Controlling contamination by target material in an EUV radiation source

Abstract

Disclosed are systems and methods for producing extreme ultraviolet (EUV) radiation from a target material in a source vessel in which gas flows carry stray target material vapor and in which measures are adopted to reduce the amount of stray target material that is able to escape the source vessel and reach downstream modules and components.

Description

CONTROLLING CONTAMINATION BY TARGETMATERIAL IN AN EUV RADIATION SOURCECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US Application No. 63 / 739,887, filed on December 30, 2024, titled CONTROLLING CONTAMINATION BY TARGET MATERIAL IN AN EUV RADIATION SOURCE, and US Application No. 63 / 910,145, filed on November 3, 2025, titled CONTROLLING CONTAMINATION BY TARGET MATERIAL IN AN EUV RADIATION SOURCE, which are incorporated herein by reference in their entireties.FIELD

[0002] The present disclosure relates to sources for generating extreme ultraviolet (“EUV”) radiation through conversion of a target material. In particular, this disclosure relates to apparatuses for and methods of controlling the dispersal of target material in exposure systems such as photolithographic systems, inspection systems or metrology systems including such sources.BACKGROUND

[0003] Light generated by means of a radiation source can be used by exposure apparatuses for semiconductor manufacturing processes. Examples of such exposure apparatuses include a photolithographic apparatus, a metrology apparatus, and an inspection apparatus, the last more specifically a wafer inspection apparatus, a mask inspection apparatus and even more specifically an actinic mask inspection apparatus.

[0004] A photolithographic apparatus is a machine designed and constructed to create a desired pattern on a substrate. A photolithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A photolithographic apparatus may, for example, project a pattern from a patterning device (e.g., a mask) onto a layer of radiation -sensitive material (e.g., a photoresist or resist) provided on a substrate.

[0005] During a semiconductor manufacturing process, specifically during various stages such as photolithography, etching, deposition, and chemical mechanical polishing, an inspection apparatus or a metrology apparatus can leverage the radiation to scan a surface of the wafer, pattern defects, or any anomalies that may impact yield. For reticle inspection, the inspection or the metrology apparatus examines the reticles for defects such as missing features, extra features, or contamination, which could be transferred to the wafer during the photolithography process. The metrology can even provide overlay measurement, ensuring that different layers of the devices are aligned with each other during the manufacturing process. Moreover, the inspection or the metrology apparatus offers in-line process control by providing real-time feedback, allowing users to adjust process parameters on the fly.

[0006] The exposure apparatus uses electromagnetic radiation to project the pattern onto the substrate. The wavelength of this electromagnetic radiation determines the minimum size of features which can be formed on the substrate. A photolithographic apparatus which uses EUV radiation, having a wavelength within the range 4-20 nm, for example 6.7 nm or 13.5 nm, may be used to form smaller features on a substrate than a photolithographic apparatus which uses, for example, radiation with a wavelength of 193 nm.

[0007] Methods for generating EUV radiation include converting the state of a gaseous, liquid, or solid target material to a plasma state. The target material includes at least one element, e.g., xenon, lithium, or tin, with one or more emission lines in the EUV portion of the electromagnetic spectrum. In one such method, often termed laser produced plasma (“LPP”), the required plasma can be produced by using a radiation source such as a laser beam to irradiate and convert a target material having the required line-emitting element.

[0008] One LPP technique involves generating a stream of target material droplets and irradiating at least some of the droplets with one or more pulses of laser radiation. In some embodiments, one or more drive lasers generate the pulses of laser radiation. The pulses may include infrared (IR) radiation, for example, with a wavelength of approximately from about 1 micrometer (pm) to about 10 pm. The drive laser includes a solid-state laser or a gas laser, directing the laser beam to be incident on the target material and form plasma in a plasma formation region. A solid-state laser, as used herein, refers to a laser source which uses a lasing medium that is a solid, for example, a neodymium -doped yttrium aluminum garnet (Nd:YAG) laser or an yttrium-doped yttrium aluminum garnet (Yb:YAG) laser. A gas laser, as used herein, refers to a laser source in which an electric current is discharged through a gas to produce coherent light, for example, a carbon dioxide (CO2) laser, carbon monoxide (CO) laser, helium-neon (HeNe) laser, or a nitrogen (N2) laser. For this process, the plasma is typically produced in a sealed vessel, e.g., a chamber defined by a source vessel, and various properties of the resultant EUV radiation are monitored using corresponding types of metrology equipment.

[0009] The processes used to generate EUV radiation from a plasma also typically generate undesirable byproducts in the plasma chamber which can include out-of-band radiation (e.g., IR radiation), high energy ions, and debris, e.g., atoms and / or clumps / microdroplets of target material. These processes can also produce target material vapor, which can cause pools or clusters of target material to accumulate at various locations within the chamber. Herein, the target material debris byproduct is sometimes referred to as stray target material, and the stray target material and the target material vapor are sometimes referred to together as waste target material.

[0010] Stray target material can obstruct propagation of EUV radiation within the chamber. The EUV radiation is emitted from the plasma in all directions. In one common arrangement, a nearnormal-incidence mirror (often termed a “collector mirror” or simply a “collector”) is positioned to collect, direct, and, in some arrangements, focus at least a portion of the radiation to an intermediatefocal location. At the wavelengths typically involved, the collector is advantageously implemented as a multi-layer mirror (“MLM”). As its name implies, this MLM is generally made up of alternating layers of material (the MLM stack) over a foundation or substrate. System optics may also be configured as a coated optical element even if it is not implemented as an MLM.

[0011] The collected radiation may then be relayed from the intermediate location to a downstream set of optics, a reticle, detectors and ultimately to an exposure apparatus, such as a scanner. The ray paths of the EUV radiation in the source vessel or the chamber thus define a cone with the collector optics as its base and the intermediate focus of the collector optics as its vertex.

