JP2010050300A - Excimer laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive and simple excimer laser device with slippage of alignment reduced. <P>SOLUTION: This excimer laser device includes a laser chamber 11, resonators 2 provided on one side of the laser chamber 11 and on the other side opposite to it, a laser gas filled inside the laser chamber 11, a means to excite the laser gas, two optical windows 13 provided in the laser chamber 11 for light generated from the excited laser gas to be emitted to the outside of the laser chamber 11, a cross flow fan 14 to circulate the laser gas, and a vibration absorbing means 40 to support the laser chamber 11, and the vibration absorbing means 40 has an air spring 41 to expand and contract gas by making it flow in and discharging it, and a vessel 42 to regulate horizontal expansion and contraction of the air spring 41. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an excimer laser device, and more particularly to a vibration absorber used in an excimer laser system used as a light source for a semiconductor exposure apparatus.

  FIG. 5 is a diagram showing a conventional general excimer laser system 1 and a resonator 20.

  The laser chamber 11 is used by sealing a laser gas inside the laser chamber 11. In the case of ArF excimer laser, Ar, fluorine, Ne or He, Xe is used, and in the case of KrF excimer laser, Kr, fluorine, Ne or He is used.

  The laser chamber 11 has two electrodes 12 facing each other, and a voltage is applied to one of them to generate a discharge between the two electrodes 12. The light generated by the discharge passes through the optical window 13 as a window, reciprocates between the resonators 20, becomes laser light, passes through the partial reflection mirror 21, and is extracted as output energy.

  At one end of the resonator 20, a partial reflection mirror 21 is housed in a holder and attached to the cavity 22. Further, at the other end of the resonator 20, a box 26 containing a prism 24 for expanding a beam and a diffraction grating 25 for selecting a wavelength is attached to the cavity 22. These cavities 22 are attached to the first surface plate 31.

  When a roller is used for the laser chamber 11, the laser chamber 11 is fixed to the rail or the second surface plate 32 so that the laser chamber 11 does not move by the roller.

  The partial reflection mirror 21, the prism 24, and the diffraction grating 25 are adjusted in advance so that the beam is incident at a predetermined angle. FIG. 6 shows a state in which the light is incident on the partial reflection mirror 21 at a right angle, adjusted to be incident on the prism 24 at θ1 and on the diffraction grating 25 at θ2.

  The laser chamber 11 further includes a cross flow fan 14 for circulating laser gas, and is connected to a motor 15 attached to the laser chamber 11. The cross flow fan 14 is rotated by the motor 15 to circulate the laser gas inside the laser chamber 11.

  The purpose of the laser gas circulation is to perform heat exchange with a radiator (not shown) installed in the laser chamber 11 and to always supply a fresh laser gas between the electrodes 12.

  The cross flow fan 14 rotates to generate vibration. This vibration is caused by the unbalance amount of the cross flow fan.

  The laser chamber 11 is fixed to the second surface plate 32, and the second surface plate 32 is fixed to the first surface plate 31 via the vibration absorbing means 40.

  The vibration generated in the laser chamber 11 propagates to the second surface plate 32, the vibration absorbing means 40, and the first surface plate 31. However, when the vibration absorbing means 40 is present, the propagating vibration is small.

  The propagated vibration displaces the partial reflection mirror 21, the prism 24, and the diffraction grating 25 through the cavity 22 attached to the first surface plate 31. As a result, each incident angle may shift and cause wavelength variation.

  FIG. 6 is a diagram illustrating a relationship between the partial reflection mirror 21, the prism 24, and the diffraction grating 25 in a normal case, and FIG. 7 is a diagram illustrating an example in which the partial reflection mirror 21, the prism 24, and the diffraction grating 25 are displaced.

  Normally, the relationship between the partial reflection mirror 21, the prism 24, and the diffraction grating 25 is adjusted so that light enters at a predetermined incident angle as shown in FIG. However, as shown in FIG. 7, when the partial reflection mirror 21, the prism 24, and the diffraction grating 25 are displaced due to vibration or the like, the respective incident angles change, the wavelength changes, the spectral line width changes, the output The energy was changing.

  Next, the influence of vibration in the MOPA and Injection Lock systems that are becoming mainstream in recent years will be described. FIG. 8 is a diagram showing a system in which two chambers shown in FIG. 5 are arranged. The line width of the laser light is narrowed by the lower chamber 11 (hereinafter referred to as the oscillator chamber) and the resonator 20, and the upper chamber 61 (hereinafter referred to as the injection optical axis in the figure) is passed through several folding mirrors 50. Called the amplifier chamber).

