Capacitor system for a radiation source of a lithographic apparatus

Abstract

A lithographic apparatus includes a projection system and an illumination system that includes an electrode and a set of capacitance structures. The electrode has an elongate shape. A length-wise strip of the electrode is defined from a first end of the elongate shape to a second end of the elongate shape. The length-wise strip includes electrical coupling positions including a first end coupling position proximal to the first end, a second end coupling position proximal to the second end, and a series of intermediary coupling positions between the first end coupling position and the second end coupling position. Each capacitance structure of the first set is coupled to a respective one of the electrical coupling positions. A capacitance value of a capacitance structure coupled to one of the intermediary coupling positions is less than a capacitance value of a capacitance structure coupled to the first end coupling position.

Description

CAPACITOR SYSTEM FOR A RADIATION SOURCE OF A LITHOGRAPHIC APPARATUSCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 621,904 which was filed on 17 January 2024 which is incorporated herein in its entirety by reference.FIELD

[0002] The present disclosure relates to radiation sources, for example, an illumination sources for lithographic apparatuses and systems.BACKGROUND

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which can be a mask or a reticle, can be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., comprising part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiationsensitive material (photoresist or simply “resist”) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatuses include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”- direction) while synchronously scanning the target portions parallel or anti-parallel to this scanning direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0004] During an exposure step of a lithographic process, photoresist can be irradiated using a radiation source. It is desirable for the radiation source to be stable and long lasting. Radiation sources for lithographic use can be complex and difficult to service. In the event a radiation source for a lithographic process experiences downtime for maintenance, precious fabrication time is lost. It is desirable for a lithographic systems to be able to operate for long periods of time uninterrupted with high performance in order to maximize throughput. One of the causes of degraded performance in a radiation source is sub-optimal design of the components.SUMMARY

[0005] Accordingly, it is desirable to improve performance and reliability of radiation sources in order to improve lithographic fabrication throughput. Aspects described herein can be implemented to provide radiation sources with increased performance, reliability, and lifetime of operation.

[0006] In some aspects, a lithographic apparatus comprises a projection system and an illumination system. The projection system is configured to project an image of a pattern onto a substrate. The illumination system is configured to illuminate the pattern of a patterning device. The illumination system comprises an electrode and a first set of capacitance structures. The electrode is configured to deliver an electrical pulse to a gas to generate radiation. The electrode has an elongate shape. A lengthwise strip of the electrode is defined from a first end of the elongate shape to a second end of the elongate shape. The length-wise strip comprises electrical coupling positions comprising a first end coupling position proximal to the first end, a second end coupling position proximal to the second end, and a series of intermediary coupling positions between the first end coupling position and the second end coupling position. The first set of capacitance structures is configured to transmit the electrical pulse to the electrode. Each capacitance structure of the first set is coupled to a respective one of the electrical coupling positions. A capacitance value of a capacitance structure coupled to one of the intermediary coupling positions is less than a capacitance value of a capacitance structure coupled to the first end coupling position.

[0007] In some aspects, a pulsed-discharge radiation source is configured to generate radiation. The pulsed-discharge radiation source comprises an electrode and a first set of capacitance structures. The electrode is configured to deliver an electrical pulse to a gas to generate radiation. The electrode has an elongate shape. A length- wise strip of the electrode is defined from a first end of the elongate shape to a second end of the elongate shape. The length-wise strip comprises electrical coupling positions comprising a first end coupling position proximal to the first end, a second end coupling position proximal to the second end, and a series of intermediary coupling positions between the first end coupling position and the second end coupling position. The first set of capacitance structures is configured to deliver the electrical pulse to the electrode. Each capacitance structure of the first set is coupled to a respective one of the electrical coupling positions. A capacitance value of a capacitance structure coupled to one of the intermediary coupling positions is less than a capacitance value of a capacitance structure coupled to the first end coupling position.

[0008] In some aspects, a method for optimizing performance of an electrode of a pulsed discharge radiation source comprising a first set of capacitance structures can comprise one or more of the following operations. The method comprises arranging capacitance structures of the first set. The electrode has an elongate shape. A length-wise strip of the electrode is defined from a first end of the elongate shape to a second end of the elongate shape. The length-wise strip comprises electrical coupling positions comprising a first end coupling position proximal to the first end, a second end coupling position proximal to the second end, and a series of intermediary coupling positions between the first end coupling position and the second end coupling position. The arranging also comprises coupling each capacitance structure of the first set to a respective one of the electrical coupling positions such that a capacitance value of a capacitance structure coupled to one of the intermediary coupling positions is less than a capacitance value of a capacitance structure coupled to the first end couplingposition. The method also comprises delivering an electrical pulse to a gas via the electrode to generate radiation. The delivering comprises transmitting the electrical pulse to the electrode via the first set of capacitors. A capacitance value of the capacitance structure coupled to the one of the intermediary coupling positions may be less than the capacitance value of the capacitance structure coupled to the first end coupling position.

[0009] Further features of various aspects of the present disclosure are described in detail below with reference to the accompanying drawings. It is noted that the present disclosure is not limited to the specific aspects described herein. Such aspects are presented herein for illustrative purposes only. Additional aspects will be apparent to those skilled in the relevant art(s) based on the teachings contained herein.BRIEF DESCRIPTION OF THE DRAWINGS / FIGURES

[0010] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and to enable those skilled in the relevant art(s) to make and use aspects described herein.

[0011] FIG. 1 shows a lithographic apparatus, according to some aspects.

[0012] FIG. 2 shows a lithographic cell, according to some aspects.

[0013] FIGS. 3-6 show radiation sources, according to some aspects.

[0014] FIG. 7-10 show different configurations of capacitance structures, according to some aspects.

[0015] FIG. 11 shows a flowchart of a method for optimizing performance of an electrode of a pulsed discharge radiation source, according to some aspects.

