WO2025201798A1 - Apparatus and method for controlling contaminant dispersal in euv radiation source - Google Patents

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 target material vapor and deposit some of the target material on surfaces within the vessel where the target material accumulates and in which measures are adopted to reduce the amount of deposited target material that is able to reenter the gas flows.

Description

APPARATUS AND METHOD FOR CONTROLLING CONTAMINANT DISPERSAL IN EUV RADIATION SOURCE

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to US Application No. 63/571,098, filed March 28, 2024, titled APPARATUS AND METHOD FOR CONTROLLING CONTAMINANT DISPERSAL IN EUV RADIATION SOURCE, which is incorporated herein by reference in its entirety.

TEHCNICAL FIELD

[0002] The present disclosure relates to apparatuses for and methods of generating extreme ultraviolet (“EUV”) radiation from a plasma created through conversion of a target material in a source vessel (e.g., a plasma generation volume). In particular this disclosure relates to apparatuses for and methods of controlling the dispersal of target material within a chamber in a system for generating EUV radiation.

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 are a lithographic apparatus, a metrology, or an inspection apparatus, more specifically a mask inspection apparatus and even more specifically an actinic mask inspection apparatus.

[0004] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic 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. To project a pattern on a substrate a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which can be formed on the substrate. A lithographic 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 lithographic apparatus which uses, for example, radiation with a wavelength of 193 nm.

[0005] Methods for generating EUV radiation include converting a 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. The target material can be solid, liquid, or gas. 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. [0006] 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. Sources using this technique generate EUV radiation by coupling laser energy into a target material having at least one EUV emitting element, creating a highly ionized plasma with electron temperatures of several 10’s of eV. [0007] For this process, the plasma is typically generated in a source vessel, e.g., a vacuum chamber, and various properties of the resultant EUV radiation are monitored using corresponding types of metrology equipment.

[0008] 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, 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. In the case where the target material is tin, the tin vapor can cause the formation of tin wool which can block orifices in the chamber such as for a gas circulation system as described in more detail below. 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.

[0009] Stray target material can also 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 intermediate focal location. At the wavelengths involved, the collector is advantageously implemented as a multilayer 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.

[0010] The collected radiation may then be relayed from the intermediate location to a set of optics, a reticle, detectors and ultimately to a scanner. The ray paths of the EUV radiation in the chamber thus define a cone with the collector optics as its base and the intermediate focus of the collector optics as its vertex.

[0011] In some systems a buffer gas is used to establish flow patterns in the chamber to protect the collector optics and carry off the plasma generation byproducts. For example, molecular hydrogen (H2) gas at pressures in the range of about 0.5 mbar to about 3 mbar may be used in the vacuum chamber as a buffer gas to control target material dispersal for debris mitigation. In the absence of a gas, at vacuum pressure, it would be difficult to protect the collector adequately from target material debris ejected from the irradiation region. Hydrogen is relatively transparent to EUV radiation having a wavelength of about 13.5 nm and so is preferred to other candidate gases such as He, Ar, or other gases which exhibit a higher absorption at about 13.5 nm. [0012] Gas flows are also established within the chamber intended to keep target material from accumulating on the plasma-facing surfaces within the chamber. For example, a gas flow may be established in a direction transverse to the reflective surface of the collector. This flow is referred to as forward flow which is typically directed toward one or both of the primary focus and the intermediate focus of the collector. In addition, gas may be guided to flow substantially along the reflective surface of the collector. This flow is referred to as lateral flow. Another flow along the surface of the collector towards its center from its circumference can be referred to as the perimeter flow.

[0013] These flows, i.e., forward, lateral, and perimeter flows combine to protect the collector from plasma debris while liner flows manage target material deposition along the vessel side walls. These flows then merge with flows in the lower cone to guide the target material vapor out of the source through an exhaust.

[0014] Despite these measures management of 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 residual target material.

[0015] Still using tin as an example of a target material, as another mitigation measure a device called a scrubber may be placed in the chamber to capture target material. The scrubber has surfaces heated to above the melting point of tin, about 232 °C, over which gas containing target material debris and vapor flows and on which the tin deposits. There the tin melts (or remains molten) and is caused to flow through a drain system to a capture receptacle. This removes the tin from the buffer gas before the buffer gas travels further through the exhaust chain so to prevent tin contamination of sensitive exhaust components, such as valves and pumps. It may, however, be the case that the liquid tin collects at one or more plasma-facing positions inside of the source vessel along this exit path, for example, in the areas around the drain. As it collects, however, the liquid tin may be exposed to hydrogen radicals (FT) from the plasma in the source. Liquid tin tends to erupt in the presence of these hydrogen radicals such as are generated during EUV production thus ejecting tin back into the chamber gas flow patterns. This phenomenon is sometimes referred to a “tin spitting.” Once the liquid tin returns to the gas flow it can disperse to various locations where its presence is destructive, for example, towards and past the intermediate focus and even to the scanner contributing to target material accumulation in the scanner and target material on customer pellicles and wafers.

