JP2964202B2 - Excimer laser oscillator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an excimer laser oscillator, and more particularly to an excimer laser oscillator capable of obtaining a laser beam having a uniform beam intensity distribution in a beam cross section.

[0002]

2. Description of the Related Art Generally, an excimer laser oscillator has a shorter upper level lifetime of several nanoseconds and a higher amplification efficiency than other laser oscillators of different types, so that it tends to be multi-mode oscillation. For this reason, the beam cross-sectional intensity of the laser light emitted from the excimer laser oscillator is extremely non-uniform.

For example, a discharge excitation type excimer laser oscillator has a flat-top intensity distribution in the direction of the electrodes and a Gaussian-like intensity distribution in the direction perpendicular to the electrodes.

An outline will be given based on FIGS. 7 to 9. FIG.
FIG. 1 is a schematic perspective view of a general excimer laser oscillator 1. The excimer laser oscillator 1 includes a laser container 2 and light having a total reflection mirror 3 and a partial reflection mirror 4 provided before and after the laser container 2, respectively. And a resonator 5.

[0005] The laser vessel 2 contains a pair of discharge electrodes 6 and a gas medium for laser oscillation, generates plasma by discharge between the discharge electrodes 6, and generates an optical resonator 5.
Causes laser oscillation.

Each of the pair of discharge electrodes 6 has a semicircular cross section so as to generate a discharge state as uniform as possible therebetween, and has a length of 2 L.

As shown in the drawing, the length direction parallel to the top surface 6A of the discharge electrode 6 is defined as the X axis (optical axis), and is within the plane including the pair of discharge electrodes 6 and along the length direction of the discharge electrode 6. The direction passing through the center is defined as the Y axis, and the length direction of the discharge electrode 6 (optical axis,
A direction perpendicular to the X-axis) and the center direction (Y-axis) is defined as a Z-axis.

[0008] Between the discharge electrodes 6, the portion of the top surface 6A is in the best discharge state, so that the beam intensity of the emitted laser light is maximized from this portion. However, the actual beam intensity is measured outside the partial reflecting mirror 4, but for convenience of explanation, it will be described below based on the X axis, Y axis and Z axis.

That is, as shown in FIG.
The beam intensity in the Y plane (the beam intensity as viewed in the X-axis direction by cutting in the XY plane) is the maximum, and the beam intensity gradually weakens as it shifts in the positive and negative directions of Z from here (Gaussian-like). Intensity distribution).

[0010] As shown in FIG. 9, Y is perpendicular to the X axis.
The beam intensity in the Z plane (the beam intensity as viewed in the X-axis direction by cutting along the YZ plane) is the largest at a portion corresponding to the interval 2D between the top surfaces 6A of the discharge electrodes 6, and the positive and negative directions of Y from here. As the beam shifts in the direction, the beam intensity gradually decreases (flat-top intensity distribution).

Therefore, in applying the oscillated laser light to various applications, it is important to make the beam intensity distribution uniform, but the oscillation direction is perpendicular to the direction (the direction between the electrodes and the oscillation direction). Is the vertical direction;
There is a problem that it is difficult to obtain a uniform beam intensity distribution (or flat-top intensity distribution) in the Z-axis direction.

Conventionally, an optical system called a beam homogenizer is provided outside the optical resonator 5 of the excimer laser oscillator 1 in order to eliminate such non-uniform beam intensity.

This beam homogenizer combines a plurality of prisms, reflecting mirrors, lenses, etc., divides a beam into a plurality of beams, and then superimposes the plurality of beams again, and performs an integration effect by the superimposition. The purpose is to make the beam intensity uniform. Such a homogenizer is disclosed in, for example, JP-A-2-323.

As a method of making the beam intensity uniform by reducing the beam divergence angle, a method of devising the configuration of an optical resonator is disclosed in “Laser Research”, October 1991, pages 966 to 969.

An excimer laser oscillator 10 having this configuration shown in FIG. 10 is provided with an optical resonator 12 having a partially reflecting mirror 4 and a prism 11 outside a laser vessel 2.

However, the conventional method has the following problems because the optical system 13 such as a beam homogenizer for equalizing the beam intensity is installed outside the optical resonator 12 of the excimer laser oscillator 10.

