Electrode in discharge chamber of radiation source

Abstract

A system for use in a deep ultraviolet radiation source for managing purge and replenishment of gas in a discharge region between the tips of two electrodes in a discharge chamber in which a tip of at least one of the electrodes has a shape transverse to the length of the electrode that promotes the flow of gas through the discharge region.

Description

ELECTRODE IN DISCHARGE CHAMBER OF RADIATION SOURCECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to US Application No. 63 / 526,832, filed July 14, 2023, titled IMPROVED GAS FLOW IN A DUV DISCHARGE CHAMBER, which is incorporated herein by reference in its entirety.FIELD

[0002] The disclosed subject matter relates to systems for replenishing gas in a laser discharge chamber of a deep ultraviolet (DUV) radiation laser source.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 produced in a discharge region between electrodes in a discharge chamber. More precisely, the 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 up to, for example, 6 kHz (6000 times per second), and thus produces a train of DUV radiation emission pulses.

[0005] During a discharge the gas in the discharge region between the electrodes becomes depleted of one or more components. Thus, between pulses the gas for plasma generation is purged and replenished by introducing fresh gas into the discharge region using a blower fan in the discharge chamber.

[0006] It may be the case in some instances that the gas is incompletely replenished between discharges. As a result the characteristics of a subsequent discharge breakdown and the DUV emission energy of the later pulses may be adversely affected. This phenomenon can lead to a so-called energy burst transient, which is an undesired performance behavior with respect to laser dose control. The energy burst transient is more pronounced when the chamber is young and the electrodes are new.

[0007] It would be advantageous to improve the process of replenishing gas in the discharge region of a DUV laser source. It is in this context that the need for the subject matter of the present disclosure arises.SUMMARY

[0008] 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 or all embodiments. Its sole purpose is to present some concepts relating to one or more embodiments in a streamlined form as a prelude to the more detailed description that is presented later.

[0009] According to an aspect of an embodiment there is disclosed a discharge chamber for a deep ultraviolet laser, the discharge chamber comprising a chamber enclosure, a first electrode having a first electrode tip structure positioned in the chamber enclosure, a second electrode having a second electrode tip structure positioned in the chamber enclosure, the second electrode tip structure confronting the first electrode tip structure to define a discharge region therebetween, and a fan arranged to cause a flow of gas through the discharge region from a region upstream of the discharge region to a region downstream of the discharge region along a direction of the flow of the gas, at least one of the first electrode tip structure and the second electrode tip structure being configured such that a first distance between the first electrode tip structure and the second electrode tip structure at an upstream side of the discharge region is greater than a second distance between the first electrode tip structure and the second electrode tip structure at a downstream side of the discharge region.

[0010] The first electrode may be one of a cathode and an anode and the second electrode may be the other of a cathode and an anode. The first electrode tip structure may have a first surface and the second electrode tip structure may have a second surface with the first surface and the second surface confronting one another across a discharge gap having a decreasing width along the direction of the flow of the gas.

[0011] The first surface and the second surface may be asymmetric with respect to a plane passing through the at least one of the first surface and the second surface and orthogonal to the direction of the flow of the gas through the discharge region. At least one of the first surface and the second surface may be slanted with respect to the direction of the flow of the gas through the discharge region. At least one of the first surface and the second surface may be slanted by an angle in a range of about 5 degrees to about 30 degrees.

[0012] Both the first surface and the second surface may be asymmetric with respect to a plane passing through the first surface and the second surface and orthogonal to the direction of the flow of the gas through the discharge region. Both the first surface and the second surface may be slanted with respect to the direction of the flow of the gas through the discharge region.

[0013] The first surface may be slanted by an angle in a range of about 5 degrees to about 30 degrees and the second surface may be slanted by an angle in a range of about 5 degrees to about 30 degrees.

[0014] According to another aspect of an embodiment there is disclosed an electrode arrangement for a discharge chamber for a deep ultraviolet laser, the electrode arrangement comprising a first electrodeextending in a first direction in the discharge chamber and having a first discharge surface and a second electrode extending in the first direction in the discharge chamber parallel to the first electrode and having a second discharge surface extending in the first direction, facing the first discharge surface, and spaced away from the first discharge surface in a second direction transverse to the first direction to define a gap between the first discharge surface and the second discharge surface in the second direction. At least one of the first discharge surface and the second discharge surface is slanted with respect to a plane passing through the discharge region and parallel to the first electrode and the second electrode.

