JP3190474B2 - Discharge pumped laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge excitation laser device, and more particularly to a discharge excitation laser device used for material processing, projection exposure, and the like.

[0002]

2. Description of the Related Art Conventionally, a discharge excitation type laser device has been used as a light source for photolithography for producing a circuit pattern of a large-scale integrated circuit (LSI), in addition to material processing such as marking, drilling, annealing and the like. . Excimer lasers are particularly powerful ultraviolet light sources among gas lasers.
Utilizing its characteristics, it is mainly used for marking and drilling of organic materials such as resins for material processing. The reduction projection method is mainly used for optical lithography, and the transmitted light of the original (reticle) pattern illuminated by the illumination light source is projected on the photosensitive material on the semiconductor substrate by the reduction projection optical system to form a circuit pattern. I do. The resolution of this projected image is limited by the wavelength of the light source used. For this reason, the wavelength of the light source is gradually shortened from the visible region to the ultraviolet region. Conventionally, g-line (436 nm) or i-line (3 nm) generated from a high-pressure mercury lamp has been used as a light source in the ultraviolet region.
65 nm) has been used. However, when the minimum pattern line width becomes 0.25 μm or less required for 64 MB, the wavelength of the i-line has already reached its limit. As a solution to this technical limitation, deep ultraviolet (Dee
p Ultra Violet) Laser light sources are promising. In particular, an excimer laser can obtain strong oscillation at a wavelength such as KrF (248 nm) or ArF (193 nm) depending on the composition of the medium with high output and high efficiency. On the other hand, in the deep ultraviolet region, glass and crystal materials constituting the reduction projection lens system are extremely restricted. For this reason, it is difficult to correct chromatic aberration used in a reduction projection lens system using a mercury lamp. Therefore, instead of correcting the chromatic aberration of the lens system, the difficulty is eliminated by disposing a wavelength selection element in the laser resonator and reducing the spectral width of the output light to such a degree that the chromatic aberration of the lens material can be ignored. I have. With this method, in the case of spontaneous oscillation, the output, which was several nm in spectral width, can be narrowed to several pm and narrowed.

An example of a conventional excimer laser device (the present state of excimer laser, 1987 National Institute of Electrical Engineers of Japan, page S.M.
FIG. 6 shows the structure of 1-14). As the discharge circuit, an automatic preionization type capacity transfer type circuit is generally used because of its simple structure. Primary capacitor 1 for storage by charger
01 to a predetermined voltage, and then the thyratron 10
The charging (charge transfer) of the secondary capacitor (peaking capacitor) 103 is started by the conduction of the switch element such as 2. Its current during the charge transfer main electrodes 104,
Pre-ionization discharge is generated through several tens of pre-ionization electrodes 106 connected in parallel on both sides of the pre-ionization 105 (automatic pre-ionization). The main discharge space is irradiated with the ultraviolet light thus generated, a main discharge is generated between the main electrodes 104 and 105 , a population inversion is formed in the laser medium, and laser oscillation is generated. Here, the laser is used to discharge between the main electrodes 104 and 105.
It oscillates in a direction perpendicular to the direction (perpendicular to the paper). Further, a heat exchanger 108 and a fan 109 for forcibly convection and cooling the laser medium gas are incorporated in the laser chamber 107 to enable a repetitive operation of several tens to several hundreds HZ.

[0004]

DISCLOSURE OF THE INVENTION Discharge excitation type laser devices are widely used as industrial light sources. However, in the case of application to industry, the consumption rate and the distribution of the consumption of the electrodes 104 and 105 on the anode side and the cathode side are different, and the beam shape changes asymmetrically in the discharge direction with the consumption of the discharge electrode. There's a problem. When used for processing, this change changes the transverse mode and consequently the beam focusing. It also causes a change in output, which is a practical problem.

When used as a light source for photolithography, a change in the width of output light causes the following problems in the practical use of a narrow band excimer laser. It is well known that a wavelength selection element used for narrowing a band has an angular dispersion characteristic. For example, when a diffraction grating is used, higher order diffraction is used to reduce the spectrum width.
For this reason, the angular dispersion at the operating point is large, and the divergence angle of the laser beam determined by the width of the discharge directly affects the spectrum width (Japanese Patent Application No. 2-219603). That is, when the divergence angle is large, the spectrum width is widened. Therefore, when the discharge width changes and the gain region changes, the beam divergence of the laser light changes, so that the spectrum width also changes greatly, and the performance of exposure deteriorates. Further, there is a problem that illumination unevenness occurs with a change in the beam profile.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a discharge excitation laser device in which a magnetic field is applied in a direction parallel to a discharge direction to make the beam intensity uniform in a direction along the discharge direction.