That is, since the beams divided into a plurality of beams by the optical system 13 such as a beam homogenizer have different propagation directions, there is a problem that the divergence angle of the beams after superposition increases.

Further, when a plurality of divided beams are superimposed, a range where the beam intensity becomes uniform is narrow in the beam propagation direction, and there is a problem that a uniform intensity distribution is not obtained before and after the range.

Furthermore, the more the beam intensity is to be made uniform, the more the number of divided beams must be increased.
There is a problem that the configuration of the optical system 13 such as a beam homogenizer becomes complicated and that the adjustment is difficult.

Further, since the optical system 13 having a complicated configuration is installed outside the optical resonator 12, there is a problem that the beam propagation efficiency is reduced and the energy of the laser cannot be used effectively.

Particularly, in the excimer laser oscillator 10 shown in FIG. 10, the prism 1 serving as a total reflection mirror is used.
1 is composed of two triangular prisms,
Each surface facing the laser container 2 must be adjusted to one plane, and its size must be adjusted to the width of the beam.

Further, there is a problem that adjustment is very difficult, for example, the optical axis must coincide with the boundary between the two triangular prisms.

This configuration is equivalent to a configuration in which two independent optical resonators are juxtaposed, and there is a problem that it is very difficult to make the beam intensity uniform over the entire beam.

[0024]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has an optical resonator having a simple structure, easy to adjust, and capable of equalizing beam intensity. It is an object of the present invention to provide an excimer laser oscillator.

[0025]

That is, the present invention focuses on devising a position for disposing a prism.
An excimer laser oscillator having an optical resonator including a total reflection mirror and a partial reflection mirror, wherein a prism is disposed on an optical path in the optical resonator.

The prism can be arranged at a position separated from the total reflection mirror by a predetermined distance.

The prism can be formed in a pyramid shape or a conical shape.

The prism is perpendicular to a plane including a pair of discharge electrodes (a plane including the Y-axis direction) between the optical resonators and parallel to an optical axis of the optical resonators. This can be arranged at right angles (in the Z-axis direction) to the optical axis (in the X-axis direction).

The prism is perpendicular to the plane including the pair of discharge electrodes (the plane including the Y-axis direction) between the optical resonators and parallel to the optical axis (the X-axis direction).
And the incident surface thereof can be arranged at right angles to the optical axis of the optical resonator (in the Z-axis direction).

The prism may have a vertex located on the side of the total reflection mirror.

[0031]

In the excimer laser oscillator according to the present invention, since the prism is arranged on the optical path in the optical resonator,
The above-mentioned problems caused by installing an optical system such as a beam homogenizer outside the optical resonator can be eliminated, and the beam intensity in the direction perpendicular to the discharge electrode is made uniform by the refraction of laser light by the prism. It is possible.

In particular, by making the prism conical, the beam intensity in all directions in a plane perpendicular to the optical axis can be made uniform.

[0033]

Next, an excimer laser oscillator 20 according to a first embodiment of the present invention will be described with reference to the drawings. However, in the following description, the same parts as those in FIGS. 7 to 10 are denoted by the same reference numerals, and the detailed description thereof will be omitted.

FIG. 1 shows the above-described excimer laser oscillator 20.
FIG. 8 is a schematic configuration diagram showing
It is the figure seen from the axial direction. This excimer laser oscillator 20 has a laser container 2, an optical resonator 5 having a total reflection mirror 3 and a partial reflection mirror 4, and a prism 21.

The prism 21 includes an incident surface 21A perpendicular to the optical axis, a vertex 21B, inclined surfaces 21C and 21D opposed to the incident surface 21A at a predetermined angle, and both side surfaces 21E parallel to the optical axis. It has a prismatic shape (triangular prism), for example, and is provided between the laser container 2 and the total reflection mirror 3 at a position separated from the total reflection mirror 3 by a predetermined distance.

The predetermined distance indicates a position where the beam intensity becomes the most uniform because the beam intensity changes when the prism 21 is moved.

