Pre-ionization tube for acoustics mitigation in light source

Abstract

A lithography system includes a light source. The light source generates radiation in a chamber, which includes a first electrode, a second electrode, and pre-ionization tube. A first surface of the first electrode and a first surface of the second electrode face inwards towards a discharge region. The pre-ionization tube can be adjacent to a second surface of either the first electrode or the second electrode. Altering the position of the pre-ionization tube can reduce acoustic effects in the chamber during discharge of the light source. The pre-ionization tube can be tilted by moving one end of the pre-ionization tube towards the discharge region.

Description

PRE-IONIZATION TUBE FOR ACOUSTICS MITIGATION IN LIGHT SOURCECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to US Application No. 63 / 616,015, filed December 29, 2023, titled PRE-IONIZATION TUBE TILT FOR ACOUSTICS MITIGATION IN A LIGHT SOURCE, which is incorporated herein by reference in its entirety.FIELD

[0002] The present disclosure relates to acoustic wave mitigation in a light source, for example, a deep ultraviolet light source in a lithographic apparatus and system.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] A lithographic apparatus typically includes an illumination system that conditions radiation generated by a radiation source before the radiation is incident upon a patterning device. A patterned beam of deep ultraviolet (DUV) light can be used to produce extremely small features on a substrate. DUV light generally refers to radiation having wavelengths ranging from 126 nm to 428 nm. A pulsed- discharge light source, such as a gas discharge laser, can be used to generate DUV light.

[0005] In a pulsed-discharge light source, a series of electrical pulses (i.e., discharge events) are supplied to a gas via electrodes. The discharge events can ignite a plasma of gas in a discharge region between the electrodes. The generated plasma can release radiation, thereby operating as a radiation source.

[0006] A high pressure region can form in the discharge region during discharge events. After a discharge event, the high pressure region generates acoustic waves, which propagate inside thechamber. In some aspects, acoustic waves are reflected by components in the chamber (e.g., chamber walls and / or a pre-ionization tube). Reflected waves can travel back into the discharge region, and cause a pressure disturbance that impacts future discharge events. As repetition rates of a light source (i.e., the number of discharge events per second) increase, an acoustic wave has less time to dissipate, thereby increasing pressure disturbances in the light source. In some aspects, the pressure disturbances can deflect generated radiation, thereby increasing the bandwidth of generated radiation.SUMMARY

[0007] Accordingly, a pre-ionization tube in a radiation generation chamber can be positioned to reduce reflections of acoustic waves generated during discharge events.

[0008] In some aspects, a lithography system comprises a light source for producing deep ultraviolet light. In some aspects, the light source comprises a chamber. In some aspects, the chamber comprises a first electrode, a second electrode, and a pre-ionization tube. In some aspects, a first surface of the first electrode and a first surface of the second electrode face inwards towards a discharge region. In some aspects, the pre-ionization tube is adjacent to a second surface of the first electrode or a second surface of the second electrode. In some aspects, the pre-ionization is tilted by moving one end of the preionization tube towards center of the discharge region.

[0009] In some aspects, a light source comprises a chamber. In some aspects, the chamber comprises a first electrode, a second electrode, and a pre-ionization tube. In some aspects, the pre-ionization tube is tilted with respect to a plane intersecting a region between a first surface of the first electrode and a first surface of the second electrode.

[0010] In some aspects, a method of reducing acoustic reflections in a radiation generation chamber of a light source comprises positioning a first electrode and a second electrode. In some aspects, the method further comprises positioning a pre-ionization tube at an angle relative to the first electrode and / or second electrode. In some aspects, a predetermined shape is produced in the radiation generation chamber to reduce acoustic effects during discharge of the light source.

[0011] 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

[0012] 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.

[0013] FIG. 1 shows a lithographic apparatus, according to some aspects.

[0014] FIG. 2 shows a lithographic cell, according to some aspects.

[0015] FIGS. 3-4 show radiation sources, according to some aspects.

[0016] FIGS. 5A-5C show positions of a pre -ionization tube in a radiation generation chamber, according to some aspects.