[0016] The features of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and / or structurally similar elements. Additionally, generally, the leftmost digit(s) of a reference number identifies the drawing in which the reference number first appears. Unless otherwise indicated, the drawings provided throughout the disclosure should not be interpreted as to-scale drawings.DETAILED DESCRIPTION

[0017] The aspects described herein, and references in the specification to “one aspect,” “an aspect,” “an exemplary aspect,” “an example aspect,” etc., indicate that the aspects described can include a particular feature, structure, or characteristic, but every aspect may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same aspect. Further, when a particular feature, structure, or characteristic is described in connection with anaspect, it is understood that it is within the knowledge of those skilled in the art to effect such feature, structure, or characteristic in connection with other aspects whether or not explicitly described.

[0018] Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “on,” “upper” and the like, can be used herein for ease of description to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein can likewise be interpreted accordingly.

[0019] The terms “about,” “approximately,” or the like can be used herein to indicate the value of a given quantity that can vary based on a particular technology. Based on the particular technology, the terms “about,” “approximately,” or the like can indicate a value of a given quantity that varies within, for example, 10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

[0020] Enumerative adjectives (e.g., “first,” “second,” “third,” or the like) can be used to distinguishing like elements without establishing an order, hierarchy, quantity, or permanent numeric assignment (unless otherwise noted). For example, the terms “first target” and “second target” can be used in a manner analogous to “i* target” and “j* target” so as to facilitate the distinguishing of two targets without specifying a particular order, hierarchy, quantity, or immutable numeric correspondence.

[0021] Aspects of the present disclosure can be implemented in hardware, firmware, software, or any combination thereof. Aspects of the disclosure can also be implemented as instructions stored on a computer-readable medium, which can be read and executed by one or more processors. A machine- readable medium can include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium can include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Furthermore, firmware, software, routines, and / or instructions can be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. The term “machine -readable medium” can be interchangeable with similar terms, for example, “computer program product,” “computer-readable medium,” “non-transitory computer- readable medium,” or the like. The term “non-transitory” can be used herein to characterize one or more forms of computer readable media except for a transitory, propagating signal.

[0022] Before describing such aspects in more detail, however, it is instructive to present an example environment in which aspects of the present disclosure can be implemented.

[0023] Example Lithographic Systems

[0024] FIG. 1 shows a lithographic apparatus 100, in which aspects of the present disclosure can be implemented. Lithographic apparatus 100 can comprise one or more of the following: an illuminator IL to condition a radiation beam B (e.g., deep ultra violet (DUV) radiation); a support structure MT (e.g., a mask table) to support a patterning device MA (e.g., a mask, a reticle, or a dynamic patterning device); a first positioner PM to accurately position patterning device MA; a substrate table WT (e.g., a wafer table) to hold a substrate W (e.g., a resist-coated wafer); and a second positioner PW to accurately position substrate W. Lithographic apparatus 100 can also comprise a projection system PS to project patterned radiation onto a target portion C (e.g., comprising one or more dies) of substrate W. The pattern can be imparted to radiation beam B by patterning device MA. In lithographic apparatus 100, patterning device MA and projection system PS can be transmissive.

[0025] In some aspects, illuminator IL can comprise various types of optical components, such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for directing, shaping, or controlling the radiation beam B.

[0026] In some aspects, support structure MT can hold patterning device MA in a manner that depends on the orientation of patterning device MA with respect to a reference frame, a design of lithographic apparatus 100, and other conditions, such as whether or not patterning device MA is held in a vacuum environment. Support structure MT can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device MA. Support structure MT can be, for example, a frame or a table (e.g., can be fixed or movable). By using one or more positioning sensors (e.g., alignment sensor), support structure MT can ensure that patterning device MA is at a desired position, for example, with respect to the projection system PS.

[0027] In some aspects, the term “patterning device” can refer to a device that can be used to create a pattern of radiation at a cross-section of radiation beam B, such as to create a pattern at target portion C of substrate W. The pattern imparted to radiation beam B can correspond to a particular functional layer in a device being created at target portion C to form an integrated circuit. Examples of patterning devices MA include, for example, reticles, masks, or programmable LCD panels. Masks types used in lithography can include binary, alternating phase shift, or attenuated phase shift, as well as various hybrid mask types.

[0028] In some aspects, the term “projection system” can refer to any type of projection system (e.g., refractive, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof) suitable for the exposure radiation being used. Features of projection systems can account for additional factors, such as the use of an immersion liquid on the substrate W or the use of a vacuum. For example, a projection system can be designed for use in a controlled gas environment such that the beam path can be conditioned as desired.

[0029] In some aspects, lithographic apparatus 100 can be of a type having two (dual stage) or more substrate tables WT (and / or two or more mask tables). In such “multiple stage” machines, the additionalsubstrate tables WT can be used in parallel, or preparatory steps can be carried out on one or more tables while one or more other substrate tables WT are being used for exposure. In some situations, the additional table may not be a substrate table.

[0030] In some aspects, lithographic apparatus 100 can also be of a type in which at least a portion of substrate W can be covered by a liquid having a relatively high refractive index, e.g., water, so as to fill a space between projection system PS and substrate W. An immersion liquid can also be applied to other spaces in lithographic apparatus 100, for example, between patterning device MA and projection system PS. Immersion techniques can increase the numerical aperture (NA) of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid. For example, a liquid can be disposed between projection system PS and substrate W during exposure.

[0031] In some aspects, illuminator IL can receive a radiation beam from source SO (e.g., radiation source). Source SO and lithographic apparatus 100 can be separate physical entities. For example, source SO can be a detached excimer laser such as a krypton fluoride (KrF) laser or an argon fluoride laser (ArF). In such cases, source SO is not considered to be part of the lithographic apparatus 100 and radiation beam B passes from source SO to illuminator IL with the aid of a beam delivery system BD. Beam delivery system BD can include, for example, suitable directing mirrors and / or a beam expander.

