Apparatus and method for combining a plurality of laser beams

Abstract

To provide apparatus for and methods of combining multiple laser beams.SOLUTION: The invention provides apparatus for and methods of combining multiple, i.e., two or more laser beams to reduce to the point of elimination where a transverse gap between the two or more beams caused, for example, by a space between a coating on a surface of a mirror and an edge of the mirror or by optic geometry is avoided.SELECTED DRAWING: Figure 3B

Description

Technical Field

[0001] Cross - reference to related applications

[0001] This application claims the priority of U.S. Application No. 62 / 941,971, entitled "APPARATUS FOR AND METHODS OF COMBINING MULTIPLE LASER BEAMS", filed on November 29, 2019, the entire disclosure of which is incorporated herein by reference.

[0002]

[0002] This disclosure relates to combining multiple laser beams for use, for example, in a lithographic apparatus.

Background Art

[0003]

[0003] A lithographic apparatus applies a desired pattern onto a substrate, such as a wafer of semiconductor material, usually onto a target portion of the substrate. Alternatively, a patterning device, also called a mask or reticle, can be used to generate the circuit pattern to be formed on individual layers of the wafer. Transfer of the pattern is typically achieved by imaging onto a layer of radiation - sensitive material (resist) provided on the substrate. Generally, a single substrate will contain adjacent target portions that are successively patterned.

[0004]

[0004] A lithographic apparatus includes a so - called stepper in which each target portion is irradiated by exposing the entire pattern to the target portion in one go, and a so - called scanner in which the substrate is scanned synchronously in a given direction (the "scan" direction), either parallel or antiparallel, while the pattern is scanned with a radiation beam in a given direction (the "scan" direction), so that each target portion is irradiated. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate. For convenience, both the stepper and the scanner are simply referred to herein as a scanner.

[0005]

[0005] The light source used to illuminate the pattern and project it onto the substrate is any one of several configurations. Deep ultraviolet excimer lasers commonly used in lithography systems include a krypton fluoride (KrF) laser at a wavelength of 248 nm and an argon fluoride (ArF) laser at a wavelength of 193 nm.

[0006]

[0006] There can be instances where it is preferable to use multiple, for example two, laser beams. As an example, there can be instances where it is desirable to have the function of changing the wavelength between pulses. In another instance, it may be desirable to increase the power and / or repetition rate of the laser system by combining two laser beams so as to deliver power simultaneously or on alternate pulses. Irrespective of location, "combining" is used to imply propagating the beams in any common direction that is either collinear or parallel to each other.

[0007]

[0007] In other words, the wafer throughput can be increased when the need for an additional exposure pass can be avoided. It is also beneficial that the amount of power (dose) delivered to the wafer can be increased beyond the limit that a single laser can provide. This can theoretically be achieved by using two lasers along with the overlay beam sent to the scanner, thus enabling multiple wavelength exposures to be achieved within a single pass. By combining each KrF laser at its maximum power, a higher total power can be achieved.

Summary of the Invention

[0008]

[0008] The following presents a simplified schematic of one or more embodiments to facilitate a basic understanding. This schematic is not an extensive overview of all contemplated embodiments, nor is it intended to identify the important or essential elements of all embodiments or to define the scope of any or all embodiments. Its purpose is simply to present some concepts of one or more embodiments in a simplified form as a prelude to the more detailed description that follows.

[0009]

[0009] According to one aspect of an embodiment, a gas discharge laser system is disclosed that includes a first laser chamber module adapted to generate a first beam of laser radiation, a second laser chamber module adapted to generate a second beam of laser radiation, and a beam combiner arranged to receive the first beam and the second beam and adapted to propagate the first beam and the second beam in a common direction. The beam combiner includes a mirror having a reflective surface and a beveled edge that forms an acute angle. The mirror is arranged such that the first beam of laser radiation is reflected from the reflective surface in a common direction and the second beam of laser radiation propagates in a common direction directly adjacent to the acute angle. The system may further include an aperture arranged such that the second beam passes through the aperture, and the aperture limits the dimensional extent of the second beam of laser radiation such that the second beam of laser radiation does not impinge on the acute angle. The width of the aperture may be adjustable.