[0012] Despite countermeasures stray target material dispersal remains a technical challenge. The process of transforming the target material into vapor and particles deposits residual target material on every surface for which there is an unobstructed path between the irradiation site and the surface as well as in the exhaust path of gases that entrain stray target material. Once in the gas flow the stray target material can disperse to various locations where its presence is destructive, for example, towards and past the intermediate focus and even to the scanner. This contributes to target material accumulation in the scanner, including on customer pellicles and wafers.

[0013] For example, stray target material in the form of target material particles or vapor escaping from the EUV source through the intermediate focus are known to cause the subsequent optical lifetime degradation and reticle or wafer defectivity. To combat this the source-to-exposure interface may use a dynamic gas lock (“DGL”) near the intermediate focus to achieve separation between the source and scanner. The “exposure” feature refers to an apparatus where the radiation is delivered to the apparatus’ optical or detector subsystem. While the DGL can in general be effective in suppressing the passage of vapor (molecular) target material through the intermediate focus, in some instances, it has only a limited capability to stop larger, ballistic target material particles. Yet it is expected that suppressing target material particle transit through the source-to-exposure interface will be crucial in meeting future source and scanner performance specifications.

[0014] In other words, there are circumstances in which the current DGL design may provide insufficient blockage of fast-moving target material particles as they travel through the exposure-side portion of the source vessel. A velocity contour of the exposure-side portion of the source vessel shows that a strong center downward jet forms below the DGL injection area. This downward jet is effective in blocking a central portion of the exposure-side vessel cross section which is not sufficient for the total flow cross section. If a particle achieves an escape trajectory close to the vessel wall, the current exposure-side vessel flow design offers limited drag forces to impede it.

[0015] In some instances, a symmetrical DGL injection also creates a stagnation (high pressure) zone near the intermediate focus. This stagnation zone absorbs a disproportionate amount of the EUV radiation passing through the intermediate focus. It would be beneficial to reduce the pressure of the static pressure peak to in turn reduce both the leakage flow through the source-to-exposureinterface (e.g., the source-to-scanner leakage flow rate) and improve EUV transmission near the intermediate focus.

[0016] It is in this context that the need for the presently disclosed subject matter arises.SUMMARY

[0017] The following presents a succinct summary of one or more embodiments in order to provide a basic understanding of the embodiments. This summary is not an extensive overview of all contemplated embodiments and is not intended to identify as key or critical any elements of the embodiments nor delineate the scope of any or all embodiments. Its sole purpose is to present some concepts of one or more embodiments in a streamlined form as a prelude to the more detailed description presented later.

[0018] According to an aspect of an embodiment there is disclosed a lithography system comprising a source of extreme ultraviolet (EUV) radiation, the source including a source vessel and a vessel aperture through which the EUV radiation exits the source vessel along an optical axis, a scanner system arranged to receive the EUV radiation from the source vessel through the vessel aperture, structure defining a plenum positioned between the source and the scanner system, and a source -to-exposure interface assembly positioned in the plenum, the source -to-exposure assembly being arranged and configured to impart a vorticial flow to gas flowing through the plenum to cause particulate matter entrained in the gas to be urged away from the optical axis.

[0019] The plenum may be configured as a frustoconical structure having an axis of symmetry coincident with the optical axis. The source -to-exposure interface assembly may comprise a plurality of blades arranged in the plenum. The blades may be stationary. The plurality of stationary blades may be arranged radially around the optical axis. The plurality of stationary blades are arranged rotationally symmetrically around the optical axis.

[0020] The lithography system may further comprise a disk-shaped member arranged between the plenum and an intermediate focus of the source and at an angle from about 45° to about 90° with respect to the optical axis, the disk-shaped member being provided with a central aperture through which the optical axis passes and a surrounding plurality of secondary apertures, the disk-shaped member being further arranged such that gas flow past the disk-shaped member is through the central aperture and the plurality of secondary apertures. The plurality of secondary apertures may be arranged as an irregular array of secondary apertures.

[0021] According to another aspect of an embodiment there is disclosed a lithography system comprising a source of extreme ultraviolet (EUV) radiation, the source including a source vessel and a vessel aperture through which the EUV radiation exits the source along an optical axis, a scanner system arranged to receive the EUV radiation from the source vessel through the vessel aperture, structure defining a frustoconical plenum having an axis of symmetry coincident with the optical axis positionedbetween the source and the scanner system, a source-to-exposure interface assembly positioned in the plenum, the source-to-exposure comprising a plurality of stationary blades arranged in the plenum radially and rotationally symmetrically around the optical axis; the plurality of a stationary blades being arranged and configured to impart a vorticial flow to gas flowing through the plenum to cause particulate matter entrained in the gas to be urged away from the optical axis, and a disk-shaped member arranged between the plenum and an intermediate focus of the source and at an angle between 85° and 95° with respect to the optical axis, the disk-shaped member being provided with a central aperture through which the optical axis passes and a surrounding array of secondary apertures, the disk-shaped member being further arranged such that gas flow past the disk-shaped member is through the central aperture and the array of secondary apertures.

[0022] According to another aspect of an embodiment there is disclosed a method, for use in a lithography system, of limiting passage of stray target material from a source of extreme ultraviolet (EUV) radiation, the source including a source vessel and a vessel aperture through which the EUV radiation exits the source vessel along an optical axis to a scanner system arranged to receive the EUV radiation from the source vessel through the vessel aperture, the method comprising flowing gas passing from the scanner system to the source through a source-to-exposure interface assembly arranged and configured to impart a vorticial flow to gas flowing through the source-to-exposure interface assembly to cause particulate matter entrained in the gas to be urged away from the optical axis.

[0023] The source-to-exposure interface assembly may comprise a plurality of blades arranged in the plenum. The blades may be stationary. The plurality of stationary blades may be arranged radially around the optical axis. The plurality of a stationary blades may be arranged rotationally symmetrically around the optical axis. The method may further comprise flowing the gas through a disk-shaped member arranged between the plenum and an intermediate focus of the source, the disk-shaped member being provided with a central aperture through which the optical axis passes and a surrounding array of secondary apertures.