  In the amplifier chamber 61, the laser light rises based on the injected laser light, resonates between the amplifier rear mirror 62 and the amplifier front mirror 63, and is emitted from the amplifier front mirror 63.

  In such a system, it goes without saying that the mirror 21, the prism 24 and the diffraction grating 25 constituting the resonator 20 of each chamber 11, 61 are affected by the vibration of the laser chambers 11, 61. In addition to these, there is also an adverse effect on the folding mirror 50. The injection optical axis is very important for such a system, and when the position and angle of the injection optical axis are shifted, almost all optical quality is deteriorated.

  Therefore, it is very important not to transmit vibration to the folding mirror 50 in such a system.

In recent years, such KrF and ArF excimer laser systems have become mainstream as light sources for semiconductor exposure apparatuses. The performance required for the light source for the exposure apparatus is as shown in the following (1) to (3).

  (1) In order to ensure high dose stability and improve throughput, an output of 20 W or more is required (approximately 40 W or more for KrF and approximately 60 W or more for ArF).

  (2) The NA of the projection lens is being increased to increase the resolution of the projection lens. Along with this, chromatic aberration becomes a problem, and a narrow band is required.

  (3) In order to realize stable exposure, high stabilization of wavelength and output energy is required.

In recent years, light sources for exposure apparatuses adopting the MOPA method (Master Oscillator Power Amplifier) and Injection Lock method (injection locking) are becoming mainstream in order to achieve higher output and narrower bandwidth.

  In the MOPA method or the injection lock method, two or more laser chambers are used, one is used as an oscillation stage, and laser light emitted from the oscillation stage is injected into the amplification stage at a predetermined timing. A narrow band is realized in the oscillation stage, and a high output is realized in the amplification stage.

Compared with conventional laser systems that use only one laser chamber, alignment of the laser optical axis is very important in the MOPA method and the injection lock method. How laser light is injected from the oscillation stage to the amplification stage is particularly important, and it can be said that almost all optical performance changes depending on the injection method. For this reason, the deviation of the optical axis changes the injection method and degrades the optical performance.

  To stabilize the oscillation wavelength and output energy, it is effective to reduce vibration. The vibration generated in the excimer laser system vibrates a partially reflecting mirror, prism, diffraction grating, and slit that are adjusted in advance. This vibration causes a shift in the laser optical axis, causing fluctuations in oscillation wavelength or output energy.

  The fluctuation of the oscillation wavelength occurs when the angle of incidence on the diffraction grating varies due to the deviation of the laser optical axis. It is assumed that the fluctuation of the output energy is caused by the fact that the passing gain region is slightly shifted in addition to the reason of the fluctuation of the oscillation wavelength.

  As described above, the vibration in the excimer laser system greatly affects the stability of the wavelength and the output energy. Therefore, the stability of the wavelength and the output energy has been improved mainly by taking two measures.

  One is to reduce the vibration itself. Vibrations that occur in the excimer laser system and adversely affect the stability of wavelength and output energy are generated in the laser chamber.

  Excimer lasers have a laser chamber that encloses a laser gas. In the laser chamber, two electrodes facing each other, a cross flow fan for circulating the laser gas, a radiator for exchanging heat of the circulating gas, and the like are installed. The cross flow fan is rotated by a motor attached to the chamber.

  The cross flow fan is a rotating body, and it is ideal that the center of gravity exists on the central axis of the cross flow fan, and the cross flow fan is adjusted as such. However, it is impossible to adjust the position of the center of gravity completely on the center axis of the cross flow fan, and a slight unbalance amount is generated. The laser chamber vibrates due to the unbalanced amount and propagates into the laser casing.

  Therefore, reducing the vibration by reducing the unbalance amount as much as possible can be a countermeasure. However, in practice, it is extremely difficult to completely eliminate the unbalance amount. Further, in recent years, as the exposure light source is required to have a high repetition rate, the rotational speed of the cross flow fan has increased. That is, even if the unbalance amount is reduced, the cross flow fan rotates at a rotational speed that exceeds the effect, so that the overall effect is small.

  The second measure is to provide vibration isolation and vibration isolation. Regarding this countermeasure, the following techniques are disclosed.

  First, by arranging a vibration damping member between the chamber that is the excitation source and the holder that holds the optical element that determines the optical performance, the vibration of the laser chamber and the optical element holder is reduced. There is a technique in which a vibration damping member is disposed between them (Patent Document 1).

In addition, an air spring is raised as a vibration absorbing means, and a position detecting means is further added to vibrate between the first surface plate to which the optical system for laser oscillation is fixed and the second surface plate to which the laser chamber is fixed. There is a technique in which an absorbing means is arranged (Patent Document 2).