The prism 21 is arranged in a direction parallel to the Z axis (perpendicular to the optical axis of the optical resonator 5) and in a plane (XY plane) including the discharge electrode 6. The incident surface 21A is directed at right angles to the light source, and the apex 21B is directed toward the total reflection mirror 3 side.

Various shapes can be adopted as the shape of the prism in the present invention. For example, the prism 22 shown in FIG. 2 includes an incident surface 22A perpendicular to the optical axis and a vertex angle portion 22A.
B and a slope 22C facing the incident surface 22A at a predetermined angle.
And a slope 22D, a left side 22E and a right side 22F parallel to the optical axis, and an upper surface 22G and a lower surface 2 parallel to the optical axis.
It is a pentagonal prism having 2H.

The prism 23 shown in FIG. 3 has an incident surface 23A perpendicular to the optical axis, an apex 23B, and a slope 23C, a slope 23D, and a slope 23E that face the incidence surface 23A at a predetermined angle.
And a slope 23F, a left side 23G and a right side 23H parallel to the optical axis, and an upper surface 23I and a lower surface 2 parallel to the optical axis.
It is a pentagonal prism having 3J. The slope 23C, the slope 23D, the slope 23E, and the slope 23F form a quadrangular pyramid.

Hereinafter, the operation of the excimer laser oscillator 20 will be described. The beam emitted from the laser container 2 enters the prism 21. The incident beam is deflected by the prism 21 in two directions. That is, the upper beam is deflected downward and the lower beam is deflected upward from the optical axis.

The deflected light is reflected by the total reflection mirror 3, is deflected again by the prism 21, and is emitted as a beam parallel to the optical axis through the partial reflection mirror 4.

Since the beam deflected by the prism 21 converges on the surface of the total reflection mirror 3,
The total reflection mirror 3 can be made smaller than conventional ones.

More specifically, a beam generated at a point P1 far from the optical axis and a point Q1 near the optical axis is closer to the optical axis by the prism 21 and the total reflection mirror 3, respectively. It passes through the point P2 and the point Q2 far from the optical axis.

That is, in the arrangement orientation of the illustrated prism, that is, in the Z-axis direction, the beam generated at the center with respect to the optical axis moves to the outer periphery, and the beam generated at the outer periphery moves to the center.

Such a movement is repeatedly performed between the partial reflecting mirror 4 and the total reflecting mirror 3, so that a kind of superposition is performed, and a part thereof becomes an output beam. This beam has a uniform beam intensity due to the superposition of the laser beams in the Z-axis direction.

Although all the surfaces of the prism 21 are formed as flat surfaces, for example, the inclined surfaces 22C and 22D of the prism 22 shown in FIG. 2 are formed into curved surfaces such as spherical surfaces or aspherical surfaces excluding flat surfaces. The lens, the slope 23C, the slope 23D, and the slope 23E of the prism 23 shown in FIG.
And a slope 23F, spherical, or lenses with curved surfaces, such as aspheric excluding plane may also be used.

For example, FIG. 4 shows still another example of the prism according to the present invention, in which the prism is a conical prism 24.

The prism 24 shown in FIG. 4 has an incident surface 24A perpendicular to the optical axis, a vertex 24B, a conical slope 24C facing the incident surface 24A at a predetermined angle, and a circle parallel to the optical axis. And a peripheral surface 24D.

When such a prism 24 is used, the plane on which the beam intensity is made uniform is defined by the above-described prisms 21, 22,.
23, it is possible not only to make the beam intensity uniform in the Z-axis direction without depending on the number of the slopes, but also in the direction around the X-axis (optical axis), that is, 360 degrees around the optical axis. By superimposing laser beams in all directions, uniformity in all directions can be achieved.

Accordingly, the discharge state becomes non-uniform due to dust on the discharge electrode 6 or slight displacement thereof, distortion of each component due to heat generated by laser oscillation, etc., and non-uniformity of the beam intensity due to this discharge state. Even if it occurs, it is possible to properly equalize it.

FIG. 5 shows an excimer laser oscillator 30 according to a second embodiment of the present invention. The prism 21 is attached to a prism moving mechanism 31.

