Apparatus for and method of generating multiple laser beams

Abstract

To provide an apparatus and method for generating multiple laser beams using multiple laser chambers.SOLUTION: The relative timing of the beams is controllable to be interleaved, to overlap, to be prevented from overlapping, or to occur in rapid sequence. The beams may have different spectral and power characteristics such as different wavelengths. Also disclosed is a system in which at least one of the multiple laser chambers is configured to generate radiation of two different wavelengths.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Application No. 62 / 853,772, entitled APPARATUS FOR AND METHOD OF GENERATING MULTIPLE LASER BEAMS, filed May 29, 2019, and U.S. Application No. 62 / 978,515, entitled APPARATUS FOR AND METHOD OF GENERATING MULTIPLE LASER BEAMS, filed February 19, 2020, each of which is incorporated by reference in its entirety.

[0002]

[0002] This application also claims priority to U.S. Application No. 62 / 851,147, entitled CONTROL SYSTEM FOR A PLURALITY OF DEEP ULTRAVIOLET OPTICAL OSCILLATORS, filed May 22, 2019, and U.S. Application No. 63 / 006,162, entitled CONTROL SYSTEM FOR A PLURALITY OF DEEP ULTRAVIOLET OPTICAL OSCILLATORS, filed April 7, 2020, each of which is incorporated by reference in its entirety.

[0003]

[0003] The present disclosure relates to generating multiple laser beams, for example for use in a lithography apparatus. [Background technology]

[0004] 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. The patterning device, alternatively called a mask or reticle, may be used to generate the circuit pattern to be formed on an individual layer of the wafer. Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain adjacent target portions that are successively patterned.

[0005] Lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing the entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the radiation beam across the pattern in a given direction (the "scan" direction) while synchronously scanning the substrate parallel or anti-parallel to the given direction (the "scan" direction). 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 steppers and scanners will be referred to herein simply as scanners.

[0006]

[0006] The light source used to illuminate and project the pattern onto the substrate may be any one of a number of configurations. Deep ultraviolet excimer lasers commonly used in lithography systems include krypton fluoride (KrF) with a wavelength of 248 nm and argon fluoride (ArF) with a wavelength of 193 nm. Excimer lasers are generally designed to work with specific gas mixtures. Small, slow adjustments of wavelength are easily made, while rapidly changing wavelengths are not trivial.

[0007]

[0007] However, there may be cases where it is desirable to have the ability to change the wavelength. For example, in 3D NAND, layers of memory capacity are stacked. The transition from 2D to 3D NAND architecture requires major changes in the manufacturing process. In 3D NAND manufacturing, the challenges are primarily determined by the etching and deposition processes at extreme aspect ratios (e.g., the ratio of the hole diameter to its depth). Building complex 3D structures with ultra-high aspect ratio (HAR) features is complex and requires extremely high precision, and ultimately process uniformity and process repeatability, to achieve reliable mass production. Furthermore, as the multilayer stack height increases, the difficulty of obtaining consistent etching and deposition results at the top and bottom of the memory array also increases.

[0008] These considerations lead to the need for a larger depth of focus. The lithographic depth of focus (DOF) is defined by the relationship DOF=±mλ / (NA) 2 where λ is the wavelength of the illumination light, NA is the numerical aperture, and m is a practical factor that depends on the resist process. Because the depth of focus requirements in 3D NAND lithography are large, two or more exposure passes may be performed on the wafer, using a different focal plane for each pass. One method involves changing the wafer stage height for each pass. Another way to achieve the same effect is to change the wavelength. The materials that make up the lenses that focus laser radiation usually have some non-zero dispersion, causing different wavelengths to be focused to different depths. For this reason, it can be desirable to have the ability to rapidly change the wavelength.

[0009]

[0009] Beyond wavelength considerations, the use of high dose resist for KrF lasers leads to the need for KrF lasers with higher power outputs. For example, it may be desirable for some applications to have a KrF laser that can provide as much as 120 W.

[0010]

[0010] There is a need for a laser system that can provide flexible wavelength switching and / or higher output illumination. Summary of the Invention

[0011] The following presents a simplified summary of one or more embodiments to provide a basic understanding of the embodiments. This summary is not an extensive overview of all contemplated embodiments, and is not intended to identify key or critical elements of all embodiments or to delineate the scope of all embodiments. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to the more detailed description that is presented later.

[0012] According to one aspect of an embodiment, a laser system is disclosed having two independent laser chambers or cavities. Control of at least two wavelengths can be achieved by these two independent cavities. The beams may be spatially or temporally overlapped to provide higher power than can be delivered by either beam individually. Combining the two beams on one platform does not increase operating costs for lower power processes because only one cavity is used at a time. Combining the two lasers with one scanner can double the service interval when higher power is not required. This is not possible with main power amplifiers (MOPAs) or similar two-chamber systems.

[0013]

[0013] According to another aspect of an embodiment, the system may include components that allow a user to use either of the chambers alone for a low-power process or to use two chambers simultaneously for a high-power process.

[0014]

[0014] According to another aspect of one embodiment, the relative firing times of the two chambers may be controlled so that the chambers are fired simultaneously or one chamber is fired slightly later than the other, or the firings can be interleaved to essentially double the efficient repetition used in the scanner.

[0015] According to another aspect of an embodiment, a gas discharge laser system is disclosed, comprising: a first laser chamber module adapted to generate a first laser radiation beam at a first wavelength; a second laser chamber module adapted to generate a second laser radiation beam at a second wavelength different from the first wavelength; and a beam combiner positioned to receive the first beam and the second beam and adapted to cause the first beam and the second beam to propagate along a common output beam path. The first laser chamber module may include a first excimer laser chamber module. The first laser chamber module may include an ArF laser chamber module. The first excimer laser chamber module may include a KrF laser chamber module. The second laser chamber module may include a second excimer laser chamber module. The second laser chamber module may include an ArF laser chamber module. The second excimer laser chamber module may include a KrF laser chamber module. The gas discharge laser system may further include a third laser chamber module adapted to generate a third beam of laser radiation, and the beam combiner may be positioned to receive the third beam and propagate the third beam along a common output beam path.

[0016] The gas discharge laser system may further include a discharge timing circuit arranged to control the relative timing of discharges between the first laser chamber module and the second laser chamber module. The discharge timing circuit may be adapted to control the relative timing of discharges between the first laser chamber module and the second laser chamber module so that the first laser chamber module discharges at a first repetition rate and the second laser chamber module discharges at a second repetition rate that is substantially the same as the first repetition rate and offset from the first repetition rate by half the period of the first repetition rate. The discharge timing circuit may be adapted to control the relative timing of discharges between the first laser chamber module and the second laser chamber module so that the first laser chamber module and the second laser chamber module discharge at substantially the same repetition rate, and the second laser chamber module discharges substantially immediately after the first laser chamber module finishes discharging. The discharge timing circuit may be adapted to control the relative discharge timing of the first laser chamber module and the second laser chamber module so that the first laser chamber module and the second laser chamber module discharge substantially simultaneously. The discharge timing circuit may be adapted to control the relative discharge timing of the first laser chamber module and the second laser chamber module so that the first laser chamber module and the second laser chamber module do not discharge substantially simultaneously. The discharge timing circuit may be adapted to generate a common command to fire both the first laser chamber module and the second laser chamber module.