JP 2003-218432 A JP-A-3-274780

  However, the device described in Patent Document 1 has a problem in durability of the vibration damping member. The vibration damping member changes with time during use. The change over time in the case of the vibration-proof rubber is well known as sag. Since the sinking occurs and the curing occurs, the predetermined laser performance cannot be obtained.

  In addition, what is described in Patent Document 2 has a great feature that the vibration damping member is an air spring. Since the air spring is constantly applied with a reaction force by applying air pressure, it does not change over time.

  However, what is described in Patent Document 2 has the following problems.

  First, since the air spring can be deformed in various directions, the alignment tends to shift. For example, consider a case where the vibration transmitted from the laser chamber, which is the excitation source, to the cavity is insulated by an air spring. A diffraction grating for selecting a wavelength, a prism for expanding a beam, and a partial reflection mirror are attached to the cavity. The air spring can move in any direction, and can be displaced / deformed in the vertical and horizontal directions where a load is applied.

  In recent years, as the wavelength of light used for exposure becomes shorter, it is necessary to purge the optical path in the laser with nitrogen. Therefore, as shown in FIG. 9, the laser chamber 11 and the cavity 22 must be connected by a duct 70, for example.

  In the system configured as described above, if the air spring can freely move, a force is applied from the laser chamber 11 to the cavity 22 through the duct 70 connecting the laser chamber 11 and the cavity 22. The cavity 22 is deflected by the force, and the alignment is shifted.

In recent years, MOPA systems and I / L systems are often used in response to demands for high output of light sources, but both are very sensitive to misalignment and must be overcome.

  Second, when air pressure is applied to the air spring, it acts as a spring. On the other hand, if the air pressure is released, the chamber does not act as a spring and the chamber may sink.

  For example, when an air spring is employed in the laser system, the air pressure is lost and the chamber sinks when a power failure occurs. At this time, force is applied to the cavity through the duct, resulting in misalignment.

  Third, a compressor was required to operate the air spring. The air spring exerts a predetermined vibration isolation effect only when air pressure is applied. In order to increase the air pressure, a compressor was required. Therefore, the cost for installing the compressor is required, and the vibration of the compressor needs to be considered.

  The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide an excimer laser device that reduces the misalignment and has a simple structure and a low cost.

  For this purpose, the present invention comprises a laser chamber, a resonator installed on one side of the laser chamber and the opposite side thereof, a laser gas sealed inside the laser chamber, means for exciting the laser gas, and excitation Two windows provided in the laser chamber for emitting light generated from the laser gas emitted to the outside of the laser chamber, a cross flow fan for circulating the laser gas, and vibration absorbing means for supporting the laser chamber The vibration absorbing means includes an air spring that expands and contracts by injecting and discharging gas, and a container that controls expansion and contraction of the air spring in the horizontal direction. To do.

  Further, the vibration absorbing means has a connecting member having one end attached to the air spring and the other end attached to the chamber side, and the container has an opening through which the connecting member is inserted. To do.

  Further, the purge gas for purging the laser gas or the optical path is caused to flow into and out of the air spring.

  The vibration absorbing means may include a detachable rigid body that connects and fixes both ends of the air spring.

  Further, a plurality of the laser chambers are provided.

  The excimer laser device of the present invention can reduce misalignment and can keep the cost low with a simple structure.

  Hereinafter, an excimer laser device according to an embodiment of the present invention will be described.

  FIG. 1 is a diagram showing an excimer laser system 1 and a resonator 20 according to the present invention.

  The laser chamber 11 is used by sealing a laser gas inside the laser chamber 11. In the case of ArF excimer laser, Ar, fluorine, Ne or He, Xe is used, and in the case of KrF excimer laser, Kr, fluorine, Ne or He is used.

  The laser chamber 11 has two electrodes 12 facing each other, and a voltage is applied to one of them to generate a discharge between the two electrodes 12. The light generated by the discharge passes through the optical window 13, reciprocates between the resonators 20, becomes laser light, passes through the partial reflection mirror 21, and is extracted as output energy.

  At one end of the resonator 20, a partial reflection mirror 21 is accommodated in a holder 22 and attached to the cavity 22. Further, at the other end of the resonator 20, a box 26 containing a prism 24 for expanding a beam and a diffraction grating 25 for selecting a wavelength is attached to the cavity 22. These cavities 22 are attached to the first surface plate 31.

The laser chamber 11 is provided with a roller 33 for facilitating movement. The laser chamber 11 is fixed to the rail 34 and operated so as not to move the laser chamber 11 by the roller 33.