The prism moving mechanism 31 includes a uniaxial stage fixing section 32, a uniaxial stage moving section 33, a holder fixing section 34, a prism moving section 35, and a tilt adjusting screw 36.
And

The uniaxial stage movable section 33 is attached to the uniaxial stage fixing section 32 so as to be movable along the optical path, and the holder fixing section 34 is fixed on the uniaxial stage movable section 33.

The prism movable section 35 is
To be able to move vertically with respect to the optical path.

The prism 21 is held by the prism movable section 35, and the optical axis of the prism 21 and the laser beam are made parallel by adjusting the inclination adjusting screw 36.

One of the important factors in the present invention is the distance between the total reflection mirror 3 and the prism 21. That is, the beam intensity when the beams are superimposed is governed by the distance between the total reflection mirror 3 and the prism 21.

FIG. 6A shows an example of the relationship between the distance between the total reflection mirror 3 and the prism 21 and the beam intensity.
(B), (c) and (d) show. In FIG. 6, FIG.
9, the vertical axis indicates the beam intensity, and the horizontal axis indicates the cross-sectional position in the direction perpendicular to the discharge electrode 6 (the Z-axis direction in FIG. 7). Corner 2
1A) is 5.5 mm, and FIG.
The case of 7.0 mm is shown in (b), the case of 9.0 mm is shown in (c), and the case of 11.0 mm is shown in (d).

As is apparent from FIG. 6, when the distance between the total reflection mirror 3 and the prism 21 is short, a Gaussian-like beam cross-sectional intensity distribution is exhibited as shown in FIG. As the distance from the reflecting mirror 3 increases, the distribution changes to a uniform distribution as shown in FIG. Eventually, the distribution is no longer uniform and changes to a complicated distribution depending on the shape of the prism 21.

As described above, the superposed beam intensity distribution depends on the distance between the total reflection mirror 3 and the prism 21. Therefore, when a uniform beam is required, the above-described uniaxial stage movable section 33 is moved to set the distance between the total reflection mirror 3 and the prism 21 to a predetermined distance (9.0 mm in the example shown in FIG. 6). ).

When a beam having a uniform distribution is not required, a beam having an arbitrary beam width can be obtained by moving the uniaxial stage movable portion 33 with respect to the total reflection mirror 3.

If the optical axis shifts due to mechanical backlash or the like due to the movement of the prism 21, it can be adjusted by using the tilt adjusting screw 36.

In the above embodiment, the laser container 2
The description has been given of the so-called external resonator type in which the optical resonator 5 is provided on the outside of the laser cavity.

Further, instead of moving the prism 21, the total reflection mirror 3 can be moved.

Further, the prism 21 or the total reflection mirror 3
Is not limited to the above-described embodiment, and at least the prism 21 and the total reflection mirror 3 are moved.
It is sufficient if any one of them can be moved along the optical path.

For example, the prism 21 may be attached to the total reflection mirror 3 or the laser container 2 so as to be movable along the optical path.

The above-described prisms 21, 22, 23,
It is preferable to apply an anti-reflection coating to the 24 beam passage surfaces.

[0067]

As described above, according to the present invention, by arranging the prism before the total reflection mirror of the optical resonator of the excimer laser oscillator, the beam intensity of the beam emitted from the excimer laser oscillator is made uniform. be able to.

[0068]

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an excimer laser oscillator 20 according to a first embodiment of the present invention.

FIG. 2 is a front view and a right side view showing an example (prism 22) of a modification of the prism.

FIGS. 3A and 3B are a front view and a right side view showing another modification example of the prism (prism 23). FIGS.

FIG. 4 is a front view and a right side view showing still another example of the prism deformation (conical prism 24).

FIG. 5 is a schematic configuration diagram showing an excimer laser oscillator 30 according to a second embodiment of the present invention.

FIG. 6 is a graph showing the relationship between the distance between the total reflection mirror 3 and the prism 21 of the excimer laser oscillator and the beam intensity.

FIG. 7 is a schematic perspective view of a conventional excimer laser oscillator 1.

FIG. 8 is a graph of the beam intensity on the XY plane in the Z-axis direction.

FIG. 9 is a graph of the beam intensity on the YZ plane in the X-axis direction.