[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 that is presented later.

[0018] According to an aspect of an embodiment there is disclosed apparatuses and methods for limiting the effects of target material spitting and splashing, and, in particular, for limiting the re- introduction of target material into the gas streams in the chamber from agglomerations of deposited target material.

[0019] According to an aspect of an embodiment there is disclosed an apparatus for generating extreme ultraviolet radiation by irradiating a target material, the apparatus comprising a chamber, a target material deposition surface arranged to receive target material deposited from a gas flow when the gas flow passes over the target material deposition surface, drain in fluid communication with the target material deposition surface, the drain including a drain mouth and a rim surface adjacent the drain mouth, and a shield covering at least a portion of the rim surface and positioned to prevent target material from being ejected back into the gas flow.

[0020] The target material deposition surface may be coupled to a surface of a scrubber. The surface of the scrubber may comprise a plurality of fin structures. The shield may comprise molybdenum. The thickness of the shield may range from about 1 millimeter (mm) to about 8 mm. The shield may comprise at least one of titanium, zirconium, and molybdenum. The shield may comprise stainless steel.

[0021] The target material may comprise tin and at least a portion of a surface of the shield may be provided with a layer comprising a tin philic material. An upper edge of the shield may be curved. [0022] The shield may have an upper surface and a side surface with the upper surface being at an angle to the side surface and wherein the shield is oriented in the scrubber so that the upper surface is at an angle with respect to gravity in a range of about 0° to about 45° and the side surface is a plasmafacing surface having an angle with respect to gravity in the range of about 20° to about 70°.

[0023] The target material deposition surface may comprise a surface of an exhaust plenum. The shield may be a substantially planar element which extends over and is spaced away from the drain mouth and is inclined with respect to horizontal.

[0024] According to another aspect of an embodiment there is disclosed a target material scrubber for an apparatus for generating extreme ultraviolet radiation by irradiating a target material, the target material scrubber comprising a plurality of target material deposition surfaces arranged such that gas carrying target material passes over the target material deposition surfaces in such a way that target material transfers from the gas to the target material deposition surfaces, a drain positioned such that target material transferred to the target material deposition surfaces flows to the drain, the drain having a rim area, and a shield positioned over at least a portion of the rim area of the drain to prevent target material from being ejected back into the gas. [0025] According to another aspect of an embodiment there is disclosed Apparatus for generating extreme ultraviolet radiation by irradiating a target material, the apparatus comprising a chamber, a waste target material management system arranged in the chamber and configured to exhaust gas carrying stray target material, the waste target material handling system including at least one location at which liquid waste target material accumulates while the apparatus is in operation, and a shield arranged over at least a portion of the at least one location at which liquid waste target material accumulates while the apparatus is in operation to prevent waste target material from being ejected back into the gas.

[0026] According to another aspect of an embodiment there is disclosed a method of manufacturing a semiconductor device comprising providing a substrate having a surface with a photoresist layer, directing radiation to the surface with the photoresist layer from a radiation source comprising a chamber, a waste target material management system arranged in the chamber and configured to exhaust gas carrying stray target material, the waste target material handling system including at least one location at which liquid waste target material accumulates while the apparatus is in operation, and a shield arranged over at least a portion of the at least one location at which liquid waste target material accumulates while the apparatus is in operation to prevent waste target material from being ejected back into the gas 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.

[0027] 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

[0028] 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 to explain 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.

[0029] FIG. 1 is a schematic diagram of an EUV source.

[0030] FIG. 2 is a schematic diagram of an EUV source including a scrubber.

[0031] FIG. 3 A is a side view diagram of a scrubber for an EUV source.

[0032] FIG. 3B is a side view diagram of the scrubber of FIG. 3 A from another perspective.

[0033] FIG. 4A is a diagram of a portion of a scrubber for an EUV source. [0034] FIG. 4B is a diagram of a portion of a scrubber for an EUV source according to an aspect of an embodiment.