[0024] Further features and advantages of the disclosed subject matter, as well as the structure and operation of various embodiments of the disclosed subject matter, are described in detail below with reference to the accompanying drawings. It is noted that the disclosed subject matter is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein.BRIEF DESCRIPTION OF THE DRAWING

[0025] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the disclosed subject matter and, together with the description, further serve toexplain the principles of the disclosed subject matter and to enable a person skilled in the relevant art(s) to make and use the disclosed subject matter. The drawings are not to scale unless otherwise indicated.

[0026] FIG. 1 is a schematic diagram of a photolithographic system.

[0027] FIG. 2A is a schematic diagram of the source-to-exposure interface of an EUV source.

[0028] FIG. 2B is a schematic diagram of dynamic gas lock for the source-to-exposure interface of an EUV source shown in FIG. 2A.

[0029] FIG. 3 is a side view diagram of a portion of a source-to-exposure interface for an EUV source according to an aspect of an embodiment.

[0030] FIG. 4 is a diagram of gas flows at a source-to-exposure interface for an EUV source according to an aspect of an embodiment.

[0031] Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. It is noted that the invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art based on the teachings contained herein.DETAILED DESCRIPTION

[0032] Various embodiments are now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to promote a thorough understanding of one or more embodiments. It may be evident in some or all instances, however, that any embodiment described below can be practiced without adopting the specific design details described below. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate description of one or more embodiments.

[0033] In the description that follows and in the claims the terms “up,” “down,” “top,” “bottom,” “vertical,” “horizontal,” and like terms may be employed. These terms are intended to show relative orientation only and not any orientation with respect to gravity unless otherwise indicated or clear from context.

[0034] FIG. 1 shows a lithographic system comprising a radiation source SO and a scanner system SC together making up a lithographic apparatus. The radiation source SO is configured to generate an EUV radiation beam B and to supply the EUV radiation beam B to the scanner system SC. The scanner system SC comprises a scanner system IL, a support structure MT configured to support a patterning device MA (e.g., a mask), a projection system PS and a substrate table WT configured to support a substrate W.

[0035] The scanner system SC is configured to condition the EUV radiation beam B beforethe EUV radiation beam B is incident upon the patterning device MA. The illumination system IL may include a faceted field mirror device 100 and a faceted pupil mirror device 110. The faceted field mirror device 100 and faceted pupil mirror device 110 together provide the EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. The illumination system IL may include other mirrors or devices in addition to, or instead of, the faceted field mirror device 100 and faceted pupil mirror device 110.

[0036] After being thus conditioned, the EUV radiation beam B interacts with the patterning device MA. As a result of this interaction, a patterned EUV radiation beam B’ is generated. The projection system PS is configured to project the patterned EUV radiation beam B’ onto the substrate W. Forthat purpose, the projection system PS may comprise mirrors 130, 140 which are configured to project the patterned EUV radiation beam B’ onto the substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B’, thus forming an image with features that are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 may be applied. Although the projection system PS is illustrated as having only two mirrors 130, 140 in FIG. 1, the projection system PS may include a different number of mirrors (e.g., six or eight mirrors).

[0037] The substrate W may include previously formed patterns. Where this is the case, the scanner system SC aligns the image, formed by the patterned EUV radiation beam B’, with a pattern previously formed on the substrate W.

[0038] A relative vacuum, i.e. a small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure, may be provided in the radiation source SO, in the illumination system IL, and / or in the projection system PS.

[0039] The radiation source SO shown in FIG. 1 is, for example, of the type referred to above as a laser produced plasma (LPP) source. A laser system 10, which may, for example, include a CO2 laser, is arranged to deposit energy via a laser beam 20 into a target material, such as tin (Sn) which is provided from, e.g., a droplet generator 30. The target material may, for example, be in liquid form, and may, for example, be a metal such as tin or an alloy. The droplet generator 30 may comprise a nozzle configured to direct target material, e.g. in the form of droplets, along a trajectory towards an irradiation site 40. The laser beam 20 is incident upon the target material at the irradiation site 40. The deposition of laser energy into the target material creates a target material plasma 70 at the irradiation site 40. Radiation, including EUV radiation, is emitted from the plasma 70 during de-excitation and recombination of electrons with ions of the plasma.

[0040] The EUV radiation from the plasma is collected and focused by a collector 50. Collector 50 comprises, for example, a near-normal incidence radiation collector (sometimes referred to more generally as a normal -incidence radiation collector). The collector 50 may have a multilayer mirror structure which is arranged to reflect EUV radiation (e.g., EUV radiation having a desiredwavelength such as 13.5 nm). The collector 50 may have an ellipsoidal configuration, having two focal points. The first one of the focal points may be at the irradiation site 40, and the second one of the focal points may be at an intermediate focus 60, as discussed below.

[0041] The laser system 10 may be spatially separated from the radiation source SO. Where this is the case, the laser beam 20 may be passed from the laser system 10 to the radiation source SO with the aid of a beam delivery system (not shown) comprising, for example, suitable directing mirrors and / or a beam expander, and / or other optics. The laser system 10, the radiation source SO and the beam delivery system may together be considered to be a radiation system.

[0042] Radiation that is reflected by the collector 50 forms the EUV radiation beam B. The EUV radiation beam B is focused at intermediate focus 60 to form an image at the intermediate focus 60 of the plasma present at the irradiation site 40. The image at the intermediate focus 60 acts as a virtual radiation source for the illumination system IL. The radiation source SO is arranged such that the intermediate focus 60 is located at or near a vessel aperture 80 in an enclosing structure 90 of the radiation source SO. The area including the vessel aperture 80 and the intermediate focus 60 may be regarded as source-to-exposure interface. As used herein, the term “exposure” refers to any process, apparatus, or system in which the EUV radiation beam B is directed toward a target for lithography, metrology or inspection purposes.

