JP4358052B2 - Grating attitude control device - Google Patents

Description

  The present invention relates to a grating attitude control device that controls the attitude of an echelle grating used for wavelength selection of a laser device and matches the optical axis of incident light with the optical axis of reflected light.

  As a light source of the semiconductor exposure apparatus, an ultraviolet laser apparatus such as a narrow band excimer laser apparatus, a line select fluorine molecular laser apparatus, or a narrow band fluorine laser apparatus is used.

FIG. 1 is a diagram showing a configuration of a narrow-band excimer laser device.
The laser chamber 1 is metallic, and a laser gas serving as a laser medium is sealed inside. The laser gas is mainly composed of a gas such as a halogen gas, a buffer gas, or a rare gas. Fluorine gas (F2) is used as the halogen gas, and neon gas (Ne) is used as the buffer gas. In the case of a KrF excimer laser, krypton (Kr) is used as a rare gas, and in the case of an ArF excimer laser, argon (Ar) is used as a rare gas. A pair of discharge electrodes 3 facing each other is provided inside the laser chamber 1, and a high voltage pulse power source is provided outside. In FIG. 1, the pair of discharge electrodes 3 are arranged to face each other in the direction orthogonal to the drawing, and the high voltage pulse power source is not shown.

  In this specification, the opposing direction of the pair of discharge electrodes 3 is referred to as a vertical direction, and the direction orthogonal to the vertical direction is referred to as a horizontal direction. In FIG. 1, the direction orthogonal to the drawing is the vertical direction, and the direction parallel to the drawing is the horizontal direction. A plane parallel to the vertical direction is called a vertical plane, and a plane parallel to the horizontal direction is called a horizontal plane.

  CaF 2 windows 4 and 5 are provided on both sides (left and right in the drawing) of the laser chamber 1. On the optical axis on the window 4 side, a grating 26 having one or more (one in FIG. 1) prisms 25 and a diffraction surface 26a formed with a plurality of grooves parallel to each other is provided. Since the prism 25 has a function of expanding light emitted from the laser chamber 1 in a specific direction, it is also called a beam expander. The grating 26 includes a plurality of diffraction grooves parallel to each other and a reflection surface formed for each of these diffraction grooves in the diffraction surface 26a. Such a grating 26 is called an echelle grating. The grating 26 has a function of reflecting light incident on the diffraction surface 26a in a direction corresponding to the wavelength. In other words, the grating 26 reflects light having a wavelength within a specific narrow band in a specific direction. According to such a configuration, only the light having a wavelength within a specific narrow band of the light emitted from the laser chamber 1 returns to the laser chamber 1 side again, and the prism 25 and the grating 26 are referred to as a narrow band element. A monitor box 8 incorporating a front mirror 7 is provided on the optical axis on the window 5 side. The prism 25, the grating 26, and the front mirror 7 constitute an optical resonator.

  Usually, the band narrowing elements such as the prism 25 and the grating 26 are included in the housing 20. This unit is referred to as a narrowband module 2. In the narrow-band module 2, the inside of the housing is purged with dry clean nitrogen gas or rare gas in order to discharge the dust that causes damage to each optical element and the oxygen that generates ozone from the housing. The

  Here, the operation of the narrow-band excimer laser device will be described with reference to FIG. When a current is supplied to the pair of discharge electrodes 3 from a high voltage pulse power source (not shown) and the voltage between the discharge electrodes 3 exceeds the breakdown voltage, a discharge occurs between the discharge electrodes 3 in the laser chamber 1. The laser gas is excited by this discharge, and light is generated when the state further shifts to the ground state. The light transmitted through the window 4 enters the prism 25. In the prism 25, the width of light is expanded in a predetermined direction. The light emitted from the prism 25 enters the diffraction surface 26 a of the grating 26. Of the light incident on the diffraction surface 26 a, only light having a wavelength within a specific narrow band is reflected to the laser chamber 1 side via the prism 25. The light that has returned to the laser chamber 1 passes through the window 5, enters the front mirror 7, and is reflected toward the laser chamber 1 side. Thus, the light reciprocates between the grating 26 and the front mirror 7 a plurality of times through the laser chamber 1. Meanwhile, the energy of the light having a wavelength in the specific narrow band is amplified, and when the energy reaches a certain level, the laser light is emitted from the front mirror 7.