[0017] The first laser chamber module may be adapted to fire without a delay after the common command. The first laser chamber module may be adapted to fire with a delay after the common command. The second laser chamber module may be adapted to fire without a delay after the common command. The second laser chamber module may be adapted to fire with a delay after the common command.

[0018] The discharge timing circuit may be adapted to generate a first command to cause the first laser chamber module to fire and a second command to cause the second laser chamber module to fire. The first laser chamber module may be adapted to fire without a delay after the first command. The first laser chamber module may be adapted to fire with a delay after the first command. The second laser chamber module may be adapted to fire without a delay after the second command. The second laser chamber module may be adapted to fire with a delay after the command. The first laser chamber module may be caused to fire at a first repetition rate and the second laser chamber module may be caused to fire at a second repetition rate different from the first repetition rate. The discharge rate ratio of the first repetition rate to the second repetition rate may be a ratio of two integers, for example, 2:1 or 3:2.

[0019] The gas discharge laser system may further include a control system adapted to control both the first laser chamber module and the second laser chamber module. The gas discharge laser system may further include a gas supply system adapted to supply gas to both the first laser chamber module and the second laser chamber module. The gas discharge laser system may further include a first laser chamber metrology unit arranged to measure parameters of the light beam generated by the first laser chamber module. The gas discharge laser system may further include a second laser chamber metrology unit arranged to measure parameters of the light beam generated by the second laser chamber module. The gas discharge laser system may further include a combined beam metrology unit arranged to measure parameters of a combination of the light beam generated by the first laser chamber module and the light beam generated by the second laser chamber module. The gas discharge laser system may further include a control unit arranged to receive output from the first laser chamber metrology unit and configured to control the wavelength of the light beam generated by the first laser chamber module based at least in part on the output of the first laser chamber metrology unit. The gas discharge laser system may further comprise a control unit disposed to receive an output from the second laser chamber metrology unit and configured to control a wavelength of the light beam generated by the second laser chamber module based at least in part on the output of the second laser chamber metrology unit. The gas discharge laser system may further comprise a control unit disposed to receive an output of the combined beam metrology unit and configured to control a spectrum of a combination of the light beam generated by the first laser chamber module and the light beam generated by the second laser chamber module based at least in part on the output of the combined beam metrology unit.The gas discharge laser system may further include a first laser chamber line narrowing module arranged to receive the light beam from the first laser chamber module and configured to narrow the bandwidth of the light beam from the first laser chamber module. The gas discharge laser system may further include a second laser chamber line narrowing module arranged to receive the light beam from the second laser chamber module and configured to narrow the bandwidth of the light beam from the second laser chamber module. The gas discharge laser system may further include a second laser chamber line narrowing module arranged to receive the light beam from the second laser chamber module and configured to narrow the bandwidth of the light beam from the second laser chamber module, and a control unit connected to the first laser chamber line narrowing module and the second laser chamber line narrowing module and adapted to control the first laser chamber line narrowing module and the second laser chamber line narrowing module such that the first bandwidth is substantially the same as the second bandwidth. The gas discharge laser system may further include a second laser chamber line narrowing module arranged to receive the light beam from the second laser chamber module and configured to narrow the bandwidth of the light beam from the second laser chamber module, and a control unit connected to the first laser chamber line narrowing module and the second laser chamber line narrowing module and adapted to control the first laser chamber line narrowing module and the second laser chamber line narrowing module so that the first bandwidth is different from the second bandwidth.

[0020] According to another aspect of an embodiment, a lithography apparatus is disclosed, the lithography apparatus comprising: a first laser chamber module adapted to generate a first laser radiation beam at a first wavelength; a second laser chamber module adapted to generate a second laser radiation beam at a second wavelength different from the first wavelength; a beam combiner arranged to receive the first beam and the second beam and adapted to propagate the first beam and the second beam along a common output beam path; and a scanner arranged to receive the first beam and the second beam, the scanner configured to provide instructions for adjusting the first and second wavelengths. The lithography apparatus may further comprise a discharge timing circuit arranged to control relative discharge timing between the first laser chamber module and the second laser chamber module. The discharge timing circuit may be adapted to control the relative discharge timing between the first laser chamber module and the second laser chamber module such that the first laser chamber module and the second laser chamber module discharge at substantially the same repetition rate but 180 degrees out of phase with each other. The discharge timing circuit may be adapted to control the relative timing of discharge between the first laser chamber module and the second laser chamber module so that the first laser chamber module and the second laser chamber module discharge at substantially the same repetition rate, and the second laser chamber module discharges substantially immediately after the first laser chamber module finishes discharging. The discharge timing circuit may be adapted to control the relative timing of discharge between the first laser chamber module and the second laser chamber module so that the first laser chamber module and the second laser chamber module discharge substantially simultaneously. The discharge timing circuit may be adapted to control the relative timing of discharge between the first laser chamber module and the second laser chamber module so that the first laser chamber module and the second laser chamber module do not discharge substantially simultaneously.The lithographic apparatus may further comprise a control system adapted to control both the first laser chamber module and the second laser chamber module.The lithographic apparatus may further comprise a gas supply system adapted to supply gas to both the first laser chamber module and the second laser chamber module.

[0021] According to another aspect of an embodiment, there is disclosed a method of exposing a substrate in a lithographic apparatus, the method comprising the steps of receiving an indication of one or more target wavelengths from a scanner, generating a first laser radiation beam at the first wavelength using a first laser chamber module in response to the indication, generating a second laser radiation beam at a second wavelength different from the first wavelength using a second laser chamber module in response to the indication, propagating the first beam and the second beam along a common output beam path, and using the first beam and the second beam with the scanner to expose the substrate to radiation at the first wavelength and radiation at the second wavelength in a single pass. The method may further comprise the step of controlling the relative timing of generating the first laser radiation beam at the first wavelength and generating the second laser radiation beam at the second wavelength different from the first wavelength. Controlling the relative timing of the steps of generating a first laser radiation beam at a first wavelength and generating a second laser radiation beam at a second wavelength different from the first wavelength may comprise generating the first laser radiation beam and the second laser radiation beam at substantially the same repetition rate and 180 degrees out of phase with each other. Controlling the relative timing of the steps of generating a first laser radiation beam at a first wavelength and generating a second laser radiation beam at a second wavelength different from the first wavelength may comprise generating the first laser radiation beam and the second laser radiation beam at substantially the same repetition rate, and generating the second beam substantially immediately after generating the first beam. Controlling the relative timing of the steps of generating a first laser radiation beam at a first wavelength and generating a second laser radiation beam at a second wavelength different from the first wavelength may comprise generating the first laser radiation beam and the second laser radiation beam substantially simultaneously. Controlling the relative timing of generating a first laser radiation beam at a first wavelength and generating a second laser radiation beam at a second wavelength different from the first wavelength may include generating the first laser radiation beam and the second laser radiation beam substantially simultaneously.

