Discharge chamber accommodating multiple discharges

Abstract

A discharge chamber for use in a deep ultraviolet radiation source, the discharge chamber containing a first pair of electrodes that may serve to provide a seed pulse and second pair of electrodes that may serve to amplify the seed pulse, the discharge chamber also containing a gas circulatory system including at least one fan that establishes a closed curve circulatory flow loop of lasing gas in the discharge chamber.

Description

DISCHARGE CHAMBER ACCOMMODATING MULTIPLE DISCHARGESCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 679,905 which was filed on August 06, 2024 and which is incorporated herein in its entirety by reference.FIELD

[0002] The disclosed subject matter relates to systems using multiple discharges for generating deep ultraviolet (DUV) laser radiation.BACKGROUND

[0003] Photolithography is a process by which semiconductor circuitry is patterned on a substrate such as a silicon wafer. A photolithography radiation source provides DUV radiation (radiation having wavelengths in a range of about 100 nanometers (nm) to about 400 nm) used to expose a photoresist on the wafer. Often, the radiation source is a laser source and the radiation is a pulsed laser beam. The radiation beam is passed through a beam delivery unit, then through or reflected by a reticle or a mask, and then projected onto a silicon wafer coated with photoresist. In this way, a chip design is patterned onto a photoresist that is then etched and cleaned.

[0004] Many systems that produce a beam of DUV laser radiation do so by creating discharges in a discharge region between electrodes in one or more discharge chambers. More precisely, each DUV discharge chamber has a pair of electrodes (a pair being comprised of one anode and one cathode) arranged to generate plasma discharges from a lasing gas (generally a gas mixture) when a high voltage is applied across the electrodes. The discharge is pulsed at a repetition rate of, for example, 6 kHz (6000 times per second), and thus produces a train or burst of DUV radiation emission pulses.

[0005] One known system obtains higher pulse energies by using a dual chamber architecture having two separate gain chambers. One of the gain chambers may be a seed pulse chamber such as a master oscillator (MO) chamber and the other of the chambers may be an amplification chamber such as a power amplifier (PA) chamber arranged to receive and amplify the seed pulse.

[0006] During a discharge the gas in the discharge region between the electrodes becomes depleted of one or more components. Thus a DUV discharge chamber typically includes a fan, e.g., a cross flow blower to create and sustain the gas flow in the discharge chamber. The gas flow replaces the residual gas in the discharge region with fresh gas from elsewhere in the chamber for the next discharge event.

[0007] As demand for higher throughput increases there is a concomitant demand for higher discharge repetition rates. Higher repetition rates in turn require faster gas flow speeds to clear ionized gases from the discharge region between the electrodes from one pulse to the next. This presents a design challengebecause the gas speeds inside the chambers are already so high that there is insufficient space to fit bigger fans or larger motors needed to increase the interelectrode flow speed substantially.

[0008] The fan can consume a substantial amount of energy while driving a flow of gas in the discharge chamber. The amount of energy can constitute a non-negligible fraction of the total energy used by the overall DUV laser system in discharge production. The amount of energy used by the blower motor limits the overall ability to control energy consumption. It also poses a major obstacle to increasing the blower speed to achieve a higher gas clearance ratio without a redesign of the blower motor.

[0009] There is thus a need to increase repetition rates without increasing cost, footprint, or power consumption. It is in this context that the need for the subject matter of the present disclosure arises.SUMMARY

[0010] The following presents a succinct summary of one or more embodiments in order to promote a basic understanding of the presently disclosed subject matter. This summary is not an extensive overview of all contemplated embodiments and is not intended to identify as key or critical any elements of any embodiments nor delineate the scope of any embodiments. Its sole purpose is to present some concepts relating to the embodiments in a streamlined form as a prelude to the more detailed description that is presented later.

[0011] According to an aspect of an embodiment there is disclosed a discharge chamber for a laser radiation source, the discharge chamber comprising a chamber body defining a chamber cavity, a first pair of electrodes arranged to define a first discharge gap in the chamber cavity, at least one fan arranged in the chamber cavity, and a second pair of electrodes arranged to define a second discharge gap in the chamber cavity, the first discharge gap, at least one fan, and second discharge gap being arranged to define a closed curve circulatory flow loop through the chamber cavity.

[0012] The at least one fan may comprise a first fan positioned in the closed curve circulatory flow loop immediately upstream of the first discharge gap. The at least one fan may comprise a first fan and may further comprise a second fan wherein the first fan and the second fan rotate on the same direction.

[0013] The chamber cavity may have an upper portion and a lower portion and the first discharge gap and the second discharge gap may both be located in the same portion. The chamber cavity may have an upper portion and a lower portion and the first discharge gap may be located in one of the upper portion and a lower portion and the second discharge gap may be located in the other of the upper portion and the lower portion.

[0014] The discharge chamber may further comprise a second fan positioned in the closed curve circulatory flow loop immediately downstream of the second discharge gap. The discharge chamber may further comprise a second fan positioned in the closed curve circulatory flow loop immediately upstream of the second discharge gap. The first fan may comprise a cross flow blower fan turning in a first rotational direction about a first rotational axis.

[0015] The discharge chamber may further comprise a second fan positioned in the closed curve circulatory flow loop immediately upstream of the second discharge gap and the second fan may comprise a cross flow blower fan turning in the first rotational direction about a second rotational axis parallel to the first rotational axis.

[0016] The discharge chamber may further comprise at least one heat exchange system arranged in the chamber cavity and positioned in the closed curve circulatory flow loop.

[0017] According to another aspect of an embodiment there is disclosed a discharge chamber for a laser radiation source, the discharge chamber comprising a chamber body having a first surface and a second surface facing the first surface and so defining a chamber cavity therebetween a pair of seed pulse electrodes arranged to define a first discharge gap in the chamber cavity extending to the first surface, at least one fan arranged in the chamber cavity, and a pair of amplification electrodes arranged to define a second discharge gap in the chamber cavity adjacent to the second surface, the first discharge gap, at least one fan, and second discharge gap being arranged to define a single closed curve circulatory flow loop through the chamber cavity.