[0015] The first electrode may be one of a cathode and an anode and the second electrode may be the other of a cathode and an anode. At least one of the first discharge surface and the second discharge surface may be slanted by an angle in a range of about 5 degrees to about 30 degrees with respect to the plane passing through the discharge region and parallel to the first electrode and the second electrode.

[0016] Both the first discharge surface and the second discharge surface may be asymmetric with respect to the plane passing through the discharge region and parallel to the first electrode and the second electrode. Both the first discharge surface and the second discharge surface may be slanted with respect to the plane passing through the discharge region and parallel to the first electrode and the second electrode.

[0017] The first discharge surface may be slanted by an angle in a range of about 5 degrees to about 30 degrees and the second discharge surface may be slanted by an angle in a range of about 5 degrees to about 30 degrees.

[0018] According to another aspect of an embodiment there is disclosed an electrode for generating a plasma to create deep ultraviolet emission, the electrode comprising an electrode body which is elongated in a first direction and an electrode tip extending along the electrode body and extending from the electrode body in a second direction transverse to the first direction into a gas flow region where the plasma may be formed, a gas in the gas flow region flowing across the electrode tip from an upstream region to a downstream region, the electrode tip having an asymmetric shape such that the electrode tip has an extension from the electrode body in the upstream region that less than an extension from the electrode body of the electrode tip in the downstream region.

[0019] The asymmetric shape may comprise the electrode tip having a tip surface angled towards the upstream region. The asymmetric shape may comprise the electrode tip having a tip surface angled towards the upstream region by an angle in a range of about 5 degrees to about 30 degrees.

[0020] 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

[0021] 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 toexplain 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.

[0022] FIG. 1 is a functional block diagram, not to scale, of an overall broad conception of a photolithography system.

[0023] FIG. 2 is a functional block diagram, not to scale, of an overall broad conception of an illumination system such as might be used in the photolithography system of FIG. 1.

[0024] FIG. 3 is a diagram, not to scale, of a discharge chamber for a DUV radiation source.

[0025] FIGS. 4A and 4B are diagrams, not to scale, of an electrode for use in a discharge chamber for a DUV radiation source.

[0026] FIG. 5 is a diagram, not to scale, of an arrangement for electrodes in a discharge chamber for a DUV radiation source, according to an aspect of an embodiment.

[0027] FIG. 6 is a diagram, not to scale, of an arrangement for electrodes in a discharge chamber for a DUV radiation source, according to an aspect of an embodiment.

[0028] FIGS . 7A and 7B are diagrams, not to scale, of geometries for electrodes in a discharge chamber for a DUV radiation source, according to aspects of embodiments.

[0029] FIG. 8 is a graph of gas residual levels versus time comparing simulations of performance of a conventional electrode arrangement with performance of an electrode arrangement according to an aspect of an embodiment.

[0030] 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.DETAIUED DESCRIPTION

[0031] 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 below. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate description of one or more embodiments.

[0032] 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 105includes 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 wafer 120 and connected to a positioner 130 configured to accurately position the wafer 120 in accordance with certain parameters. The pulsed radiation beam 110 may have a wavelength in the DUV range.

[0033] 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 along one or more directions, such as along an optical axis of the pulsed radiation beam 110 or in a plane that is perpendicular to the 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.

[0034] 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 that determine the parameters of the beam 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 to constitute an illumination dose.

[0035] 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 and may or may not be part of or subsume the control system 185 described below.

[0036] 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 single chamber laser system or a laser system having more than two chambers. The gas discharge laser system 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.

[0037] The MO seed laser system 200 may also include a master oscillator output coupler (“MO OC”) 230, which may comprise a partially reflective mirror, forming an MO discharge chamber 220 with an oscillator cavity, defined in part by a reflective grating (not shown) in a line narrowing module (“LNM”) 235, 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”) 245may 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).