[0010] According to another aspect of an embodiment, a first laser chamber module adapted to generate a first beam of laser radiation, a second laser chamber module adapted to generate a second beam of laser radiation, and a beam combiner arranged to receive the first beam and the second beam and adapted to propagate the first beam and the second beam in a common direction, the beam combiner comprising an optical element having a surface with a first portion having a reflective coating and a second portion not having a reflective coating, the optical element being arranged such that the first beam of laser radiation is reflected from the reflective surface in a common direction and the second beam of laser radiation passes through the optical element and the second portion of the surface of the optical element in a common direction, a gas discharge laser system is disclosed.

[0011] According to another aspect of an embodiment, a gas discharge laser system is disclosed that includes a first laser chamber module adapted to generate a first beam of laser radiation, a second laser chamber module adapted to generate a second beam of laser radiation, and a beam combiner arranged to receive the first beam and the second beam and adapted to propagate the first beam and the second beam in a common direction, the beam combiner including a mirror and an actuator mechanically coupled to the mirror. The first beam of laser radiation initially travels in a first direction and strikes the mirror at a first location, and the second beam of laser radiation initially travels at an angle to the first direction in a second direction and strikes the mirror at the first location. The actuator is arranged to rotate the mirror between a first position where the first beam of laser radiation propagates in a third direction and a second position where the second beam of laser radiation propagates in the third direction. The first direction can be at an angle θ to the second direction when the actuator is applied to rotate the mirror by an angle θ / 2. The first laser chamber module can be adapted to generate a first pulsed beam of laser radiation, the second laser chamber module can be adapted to generate a second pulsed beam of laser radiation between pulses of the first pulsed beam of laser radiation, and the actuator can be adapted to position the mirror at the first position during a pulse of the first pulsed beam of laser radiation and to position the mirror at the second position during a pulse of the second pulsed beam of laser radiation.

[0012] According to another aspect of an embodiment, a method of combining a first pulsed laser beam and a second pulsed laser beam within a lithographic apparatus is disclosed. The method includes arranging a mirror in a first state in which a pulse of the first pulsed laser beam hitting the mirror is reflected in a direction enabling use of the pulse; generating one or more pulses of the first beam of laser radiation; arranging the mirror in a second state in which a pulse of the second pulsed laser beam hitting the mirror is reflected in a direction enabling use of the pulse; and generating one or more pulses of the second beam of laser radiation. The step of arranging the mirror in the first state in which the pulse of the first pulsed laser beam propagates in a direction enabling use of the pulse may include arranging the mirror in a first rotational position, and the step of arranging the mirror in the second state in which the pulse of the second pulsed laser beam propagates in a direction enabling use of the pulse may include arranging the mirror in a second rotational position. The first pulsed laser beam and the second pulsed laser beam may hit the mirror at an angle θ with respect to each other, and the first rotational position and the second rotational position may be at an angle θ with respect to each other.

[0013] Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, will be described in detail below with reference to the accompanying drawings. It should be noted that the present invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to those skilled in the art based on the teachings contained herein.

[0014] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate the invention and, together with the description, serve to explain the principles of the invention and to enable a person skilled in the art to make and use the invention.

Brief Description of the Drawings

[0015]

Figure 1

[0015] It is a functional block diagram showing a conventional two-chamber laser system.

Figure 2

[0016] A functional block diagram showing a two-chamber laser system according to one aspect of an embodiment.

Figure 3A

[0017] A diagram showing the arrangement of a beam combiner using a pick-off mirror.

Figure 3B

[0018] A diagram showing an enlarged portion of FIG. 3B.

Figure 4

[0019] A diagram showing a possible arrangement of a beam combiner according to one aspect of an embodiment.

Figure 5A

[0020] A plan view showing optical elements used in a beam combiner according to one aspect of an embodiment.

Figure 5B

[0020] A diagram showing a possible arrangement of a beam combiner incorporating the optical element of FIG. 5A according to one aspect of an embodiment.

Figure 6A

[0021] A plan view showing a beam combiner according to one aspect of an embodiment at a first position.

Figure 6B

[0021] A plan view showing the beam combiner of FIG. 6A at a second position.