[0018] The first and second discharge gaps may be disposed in series along the single closed curve circulatory flow loop. The at least one fan may be disposed between the first discharge gap and the second discharge gap. The at least one fan may comprise a first fan positioned in the closed curve circulatory flow loop immediately upstream of the first discharge gap. The at least one fan may comprise a first fan and may further comprise a second fan wherein the first fan and the second fan rotate in the same direction.

[0019] The chamber cavity may have an upper portion and a lower portion and the first discharge gap and the second discharge gap may both be located in the same portion. The chamber cavity may have an upper portion and a lower portion and the first discharge gap may be located in one of the upper portion and a lower portion and the second discharge gap may be located in the other of the upper portion and a lower portion.

[0020] The discharge chamber may further comprise a second fan positioned in the closed curve circulatory flow loop immediately downstream of the second discharge gap. The discharge chamber may further comprise a second fan positioned in the closed curve circulatory flow loop immediately upstream of the second discharge gap. The first fan may comprise a cross flow fan turning in a first rotational direction about a first rotational axis.

[0021] The discharge chamber may further comprise a second fan positioned in the closed curve circulatory flow loop immediately downstream of the second discharge gap wherein the second fan may comprise a cross flow fan turning in the first rotational direction about a second rotational axis parallel to the first rotational axis. The discharge chamber may further comprise a second fan positioned in the closed curve circulatory flow loop immediately upstream of the second discharge gap wherein the second fan may comprise a cross flow fan turning in the first rotational direction about a second rotational axis parallel to the first rotational axis.

[0022] The discharge chamber may further comprise at least one heat exchange system arranged in the chamber cavity and positioned in the closed curve circulatory flow loop.

[0023] The discharge chamber may be one in which the pair of seed pulse electrodes and the pair of amplification electrodes are arranged on opposing portions of the closed curve circulatory flow loop such that a flow between the pair of seed pulse electrodes is a direction opposite to a direction of flow between the pair of amplification electrodes. The discharge chamber of claim 11 in which pair of seed pulse electrodes and the first fan are arranged in 180 degree rotational symmetric relationship about a center of the discharge chamber with the pair of amplification electrodes and the second fan.

[0024] The discharge chamber may further comprise at least one heat exchange system arranged in the chamber cavity and positioned in the closed curve circulatory flow loop.

[0025] According to another aspect of an embodiment there is disclosed a radiation source comprising a chamber body defining a cavity, a pair of seed pulse electrodes spaced by a first discharge gap, a pair of amplification electrodes spaced by a second discharge gap, wherein the first discharge gap is in fluid communication with the second discharge gap through the cavity and via a single loop gas flow loop, a lasing gas disposed in the cavity, and at least one fan disposed in the cavity configured to circulate the lasing gas through the cavity, the first discharge gap, and the second discharge gap.

[0026] The first pair of electrodes may be on an opposite side of the chamber body from the second pair of electrodes. The at least one fan may comprise a first fan positioned immediately upstream of the first discharge gap. The radiation source may further comprise a second fan positioned immediately downstream of the second discharge gap. The second fan may turn in the same direction as the first fan. The second fan may be positioned immediately upstream of the second discharge gap and the second fan may turn in the same direction as the first fan.

[0027] The at least one fan may comprise a cross flow fan turning in a first rotational direction about a first rotational axis. The radiation source may further comprise a second fan positioned immediately upstream of the second discharge gap wherein the second fan may comprise a cross flow fan turning in the first rotational direction about a second rotational axis parallel to the first rotational axis. The radiation source may further comprise at least one heat exchange system arranged in the chamber cavity and positioned in the closed curve circulatory flow loop.

[0028] According to another aspect of an embodiment there is disclosed a method of increasing an effective repetition rate for pulsed radiation source comprising providing a discharge chamber having a plurality of electrode pairs, each electrode pair being arranged to define a discharge gap and so together defining a plurality of discharge gaps and causing discharges to occur sequentially in the discharge gaps.

[0029] According to another aspect of an embodiment there is disclosed a method of increasing an effective repetition rate for pulsed radiation source comprising providing a discharge chamber having a first electrode pair defining a first discharge gap and a second electrode pair defining a seconddischarge gap and repeatedly causing a discharge to occur in the first discharge gap and then causing a discharge to occur in the second discharge gap.

[0030] Further embodiments, features, and advantages of the subject matter of the present disclosure, as well as the structure and operation of the various embodiments, are described in detail below with reference to the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the presently disclosed subject matter and, together with the description, further serve to explain the principles of the presently disclosed subject matter and to enable a person skilled in the relevant art to make and use the presently disclosed subject matter. The drawings are not to scale unless otherwise indicated.

[0032] FIG. 1 is a functional block diagram of an overall broad conception of a photolithography system.

[0033] FIG. 2 is a functional block diagram of an overall broad conception of an radiation source such as might be used in the photolithography system of FIG. 1.

[0034] FIG. 3 is a cross-sectional diagram of a discharge chamber for a DUV radiation source.

[0035] FIG. 4 is a cross-sectional diagram of a discharge chamber for a DUV radiation source according to an aspect of an embodiment.

[0036] FIG. 5 is a cross-sectional diagram of a discharge chamber for a DUV radiation source according to an aspect of an embodiment.

[0037] Further features and advantages of the presently disclosed subject matter, as well as the structure and operation of various embodiments of the presently disclosed subject matter, are described in detail below with reference to the accompanying drawings. It is noted that the scope of the presently disclosed subject matter is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art based on the teachings presented herein.DETAILED DESCRIPTION

[0038] Various embodiments are now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to promote a thorough understanding of one or more embodiments. It may be evident in some or all instances, however, that any embodiment described below can be practiced without adopting the specific design details associated with it.