[0007]

To achieve the above object, a first aspect of the present invention is a discharge excitation laser apparatus having an electrode for generating a discharge for exciting a laser in a direction orthogonal to an optical axis. in the device, a wavelength selecting element having angular dispersion characteristics as narrowing element, wherein both electrodes
And a permanent magnet that is disposed on the back of the device with the opposite magnetic poles facing each other and generates a magnetic field having lines of magnetic force substantially parallel to the discharge direction of the electrodes in a discharge region between the electrodes, and in a direction orthogonal to the optical axis. The width of the permanent magnet is wider than the width of the electrode in a direction perpendicular to the optical axis.

Second, in a discharge excitation laser device having an electrode for generating a discharge for exciting a laser, there is provided means for generating a magnetic field having lines of magnetic force substantially parallel to the discharge direction of the electrode in a discharge region between the electrodes. The anode return wire and the cathode wire connecting between the electrode and the peaking capacitor of the discharge circuit are made of permanent magnet material or ferromagnetic material, and the magnetic path is formed by the anode return wire and the cathode wire. Features.

[0009]

According to the first configuration, the following functions and effects can be obtained. The paragraph number [0002] summarizes, "To shorten the wavelength of the light source, increase the output, increase the efficiency, and obtain a strong oscillation, to arrange a wavelength selection element in the laser resonator", That is, the advantage of the wavelength selection element is described. On the other hand, the paragraph [0005] summarizes, "Because the wavelength selection element used for narrowing the band has an angular dispersion characteristic, the discharge excitation laser device in which the angular dispersion at the operating point is determined by the discharge width is a laser beam. The divergence angle has an effect on the spectrum width. " On the other hand, the discharge excitation laser device of the first configuration also has the wavelength selecting element having the above-described length. However, in the above-described first configuration, the " direction orthogonal to the optical axis " is used to suppress the disadvantages while utilizing the advantages of the wavelength selection element.
And a permanent magnet that generates a magnetic field having magnetic lines of force substantially parallel to the discharge direction of the electrodes in the discharge region between the electrodes. In other words, the beam intensity is made uniform in the direction along the discharge direction by the permanent magnet , thereby making the most of the advantage of the wavelength selection element and orthogonal to the optical axis, which is a defect.
The variation of the discharge width in the direction is suppressed, and the variation of the beam divergence is suppressed, thereby suppressing the variation of the spectrum width. In addition, the opposite poles on the back of both electrodes
And the width of the permanent magnet in the direction perpendicular to the optical axis is made larger than the width of the electrode.
The influence of the spread of the magnetic field lines at the width direction ends can be reduced, and the electrode can be placed in a uniform and parallel magnetic field having a magnetic field line with a small spread , so that the charged particles in the discharge region are not affected by the magnetic field lines
The discharge width spreads or changes because it moves almost straight along
The movement is reliably and accurately suppressed, the stability of the beam shape can be further improved, and the fluctuation of the spectrum width can be further suppressed.

According to the second configuration, the following operation and effect can be obtained. The third configuration, the anode return wire for connecting the <br/> the peaking capacitor electrode and the discharge circuit and having a means for generating a magnetic field with substantially parallel field lines in the discharge direction of the electrode in the discharge region between the electrodes And the cathode wire is made of a permanent magnet material or a ferromagnetic material. For this reason, the anode return wire and the cathode wire form a magnetic path with little leakage flux. Therefore, the intensity of the magnetic field in the discharge region between the electrodes by the means for generating the magnetic field is increased, and the beam stability is improved. Further, in the second configuration, since the magnetic path is formed so that the gap length at the end of the magnetic path is reduced, the intensity of the magnetic field formed between the electrodes is further increased, and the stability of the beam is further improved.

[0011]

THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention with reference to FIGS. 1 to 5 will be described. FIG. 1 is an enlarged schematic view of an electrode portion of a first embodiment showing a basic configuration of the present invention . In FIG. 1, electrodes 1 and 2 are provided in a laser chamber (not shown), a cathode electrode 1 is attached to an insulating material 3, and an anode electrode 2 is provided to face the electrode 1. The cathode electrode 1 is connected to a high voltage circuit by a cathode wire 4, and the anode electrode 2 is grounded by an anode return wire 5.
The electrodes 1 and 2 are permanent magnets and face each other with different magnetic poles. Here, the N pole of the cathode electrode 1, that have to face the S pole of the anode electrode 2. The same effect can be obtained even if the directions of the N pole and the S pole are opposite to each other. As the magnet, an alnico magnet containing aluminum, nickel, or cobalt as a main component, a ferrite magnet, a manganese aluminum magnet, a samarium cobalt magnet, a neodymium iron boron magnet, or the like can be used. Since this magnet is exposed to a laser gas, active ions at the time of discharge, or sputtering, the surface is preferably coated (plated, ion-plated, etc.) with a corrosion-resistant material such as nickel or gold to improve corrosion resistance. In the drawing, the solid line indicates the magnetic force line M, and the dotted line indicates the electric force line P. Although other configurations are not shown, they are the same as those of the conventional laser device. Directly in the direction of discharge between the electrodes 1 and 2 and the direction of the magnetic field
Has a laser optical axis in the intersecting direction (perpendicular to the paper)
You.