[0016]

[0022] The features and advantages of the present invention will become more apparent by reading the following detailed description with reference to the drawings that identify corresponding elements throughout with like reference numerals. In the drawings, generally, like reference numbers indicate identical, functionally similar, and / or structurally similar elements.

DETAILED DESCRIPTION OF THE INVENTION

[0017]

[0023] This specification discloses one or more embodiments incorporating features of the present invention. The one or more disclosed embodiments merely illustrate the present invention. The scope of the present invention is not limited to the one or more disclosed embodiments. The present invention is defined by the claims appended hereto.

[0018]

[0024] When the described embodiments and the present specification refer to "one embodiment", "an embodiment", "exemplary embodiment", etc., it indicates that the described embodiments can include specific features, structures, or characteristics, but each embodiment may not necessarily include specific features, structures, or characteristics. Furthermore, such phrases do not necessarily refer to the same embodiment. Moreover, when a specific feature, structure, or characteristic is described in relation to an embodiment, it is understood that such a feature, structure, or characteristic can be implemented in relation to other embodiments, whether explicitly described or not, within the knowledge of those skilled in the art.

[0019]

[0025] Before detailing the embodiments, it may be useful to present an exemplary environment in which the embodiments of the present invention can be implemented. FIG. 1 is a functional block diagram of a conventional two-chamber laser system 10. In this embodiment, a laser beam is provided to an input port of a lithography machine 12 such as a stepper or scanner machine. The main components of the laser system 10 can be installed below the floor 14 where the scanner 12 is installed as shown in the figure. The laser system 10 includes a beam delivery unit 16 that provides a closed beam path for delivering the laser beam to the input port of the scanner 12. The particular light source system shown includes a master oscillator 18 and a power amplifier 20 and is a type of laser system known as a master oscillator power amplifier or MOPA system. The laser system 10 also generally includes various components for controlling the spectral characteristics of the pulse, pulse shaping, etc., shown as optical systems 22 and 24. The master oscillator 18 generates a first laser beam that is amplified by two paths through the power amplifier 20 to generate an output laser beam as indicated by the arrow in FIG. 1. Such a single MOPA configuration is merely an example. It will be apparent to those skilled in the art that the principles disclosed herein are also applicable to other configurations such as MOMO and laser systems having multiple MOPA configurations.

[0020]

[0026] According to one aspect of an embodiment, the need to apply multiple passes to the wafer is avoided by exposing the wafer to two beams. In the arrangement shown in FIG. 2, a first resonant charger 40 supplies electrical energy to a first commutator 42 and a second commutator 44. The first commutator 42 supplies pulses to a first compression head 46. The second commutator 44 supplies pulses to a second compression head 48. The first compression head 46 causes a discharge within a first laser chamber module 50. The second compression head 48 causes a discharge within a second laser chamber module 52. FIG. 3 also shows an optical system for adjusting the laser beam, such as a first line narrowing module 54 and a second line narrowing module 56, a first optical coupler 58 and a second optical coupler 60, and a first stabilization module 62 and a second stabilization module 64. The beam generated by the laser chamber module is line narrowed to produce a bandwidth much smaller than the natural bandwidth of the gas discharge system. The control circuit 70 can control the first line narrowing module 54 and the second line narrowing module 56 such that the bandwidths and wavelengths of the optical beams generated by the first laser chamber module 50 and the second laser chamber module 52 can be different from each other.

[0021]

[0027] Various trigger arrangements are possible. For example, using one trigger, both chambers can be fired whether or not there is a delay between the time of the trigger and the discharge of one or both of the chambers. Alternatively, the trigger can be generated separately such that the two chambers have individual voltage / energy commands, i.e., by separate circuit elements.

[0022]

[0028] Various system components that can be commonly used by the first laser chamber module 50 and the second laser chamber module 52, such as a gas handling system, a control system, an interface, a power distribution system, a cooling water system, a chamber filter, and power for blowers, and a beam path purge system, are also generally indicated by 68. Thus, in the arrangement shown in the figure, the two laser chambers can share these components and do not need to have two of each of them.

[0023]

[0029] The arrangement of FIG. 2 also includes a control circuit 70 that can operate two lasers with independent energy, control the relative emission time, bandwidth, and wavelength, and a scanner interface that can divide the energy / pulse command between the two lasers.