[0035] FIG. 4C is a perspective view of a portion of a scrubber for an EUV source according to an aspect of an embodiment.

[0036] FIG. 5 is a diagram depicting an orientation of a drain shield in a portion of a scrubber for an EUV source according to an aspect of an embodiment.

[0037] FIG. 6 is a perspective view of a portion of a scrubber for an EUV source according to an aspect of another embodiment.

[0038] FIG. 7 is a schematic diagram of an EUV source including an exhaust plenum.

[0039] FIG. 8 A is a diagram of the front of an exhaust plenum drain of an EUV source.

[0040] FIG. 8B is a diagram of an exhaust plenum drain of an EUV source.

[0041] FIG. 9A is a front view diagram of a portion of an EUV source chamber with an exhaust plenum according to an aspect of an embodiment.

[0042] FIG. 9B is a side view diagram of a portion of an EUV source chamber with an exhaust plenum according to an aspect of an embodiment.

[0043] FIG. 10 is a side view diagram of a portion of an EUV source chamber with an exhaust plenum according to an aspect of an embodiment.

[0044] FIG. 11 is a front view diagram of a portion of an EUV source chamber with an exhaust plenum according to an aspect of an embodiment.

[0045] FIG. 12 is a side view diagram of a portion of an EUV source chamber with an exhaust plenum according to an aspect of an embodiment.

[0046] 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

[0047] 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. [0048] Before describing such embodiments in more detail, however, it is useful to present an example of an environment in which embodiments may be implemented. 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.

[0049] With initial reference to FIG. 1 there is shown a schematic view of an exemplary EUV radiation source, e.g., a laser produced plasma EUV radiation source 10 according to one aspect of an embodiment. As shown, the EUV radiation source 10 may include a pulsed or continuous laser source 22, which may for example be a pulsed gas discharge CO2 laser source producing a beam 12 of radiation at from about 1pm to about 10.6 pm. The pulsed gas discharge CO2 laser source may have DC or RF excitation operating at high power and at a high pulse repetition rate.

[0050] The EUV radiation source 10 also includes a target material delivery system 24 for delivering target material in the form of liquid droplets or a continuous liquid stream. In this example, the target material is a liquid, but it could also be a solid or gas. The target material may be made up of tin or a tin compound, although other materials could be used. In the system depicted the target material delivery system 24 introduces droplets 14 of the target material into the interior of a vacuum chamber 26 having walls 27 to an irradiation region 28 where the target material may be irradiated to produce plasma. The vacuum chamber 26 may be provided with a liner 29. It should be noted that as used herein an irradiation region is a region where target material irradiation may or is intended to occur, and is an irradiation region even at times when no irradiation is actually occurring. The EUV light source may also include a beam steering system 32.

[0051] In the system shown, the components are arranged so that the droplets 14 travel substantially horizontally. The direction from the laser source 22 towards the irradiation region 28, that is, the nominal direction of propagation of the beam 12, may be taken as the Z axis. The path the droplets 14 take from the target material delivery system 24 to the irradiation region 28 may be taken as the X axis. The view of FIG. 1 is thus normal to the XZ plane. While a system in which the droplets 14 travel substantially horizontally is depicted, it will be understood by one having ordinary skill in the art the other arrangements can be used in which the droplets travel vertically or at some angle with respect to gravity between and including 90° (horizontal) and 0° (vertical).

[0052] The EUV radiation source 10 may also include an EUV light source controller system 60, a laser firing control system 65, along with the beam steering system 32. The EUV radiation source 10 may also include a detector such as a target position detection system which may include one or more droplet imagers 70 that generate an output indicative of the absolute or relative position of a target droplet, e.g., relative to the irradiation region 28, and provide this output to a target position detection feedback system 62. [0053] As shown in FIG. 1, the target material delivery system 24 may include a target delivery control system 90. The target delivery control system 90 is operable in response to a signal, for example, the target error described above, or some quantity derived from the target error provided by the system controller 60, to adjust paths of the droplets 14 through the irradiation region 28. This may be accomplished, for example, by repositioning the point at which a target delivery mechanism 92 releases the droplets 14. The droplet release point may be repositioned, for example, by tilting the target delivery mechanism 92 or by laterally translating the target delivery mechanism 92. The target delivery mechanism 92 extends into the chamber 26 and is externally supplied with target material and a gas source to place the target material in the target delivery mechanism 92 under pressure. The system also includes a target material receptacle 96 that catches unused droplets of target material, that is, droplets of target material that have not been converted.