[0038] 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.

[0039] 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. One purpose of the OPuS 270 may be, e.g., to convert a single output laser pulse into a pulse train. Secondary pulses created from the original single output pulse may be delayed with respect to each other. By distributing the original laser pulse energy into a train of secondary pulses, the effective pulse length of the laser can be expanded and at the same time the peak pulse intensity reduced. The OPuS 270 may accordingly be arranged to receive the laser beam from the BAM 265 and direct its output to the CASMM 275.

[0040] 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, including, e.g., ArF, KrF, F2, XeF, and / or XeCl, 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.

[0041] FIG. 3 is a stylized cross-sectional diagram of a discharge chamber 300. The discharge chamber 300 includes an upper electrode 310 acting as a cathode and a lower electrode 320 acting as an anode. The electrodes are generally elongated in a lengthwise direction orthogonal to the plane of the figure. Thus, if the figure is in the XY plane as shown, then the electrodes extend in the + / - Z direction. One or both of the lower electrode 300 and the upper electrode 310 may be entirely contained in the pressure envelope of chamber 300 defined by the chamber wall 305 or one of the electrodes may not be so contained.

[0042] Lasing gas discharges occur between these two electrodes in a gap having an interelectrode width A transverse to the lengths of the electrode. The interelectrode width A is generally constant , i.e., does not vary in the discharge region, at least with a new electrode, although small differences in the magnitude and uniformity of the interelectrode gap may arise overtime.

[0043] Also shown in FIG. 3 are an upper insulator 315 and a lower insulator 325. The lower electrode 320 is electrically connected to the wall 305 of the chamber 300. For safety reasons it is desirable to maintain the chamber wall 300 and so the lower electrode 320 at ground potential. In the embodiment shown in FIG. 3, the upper electrode 310 is driven by a voltage supply 340 at a voltage which is negative with respect to the lower electrode 320.

[0044] The voltage supply 340 which establishes a voltage gradient between cathode 310 and anode 320. While the notation (-) is shown for the polarity of the output of the voltage supply 340 it will be understood that this is a relative rather than absolute polarity, that is, relative to the polarity of the lower electrode 320, which will generally be in electrical contact with the body 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.

[0045] 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. Thus, between pulses the gas for plasma generation is replenished by introducing fresh gas into the discharge region, for example by using a blower fan in the discharge chamber 300. This is represented in FIG. 3 by a fan 330 which blows gas in the chamber 300 in the direction shown by the outline arrow. It will be appreciated by one of ordinary skill in the art that the positioning of the fan 330 is not necessarily as shown in FIG. 3 and that instead the fan can be placed anywhere where it can introduce fresh gas, that is, gas which has not been subject to a discharge, into the discharge region between the electrodes 310, 320.

[0046] FIG. 4A is a cross-sectional diagram of one of the electrodes, in this example anode 320. As can be seen, the view of FIG. 4A is end-on with the anode 320 extending in the + / - Z direction, i.e., in and out of the plane of the figure. The anode 320 can be made up of an anode body 322 and a tip structure 324. The tip structure may be thought of as a ridge-like element extending in and out of the plane of the figure. The tip structure 324 may be integral with the anode body 322 or, as shown, can be made up of a separate element inserted into the anode body 322.

[0047] FIG. 4B is an enlarged view of the portion of FIG. 4A within the dashed circle of FIG. 4A. As can be seen, the upper surface 326 of the tip structure 324 has a curved profile in the XY plane. In some embodiments, the curved profile is generally rounded or ellipsoidal. The curved profile is generally mirror symmetric across the YZ plane 328 passing through a midpoint in the X direction of the tip structure 324, the plane 328 being seen edge-on in FIG. 4B. The plane 328 in general divides anode 320 between a side that is upstream with respect to gas flow and a side that is downstream with respect to gas flow as indicated by the open arrow. The upstream portion of the tip structure 324 is thus a mirror image of the downstream portion of the tip structure 324 across the plane 328. While this example relates to the anode 320, it will be understood that it may apply equally to the cathode 310.