  As disclosed in Patent Document 1 below, when the angle formed by the prism and the optical axis is changed in the horizontal plane, the angle formed by the diffraction surface of the grating and the optical axis changes, and as a result, the laser beam emitted from the front mirror is changed. Wavelength changes. Further, even if the angle of the grating itself is changed in the horizontal plane, the angle formed by the diffraction surface of the grating and the optical axis changes, so that the same result can be obtained. Further, as disclosed in Patent Document 2, the light emitted from the prism is reflected by the high reflection mirror and is incident on the grating, and the angle between the high reflection mirror and the optical axis is changed in the horizontal plane. However, since the angle between the diffraction surface of the grating and the optical axis changes, the same result can be obtained. Patent Document 2 discloses a narrowband module having a plurality of prisms.

  As described so far, wavelength selection is performed using the grating 26 in the narrow-band excimer laser device. What is important in this wavelength selection is that the grating 26 maintains an appropriate posture, and light is appropriately incident on the diffraction surface 26 a of the grating 26. One means for controlling the attitude of the grating 26 is a method of controlling the angle between the grating 26 and the optical axis in the above-described horizontal plane to obtain a desired angle. Another method is to control the angle between the grating 26 and the optical axis in the vertical plane. This control is performed by a grating attitude control device described below.

  5A is a plan view of a conventional grating angle control device, FIG. 5B is a front view of the conventional grating angle control device, and FIG. 5C is a side view of the conventional grating angle control device. FIG. 5A to 5C, the chain line indicates the edge in the range where the laser beam exists.

  In FIG. 5, of the two directions orthogonal to the diffraction surface 26a, the light incident side is referred to as the front, and the opposite direction is referred to as the rear. In the drawing, the downward direction of FIG. 5 (a), the forward direction of FIG. 5 (b) and the right direction of FIG. 5 (c) are the front, the upward direction of FIG. 5 (a), and FIG. ) In the drawing back direction and the left direction in FIG. Of the two directions parallel to the diffraction groove 26 b of the grating 26, the direction from the center of the grating 26 toward the upper surface of the grating 26 is referred to as “upward”, and the direction toward the bottom surface of the grating 26 is referred to as “downward”. Speaking of the drawings, the forward direction of FIG. 5A, the upward direction of FIG. 5B and FIG. 5C are the upper direction, the backward direction of FIG. 5A, FIG. 5B and FIG. The downward direction in FIG. 5C is downward. The front and rear defined here are parallel to the horizontal plane, and the upper and lower sides are parallel to the vertical plane.

  The bottom surface of the grating 26 is attached to the surface of the fixed plate 61. The back surface of the fixed plate 61 faces the surface of the pedestal 66. Two spherical bodies 62 and 63 and an elastic body 67 are provided between the back surface of the fixed plate 61 and the surface of the pedestal 66. The two spheres 62 and 63 are arranged on a straight line parallel to the diffractive surface 26 a, and abut the back surface of the fixed plate 61 and the surface of the pedestal 66. A straight line where the two spheres 62 and 63 exist, that is, a straight line connecting the centers of the spheres 62 and 63 becomes the rotation axis 69 of the grating 26. The elastic body 67 is attached to the back surface of the fixed plate 61 and the surface of the pedestal 66. The elastic body 67 is disposed behind the rotation shaft 69.

  The elastic body 67 may be any elastic material such as a leaf spring, a spring, or rubber. However, since there is a possibility of irradiation with scattered ultraviolet rays, a material that does not easily deteriorate in an ultraviolet irradiation environment is desirable. The elastic body 67 attracts the fixing plate 61 and the pedestal 66. That is, as shown in FIGS. 5B and 5C, when the fixing plate 61 and the pedestal 66 are separated, the spring is in an extended state, and the fixing plate 61 is attracted to the pedestal 66 side. The same applies to leaf springs and rubber.