[0054] Continuing with FIG. 1, the radiation source 10 may also include one or more optical elements. In the following discussion, a collector 30 is used as an example of such an optical element, but the discussion applies to other optical elements as well. The collector 30 may be a normal incidence reflector, for example, implemented as an MLM with additional thin barrier layers, for example B C. ZrC, SisN4 or C, deposited at each interface to effectively block thermally -induced interlayer diffusion. Other substrate materials, such as aluminum (Al) or silicon (Si), can also be used. The collector 30 may be in the form of a prolate ellipsoid, with a central aperture to allow the laser radiation 12 to pass through and reach the irradiation region 28. The collector 30 may be, e.g., in the shape of a ellipsoid that has a first focus at the irradiation region 28 and a second focus at a so-called intermediate point 40 (also called the intermediate focus) where the EUV radiation may be output from the EUV radiation source 10 and input to, e.g., an integrated circuit lithography scanner 50 which uses the radiation, for example, to process a silicon wafer workpiece 52 in a known manner using a reticle or mask 54. The silicon wafer workpiece 52 is then additionally processed in a known manner to obtain an integrated circuit device. In some embodiments, the EUV radiation may input to an inspection apparatus for detecting defects or measuring dimensions during the semiconductor manufacturing process.

[0055] FIG. 2 is a schematic diagram of an EUV chamber 126 having a scrubber 120. In operation, a buffer gas such as hydrogen flows into the chamber 26 through one or more inlets including a forward flow inlet 100 disposed at the center of a collector 130. The buffer gas flows as indicated by the open arrow A through the chamber 126 through a scrubber 120 and out through an exhaust outlet 110 through a liner 129 as indicated by the open arrow B. An intermediate focus for the collector 130 is disposed at the vertex of the EUV light cone having a base defined by the collector 130.

[0056] In some embodiments, the scrubber 120 is tilted with respect to gravity as indicated by the arrow G so that liquid target material deposited on fins or vanes of the scrubber 120 will flow along gutters 155 in the scrubber 120 to a drain 140. The liquid target material then flows from the drain 140 as indicated by the arrow T to a drain module 145 and is thus removed from the interior of the chamber 126.

[0057] FIG. 2 shows a scrubber 120 having three layers and three drains. It will be understood by one of ordinary skill in the art that the scrubber may have fewer or more layers.

[0058] FIG. 3 A is a front view of an embodiment of a scrubber 120. As can be seen, the example of scrubber 120 shown in FIG. 3 A has three layers or tiers, with each layer having a series of slanted fins 150 and a gutter 155. The fins 150 on the left side of the scrubber 120 as oriented in FIG. 3 A are slanted left to right while the fins 150 on the right side of the scrubber 120 are slanted right to left. This creates a column of trapezoidal spaces 152 between the right-slanted and left-slanted fins. A drain 140 is disposed at the base of each of the trapezoidal spaces 152.

[0059] FIG. 3B is a side view of the scrubber 120 of FIG. 3A. In the arrangement shown in FIG. 3B, molten target material flows in the directions indicated by the solid black arrows. As can be seen, the molten target material flows down the fins 150 and then along the gutters 155 to respective drains 140. Each of the drains 140 communicates with the drain module 145.

[0060] As mentioned, molten target material can accumulate in the vicinity of the drains 140, for example, at the position where the back wall 160 meets the surfaces around the mouth of the drain 140. FIG. 4A depicts an example of an arrangement in which this can occur. As shown in FIG. 4A, molten target material flows along an intended target material flow path T along an upper surface of a gutter 155 to drain 140. Part of the flow path T runs through a gap between the upper surface of the gutter 155 and the bottom of the back wall 160. The gap has a width H. Due to the narrowness of the gap, target material can accumulate at the upstream side of the gap at a target material accumulation site 200.

[0061] This molten target material can spit when exposed to hydrogen radicals present in the chamber 126. The target material ejected when spitting occurs can reenter the gas flowing inside of the chamber 126 and travel to other parts of the source where its presence is harmful such as through the intermediate focus and out towards the scanner or the inspection apparatus.