[0017] FIG. 6 shows a method of reducing acoustic reflections in a radiation generation chamber, according to some aspects.

[0018] 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

[0019] 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 an aspect, 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.

[0020] 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.

[0021] 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).

[0022] Enumerative adjectives (e.g., “first,” “second,” “third,” or the like) can be used to distinguish 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 amanner analogous to “ith target” and “jth target” so as to facilitate the distinguishing of two targets without specifying a particular order, hierarchy, quantity, or immutable numeric correspondence.

[0023] 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.

[0024] 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.

[0025] Example Lithographic Systems

[0026] 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.

[0027] 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.

[0028] 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 vacuumenvironment. 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.

[0029] 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.

[0030] 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.

[0031] 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 additional substrate 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.

[0032] 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.

[0033] 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.

[0034] In some aspects, source SO can be an integral part of the lithographic apparatus 100. For example, source SO can be a mercury lamp integrated with lithographic apparatus 100. A radiation system (or illumination system) can comprise source SO, illuminator IL, and / or beam delivery system BD.

[0035] 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 “n-outer” and “n-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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] Example Lithographic Cell

[0040] 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. Supervisorycontrol 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.

[0041] Example Radiation Source

[0042] There are many applications of pulsed-discharge radiation sources. In some aspects, 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. Pulsed-discharge radiation sources can generate acoustic waves during operation. In some aspects, acoustic waves can deflect generated radiation, thereby reducing stability of the radiation source.

[0043] 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 apparatuses 100 (FIG. 1) can implement radiation source 300. Radiation source 300 can comprise a chamber 302, wavelength selector 304, and an optical coupler 306.

[0044] In some aspects chamber 302 comprises a first window 308, a second window 310, a conduit system 312, and one or more electrodes 314 (also “electrical connection”). Conduit system 312 can comprise a network of valves, conduits, and contaminant filters (not shown).

[0045] In some aspects, gas chamber 302 can confine a gas 316. Gas 316 can comprise fluorine, neon, krypton, argon, and the like. Gas 316 can be rarified via a pressure control system (e.g., vacuum system) that controls a pressure within gas chamber 302. Conduit system 312 is connected to gas chamber 302. Conduit system 312 can allow management of gas 316 in gas chamber 302. For example, conduit system 312 can direct a flow (e.g., circulation) of gas 316 to a filter within conduit system 312 to purify gas 316. A voltage / current can be supplied to gas 316 (e.g., via one or more electrodes 314) in discharge region 318 to generate radiation 320. The voltage / current can be in the form of a pulse, or a series of pulses, with sufficient power to create a plasma of gas 312 in a region between electrodes 314. The plasma can generate radiation with a set of wavelengths that depend on energy states of the plasma. The type of gas 312 (e.g., a mixture of argon and fluorine with additional gasses, or a mixture of krypton and fluorine with additional gasses) can determine the wavelengths that are produced (e.g., DUV wavelengths such as 157 nm, 193 nm, 248 nm). Windows 308 and 310 can allow radiation 320 to exit gas chamber 302.

[0046] A narrow and stable wavelength is desirable for lithographic processes because wavelength instabilities can adversely impact the accuracy of patterns that get printed on a substrate. As a nonlimiting example, beam of radiation 320 can have a DUV wavelength of approximately 193 nm, which can be used for a lithographic process. Therefore, it is desirable to select a narrowband wavelength from the plurality of wavelengths that are generated in the plasma of gas 316.

[0047] In some aspects, wavelength selector 304 can be used to perform wavelength selection. The wavelength selection process can rely on lasing to further amplify the radiation at the desired wavelength in comparison to the unselected wavelengths (e.g., higher signal-to-noise (SNR)). The process can begin by allowing radiation 320 to propagate toward wavelength selector 304 (e.g., can be achieved via implementation of window(s), such as window 310). Wavelength-dependent reflector 322 can reflect a portion of radiation 320 (the portion that has the selected wavelength) along a “gain path” while rejecting other portions of radiation 320 that have undesirable wavelengths (e.g., diverting unselected wavelengths toward a beam dump). Hence, the wavelength of radiation 320 can be narrowed to a narrowband having a peak central wavelength and a small full -width-half-maximum. Wavelength selector 304 can be referred to as a narrowing device, narrowing module, line narrowing module (LNM), or the like.