[0039] Systems such as those described herein may render benefits in a wide range of applications and implementations. For the sake of having a specific nonlimiting example to facilitate description,one such application is in semiconductor photolithography. FIG. 1 shows a photolithography system 100 that includes an illumination system 105. As described more fully below, the illumination system 105 includes a radiation source that produces a pulsed radiation beam 110 and directs it to a photolithography exposure apparatus 115 such as a scanner that patterns microelectronic features on a wafer 120. The wafer 120 is placed on a wafer table 125 constructed to hold the wafer 120 and connected to a positioner 130 configured to position the wafer 120 in accurately accordance with certain parameters. The pulsed radiation beam 110 may have a wavelength in the DUV range.

[0040] The photolithography exposure apparatus 115 includes an optical arrangement 135 having, for example, one or more condenser lenses, a mask, and an objective arrangement. The mask is movable in one or more directions, such as along an optical axis of the pulsed radiation beam 110 or in a plane perpendicular to that optical axis. The objective arrangement includes a projection lens and enables an image transfer to occur from the mask to photoresist on the wafer 120. The illumination system 105 adjusts the range of angles for the pulsed radiation beam 110 impinging on the mask. The illumination system 105 also homogenizes (makes uniform) the intensity distribution of the pulsed radiation beam 110 across the mask.

[0041] The photolithography exposure apparatus 115 can include, among other features, a lithography controller 140 that controls how layers are printed on the wafer 120. The lithography controller 140 may include a memory that stores information such as process recipes. The process recipes among other things determine the parameters of the pulsed radiation beam 110 including a length of the exposure on the wafer 120 based on, for example, the mask used, as well as other factors that affect exposure. During lithography, a burst of pulses of the pulsed radiation beam 110 illuminates the same area of the wafer 120 a specified number of times to constitute an illumination dose for that area.

[0042] The photolithography system 100 also preferably includes a control system 145. In general, the control system 145 includes one or more of digital electronic circuitry, computer hardware, firmware, and software. The control system 145 can be centralized or be partially or wholly distributed throughout the photolithography system 100.

[0043] FIG. 2 shows a pulsed laser source that produces a pulsed laser beam as the radiation beam 110 as an example of an illumination system 105. FIG. 2 shows a two-chamber laser system as a nonlimiting example but it will be understood that the principles explained herein are equally applicable to a laser system having more than two chambers. The pulsed laser source may include, e.g., a solid state or gas discharge master oscillator (“MO”) seed laser system 200, an amplification stage, e.g., a power ring amplifier (“PRA”) stage 205, relay optics 210, and laser system output subsystem 215. The MO seed system 200 may include, e.g., an MO discharge chamber 220 which includes a pair of electrodes 222 and 224.

[0044] The MO seed laser system 200 may also include a master oscillator output coupler (“MO OC”) 230, which may comprise a partially reflective mirror, and a reflective grating (not shown) in a line narrowing module (“LNM”) 235 disposed on opposite sides of the MO discharge chamber 220. TheLNM 235, the MO discharge chamber 220, and the MO OC 230 may form an oscillator cavity that oscillates to generate the seed laser output pulse. The MO seed laser system 200 may also include a line-center analysis module (“LAM”) 240. A MO wavefront engineering box (“WEB”) 245 may serve to redirect the output of the MO seed laser system 200 toward the amplification stage 205, and may include, e.g., a multi prism beam expander (not shown) and an optical delay path (not shown).

[0045] The amplification stage 205 may include, e.g., a PRA discharge chamber 250, which also may be an oscillator, e.g., formed by seed beam injection and output coupling optics (not shown) that may be incorporated into a PRA WEB 255. The beam may be redirected back through the gain medium in the PRA discharge chamber 250 by a beam reverser (“BR”) 260. The PRA WEB 255 may incorporate a partially reflective input / output coupler (not shown) and a maximally reflective mirror for the nominal operating wavelength (e.g., at around 193 nm for an ArF system) and one or more prisms. The PRA discharge chamber 250 may also include a pair of electrodes 252 and 254.

[0046] The laser output radiation beam of pulses from the PRA discharge chamber 250 then passes through the PRA WEB 255. A bandwidth analysis module (“BAM”) 265 is arranged to receive the output laser radiation beam of pulses from the PRA WEB 255 and divert a portion of the radiation beam for metrology purposes, e.g., to measure the output linewidth and pulse energy. The remainder of the radiation beam then passes to an optical pulse stretcher (“OPuS”) 270 and an autoshutter, in this case a combined autoshutter metrology module (“CASMM”) 275, which may also be the location of a pulse energy meter. The OPuS 270 may accordingly be arranged to receive the laser beam from the BAM 265 and direct its output to the CASMM 275.

[0047] The PRA discharge chamber 250 and the MO discharge chamber 220 are configured as chambers in which electrical discharges between the electrodes cause lasing gas discharges in a lasing gas to create an inverted population of high energy molecules or excimers. The lasing gas may be, for example, ArF, KrF, F2, XeF, and / or XeCl. The lasing gas is selected to produce relatively broad band radiation that may be line narrowed to a relatively very narrow linewidth and center wavelength selected in the LNM 235.

[0048] FIG. 3 is a cross-sectional diagram of a discharge chamber 300. The laser discharge chamber 300 may serve, for example, as the PRA discharge chamber 250 or the MO discharge chamber 220 of the exemplary arrangement shown in FIG. 2. The discharge chamber 300 has a chamber wall 305 that encloses an interior volume 307. The discharge chamber 300 contains an upper electrode 310 acting in the example shown as a cathode and a lower electrode 320 acting in the example shown as an anode. It will be understood, however, that this polarity may be reversed. The electrodes are generally elongated in a lengthwise direction orthogonal to the plane of the figure. Thus, if the figure is in the YZ plane then the electrodes extend in the + / - X direction. One or both of the anode 320 and the cathode 310 may be entirely contained in the pressure envelope of discharge chamber 300 defined by the discharge chamber wall 305 (which may form a body of the chamber) or one of the electrodes may not be entirely contained.Lasing gas discharges occur in the gap between the two electrodes. Also shown in FIG. 3 are an upper insulator 315 and a lower insulator / anode support bar 325.

