Apparatus for and method of controlling contaminant dispersal in EUV radiation source

Abstract

Disclosed are systems and methods for producing extreme ultraviolet (EUV) radiation from a target material in a vessel in which gas flows carry target material vapor and debris and deposit some of the target material on surfaces within the vessel including interior surfaces of an exhaust port and in which measures are adopted to reduce the amount of deposited target material that is able to reenter the gas flows.

Description

APPARATUS FOR AND METHOD OF CONTROLLINGCONTAMINANT DISPERSAL IN EUV RADIATION SOURCECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to US Application No. 63 / 571,152, filed March 28,2024, titled APPARATUS FOR AND METHOD OF CONTROLLING CONTAMINANT DISPERSAL IN EUV RADIATION SOURCE, which is incorporated herein by reference in its entirety.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 vessel. 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 thistechnique 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 produced 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 contamination 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 near-normal -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, detectors, and ultimately to a scanner including a reticle. 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. It may, however, be the case that the liquid tin collects at one or more plasma-facing positions inside of the 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 reticles, 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 someconcepts 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, 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 gas flow system arranged to cause a flow of gas through a portion of the chamber, the gas flow system having at least one exhaust outlet positioned in a wall of the chamber, the gas carrying target material as the gas passes through an exhaust outlet, a passageway arranged around at least part of an inner surface of the exhaust outlet, and a heater in thermal communication with the passageway.

[0020] The apparatus may further comprise a controller arranged to control a temperature of the heater in which the apparatus has a first state and a second state, the controller controlling the heater so that the passageway assumes a first temperature below the melting temperature of the target material when the apparatus may be in the first state and so that the passageway assumes a second temperature above the melting temperature of the target material when the apparatus may be in the second state.

[0021] The first state may be a plasma on state in which target material may be irradiated at the irradiation site to generate extreme ultraviolet radiation and the second state may be a plasma off state in which no target material may be irradiated at the irradiation site.

[0022] The apparatus may further comprise a drive laser for irradiating the target material and the first state may be a drive laser on state in which the drive laser generates continuous or pulsed laser radiation and the second state may be a drive laser off state in which the drive laser does not generate continuous or pulsed laser radiation.

[0023] The apparatus may further comprise a gas channel in thermal communication with the passageway. The heater may comprise at least one electrically resistive in thermal communication with the passageway. The at least one electrically resistive wire may be wound around an outer periphery of the passageway. The at least one electrically resistive wire may be arranged in a serpentine pattern around an outer periphery of the passageway. A lateral spacing of adjacent portions of the at least one electrically resistive wire around that outer periphery of the passageway may be varied.

[0024] According to an aspect of an embodiment there is disclosed an apparatus for generating extreme ultraviolet radiation by irradiating a target material, the apparatus having a first state and a second state, the apparatus comprising a chamber, a gas flow system arranged to cause a flow of gas through a portion of the chamber, the gas flow system having at least one exhaust outlet positioned in a wall of the chamber, the gas carrying target material as the gas passes through an exhaust outlet, a passageway arranged around at least part of an inner surface of the exhaust outlet, a gas channel in thermal communication with the passageway, a heater in thermal communication with the passageway,the heater comprising at least one electrically resistive in thermal communication with the passageway, and a controller arranged to control a temperature of the heater, the controller controlling the heater so that the passageway assumes a first temperature below the melting temperature of the target material when the apparatus may be in the first state and so that the passageway assumes a second temperature above the melting temperature of the target material when the apparatus may be in the second state.

[0025] The first state may be a plasma on state in which target material may be irradiated at the irradiation site to generate extreme ultraviolet radiation and the second state may be a plasma off state in which no target material may be irradiated at the irradiation site.

[0026] The apparatus may further comprise a drive laser for irradiating the target material and the first state may be a drive laser on state in which the drive laser generates continuous or pulsed laser radiation and the second state may be a drive laser off state in which the drive laser does not generate continuous or pulsed laser radiation.

[0027] The at least one electrically resistive wire may be arranged as windings around an outer periphery of the passageway. A density of the windings may be varied so that positions on the passageway acquiring greater amounts of target material are provided with more heat than positions on the passageway acquiring lower amounts of target material. The at least one electrically resistive wire may be arranged in a serpentine pattern on an internal surface of the passageway. The spacing of turns of the electrically resistive wire in the serpentine pattern may vary so that positions on the passageway acquiring greater amounts of target material are provided with more heat than positions on the passageway acquiring lower amounts of target material.