[0048] Thus, the discharge electrodes conventionally have a tip shape with an upper (away from the electrode body) surface having an ellipsoidal tip shape in the transverse (with respect to the directionof elongation of the electrode) direction. This upper surface, which, together with the confronting upper surface of the other electrode defines the discharge gap or region, is mirror symmetric between the upstream and downstream direction of the purge gas flow as indicated by the outline arrows in FIGS. 4A and 4B.

[0049] The tip geometry is in general selected for its electrical properties with respect to the discharge. According to an aspect of an embodiment the tip geometry is also configured to promote a flow of gas through the discharge region. In particular, according to an aspect of an embodiment, the tip geometry is configured to promote and even optimize the process of replenishing the lasing gas in the discharge region.

[0050] In particular, according to an aspect of an embodiment, one or both electrodes are provided with a tip geometry such that the discharge region is wider at its upstream side than it is at its downstream side. According to another aspect of an embodiment, one or both the electrodes are provided with a tip having a geometry that is at least slightly asymmetric between its upstream side and its downstream side. For example, the upper tip surface may be at a slight angle with respect to the upstream direction of the gas flow, which can guide the gas flow on the tip surface and improve gas replenishing. This design can be applied to just the cathode, just the anode, or both.

[0051] The tip shape modification aims at optimizing the gas flow on the electrode surface while minimizing the impact on the discharge when the electrodes are new. It has the potential to mitigate energy burst transients when the chamber is young, i.e., at an early chamber stage.

[0052] FIG. 5 is a diagram showing an arrangement in which a cathode 510 is supplied with a tip structure 515 that is asymmetric with respect to the YZ plane 517. Stated alternatively, the portion of the tip structure 515 to the left of YZ plane 517 is shaped differently than the portion of the tip structure 515 to the right of YZ plane 517. The direction of gas flow is generally in the +X direction as indicated by the arrow in outline. Thus, the gap between electrode tip structures 515, 525 appears differently when viewed from the upstream region than when viewed from the downstream region. In the arrangement shown in FIG. 5, the anode 520 is also supplied with a tip, tip structure 525, that is asymmetric with respect to the YZ plane 517. In the example shown in FIG. 5 both tip structures are slanted with respect to an XZ plane 518 passing through the discharge region, the XZ plane being generally parallel to the longitudinal (Z -direction) extent of the cathode 510 and the anode 520. In the arrangement shown in FIG. 5, the net effect of the shapes and relative positioning of the tip structure 515 and the tip structure 525 is to create a gap which is wider on the upstream side of the gas flow than at the downstream side of the gas flow. This geometry promotes the flow of gas through the discharge region defined by the gap between the opposed surfaces of the tip structure 515 and the tip structure 525.

[0053] FIG. 6 is a not-to-scale diagram of an electrode arrangement for a discharge chamber. Certain dimensions such as the extent of the electrode tips from the electrode bodies are exaggerated in FIG. 6 for purposes of clarity. It will also be understood that although FIG. 6 shows geometries having straightlines meeting at sharp angles in some embodiments it will be desirable to use curves rather than sharp angles to join surfaces to improve flow properties.

[0054] In the arrangement shown in FIG. 6, the cathode 510 has a tip structure 515. The surface of the tip structure 515 facing and defining the discharge region or a tangent to that surface makes an angle 0Cwith the direction shown by the broken line of a streamline of gas flowing through the gap between tip structure 515 and tip structure 525. The tip structure 515 thus has a cathode tip upstream length CUL toward the anode 520 on its upstream side and a cathode tip downstream length CDL on its downstream side. In an embodiment CUL is in general less than CDL.

[0055] In the arrangement of FIG. 6 the anode tip structure 525 is provided with a similar geometry to that of the cathode tip structure 515 with the surface of the tip structure 525 of the anode tip structure 525 that faces or confronts the cathode tip structure 515 or a tangent to that surface making an angle 0A with the direction of gas flow between the electrodes. This results in a tip having a length AUL on the upstream side of the tip structure 525 and a length ADL on the downstream side of the tip structure 525. In an embodiment AUL is in general less than ADL.