[0049] A voltage supply applies a voltage pulse to the cathode 310 and anode 320. The pulse may be compressed by a compression head 316 as shown. The lower electrode 320 is generally in electrical contact with the discharge chamber wall 305 of the chamber 300 and so is held at a ground (0) potential. The upper electrode (cathode 310) is charged to a large (for example ~20 kV) negative voltage. This voltage gradient causes discharges in the gas in the gap between the electrodes.

[0050] As mentioned, during a discharge the gas in the discharge region between the cathode 310 and anode 320 becomes depleted of one or more components. It thus is necessary to replenish the gas between pulses by circulating the gas in the discharge chamber to introduce fresh gas into the discharge region. This is accomplished in the example shown in FIG. 3 through provision of a gas circulation system comprising a gas circulation fan, which may be, e.g., a generally cylindrical cross flow blower fan 330 as shown. The cross flow blower fan 330 serves to move gas within the interior of the discharge chamber 300, generally along a closed curved flow path, to remove gas that contains ionized particles and debris and is depleted of, e.g., F2 from the discharge region between successive gas discharges, and thus to replenish the discharge region with fresh gas before and in preparation for the next discharge.

[0051] The cross flow blower fan 330 includes an impeller 331 made up of an arrangement of forward-curved blades 332, the outer edges of which define a circle 334 having a center 336. The blades 332 rotate together around the center 336 in a direction that is clockwise in the orientation of FIG. 3 as shown by the arrow A. This defines an intake region 375 in the lower portion of the arrangement as oriented in the figure and an exhaust region 377 in the upper part of the arrangement as oriented in the figure. Gas in the intake region 375 is driven by the impeller 331 to the exhaust region 377 and flows as indicated by the arrow B to the discharge region between the electrodes 310 and 320. The top surface 327 of the lower insulator 325 defines a vortex wall 329 for cross blower fan 330 while the part of the discharge chamber wall 305 adjacent a lower portion of the cross blower fan 330 defines a rear wall 380 for the cross blower fan 330.

[0052] Cross flow blower fans are a form of radial fan in which the gas flows around the transverse length of the axis of rotation in the same manner that water flows past a waterwheel. One technical issue arising from the use of a cross flow blower is that these fans are relatively inefficient, i.e., they have a low thrust-to-power ratio. This is because only one half segment of the fan is moving gas into the discharge gap while the other segment is working against the flow, thus being slowed down by incoming gas. Thus, these fans have only a limited gas clearing ratio, i.e., the ratio of spent gas to fresh gas in the mixture of gases in the discharge region. As a result the use of a cross flow blower fan imposes limitations on reaching higher pulse repetition rates because the higher repetition rates leave less time for clearing and replenishing the gases in the discharge region between pulses.

[0053] FIG. 3 also shows a heat exchange system 390 which, in the example shown in FIG. 3 that includes three heat exchangers 392, 394, and 396 which extract heat from the gas circulating in thedischarge chamber 300, one of the primary sources of heat being the motor for the cross flow blower fan 330.

[0054] As mentioned, there is a need to achieve higher repetition rates without increasing the cost, footprint, or power consumption of the source. According to an aspect of an embodiment, cost, service, power and space efficiencies are gained by using a single chamber to generate seed pulses and amplify them with a shared flow circuit, and which may also share heat exchangers, as well as external interfaces such as water, gas, temperature control, and dust mitigation. Furthermore, production efficiencies may be gained by building and stocking half as many chamber modules.

[0055] For example, a single chamber may accommodate a side-by-side arrangement of MO and PRA discharges on the same side of the single chamber. Such an arrangement is shown in FIG. 4, which is a stylized cross-sectional diagram of a discharge chamber 400 according to an aspect of an embodiment. The laser discharge chamber 400 may serve, for example, as both the PRA discharge chamber 250 and the MO discharge chamber 220 of the exemplary arrangement shown in FIG. 2. The discharge chamber 400 has a chamber wall 405 that encloses an interior volume 407. The discharge chamber 400 contains a first pair of electrodes including an upper electrode 410 acting in the example shown as a cathode and a lower electrode 420 acting in the example shown as an anode. It will be understood, however, that this polarity may be reversed. The electrodes are generally elongated in a lengthwise direction orthogonal to the plane of the figure. Thus, if the figure is in the YZ plane then the electrodes extend in the + / - X direction. One or both of the anode 420 and the cathode 410 may be entirely contained in the pressure envelope of discharge chamber 400 defined by the discharge chamber wall 405 (which may form a body of the chamber) or one of the electrodes may not be so contained. Also shown in FIG. 4 are an upper insulator 415 and a lower insulator / anode support bar 425.

[0056] As in the arrangement described above in connection with FIG. 3, a voltage supply applies a voltage pulse to the cathode 410 and anode 420. The pulse may be compressed by a compression head 416 as shown. Other details of the arrangement shown are similar to those described in connection with FIG. 3.

[0057] The discharge chamber 400 also contains a second pair of electrodes including an upper electrode 460 acting in the example shown as a cathode and a lower electrode 470 acting in the example shown as an anode. It will be understood, however, that this polarity may be reversed. The electrodes are also generally elongated in a lengthwise direction orthogonal to the plane of the figure. One or both of the anode 470 and the cathode 460 may be entirely contained in the pressure envelope of discharge chamber 400 defined by the discharge chamber wall 405 or one of the electrodes may not be so contained. The anode 470 may be supported by the same lower insulator / anode support bar 425 that supports the anode 420 or a separate structure may be used. In the example shown in the figure the lower insulator / anode support bar 425 is a unitary structure. In some environments, it may be desirable to electrically separate the structures supporting the anode 420 and the anode 470. In some embodiments, it may also be desirable to position a single element so that there is no flow path passingthrough a line between the center of the fan 430 and the center of the fan 480. If such a flow path were permitted, the fans would no longer be acting precisely in series in that there would be an uncontrolled gas exchange that may be sensitive to relative fan speeds or different fan efficiencies as dictated by the asymmetry in the respective geometries experienced by the fans.