[0062] According to an aspect of an embodiment this contamination is reduced and even avoided by interposing one or more physical barriers to prevent accumulated target material from spitting back into the gas flowing within the chamber. For example, in the case where the target material accumulates around the mouth or rim of a drain, the physical barrier or shield may be placed partially around or upstream of the drain and the surrounding structure to block target material ejection while allowing the target material to continue to drain beneath it. Such a shield could be beneficial anywhere in the source where target material could accumulate. The shield can be configured as a serviceable part that could be added to sources that are already deployed in the field. According to another aspect of an embodiment the surfaces of the shield are positioned and angled to allow a thin layer of target material to flow off of the shield surfaces and onto the intended drain path while blocking at least part of a line-of-sight path from the accumulation site to the intermediate focus. [0063] Thus, in accordance with an aspect of an embodiment, as shown in FIG. 4B, a shield 170 is positioned so as to block ejected molten target material from reentering the gas flows. At the same time, the shield 170 is positioned so as to permit molten target material to reach and flow into the drain 140. As shown in FIG. 4C the shield 170 is mechanically engaged with fins 150 on either side of the trapezoidal space 152 and vertically displaced from the gutter 155. The shield 170 in the example shown has a top shield surface 175 and a plasma-facing shield surface 180. The surfaces of the shield 170 are angled so as to promote the flow of target material captured by the shield 170 to the drain 140. Thus, as shown in FIG. 5, the top shield surface 175 can for example have an angle 0i with respect to horizontal in the range of about 20° to about 90°, more specifically in the range of about 20° to about 30°. A smaller angle 0i could permit target material to accumulate on the top shield surface while a larger angle 0i would potentially create a pocket in which target material could accumulate. The plasma-facing shield surface 180 may for example have an angle with respect to gravity in the range of about 0° to about 45°, for example, 0°. A larger angle 02 would potentially open up the gap between the bottom edge of the plasma-facing shield 180 and the target material accumulation site 200 thus a path for target material to inject itself into gas flows out of the chamber 126 and towards the scanner. In some embodiments, a distance between a bottom edge of shield 170 and a top surface of gutter 155 ranges from about 1 centimeter to about 10 centimeters. If the distance is smaller than 1 center meter, in some instances, the molten target material clogs easily. If the distance is greater than 10 centimeters, in some instances, the result of blocking ejection is not significant.

[0064] In general, the bulk or body of the shield 170 may be made of a material such as molybdenum or a molybdenum alloy such as titanium zirconium molybdenum (TZM). Other suitable materials include stainless steel. The surfaces of the shield 170 may be coated to make the material surface more tin philic, i.e., to have more of an affinity for the liquid target material by analogy to water and the property of being hydrophilic, causing the molten target material to spread across the surface to maximize contact. For example, in applications where the target material is tin, the shield 170 may be coated with a layer of tin.

[0065] Another measure for limiting the amount of target material ejection entails restricting the amount of target material that is permitted to reach the target material accumulation site 200. In other words, a shield can be positioned to prevent the flow of liquid target material to positions where the target material will tend to accumulate. FIG. 6 is a perspective view of an arrangement limiting accumulation of target material in which a target material accumulation shield 210 is positioned to prevent target material from reaching the target material accumulation site between the back wall 160 and the surface of the drain 140 (not visible in FIG. 6). In this embodiment, because the target material accumulation site is blocked by target material accumulation shield 210, the molten target material flows between fins and towards the drain behind the back wall. The target material accumulation shield 210 may be made of the same materials as the shield 170 described above and may also be coated with a tin philic material to promote the flow of molten target material over the surface. As can be seen, the front surface of the target material accumulation shield 210 is slanted with respect to gravity at an angle of about 20° to about 90° (90° being vertical).

[0066] In EUV chambers that have an exhaust plenum in the buffer gas exhaust path there may be a target material accumulation site near a drain for the exhaust plenum. Such an arrangement is shown in FIG. 7, where buffer gas flows out of the chamber 326 defined by the chamber wall 327 through an exhaust plenum 300 as indicated by the open arrow B. In the depicted arrangement liquid target material deposits on the interior surfaces of the exhaust plenum 300 and flows to a drain 310 and from there to a drain module 330.

[0067] Target material will deposit on the surfaces over which the buffer gas flows over. The deposited target material will flow towards the drain 310 and from there into a drain module 330. In general it is advantageous to select the angles with respect to gravity of the surfaces surrounding the drain to allow liquid target material to flow and escape into the drain. For example, in some embodiments the angle of the surfaces should be greater than about 20°. Even adherence to this principle, however, does not ensure full target material draining, and target material can still accumulate in the area adjacent to the drain.