[0022] According to another aspect of an embodiment, there is disclosed a method of exposing a substrate in a lithographic apparatus, the method comprising: generating a first laser radiation beam at a first wavelength using a first laser chamber module to obtain a first number of pulses and propagating the pulses along an output beam path to the substrate; and generating a second laser radiation beam at a second wavelength using a second laser chamber module to obtain a second number of pulses and propagating the pulses along the output beam path to the substrate. The first wavelength may be substantially the same as the second wavelength. The first wavelength may be different from the second wavelength. The first number of pulses may be the same as the second number of pulses. The first number of pulses may be different from the second number of pulses. The first beam may have a first pulse energy and the second beam may have a second pulse energy different from the first pulse energy. The method may further comprise narrowing a bandwidth of the light beam generated by the first laser chamber module. The method may further include narrowing the bandwidth of the light beam generated by the second laser chamber module. The method may further include narrowing the bandwidth of the light beam generated by the first laser chamber module by a first amount and narrowing the bandwidth of the light beam generated by the second laser chamber module by a second amount different from the first amount. The method may further include generating a command signal, wherein the generating the first laser radiation beam and the generating the second laser radiation beam are performed in response to the command signal. The method may further include generating a first command signal and a second command signal, wherein the generating the first laser radiation beam is performed in response to the generating the first command signal and the second command signal, and the generating the second laser radiation beam is performed in response to the second command signal.

[0023]

[0023] Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are 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 relevant art based on the teachings contained herein. [Brief explanation of the drawings]

[0024]

[0024] The accompanying drawings, which are incorporated in and form part of this specification, illustrate the invention and, together with the description, serve to further explain the principles of the invention and to enable those skilled in the art to make and use the invention.

[0025] [Figure 1] FIG. 1 is a functional block diagram of a conventional two-chamber laser system. [Figure 2]

[0026] FIG. 2 is a functional block diagram of a conventional pulse power circuit that may be used in the system of FIG. 1. [Figure 3]

[0027] FIG. 1 is a functional block diagram of a two-chamber laser system according to an aspect of an embodiment. [Figure 4]

[0028] FIG. 10 illustrates the relative timing of possible discharges in two laser chambers according to an aspect of an embodiment. [Figure 5]

[0029] FIG. 10 illustrates another possible relative timing of discharges in two laser chambers according to an aspect of an embodiment. [Figure 6]

[0030] FIG. 1 is a diagram of a line narrowing module that may be advantageously used in accordance with certain aspects of an embodiment. [Figure 7]

[0031] 1 is a conceptual graph of an output spectrum that may be generated in accordance with certain aspects of an embodiment.

[0026]

[0032] The features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the drawings, in which like reference numerals identify corresponding elements throughout, and in which like reference numerals generally indicate identical, functionally similar, and / or structurally similar elements. DETAILED DESCRIPTION OF THE INVENTION

[0027]

[0033] Avoiding the need for additional exposure passes benefits wafer throughput rates. It would also be beneficial to be able to increase the amount of power delivered to the wafer beyond the limits of what a single laser can provide. This could theoretically be achieved by using two lasers with overlapping beams connected to a scanner, allowing multi-wavelength exposures to be achieved in a single pass. Because a single KrF laser has the maximum output power, higher powers can be achieved by connecting two lasers to a single scanner. However, using two separate lasers occupies additional floor space in a fabrication facility and involves duplicating the laser subsystem (e.g., gas handling, power distribution, sealing, and mechanical structures). An efficient method for generating multiple laser beams without completely duplicating all of the components of the entire laser system is needed.

[0028]

[0034] This specification discloses one or more embodiments incorporating features of the present invention. The disclosed embodiment or embodiments are merely exemplary of the invention. The scope of the invention is not limited to the disclosed embodiment or embodiments. The invention is defined by the claims appended hereto.

[0029]

[0035] References to described embodiments, and to "one embodiment," "an embodiment," "an exemplary embodiment," etc., herein indicate that the described embodiments may include a particular feature, structure, or characteristic, but that each embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with one embodiment, it is understood that it is within the knowledge of one of ordinary skill in the art to implement such feature, structure, or characteristic in connection with other embodiments, whether or not explicitly described.

[0030]

[0036] Before describing the embodiments in more detail, it is helpful to illustrate an exemplary environment in which embodiments of the present invention may 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 at the input port of a lithography machine 12, such as a stepper or scanner machine. The main components of the laser system 10 may be located below floor 14, where the scanner 12 is located as shown. The laser system 10 includes a beam delivery unit 16, which provides a sealed beam path for delivering the laser beam to the input port of the scanner 12. The particular light source system illustrated 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 includes various components, generally designated optics 22 and 24, for controlling the spectral characteristics of the pulses and for shaping the pulses. Further details of the construction and operation of such laser systems can be found, for example, in U.S. Patent No. 7,079,564, entitled "Control System for a Two Chamber Gas Discharge Laser," issued July 18, 2006, the entire contents of which are incorporated herein by reference.

[0031]

[0037] The master oscillator 18 and power amplifier 20 each contain two elongated electrodes, a laser gas, a fan for circulating the gas between the electrodes, and a water-cooled, finned heat exchanger. The master oscillator 18 generates a first laser beam that is amplified in two passes by the power amplifier 20 to produce an output laser beam indicated by the arrow in FIG.

[0032]

[0038] Referring to Figure 2, for example, there is shown a pulse power circuit including a high voltage resonant power supply 30, a commutator module 32, a compression head module 34, and a laser chamber module 36. The high voltage resonant power supply module 30 converts three-phase utility plant power to a high DC voltage. The commutator module 32 and the compression head module 34 compress and amplify the electrical energy from the resonant power supply module 30 so that a desired discharge voltage is applied across electrodes in the laser chamber module 36 to generate pulses. Further details regarding the operation of this circuit can be found in U.S. Patent No. 7,002,443, entitled "Method and Apparatus for Cooling Magnetic Circuit Elements," issued February 21, 2006, the entire contents of which are incorporated herein by reference.

[0033]

[0039] Light sources used in advanced photolithography typically require sources with narrow spectral bandwidths to support achieving the required uniformity of the critical dimensions printed on the substrate (CD uniformity, or CDU). However, this also limits the process window available to semiconductor manufacturers in high-NA systems with small depth of focus. A particular challenge for contact layers is that the process window area shrinks as feature sizes shrink.

[0034]

[0040] A technique called focal drilling technology supports a larger process window in the patterning of contact and via layers. Focal drilling requires wide spectral bandwidth tuning capability along with the necessary supporting metrology and control capabilities, thereby providing semiconductor manufacturers with greater process latitude. One method of spectral tuning is called RELAX. See I. Lalovic et al., "RELAX: Resolution Enhancement by Laser-spectrum Adjusted Exposure," Optical Microlithography VXIII, Proc. of SPIE Vol. 5754, 2005, the contents of which are incorporated herein by reference.

[0035]

[0041] As mentioned above, depth of focus is a function of wavelength. DOF is particularly important for 3D NAND. In this technology, the applied photoresist is very thick, about 1-15 μm, significantly exceeding the typical DOF of scanner systems. Currently, manufacturing requires a two-step process in which the focus is set a few microns below the bottom of the structure, and then for a second pass, the wafer is transported with the focus some distance higher, for example, in the range of about 1 μm to about 4 μm.

[0036]

[0042] According to certain aspects of certain embodiments, the need for multiple passes of the wafer is avoided by exposing the wafer to two different wavelength beams generated by two separate laser cavities during a single exposure, thus enabling shot-by-shot adjustment of the focal plane depth and single-pass illumination of each target portion of the substrate with multiple wavelengths.

[0037]

[0043] In the configuration shown in FIG. 3 , 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 generates a discharge in a first laser chamber module 50. The second compression head 48 generates a discharge in a second laser chamber module 52. Also shown in FIG. 3 are optical components for conditioning 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 may control the first line narrowing module 54 and the second line narrowing module 56 so that the bandwidths and wavelengths of the light beams generated by the first laser chamber module 50 and the second laser chamber module 52 are different from each other.