[0032] In some aspects, source SO can be an integral part of the lithographic apparatus 100. A radiation system (or illumination system) can comprise source SO, illuminator IL, and / or beam delivery system BD.

[0033] In some aspects, illuminator IL can comprise an adjuster AD for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and / or inner radial extent (commonly referred to as “o-outer” and “o-inner,” respectively) of the intensity distribution in a pupil plane of illuminator IL can be adjusted. In addition, illuminator IL can comprise various other components, such as an integrator IN and a condenser CO. Illuminator IL can be used to condition the radiation beam B to have a desired uniformity and intensity distribution in its cross section.

[0034] In some aspects, radiation beam B can be incident on patterning device MA, which is held on support structure MT, and is patterned by patterning device MA. Having traversed patterning device MA, radiation beam B can pass through projection system PS, which focuses the beam onto a target portion C of substrate W. Projection System PS has a pupil conjugate PPU to an illumination system pupil IPU. Portions of radiation emanate from the intensity distribution at the illumination system pupil IPU and traverse a mask pattern without being affected by diffraction at the mask pattern and create an image of the intensity distribution at the illumination system pupil IPU.

[0035] In some aspects, projection system PS can project an image of a pattern MP of patterning device MA. The image can be formed by diffracted beams produced from the pattern MP by radiation from the intensity distribution. The image can be projected on a photoresist layer coated on the substrate W. For example, pattern MP can comprise an array of lines and spaces.

[0036] In some aspects, lithographic apparatuses can comprise a deep ultraviolet (DUV) source, which is configured to generate a beam of DUV radiation for DUV lithography. In general, the DUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the DUV radiation beam of the DUV source.

[0037] Example Lithographic Cell

[0038] FIG. 2 shows a lithographic cell 200, also sometimes referred to a lithocell or cluster, according to some aspects. Lithographic apparatus 100 can form part of lithographic cell 200. Lithographic cell 200 can also include one or more apparatuses to perform pre- and post-exposure processes on a substrate. Examples of such apparatuses can include spin coaters SC to deposit resist layers, developers DE to develop exposed resist, chill plates CH, and bake plates BK. A substrate handler, or robot, RO can pick up substrates from input / output ports I / Ol, I / O2, move them between the different process apparatuses and deliver the substrates to a loading bay LB of lithographic apparatus 100. The different apparatuses, which are often collectively referred to as the track, can be under the control of a track control unit TCU, which can itself be controlled by a supervisory control system SCS. Supervisory control system can also control lithographic apparatus 100 via lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.

[0039] Example Radiation Source

[0040] In some aspects, a pulsed-discharge radiation source (e.g., a pulsed-discharge laser) can be used for lithographic processes, medical procedures, machining via laser ablation, laser imprinting, and more. A lithographic apparatus is one example in which a stable radiation source is desirable. If for any reason a radiation source becomes unstable (e.g., producing an incorrect dose of radiation), servicing the radiation source can cost precious downtime of the lithographic apparatus. Lost production time can severely impact throughput and production goals.

[0041] FIG. 3 shows a radiation source 300, according to some aspects. In some aspects, radiation source 300 is a pulsed-discharge radiation source. A gas discharge laser is an example of a pulsed- discharge radiation source. Source SO of lithographic apparatus 100 (FIG. 1) can use implement radiation source 300. Radiation source 300 can comprise a gas chamber 302, a window 304, and one or more electrodes 310 (also “electrical connection”).

[0042] In some aspects, gas chamber 302 can confine a gas 308. Gas 308 can comprise fluorine, neon, krypton, argon, and the like. Gas 308 can be rarified via a pressure control system (e.g., vacuum system) that controls a pressure within gas chamber 302. A voltage / current can be supplied to gas 308 (e.g., via one or more electrodes 310) to generate radiation 312. The voltage / current can be in the form of a pulse with sufficient power to ionize gas 308 and strike a plasma. The plasma can generate radiation with a set of wavelengths that depend on energy states of the plasma. The wavelengths that are produced (e.g., DUV wavelengths) can depend on the type of gas (e.g., mixtures of krypton, fluorine, and other gasses or mixtures of argon, fluorine, and other gasses). Window 304 can allow radiation 312 to exit gas chamber 302.

[0043] FIG. 4 shows a radiation source 400, according to some aspects. In some aspects, the view in FIG. 4 can represent a more detailed and / or different view of a portion of radiation source 300 (FIG. 3) (some omissions can be made for clarity of drawing). Structures and functions of commonly numbered elements in FIGS. 3 and 4 are described above (e.g., matching elements can have reference numbers that share the two right-most numeric digits). Such elements can include gas chamber 402, gas 408, and electrodes 410.

[0044] In some aspects, radiation source 400 can comprise gas chamber 402, one or more electrodes 410, and a gas circulator 414. Gas circulator 414 can be blower or an external pressure system that is connected to gas chamber 402 via ducting. Gas chamber 402 can confine a gas. The gas can comprise fluorine, neon, krypton, argon, or other similar species (for example, argon fluoride). To generate radiation 312 (FIG. 3), an electrical pulse can be supplied to gas 408 via electrodes 410, thereby creating a plasma of gas 408 at a plasma region 416 between electrodes 410. The generated plasma can release radiation, thereby operating as a source of radiation. The point of view in FIG. 4 can be considered as being rotated 90 degrees with respect to the point of view of FIG. 3 (e.g., whereas radiation 312 is shown in FIG. 3 traveling to the right of the page (can also be left of the page), radiation can travel in / out of the page in FIG. 4).