[0028] According to an aspect of an embodiment there is disclosed a method of generating extreme ultraviolet radiation using a source in which laser irradiation of a target material occurs in a chamber having an exhaust outlet and a passageway, the method comprising controlling a temperature of at least part of the passageway to be below the melting temperature of the source may be in a first state and controlling the temperature of the at least part of the passageway to be above the melting temperature of the target material at least part of a time when the source may be in a second state.

[0029] The first state may be a plasma on state in which the source irradiates target material to generate extreme ultraviolet radiation and the second state may be a plasma off state in which the source does not irradiate target material at the irradiation site.

[0030] The source may further comprise a drive laser for irradiating the target material, the first state may be a drive laser on state in which the drive laser generates continuous or pulsed laser radiation, and the second state may be a drive laser off state in which the drive laser does not generate continuous or pulsed laser radiation.

[0031] According to an 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 achamber, a gas flow system arranged to cause a flow of gas through a portion of the chamber, the gas flow system having at least one exhaust outlet positioned in a wall of the chamber, the gas carrying target material as the gas passes through an exhaust outlet, a passageway arranged around at least part of an inner surface of the exhaust outlet, and a heater in thermal communication with the passageway 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.

[0032] 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.BRIEF DESCRIPTION OF THE DRAWINGS

[0033] 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.

[0034] FIG. 1 is a schematic diagram of an EUV source.

[0035] FIG. 2A is a side view diagram of an EUV source having an exhaust port in accordance with an aspect of an embodiment.

[0036] FIG. 2B is a side view diagram of an EUV source having an exhaust port in accordance with an aspect of an embodiment.

[0037] FIG. 3 is a perspective view of a heater assembly for a passageway for an EUV source in accordance with an aspect of an embodiment.

[0038] FIG. 4A is a front perspective view of a heater assembly for a passageway for an EUV source in accordance with an aspect of an embodiment.

[0039] FIG. 4B is a side perspective view of a heater assembly for a passageway for an EUV source in accordance with an aspect of an embodiment.

[0040] FIG. 5A is a perspective view of a portion of a passageway for an exhaust port for anEUV source in accordance with an aspect of an embodiment.

[0041] FIG. 5B is enlarged view of a portion of FIG. 5A.

[0042] FIG. 6 is a functional block diagram of a system for controlling a heater assembly for a passageway for an EUV source in accordance with an aspect of an embodiment.

[0043] FIG. 7 is a timing diagram for operation of a passageway in accordance with an aspect of an embodiment.

[0044] FIG. 8 is a flow chart for a method of operating a passageway in accordance with an aspect of an embodiment.

[0045] FIG. 9 is a flow chart for a method of operating a passageway in accordance with an aspect of an embodiment.

[0046] FIG. 10 is a flow chart for a method of operating a passageway in accordance with an aspect of an embodiment.

[0047] It is noted that the invention is not limited to the specific embodiments shown in the drawings. Such embodiments are depicted 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

[0048] 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.

[0049] 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.

[0050] 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 drive laser source 22, which may for example be a pulsed gas discharge CO2 laser source producing a beam 12 of radiation at from about 1 pm 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.

[0051] 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. 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 anirradiation region even at times when no irradiation is actually occurring. The EUV light source may also include a beam steering system 32.

[0052] In the system shown, the components are arranged so that the droplets 14 travel substantially horizontally. The direction from the drive laser 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 degrees (horizontal) and 0 degrees (vertical).

[0053] The EUV radiation source 10 may also include an EUV light source controller system60, 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.

[0054] 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.

[0055] 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 EEC, ZrC, SisN4or 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 calledthe 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.

[0056] As mentioned, in some embodiments gas flows are established within the chamber intended to keep target material debris from accumulating on the plasma-facing surfaces within the chamber. 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 debris and vapor out of the source through an exhaust.

[0057] When the collector-protecting flows change direction to leave through an exhaust outlet, the buffer gas, e.g., hydrogen, carrying target material debris impinges on an upper portion of the exhaust outlet. This results in large amounts of target material deposition on the chamber liner and the throat of the exhaust outlet. Because the surfaces in the chamber are typically at temperatures well below the melting temperature of the target material, any target material that accumulates due to deposition on these surfaces will remain in place.

[0058] An excessive amount of target material debris accumulating on these surfaces can obstruct the EUV light cone extending from the collector as its base to the intermediate focus as its apex. It also increases the risk of formation of tin contamination which can extend into the EUV light cone and compromise source performance. Also, the accumulated target material may be melted by the drive laser during times when the laser is firing but not irradiating droplets. This increases the risk of spitting. It would thus be advantageous to manage target material accumulation around these surfaces, and, in particular, in and around the exhaust outlet.

[0059] One measure for managing target material debris accumulation in and around the exhaust outlet requires the throat area to be manually cleaned as part of an invasive service action. It would be advantageous to be able to avoid having to perform such service actions.