[0038]

[0044] Various triggering configurations may be employed. For example, one trigger may be used to fire both chambers, with or without a delay between the trigger and the discharge of one or both chambers. Alternatively, the trigger may be generated separately, i.e., by separate circuitry, so that the two chambers have different voltage / energy commands.

[0039]

[0045] Additionally, various system components that may be used in common by the first laser chamber module 50 and the second laser chamber module 52, such as gas handling systems, control systems, interfaces, power distribution systems, cooling water systems, power supplies for the chamber filters and blowers, beam path purge systems, etc., are indicated generally by 68. Thus, in the configuration shown, the two laser chambers can share these components, and having two of each component is unnecessary.

[0040]

[0046] The configuration of FIG. 3 also includes a control circuit 70 that can operate the two lasers with independent energies and control the relative firing times, bandwidths, and wavelengths, and a scanner interface that can divide the energy / pulse commands between the two lasers.

[0041]

[0047] 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. One way to cause the combination of the beams from these two lasers in a single pass is to transmit the beams through a rotating prism. In one embodiment, the first laser chamber module 50 generates laser radiation at a first wavelength, while the second laser chamber module 52 generates laser radiation at a second wavelength that is different from the first wavelength. Thus, the two chambers work together to produce radiation at different wavelengths that have different focal planes on the wafer and operate at different depths.

[0042]

[0048] FIG. 3 also shows a first metrology unit 72 arranged to measure parameters, including the wavelength, of the light beam generated by the first laser chamber module 50. The configuration shown in FIG. 3 also includes a second metrology unit 74 arranged to measure parameters, including the wavelength, of the light 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 combined light beam from the first laser chamber module and the light beam from the second chamber module. It will be understood that the combined beam may simply be the beam from one laser chamber when the other chamber is not firing. The metrology units provide the results of the measurements to a control circuit 70. The metrology units as shown can independently measure the wavelengths of the light from the two laser chamber modules and the wavelength of the combined beam. The control circuit 70 can use the measurement results to control the wavelength of the light beam generated by each laser chamber module.

[0043]

[0049] By interleaving the firing of the two chambers, an effective repetition rate of twice the normal can be achieved. This is shown in FIG. 4. The top timing diagram shows when the first laser chamber module 50 can fire, and the middle timing diagram shows when the second laser chamber module 52 can fire. By combining the beams from the two lasers, an effective repetition rate can be achieved that is twice the repetition rate of either of the two lasers, as shown in the bottom timing diagram. As mentioned above, any one of a number of configurations can be used to combine the beam paths of multiple lasers.

[0044]

[0050] The firing sequence of two (or more) laser chamber modules can be set in any one of a variety of patterns. For example, the sequence can be set so that the chambers alternate firing shot by shot. Alternatively, the sequence can be set so that a first laser chamber module fires a first number of shots, followed by a second chamber firing a second number of shots, where the first and second numbers can be equal or unequal. These sequences can be employed with laser chamber modules generating light of the same wavelength or different wavelengths. Also, laser chamber modules generating light at two different wavelengths can be fired at substantially different repetition rates to create spectra with different energy contents in each of the two wavelength beams. The second discharge rate can be, for example, an integer multiple of the first discharge rate, resulting in a discharge rate ratio of, for example, 2:1. The relationship between the first discharge rate and the second discharge rate can also be a ratio of two integers, such as 3:2.

[0045]

[0051] 5, the timing difference Δt between the firing of the two lasers can be set to essentially any value, including 0 (assuming the optics can withstand twice the instantaneous power level) or so small that the two pulses occur one after the other (i.e., during the same exposure) rather than simultaneously, resulting in twice the effective dose as shown. The top timing diagram shows when the first laser chamber module 50 can fire, and the middle timing diagram shows when the second laser chamber module 52 can fire. Thus, the beams from the two lasers can be generated one after the other as shown and combined to obtain an effective dose that is twice the dose of either of the two lasers, as shown in the bottom timing diagram.

[0046]

[0052] According to another aspect of some embodiments, both chambers are operated simultaneously, but if the end user desires lower power output, they can use only one or the other of the chambers. By alternating which chamber is used for one chamber operation, the wear on the chambers can be balanced and the lifespan can be maximized.

[0047]

[0053] It should be noted that there may be situations where the outputs of both lasers firing simultaneously could damage the system optics. In such situations, it may be beneficial to have control circuitry that prevents simultaneous firing. However, such lasers may be fired one after the other to obtain higher doses per interval without damaging the optics.

[0048]

[0054] According to another aspect of an embodiment, one or both of the line narrowing modules 54 and 56 shown in FIG. 3 can be configured to produce two wavelengths, i.e., two-color output. The wavelengths may be peak separations around a center wavelength. When both line narrowing modules are configured to produce two wavelengths in this manner, the peak separations may be the same or different. Using such a configuration, up to four wavelengths can be produced.

[0049]

[0055] As shown in Figure 6, a line narrowing module 80, which may function as one or both of the line narrowing modules 54 and 56 of Figure 3, may include prisms 82, 84, and 86 that together form a prism beam expander, a mirror 90 with an actuator 92, and a grating 96. The angle of the beam incident on the grating 96 determines the wavelength of the laser. Adjusting this angle therefore results in wavelength tuning of the laser. By actuating the prism (dither), split mirror 90, or split grating 96, a dual-peak spectrum can be generated pulse-to-pulse in the line narrowing module 80.

[0050]

[0056] 7 shows an exemplary output spectrum when two line narrowing modules are configured for two-color output. The x-axis is wavelength in arbitrary units, and the y-axis is intensity in arbitrary units. Peaks 100 and 102 are produced by the first laser chamber module 50, and peaks 110 and 112 are produced by the second laser chamber module 52. This four-wavelength spectrum may be useful for exposing thicker photoresists and may serve as an alternative (or complement) to meeting higher power requirements.

[0051]

[0057] The laser firing pattern can be "tic-toc," where one laser fires first, then the other, then the first again, with the same firing interval, or "stutter," where the interval between firings of the two lasers is less than half the interval between successive firings of the same laser.

[0052]

[0058] As mentioned above, the beam from the first laser chamber module 50 and the beam from the second laser chamber module 52 may be combined by the beam combiner 66. Another way to combine two beams when they have different wavelengths is to use a dichroic mirror. A dichroic mirror functions so that one wavelength (short pass) is transmitted and the other wavelength is reflected. Another technique for combining two laser beams having the same or different wavelengths involves the use of a pick-off mirror. Another configuration for combining two beams includes a mirror with a reflective coating 130 on a portion of the mirror. One laser beam may be reflected from the reflective coating while the other propagates through the uncoated portion of the mirror. Yet another configuration for combining two beams includes impinging the beams on a mirror in a first position where one beam propagates in a use direction and the second beam propagates in another direction, and then moving the mirror (e.g., by rotation) to a second position where only the second beam propagates in the use direction. The same effect can be achieved by not moving the mirrors but dithering the propagation direction of one or both of the beams.

[0053]

[0059] While the foregoing description is a specific example of two laser chambers, it will be apparent that more than two chambers may be used, with one or more of the chambers configured to generate laser radiation having multiple frequencies.

[0054]

[0060] A single system with two laser chambers and shared auxiliary systems may be more compact than two complete laser systems, less expensive to operate than a 60 W or less MOPA laser, and may provide more precise wavelength control than can be achieved by dithering the wavelength with a single laser, allowing for higher repetition rates with the potential for better dose management.