[0068] This arrangement thus has the same technical issue as the arrangement described above in that the target material deposits at the surface surrounding the drain 310, that is, the mouth of the drain 310, some of which can be ejected back into the flow of gas which carries it back into the interior volume of chamber 326, and then toward and out of the intermediate focus.

[0069] FIG. 8A shows drain 310 through aperture or drain entrance throat 320 in a section of the wall 305 of the exhaust plenum 300 from the perspective of the interior of the exhaust plenum 300. The surface around the drain 310 includes a drain rim 330 which meets a drain entrance back wall 340.

There is a target material accumulation site 350 where the drain rim 330 meets the drain entrance back wall 340.

[0070] FIG. 8B is a side view of the arrangement of FIG. 8A. As can be seen, the exhaust plenum 300 extends from the liner 329. The exhaust plenum 300 has a drain entrance throat 320 which leads into a cavity drained by the drain 310 surrounded by the drain rim 330. A target material accumulation site 350 is formed where the drain rim 330 meets the drain entrance back wall 340.

[0071] According to an aspect of an embodiment target material which accumulates at the target material accumulation site 350 is prevented from returning to the gas flowing through the exhaust plenum 300 by placing a drain shield over the target material accumulation site 350. This shield is arranged so that it captures target material which spits from the target material accumulation site but does not interfere with the flow of liquid target material into the drain 310. Additionally, in some embodiments the shield may be arranged to capture target material that drains toward the drain hole and splashes back due to impact with the drain channel walls. The shield in some embodiments may also be arranged to capture target material dynamically, that is target material that spits while it drains and not only from static accumulated tin. The shield in some embodiments may also be arranged to capture target material that drips from a surface onto the drain channel from above, the target material otherwise splashing above toward the source vessel. As with the shield described above, the surface of the shield may have engineered target material wetting properties so that the effective number of particles and volume of target material making its way towards intermediate focus can be minimized. [0072] Such an arrangement is shown in FIG. 9A which is from the same perspective as FIG. 8A. The depicted features are the same as those described in connection with FIG. 8A except a drain shield 360 has been positioned above the target material accumulation site 350 and spaced away from the drain 310. FIG. 9B is a side view of the arrangement of FIG. 9A and includes the drain shield 360. In some embodiments, the drain shield 360 has a U-shaped or V-shaped cross-sectional view, which is similar to the shield 170 in FIG. 4B. As in the case of the shields in the earlier-described embodiments, the body or bulk of the drain shield 360 may be made of a material such as molybdenum or a molybdenum alloy or stainless steel. The body or bulk of the drain shield 360 may be coated with a material such as titanium nitride or tin in cases where a tin philic surface is desired. [0073] In the embodiment shown the drain shield 360 is a substantially planar element but the drain shield 360 may have a different shape as long as it performs the function of blocking ejected target material from reentering the gas flow. In some embodiments, an upper edge of the drain shield 360 is curved (i.e., concave upwards or downwards) so that molten target material on the drain entrance back wall 340 can flow towards the drain 310 as shown in FIG. 10. In such instances, from the side view FIG 9B the drain shield 360 is separate from the drain entrance back wall 340. Only two ends of the upper edge of the drain shield 360 are connected to the drain entrance back wall 340. In some embodiments, a lower edge of the drain shield 360 is curved (i.e., concave upwards or downwards) to substantially align a corresponding edge of the drain entrance throat 320 as shown in FIG. 10.

[0074] In some embodiments, the drain shield 360 may be oriented at an angle with respect to gravity in a range, for example, of about +100° to about -100°. A smaller angle with respect to gravity may open a line-of-sight path from the target material accumulation site 350 to the intermediate focus. A larger angle may start to restrict the flow of target material to the drain 310. In some embodiments that shield is inclined at least 20° with respect to horizontal to avoid target material accumulation on the shield itself. The drain shield 360 may have a thickness in a range, for example, of about 1 millimeter (mm) to about 8 mm. A drain shield having a thickness below this range may lack sufficient rigidity while thicknesses above this range provide no additional benefit in terms of required mechanical strength. The drain shield 360 may be installed, for example, by attachment using any suitable method to a wall rising up from around the drain 310. [0075] As an example using tin as the target material, the area around the drain may be also made of molybdenum or a molybdenum alloy or stainless steel and provided with a titanium nitride coating which acts as a barrier layer between the underlying bulk material structure and the liquid target material. This titanium nitride coating is highly tin phobic, i.e., liquid tin forms droplets on the surface rather than depositing as a thin layer. In contrast, a tin plating on top of stainless steel surfaces results in a tin philic surface on which tin deposits as a thin layer of tin spread over the larger surface. This produces much less tin spitting with smaller particles which are less likely to be transported through the intermediate focus aperture. Thus, in the context of this example, the spit blocking shield may advantageously be made from stainless steel with a thin tin coating. The combination of the titanium nitride coated drain with a separate tin -coated spit shield yields as optimized combination of lifetime and performance.