[0024]

[0030] In one embodiment, the first laser chamber module 50 can generate laser emission at a first wavelength, and the second laser chamber module 52 generates laser emission at a second wavelength different from the first wavelength. Thus, in this case, the two chambers cooperate to generate emissions at different wavelengths that have different focal planes on the wafer and operate at different depths.

[0025]

[0031] Figure 2 also shows a first metrology unit 72 arranged to measure parameters including the wavelength of the optical beam generated by the first laser chamber module 50. The arrangement shown in Figure 2 also includes a second metrology unit 74 arranged to measure parameters including the wavelength of the optical beam generated by the second laser chamber module 52. A third metrology unit 76 is arranged to measure parameters including the wavelength of the combined beam, i.e., the parameters of the combination of the optical beam from the first laser chamber module and the optical beam from the second laser chamber module. It will be appreciated that there may be cases where the combined beam is simply a beam from one of the laser chambers and the other chamber is not emitting. The metrology units supply the results of their measurements to the control circuit 70. The metrology units as shown in the figure can independently measure the wavelengths of the light from the two laser chamber modules and the wavelength of the combined beam. The control unit 70 can use the measured values to control the wavelength of the optical beam generated by each laser chamber module.

[0026]

[0032] The emissions of the two chambers can be interleaved to achieve an effective double repetition rate. It is possible to combine the beams from the two lasers to achieve an effective repetition rate that is twice the repetition rate of either of the two lasers, as shown at the bottom of the timing diagram. As described above, the beam paths of multiple lasers can be combined using any one of several arrangements.

[0027]

[0033] The firing order of two (or more) laser chamber modules can be set to any one of various patterns. For example, the order can be set so that the chambers alternate firing for each shot. Alternatively, the order can be set so that after the first laser chamber module fires a first number of shots, the second chamber fires a second number of shots, and the first number and the second number may or may not be equal. These orders can be employed in laser chamber modules that generate light of the same wavelength or different wavelengths. Also, laser chamber modules that generate light at two different wavelengths can fire at substantially different repetition rates to create spectra with different energy contents for each of the two wavelength beams. Since the second discharge rate can be, for example, an integer multiple of the first discharge rate, the discharge rates can be, for example, in a ratio of 2:1. The relationship between the first and second discharge rates may also be a ratio of two integers such as 3:2.

[0028]

[0034] In the case of the foregoing embodiments, the timing difference Δt between the firings of the two lasers can be set to any value (assuming the optical system can withstand twice the instantaneous power level) that essentially includes zero or is small enough that the two pulses are not simultaneous but one occurs immediately after the other (i.e., during the same exposure), and thus doubles the effective dose. Accordingly, the beams from the two lasers can be generated one immediately after the other as shown in the figure, and are combined to achieve an effective dose that is twice the dose of either of the two lasers, as shown in the lower timing diagram.

[0029]

[0035] The beam from the first laser chamber module 50 and the beam from the second laser chamber module 52 are combined by a beam combiner 66. When having different wavelengths, another technique for combining the two beams is to use a dichroic mirror. The dichroic mirror acts such that one wavelength (short pass) is transmitted and the other wavelength is reflected. However, this technique only works for combining beams having different wavelengths.

[0030]

[0036] Techniques for combining two laser beams having the same or different wavelengths include the use of a pick-off mirror. For example, in FIG. 3A, beam 100 is reflected by pick-off mirror 110 and travels in a first direction A, and a second beam 120 travels near the edge of pick-off mirror 110 and also propagates in direction A. Direction A is considered the direction in which the beams propagate for further use. Due to manufacturing constraints in placing the reflective coating 130 on the surface of mirror 110, there is a space B between the edge 112 of mirror 110 and the edge 132 of coating 130 (exaggerated in FIG. 3B, which is an enlarged version of the content shown in the dashed box of FIG. 3A). There is also a gap C between the coating 130 on the upper surface 114 of the mirror and the back surface 116 of the mirror. Coating 130 is typically applied within 1 mm from the edge of mirror 110, i.e., within distance B, and has a thickness of about 10 mm. The space B and the thickness of mirror 110 supported by gap C contribute to the thickness of the gap G between the two beams 110 and 120, which has a width of approximately 10 mm. This gap G can cause problems in the downstream optical system, and from a technical perspective, it may be desirable to reduce the width of gap G as much as possible for some applications.