[0058] As in the arrangement described above in connection with FIG. 3, a voltage supply applies a voltage pulse to the cathode 460 and anode 470. The pulse may be compressed by a compression head 466 as shown.

[0059] Thus, in the arrangement shown in FIG. 4, there are two pairs of electrodes. One pair of electrodes may be used to generate a seed pulse and the other pair of electrodes may be used to amplify the seed pulse. Alternatively, the two pairs of electrodes may be used to alternately generate the same kind of pulse to create the possibility of doubling the effective repetition rate.

[0060] The arrangement shown in FIG 4 also includes a gas circulation system which includes a first gas circulation fan 430 and a second gas circulation fan 480. Either or both of these fans may be a generally cylindrical cross flow blower fan as shown in the exemplary arrangement of FIG. 4, which serves to move gas within the interior of the discharge chamber 400 in order to remove depleted gas that contains ionized particles and debris from the discharge region between successive gas discharges. Thus both fans include an impeller made up of an arrangement of forward-curved blades which rotate together around the center in a direction that is clockwise in the orientation of FIG. 4 as shown by the arrow A.

[0061] In the arrangement of FIG. 4, both fan 430 and fan 480 rotate in the same direction, in the example, clockwise in the figure, as indicated by the arrow A. This establishes a single closed curve circulatory flow loop 485, e.g., circular or elliptical, which is rotationally unidirectional, i.e., clockwise in the figure. In other words, the gas flow path is configured as a single loop passing through the two discharge regions. The discharge regions are in series in the loop. In the configuration shown the second discharge region is directly downstream of first discharge region without the interposition of any additional elements. One of ordinary skill in the art will understand, however, that the first and second discharge regions are in a series arrangement regardless of the presence of intervening elements in the flow path between them.

[0062] Because the fans operate together to establish the flow 485, the load on either individual fan is less, which means that higher flow rates can be achieved without unduly increasing the fans’ power consumption. This in turn facilitates attaining higher repetition rates.

[0063] FIG. 4 also shows a heat exchange system 490 which, in the example shown in FIG. 4 includes three heat exchangers 492, 494, and 496 which extract heat from the gas circulating in the discharge chamber 400.

[0064] In some circumstances a side-by side arrangement such as that shown in FIG. 4 may present issues caused by ions from the upstream discharge influencing the downstream discharge. A similar issue may present itself with respect to acoustic disturbances that may propagate from one discharge toa physically displaced later discharge. Another potential issue that arises with arranging two electrode pairs on the same side of the chamber is maintenance of a sufficient electrical standoff between the pairs in a small space. This last issue may be particularly acute in arrangements in which the delay between discharges, e.g., dtMOPA, is similar to the duration of the electrode charge / discharge cycle so that the entire voltage differential must be held off without arcing in a very small space.

[0065] Thus, according to another aspect of an embodiment, the electrode pairs in the chamber are arranged so that they are physically separated either by an increased displacement between them, or by intervening structures, or both. For example, the discharge chamber may have two opposed sides and the discharges may be caused to occur on opposite sides of the discharge chamber. As another example, one or more structures may be interposed between the electrode pairs. Such a geometry is shown in FIG. 5.

[0066] The arrangement shown in FIG. 5 includes a discharge chamber 500 having a chamber wall 505 defining a chamber cavity 507. The discharge chamber 500 has a first pair of electrodes 510, 520 and the second pair of electrodes 560, 570. The first pair of electrodes 510, 520 defines a discharge region 515 while the second pair of electrodes 560, 570 defines a discharge region 565. As can be seen, the discharge region 515 is located at an upper portion of the chamber 500 while the discharge region 565 is located in a lower portion of the chamber 500 and there is no unobstructed direct path between the discharge regions. Thus, the discharge regions are more separated than they are in the arrangement of FIG. 4. Of course, it will be understood that “upper” and “lower” in this context and in the claims refers to a relative orientation and not necessarily any orientation with respect to gravity.

[0067] In addition, the electrode 520 and the electrode 570 are located on a common support structure 540 which in the arrangement of FIG. 5 is interposed between the discharge region 515 and the discharge region 565. This imposes an additional level of separation between the two discharge regions.

[0068] The arrangement of FIG. 5 also includes a first fan 530 and a second fan 580. As with the previous embodiments, these fans may be implemented as cross flow blower fans rotating clockwise as oriented in the figure. The fans thus establish a closed curve circulatory flow loop 585 which passes through the first discharge region 515, the fan 580, the second discharge region 565, and the fan 530. This flow is rotationally unidirectional in the sense that it goes in only one direction, clockwise in the figure, but because of the displacement of the electrode pairs the flow through the first discharge region 515 is in a direction (left to right in the figure) opposite to the flow through the second discharge region 565 (right to left in the figure) because they are on opposed portions of the closed curve circulatory flow loop.

[0069] . The discharge regions 515 and 565 are in series in the closed curve circulatory flow loop 585. In the configuration shown the second discharge region is downstream of first discharge region with the interposition of any additional elements such as a heat exchange system 585 and the fan 580. One of ordinary skill in the art will understand, however, that the first and second discharge regions are in aseries arrangement regardless of the presence or absence of intervening elements in the flow path between them.

[0070] As noted, the exemplary arrangement shown in FIG. 5 also includes a first heat exchange system 590 made up of heat exchangers 591, 592, and 593, and a second heat exchange system 595 including heat exchangers 596, 597, and 598.

[0071] One of ordinary skill in the art will appreciate that the positioning and numbers of elements in the chamber 500 may be modified without departing from the essential teachings of this disclosure. Thus, although the embodiment shown in FIG. 5 has two fans for some implementations it may be possible to use only a single fan. Similarly, while the embodiment depicted in FIG. 5 includes two heat exchange systems it may be possible in some implementations to use only a single heat exchange system. Also, the heat exchange systems as shown a FIG. 5 are made up of three heat exchangers. It will be apparent ordinary skill in the art that a smaller or greater heat exchangers might be used in some implementations.