[0045] In some aspects, in the process of generating radiation, gas 408 and electrodes 410 can interact chemically. For example, a material of electrodes 410 (e.g., copper) can chemically interact with a chemical content of gas 408 (e.g., fluorine). As a result of the chemical interaction, metal atoms from the electrode can chemically combine with atoms in the gas to create a dust-like byproduct (e.g., metal- fluoride byproduct). The byproduct can be filtered out by filters and cleaning systems in the path of a gas flow 418 (indicated by arrows). Gas circulator 414 can generate gas flow 418. Additional details about blower functions are described in WO 2022 / 140074, published on June 30, 2022, which is incorporated by reference herein in its entirety.

[0046] Example Capacitor Systems

[0047] FIG. 5 shows a portion of a radiation source 500, according to some aspects. In some aspects, the view in FIG. 5 can represent a more detailed and / or different view of a portion of radiation sources 300 and / or 400 (FIGS. 3 and 4) (some omissions can be made for clarity of drawing). Structures and functions of commonly numbered elements in FIGS. 3 and 4 are described above (e.g., matching elements can have reference numbers that share the two right-most numeric digits). Such elements can include gas 508, gas flow 518, electrodes 510 and 510’, and plasma region 516. Radiation source 500 can also comprise a power supply 522 and a capacitor system 524 (e.g., a capacitor bank).

[0048] In some aspects, electrode 510 can be referred to as a cathode 510 and electrode 510’ can be referred to as an anode 510’. (In various implementations, the cathode and anode functions of electrodes can be swapped). One or both of cathode 510 and anode 510’ can be included in the envelope of gas chamber 402 (FIG. 4).

[0049] In some aspects, a power supply 522 can provide electrical power to cathode 510. Power supply 522 can be electrically coupled to cathode 510. And, though obstructed in the point of view of FIG. 5, it is to be understood that power supply 522 can be coupled to anode 510’ to complete a circuit. As will be described below with respect to FIGS. 6-10, the coupling between power supply 522 and cathode 510 can also include a coupling through capacitor system 524, which can be used to store energy over time and quickly release it to generate the high power electrical pulses for generating a plasma.

[0050] In some aspects, electrical discharges to gas 508 (e.g., for lasing) can occur at a gap between cathode 510 and anode 510’, the gap having a distance A. In various implementations, cathode 510 and / or anode 510’ can be manufactured such that each electrode has (or eventually grows) additional material 520 and 520’ (e.g., a coating, additional electrode metal) to protect the surfaces of the electrode(s).

[0051] In some aspects, cathode 510 and anode 510’ can have an elongate shape (e.g., see FIG. 6 for a clearer perspective). Plasma region 516 can also be elongate (in / out of the page) according to a length of the cathode 510 and anode 510’. In other words, when electrical power is delivered to plasma region 516, a long strip of plasma volume is formed. The long strip of plasma is conducive for a gain medium that allows lasing.

[0052] In some aspects, arrangements of capacitance structures of capacitor system 524 can be used to improve the performance of cathode 510 and / or anode 510’.

[0053] FIG. 6 shows a portion of a radiation source 600, according to some aspects. In some aspects, the view in FIG. 6 can represent a more detailed and / or different view of a portion of radiation sources 300, 400, and / or 500 (FIGS. 3-5) (some omissions can be made for clarity of drawing). Structures and functions of commonly numbered elements in FIGS. 3-5 are described above (e.g., matching elements can have reference numbers that share the two right-most numeric digits). Such elements can include electrode 610 and capacitor system 624.

[0054] In some aspects, radiation source 600 can also comprise a set of electrical connectors 632 (e.g., high voltage connectors). Capacitor system 624 can comprise a set 626 of capacitance structures (e.g., first set of capacitance structures). Capacitor system 624 can also comprise a set 628 of capacitance structures (e.g., second sets of capacitance structures). Additional sets of capacitance structures can be included in capacitor system 624 (e.g., a third set, a fourth set, and so on). Electrical connectors can provide electrical coupling between electrode 610 and the capacitance structures of capacitor system 624. Electrical power is routed, from power supply 522 to electrode 610, through sets of capacitance structures 626 and 628 and set of electrical connectors 632. Capacitor system 624 can transmit the electrical power from power supply 522 (FIG. 5) as a high-power electrical pulse. As explained above, a long strip of plasma is to be generated. Therefore, the connections of capacitance structures to electrode 610 are spaced and distributed along a length-wise strip of electrode 610. In this manner, electrical power can be spread evenly along a length-wise strip of electrode 610.

[0055] In some aspects, electrode 610 has an elongate shape (e.g., represented as length-wise strip 620, which can correspond to additional material 520 (FIG. 5)). The elongate shape has opposite ends 634 and 636 (e.g., a first end disposed opposite from a second end). Electrical coupling positions can be defined along length-wise strip 620 of electrode 610. Electrode 610 can receive an evenly distributed high voltage electrical signal via the spread-out arrangement of the electrical coupling positions. A nonlimiting arrangement of electrical coupling positions is shown, which comprise an end coupling position 638 (e.g., a first end coupling position), an end coupling position 642 (e.g., a second end coupling position), and a series of intermediate coupling positions 640-n, with n=l, 2, 3, and so on. Of the electrical coupling positions, end coupling position 638 can be disposed most proximal to end 634 (e.g., the first end coupling position is proximal to the first end). End coupling position 642 can be disposed most proximal to end 636 (e.g., the second end coupling position is proximal to the second end). The series of intermediate coupling positions 640-n can be disposed between end coupling positions 638 and 642. For purposes of discussion only, FIG. 6 shows fourteen electrical coupling positions (some aspects are envisaged implementing more or fewer electrical coupling positions).

[0056] In some aspects, FIG. 6 illustrates capacitance structures and electrical connectors in row arrangements. It is to be appreciated that other arrangements are envisaged (e.g., staggered, array) since it is the electrical coupling positions at length-wise strip 620 that determine the spread of the high power pulse (e.g., a physical location of a capacitor is not as important as the electrical coupling position it is connected to). The row arrangement of capacitance structures and electrical connectors merely provide clarity of illustration and description.