[0048] In some aspects, the “gain path” can be defined between wavelength-dependent reflector 322 and output coupler 306, with the plasma of gas 316 being the gain medium. Lasing can be achieved as radiation 320 (at the selected wavelength) bounces back and forth between wavelength-dependent reflector 322 and output coupler 306 (output coupler 306 can have a reflective property). Output coupler 306 can comprise a partial reflector that allows a fraction of the, now amplified, radiation 320 (at the selected wavelength) to be output as beam of radiation 324.

[0049] In some aspects, chamber 302 can be referred to as a master oscillator (MO) chamber since radiation 320 is generated at chamber 302 and oscillates back and forth through chamber 302 to achieve intensity gains.

[0050] In some aspects, adjusting the wavelength (e.g., selecting another wavelength) can be achieved by adjusting a position of wavelength-dependent reflector 322 (e.g., rotating a diffractive or refractive element). Diffractive and refractive elements have wavelength -dependent scattering directions. As the position of the diffractive (or refractive) element is changed, a different wavelength can be aligned along the gain path while other wavelengths are directed away from the gain path. The lasing process can then amplify radiation 320 for the adjusted wavelength.

[0051] In some aspects, wavelength selector 304 can also comprise an actuator 326. Wavelengthdependent reflector 322 can be disposed on actuator 326. Controller 328 can be used in to perform the wavelength selection or adjustment by actuating wavelength -dependent reflector 322 via actuator 326. It is desirable for actuator 326 to be capable of high positional accuracy, as well as high frequency adjustments (e.g., greater than 1 kHz, 10 kHz, or the like). Controller 328 can send a control signal 330 (e.g., a command, instructions, voltage / current signal, or the like). Actuator 326 can move according to control signal 330.

[0052] In some aspects, radiation source 300 can comprise a detector 332 to interrogate a portion of radiation 320. Detector 332 can be disposed at wavelength selector 304. Detector 332 can be referred to as a line-center analysis module (LAM) for analyzing one or more performance criteria (e.g., wavelength) of the line narrowing module (wavelength selector 304). In some aspects, detector 332 canbe disposed at other suitable locations for receiving a portion of radiation 320 or a portion of beam of radiation 324. Detector 332 can generate a measurement signal 334 that is indicative of the wavelength of beam of radiation 324. Measurement signal 334 can be received at controller 328, as well as at other processing systems. Measurement signal 334 can be used for reporting a real-team status of the wavelength of beam of radiation 324.

[0053] In some aspects, radiation source 300 can also comprise one or more additional amplification chambers 336. Amplification chambers 336 can provide additional amplification of beam of radiation 324. Amplification chambers 336 can also be referred to as power amplifier (PA) chambers.

[0054] Additional details about wavelength-selection are described in U.S. Patent No. 8,254,420, issued on August 28, 2012, which is incorporated by reference herein in its entirety.

[0055] 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, electrodes 414, gas 416, and discharge region 418.

[0056] In some aspects, radiation source 400 can comprise gas chamber 402, one or more electrodes 414, a gas circulator 438, and a pre -ionization tube 440. Gas circulator 438 can be a 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 320 (FIG. 3), an electrical pulse can be supplied to gas 416 via electrodes 414, thereby igniting a plasma of gas 416 in discharge region 418 (between electrodes 414) of gas chamber 402. The generated plasma can release DUV radiation, thereby operating as a DUV radiation source. In some aspects, pre -ionization tube 440 can provide electrons to gas 416 (e.g., ionize the gas) before an electrical pulse is supplied to the gas. The perspective in FIG. 4 can be considered as being 90 degrees with respect to the perspective 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).