[0076] In some embodiments, the upper edge and/or the lower edge of the shield may be curved in a concave (curve above tangent line) manner. FIG. 11 shows an arrangement in which a shield 370 has both an upper curved edge 372 and a lower curved edge 374. In addition, instead of using a shield having a substantially flat 2D configuration, the shield may have a 3D configuration. For example, FIG. 12 shows an arrangement in which a shield 380 has a hairpin (V or U) shape such as described above in connection with the scrubber shield. One of ordinary skill in the art provided with this disclosure will appreciate that other configurations are possible.

[0077] 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.

[0078] 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.

[0079] The above description includes examples of multiple embodiments. It is, of course, not possible to describe every conceivable combination of components or methodologies for each of these embodiments, but one of ordinary skill in the art may recognize that many further combinations and permutations of elements of the various embodiments are possible based on the disclosure. Accordingly, the described embodiments are intended to be representative of and encompass all such alterations, modifications, and variations that fall within the spirit and scope of the appended claims. [0080] 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.

[0081] 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.

[0082] 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.

[0083] 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. [0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] The scope of the present disclosure is not intended to be limited by the specific disclosures of preferred embodiments in this section or elsewhere in this specification, and may be defined by claims as presented in this section or elsewhere in this specification or as presented in the future. The language of the claims is to be interpreted broadly based on the language employed in the claims and not limited to the examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive.

[0090] Aspects and implementations of the present disclosure can be further described using the following numbered clauses:

1. Apparatus for generating extreme ultraviolet radiation by irradiating a target material, the apparatus comprising: a source vessel; a target material deposition surface arranged to receive target material deposited from a gas flow when the gas flow passes over the target material deposition surface; a drain in fluid communication with the target material deposition surface, the drain including a drain mouth and a rim surface adjacent the drain mouth; and a shield covering at least a portion of the rim surface and positioned to prevent target material from being ejected back into the gas flow.

2. The apparatus of clause 1 wherein the target material deposition surface is coupled to a surface of a scrubber.

3. The apparatus of clause 2 wherein the surface of the scrubber comprises a plurality of fin structures.

4. The apparatus of clause 1 wherein the shield comprises molybdenum.

5. The apparatus of clause 1 wherein a thickness of the shield is in a range of about 1 mm to about 8 mm.

6. The apparatus of clause 1 wherein the shield comprises titanium zirconium molybdenum.

7. The apparatus of clause 1 wherein the shield comprises stainless steel.

8. The apparatus of clause 1 wherein the target material comprises tin and wherein at least a portion of a surface of the shield is provided with a layer comprising a tin philic material.

9. The apparatus of clause 1 wherein an upper edge of the shield is curved.

10. The apparatus of clause 2 wherein the shield has an upper surface and a side surface with the upper surface being at an angle to the side surface and wherein the shield is oriented in the scrubber so that the upper surface is at an angle with respect to gravity in a range of about 0° to about 45° and the side surface is a plasma-facing surface having an angle with respect to gravity in the range of about 20° to about 70°.

11. The apparatus of clause 1 wherein the target material deposition surface comprises a surface of an exhaust plenum.

12. The apparatus of clause 11 wherein the shield is a substantially planar element which extends over and is spaced away from the drain mouth and is inclined with respect to horizontal.

13. A target material scrubber for an apparatus for generating extreme ultraviolet radiation by irradiating a target material, the target material scrubber comprising: a plurality of target material deposition surfaces arranged such that gas carrying target material passes over the target material deposition surfaces in such a way that target material transfers from the gas to the target material deposition surfaces; a drain positioned such that target material transferred to the target material deposition surfaces flows to the drain, the drain having a rim area; and a shield positioned over at least a portion of the rim area of the drain to prevent target material from being ejected back into the gas.

14. The target material scrubber of clause 13 wherein the scrubber is coupled to a plasma generation volume of the radiation source.

15. The target material scrubber of clause 14 wherein the shield is positioned between the scrubber and the plasma generation volume of the radiation source.