The operation and characteristics of the discharge in the first embodiment will be described. Charged particles (ions,
The electron (electron) moves along the line of electric force P due to the Coulomb force due to the electric field E applied between the electrodes 1 and 2, forms an excitation region having laser activity, and excites the laser. Conventionally, since only the electric flux lines P restrain the charged particles, the discharge current density to be excited is high in the portion where the electric flux density distribution of the electric flux lines P (congestion of the electric flux lines P) is large, and the gain of the laser gas is also high. high. Accordingly, when the electrodes 1 and 2 are worn out, the electrode shape changes, and the like, causing a change in the line of electric force P. Thus, the electric flux density distribution in the discharge direction changes. That is, the change in the electric force line P directly causes the change in the movement path of the charged particles, and the change in the discharge region, that is, the change in the laser beam shape.

In order to suppress this change, the first embodiment has a structure in which the magnetic field B is applied in parallel with the electric field E as described above. Generally, the Lorentz force acts on charged particles existing in the electric field E and the magnetic field B. Ideally, when the direction of the electric field E coincides with the direction of the magnetic field B in a straight line and in parallel, the charged particle (charge q) moving at the velocity V has a plane perpendicular to the magnetic field B as a force. Moves in the direction of the electric field E while performing a circular motion in the inside, and its trajectory becomes spiral (so-called cyclotron motion). FIG. 2 shows a uniform magnetic field B
FIG. 2A shows a spiral motion of electrons a and ions b in FIG.
2 shows a side view, and FIG. 2B shows a plan view. Note that rc indicates a radius of rotation (rce is the radius of rotation of the electron a, and rci is the radius of rotation of the ion b). In this case, the charged particles are constrained by the lines of magnetic force M, and the spread of discharge due to diffusion is suppressed.

[0014] Now, if changes in the depletion or the like of the direction of the lines of electric force P is the electrode 1, 2, considering a case in which changes to convex outward, which are equivalently generate an electric field Ex components outward
You . In this case, the spiral radius of the cyclotron motion increases or decreases depending on the relationship between the motion direction and the electric field direction, and drifts in the E × B direction (so-called E × B drift) as shown in FIG. In FIG. 3, when there is a uniform magnetic field B (magnetic flux density B) and a uniform electric field E perpendicular thereto, the charged particles performing cyclotron motion change every half cycle in the process of the swirling motion. to undergo an acceleration force and deceleration forces due to q E becomes electric field E, the increase or decrease of the velocity vi for respective time, and occurs decrease of the turning radius rc with it. As a result, the charged particles move in the direction of the vector product E × B regardless of the sign of the charge. Therefore, since the charged particles move in the direction perpendicular to the direction of the electric field E, the spread of the discharge due to the spread of the lines of electric force P can also be suppressed in this case.

FIG. 4 is an enlarged schematic view of the electrode portion of the second embodiment. In FIG. 4, electrodes 21 and 22 are made of aluminum, zinc,
It is a paramagnetic metal such as chromium, copper, gold or platinum, an alloy thereof, or a conductive ceramic, is formed to face each other, and has permanent magnets 23, 24 on the electrodes 21, 22. Optical axis in a direction orthogonal to the discharge direction between electrodes 21 and 22
And the width of the permanent magnets 23 and 24 in a direction orthogonal to the optical axis.
Is wider than the width of the electrodes 21 and 22 in the direction orthogonal to the optical axis.
Comb. The permanent magnet 23 provided on the back of the cathode electrode 21 is attached to the insulating material 3. The cathode electrode 21 is connected to a high voltage circuit by the cathode wire 4 and the anode electrode 2
2 is grounded (earthed) by an anode return wire 5. The permanent magnets 23 and 24 face each other with different magnetic poles across the electrodes 21 and 22. Here, the permanent magnet 2
Numeral 3 indicates that the cathode electrode 21 has an N pole and the permanent magnet 24 has an anode electrode 22 which has an S pole.