[0043] Although FIG. 1 depicts the radiation source SO as a laser produced plasma (LPP) source, any suitable source such as a discharge produced plasma (DPP) source or a free electron laser (FEL) may be used to generate EUV radiation.

[0044] FIG. 2A is a schematic diagram of a portion of the source SO shown In FIG. 1. In FIG.2A a light cone or EUV volume 200 is defined at its base by the collector 50 and at its apex by the intermediate focus 60. The EUV volume 200 is also referred as a radiation source vessel. A beam path 210 which refers to an optical axis of the source SO extends from the irradiation site 40 up through the intermediate focus 60 and into the exposure apparatus used during the semiconductor manufacturing process, such as a photolithographic scanner, a metrology tool, or an inspection tool. At least one liner 95 may be provided to enclose the EUV volume 200. The intermediate focus 60 coincides with the vessel aperture 80 through which the beam of EUV radiation from the source SO passes to an exposure apparatus such as the scanner.

[0045] FIG. 2B shows an arrangement for a DGL 150 for the source SO. The DGL 150 restricts target material debris from exiting the radiation source SO and entering the exposure apparatus, such as lithographic apparatus LA, an inspection apparatus, or a metrology apparatus. It creates gas flows that are injected at a differential pumping interface between the radiation source SO and exposure apparatus in the vicinity of the vessel aperture 80 in the enclosure 90 of the radiation source SO. The DGL 150 comprises one or more nozzles which are arranged to provide both: (i) a flow of gas 155 into an interior of the radiation source SO; and (ii) a flow of gas 157 into an interior of the exposureapparatus. These gas flows 155, 157 may comprise jets having gas velocities that are supersonic or near supersonic.

[0046] The flow of gas 155 into the radiation source SO (which comprises a high speed jet) reduces the number of target material particles that pass through the vessel aperture 80 from the radiation source SO to the exposure apparatus, such as the scanner system SC. Target material contamination in the scanner system SC can lead to several significant problems including: (a) a loss of transmission of optics in the exposure apparatus; and (b) defects on the patterning device MA (reticle) or wafer W that can lead to wafer die yield loss.

[0047] In some embodiments, in the DGL 150 the two dynamic gas lock flows 155,157 are symmetric and generally aligned with the optical axis 210 of the system. As a result, the flow of gas 157 into the exposure apparatus points directly at an entrance aperture of the exposure apparatus.

[0048] In the schematic illustration shown in FIG. 2B, the DGL 150 comprises multiple rows of apertures (e.g., multiple apertures from each row are visible in the cross section of FIG. 2B) at positions displaced along the optical axis 210. In some embodiments, a first row of apertures is in fluid communication with a first manifold or inlet 160 and generally supplies the flow of gas 155 into the radiation source SO. A second row of apertures is in fluid communication with a second manifold or inlet 170 and generally supplies the flow of gas 157 into the exposure apparatus. It is to be understood that each of the first flow of gas 155 and the second flow of gas 157 is not limited to a single row of apertures. In some embodiments, each flow of gas is provided through multiple rows of apertures, for example, two to four rows.

[0049] However, there is a pressure difference between the source vessel 200 and the exposure apparatus. As a result of this pressure difference, any particles that make it through the vessel aperture 80 from the radiation source SO to the exposure apparatus experience a substantial acceleration as they enter the gas flow 157 into the exposure apparatus. Furthermore, once accelerated, these particles enter into a relatively low-pressure environment (and thus experience relatively low drag force) and travel along a path similar to the path of the radiation beam B. This stray target material may propagate to locations in the system in which it can damage or degrade the performance of various components and modules. In particular, stray target material may escape the source vessel 200 through the source-to-exposure interface and infiltrate the scanner. It is desirable to prevent this from occurring.

[0050] According to an aspect of an embodiment, contaminants such as target material debris and / or vapor are impeded from escaping the source vessel at the source -to-exposure interface by establishing a highly swirling flow field at or near the source-to-exposure interface that centrifuges the contaminants away from the optical axis. This enhances the contaminant transit suppression effectiveness.

[0051] According to another aspect of an embodiment the highly swirling flow field enables contaminant transit suppression at reduced static pressure at or near the intermediate focus. This reducedstatic pressure increases EUV transmissivity near the intermediate focus.

[0052] According to another aspect of an embodiment the reduced static pressure near the intermediate focus reduces the rate of gas leakage from the source to the exposure apparatus through the source-to-exposure interface, thus creating the potential for reduced demand for pumping infrastructure on the exposure side.

[0053] In some embodiments structure defining a plenum is provided around the EUV beam path near the intermediate focus, and a disk with small orifices referred to herein as a shower plate is interposed in the contaminant path to introduce the contaminant suppression flow. Because the diameter of the shower plate is larger than that of the apertures, this enables a less aggressive flow area expansion towards a collector region of the source vessel, thus delaying flow detachment from the source vessel walls.

[0054] In some embodiments a swirling flow mechanism, such as a number of guide vanes or a number of stationary blades are positioned in the plenum outside of the EUV beam path. As an example, six blades are positioned in the plenum in a rotationally symmetric arrangement but one of ordinary skill in the art will appreciate that fewer or more blades may be used. The blades are shaped and positioned to induce flow rotation around the EUV beam path, also referred to as the optical axis or the z-axis. This not only forces the flow to stay attached to the vessel walls, but also imparts a tangential velocity component on target material contaminants approaching the influence of this swirling flow field, centrifuging the contaminants away from the optical axis.

[0055] In some embodiments the DGL injection nozzles are eliminated or reduced, thus reducing the static pressure near the intermediate focus, and improving EUV transmission in this area.