  The partial reflection mirror 21, the prism 24, and the diffraction grating 25 are adjusted in advance so that the beam is incident at a predetermined angle.

  The laser chamber 11 further includes a cross flow fan 14 for circulating laser gas, and is connected to a motor 15 attached to the laser chamber 11. The cross flow fan 14 is rotated by the motor 15 to circulate the laser gas inside the laser chamber 11.

  The purpose of the laser gas circulation is to perform heat exchange with a radiator (not shown) installed in the laser chamber 11 and to always supply a fresh laser gas between the electrodes 12.

  FIG. 2 is a view showing the vibration absorbing means 40. As shown in FIG. 2, the vibration absorbing means 40 of this embodiment has an air spring 41 placed in a cylinder 42 as a container. The air spring 41 is inflated and contracted by causing gas to flow in and out, and is in contact with the cylinder 42 so that expansion in the horizontal direction is restricted to a predetermined position. One end of a shaft 43 as a connecting member is attached to the air spring 41. The other end of the shaft 43 is attached to the laser chamber 11 side via a rail 34. The shaft 43 can move up and down in the cylinder opening 42 a above the cylinder 42 by the expansion and contraction of the air spring 41.

  In the present embodiment, a purge gas N2 for baraging the optical path is used as a gas for expanding and contracting the air spring 41. In the laser system 1, there is an N2 line 44 as a purge line for purging the optical path. The N2 line 44 is used for purging after being appropriately depressurized in the laser system 1, but the high pressure N2 before depressurizing is used as the driving pressure of the air spring 41, so that a compressor is not required and the cost is reduced. Can be realized.

  The driving pressure of the air spring 41 is controlled by a control means (not shown). As an input, it is preferable to use the position detection device 47 including an acceleration sensor, a speed sensor, a displacement sensor, or the like shown in FIG.

  The displacement of the air spring 41 in various directions causes misalignment, and in particular, horizontal displacement / deformation significantly affects laser performance. This is because the horizontal direction is the wavelength dispersion direction, and if the alignment in this direction is shifted, it is presumed that the wavelength fluctuation is deteriorated and the line width is deteriorated. In the present embodiment, by using the air spring 41 in the cylinder 42, horizontal displacement / deformation can be reduced.

  Misalignment can also occur when the laser system 1 is transported. When the laser system 1 is transported, a large impact may be applied. The impact causes the laser chamber 11 to be displaced and deformed, resulting in misalignment. At the shipping destination, alignment adjustment is required again, and the time required for startup is extended.

  Since the displacement and deformation at the time of transportation of the laser system 1 are caused by a large impact, the above structure alone is not sufficient. As a countermeasure, a transportation jig 45 for transportation as illustrated in FIG. 2 is prepared so that the air spring is not displaced or deformed.

The transport jig 45 supports the load of the laser chamber 11 and the roller 33 and the like above the rail 34 at a flat place such as the mounting portion 45a, and is fixed to the upper portion of the transport jig 45 with the rail 34 and the first screw 45b. The bottom plate is fixed with a surface plate or frame 31 and the second screw 45c. The transport jig 45 is made of metal and has a structure capable of supporting at least the load of the laser chamber 11 and the like.

  FIG. 3 shows a view when the transport jig 45 is attached to the laser chamber 11. By attaching the transport jig 45 in this manner, the load of the laser chamber 11 and the like is not applied to the air spring 41, and displacement of the laser chamber 11 can be prevented.

  Such a transport jig 45 is not used while the laser is operating. Only when a large impact is expected, such as during transportation, the transportation jig 45 is attached as shown in FIG. Also, the transport jig 45 is removed as soon as transport is completed. If the transport jig 45 is attached when the laser chamber 11 is in operation, the vibration isolation effect cannot be obtained at all, and the wavelength fluctuation and energy stability will deteriorate.

  The air spring 41 uses a gas pressure as a driving force. Therefore, if the supply of pressure stops, the air spring 41 contracts. In the case of the laser system 1 of the present embodiment, the laser chamber 11 and the like are mounted on the air spring 41.

  If the supply of pressure is stopped in such a situation, a misalignment occurs. If the amount of reduction of the air spring 41 is large, even the possibility of destruction is considered.

  FIG. 4 is a diagram schematically showing the position of the laser chamber 11 before and after the supply of the purge gas N2 is stopped.

  In the present invention, when the supply of air is stopped, when the air pressure is supplied or not, in order to prevent the laser chamber 11 from sinking and being dragged by the surrounding structure, resulting in distortion. The design was made so that the difference in the position of the laser chamber 11 was as small as 1 mm to 2 mm. The reason why the difference of several mm is left is to obtain the parallelism of the plane formed by the rail 34 on which the laser chamber 11 is placed.