16. Apparatus for generating extreme ultraviolet radiation by irradiating a target material, the apparatus comprising: a chamber; a waste target material management system arranged in the chamber and configured to exhaust gas carrying stray target material, the waste target material handling system including at least one location at which liquid waste target material accumulates while the apparatus is in operation; and a shield arranged over at least a portion of the at least one location at which liquid waste target material accumulates while the apparatus is in operation to prevent waste target material from being ejected back into the gas.

17. A method of manufacturing a semiconductor device comprising: providing a substrate having a surface with a photoresist layer; directing radiation to the surface with the photoresist layer from a radiation source comprising a source vessel, a waste target material management system arranged in the source vessel and configured to exhaust gas carrying stray target material, the waste target material handling system including at least one location at which liquid waste target material accumulates while the radiation source is in operation, and a shield arranged over at least a portion of the at least one location at which liquid waste target material accumulates while the radiation source is in operation to prevent waste target material from being ejected back into the gas 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.

18. The method of clause 17 wherein the waste target material management system surrounds the source vessel.

19. The method of clause 17 wherein the waste target material management system includes a plurality of fins arranged around an interior of the source vessel.

[0091] The above-described aspects and implementations and other implementations are within the scope of the following claims.

Claims

1. Apparatus for generating extreme ultraviolet radiation, the apparatus comprising: a source vessel; a target material deposition surface arranged to receive target material deposited from a gas flow when the gas flow passes over the target material deposition surface; a drain in fluid communication with the target material deposition surface, the drain including a drain mouth and a rim surface adjacent the drain mouth; and a shield covering at least a portion of the rim surface.

2. The apparatus of claim 1 wherein the target material deposition surface is coupled to a surface of a scrubber.

3. The apparatus of claim 2 wherein the scrubber comprises a plurality of fin structures.

4. The apparatus of claim 1 wherein the shield is configured to prevent the target material from being ejected back in to the gas flow.

5. The apparatus of claim 1 wherein a thickness of the shield is in a range of about 1 millimeter (mm) to about 8 mm.

6. The apparatus of claim 1 wherein the shield comprises at least one of titanium, zirconium, and molybdenum.

7. The apparatus of claim 1 wherein the shield comprises stainless steel.

8. The apparatus of claim 1 wherein the target material comprises tin and wherein at least a portion of a surface of the shield is provided with a layer comprising a tin philic material.

9. The apparatus of claim 1 wherein an upper edge of the shield is curved.

10. The apparatus of claim 2 wherein the shield has an upper surface and a side surface with the upper surface being at an angle to the side surface and wherein the shield is oriented in the scrubber so that the upper surface is at an angle with respect to gravity in a range of about 0° to about 45° and the side surface is a plasma-facing surface having an angle with respect to gravity in the range of about 20° to about 70°.

11. The apparatus of claim 1 wherein the target material deposition surface comprises a surface of an exhaust plenum.

12. The apparatus of claim 11 wherein the shield is a substantially planar element which extends over and is spaced away from the drain mouth and is inclined with respect to horizontal.

13. A scrubber for a radiation source comprising: a plurality of target material deposition surfaces arranged such that gas carrying target material passes over the target material deposition surfaces in such a way that the target material transfers from the gas to the target material deposition surfaces;

; and a shield configured to prevent target material from being ejected back into the gas.

14. The scrubber of claim 13 further comprising a drain positioned such that the target material transferred to the target material deposition surface flows to the drain,

15. The scrubber of claim 14 wherein the drain has a rim area, and the shield is positioned over at least a portion of the rim area.

16. The scrubber of claim 13 wherein the scrubber is coupled to a plasma generation volume of the radiation source.

17. The scrubber of claim 16 wherein the shield is positioned between the scrubber and the plasma generation volume of the radiation source.

18. A method of manufacturing a semiconductor device comprising: providing a substrate having a surface with a photoresist layer; directing radiation to the surface with the photoresist layer from a radiation source comprising a source vessel, a waste target material management system arranged in the source vessel and configured to exhaust gas carrying stray target material, the waste target material handling system including at least one location at which liquid waste target material accumulates while the radiation source is in operation, and a shield arranged over at least a portion of the at least one location at which liquid waste target material accumulates while the radiation source is in operation to prevent waste target material from being ejected back into the gas; and removing a portion of the photoresist layer to form a pattern over the substrate.

19. The method of claim 18 wherein the waste target material management system surrounds the source vessel.

20. The method of claim 18 wherein the waste target material management system includes a plurality of fins arranged around an interior of the source vessel.