[0057] Additional details about pulsed-discharge sources, electrodes, and capacitor connections are described in U.S. Patent NO. 11,349,273, issued on May 31, 2022, which is incorporated by reference herein in its entirety. The use of capacitance structures as described with respect to aspects herein can also be used in non-pulsed radiation sources (e.g., continuous discharge sources).

[0058] In some aspects, each capacitance structure of set of capacitors 626 is coupled to a respective one of the electrical coupling positions. Similarly, each capacitance structure of set of capacitors 628 is also coupled to a respective one of the electrical coupling positions. For example, one capacitance structure of set of capacitors 626 and one capacitance structure of set of capacitors 628 are connected, in parallel, to a same coupling position. For two parallel capacitance structures, the effective capacitance is a sum of the capacitance values.

[0059] In some aspects, the majority of capacitance structures in a set can have the same value, with a few capacitance structures deviating from the rest. For example, the left-most capacitance structure of set 626 of capacitance structures (connected to end coupling position 638) may have a vacant capacitor connection structure (no capacitor). The absence of a capacitor can be interpreted as a capacitance structure with a capacitance value of zero. Alternatively, instead of a vacant capacitor structure, a capacitor of lower value, but non-zero, can be coupled at coupling position 638. The capacitance distribution across the electrical coupling connections can be tailored for achieving a desiredperformance (e.g., a peak performance, or an average performance, or a lifetime performance) of electrode 610.

[0060] FIG. 7 shows a layout of a capacitor system 724, according to some aspects. In some aspects, the view in FIG. 7 can represent a more detailed and / or different view of a portion of capacitor systems 524 and 624 (FIGS. 5 and 6) (some omissions can be made for clarity of drawing). Structures and functions of commonly numbered elements in FIGS. 5 and 6 are described above (e.g., matching elements can have reference numbers that share the two right-most numeric digits). Such elements can include set 726 of capacitance structures, end coupling positions 738 and 742, and intermediate coupling positions 740-n.

[0061] In some aspects, a capacitance value at intermediate coupling position 740-2 is less than a capacitance value at end coupling position 738. The reduced capacitance value can be achieved by using a capacitor of lesser value or leaving the capacitor connection structure vacant. Intermediate coupling position 740-2 is displaced at least two coupling positions from end coupling position 738. The capacitance value at intermediate coupling position 740-2 can be less than a capacitance value at intermediate coupling position 740-1 (intermediate coupling position 740-1 is a coupling position that is displaced by one coupling position from end coupling position 738). The capacitance value at intermediate coupling position 740-2 can be less than a capacitance value at each coupling position adjacent thereto (e.g., less than the capacitance value at intermediate coupling position 740-3). A distribution of capacitance values across the electrical coupling positions can be asymmetric or can lack mirror symmetry. If another set of capacitance structures are present (e.g., set 628 of capacitance structures (FIG. 6), the configuration in the other set of capacitance structures can be independent from the configuration of set of capacitance structures 724. For example, set 628 of capacitance structures (FIG. 6) can have a full set of capacitors (e.g., no vacancy) or have different distributions of capacitance values.

[0062] FIG. 8 shows a layout of a capacitor system 824, according to some aspects. In some aspects, the view in FIG. 8 can represent a more detailed and / or different view of a portion of capacitor systems 524 and 624 (FIGS. 5 and 6) (some omissions can be made for clarity of drawing). Structures and functions of commonly numbered elements in FIGS. 5 and 6 are described above (e.g., matching elements can have reference numbers that share the two right-most numeric digits). Such elements can include set 826 of capacitance structures, end coupling positions 838 and 842, and intermediate coupling positions 840-n.

[0063] In some aspects, a capacitance value at intermediate coupling position 840-2 is less than a capacitance value at end coupling position 838 (e.g., similar to FIG. 7). The relationship of the capacitance value at intermediate coupling position 840-2 relative to its neighboring electrical coupling positions can be as described above for intermediate coupling position 740-2 (FIG. 7). A capacitance value at intermediate coupling position 840-n- 1 (n minus 1) is less than a capacitance value at end coupling position 842. That is, a capacitance value at another one of the intermediary coupling positionsis less than a capacitance value at the opposite end coupling position. Intermediate coupling position 840-n-l is displaced at least two coupling positions from end coupling position 842. The relationship of the capacitance value at intermediate coupling position 840-n-l relative to its neighboring electrical coupling positions can be as described above for intermediate coupling position 740-2 (FIG. 7).

[0064] In some aspects, a distribution of capacitance values across the electrical coupling positions can have mirror symmetry or can lack mirror symmetry. For example, let intermediary coupling position 840-2 be a first number of coupling positions displaced from end coupling position 838. Also let intermediary coupling position 840-n-l be a second number of coupling positions displaced from end coupling position 842. For mirror symmetry, the first number is the same as the second number (FIG. 8 illustrates this scenario). For lack of mirror symmetry, the first number is different from the second number (not shown). If another set of capacitance structures is present (e.g., set 628 of capacitance structures (FIG. 6), the configuration in the other set of capacitance structures can be independent from the configuration of set of capacitance structures 824. For example, set 628 of capacitance structures (FIG. 6) can have a full set of capacitors (e.g., no vacancy) or have different distributions of capacitance values.

[0065] FIG. 9 shows a layout of a capacitor system 924, according to some aspects. In some aspects, the view in FIG. 9 can represent a more detailed and / or different view of a portion of capacitor systems 524 and 624 (FIGS. 5 and 6) (some omissions can be made for clarity of drawing). Structures and functions of commonly numbered elements in FIGS. 5 and 6 are described above (e.g., matching elements can have reference numbers that share the two right-most numeric digits). Such elements can include set 926 of capacitance structures, set 928 of capacitance structures, end coupling positions 938 and 942, and intermediate coupling positions 940-n.