[0072] In this geometry, the compression head 516 for one pair of electrodes 510, 520 could be positioned on the top (relatively, not necessarily gravitationally) of the discharge chamber 500 and the compression head 566 for the other pair of electrodes 560, 570 could be positioned on the bottom (relatively, not necessarily gravitationally) of the discharge chamber 500. One of ordinary skill in the art will appreciate that there may also be arrangements in which one pair of electrodes is positioned in one lateral portion of the chamber, e.g., the left half, while the other of the electrodes is positioned in a diametrically opposed portion of the chamber, e.g., the right half of the chamber. In other words, one of ordinary skill in the art will readily appreciate that the depicted orientation could be rotated ninety degrees for a side-by-side, left / right layout. In such an orientation the compression head for one pair of electrodes could be positioned on the left hand side of the discharge chamber and the compression head for the other pair of electrodes could be positioned on the right hand side of the discharge chamber.

[0073] Also, the embodiment shown in FIG. 5 has 180 degree rotational symmetry around a central point 545 of the arrangement of elements and surfaces of the chamber 500. As shown, this configuration permits an increased displacement between the two discharge regions. Also, in some implementations, such symmetry may promote manufacturability as well as make it possible to stock fewer types of chamber portions, i.e., an upper chamber half could also be used as a lower chamber half.

[0074] The designs disclosed herein can be implemented by modification of existing chamber components. For example, a chamber may be made up of an upper chamber half portion and a lower chamber half portion and the above systems might be implemented by modification of one of these portions. Even in circumstances in which components would be duplicated for each pair of electrodes, there is potential for making processing and testing more efficient, reducing the overall cost significantly. Also, there is potential that the total fan power could be considerably reduced compared to two individual chambers. This could be through both improved flow efficiency on the intake of thefan as well as any efficiencies from having two fans working in concert, both moving the flow in the same direction resulting in less energy dissipation in a slow flow area.

[0075] The above describes a laser discharge chamber arranged to accommodate multiple pairs of electrodes and hence multiple discharge regions generating pulses. The above examples are of arrangements in which one pair of electrodes generates a pulse used for a first purpose, e.g., as a seed pulse and the other pair of electrodes generates a pulse used for another purpose, e.g., to amplify the seed pulse. The above-described arrangements, however, can alternatively be used in implementations in which it is desired to generate two pulses for the same purpose. For example, in implementations in which pulse amplification is not necessary it is possible to effectively double the repetition rate by having two discharges that fire alternately, i.e., interleaved in time. Thus, this disclosure should not be considered as being limited to arrangements in which the two pulses are used for respectively different purposes but instead should be regarded as encompassing arrangements in which the two pulses are used for the same purpose.

[0076] In other words, the foregoing encompasses a method of increasing an effective repetition rate for pulsed radiation source in which the method includes alternately causing a discharge to occur in a first discharge gap and then causing a discharge to occur in the a discharge gap. More generally the method may include providing a discharge chamber having a plurality of electrode pairs, each electrode pair being arranged to define a discharge gap and so together defining a plurality of discharge gaps and causing discharges to occur sequentially in the discharge gaps.

[0077] Some of the above description is in terms of functional block diagrams with some functions allocated to some blocks and other functions allocated to other blocks. It will be understood that the division between blocks and the allocations are arbitrary and that different divisions and allocations are possible so long as the overall functions are carried out as described above.

[0078] The above description includes examples of multiple embodiments. It is, of course, not possible to describe every conceivable combination of components or methodologies for each of these embodiments, but one of ordinary skill in the art may recognize that many further combinations and permutations of elements of the various embodiments are possible based on the disclosure. Accordingly, the described embodiments are intended to be representative of and encompass all such alterations, modifications, and variations that fall within the spirit and scope of the appended claims.

[0079] Furthermore, to the extent that the term “includes” is used in either the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term “comprising” as “comprising” is construed when employed as a transitional word in a claim. Also, although elements of the described aspects and / or embodiments may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is explicitly stated. Additionally, all or a portion of any aspect and / or embodiment may be utilized with all or a portion of any other aspect and / or embodiment, unless stated otherwise.

[0080] Features, materials, characteristics, or groups described in conjunction with a particular aspect, embodiment, or example are to be understood to be applicable to any other aspect, embodiment or example described in this section or elsewhere in this specification unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract, and drawings) may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. The protection is not restricted to the details of any foregoing embodiments. The protection extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0081] Furthermore, certain features that are described in this disclosure in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations, one or more features from a claimed combination can, in some cases, be excised from the combination, and the combination may be claimed as a subcombination or variation of a subcombination.

[0082] Furthermore, the features and attributes of the specific embodiments disclosed above may be combined in different ways to form additional embodiments, all of which fall within the scope of the present disclosure. Also, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described components and systems can generally be integrated together in a single product or packaged into multiple products.

[0083] For purposes of this disclosure, certain aspects, advantages, and novel features are described herein. Not necessarily all such advantages may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the disclosure may be embodied or carried out in a manner that achieves one advantage or a group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.

[0084] Conditional language, such as “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements, and / or steps. Thus, such conditional language is not generally intended to imply that features, elements, and / or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without user input or prompting, whether these features, elements, and / or steps are included or are to be performed in any particular embodiment.

[0085] Conjunctive language such as the phrase “at least one of X, Y, and Z,” unless specifically stated otherwise, is otherwise understood with the context as used in general to convey that an item, term, etc. may be either X, Y, or Z. Thus, such conjunctive language is not generally intended to implythat certain embodiments require the presence of at least one of X, at least one ofY, and at least one of Z.

[0086] Language of degree used herein, such as the terms “approximately,” “about,” “generally,” and “substantially” as used herein represent a value, amount, or characteristic close to the stated value, amount, or characteristic that still performs a desired function or achieves a desired result. For example, the terms “approximately”, “about”, “generally,” and “substantially” may refer to an amount that is within less than 10% of, within less than 5 % of, within less than 1% of, within less than 0.1 % of, and within less than 0.01 % of the stated amount. As another example, in certain embodiments, the terms “generally parallel” and “substantially parallel” refer to a value, amount, or characteristic that departs from exactly parallel by less than or equal to 15 degrees, 10 degrees, 5 degrees, 3 degrees, 1 degree, or 0.1 degree.