[0056] One of ordinary skill in the art will understand that these dimensions will in general be selected to optimize gas flow through the discharge region. Thus, 0c may be in the range of about 5 degrees to about 30 degrees.

[0057] Similarly if the anode 520 is supplied with a tip structure 525 having a gas flow promoting geometry, 0A may be in the range of about 5 degrees to about 30 degrees. If both the first tip structure and the second tip structure are slanted with respect to the direction of gas flow then they may be slanted with respect to each other by an angle in the range of about 10 degrees to about 60 degrees.

[0058] These geometries will in general result in a gap A’ between the tip structure 515 and the tip structure 525 which is not constant but will instead depend on where the gap is measured in relation to the direction of gas flow between the upstream and downstream sides of the electrode tips. In some embodiments this results in a gap which is wider on the upstream side than on the downstream side.

[0059] The above examples are all in terms of electrode tips having a chiseled or slanted surface confronting a similarly configured surface on an opposing electrode. One of ordinary skill in the art will understand that other geometries can be used as long as the goal of promoting gas flow through the discharge region is met.

[0060] For example, as shown in FIG. 7A the electrode tip surfaces are curved rather than straight. This curve may be part of an ellipsoid, or some other curved geometry such as parabolic. The curve is selected, however, so that it is asymmetric with respect to a portion of a YZ plane 517 passing through the electrode tip surface and oriented as shown in FIG. 7A. Stated alternatively, the portion of tip structure 515 to the left of YZ plane 517 is not of the same shape as the portion of the tip structure 515 on the right side of the YZ plane, i.e. tip structure 515 is not symmetric about YZ plane 517. Similarly, FIG. 7B shows a geometry in which the gap between the electrodes decreases and then increases in the direction of gas flow. Again, the arrangement is asymmetric with respect to a portion of a YZ plane 517passing through the electrode tip surface and oriented as shown in FIG. 7A. In general, according to an aspect of an embodiment, the gap between the tip structure 515 and the tip structure 525 will, for at least a portion of the gap, have a decreasing width to form a flow restriction.

[0061] FIG. 8 is a graph of results of a simulation of gas residual levels with time for a conventional tip geometry (solid line) and for a gas flow promoting tip geometry (broken line). The comparison shows that using the gas flow promoting tip geometry can be expected to permit much faster residual reduction than using a conventional tip geometry.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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), and / or all of the steps of any method or process so disclosed, 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.

[0066] 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 implementedin 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.

[0067] Moreover, while operations may be depicted in the drawings or described m the specification in a particular order, such operations need not be performed in the particular order shown or in sequential order, or that all operations be performed, to achieve desirable results. Other operations that are not depicted or described can be incorporated in the example methods and processes. For example, one or more additional operations can be performed before, after, simultaneously, or between any of the described operations. Further, the operations may be rearranged or reordered in other implementations. Those skilled in the art will appreciate that in some embodiments, the actual steps taken in the processes illustrated and / or disclosed may differ from those shown in the figures. Depending on the embodiment, certain of the steps described above may be removed, others may be added.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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 imply that certain embodiments require the presence of at least one of X, at least one of Y, and at least one of Z.

[0072] 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.

[0073] 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.