[0031]

[0037] To combine the two beams 100 and 120 and minimize the gap therebetween, an arrangement as shown in FIG. 4 may be used. In FIG. 4, the inclined mirror 150 is cut so that the beam 120 can propagate without hitting the mirror surface, as shown in the figure. The adjustable aperture may be positioned and dimensioned to help ensure that the beam 120 propagates without hitting the mirror surface. The beam 100 is reflected by the inclined mirror 150 near the edge of the inclined mirror 160. The resulting combined beam profile has a reduced gap, on the order of, for example, about 1 mm, compared to the gap G. The beam 100 and the beam 120 are propagated parallel to each other in the direction A, adjacent to each other, and such that one is transformed with respect to the other in a direction perpendicular to the direction A.

[0032]

[0038] Another arrangement for combining the two beams 100 and 120 and minimizing the gap therebetween is shown in FIGS. 5A and 5B. As shown in FIG. 5A, a reflective coating 130 is applied to a portion, for example, a portion of the mirror 180 (regardless of the mirror shape). As shown in FIG. 5B, the laser beam 100 is reflected by the reflective coating 130 while the laser beam 120 propagates through the portion of the mirror 180 without the coating. The two beams can be combined with a gap having a width that can in principle be reduced to zero.

[0033]

[0039] Another arrangement for combining two beams 100 and 120 to minimize the gap therebetween is shown in FIGS. 6A and 6B, and such an arrangement is particularly useful in a system in which the beams 100 and 120 are not emitted simultaneously but rather in alternating pulses. The solid lines are the active beams, and the dashed lines indicate the positions of the mirrors and the beams when the mirrors and the beams are in other positions. The beams propagate such that the angle between them is θ. As shown in FIG. 6A, the beam 100 strikes the mirror 200 at a first position where the beam 100 propagates in direction A, i.e., the direction of use, while the second beam 120 propagates in direction B. Then, as shown in FIG. 6B, the mirror 200 rotates by θ / 2 to a second position such that the beam 120 propagates in direction A while the beam 100 propagates in direction C. The mirror 200 is rotated, i.e., dithered, between the first position and the second position by the actuator 210 according to a control signal applied by the controller 220. If the beams 100 and 120 are emitted as alternating pulses at a given repetition rate and the mirror is dithered at the same repetition rate, the beams can essentially combine the two beams and propagate collinearly in direction A. The same effect can also be achieved by maintaining the mirror 200 in a stationary state and dithering the propagation direction of one or both of the beams 100 and 120.

[0034]

[0040] It should be understood that, for interpreting the claims, the section "Detailed Description of the Invention" rather than the sections "Summary of the Invention" and "Abstract" is intended to be used. The sections "Summary of the Invention" and "Abstract" can describe one or more exemplary embodiments of the invention as contemplated by the inventor, but cannot describe all exemplary embodiments and thus are not intended to limit the invention and the appended claims in any sense.

[0035]

[0041] This disclosure is made with the aid of functional building blocks that illustrate examples of specific functions and their relationships. The boundaries of these functional building blocks are arbitrarily defined herein for convenience of explanation. Alternative boundaries may be defined as long as the specific functions and their relationships are properly implemented.

[0036]

[0042] The foregoing description of specific embodiments fully reveals the overall nature of the invention, so that by applying the knowledge of the relevant art, without undue experimentation and without departing from the overall concept of the invention, such specific embodiments can be easily modified and / or adapted to various uses. Accordingly, such adaptations and modifications are intended to fall within the meaning and scope of the equivalents of the disclosed embodiments based on the teachings and guidance presented herein. Since the expressions or terms herein are for description by way of example rather than limitation, it should be understood that the expressions or terms herein should be interpreted by those skilled in the art from the perspective of the teachings and guidance.