[0056] In some embodiments, space between the tip of the blades are closed (shrouded blades) to enable a separation of swirling flow and DGL flow.

[0057] In some embodiments the total exposure-side vessel flow rate ranges from about 100 slm to about 200 slm above an exhaust, and no additional volume is required to implement the plenum and a swirling flow mechanism.

[0058] A system such as that just described is able to realize several improvements. One improvement is in suppressing contaminant transit through the intermediate focus. This improvement is realized because the downward (back toward the primary focus) axial (along the beam path which defines the optical axis) velocity is increased to increase drag force along the “-z” direction, that is, opposite the direction of propagation of the beam path. This effectively decelerates contaminants approaching the intermediate focus.

[0059] Second, the vorticial flow rotation created by the swirling flow mechanism, such as guide vanes or stationary blades centrifuges the contaminants approaching the intermediate focus thus effectively urging them laterally from the optical axis.

[0060] Third, as mentioned, the transmission of EUV radiation through the intermediate focusis improved and source-to-exposure leakage flow rate through the intermediate focus is reduced. The design avoids the formation of a static pressure spike near the intermediate focus. As a consequence the pressure along the EUV beam path can be maintained below a certain threshold, e.g., below 165 Pa. Given that the intensity of the EUV radiation is highest near the intermediate focus the elimination of the pressure spike yields a substantial increase in EUV transmission and reduction in source-to-exposure leakage flow.

[0061] FIG. 3 is a diagram of the source-to-exposure interface which includes a source-to-exposure assembly 300 according to an aspect of an embodiment. As can be seen, the EUV volume 200 has a multi-stage configuration. In a two-stage configuration, a first stage refers to a portion between a collector mirror (not shown) and a “throat” which has a reduced cross-sectional area (and diameter), and a second stage refers to a portion between the throat and the intermediate focus 60. The first stage of the EUV volume 200 has a generally conical or frustoconical shape extending along the optical axis 210 and includes a plasma generation region wherein the plasma is generated from the target material (e.g., liquid tin droplets) irradiated by a drive laser beam, and the second stage of the EUV volume 200 is widened into create a plenum 310. The second stage (i.e., the plenum 310) defines a volume having a cross-sectional area greater than or equal to that to the throat and sufficient to establish the desired pressure differential and optical path clearance. In some embodiments, the multi-stage configuration preserves the plasma generation region required for efficient radiation collection and transmission while introducing optimized flow and optical control characteristics in comparison with a single-stage configuration. For example, a controlled pressure differential between the first stage and the second stage helps to reduce contaminants travelling through the intermediate focus 60, and a outwardly expansion of the second stage helps to reduce IR radiation directly propagating toward the exposure apparatus. In some embodiments the plenum 310 is configured as a frustoconical structure or a columnar structure having an axis of symmetry coincident with the optical axis 210. In some embodiments, an inner wall of the second stage is inclined outward at an angle of from about 90° to 120° relative to the optical axis 210. This angular configuration is selected to redirected contaminants and IR reflections away from the intermediate focus 60 while maintaining full EUV volume 200 cleanliness. In some embodiments, the EUV volume 200 has a frustoconical with a cylindrical / prismatic extension configuration. In some embodiments, the EUV volume 200 has an hourglass or an inverted conical configuration, in which the first stage is fluidly coupled to the second stage via the throat. In at least one embodiment, the second stage is operated at a higher pressure than that of the first stage. The resulting pressure differential is sufficient to suppress the advection of contaminant-laden flow. Optionally, the second stage inner wall is coated with a surface layer having high IR absorption and moderate thermal conductivity. Suitable materials include textured molybdenum, silicon carbide, or tungsten carbide with an emissivity of 0.6 to 0.9 in the IR range. Disposed within the plenum 310 is a swirling flow mechanism, such as a plurality of guide vanes or a plurality of blades 320. In someembodiments these blades 320 are stationary. The disclosed embodiment has six stationary blades but one of ordinary skill in the art will appreciate that fewer or more blades could be used. In some embodiments the blades 320 are arranged rotationally symmetrically around the optical axis.

[0062] The blades 320 are curved and angled to cause gas flowing past the blades 320 to swirl. In other words, the blades 320 impart a vorticial force to the gas causing the gas to flow in a vorticial pattern. The vorticial force imparts a centrifugal force to particulate matter entrained in the gas. This causes the entrained particulate matter to accelerate radially outward from the optical axis 210. The transverse component of the velocity of the particulate matter makes it less likely that that particulate matter will pass through the source-to-exposure interface.

[0063] FIG. 3 also shows a shower plate 330 which is a disk positioned above, that is on the scanner side of, the blades 320. The shower plate 330 has a central aperture through which the optical axis passes and a surrounding multitude of secondary apertures which also serve to block particulate matter which may be entrained in the gas flowing through the source-to-exposure interface. The shower plate 330 is arranged such that gas flow past the disk-shaped member is through the central aperture and the secondary apertures. In the embodiment shown, the shower plate 330 is a circular disk-shaped member but other configurations could be used. The shower plate 330 is oriented askew or transversely to the optical axis 210, that is, making an angle from about 45° to about 90° with respect to the optical axis 210. If the angle is smaller than 45°, in some instances, a swirling flow is insufficient to block the target material from traveling toward the intermediate focus. If the angle is greater than 90°, in some instances, a flow is generated to guide the target material toward the exposure apparatus. In the arrangement shown the apertures are arranged in the shower plate 330 in an irregular array but one of ordinary skill in art will realize that the apertures could also be arranged in a regular, periodic array.

[0064] Also visible in FIG. 3 are the intermediate focus 60 and a hydrogen manifold arranged to introduce gas for a dynamic gas lock if one is being used.

[0065] FIG. 4 is a partially cutaway perspective view of the source-to-exposure assembly 300 depicted in FIG. 3. Thus, the embodiment shown in FIG. 4 includes the plenum 310, the plurality of blades 320, and the shower plate 330.