[0066] In some aspects, for set 926 of capacitance structures, a capacitance value at intermediate coupling position 940-n- 1 is less than a capacitance value at end coupling position 942. Also, for set 928 of capacitance structures, a capacitance value at intermediate coupling position 940-2 is less than a capacitance value at end coupling position 942. That is, a capacitance value at another one of the intermediary coupling positions, from another set of capacitance structures, is less than a capacitance value at an end coupling position. The relationship of the capacitance value at a given intermediate coupling position 940-n- 1 relative to its neighboring electrical coupling positions can be as described above for intermediate coupling position 740-2 (FIG. 7).

[0067] In some aspects, a distribution of capacitance values across the electrical coupling positions can lack mirror symmetry, but can have rotational symmetry.

[0068] FIG. 10 shows a layout of a capacitor system 1024, according to some aspects. In some aspects, the view in FIG. 10 can represent a more detailed and / or different view of a portion of capacitor systems 524 and 624 (FIGS. 5 and 6) (some omissions can be made for clarity of drawing). Structures and functions of commonly numbered elements in FIGS. 5 and 6 are described above (e.g., matching elements can have reference numbers that share the two right-most numeric digits). Such elements caninclude set 1026 of capacitance structures, set 1028 of capacitance structures, end coupling positions 1038 and 1042, and intermediate coupling positions 1040-n.

[0069] In some aspects, capacitor system 1024 also comprises a set 1030 of capacitance structures (e.g., a third set of capacitance structures). The reduced capacitance values are disposed as follows. For set 1026, reduced capacitance occurs at intermediate coupling position 1040-n-3 (n minus 3). For set 1028, reduced capacitance occurs at intermediate coupling position 1040-3. For set 1030, reduce capacitance occurs at intermediate coupling position 1040-2 and at intermediate coupling position 1040-n- 1.

[0070] FIG. 11 shows a method 1100 for fabricating a semiconductor device, which includes optimizing performance of an electrode 610 (FIG. 6) of a pulsed discharge radiation source. Functions can be described in reference to FIGS. 1-10, according to some aspects.

[0071] In some aspects, capacitance structures of set 726 (FIG. 7) are arranged. The arrangement can be as described above with respect to FIGS. 6-10.

[0072] In some aspects, at step 1104, an electrical pulse is delivered to a gas 408 (FIG. 4) to generate radiation.

[0073] When delivering the electrical pulse to gas 408 (FIG. 4), at step 1106, the electrical pulse is transmitted to electrode 610 (FIG. 6) via set 726 (FIG. 7) of capacitance structures. An intensity distribution of the electrical pulse (e.g., a distribution of energy, instantaneous power, peak power, instantaneous current, or peak current) across electrode 610 (FIG. 6) is based on each capacitance structure of set 726 (FIG. 7) being coupled to a respective one of the electrical coupling positions (end coupling position 738, intermediate coupling positions 740-n, and end coupling position 742 (FIG. 7). The intensity distribution of the electrical pulse across electrode 610 (FIG. 6) is further based on a capacitance value at intermediate coupling position 740-2 (FIG. 7) being less than a capacitance value at end coupling position 738 (FIG. 7).

[0074] The method steps of FIG. 11 described above merely reflect an example of steps and are not limiting. That is, further method steps and functions are envisaged based on aspects described in reference to FIGS. 1-10. For example, the intensity distribution of the electrical pulse can be set according to the different capacitance configurations described in reference to FIGS. 6-10.

[0075] The terms “radiation,” “beam,” “light,” “illumination,” or the like can be used herein to refer to one or more types of electromagnetic radiation, for example, ultraviolet (UV) radiation (for example, having a wavelength I of 365, 248, 193, 157 or 126 nm). Generally, radiation having wavelengths between about 400 to about 700 nm is considered visible radiation; radiation having wavelengths between about 780-3000 nm (or larger) is considered IR radiation. UV refers to radiation with wavelengths of approximately 100-400 nm. Within lithography, the term “UV” also applies to the wavelengths that can be produced by a mercury discharge lamp: G-line 436 nm; H-line 405 nm; and / or, I-line 365 nm. Vacuum UV, or VUV (i.e., UV absorbed by gas), refers to radiation having a wavelength of approximately 100-200 nm. Deep UV (DUV) generally refers to radiation having wavelengths ranging from 126 nm to 428 nm, and in some aspects, an excimer laser can generate DUV radiationused within a lithographic apparatus. It should be appreciated that radiation having a wavelength in the range of, for example, 180-200 nm relates to radiation with a certain wavelength band, of which at least part is in the range of 180-200 nm.

[0076] It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by those skilled in relevant art(s) in light of the teachings herein.

[0077] The present disclosure has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed. The foregoing description of specific aspects will so fully reveal the general nature of the present disclosure that others can, by applying knowledge within the skill of the art, readily modify and / or adapt for various applications such specific aspects, without undue experimentation and without departing from the general concept of the present disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed aspects, based on the teaching and guidance presented herein.