  The pedestal 66 is provided with a screw 68 screwed from the back side. The tip of the screw 68 passes through the pedestal 66 and contacts the back surface of the fixing plate 61. The screw 68 can be displaced upward or downward by applying a rotational motion.

  When the screw 68 is displaced upward, the elastic body 67 is extended, and the fixing plate 61 and the grating 26 are inclined forward. When the screw 68 is displaced downward, the elastic body 67 is contracted, and the fixing plate 61 and the grating 26 are inclined rearward. For example, as shown in FIG. 5C, when the diffraction surface 26a ′ and the optical axis of the incident light are not orthogonal to each other when the grating 26 is viewed from the side, the fixing plate 61 and the grating 26 are inclined forward by the screw 68. Is done.

Thus, the conventional grating attitude control device corrects the angle of the diffractive surface 26 so that the optical axis of the incident light coincides with the optical axis of the reflected light.
Japanese Patent No. 2631554 (FIG. 2) JP-A-5-283785 (FIG. 6)

  However, the conventional grating angle correction device has a problem.

FIG. 6 is an enlarged view showing a plan view of the diffraction surface of the grating.
As described above, the diffractive surface 26a of the echelle grating 26 looks planar to the naked eye, but is actually very fine and has a number of diffraction grooves 26b parallel to each other. A reflective surface 26c is formed in each diffraction groove 26b. Each reflecting surface 26c is a flat surface and faces the same direction.

  An arrow L in FIG. 6 indicates a substantially parallel laser beam incident on each diffraction surface 26a. These laser beams are reflected by each reflecting surface 26c. The reflected light interferes and strengthens, and as a result, only light within a specific narrow wavelength band is reflected in the direction opposite to the traveling direction of the incident light. If the angle of the grating 26 is appropriately corrected, the optical axes of the incident light and the reflected light coincide.

  Here, as shown in FIG. 5C, it is assumed that the diffraction surface 26a 'and the optical axis of the incident light are not orthogonal to each other when the grating 26 is viewed from the side. In such a case, the optical axis of incident light and the optical axis of reflected light do not coincide. Therefore, as shown in FIG. 7, it is assumed that the posture is corrected by inclining the grating 26 with the rotation shaft 69 as the rotation center. The state of the reflecting surface 26c before and after the grating inclination will be described with reference to FIGS.

  FIG. 8A is a plan view of the reflecting surface, and FIG. 8B is a side view of the reflecting surface. Similarly, FIG. 9A is a plan view of the reflecting surface, and FIG. 9B is a side view of the reflecting surface. FIG. 8 shows a state before the posture of the grating 26 is corrected, and FIG. 9 shows a state after the posture of the grating 26 is corrected.

  As shown in FIG. 8A, before correction, the optical axis of the incident light and the optical axis of the reflected light coincide in the horizontal plane, but in the vertical plane as shown in FIG. 8B. The optical axis of incident light and the optical axis of reflected light are different. In order to make the optical axis of the incident light and the optical axis of the reflected light coincide with each other in the vertical plane, the screw 68 is displaced upward, and the fixing plate 61 and the grating 26 are inclined forward about the rotation shaft 69 as the rotation center. . As a result, as shown in FIG. 9B, the optical axis of the incident light and the optical axis of the reflected light may coincide with each other in the vertical plane. However, as shown in FIG. Then, the optical axis of incident light and the optical axis of reflected light do not coincide.

This is because the rotation axis 69 is used to correct the incident light so that it enters the reflecting surface 26c perpendicularly. When the grating 26 is inclined with the rotation axis 69 as the rotation center, the angles of the horizontal and vertical surfaces of the reflection surface 26c change simultaneously. Accordingly, the result shown in FIG. 9A is obtained, and a problem that the posture of the grating cannot be corrected appropriately occurs.
In addition, there is a problem that the correction amount in the vertical plane with respect to the displacement amount of the screw 68 is small.

  The present invention has been made in view of such a situation, and an object of the present invention is to correctly control the attitude of the grating by changing the angle of the reflecting surface of the grating only in the vertical plane.