[0074] The embodiments can be further described using the following clauses:1. A discharge chamber for a deep ultraviolet laser, the discharge chamber comprising: a chamber enclosure; a first electrode having a first electrode tip structure positioned in the chamber enclosure; a second electrode having a second electrode tip structure positioned in the chamber enclosure, the second electrode tip structure confronting the first electrode tip structure to define a discharge region therebetween; and a fan arranged to cause a flow of gas through the discharge region from a region upstream of the discharge region to a region downstream of the discharge region along a direction of the flow of the gas, at least one of the first electrode tip structure and the second electrode tip structure being configured such that a first distance between the first electrode tip structure and the second electrode tip structure at an upstream side of the discharge region is greater than a second distance between the first electrode tip structure and the second electrode tip structure at a downstream side of the discharge region.2. The discharge chamber of clause 1 wherein the first electrode is one of a cathode and an anode and the second electrode is the other of a cathode and an anode.3. The discharge chamber of clause 1 wherein the first electrode tip structure has a first surface and the second electrode tip structure has a second surface with the first surface and the second surface confronting one another across a discharge gap having a decreasing width along the direction of the flow of the gas.4. The discharge chamber of clause 3 wherein at least one of the first surface and the second surface is asymmetric with respect to a plane passing through the at least one of the first surface and the second surface and orthogonal to the direction of the flow of the gas through the discharge region.5. The discharge chamber of clause 3 wherein at least one of the first surface and the second surface is slanted with respect to the direction of the flow of the gas through the discharge region.6. The discharge chamber of clause 5 wherein at least one of the first surface and the second surface is slanted by an angle in a range of about 5 degrees to about 30 degrees.7. The discharge chamber of clause 1 wherein both the first surface and the second surface are asymmetric with respect to a plane passing through the first surface and the second surface and orthogonal to the direction of the flow of the gas through the discharge region.8. The discharge chamber of clause 7 wherein both the first surface and the second surface are slanted with respect to the direction of the flow of the gas through the discharge region.9. The discharge chamber of clause 5 wherein the first surface is slanted by an angle in a range of about 5 degrees to about 30 degrees and the second surface is slanted by an angle in a range of about 5 degrees to about 30 degrees.10. An electrode arrangement for a discharge chamber for a deep ultraviolet laser, the electrode arrangement comprising: a first electrode extending in a first direction in the discharge chamber and having a first discharge surface; and a second electrode extending in the first direction in the discharge chamber parallel to the first electrode and having a second discharge surface extending in the first direction, facing the first discharge surface, and spaced away from the first discharge surface in a second direction transverse to the first direction to define a gap between the first discharge surface and the second discharge surface in the second direction, at least one of the first discharge surface and the second discharge surface being slanted with respect to a plane passing through the discharge region and parallel to the first electrode and the second electrode.11. The electrode arrangement of clause 10 wherein the first electrode is one of a cathode and an anode and the second electrode is the other of a cathode and an anode.12. The electrode arrangement of clause 10 wherein at least one of the first discharge surface and the second discharge surface is slanted by an angle in a range of about 5 degrees to about 30 degrees with respect to the plane passing through the discharge region and parallel to the first electrode and the second electrode.13. The electrode arrangement of clause 10 wherein both the first discharge surface and the second discharge surface are asymmetric with respect to the plane passing through the discharge region and parallel to the first electrode and the second electrode.14. The electrode arrangement of clause 10 wherein both the first discharge surface and the second discharge surface are slanted with respect to the plane passing through the discharge region and parallel to the first electrode and the second electrode.15. The electrode arrangement of clause 14 wherein the first discharge surface is slanted by an angle in a range of about 5 degrees to about 30 degrees and the second discharge surface is slanted by an angle in a range of about 5 degrees to about 30 degrees.16. An electrode for generating a plasma to create deep ultraviolet emission, the electrode comprising: an electrode body which is elongated in a first direction; and an electrode tip extending along the electrode body and extending from the electrode body in a second direction transverse to the first direction into a gas flow region where the plasma is formed, a gas in the gas flow region flowing across the electrode tip from an upstream region to a downstream region, the electrode tip having an asymmetric shape such that the electrode tip has an extension from the electrode body in the upstream region that less than an extension from the electrode body of the electrode tip in the downstream region.17. The electrode of clause 16 wherein the asymmetric shape comprises the electrode tip having a tip surface angled towards the upstream region.18. The electrode of clause 16 wherein the asymmetric shape comprises the electrode tip having a tip surface angled towards the upstream region by an angle in a range of about 5 degrees to about 30 degrees.

[0075] The above described implementations and other implementations are within the scope of the following claims.

Claims

CLAIMS1. A discharge chamber for a deep ultraviolet laser, the discharge chamber comprising: a chamber enclosure; a first electrode having a first electrode tip structure positioned in the chamber enclosure; a second electrode having a second electrode tip structure positioned in the chamber enclosure, the second electrode tip structure confronting the first electrode tip structure to define a discharge region therebetween; and a fan arranged to cause a flow of gas through the discharge region from a region upstream of the discharge region to a region downstream of the discharge region along a direction of the flow of the gas, at least one of the first electrode tip structure and the second electrode tip structure being configured such that a first distance between the first electrode tip structure and the second electrode tip structure at an upstream side of the discharge region is different from a second distance between the first electrode tip structure and the second electrode tip structure at a downstream side of the discharge region.