[0078] Other aspects of the invention are set out in the following numbered clauses:1. A lithographic apparatus comprising: a projection system configured to project an image of a pattern onto a substrate; and an illumination system configured to illuminate the pattern of a patterning device, the illumination system comprising: an electrode configured to deliver an electrical pulse to a gas to generate radiation, wherein the electrode has an elongate shape, a length- wise strip of the electrode is defined from a first end of the elongate shape to a second end of the elongate shape, and the length- wise strip comprises electrical coupling positions comprising: a first end coupling position proximal to the first end; a second end coupling position proximal to the second end; and a series of intermediary coupling positions between the first end coupling position and the second end coupling position; and a first set of capacitance structures configured to transmit the electrical pulse to the electrode, wherein each capacitance structure of the first set is coupled to a respective one of the electrical coupling positions, and wherein a capacitance value of a capacitance structure coupled to one of the intermediary coupling positions is less than a capacitance value of a capacitance structure coupled to the first end coupling position.2. The lithographic apparatus of clause 1, wherein the capacitance structure coupled to the one of the intermediary coupling positions comprises a vacant capacitor connection structure.3. A radiation source configured to generate radiation, comprising:an electrode configured to deliver an electrical pulse to a gas to generate radiation, wherein the electrode has an elongate shape, a length-wise strip of the electrode is defined from a first end of the elongate shape to a second end of the elongate shape, and the length- wise strip comprises electrical coupling positions comprising: a first end coupling position proximal to the first end; a second end coupling position proximal to the second end; and a series of intermediary coupling positions between the first end coupling position and the second end coupling position; and a first set of capacitance structures configured to deliver the electrical pulse to the electrode, wherein each capacitance structure of the first set is coupled to a respective one of the electrical coupling positions, and wherein a capacitance value of a capacitance structure coupled to one of the intermediary coupling positions is less than a capacitance value of a capacitance structure coupled to the first end coupling position.4. The radiation source of clause 3, wherein the one of the intermediary coupling positions is at least two coupling positions displaced from the first end coupling position.5. The radiation source of clause 3, wherein: a capacitance value of a further capacitance structure coupled to a further one of the intermediary coupling positions is less than a capacitance value of a capacitance structure coupled to the second end coupling position.6. The radiation source of clause 5, wherein: the one of the intermediary coupling positions is a first number of coupling positions displaced from the first end coupling position; the further one of the intermediary coupling positions is a second number of coupling positions displaced from the second end coupling position; and the first number is same as the second number.7. The radiation source of clause 5, wherein: the one of the intermediary coupling positions is a first number of coupling positions displaced from the first end coupling position; the further one of the intermediary coupling positions is a second number of coupling positions displaced from the second end coupling position; and the first number is different than the second number.8. The radiation source of clause 3, further comprising a second set of capacitance structures configured to deliver the electrical pulse to the electrode, wherein each capacitance structure of the second set is coupled to a respective one of the electrical coupling positions.9. The radiation source of clause 8, wherein a capacitance value of a capacitance structure of the second set coupled to one of the intermediary coupling positions is less than acapacitance value of a capacitance structure of the second set coupled to the first end coupling position.10. The radiation source of clause 8, further comprising a third set of capacitance structures configured to deliver the electrical pulse to the electrode, wherein each capacitance structure of the third set is coupled to a respective one of the electrical coupling positions.11. The radiation source of clause 3, the capacitance structure coupled to the one of the intermediary coupling positions comprises a vacant capacitor connection structure.12. A method for optimizing performance of an electrode of a radiation source comprising a first set of capacitance structures, the method comprising: arranging capacitance structures of the first set, wherein the electrode has an elongate shape, a length-wise strip of the electrode is defined from a first end of the elongate shape to a second end of the elongate shape, and the length- wise strip comprises electrical coupling positions comprising: a first end coupling position proximal to the first end; a second end coupling position proximal to the second end; and a series of intermediary coupling positions between the first end coupling position and the second end coupling position, wherein the arranging comprises coupling each capacitance structure of the first set to a respective one of the electrical coupling positions such that a capacitance value of a capacitance structure coupled to one of the intermediary coupling positions is less than a capacitance value of a capacitance structure coupled to the first end coupling position; delivering an electrical pulse to a gas via the electrode to generate radiation, wherein the delivering comprises: transmitting the electrical pulse to the electrode via the first set of capacitors.13. The method of clause 12, wherein the coupling is performed such that the one of the intermediary coupling positions is at least two coupling positions displaced from the first end coupling position.14. The method of clause 12, wherein: the coupling is performed such that a capacitance value of a further capacitance structure coupled to a further one of the intermediary coupling positions is less than a capacitance value of a capacitance structure coupled to the second end coupling position.15. The method of clause 14, wherein: the coupling is performed such that the one of the intermediary coupling positions is a first number of coupling positions displaced from the first end coupling position and the further one of the intermediary coupling positions is the first number of coupling positions displaced from the second end coupling position.16. The method of clause 14, wherein:the coupling is performed such that the one of the intermediary coupling positions is a first number of coupling positions displaced from the first end coupling position and the further one of the intermediary coupling positions is a second number of coupling positions displaced from the second end coupling position; and the first number is different than the second number.17. The method of clause 12, wherein: the radiation source further comprises a second set of capacitance structures; the arranging further comprises coupling each capacitance structure of the second set to a respective one of the electrical coupling positions such that a capacitance value of a capacitance structure coupled to one of the intermediary coupling positions is less than a capacitance value of a capacitance structure coupled to the first end coupling position; the transmitting is performed further via the second set of capacitors.18. The method of clause 17, wherein: the coupling each capacitance structure of the second set is performed such that a capacitance value of a capacitance structure of the second set coupled to one of the intermediary coupling positions is less than a capacitance value of a capacitance structure of the second set coupled to the first end coupling position.19. The method of clause 17, wherein: the radiation source further comprises a third set of capacitance structures; the arranging further comprises coupling each capacitance structure of the third set to a respective one of the electrical coupling positions; and the transmitting is performed further via the third set of capacitors.20. The method of clause 12, wherein the capacitance structure coupled to the one of the intermediary coupling positions comprises a vacant capacitor connection structure.

[0079] It is to be understood that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections can set forth one or more, but not necessarily all, aspects of the present disclosure as contemplated by the inventor(s), and thus, are not intended to limit the present disclosure and the appended claims in any way. The breadth and scope of the protected subject matter should not be limited by any of the above-described aspects, but should be defined in accordance with the following claims and their equivalents.