[0055]

[0061] Also, more than two laser chamber modules may be present and used. For example, a MOPA / MOPA chamber pair may be incorporated into a system offering higher repetition rates or power. (Similarly, a dual "MOPRA" chamber pair may be incorporated into a system where the power amplifier includes some optical recycling through the gain medium; MOPA / MOPRA pairs are also contemplated.) These chambers can be made physically compact because each low repetition rate can be used independently.

[0056]

[0062] It is to be understood that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. While the Summary and Abstract sections may describe one or more exemplary embodiments of the invention as contemplated by the inventors, they are not exhaustive and therefore are not intended to limit the scope of the invention and the appended claims in any way.

[0057]

[0063] The present invention has been described above using functional units that represent the performance of specific functions and relationships between them. The boundaries of these functional units have been arbitrarily defined herein for the convenience of description. Other boundaries may be defined as long as the specific functions and relationships between them are appropriately performed.

[0058]

[0064] The foregoing description of specific embodiments fully discloses the general nature of the present invention, so that others, applying knowledge within the skill of the art, will be able to readily modify and / or adapt such specific embodiments for various applications without undue experimentation without departing from the basic concepts of the present invention. Such adaptations and modifications are therefore intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description rather than limitation, and that the terms or phrases herein should be interpreted in light of the above teaching and guidance by those of ordinary skill in the art.

[0059]