[0037]

[0043] The embodiments of this disclosure can be described in more detail using the following clauses. 1. A gas discharge laser system comprising a beam combiner arranged to receive a first beam of laser radiation and a second beam of laser radiation and adapted to propagate the first beam and the second beam in a common direction, wherein the beam combiner comprises a mirror having a reflective surface and an inclined edge forming an acute angle with the reflective surface, and the mirror is arranged such that the first beam of laser radiation is reflected from the reflective surface in a common direction and the second beam of laser radiation propagates in a common direction directly adjacent to the acute angle. The beam combiner comprises a mirror having a reflective surface and an inclined edge forming an acute angle with the reflective surface, and the mirror is arranged such that the first beam of laser radiation is reflected from the reflective surface in a common direction and the second beam of laser radiation propagates in a common direction directly adjacent to the acute angle. Gas discharge laser system. 2. The gas discharge laser system according to clause 1, further comprising a first laser chamber module adapted to generate a first beam of laser radiation and a second laser chamber module adapted to generate a second beam of laser radiation. 3. The gas discharge laser system according to clause 1, further comprising an aperture arranged such that a second beam of laser radiation passes through the aperture, the aperture restricting the dimensional range of the second beam of laser radiation so that the second beam of laser radiation does not collide at an acute angle. 4. The gas discharge laser according to clause 3, wherein the width of the aperture is adjustable. 5. The gas discharge laser system according to clause 1, wherein the beam combiner is adapted to propagate the first beam and the second beam parallel to each other. 6. The gas discharge laser system according to clause 1, wherein the first beam of laser radiation has a first wavelength and the second beam of laser radiation has a second wavelength different from the first wavelength. 7. The gas discharge laser system according to clause 1, wherein the first beam of laser radiation is triggered to be emitted first, the beam of laser radiation is triggered to be emitted second, and the difference between the first and second times is Δt. 8. The gas discharge laser system according to clause 7, wherein Δt is substantially equal to zero. 9. The gas discharge laser system according to clause 7, wherein Δt is selected such that the first and second of the laser radiation are triggered immediately after the first beam of laser radiation stops emitting. 10. A first laser chamber module adapted to generate a first beam of laser radiation, A second laser chamber module adapted to generate a second beam of laser radiation, A beam combiner arranged to receive the first beam and the second beam and adapted to propagate the first beam and the second beam in a common direction, the beam combiner comprising an optical element having a surface with a first portion having a reflective coating and a second portion not having a reflective coating, the optical element being arranged such that the first beam of laser radiation is reflected from the reflective surface in a common direction and the second beam of laser radiation passes through the optical element and the second portion of the surface of the optical element in a common direction, the beam combiner; A gas discharge laser system comprising. 11. The gas discharge laser system according to clause 10, wherein the first beam of laser radiation has a first wavelength, and the second beam of laser radiation has a second wavelength different from the first wavelength. 12. The gas discharge laser system according to clause 10, wherein the first beam of laser radiation is pulsed and triggered to be emitted for the first time, and the beam of laser radiation is pulsed and triggered to be emitted for the second time, and the difference between the first time and the second time is Δt. 13. The gas discharge laser system according to clause 12, wherein Δt is substantially equal to zero. 14. The gas discharge laser system according to clause 12, wherein Δt is selected such that the first and second of the laser radiation are triggered immediately after the first beam of laser radiation stops emitting. 15. A first laser chamber module adapted to generate a first beam of laser radiation, A second laser chamber module adapted to generate a second beam of laser radiation, A beam combiner arranged to receive the first beam and the second beam and adapted to propagate the first beam and the second beam in a common direction, the beam combiner comprising a mirror and an actuator mechanically coupled to the mirror, the beam combiner, A gas discharge laser system comprising: The first beam of laser radiation initially travels in a first direction and hits the mirror at a first location, and the second beam of laser radiation initially travels at an angle with respect to the first direction in a second direction and hits the mirror at the first location, The actuator is arranged to rotate the mirror between a first position where the first beam of laser radiation propagates in a third direction and a second position where the second beam of laser radiation propagates in the third direction. Gas discharge laser system. 16. The gas discharge laser system according to clause 15, wherein the first direction is at an angle θ with respect to the second direction when the actuator is applied to rotate the mirror by an angle θ / 2. 17. The first laser chamber module is adapted to generate a first pulsed beam of laser radiation, the second laser chamber module is adapted to generate a second pulsed beam of laser radiation between the pulses of the first pulsed beam of laser radiation, and the actuator is adapted to place the mirror at a first position during the pulse of the first pulsed beam of laser radiation and to place the mirror at a second position during the pulse of the second pulsed beam of laser radiation, the gas discharge laser system according to clause 15. 18. A method of combining a first pulsed laser beam and a second pulsed laser beam in a lithographic apparatus, placing the mirror in a first state in which the pulse of the first pulsed laser beam hitting the mirror is reflected in a direction enabling the use of the pulse; generating one or more pulses of the first beam of laser radiation; placing the mirror in a second state in which the pulse of the second pulsed laser beam hitting the mirror is reflected in a direction enabling the use of the pulse; and generating one or more pulses of the second beam of laser radiation, method. 19. The method according to clause 18, wherein the step of placing the mirror in a first state in which the pulse of the first pulsed laser beam propagates in a direction enabling the use of the pulse includes placing the mirror in a first rotational position, and the step of placing the mirror in a second state in which the pulse of the second pulsed laser beam propagates in a direction enabling the use of the pulse includes placing the mirror in a second rotational position. 20. The method according to clause 18, wherein the first pulsed laser beam and the second pulsed laser beam hit the mirror at an angle θ with respect to each other, and the first rotational position and the second rotational position are at an angle θ with respect to each other. 21. A beam combiner arranged to receive a first beam and a second beam and adapted to cause the first beam to propagate in a common direction in the first and second beams, the beam combiner comprising a mirror having a reflective surface and an inclined edge forming an acute angle with the reflective surface, the mirror being arranged such that a first beam of laser radiation is reflected from the reflective surface in a common direction and a second beam of laser radiation propagates in a common direction directly adjacent to the acute angle. 22. The beam combiner according to clause 21, wherein the first beam is generated by a first laser chamber module and the second beam is generated by a second laser chamber module.