[0057] In various implementations of radiation source 400, after a volume of gas has been converted to plasma, it may not be immediately suitable for another conversion to plasma for producing DUV radiation. For example, in the process of generating radiation, gas 416 and electrodes 414 can interact chemically. For example, materials in electrodes 414 (e.g., copper) can chemically interact with a chemical content of gas 416 (e.g., fluorine) to create a dust-like byproduct (e.g., metal-fluoride by product). The byproduct can become a contaminant that absorbs radiation in subsequent radiation pulses. Therefore, a gas flow 442 (indicated by arrows) can be implemented in order to optimize the production of radiation by circulating the spent portion of gas 416 and contaminants out of the plasmageneration region 418 while supplying unspent gas for the next plasma ignition. Gas circulator 438 cangenerate gas flow 442. 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.

[0058] Example acoustic wave mitigation

[0059] In some aspects, a high pressure forms in discharge region 418 during discharge events. After a discharge event, the high pressure generates acoustic waves, which propagate inside the chamber. In some aspects, acoustic waves are reflected by components in the chamber (e.g., chamber walls and / or the pre-ionization tube). Reflected waves can travel back into the discharge region, and cause a pressure disturbance that impacts future discharge events. As repetition rates of a light source (i.e., the number of discharge events per second) increase, an acoustic wave has less time to dissipate, thereby increasing pressure disturbances in the gas discharge gain medium of the light source during discharge. In some aspects, the pressure disturbances can deflect generated radiation, which increases the bandwidth of radiation generated by the light source.

[0060] In some aspects, altering the shape and / or position of components in a radiation generation chamber can reduce reflections of acoustic waves.

[0061] FIGS. 5A-5C show positions of a pre-ionization tube 540 in a radiation source 500, according to some aspects. In some aspects, the view in FIGS. 5A-5C can represent a more detailed and / or different view of a portion of radiation sources 300 and 400 (FIG. 3 and 4) (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 gas chamber 502, wavelength selector 504, optical coupler 506, electrodes 514, and discharge region 518.

[0062] FIGS. 5A-5C show a side view of electrodes 514, according to some aspects. In some aspects, electrodes 514 (i.e., electrodes 514a and 514b) can comprise first surfaces 542a and 542b (collectively referred to as first surfaces 542) and second surfaces 544a and 544b (collectively referred to as second surfaces 544). In some aspects, first surfaces 542 face inwards towards discharge region 518. In some aspects, second surfaces 544 are “perpendicular” to first surfaces 542. In some aspects, pre-ionization tube 540 is adjacent to second surfaces 544 of an electrode 514. In FIGS. 5A-5C pre-ionization tube 540 is in front of a second surface 544 of an electrode 514.

[0063] In some aspects, pre-ionization tube 540 comprises a first end 546 and a second end 548. In some aspects, both first end 546 and second end 548 are below a first surface 542 of an electrode 514. In some aspects, both first end 546 and second end 548 are above a first surface 542 of an electrode 514. In some aspects, first end 546 is above and second end 548 is below a first surface 542 of an electrode 514. In some aspects, second end 548 is above and first end 546 is below a first surface 542 of an electrode 514.

[0064] In some aspects, a plane 550 can be defined in discharge region 518. Plane 550 can be used as a reference to describe relative tilts of pre-ionization tube 540. In some aspects, plane 550 is an x-yplane as described by the axes in FIGS 3, 4, and 5A-5C. In FIGS. 5A-5C, plane 550 is represented by a dashed line.

[0065] FIG. 5A shows an initial position of pre -ionization tube 540, according to some aspects. In some aspects, pre-ionization tube 540 is “parallel” to discharge region 518 (i.e., a long axis of preionization tube 540 is approximately parallel to plane 550). In some aspects, the position of preionization tube 540 in FIG. 5A is not optimized to reduce reflections of acoustic waves.

[0066] In some aspects, pre-ionization tube 540 can be tilted to reduce reflections of acoustic waves that are generated during discharge events in chamber 502.