[0066] As indicated above the plurality of blades 320 impart a swirling flow to the gas flowing through the source-to-exposure interface. This is represented qualitatively in FIG. 4, which includes a rendering of dashed arrows representing the gas streamlines as twisted by the blades 320. The blades 320 impart a component to the velocity of the gas that is horizontal in the figure causing the gas to circulate around the optical axis. Drag forces cause stray target material in the form of entrained particulate matter to be carried along with the gas so that the stray target material is urged sideways and deflected from travelling towards the intermediate focus 60.

[0067] In some embodiments, a source-to-exposure assembly as described above could be used in conjunction with a DGL as an additional measure to prevent stray target material from escapingthe source through the intermediate focus. As mentioned above, however, a source-to-exposure assembly as described above could be used instead of a DGL thus eliminating the need for DGL apertures or nozzles in the vicinity of the intermediate focus. Aspects and implementations of the present disclosure can be further described using the following numbered clauses:1. A lithography system comprising:a source of extreme ultraviolet (EUV) radiation, the source including a source vessel and a vessel aperture through which the EUV radiation exits the source vessel along an optical axis;a scanner system arranged to receive the EUV radiation from the source vessel through the vessel aperture;structure defining a plenum positioned between the source and the scanner system; anda source-to-exposure interface assembly positioned in the plenum, the source-to-exposure assembly being arranged and configured to impart a vorticial flow to gas flowing through the plenum to cause particulate matter entrained in the gas to be urged away from the optical axis.2. The lithography system of clause 1, wherein the plenum is configured as a frustoconical structure having an axis of symmetry coincident with the optical axis.3. The lithography system of clause 1, wherein the source-to-exposure interface assembly comprises a plurality of blades arranged in the plenum.4. The lithography system of clause 3, wherein the blades are stationary.5. The lithography system of clause 3, wherein the plurality of stationary blades are arranged radially around the optical axis.6. The lithography system of clause 3, wherein the plurality of stationary blades are arranged rotationally symmetrically around the optical axis.7. The lithography system of clause 3, further comprising a disk-shaped member arranged between the plenum and an intermediate focus of the source and at an angle from about 45° to about 90° with respect to the optical axis, the disk-shaped member being provided with a central aperture through which the optical axis passes and a surrounding plurality of secondary apertures, the disk-shaped member being further arranged such that gas flow past the disk-shaped member is through the central aperture and the plurality of secondary apertures.8. The lithography system of clause 7, wherein the plurality of secondary apertures is arranged as an irregular array of secondary apertures.9. A lithography system comprising:a source of extreme ultraviolet (EUV) radiation, the source including a source vessel and a vessel aperture through which the EUV radiation exits the source along an optical axis;a scanner system arranged to receive the EUV radiation from the source vessel through the vessel aperture;structure defining a frustoconical plenum having an axis of symmetry coincident with the optical axis positioned between the source and the scanner system;a source-to-exposure interface assembly positioned in the plenum, the source -to-exposure comprising a plurality of stationary blades arranged in the plenum radially and rotationally symmetrically around the optical axis; the plurality of a stationary blades being arranged and configured to impart a vorticial flow to gas flowing through the plenum to cause particulate matter entrained in the gas to be urged away from the optical axis; anda disk-shaped member arranged between the plenum and an intermediate focus of the source and at an angle between 85° and 95° with respect to the optical axis, the disk-shaped member being provided with a central aperture through which the optical axis passes and a surrounding array of secondary apertures, the disk-shaped member being further arranged such that gas flow past the disk-shaped member is through the central aperture and the array of secondary apertures.10. In a lithography system, a method of limiting passage of stray target material from a source of extreme ultraviolet (EUV) radiation, the source including a source vessel and a vessel aperture through which the EUV radiation exits the source vessel along an optical axis to a scanner system arranged to receive the EUV radiation from the source vessel through the vessel aperture, the method comprising flowing gas passing from the scanner system to the source through a source-to-exposure interface assembly arranged and configured to impart a vorticial flow to gas flowing through the source-to-exposure interface assembly to cause particulate matter entrained in the gas to be urged away from the optical axis.11. The method of clause 10, wherein the source-to-exposure interface assembly comprises a plurality of blades arranged in the plenum.12. The method of clause 11, wherein the blades are stationary.13. The method of clause 12, wherein the plurality of stationary blades are arranged radially around the optical axis.14. The method of clause 12, wherein the plurality of a stationary blades are arranged rotationally symmetrically around the optical axis.15. The method of clause 12, further comprising flowing the gas through a disk-shaped member arranged between the plenum and an intermediate focus of the source, the disk-shaped member being provided with a central aperture through which the optical axis passes and a surrounding array of secondary apertures.16. A radiation source comprising:a first stage defining a plasma generation region configured to receive a liquid metal target and a drive laser beam to generate EUV radiation;a second stage disposed above the first stage and fluidly connected thereto through a throat region, the second stage having an interior volume arranged to receive the EUV radiation through the throat region; anda gas supply system coupled to the first stage and the second stage such that a pressure in the second stage is maintained higher than a pressure in the first stage, wherein the second stage has wall surfaces angled outward relative to an optical axis of the EUV radiation, the throat region and the angled wall surfaces together forming an hourglass -shaped internal geometry that suppresses upward transport of tin debris from the first stage to the second stage.17. The radiation source of clause 16, wherein the angled wall surfaces of the second stage are oriented to redirect infrared radiation emitted from the plasma away from an intermediate focus region, such that the infrared radiation undergoes multiple reflections before reaching the intermediate focus.18. The radiation source of clause 16, wherein the second stage includes one or more gas inlets positioned near an upper periphery of the second stage, the gas inlets arranged to generate recirculating gas flow regions that reduce momentum of tin particles within the second stage.19. The radiation source of clause 16, further comprising one or more replaceable liners disposed on interior surfaces of the second stage, the liners being adapted to capture tin deposits generated in the plasma generation region.20. The radiation source of clause 16, wherein the throat region between the first stage and the second stage has a restricted diameter relative to either stage, thereby increasing drag on upward-moving particles and limiting line-of-sight infrared transmission toward the intermediate focus.21. A method of operating a radiation source comprising:generating a plasma from liquid metal droplets in a first stage of a source vessel to emit EUV radiation; maintaining a second stage of the source vessel at a higher gas pressure than the first stage, the second stage being positioned above the first stage and connected thereto through a throat region; and directing the EUV radiation through the throat region toward an intermediate focus, wherein the pressure differential between the second stage and the first stage suppresses tin vapor and particle transport from the plasma region into the second stage.22. The method of clause 21, further comprising introducing a flow of hydrogen gas into the second stage through peripherally located inlets to establish a recirculating flow field that decelerates ballistic tin particles and prevents their entry into the intermediate focus region.23. The method of clause 21, further comprising reflecting infrared radiation emitted from the plasma at wall surfaces of the second stage angled away from the optical axis such that multiple reflections occur before any portion of the infrared radiation reaches the intermediate focus, thereby reducing infrared coupling into the scanner.24. A radiation source comprisinga target material supply unit configured to deliver droplets of a metal target material into a plasma generation region;a drive laser arranged to irradiate the droplets to generate a plasma that emits EUV radiation;a dual-stage vessel defining a first internal volume and a second internal volume fluidly connected through an intermediate constricted section, wherein the first internal volume defines the plasma region and is maintained at a first pressure, the second internal volume is maintained at a higher pressure relative to the first pressure, and a collector mirror disposed within the second internal volume and aligned along an optical axis extending through the constricted section.25. A gas flow control system for a radiation source comprising:a dual-stage vessel defining axially aligned lower and upper regions connected by a reduced crosssection throat;a hydrogen gas injection manifold coupled to the lower region to generate a protective gas curtain proximate to a plasma generation zone;a pressure control unit coupled to the upper region to maintain the upper region at a higher hydrogen partial pressure than the lower region; anda feedback controller configured to dynamically adjust gas flow rates based on pressure sensors disposed in each region, wherein the differential pressure established across the throat retards the flow of tin vapor from the lower region toward an intermediate focus, and the gas flow pattern generated in the upper region slows ballistic tin particles and redirects them away from the optical axis of the EUV radiation beam.