  As another method for solving this problem, an automatic closing valve 46 is attached somewhere on the N2 line 44 connected to the air spring 41 so that the automatic closing valve 46 is automatically closed when a power failure or the like occurs. . Further, if the driving gas leaks from the air spring 41, the laser chamber 11 can be prevented from sinking.

  Further, a plurality of laser chambers 11 as shown in FIG. 8 may be provided. Even for an apparatus that supports high output and narrow bandwidth, such as the excimer laser apparatus 1 having a plurality of laser chambers 11, it is possible to reduce misalignment and to keep costs low with a simple structure.

  Thus, the excimer laser device 1 of the present embodiment includes the laser chamber 11, the resonator 2 installed on one side of the laser chamber 11 and the opposite side, the laser gas sealed in the laser chamber 11, Means for exciting the laser gas, two optical windows 13 provided in the laser chamber 11 for emitting light generated from the excited laser gas to the outside of the laser chamber 11, a cross flow fan 14 for circulating the laser gas, and a laser In the excimer laser device 1 including the vibration absorbing means 40 that supports the chamber 11, the vibration absorbing means 40 includes an air spring 41 that expands and contracts by flowing in and out gas, and an expansion and contraction of the air spring 41 in the horizontal direction. And a cylinder 42 that regulates the movement, so that the misalignment can be reduced and the cost can be reduced with a simple structure. It can be suppressed low.

Further, the vibration absorbing means 40 has a shaft 43 with one end attached to the air spring 41 and the other end attached to the laser chamber 11 side, and the cylinder 42 has an opening 42a through which the shaft 43 is inserted. With a simple configuration, the misalignment can be reduced and the cost can be kept low.

  Further, since the purge line 44 for flowing the purge gas for purging the laser gas and the optical path into and out of the air spring 41 is provided, the cost can be reduced with a simpler configuration.

  In addition, since a plurality of laser chambers 11 are provided, it is possible to reduce misalignment and reduce the cost with a simple structure even for an apparatus that supports high output and narrow bandwidth.

It is a figure which shows the excimer laser system and resonator which concern on this invention. It is a figure which shows a vibration absorption means. Shown when the transport jig is attached to the laser chamber It is the figure which showed typically the mode of the position of the laser chamber before and behind supply of purge gas N2. 1 is a diagram showing a general excimer laser system 1 and a resonator 20. FIG. It is a figure which shows the relationship between the partial reflection mirror in the normal case, a prism, and a diffraction grating. It is a figure which shows the example which the partial reflection mirror, the prism, and the diffraction grating displaced. It is a figure which shows the system which arranged two chambers shown in FIG. It is a figure which shows the connection of a laser chamber and a cavity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Laser system 11 ... Laser chamber 12 ... Electrode 13 ... Optical window 14 ... Cross flow fan 15 ... Motor 20 ... Resonator 21 ... Partial reflection mirror 22 ... Cavity 24 ... Prism 25 ... Diffraction grating 26 ... Box 31 ... First Surface plate 32 ... Second surface plate 33 ... Roller 34 ... Rail 40 ... Vibration absorbing means 41 ... Air spring 42 ... Cylinder (container)
43 ... Shaft (connecting member)
44 ... N2 line (purge line)
45 ... Transport jig 46 ... Valve 47 ... Position detection device 50 ... Folding mirror 61 ... Laser chamber 62 ... Amplifier rear mirror 63 ... Amplifier front mirror 70 ... Duct

Claims (5)

A laser chamber;
A resonator installed on one side of the laser chamber and on the opposite side;
A laser gas sealed inside the laser chamber;
Means for exciting the laser gas;
Two windows provided in the laser chamber for emitting light generated from the excited laser gas to the outside of the laser chamber;
A cross flow fan for circulating the laser gas;
Vibration absorbing means for supporting the laser chamber;
In an excimer laser device comprising:
The vibration absorbing means is
An air spring that expands and contracts by allowing gas to flow in and out;
A container that regulates expansion and contraction of the air spring in the horizontal direction;
An excimer laser device comprising: The vibration absorbing means has a connecting member having one end attached to the air spring and the other end attached to the chamber side,
The excimer laser device according to claim 1, wherein the container has an opening through which the connecting member is inserted. 3. The excimer laser device according to claim 1, wherein a purge gas for purging the laser gas or the optical path is caused to flow into and out of the air spring. 4. The excimer laser device according to claim 1, wherein the vibration absorbing unit has a detachable rigid body that connects and fixes both ends of the air spring. 5. The excimer laser device according to claim 1, comprising a plurality of the laser chambers.

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