[0067] FIG. 5B shows a pre-ionization tube 540 that has a tilt with respect to plane 550 in plasma region 518, according to some aspects. In some aspects, pre-ionization tube 540 is tilted with first end 546 closer to the center of discharge region 518 than second end 548. In some aspects, pre-ionization tube 540 is about 50 cm long and first end 546 is 2-3 mm closer to the center of discharge region 518 than is second end 548. In some aspects, a long axis of pre-ionization tube 540 is tilted at an angle 552 relative to plane 550. In some aspects, angle 552 comprises a value of 0.15 to 0.40 degrees.

[0068] In some aspects, pre-ionization tube 540 is adjacent to second surface 544a of electrode 514a. In some aspects, electrode 514a can be a cathode or an anode. In some aspects, first end 546 can be moved downward towards the center of discharge region 518.

[0069] In some alternate aspects, pre-ionization tube 540 is adjacent to second surface 544b of electrode 514b (not shown). In some aspects 514b can be a cathode or an anode. In some aspects, first end 546 can be moved upward towards the center of discharge region 518.

[0070] In some aspects, first end 546 of pre-ionization tube 540 may be adjacent to wavelength selector 504 (i.e., line narrowing module) and second end 548 may be adjacent to optical coupler 506.

[0071] FIG. 5C shows a pre-ionization tube 540 that has a tilt with respect to plane 550 in discharge region 518. In some aspects, pre-ionization tube 540 is tilted with second end 548 closer to discharge region 518 than first end 546. In some aspects, pre-ionization tube 540 is about 50 cm long and second end 548 is 2-3 mm closer to discharge region 518 than is first end 546. In some aspects, a long axis of pre-ionization tube 540 is tilted at an angle 552 relative to plane 550. In some aspects, angle 552 comprises a value of 0. 15 to 0.40 degrees.

[0072] In some aspects, pre-ionization tube 540 is adjacent to second surface 544a of electrode 514a. In some aspects, electrode 514a may be a cathode or an anode. In some aspects, second end 548 can be moved downward towards the center of discharge region 518.

[0073] In some aspects, pre-ionization tube 540 is alternatively adjacent to second surface 544b of electrode 514b (not shown). In some aspects 514b can be a cathode or an anode. In some aspects, second end 548 can be moved upward towards the center of discharge region 518.

[0074] In some aspects, first end 546 of pre-ionization tube 540 may be adjacent to wavelength selector 504 (i.e., line narrowing module) and second end 548 may be adjacent to optical coupler 506.

[0075] While the examples shown in FIGS. 3, 4, and 5A-5C illustrate the electrodes as having a rectangular, or squared shape, it should be understood by those of ordinary skill in the art that these are merely used for illustrative purposes.

[0076] FIG. 6 shows a method 600, according to some aspects. For example, method 600 can be for positioning a first electrode, a second electrode, and pre-ionization tube in a radiation chamber of a light source, according to some aspects. In some aspects, method 600 comprises step 602 and step 604.

[0077] Step 602 comprises positioning a first electrode and a second electrode in a radiation generation chamber. In some aspects, the pair of electrodes may comprise an anode and a cathode.

[0078] Step 604 comprises positioning a pre-ionization tube in a radiation generation chamber. In some aspects, the pre-ionization tube can be positioned at an angle relative to the first electrode and / or the second electrode. In some aspects, the positioning of the pre-ionization tube produces a shape that reduces acoustic effects during discharge of the light source.

[0079] In some aspects, the pre-ionization tube can be tilted as shown in FIGS. 5B-5C and described above.

[0080] In some aspects, the pre-ionization tube can be placed adjacent to either the first electrode or the second electrode.

[0081] In some aspects, the pre-ionization tube is tilted at an angle of 0.15-0.40 degrees relative to a plane intersecting a region between the first electrode and the second electrode.

[0082] In some aspects, the light source is a pulsed-discharge laser operating at a repetition rate of at least 6,000 Hz.

[0083] The method steps of FIG. 6 can be performed in any conceivable order and it is not required that all steps be performed. Moreover, the method steps of FIG. 6 described above merely reflect an example of steps and are not limiting. That is, further method steps and functions are envisaged based aspects described in reference to FIGS. 1-5.

[0084] 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 X 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 radiation used 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.