[0065] Other aspects of the invention are described in the following numbered clauses. 1. A first laser chamber module adapted to generate a first laser radiation beam at a first wavelength; a second laser chamber module adapted to generate a second beam of laser radiation at a second wavelength different from the first wavelength; a beam combiner positioned to receive the first beam and the second beam and adapted to propagate the first beam and the second beam along a common output beam path. 2. The gas discharge laser system of clause 1, wherein the first laser chamber module comprises a first excimer laser chamber module. 3. The gas discharge laser system of clause 2, wherein the first excimer laser chamber module comprises an ArF laser chamber module. 4. The gas discharge laser system of clause 2, wherein the first excimer laser chamber module comprises a KrF laser chamber module. 5. A gas discharge laser system as described in any one of clauses 1 to 4, wherein the second laser chamber module comprises a second excimer laser chamber module. 6. The gas discharge laser system of clause 5, wherein the second excimer laser chamber module is an ArF laser chamber module. 7. The gas discharge laser system of clause 5, wherein the second excimer laser chamber module is a KrF laser chamber module. 8. The gas discharge laser system of clause 1, further comprising a third laser chamber module adapted to generate a third beam of laser radiation, wherein a beam combiner is positioned to receive the third beam and adapted to propagate the third beam along a common output beam path. 9. The gas discharge laser system of clause 1, further comprising a discharge timing circuit arranged to control the relative discharge timing of the first laser chamber module and the second laser chamber module. 10. A gas discharge laser system as described in clause 9, wherein the discharge timing circuit is adapted to control the relative discharge timing of the first laser chamber module and the second laser chamber module so that the first laser chamber module discharges at a first repetition rate and the second laser chamber module discharges at a second repetition rate that is substantially the same as the first repetition rate and offset relative to the first repetition rate by half the period of the first repetition rate. 11. The gas discharge laser system of clause 9, wherein the discharge timing circuit is adapted to control the relative discharge timing of the first laser chamber module to the second laser chamber module so that the first laser chamber module and the second laser chamber module discharge at substantially the same repetition rate, and the second laser chamber module discharges substantially immediately after the first laser chamber module finishes discharging. 12. A gas discharge laser system as described in clause 9, wherein the discharge timing circuit is adapted to control the relative discharge timing of the first laser chamber module and the second laser chamber module so that the first laser chamber module and the second laser chamber module discharge substantially simultaneously. 13. The gas discharge laser system of clause 9, wherein the discharge timing circuit is adapted to control the relative discharge timing of the first laser chamber module and the second laser chamber module so that the first laser chamber module and the second laser chamber module do not discharge substantially simultaneously. 14. The gas discharge laser system of clause 9, wherein the discharge timing circuit is adapted to generate a common command to fire both the first laser chamber module and the second laser chamber module. 15. A gas discharge laser system as described in clause 14, wherein the first laser chamber module is adapted to fire without delay after a common command. 16. The gas discharge laser system of clause 14, wherein the first laser chamber module is adapted to fire with a delay after a common command. 17. A gas discharge laser system according to any one of clauses 14, 15 and 16, wherein the second laser chamber module is adapted to fire without delay after a common command. 18. A gas discharge laser system as described in any one of clauses 14, 15 and 16, wherein the second laser chamber module is adapted to fire with a delay after a common command. 19. A gas discharge laser system as described in clause 9, wherein the discharge timing circuit is adapted to generate a first command to cause the first laser chamber module to fire and a second command to cause the second laser chamber module to fire. 20. The gas discharge laser system of clause 19, wherein the first laser chamber module is adapted to fire without delay after the first command. 21. The gas discharge laser system of clause 19, wherein the first laser chamber module is adapted to fire with a delay after the first command. 22. A gas discharge laser system as described in any one of clauses 19, 20 and 21, wherein the second laser chamber module is adapted to fire without delay after a second command. 23. A gas discharge laser system as described in any one of clauses 19, 20 and 21, wherein the second laser chamber module is adapted to fire after a delay on command. 24. The gas discharge laser system of clause 1, wherein the first laser chamber module fires at a first repetition rate and the second laser chamber module fires at a second repetition rate different from the first repetition rate. 25. The gas discharge laser system of clause 24, wherein the discharge rate ratio of the first repetition rate to the second repetition rate is a ratio of two integers. 26. A gas discharge laser according to clause 25, wherein the ratio of the two integers is 2:1. 27. A gas discharge laser according to clause 25, wherein the ratio of the two integers is 3:2. 28. The gas discharge laser system of clause 1, further comprising a control system adapted to control both the first laser chamber module and the second laser chamber module. 29. The gas discharge laser system of clause 1, further comprising a gas supply system adapted to supply gas to both the first laser chamber module and the second laser chamber module. 30. The gas discharge laser system of clause 1, further comprising a first laser chamber metrology unit arranged to measure parameters of the light beam generated by the first laser chamber module. 31. A gas discharge laser system according to clause 1 or 30, further comprising a second laser chamber metrology unit arranged to measure parameters of the light beam generated by the second laser chamber module. 32. A gas discharge laser system as described in any one of clauses 1, 30 or 31, further comprising a combined beam metrology unit arranged to measure parameters of a combination of the light beam generated by the first laser chamber module and the light beam generated by the second laser chamber module. 33. The gas discharge laser system of clause 30, further comprising a control unit positioned to receive output from the first laser chamber metrology unit and configured to control the wavelength of the light beam generated by the first laser chamber module based at least in part on the output of the first laser chamber metrology unit. 34. The gas discharge laser system of clause 30 or 33, further comprising a control unit positioned to receive output from the second laser chamber metrology unit and configured to control the wavelength of the light beam generated by the second laser chamber module based at least in part on the output of the second laser chamber metrology unit. 35. The gas discharge laser system of clause 32, further comprising a control unit positioned to receive the output of the combined beam metrology unit and configured to control the spectrum of the combination of the light beam generated by the first laser chamber module and the light beam generated by the second laser chamber module based at least in part on the output of the combined beam metrology unit. 36. The gas discharge laser system of clause 1, further comprising a first laser chamber line narrowing module positioned to receive the light beam from the first laser chamber module and configured to narrow the bandwidth of the light beam from the first laser chamber module. 37. The gas discharge laser system of clause 36, further comprising a second laser chamber line narrowing module positioned to receive the light beam from the second laser chamber module and configured to narrow the bandwidth of the light beam from the second laser chamber module. 38. The gas discharge laser system of clause 36, further comprising: a second laser chamber line narrowing module arranged to receive the light beam from the second laser chamber module and configured to narrow the bandwidth of the light beam from the second laser chamber module; and a control unit connected to the first laser chamber line narrowing module and the second laser chamber line narrowing module and adapted to control the first laser chamber line narrowing module and the second laser chamber line narrowing module so that the first bandwidth is substantially the same as the second bandwidth. 39. The gas discharge laser system of clause 36, further comprising: a second laser chamber line narrowing module arranged to receive the light beam from the second laser chamber module and configured to narrow a bandwidth of the light beam from the second laser chamber module; and a control unit connected to the first laser chamber line narrowing module and the second laser chamber line narrowing module and adapted to control the first laser chamber line narrowing module and the second laser chamber line narrowing module so that the first bandwidth is different from the second bandwidth. 40. A first laser chamber module adapted to generate a first laser radiation beam at a first wavelength; a second laser chamber module adapted to generate a second beam of laser radiation at a second wavelength different from the first wavelength; a beam combiner positioned to receive the first beam and the second beam and adapted to propagate the first beam and the second beam along a common output beam path; a scanner positioned to receive the first beam and the second beam, the scanner configured to provide instructions for adjusting the first and second wavelengths. 41. A lithographic apparatus according to clause 40, further comprising a discharge timing circuit arranged to control the relative timing of discharges between the first laser chamber module and the second laser chamber module. 42. A lithographic apparatus as described in clause 41, wherein the discharge timing circuit is adapted to control the relative discharge timing of the first laser chamber module and the second laser chamber module so that the first laser chamber module and the second laser chamber module discharge at substantially the same repetition rate and 180 degrees out of phase with each other. 43. A lithographic apparatus as described in clause 41, wherein the discharge timing circuit is adapted to control the relative discharge timing of the first laser chamber module and the second laser chamber module so that the first laser chamber module and the second laser chamber module discharge at substantially the same repetition rate, and the second laser chamber module discharges substantially immediately after the first laser chamber module finishes discharging. 44. A lithographic apparatus as described in clause 41, wherein the discharge timing circuit is adapted to control the relative discharge timing of the first laser chamber module and the second laser chamber module so that the first laser chamber module and the second laser chamber module discharge substantially simultaneously. 45. A lithographic apparatus as described in clause 41, wherein the discharge timing circuit is adapted to control the relative discharge timing of the first laser chamber module and the second laser chamber module so that the first laser chamber module and the second laser chamber module do not discharge substantially simultaneously. 46. A lithographic apparatus according to clause 40, further comprising a control system adapted to control both the first laser chamber module and the second laser chamber module. 47. A lithographic apparatus according to clause 40, further comprising a gas supply system adapted to supply gas to both the first laser chamber module and the second laser chamber module. 48. A method of exposing a substrate in a lithographic apparatus, the method comprising: receiving an indication of one or more target wavelengths from the scanner; In response to instructions, generating a first beam of laser radiation at a first wavelength using a first laser chamber module; In response to the instruction, generating a second beam of laser radiation using a second laser chamber module at a second wavelength different from the first wavelength; propagating the first beam and the second beam along a common output beam path; and exposing the substrate to radiation at a first wavelength and radiation at a second wavelength in a single pass using the first beam and the second beam in a scanner. 49. The method of clause 48, further comprising the step of controlling the relative timing of the steps of generating a first laser radiation beam at a first wavelength and generating a second laser radiation beam at a second wavelength different from the first wavelength. 50. The method of clause 49, wherein the step of controlling the relative timing of the steps of generating a first laser radiation beam at a first wavelength and generating a second laser radiation beam at a second wavelength different from the first wavelength comprises generating the first laser radiation beam and the second laser radiation beam at substantially the same repetition rate and 180 degrees out of phase with each other. 51. The method of clause 49, wherein the step of controlling the relative timing of the steps of generating a first laser radiation beam at a first wavelength and generating a second laser radiation beam at a second wavelength different from the first wavelength comprises generating the first laser radiation beam and the second laser radiation beam at substantially the same repetition rate, and generating the second beam substantially immediately after generating the first beam. 52. The method of clause 49, wherein the step of controlling the relative timing of the steps of generating a first laser radiation beam at a first wavelength and generating a second laser radiation beam at a second wavelength different from the first wavelength comprises generating the first laser radiation beam and the second laser radiation beam substantially simultaneously. 53. The method of clause 49, wherein the step of controlling the relative timing of the steps of generating a first laser radiation beam at a first wavelength and generating a second laser radiation beam at a second wavelength different from the first wavelength comprises generating the first laser radiation beam and the second laser radiation beam substantially simultaneously. 54. A method of exposing a substrate in a lithographic apparatus, the method comprising: generating a first beam of laser radiation at a first wavelength using a first laser chamber module to obtain a first number of pulses, and propagating the pulses along an output beam path to a substrate; generating a second beam of laser radiation at a second wavelength using a second laser chamber module to obtain a second number of pulses, and propagating the pulses along an output beam path to the substrate. 55. The method of clause 54, wherein the first wavelength is substantially the same as the second wavelength. 56. The method of clause 54, wherein the first wavelength is different from the second wavelength. 57. The method of any one of clauses 54 to 56, wherein the first number of pulses is the same as the second number of pulses. 58. The method of any one of clauses 54 to 56, wherein the first number of pulses is different from the second number of pulses. 59. The method of any one of clauses 54 to 58, wherein the first beam has a first pulse energy and the second beam has a second pulse energy different from the first pulse energy. 60. The method of any one of clauses 54 to 59, further comprising narrowing the bandwidth of the light beam generated by the first laser chamber module. 61. The method of any one of clauses 54 to 59, further comprising narrowing the bandwidth of the light beam generated by the second laser chamber module. 62. The method of clause 54, further comprising narrowing the bandwidth of the light beam generated by the first laser chamber module by a first amount and narrowing the bandwidth of the light beam generated by the second laser chamber module by a second amount different from the first amount. 63. The method of clause 54, further comprising the step of generating a command signal, wherein the steps of generating the first beam of laser radiation and generating the second beam of laser radiation are performed in response to the command signal. 64. The method of clause 54, further comprising the steps of generating a first command signal and generating a second command signal, wherein the step of generating the first laser radiation beam is performed in response to the steps of generating the first command signal and the second command signal, and the step of generating the second laser radiation beam is performed in response to the second command signal. 65. A first laser chamber module adapted to generate a first laser radiation beam having a first spectrum having a first wavelength and a second wavelength different from the first wavelength; a second laser chamber module adapted to generate a second laser radiation beam having a second spectrum having a third wavelength different from the first and second wavelengths, and a fourth wavelength different from the first, second, and third wavelengths; a beam combiner positioned to receive the first beam and the second beam and adapted to propagate the first beam and the second beam along a common output beam path. 66. The gas discharge laser system of clause 65, further comprising a discharge timing circuit arranged to control the relative discharge timing of the first laser chamber module and the second laser chamber module. 67. A gas discharge laser system as described in clause 66, wherein the discharge timing circuit is adapted to control the relative discharge timing of the first laser chamber module and the second laser chamber module such that the first laser chamber module discharges at a first repetition rate and the second laser chamber module discharges at a second repetition rate that is substantially the same as the first repetition rate and offset relative to the first repetition rate by half the period of the first repetition rate. 68. The gas discharge laser system of clause 66, wherein the discharge timing circuit is adapted to control the relative discharge timing of the first laser chamber module and the second laser chamber module so that the first laser chamber module and the second laser chamber module discharge at substantially the same repetition rate, and the second laser chamber module discharges substantially immediately after the first laser chamber module finishes discharging. 69. The gas discharge laser system of clause 66, wherein the discharge timing circuit is adapted to control the relative discharge timing of the first laser chamber module and the second laser chamber module such that the first laser chamber module and the second laser chamber module discharge substantially simultaneously. 70. The gas discharge laser system of clause 65, wherein the first laser chamber module includes a first laser chamber line narrowing module configured to generate a first laser radiation beam in the first laser chamber module having a first spectrum. 71. The gas discharge laser system of clause 70, wherein the second laser chamber module includes a second laser chamber line narrowing module configured to generate a second laser radiation beam in the second laser chamber module having a second spectrum. 72. A method of exposing a substrate in a lithographic apparatus, the method comprising: generating a first beam of laser radiation at a first wavelength and a second wavelength using a first laser chamber module; generating a second beam of laser radiation at a third wavelength and a fourth wavelength; propagating the first beam and the second beam along a common output beam path; and exposing the substrate to radiation at a first wavelength and radiation at a second wavelength in a single pass using the first beam and the second beam in a scanner; The first, second, third, and fourth wavelengths are different from each other. 73. The method of clause 72, further comprising the step of controlling the relative timing of the steps of generating the first beam of laser radiation and the second beam of laser radiation. 74. The method of clause 73, wherein the step of controlling the relative timing of the steps of generating the first laser radiation beam and the second laser radiation beam comprises generating the first laser radiation beam and the second laser radiation beam at substantially the same repetition rate and 180 degrees out of phase with each other. 75. The method of clause 73, wherein the step of controlling the relative timing of the steps of generating the first and second laser radiation beams includes generating the first and second laser radiation beams at substantially the same repetition rate, and generating the second beam substantially immediately after generating the first beam. 76. The method of clause 73, wherein the step of controlling the relative timing of the steps of generating the first laser radiation beam and the second laser radiation beam comprises generating the first laser radiation beam and the second laser radiation beam substantially simultaneously.

