, the pressure in the vacuum vessel (not described in the drawing), for example a 10¯ ² ~10¯ ⁵ torr, if more than a few atmospheres the back pressure of the valve 4, the target fluid 8,
After being injected from the supply nozzle 5, it is in a molecular flow state while undergoing adiabatic expansion and diffuses in a substantially uniform direction (downward in FIG. 1) at a speed of several hundred m / s. When the pulsed laser light 1 is converged and irradiated on the jetted target fluid 8, a strong electric field of the laser light 1 or the like optically causes dielectric breakdown (optical breakdown) to ionize the ionized electrons. A process of absorbing and heating the laser light 1 immediately occurs due to a process such as bremsstrahlung, and a high-temperature and high-density laser plasma 7 is formed very quickly within the pulse width (tens of ns) of the pulsed laser light 1. It

Although the temperature and density of the plasma vary depending on the conditions, for example, plasma having an electron temperature of several hundred eV or more and an electron density of 10 ²⁰ to 10 ²² cm ⁻³ is generated. From this laser plasma 7, bremsstrahlung of electrons,
In addition, a continuous spectrum of X-rays is emitted by the process of free-free transition or free-bound transition in the plasma recombination process, and characteristic X-ray is generated by the process of bound-bound transition in the plasma recombination process. And debris are released. It is used as an X-ray source by utilizing this X-ray.

A magnetic field 9 is applied to the laser plasma 7 by the magnetic circuit 6 in order to prevent damage to the optical mirror and the like due to the generated debris. The direction of the magnetic field is perpendicular to the traveling direction 8 of the ejected fluid target. Further, the magnetic flux density applied to the 10¯ ¹ ~10 ⁰ T. If the magnetic flux density is about this level, a commercially available strong permanent magnet is used to make the magnetic circuit 6
Can be achieved by configuring The optical mirror 20 is arranged in the direction perpendicular to the direction in which the magnetic field 9 is applied from the magnetic circuit 6.

Next, the mechanism for preventing damage to the optical mirror 20 in the present invention will be described with reference to FIG. First,
The electron temperature of the laser plasma 7 immediately after being generated is several 1
The electron density is about 00 eV or more, and the electron density is about 10 ²⁰ to 10 ²² cm ⁻³ . In order to penetrate the magnetic field into this plasma, the β value defined by the following equation must be 1 or less.

[0018]

## EQU1 ## β = nT / (B ² / 2μ0) (Equation 1) where n: plasma density (m− ³ ), T: electron temperature (J), B: magnetic flux density (T), μ0: The magnetic permeability in vacuum (1.257 × 10 ⁶ H / m).

Now, it is understood that the β value is set to 1 or less for the laser plasma 7 immediately after being generated, and B must be 10 ² T or more in order to confine the plasma in the magnetic field. Such a high-strength magnetic field is not easy to realize.

However, such a high-strength magnetic field is not necessary only for the purpose of preventing damage to the optical mirror and the like due to the generated debris. The reason is that the generated laser plasma 7 expands immediately after the generation and rapidly decreases with the plasma density and the electron temperature. For example, even if the electron temperature does not change, when the plasma volume expands 10 ⁶ times, the magnetic field can penetrate into the plasma with a magnetic flux density of 1 T or less.

At this time, the plasma immediately after generation is, as shown in FIG. 3, the advancing velocity V (m of the fluid before plasma formation.
/ S) because of the store and there is a magnetic flux density B which is perpendicular to the direction of the moving speed V of the fluid, cause V × B drift, ion matter against the plane formed by the V and B perpendicular The image is deflected in the direction (direction 12 in the figure). Therefore, since the ionic debris does not scatter in the direction 11 in which the X-rays 11 are extracted and in the direction 11 opposite to the direction 12 in the figure, the optical mirror is arranged in this direction, so that the optical mirror 20 can be prevented from being damaged. it can. Further, in the present invention, the optical mirror 20 is arranged in a direction that does not coincide with the irradiation direction of the pulse laser beam 1, and the pulse laser beam 1 is prevented from irradiating the optical mirror 20 to prevent the optical mirror 20 from being damaged.

From the laser plasma X-ray source of the present invention, X
Needless to say, it can be used in a semiconductor exposure apparatus that irradiates the optical mirror 20 with the line 11 and irradiates the mask of the semiconductor wafer with the X-ray 11 reflected by the optical mirror 20.

As described above, according to the present embodiment, by providing the magnetic field applying device for applying the magnetic field in the direction perpendicular to the jet direction of the target, it is possible to prevent damage to the optical mirror and the like due to the generated debris. effective.

[0024]

As described above, according to the present invention, not only the damage to the optical mirror due to the generated debris can be prevented, but also the debris is less likely to adhere to the optical mirror.
The recovery efficiency for taking out the wire 11 is improved.

[Brief description of drawings]

FIG. 1 is a perspective view showing the configuration of a laser plasma X-ray source that is an embodiment of the present invention.

FIG. 2 is a perspective view showing a portion of the laser plasma X-ray source shown in FIG.

FIG. 3 is a diagram for explaining the fluid ejection direction, the magnetic field application direction, and the debris deflection direction of FIG.

[Explanation of symbols]

1 ... Laser light, 2 ... Converging lens, 3 ... Target supply pipe, 4 ... Valve, 5 ... Supply nozzle, 6 ... Magnetic circuit, 7 ...
Laser plasma, 8 ... Target fluid advancing direction, 9 ...
Direction of magnetic field, 10 ... Support, 11 ... X-ray extraction direction,
12 ... Deflection direction of ionic substance, 20 ... Optical mirror.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-10-221499 (JP, A) JP-A-8-17371 (JP, A) JP-A-9-245989 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H05G 1/00-2/00

Claims (3)

(57) [Claims] 1. A device for injecting a fluid into a vacuum, and a laser plasma X-ray source for producing an X-ray from the plasma by irradiating the ejected fluid as a target with a laser beam to generate a plasma. A magnetic field applying device for applying a magnetic field in a direction perpendicular to the direction of fluid ejection of the target, and
Deflecting the ion debris in the direction perpendicular to the plane,
Laser plasma X-ray source, characterized by arranging the light studies mirror in the opposite direction of the X line and the deflection direction of the ion debris. 2. The jetted fluid is a gaseous substance, or
Claims characterized by being a gaseous substance containing fine particles
Item 2. A laser plasma X-ray source according to item 1. 3. X-rays reflected from an optical mirror are transferred to a semiconductor window.
It can be used for semiconductor exposure equipment that irradiates the mask of Eher.
The laser plasma X-ray according to claim 1,
source.