[0085] Although some aspects of the present disclosure are described in the context of lithographic apparatuses in the manufacture of ICs, it should be understood that lithographic apparatuses described herein can be used in other applications, for example, in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, LCDs, thin-fdm magnetic heads, etc. Those skilled in the art will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein can be considered as specific examples of the more general terms “substrate” or “target portion”, respectively. A substrate can be processed before or after exposure in, for example, a track unit (a tool that typically applies a layer of resist to a substrate and develops the exposed resist) and / or a metrology unit. Where applicable, aspects disclosed herein can be applied to such and other substrate processing tools. Furthermore, a substrate can be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein can also refer to a substrate that already contains multiple processed layers.

[0086] Furthermore, although some aspects of the present disclosure are described in the context of optical lithography, it should be understood that aspects of the present disclosure are not limited to optical lithography. For example, in imprint lithography, a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device can be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured.

[0087] 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.

[0088] 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.

[0089] 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. Thebreadth 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 lithography system comprising; a light source, comprising: a chamber comprising: a first electrode comprising a first surface and a second surface; a second electrode comprising a first surface and a second surface; a discharge region between the first surface of the first electrode and the first surface of the second electrode; and a pre-ionization tube, wherein the pre -ionization tube is adjacent to the second surface of the first electrode or to the second surface of the second electrode and tilted such that a first end of the preionization tube is closer to the discharge region than is a second end of the pre-ionization tube, wherein tilting the pre-ionization tube forms a shape configured to reduce acoustic effects during discharge of the light source.

2. The lithography system of claim 1, wherein the pre-ionization tube is tilted at an angle of 0.15 to 0.40 degrees.

3. The lithography system of claim 1, wherein the pre-ionization tube is tilted by moving the first end of the pre-ionization tube towards the discharge region.

4. The lithography system of claim 3, wherein the first end of the pre-ionization tube is adjacent to a line narrowing module.

5. The lithography system of claim 1, wherein the pre-ionization tube is tilted by moving the second end of the pre-ionization tube towards the discharge region.

6. The lithography system of claim 5, wherein the second end of the pre-ionization tube is adjacent to an optical coupler.

7. The lithography system of claim 1, wherein a tilt of the pre-ionization tube is configured to reduce reflections of acoustic waves in the discharge region.

8. The lithography system of claim 1, wherein the light source is configured to generate deep ultraviolet light.

9. A light source, comprising:a chamber comprising: a first electrode comprising a first surface; a second electrode comprising a first surface; and a pre-ionization tube, tilted with respect to a plane that intersects a region between the first surface of the first electrode and the first surface of the second electrode.

10. The light source of claim 9, wherein the pre-ionization tube is tilted at an angle of 0. 15 to 0.40 degrees.

11. The light source of claim 9, wherein the pre-ionization tube is tilted by moving the first end of the pre-ionization tube towards the region between the first surface of the first electrode and the first surface of the second electrode.

12. The light source of claim 9, wherein the pre-ionization tube is tilted by moving the second end of the pre-ionization tube towards the region between the first surface of the first electrode and the first surface of the second electrode.

13. The light source of claim 9, wherein the tilt of the pre-ionization tube reduces reflections of acoustic waves in the region between the first electrode and the second electrode.

14. The light source of claim 9, wherein the pre-ionization tube is adjacent to a second surface of the first electrode.

15. The light source of claim 9, wherein the pre-ionization tube is adjacent to a second surface of the second electrode.

16. A method comprising: positioning a first electrode and a second electrode in a radiation generation chamber of a light source; and positioning a pre-ionization tube at an angle relative to the first and / or the second electrode.

17. The method of claim 16, wherein the positioning of the pre-ionization tube comprises moving a first end of the pre-ionization tube.

18. The method of claim 16, wherein the positioning of the pre-ionization tube comprises moving a second end of the pre-ionization tube.

19. The method of claim 16, wherein the pre-ionization tube is tilted at an angle of 0.15-0.40 degrees relative to a plane intersecting a region between the first electrode and the second electrode.

20. The method of claim 16, wherein the light source is a pulsed-discharge laser operating at a repetition rate of at least 6,000 Hz.

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