[0060]

[0066] Still other embodiments are within the scope of the following claims.

Claims

1. a first laser chamber module adapted to generate a first beam of laser radiation at a first wavelength; a second laser chamber module adapted to generate a second beam of laser radiation at a second wavelength different from the first wavelength; a beam combiner positioned to receive the first beam and the second beam and adapted to propagate the first beam and the second beam along a common output beam path.

2. 10. The gas discharge laser system of claim 1, wherein said first laser chamber module comprises a first excimer laser chamber module.

3. 3. The gas discharge laser system of claim 2 wherein said first excimer laser chamber module comprises an ArF laser chamber module.

4. 3. The gas discharge laser system of claim 2 wherein said first excimer laser chamber module comprises a KrF laser chamber module.

5. 10. The gas discharge laser system of claim 1, wherein said second laser chamber module comprises a second excimer laser chamber module.

6. 5. The gas discharge laser system of claim 4 wherein said second excimer laser chamber module is an ArF laser chamber module.

7. 10. The gas discharge laser system of claim 1, further comprising a third laser chamber module adapted to generate a third beam of laser radiation, the beam combiner being positioned to receive the third beam and adapted to propagate the third beam along the common output beam path.

8. 10. The gas discharge laser system of claim 1, further comprising a discharge timing circuit arranged to control the relative timing of discharges between said first laser chamber module and said second laser chamber module.

9. 9. The gas discharge laser system of claim 8, wherein the discharge timing circuit is adapted to control the relative discharge timing of the first and second laser chamber modules such that the first laser chamber module discharges at a first repetition rate and the second laser chamber module discharges at a second repetition rate that is substantially the same as the first repetition rate and offset relative to the first repetition rate by one-half a period of the first repetition rate.

10. 9. The gas discharge laser system of claim 8, wherein the discharge timing circuit is adapted to control the relative timing of discharges between the first laser chamber module and the second laser chamber module such that the first laser chamber module and the second laser chamber module discharge at substantially the same repetition rate, and the second laser chamber module discharges substantially immediately after the first laser chamber module finishes discharging.

11. 9. The gas discharge laser system of claim 8, wherein the discharge timing circuit is adapted to control the relative discharge timing of the first laser chamber module and the second laser chamber module such that the first laser chamber module and the second laser chamber module discharge substantially simultaneously.

12. 9. The gas discharge laser system of claim 8, wherein the discharge timing circuit is adapted to control the relative discharge timing of the first laser chamber module and the second laser chamber module such that the first laser chamber module and the second laser chamber module do not discharge substantially simultaneously.

13. 9. The gas discharge laser system of claim 8, wherein the discharge timing circuit is adapted to generate a common command to fire both the first laser chamber module and the second laser chamber module.

14. 14. The gas discharge laser system of claim 13, wherein said first laser chamber module is adapted to fire without delay after said common command.

15. 14. The gas discharge laser system of claim 13, wherein said first laser chamber module is adapted to fire with a delay after said common command.

16. 9. The gas discharge laser system of claim 8, wherein the discharge timing circuit is adapted to generate a first command to fire the first laser chamber module and a second command to fire the second laser chamber module.

17. 17. The gas discharge laser system of claim 16, wherein said first laser chamber module is adapted to fire without delay after said first command.

18. 17. The gas discharge laser system of claim 16, wherein said first laser chamber module is adapted to fire with a delay after said first command.

19. 18. The gas discharge laser system of claim 17, wherein said second laser chamber module is adapted to fire with a delay after said command.

20. 10. The gas discharge laser system of claim 1, wherein the first laser chamber module is caused to fire at a first repetition rate and the second laser chamber module is caused to fire at a second repetition rate different from the first repetition rate.

21. 10. The gas discharge laser system of claim 1, further comprising a gas supply system adapted to supply gas to both the first laser chamber module and the second laser chamber module.

22. 10. The gas discharge laser system of claim 1, further comprising a first laser chamber metrology unit positioned to measure parameters of a light beam generated by said first laser chamber module.

23. 10. The gas discharge laser system of claim 1, further comprising a combined beam metrology unit positioned to measure parameters of a combination of the light beam generated by the first laser chamber module and the light beam generated by the second laser chamber module.

24. 24. The gas discharge laser system of claim 23, further comprising a control unit disposed to receive an output of the combined beam metrology unit and configured to control a spectrum of a combination of the light beam generated by the first laser chamber module and the light beam generated by the second laser chamber module based at least in part on the output of the combined beam metrology unit.

25. 10. The gas discharge laser system of claim 1, further comprising a first laser chamber line narrowing module positioned to receive the light beam from the first laser chamber module and configured to narrow a bandwidth of the light beam from the first laser chamber module.

26. 26. The gas discharge laser system of claim 25, further comprising: a second laser chamber line narrowing module positioned to receive the light beam from the second laser chamber module and configured to narrow a bandwidth of the light beam from the second laser chamber module; and a control unit connected to the first laser chamber line narrowing module and the second laser chamber line narrowing module and adapted to control the first laser chamber line narrowing module and the second laser chamber line narrowing module so that the first bandwidth is substantially the same as the second bandwidth.