[0060] It would also be advantageous if the measures adopted are active, that is, be able to respond to changes in operational parameters that affect target material accumulation such as changes in flow recipe, plasma configuration, or drive laser power.

[0061] According to an aspect of an embodiment a thermally-cycled module is provided to manage target material accumulation and draining in the vicinity of the exhaust outlet. This thermally- cycled module is referred to herein as a target material passageway. In one embodiment the target material passageway is implemented as a liner insert that enables active control of the exhaust surface temperatures. For example, the exhaust surface temperatures can be controlled depending on whetheror not the source is producing plasma. The target material passageway may include heating elements such as electric resistive heaters that can be activated as needed to regulate the temperature of the target material passageway plasma-facing surfaces. In some embodiments mounting and stand-off features are provided that keep the target material passageway at a fixed distance from a water cooled or a gas cooled upper liner (UL) provided to absorb excess heat.

[0062] In one implementation the target material passageway has two modes of operation or states. The target material passageway operates in a first mode or cold mode when the source is producing plasma. In this first mode, the heaters are off and any heat coupled to the target material passageway from the plasma is transferred across a gap established by a channel carrying a buffer gas gap to the water-cooled or gas cooled UL. The heat transfer from the target material passageway to the UL keeps the temperature of the target material passageway below the melting temperature of the target material and allows target material to accumulate on the exhaust port surface. The low target material passageway temperature caused by heat transfer to the UL also reduces or eliminates the risk of spitting by ensuring accumulated target material remains solid and so not susceptible to spitting.

[0063] The target material passageway operates in a second mode or hot mode when the source is not producing plasma. The heaters are on and coupling enough heat into the target material passageway to maintain the target material passageway surface temperature above the target material melting temperature while accounting for the additional heat loss across the channel to the UL. In this mode, any target material that accumulates on the target material passageway during plasma production is dripped off to an external accumulation location and away from any plasma-facing surfaces

[0064] FIG. 2A shows a source configuration according to an aspect of an embodiment having a chamber 26 defined by liner 27 and an inlet 100 through a collector 30. As also shown in FIG. 2A, the circumference or inner periphery of an exhaust port 400 is provided with a passageway 420. The passageway 420 is provided with a heater assembly 430 at the outer periphery of the passageway 420. In some embodiments, the heater assembly 430 and the passageway 420 are integral parts forming a single assembly. The passageway 420 is normally maintained at a temperature below the melting point of the target material so the target material accumulates on the passageway 420 in a solid form. When the heater assembly 430 of the passageway 420 is activated, target material which has accumulated on the passageway 420 in solid form melts, flows along the surface of the passageway 420, and drains through a drain 410 to a drain module 415. FIG. 2B is a depiction of the arrangement of FIG. 2A but from the perspective of looking directly into the exhaust port 400.

[0065] The heating element assembly 430 can be configured in accordance with any one of many possible variations. As an example, FIG. 3 shows a heater assembly 430 made up of a single resistive element 435 configured to be arranged in a serpentine pattern around the edge of the passageway. FIG. 4A is a front view of another possible arrangement of the resistive element for theheater assembly 430. FIG. 4B is a side view ofthe arrangement of FIG. 4A. As can be seen, the resistive elements are configured to be wrapped around the throat circumferentially.

[0066] In the above examples, the resistive element 435 is configured as a single resistive element. It will be apparent to one of ordinary skill in the art that it is possible to have arrangements having a single resistive element which is continuously placed in thermal communication with the passageway. It will also be apparent to one of ordinary skill in the art that it is possible to have arrangements in which there are multiple resistive elements which can be powered separately. This could be exploited to provide zonal heating control, that is, permit the application of more or less heat to different parts or zones of the passageway.

[0067] It is also advantageous in some implementations to take into account that more or less heating may be needed at some locations in determining the pattern for the positioning of the resistive element or elements around the edges of the exhaust port. In other words, the density of turns of the resistive element or elements can advantageously be selected so that there is a higher density of resistive element or elements in the areas where more heat is required and a lower density of resistive element or elements in areas where less heat is necessary.

[0068] In accordance with another aspect of an embodiment, the passageway 420 is placed in thermal communication with a gas channel as shown in FIGS. 5 A and 5B with FIG. 5B being a magnification of the inset in the dotted rectangular box in FIG. 5A. As better seen in FIG. 5B, the passageway 420 is in thermal communication with a channel 510 through which buffer gas is caused to flow. The channel 510 is in turn in thermal communication with an upper liner 500 through which a cooling fluid such as water flows or gas flows. This arrangement provides active cooling of the passageway 420 so that when the active application of heat by the resistive element is discontinued the passageway 420 will rapidly transition from above the melting temperature of the target material to below the melting temperature of the target material.