FIG. 10 is a configuration diagram of a conventional excimer laser oscillator 1 capable of equalizing the beam intensity of an output beam.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 excimer laser oscillator 2 laser container 3 total reflection mirror 4 partial reflection mirror 5 optical resonator 6 pair of discharge electrodes 6A top surface of pair of discharge electrodes 6 10 excimer laser oscillator 11 prism 12 optical resonator 13 optical system such as beam homogenizer Reference Signs List 20 excimer laser oscillator 21 prism 21A incident surface of prism 21 perpendicular to optical axis 21B apex 21C, 21D inclined surface facing prism 21A at predetermined angle 21E both sides parallel to optical axis 22 prism 22A Incident surface 22B perpendicular to optical axis 22B Vertex angle 22C, 22D Inclined surface 22E, 22F facing incident surface 22A at a predetermined angle Left and right surfaces parallel to optical axis 22G, 22H Upper and lower surfaces parallel to optical axis 23 Prism 23A Incident surface perpendicular to optical axis 23B Apex portion 23C, 23D, 23 E, 23F Inclined surface facing the incident surface 23A at a predetermined angle 23G, 23H Left and right surfaces parallel to the optical axis 23I, 23J Upper and lower surfaces parallel to the optical axis 24 Prism 24A Incident surface 24B perpendicular to the optical axis Corner 24C Conical slope facing the incident surface 24A at a predetermined angle 24D Circumferential surface parallel to the optical axis 30 Excimer laser oscillator 31 Prism moving mechanism 32 Uniaxial stage fixing part 33 Uniaxial stage movable part 34 Holder fixing part 35 Prism Movable part 36 Tilt adjusting screw 2L Length of discharge electrode 6 2D Distance between top surfaces 6A of discharge electrode 6 P1, Q2 Point far from optical axis P2, Q1 Point near optical axis

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01S 3/08 H01S 3/034

Claims (5)

(57) [Claims] 1. A laser container and a pair of parallel discharge electrodes housed in the laser container.
And poles, and an optical resonator having a single total reflection mirror and a single partially reflecting mirror provided respectively before and after the laser container, which has a pair of discharge electrodes, between the optical resonator On the optical axis
A excimer laser oscillator arranged so as to lie parallel, predetermined from Oite the total reflection mirror on the optical path within the optical resonator
At the distance of
With placing a single prism toward the mirror side, the entrance surface of the prism, the upper and lower sides of the pair of discharge electrodes
At right angles to a plane containing the center of the
This was placed at right angles to the optical axis, and further the total
The reflecting mirror, the partial reflecting mirror and the prism are
With respect to the plane including the vertical center of the pair of discharge electrodes
Excimer laser oscillators , each of which is symmetric . 2. The excimer laser oscillator according to claim 1, wherein said prism has a pyramid shape. 3. An excimer laser oscillator according to claim 1, wherein said prism has a conical shape. 4. A laser container and a pair of parallel discharge electrodes housed in the laser container.
Poles and total reflection mirrors provided before and after this laser vessel.
And an optical resonator having a partial reflecting mirror, and the pair of discharge electrodes is disposed between the optical resonator and an optical axis thereof.
Excimer lasers arranged so that they are located in parallel
An oscillator, which is provided on the optical path in the optical resonator by a predetermined
When a pyramid-shaped prism is placed at a distance of
In both cases, the entrance surface of this prism is above and below the pair of discharge electrodes.
At right angles to a plane containing the center of the
An excimer laser oscillator characterized in that it is arranged at right angles to the optical axis . 5. A laser container and a pair of mutually parallel discharge electrodes housed in the laser container.
Poles and total reflection mirrors provided before and after this laser vessel.
And an optical resonator having a partial reflecting mirror, and the pair of discharge electrodes is disposed between the optical resonator and an optical axis thereof.
Excimer lasers arranged so that they are located in parallel
An oscillator, which is provided on the optical path in the optical resonator by a predetermined amount from the total reflection mirror;
When a conical prism is placed at a distance of
In both cases, the entrance surface of this prism is above and below the pair of discharge electrodes.
At right angles to a plane containing the center of the
An excimer laser oscillator characterized in that it is arranged at right angles to the optical axis .