[0068] As mentioned, the manufacture of ICs can be accomplished by providing a substrate having a surface with a photoresist layer and directing radiation to the surface with the photoresist layer from a radiation source incorporating one or more features of the above-described embodiments or implementing the described method or both to transfer a pattern from a mask onto the photoresist layer and removing a portion of the photoresist layer to form the pattern over the substrate. Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc.

[0069] Some of the above description is in terms of functional block diagrams with some functions allocated to some blocks and other functions allocated to other blocks. It will be understood that the division between blocks and the allocations are arbitrary and that different divisions and allocations are possible so long as the overall functions are carried out as described above.

[0070] The above description includes examples of multiple embodiments. It is, of course, not possible to describe every conceivable combination of components or methodologies for each of theseembodiments, but one of ordinary skill in the art may recognize that many further combinations and permutations of elements of the various embodiments are possible based on the disclosure. Accordingly, the described embodiments are intended to be representative of and encompass all such alterations, modifications, and variations that fall within the spirit and scope of the appended claims.

[0071] Furthermore, to the extent that the term “includes” is used in either the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term “comprising” as “comprising” is construed when employed as a transitional word in a claim. Also, although elements of the described aspects and / or embodiments may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is explicitly stated. Additionally, all or a portion of any aspect and / or embodiment may be utilized with all or a portion of any other aspect and / or embodiment, unless stated otherwise.

[0072] Features, materials, characteristics, or groups described in conjunction with a particular aspect, embodiment, or example are to be understood to be applicable to any other aspect, embodiment or example described in this section or elsewhere in this specification unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract, and drawings) may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. The protection is not restricted to the details of any foregoing embodiments. The protection extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0073] Furthermore, certain features that are described in this disclosure in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations, one or more features from a claimed combination can, in some cases, be excised from the combination, and the combination may be claimed as a subcombination or variation of a subcombination.

[0074] Moreover, while operations may be depicted in the drawings or described in the specification in a particular order, such operations need not be performed in the particular order shown or in sequential order, or that all operations be performed, to achieve desirable results. Other operations that are not depicted or described can be incorporated in the example methods and processes. For example, one or more additional operations can be performed before, after, simultaneously, or between any of the described operations. Further, the operations may be rearranged or reordered in other implementations. Those skilled in the art will appreciate that in some embodiments, the actual steps taken in the processes illustrated and / or disclosed may differ from those shown in the figures.Depending on the embodiment, certain of the steps described above may be removed, others may be added.

[0075] Furthermore, the features and attributes of the specific embodiments disclosed above may be combined in different ways to form additional embodiments, all of which fall within the scope of the present disclosure. Also, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described components and systems can generally be integrated together in a single product or packaged into multiple products.

[0076] For purposes of this disclosure, certain aspects, advantages, and novel features are described herein. Not necessarily all such advantages may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the disclosure may be embodied or carried out in a manner that achieves one advantage or a group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.

[0077] Conditional language, such as “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements, and / or steps. Thus, such conditional language is not generally intended to imply that features, elements, and / or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without user input or prompting, whether these features, elements, and / or steps are included or are to be performed in any particular embodiment.

[0078] Conjunctive language such as the phrase “at least one of X, Y, and Z,” unless specifically stated otherwise, is otherwise understood with the context as used in general to convey that an item, term, etc. may be either X, Y, or Z. Thus, such conjunctive language is not generally intended to imply that certain embodiments require the presence of at least one of X, at least one of Y, and at least one of Z.