The operation and effect of the second embodiment will be described. The operation in this case is the same as that of the first embodiment, but compared to the first embodiment, the electrodes 21 and 22 are made of a different material from the permanent magnets 23 and 24, so that the electrodes 21 and 22 and the magnet 2
The durability of 3, 24 can be improved. Further, since the electrodes 21 and 22 are paramagnetic substances, their presence hardly affects the magnetic field distribution. Therefore, the electrodes 21 and 22
The change in the electrode shape due to the exhaustion of the magnetic field hardly affects the magnetic field distribution. As also illustrated in this second embodiment, the magnetic pole (permanent
Since the width of the magnets 23 and 24) is wider than the width of the paramagnetic electrodes 21 and 22 , the width of the magnetic force at the width direction end of the magnetic pole is increased.
And the discharge electrode part has a small spread magnetic field.
Since it can be placed in a uniform and parallel magnetic field having a line of force, the beam shape is more stable than in the second embodiment. Opposite to each other on the back surfaces of the electrodes 21 and 22
The permanent magnets 23 and 24 were installed with their magnetic poles facing each other.
The magnetic force line at the center in the width direction of the magnet is substantially linear
The charged particles are almost straight along the lines of magnetic force
Moving, and the spread of the discharge width is reliably and accurately suppressed.
Wear.

FIG. 5 is an enlarged schematic view of the electrode portion of the third embodiment. In FIG. 5, electrodes 31 and 32 are made of a ferromagnetic metal such as nickel, cobalt or iron or a ferromagnetic metal of an alloy thereof, are formed to face each other, and permanent magnets 33 and 34 are provided behind these electrodes 31 and 32. I have. Between electrodes 31 and 32
Has an optical axis in a direction orthogonal to the discharge direction of
The width of the permanent magnets 33 and 34 in the direction perpendicular to the optical axis is
Wider than the width of the electrodes 31 and 32 in the direction orthogonal to
You. The permanent magnet 33 provided behind the cathode electrode 31 is made of an insulating material 3
It is attached to. The cathode wire 35 through which the discharge current flows to the cathode electrode 31 is a magnet material or a ferromagnetic material, while the anode return wire 36 to the anode electrode 32 is also a magnet material or a ferromagnetic material. It is connected to a capacitor 37. Also, the permanent magnet 33,
Numeral 34 faces the electrodes 31 and 32 with different magnetic poles. Here, the permanent magnet 33 is the cathode electrode 3
One side is an N pole, and the permanent magnet 34 is an S pole on the anode electrode 32 side.

The operation and effect of the third embodiment will be described. In this case, since the cathode wire 35 and the anode return wire 36 form a magnetic path, the leakage magnetic flux is reduced, and the cathode wire 35 and the anode return wire 36 reduce the magnetic field so that the gap length at the end of the magnetic path is shortened. Since the path is formed, the intensity of the magnetic field formed in the discharge region between the electrodes 31 and 32 is further increased, the disturbance of the magnetic field is reduced, and the beam stability is further improved.

[Brief description of the drawings]

FIG. 1 is an enlarged schematic view of an electrode section of a first embodiment.

FIG. 2 is an explanatory diagram of a spiral motion of electrons and ions in a uniform magnetic field used in the embodiment.

FIG. 3 is an explanatory diagram of E × B drift movement of electrons and ions in a uniform magnetic field used in the embodiment.

FIG. 4 is an enlarged schematic view of an electrode section of a second embodiment.

FIG. 5 is an enlarged schematic view of an electrode section of a third embodiment.

FIG. 6 is a schematic diagram of a conventional discharge excitation laser device.

[Explanation of symbols]

1, 2, 11, 12, 21, 22, 31, 32, 41,
42: electrode, 3: insulating material, 4, 35: cathode wire:
5, 36: anode return wire, 13, 14, 23, 2
4, 33, 34: permanent magnet, 44: coil, 51, 5
2: Electromagnet body.

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01S 3/00-3/0979 H01S 3 / 104,3 / 134 H01S 3/22-3/227

Claims (2)

(57) [Claims] 1. A discharge which excites a laser is orthogonal to an optical axis.
In a discharge excitation laser device having an electrode generated in a direction, a wavelength selection element having an angular dispersion characteristic as a band narrowing element, and opposite magnetic poles are opposed to the back surfaces of the two electrodes.
And a permanent magnet that generates a magnetic field having lines of magnetic force substantially parallel to the discharge direction of the electrodes in the discharge region between the electrodes, and the width of the permanent magnet in a direction orthogonal to the optical axis is the optical axis. A width of the electrode in a direction orthogonal to the width direction of the discharge excitation laser device. 2. A discharge excitation laser device having an electrode for generating a discharge for exciting a laser, comprising: means for generating a magnetic field having lines of magnetic force substantially parallel to a discharge direction of the electrode in a discharge region between the electrodes; A discharge excitation laser device comprising an anode return wire and a cathode wire connected to a peaking capacitor of a discharge circuit made of a permanent magnet material or a ferromagnetic material, and a magnetic path formed by the anode return wire and the cathode wire. .