The present invention
An echelle grating including a plurality of parallel diffractive grooves and reflecting surfaces formed in the diffractive grooves, respectively, and the attitude of the grating is controlled by rotating the echelle grating around a predetermined rotation axis. A grating attitude control device comprising attitude control means;
The rotation axis is characterized by being coincident with or parallel to a straight line orthogonal to the diffraction groove and parallel to the reflecting surface.

  In the present invention, the rotation axis of the echelle grating coincides with or is parallel to a straight line that is orthogonal to the plurality of diffraction grooves and parallel to the reflecting surface formed in each of the plurality of diffraction grooves. By setting such a rotation axis, the angle of the reflecting surface changes only in the vertical plane without changing in the horizontal plane.

  According to the present invention, the angle of the reflecting surface can be changed only in the vertical plane, and the attitude of the grating can be controlled correctly.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
2A is a plan view of the grating attitude control device according to this embodiment, FIG. 2B is a front view of the grating attitude control device according to this embodiment, and FIG. It is a side view of the attitude control device of the grating according to the present embodiment. 2A to 2C, the chain line indicates the edge in the range where the laser beam exists.

  In FIG. 2, of the two directions orthogonal to the reflecting surface 26c, the light incident side is referred to as the front, and the opposite direction is referred to as the rear. In the drawing, the lower left direction in FIG. 2A, the left front direction in FIG. 2B and the right front direction in FIG. 2C are the front, the upper right direction in FIG. The back right direction of the drawing in FIG. 2B and the back left direction of the drawing in FIG. Of the two directions parallel to the diffraction groove 26 b of the grating 26, the direction from the center of the grating 26 toward the upper surface of the grating 26 is referred to as “upward”, and the direction toward the bottom surface of the grating 26 is referred to as “downward”. Speaking of the drawings, the forward direction of FIG. 2 (a), the upward direction of FIG. 2 (b) and FIG. 2 (c) are upward, the backward direction of FIG. 2 (a), FIG. 2 (b) and FIG. The downward direction in FIG. The front and rear defined here are parallel to the horizontal plane, and the upper and lower sides are parallel to the vertical plane.

  The difference between the grating posture control device of the present embodiment and the conventional one is the arrangement of the spheres 42 and 43, the elastic body 47 and the screw 48, and the position of the rotating shaft 49 realized by this arrangement.

  The bottom surface of the grating 26 is attached to the surface of the fixed plate 41. The back surface of the fixed plate 41 faces the surface of the pedestal 46. Two spherical bodies 42 and 43 and an elastic body 47 are provided between the back surface of the fixed plate 41 and the surface of the pedestal 46. The two spheres 42 and 43 are arranged on a straight line parallel to the reflecting surface 26 c, and abut the back surface of the fixed plate 41 and the surface of the pedestal 46. A straight line where the two spheres 42 and 43 exist, that is, a straight line connecting the centers of the spheres 42 and 43 becomes the rotation axis 49 of the grating 26. In the horizontal plane (FIG. 2A), the rotation axis 49 is orthogonal to the optical axis. The elastic body 47 is attached to the back surface of the fixed plate 41 and the surface of the pedestal 46. The elastic body 47 is disposed behind the rotation shaft 49.

  The elastic body 47 may be any elastic material such as a leaf spring, a spring, or rubber. However, since there is a possibility of irradiation with scattered ultraviolet rays, a material that does not easily deteriorate in an ultraviolet irradiation environment is desirable. The elastic body 47 attracts the fixing plate 41 and the base 46. That is, as shown in FIGS. 2B and 2C, when the fixing plate 41 and the pedestal 46 are separated, the spring is in an extended state, and the fixing plate 41 is attracted to the pedestal 46 side. The same applies to leaf springs and rubber.

  The pedestal 46 is provided with a screw 48 screwed from the back side. The tip of the screw 48 passes through the base 46 and comes into contact with the back surface of the fixing plate 41. The screw 48 can be displaced upward or downward by applying a rotational motion. Further, instead of the screw 48, it is also possible to use an actuator that can move in two opposing directions, such as a micrometer.