[0087] The scope of the present disclosure is not intended to be limited by the specific disclosures of preferred embodiments in this section or elsewhere in this specification, and may be defined by claims as presented in this section or elsewhere in this specification or as presented in the future. The language of the claims is to be interpreted broadly based on the language employed in the claims and not limited to the examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive.

[0088] The implementations can be further described using the following clauses.1. A discharge chamber for a laser radiation source, the discharge chamber comprising: a chamber body defining a chamber cavity; a first pair of electrodes arranged to define a first discharge gap in the chamber cavity; at least one fan arranged in the chamber cavity; and a second pair of electrodes arranged to define a second discharge gap in the chamber cavity, the first discharge gap, at least one fan, and second discharge gap being arranged to define a closed curve circulatory flow loop through the chamber cavity.2. The discharge chamber of clause 1 wherein the at least one fan comprises a first fan positioned in the closed curve circulatory flow loop immediately upstream of the first discharge gap.3. The discharge chamber of clause 1 wherein the at least one fan comprises a first fan and further comprising a second fan wherein the first fan and the second fan rotate on the same direction.4. The discharge chamber of clause 1 in which the chamber cavity has an upper portion and a lower portion and in the which the first discharge gap and the second discharge gap are both located in the same portion.5. The discharge chamber of clause 1 in which the chamber cavity has an upper portion and a lower portion and in the which the first discharge gap is located in one of the upper portion and a lower portion and the second discharge gap is located in the other of the upper portion and the lower portion.6. The discharge chamber of clause 1 further comprising a second fan positioned in the closed curve circulatory flow loop immediately downstream of the second discharge gap.7. The discharge chamber of clause 1 further comprising a second fan positioned in the closed curve circulatory flow loop immediately upstream of the second discharge gap.8. The discharge chamber of clause 1 wherein the first fan comprises a cross flow blower fan turning in a first rotational direction about a first rotational axis.9. The discharge chamber of clause 8 further comprising a second fan positioned in the closed curve circulatory flow loop immediately upstream of the second discharge gap wherein the second fan comprises a cross flow blower fan turning in the first rotational direction about a second rotational axis parallel to the first rotational axis.10. The discharge chamber of clause 1 further comprising at least one heat exchange system arranged in the chamber cavity and positioned in the closed curve circulatory flow loop.11. A discharge chamber for a laser radiation source, the discharge chamber comprising: a chamber body having a first surface and a second surface facing the first surface and so defining a chamber cavity therebetween; a pair of seed pulse electrodes arranged to define a first discharge gap in the chamber cavity extending to the first surface; at least one fan arranged in the chamber cavity; and a pair of amplification electrodes arranged to define a second discharge gap in the chamber cavity adjacent to the second surface, the first discharge gap, at least one fan, and second discharge gap being arranged to define a single closed curve circulatory flow loop through the chamber cavity.12. The discharge chamber of clause 11 wherein the first and second discharge gaps are disposed in series along the single closed curve circulatory flow loop.13. The discharge chamber of clause 12 wherein the at least one fan is disposed between the first discharge gap and the second discharge gap.14. The discharge chamber of clause 11 wherein the at least one fan comprises a first fan positioned in the closed curve circulatory flow loop immediately upstream of the first discharge gap.15. The discharge chamber of clause 11 wherein the at least one fan comprises a first fan and further comprising a second fan wherein the first fan and the second fan rotate in the same direction.16. The discharge chamber of clause 11 in which the chamber cavity has an upper portion and a lower portion and in the which the first discharge gap and the second discharge gap are both located in the same portion.17. The discharge chamber of clause 11 in which the chamber cavity has an upper portion and a lower portion and in the which the first discharge gap is located in one of the upper portion and a lower portion and the second discharge gap is located in the other of the upper portion and a lower portion.18. The discharge chamber of clause 11 further comprising a second fan positioned in the closed curve circulatory flow loop immediately downstream of the second discharge gap.19. The discharge chamber of clause 11 further comprising a second fan positioned in the closed curve circulatory flow loop immediately upstream of the second discharge gap.20. The discharge chamber of clause 11 wherein the first fan comprises a cross flow fan turning in a first rotational direction about a first rotational axis.21. The discharge chamber of clause 11 further comprising a second fan positioned in the closed curve circulatory flow loop immediately downstream of the second discharge gap wherein the second fan comprises a cross flow fan turning in the first rotational direction about a second rotational axis parallel to the first rotational axis.22. The discharge chamber of clause 11 further comprising a second fan positioned in the closed curve circulatory flow loop immediately upstream of the second discharge gap wherein the second fan comprises a cross flow fan turning in the first rotational direction about a second rotational axis parallel to the first rotational axis.23. The discharge chamber of clause 11 further comprising at least one heat exchange system arranged in the chamber cavity and positioned in the closed curve circulatory flow loop.24. The discharge chamber of clause 11 in which the pair of seed pulse electrodes and the pair of amplification electrodes are arranged on opposing portions of the closed curve circulatory flow loop such that a flow between the pair of seed pulse electrodes is a direction opposite to a direction of flow between the pair of amplification electrodes.25. The discharge chamber of clause 11 in which the pair of seed pulse electrodes and the first fan are arranged in 180 degree rotational symmetric relationship about a center of the discharge chamber with the pair of amplification electrodes and the second fan.26. The discharge chamber of clause 11 further comprising at least one heat exchange system arranged in the chamber cavity and positioned in the closed curve circulatory flow loop.27. A radiation source comprising: a chamber body defining a cavity; a pair of seed pulse electrodes spaced by a first discharge gap; a pair of amplification electrodes spaced by a second discharge gap, wherein the first discharge gap is in fluid communication with the second discharge gap through the cavity and via a single loop gas flow loop; a lasing gas disposed in the cavity; and at least one fan disposed in the cavity configured to circulate the lasing gas through the cavity, the first discharge gap, and the second discharge gap.28. The radiation source of clause 27 wherein the first pair of electrodes is on an opposite side of the chamber body from the second pair of electrodes.29. The radiation source of clause 27 wherein the at least one fan comprises a first fan positioned immediately upstream of the first discharge gap.30. The radiation source of clause 29 further comprising a second fan positioned immediately downstream of the second discharge gap.31. The radiation source of clause 30 wherein the second fan turns in the same direction as the first fan.32. The radiation source of clause 29 further comprising a second fan positioned immediately upstream of the second discharge gap.33. The radiation source of clause 32 wherein the second fan turns in the same direction as the first fan.34. The radiation source of clause 27 wherein the at least one fan comprises a cross flow fan turning in a first rotational direction about a first rotational axis.35. The radiation source of clause 34 further comprising a second fan positioned immediately upstream of the second discharge gap wherein the second fan comprises a cross flow fan turning in the first rotational direction about a second rotational axis parallel to the first rotational axis.36. The radiation source of clause 27 further comprising at least one heat exchange system arranged in the chamber cavity and positioned in the closed curve circulatory flow loop.37. A method of increasing an effective repetition rate for pulsed radiation source comprising: providing a discharge chamber having a plurality of electrode pairs, each electrode pair being arranged to define a discharge gap and so together defining a plurality of discharge gaps; and causing discharges to occur sequentially in the discharge gaps.38. A method of increasing an effective repetition rate for pulsed radiation source comprising: providing a discharge chamber having a first electrode pair defining a first discharge gap and a second electrode pair defining a second discharge gap; and repeatedly causing a discharge to occur in the first discharge gap and then causing a discharge to occur in the second discharge gap.