Claims

1. A first laser chamber module adapted to generate a first beam of laser radiation, A second laser chamber module adapted to generate a second beam of laser radiation, A beam combiner adapted to propagate the first beam and the second beam in a common direction, the beam combiner comprising an optical element having a surface with a first portion having a reflective coating and a second portion not having a reflective coating, the optical element being arranged such that the first beam of laser radiation is reflected from the first portion in the common direction and the second beam of laser radiation passes through the second portion of the surface of the optical element in the common direction, the beam combiner, A gas discharge laser system comprising.

2. The gas discharge laser system according to claim 1, wherein the first beam of laser radiation has a first wavelength and the second beam of laser radiation has a second wavelength different from the first wavelength.

3. The gas discharge laser system according to claim 1, wherein the first beam of laser radiation and the second beam of laser radiation are emitted substantially simultaneously.

4. The gas discharge laser system according to claim 1, wherein the second beam of laser radiation is emitted immediately after the first beam of laser radiation is emitted.

5. A beam combiner adapted to propagate a first beam and a second beam in a common direction, the beam combiner comprising an optical element having a surface with a first portion having a reflective coating and a second portion not having a reflective coating, the optical element being arranged such that the first beam is reflected from the first portion in the common direction and the second beam passes through the second portion of the surface of the optical element in the common direction, the first beam being generated by a first laser chamber module and the second beam being generated by a second laser chamber module, the beam combiner.

6. A beam combiner adapted to propagate a first beam and a second beam in a common direction, An aperture arranged such that the second beam passes through, A mirror having a reflective surface, a back surface opposite the reflective surface, and an inclined edge portion that forms an acute angle with the reflective surface and an obtuse angle with the back surface, wherein the mirror is arranged such that the first beam of laser radiation is reflected from the reflective surface in the common direction, and the second beam of laser radiation propagates in the common direction without hitting the back surface, the mirror, comprising, The aperture limits the dimensional range of the second beam of laser radiation so that the second beam of laser radiation does not collide with the acute angle, a beam combiner. [

7. ] The beam combiner according to claim 6, wherein the first beam is generated by a first laser chamber module and the second beam is generated by a second laser chamber module.

Images