  When the screw 48 is displaced upward, the elastic body 47 is extended, and the fixing plate 41 and the grating 26 are inclined forward. When the screw 48 is displaced downward, the elastic body 47 is contracted, and the fixing plate 41 and the grating 26 are inclined rearward. For example, as shown in FIG. 2C, when the diffraction surface 26 a ′ and the optical axis of the incident light are not orthogonal to each other when the grating 26 is viewed from the side, the fixing plate 41 and the grating 26 are inclined forward by the screw 48. Is done.

  Here, as shown in FIG. 2C, it is assumed that the diffraction surface 26a 'and the optical axis of the incident light are not orthogonal to each other when the grating 26 is viewed from the side. In such a case, the optical axis of incident light and the optical axis of reflected light do not coincide. Therefore, as shown in FIG. 3, it is assumed that the posture is corrected by inclining the grating 26 with the rotation shaft 49 as the rotation center. The state of the reflecting surface 26c before and after the grating inclination will be described with reference to FIGS.

  4A is a plan view of the reflecting surface, and FIG. 4B is a side view of the reflecting surface. FIG. 4 shows a state after the posture of the grating 26 is corrected.

  As shown in FIG. 8A, before correction, the optical axis of the incident light and the optical axis of the reflected light coincide in the horizontal plane, but in the vertical plane as shown in FIG. 8B. The optical axis of incident light and the optical axis of reflected light are different. In order to make the optical axis of the incident light and the optical axis of the reflected light coincide with each other in the vertical plane, the screw 48 is displaced upward, and the fixing plate 41 and the grating 26 are inclined forward about the rotation shaft 49 as the rotation center. . As a result, as shown in FIG. 4B, the optical axis of the incident light coincides with the optical axis of the reflected light in the vertical plane. Further, as shown in FIG. 4A, the angle of the reflecting surface 26c does not change in the horizontal plane, so that the optical axis of the incident light and the optical axis of the reflected light are kept in agreement.

  In this embodiment, the attitude of the grating 26 is controlled by the spheres 42 and 43, the elastic body 47, and the screw 48, but the attitude of the grating 26 may be controlled by another mechanism. In short, the rotational axis of the grating 26 may be coincident with or parallel to a straight line that is orthogonal to the diffraction groove 26b and parallel to the reflecting surface 26c.

  According to this embodiment, the angle of the reflecting surface can be changed only in the vertical plane, and the attitude of the grating can be controlled correctly.

FIG. 1 is a diagram showing a configuration of a narrow-band excimer laser device. 2A is a plan view of the grating attitude control device according to this embodiment, FIG. 2B is a front view of the grating attitude control device according to this embodiment, and FIG. It is a side view of the attitude control device of the grating according to the present embodiment. FIG. 3 is a perspective view of the grating according to the present embodiment. FIG. 4A is a plan view of the reflection surface after posture adjustment of the present embodiment, and FIG. 4B is a side view of the reflection surface after posture adjustment of the present embodiment. 5A is a plan view of a conventional grating posture control device, FIG. 5B is a front view of the conventional grating posture control device, and FIG. 5C is a conventional grating posture control device. It is a side view of an apparatus. FIG. 6 is an enlarged view showing a plan view of the diffraction surface of the grating. FIG. 7 is a perspective view of a conventional grating. FIG. 8A is a plan view of the reflecting surface before posture adjustment, and FIG. 8B is a side view of the reflecting surface before posture adjustment. FIG. 9A is a plan view of the reflection surface after the conventional posture adjustment, and FIG. 9B is a side view of the reflection surface after the conventional posture adjustment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 26 ... Grating 26a ... Diffraction surface 26b ... Diffraction groove 26c ... Reflection surface 41 ... Fixed plate 42, 43 ... Sphere 46 ... Base 47 ... Elastic body 48 ... Screw 49 ... Rotating shaft

Claims (1)

An echelle grating including a plurality of parallel diffractive grooves and reflecting surfaces formed in the diffractive grooves, respectively, and the attitude of the grating is controlled by rotating the echelle grating around a predetermined rotation axis. A grating attitude control device comprising attitude control means;
The grating posture control device characterized in that the rotation axis coincides with or is parallel to a straight line orthogonal to the diffraction groove and parallel to the reflecting surface.

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