2. The discharge chamber of claim 1 wherein the first distance is greater than the second distance.

3. The discharge chamber of claim 1 wherein the first electrode tip structure has a first surface and the second electrode tip structure has a second surface with the first surface and the second surface confronting one another across a discharge gap having a decreasing width along the direction of the flow of the gas.

4. The discharge chamber of claim 3 wherein at least one of the first surface and the second surface is asymmetric with respect to a plane passing through the at least one of the first surface and the second surface and orthogonal to the direction of the flow of the gas through the discharge region.

5. The discharge chamber of claim 3 wherein at least one of the first surface and the second surface is slanted with respect to the direction of the flow of the gas through the discharge region.

6. The discharge chamber of claim 5 wherein at least one of the first surface and the second surface is slanted by an angle in a range of about 5 degrees to about 30 degrees.

7. The discharge chamber of claim 1 wherein both the first surface and the second surface are asymmetric with respect to a plane passing through the first surface and the second surface and orthogonal to the direction of the flow of the gas through the discharge region.

8. The discharge chamber of claim 7 wherein both the first surface and the second surface are slanted with respect to the direction of the flow of the gas through the discharge region.

9. The discharge chamber of claim 5 wherein the first surface is slanted by an angle in a range of about 5 degrees to about 30 degrees and the second surface is slanted by an angle in a range of about 5 degrees to about 30 degrees.

10. An electrode arrangement for a discharge chamber, the electrode arrangement comprising: a first electrode extending in a first direction in the discharge chamber and having a first discharge surface extending in the first direction; and a second electrode extending in the first direction in the discharge chamber parallel to the first electrode and having a second discharge surface extending in the first direction, facing the first discharge surface, and spaced away from the first discharge surface in a second direction transverse to the first direction to define a gap between the first discharge surface and the second discharge surface in the second direction, at least one of the first discharge surface and the second discharge surface being slanted with respect to a plane passing through the gap and parallel to the first direction.

11. The electrode arrangement of claim 10 wherein the first electrode is one of a cathode and an anode and the second electrode is the other of a cathode and an anode.

12. The electrode arrangement of claim 10 wherein at least one of the first discharge surface and the second discharge surface is slanted by an angle in a range of about 5 degrees to about 30 degrees with respect to the plane passing through the gap and parallel to the first direction.

13. The electrode arrangement of claim 10 wherein both the first discharge surface and the second discharge surface are asymmetric with respect to the plane passing through the gap and parallel to the first direction.

14. The electrode arrangement of claim 10 wherein both the first discharge surface and the second discharge surface are slanted with respect to the plane passing through the gap and parallel to the first direction.

15. The electrode arrangement of claim 10 wherein the first discharge surface is slanted by a first angle and the second discharge surface is slanted by a second angle different from the first angle.

16. The electrode arrangement of claim 10 wherein the first discharge surface and the second discharge surface are symmetric to each other with respect to the plane, wherein the plane pass through the gap.

17. An electrode for generating a plasma, the electrode comprising: an electrode body which is elongated in a first direction; and an electrode tip extending along the electrode body and extending from the electrode body in a second direction transverse to the first direction into a gas flow having an upstream region and a downstream region, the electrode tip having a curved profile such that the electrode tip has an extension from the electrode body in the upstream region that shorter than an extension from the electrode body in the downstream region.

18. The electrode of claim 17 wherein the curved profile has a tip surface angled towards the upstream region.

19. The electrode of claim 17 wherein the curved profile comprises the electrode tip having a tip surface angled towards the upstream region by an angle in a range of about 5 degrees to about 30 degrees.

20. The electrode of claim 17 wherein the electrode tip has another extension from the electrode body between the extension from the electrode body in the upstream region and the extension from the electrode body in the downstream region, wherein the another extension is longer than the extension from the electrode body in the downstream region.

Images