27. 26. The gas discharge laser system of claim 25, further comprising: a second laser chamber line narrowing module positioned to receive the light beam from the second laser chamber module and configured to narrow a bandwidth of the light beam from the second laser chamber module; and a control unit connected to the first laser chamber line narrowing module and the second laser chamber line narrowing module and adapted to control the first laser chamber line narrowing module and the second laser chamber line narrowing module so that the first bandwidth is different from the second bandwidth.

28. a first laser chamber module adapted to generate a first beam of laser radiation at a first wavelength; a second laser chamber module adapted to generate a second beam of laser radiation at a second wavelength different from the first wavelength; a beam combiner positioned to receive the first beam and the second beam and adapted to propagate the first beam and the second beam along a common output beam path; a scanner positioned to receive the first beam and the second beam, the scanner configured to provide instructions for adjusting the first and second wavelengths.

29. 29. The lithographic apparatus of claim 28, further comprising a discharge timing circuit arranged to control the relative timing of discharges between the first laser chamber module and the second laser chamber module.

30. 30. The lithographic apparatus of claim 29, wherein the discharge timing circuit is adapted to control the relative discharge timing of the first laser chamber module and the second laser chamber module such that the first laser chamber module and the second laser chamber module discharge substantially simultaneously.

31. 30. The lithographic apparatus of claim 29, wherein the discharge timing circuit is adapted to control the relative discharge timing of the first laser chamber module and the second laser chamber module such that the first laser chamber module and the second laser chamber module do not discharge substantially simultaneously.

32. 29. The lithographic apparatus of claim 28, further comprising a gas supply system adapted to supply gas to both the first laser chamber module and the second laser chamber module.

33. 1. A method of exposing a substrate in a lithographic apparatus, the method comprising: receiving an indication of one or more target wavelengths from the scanner; generating a first beam of laser radiation at a first wavelength using a first laser chamber module in response to the instruction; responsive to the instruction, generating a second beam of laser radiation using a second laser chamber module at a second wavelength different from the first wavelength; propagating the first beam and the second beam along a common output beam path; and using the first beam and the second beam in the scanner to expose the substrate to radiation at the first wavelength and radiation at the second wavelength in a single pass.

34. 34. The method of claim 33, further comprising controlling the relative timing of the steps of generating the first laser radiation beam at the first wavelength and generating the second laser radiation beam at the second wavelength different from the first wavelength.

35. 35. The method of claim 34, wherein controlling the relative timing of the steps of generating the first laser radiation beam at the first wavelength and generating the second laser radiation beam at the second wavelength different from the first wavelength comprises generating the first laser radiation beam and the second laser radiation beam at substantially the same repetition rate and 180 degrees out of phase with each other.

36. 35. The method of claim 34, wherein the step of controlling the relative timing of the steps of generating the first laser radiation beam at the first wavelength and generating the second laser radiation beam at the second wavelength different from the first wavelength comprises generating the first laser radiation beam and the second laser radiation beam at substantially the same repetition rate and generating the second beam substantially immediately after generating the first beam.

37. 35. The method of claim 34, wherein controlling the relative timing of the steps of generating the first laser radiation beam at the first wavelength and generating the second laser radiation beam at the second wavelength different from the first wavelength comprises generating the first laser radiation beam and the second laser radiation beam substantially simultaneously.

38. 35. The method of claim 34, wherein controlling the relative timing of the steps of generating the first laser radiation beam at the first wavelength and generating the second laser radiation beam at the second wavelength different from the first wavelength comprises generating the first laser radiation beam and the second laser radiation beam substantially simultaneously.

39. 1. A method of exposing a substrate in a lithographic apparatus, the method comprising: generating a first beam of laser radiation at a first wavelength using a first laser chamber module to obtain a first number of pulses, and propagating the pulses along an output beam path to the substrate; generating a second beam of laser radiation at a second wavelength using a second laser chamber module to obtain a second number of pulses, and propagating the pulses along the output beam path to the substrate.

40. 40. The method of claim 39, wherein the first wavelength is substantially the same as the second wavelength.

41. 40. The method of claim 39, wherein the first wavelength is different from the second wavelength.

42. 42. The method of claim 41, wherein the first number of pulses is the same as the second number of pulses.

43. 42. The method of claim 41, wherein the first number of pulses is different from the second number of pulses.

44. 40. The method of claim 39, wherein the first beam has a first pulse energy and the second beam has a second pulse energy different from the first pulse energy.

45. 40. The method of claim 39, further comprising narrowing the bandwidth of the light beam generated by the first laser chamber module.

46. 40. The method of claim 39, further comprising narrowing the bandwidth of the light beam generated by the first laser chamber module by a first amount and narrowing the bandwidth of the light beam generated by the second laser chamber module by a second amount different from the first amount.

47. 40. The method of claim 39, further comprising generating a first command signal and generating a second command signal, wherein the generating a first beam of laser radiation is performed in response to the generating the first command signal and the generating a second command signal, and the generating a second beam of laser radiation is performed in response to the second command signal.

48. a first laser chamber module adapted to generate a first laser radiation beam having a first spectrum having a first wavelength and a second wavelength different from the first wavelength; a second laser chamber module adapted to generate a second laser radiation beam having a second spectrum having a third wavelength different from the first and second wavelengths, and a fourth wavelength different from the first, second, and third wavelengths; a beam combiner positioned to receive the first beam and the second beam and adapted to propagate the first beam and the second beam along a common output beam path.

49. 49. The gas discharge laser system of claim 48, further comprising a discharge timing circuit arranged to control the relative timing of discharges between the first laser chamber module and the second laser chamber module.

50. 50. The gas discharge laser system of claim 49, wherein the discharge timing circuit is adapted to control the relative timing of discharges between the first laser chamber module and the second laser chamber module such that the first laser chamber module and the second laser chamber module discharge at substantially the same repetition rate, and the second laser chamber module discharges substantially immediately after the first laser chamber module finishes discharging.

51. 50. The gas discharge laser system of claim 49, wherein the discharge timing circuit is adapted to control the relative timing of discharges between the first laser chamber module and the second laser chamber module such that the first laser chamber module and the second laser chamber module discharge substantially simultaneously.

52. 49. The gas discharge laser system of claim 48, wherein the first laser chamber module includes a first laser chamber line narrowing module configured to generate the first laser radiation beam having the first spectrum in the first laser chamber module.

53. 53. The gas discharge laser system of claim 52, wherein the second laser chamber module includes a second laser chamber line narrowing module configured to generate the second laser radiation beam having the second spectrum in the second laser chamber module.

54. 1. A method of exposing a substrate in a lithographic apparatus, the method comprising: generating a first beam of laser radiation at a first wavelength and a second wavelength using a first laser chamber module; generating a second beam of laser radiation at a third wavelength and a fourth wavelength; propagating the first beam and the second beam along a common output beam path; and exposing the substrate to radiation at the first wavelength and radiation at the second wavelength in a single pass using the first beam and the second beam in a scanner; The first, second, third, and fourth wavelengths are different from one another.

55. 55. The method of claim 54, further comprising controlling the relative timing of said generating said first beam of laser radiation and said second beam of laser radiation.

56. 56. The method of claim 55, wherein controlling the relative timing of generating the first beam of laser radiation and the second beam of laser radiation comprises generating the first beam of laser radiation and the second beam of laser radiation substantially simultaneously.

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