Claims

CLAIMS1. A lithographic apparatus comprising: a projection system configured to project an image of a pattern onto a substrate; and an illumination system configured to illuminate the pattern of a patterning device, the illumination system comprising: an electrode configured to deliver an electrical pulse to a gas to generate radiation, wherein the electrode has an elongate shape, a length- wise strip of the electrode is defined from a first end of the elongate shape to a second end of the elongate shape, and the length- wise strip comprises electrical coupling positions comprising: a first end coupling position proximal to the first end; a second end coupling position proximal to the second end; and a series of intermediary coupling positions between the first end coupling position and the second end coupling position; and a first set of capacitance structures configured to transmit the electrical pulse to the electrode, wherein each capacitance structure of the first set is coupled to a respective one of the electrical coupling positions, and wherein a capacitance value of a capacitance structure coupled to one of the intermediary coupling positions is less than a capacitance value of a capacitance structure coupled to the first end coupling position.

2. The lithographic apparatus of claim 1, wherein the capacitance structure coupled to the one of the intermediary coupling positions comprises a vacant capacitor connection structure.

3. A radiation source configured to generate radiation, comprising: an electrode configured to deliver an electrical pulse to a gas to generate radiation, wherein the electrode has an elongate shape, a length-wise strip of the electrode is defined from a first end of the elongate shape to a second end of the elongate shape, and the length- wise strip comprises electrical coupling positions comprising: a first end coupling position proximal to the first end; a second end coupling position proximal to the second end; and a series of intermediary coupling positions between the first end coupling position and the second end coupling position; and a first set of capacitance structures configured to deliver the electrical pulse to the electrode, wherein each capacitance structure of the first set is coupled to a respective one of the electrical coupling positions, and wherein a capacitance value of a capacitance structure coupled to one of the intermediary coupling positions is less than a capacitance value of a capacitance structure coupled to the first end coupling position.

4. The radiation source of claim 3, wherein the one of the intermediary coupling positions is at least two coupling positions displaced from the first end coupling position.

5. The radiation source of claim 3, wherein: a capacitance value of a further capacitance structure coupled to a further one of the intermediary coupling positions is less than a capacitance value of a capacitance structure coupled to the second end coupling position.

6. The radiation source of claim 5, wherein: the one of the intermediary coupling positions is a first number of coupling positions displaced from the first end coupling position; the further one of the intermediary coupling positions is a second number of coupling positions displaced from the second end coupling position; and the first number is same as the second number.

7. The radiation source of claim 5, wherein: the one of the intermediary coupling positions is a first number of coupling positions displaced from the first end coupling position; the further one of the intermediary coupling positions is a second number of coupling positions displaced from the second end coupling position; and the first number is different than the second number.

8. The radiation source of claim 3, further comprising a second set of capacitance structures configured to deliver the electrical pulse to the electrode, wherein each capacitance structure of the second set is coupled to a respective one of the electrical coupling positions.

9. The radiation source of claim 8, wherein a capacitance value of a capacitance structure of the second set coupled to one of the intermediary coupling positions is less than a capacitance value of a capacitance structure of the second set coupled to the first end coupling position.

10. The radiation source of claim 8, further comprising a third set of capacitance structures configured to deliver the electrical pulse to the electrode, wherein each capacitance structure of the third set is coupled to a respective one of the electrical coupling positions.

11. The radiation source of claim 3, the capacitance structure coupled to the one of the intermediary coupling positions comprises a vacant capacitor connection structure.

12. A method for optimizing performance of an electrode of a radiation source comprising a first set of capacitance structures, the method comprising: arranging capacitance structures of the first set, wherein the electrode has an elongate shape, a length-wise strip of the electrode is defined from a first end of the elongate shape to a second end of the elongate shape, and the length- wise strip comprises electrical coupling positions comprising: a first end coupling position proximal to the first end; a second end coupling position proximal to the second end; and a series of intermediary coupling positions between the first end coupling position and the second end coupling position, wherein the arranging comprises coupling each capacitance structure of the first set to a respective one of the electrical coupling positions such that a capacitance value of a capacitance structure coupled to one of the intermediary coupling positions is less than a capacitance value of a capacitance structure coupled to the first end coupling position; delivering an electrical pulse to a gas via the electrode to generate radiation, wherein the delivering comprises: transmitting the electrical pulse to the electrode via the first set of capacitors.

13. The method of claim 12, wherein the coupling is performed such that the one of the intermediary coupling positions is at least two coupling positions displaced from the first end coupling position.

14. The method of claim 12, wherein: the coupling is performed such that a capacitance value of a further capacitance structure coupled to a further one of the intermediary coupling positions is less than a capacitance value of a capacitance structure coupled to the second end coupling position.

15. The method of claim 14, wherein: the coupling is performed such that the one of the intermediary coupling positions is a first number of coupling positions displaced from the first end coupling position and the further one of the intermediary coupling positions is the first number of coupling positions displaced from the second end coupling position.

16. The method of claim 14, wherein: the coupling is performed such that the one of the intermediary coupling positions is a first number of coupling positions displaced from the first end coupling position and the further one of the intermediary coupling positions is a second number of coupling positions displaced from the second end coupling position; and the first number is different than the second number.

17. The method of claim 12, wherein: the radiation source further comprises a second set of capacitance structures; the arranging further comprises coupling each capacitance structure of the second set to a respective one of the electrical coupling positions such that a capacitance value of a capacitance structure coupled to one of the intermediary coupling positions is less than a capacitance value of a capacitance structure coupled to the first end coupling position; the transmitting is performed further via the second set of capacitors.

18. The method of claim 17, wherein: the coupling each capacitance structure of the second set is performed such that a capacitance value of a capacitance structure of the second set coupled to one of the intermediary coupling positions is less than a capacitance value of a capacitance structure of the second set coupled to the first end coupling position.

19. The method of claim 17, wherein: the radiation source further comprises a third set of capacitance structures; the arranging further comprises coupling each capacitance structure of the third set to a respective one of the electrical coupling positions; and the transmitting is performed further via the third set of capacitors.

20. The method of claim 12, wherein the capacitance structure coupled to the one of the intermediary coupling positions comprises a vacant capacitor connection structure.

Images