[0079] Language of degree used herein, such as the terms “approximately,” “about,” “generally,” and “substantially” as used herein represent a value, amount, or characteristic close to the stated value, amount, or characteristic that still performs a desired function or achieves a desired result. For example, the terms “approximately”, “about”, “generally,” and “substantially” may refer to an amount that is within less than 10% of, within less than 5 % of, within less than 1% of, within less than 0.1 % of, and within less than 0.01 % of the stated amount. As another example, in certain embodiments, the terms “generally parallel” and “substantially parallel” refer to a value, amount, or characteristic that departs from exactly parallel by less than or equal to 15 degrees, 10 degrees, 5 degrees, 3 degrees, 1 degree, or 0.1 degree.

[0080] The scope of the present disclosure is not intended to be limited by the specific disclosures of preferred embodiments in this section or elsewhere in this specification, and may bedefined by claims as presented in this section or elsewhere in this specification or as presented in the future. The language of the claims is to be interpreted broadly based on the language employed in the claims and not limited to the examples described in the present specification or during the prosecution of the application, which examples are to be construed as non -exclusive.

Claims

CLAIMS1. A lithography system comprising:a source of extreme ultraviolet (EUV) radiation, the source including a source vessel and a vessel aperture through which the EUV radiation exits the source vessel along an optical axis;a scanner system arranged to receive the EUV radiation from the source vessel through the vessel aperture;structure defining a plenum positioned between the source and the scanner system; and a source-to-exposure interface assembly positioned in the plenum, the source-to-exposure assembly being arranged and configured to impart a vorticial flow to gas flowing through the plenum to cause particulate matter entrained in the gas to be urged away from the optical axis.

2. The lithography system of claim 1 wherein the plenum is configured as a frustoconical structure having an axis of symmetry coincident with the optical axis.

3. The lithography system of claim 1 wherein the source-to-exposure interface assembly comprises a plurality of blades arranged in the plenum.

4. The lithography system of claim 3 wherein the blades are stationary.

5. The lithography system of claim 3 wherein the plurality of stationary blades are arranged radially around the optical axis.

6. The lithography system of claim 3 wherein the plurality of stationary blades are arranged rotationally symmetrically around the optical axis.

7. The lithography system of claim 3 further comprising a disk-shaped member arranged between the plenum and an intermediate focus of the source and at an angle from about 45° to about 90° with respect to the optical axis, the disk-shaped member being provided with a central aperture through which the optical axis passes and a surrounding plurality of secondary apertures, the diskshaped member being further arranged such that gas flow past the disk-shaped member is through the central aperture and the plurality of secondary apertures.

8. The lithography system of claim 7 wherein the plurality of secondary apertures is arranged as an irregular array of secondary apertures.

9. A lithography system comprising:a source of extreme ultraviolet (EUV) radiation, the source including a source vessel and a vessel aperture through which the EUV radiation exits the source along an optical axis;a scanner system arranged to receive the EUV radiation from the source vessel through the vessel aperture;structure defining a frustoconical plenum having an axis of symmetry coincident with the optical axis positioned between the source and the scanner system;a source-to-exposure interface assembly positioned in the plenum, the source-to-exposure comprising a plurality of stationary blades arranged in the plenum radially and rotationally symmetrically around the optical axis; the plurality of a stationary blades being arranged and configured to impart a vorticial flow to gas flowing through the plenum to cause particulate matter entrained in the gas to be urged away from the optical axis; anda disk-shaped member arranged between the plenum and an intermediate focus of the source and at an angle between 85° and 95° with respect to the optical axis, the disk-shaped member being provided with a central aperture through which the optical axis passes and a surrounding array of secondary apertures, the disk-shaped member being further arranged such that gas flow past the diskshaped member is through the central aperture and the array of secondary apertures.

10. In a lithography system, a method of limiting passage of stray target material from a source of extreme ultraviolet (EUV) radiation, the source including a source vessel and a vessel aperture through which the EUV radiation exits the source vessel along an optical axis to a scanner system arranged to receive the EUV radiation from the source vessel through the vessel aperture, the method comprising flowing gas passing from the scanner system to the source through a source-to-exposure interface assembly arranged and configured to impart a vorticial flow to gas flowing through the source-to-exposure interface assembly to cause particulate matter entrained in the gas to be urged away from the optical axis.

11. The method of claim 10 wherein the source-to-exposure interface assembly comprises a plurality of blades arranged in the plenum.

12. The method of claim 11 wherein the blades are stationary.

13. The method of claim 12 wherein the plurality of stationary blades are arranged radially around the optical axis.

14. The method of claim 12 wherein the plurality of a stationary blades are arranged rotationally symmetrically around the optical axis.

15. The method of claim 12 further comprising flowing the gas through a disk-shaped member arranged between the plenum and an intermediate focus of the source, the disk-shaped member being provided with a central aperture through which the optical axis passes and a surrounding array of secondary apertures.

16. A radiation source comprising:a first stage defining a plasma generation region and coupled to a drive laser to generate EUV radiation;a second stage fluidly coupled to the first stage and arranged between the first stage and an intermediate focus region, wherein a cross-sectional area of the second stage is greater than that of the first state; anda gas supply system coupled to the second stage such that a pressure in the second stage is maintained higher than a pressure in the first stage.

17. The radiation source of claim 16, wherein the second stage includes wall surfaces angled outward relative to an optical axis of the EUV radiation.

18. The radiation source of claim 16, wherein the second stage includes one or more gas inlets positioned near an upper periphery of the second stage, the gas inlets arranged to generate a swirling gas flow region within the second stage.

19. The radiation source of claim 16, further comprising a feedback controller configured to dynamically adjust gas flow rates based on pressure sensors disposed in the first stage and the second stage.

20. The radiation source of claim 16, wherein a throat region is between the first stage and the second stage, and the throat region has a restricted diameter relative to either stage.

Images