[0089] The above-described implementations and other implementations are within the scope of the following claims.

Claims

CLAIMS1. A discharge chamber for a laser radiation source, the discharge chamber comprising: a chamber body defining a chamber cavity; a first pair of electrodes arranged to define a first discharge gap in the chamber cavity; at least one fan arranged in the chamber cavity; and a second pair of electrodes arranged to define a second discharge gap in the chamber cavity, the first discharge gap, at least one fan, and second discharge gap being arranged to define a closed curve circulatory flow loop through the chamber cavity.

2. The discharge chamber of claim 1 wherein the at least one fan comprises a first fan positioned in the closed curve circulatory flow loop immediately upstream of the first discharge gap.

3. The discharge chamber of claim 1 wherein the at least one fan comprises a first fan and further comprising a second fan wherein the first fan and the second fan rotate on the same direction.

4. The discharge chamber of claim 1 in which the chamber cavity has an upper portion and a lower portion and in the which the first discharge gap and the second discharge gap are both located in the same portion.

5. The discharge chamber of claim 1 in which the chamber cavity has an upper portion and a lower portion and in the which the first discharge gap is located in one of the upper portion and a lower portion and the second discharge gap is located in the other of the upper portion and the lower portion.

6. The discharge chamber of claim 1 further comprising a second fan positioned in the closed curve circulatory flow loop immediately downstream of the second discharge gap.

7. The discharge chamber of claim 1 further comprising a second fan positioned in the closed curve circulatory flow loop immediately upstream of the second discharge gap.

8. The discharge chamber of claim 1 wherein the first fan comprises a cross flow blower fan turning in a first rotational direction about a first rotational axis and further comprising a second fan positioned in the closed curve circulatory flow loop immediately upstream of the second discharge gap wherein the second fan comprises a cross flow blower fan turning in the first rotational direction about a second rotational axis parallel to the first rotational axis.

9. A discharge chamber for a laser radiation source, the discharge chamber comprising: a chamber body having a first surface and a second surface facing the first surface and so defining a chamber cavity therebetween; a pair of seed pulse electrodes arranged to define a first discharge gap in the chamber cavity extending to the first surface; at least one fan arranged in the chamber cavity; and a pair of amplification electrodes arranged to define a second discharge gap in the chamber cavity adjacent to the second surface, the first discharge gap, at least one fan, and second discharge gap being arranged to define a single closed curve circulatory flow loop through the chamber cavity.

10. The discharge chamber of claim 9 in which the chamber cavity has an upper portion and a lower portion and in the which the first discharge gap is located in one of the upper portion and a lower portion and the second discharge gap is located in the other of the upper portion and a lower portion.

11. The discharge chamber of claim 9 in which the pair of seed pulse electrodes and the pair of amplification electrodes are arranged on opposing portions of the closed curve circulatory flow loop such that a flow between the pair of seed pulse electrodes is a direction opposite to a direction of flow between the pair of amplification electrodes.

12. The discharge chamber of claim 9 in which the pair of seed pulse electrodes and the first fan are arranged in 180 degree rotational symmetric relationship about a center of the discharge chamber with the pair of amplification electrodes and the second fan.

13. A radiation source comprising : a chamber body defining a cavity; a pair of seed pulse electrodes spaced by a first discharge gap; a pair of amplification electrodes spaced by a second discharge gap, wherein the first discharge gap is in fluid communication with the second discharge gap through the cavity and via a single loop gas flow loop; a lasing gas disposed in the cavity; and at least one fan disposed in the cavity configured to circulate the lasing gas through the cavity, the first discharge gap, and the second discharge gap.

14. The radiation source of claim 13 wherein the first pair of electrodes is on an opposite side of the chamber body from the second pair of electrodes.

15. The radiation source of claim 13 wherein the at least one fan comprises a first fan positioned immediately upstream of the first discharge gap.

16. The radiation source of claim 13 wherein the at least one fan comprises a cross flow fan turning in a first rotational direction about a first rotational axis.

17. The radiation source of claim 13 further comprising at least one heat exchange system arranged in the chamber cavity and positioned in the closed curve circulatory flow loop.

18. A method of increasing an effective repetition rate for pulsed radiation source comprising: providing a discharge chamber having a first electrode pair defining a first discharge gap and a second electrode pair defining a second discharge gap; and repeatedly causing a discharge to occur in the first discharge gap and then causing a discharge to occur in the second discharge gap.

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