[0069] The thermal conduction resistance of the gap or channel 510 between the target material passageway 420 and the upper liner 500 increases with increasing gap thickness, dimension D in FIG. 5B. If the dimension D is too large then the thermal resistance of the channel 510 will be too high to ensure that the temperature of the target material passageway 420 will stay below the target material melting temperature when the source is producing plasma. If D is too small, the thermal resistance of the channel 510 will be too low to ensure that temperatures of the target material passageway 420 can be maintained above target material melting temperature without requiring excessive heater power. According to one aspect of an embodiment the width D of the channel 510 is selected to be in a range of about 3 millimeters (mm) to about 8 mm.

[0070] The buffer gas flowing through the channel 510 may be carbon dioxide, helium, or hydrogen. The flow rate for the gas in the channel 510 is selected to transport sufficient amounts of heat although the primary path for heat flow will be transverse to the direction of gas flow. In accordancewith an aspect of an embodiment, the gas flow may be, for example, in the range of about one percent to about ten percent of the total system flow. In some implementations a flow of less than about one percent of total system flow incurs a risk of failing to provide sufficient cooling. In some implementations a flow of more than about ten percent total system flow incurs the risk of unduly disturbing the overall flow patterns in the chamber.

[0071] The heater assembly 430 can be powered on and off in accordance with any one of a variety of control strategies. For example, activation of the heater assembly 430 and elevation of the temperature of the passageway 420 could be part of scheduled routine maintenance after a given number of pulses (for example, several gigapulses) or a given duration of machine time operation.

[0072] Alternatively, or in addition, as shown in FIG. 6, the heater assembly 430 could be operated under the control of a heater assembly controller 450. The heater assembly controller 450 would be arranged to have a first state in which it supplies power to the heater assembly 430 and a second state in which it does not supply power to the heater assembly 430. The heater assembly for controller 450 can operate in response to a source state signal generated by the EUV light source controller system 60. The source state signal may be indicative of whether the source is in a first state or a second state. The first state may correspond to a state in which the drive laser is on, i.e., generating a continuous or pulsed drive laser beam, and the second state may correspond to a state in which the drive laser is off, i.e., not generating a continuous or pulsed drive laser beam. The first state may correspond to a state in which the drive laser is on has recently been on, i.e., generating a continuous or pulsed drive laser beam, and the second state may correspond to a state in which the drive laser is has been off, i.e., not generating a continuous or pulsed drive laser beam, for a period of time having a predetermined duration. The first state may correspond to a state in the source is producing EUV radiation, i.e., in which the drive laser is on and the laser beam is striking droplets, and the second state may correspond to a state in which the EUV source is not producing EUV radiation either because the drive laser is off or because the laser beam is missing the droplets. One of ordinary skill in the art will appreciate that other control procedures may be implemented.

[0073] In general the amount of time the target material passageway 420 is operating in the first mode or the second mode is also selectable. This may be regarded as selecting the frequency and duration of a target material drip-off period, that is, the duration of the interval when target material passageway is operating in the second mode. If the target material passageway 420 is cycled to operate in the second mode too frequently or for too long, the overall amount of EUV radiation produced by the source during a given period will decrease. If the target material passageway 420 is not cycled frequently enough, target material debris could accumulate to a thicknesses having a thermal resistance as a conduction path that is so high that the target material debris accumulating on the target material passageway 420 does not solidify. Thus, choosing the proper balance of durations and frequencies forsecond mode operation will in general involve balancing the trade-off between target material accumulation (heater off), target material draining (heater on), and overall EUV output.

[0074] FIG. 7 is a timing diagram for an example of operation in which the x-axis is time in arbitrary units. The source has a first state (e.g., plasma on or plasma generation state) and a second state (e.g., plasma off or plasma non-generation state) as described above. The temperature of the passageway 420 is below a melting temperature of the target material when the source is in the first state and the drive laser is on. When the source transitions to a second state, the passageway 420 is heated so that the temperature of the drip off throat 420 rises to above the target material melting temperature. Then, when the source transitions back to a first state, the temperature of the passageway 420 is permitted to drop below the target material melting temperature. The curved line breaks are intended to indicate that the duration of the interval in which the source is in the first state will in general be substantially longer than the interval in which the source is in the second state. The duration of the first state may be measured in terms of time taken to generate a given number of pulses, for example, several gigapulses, i.e., about 5 hours to about 20 hours. The duration of the second state may be on the order of tens of minutes, for example, in the range of about 10 minutes to about 90 minutes.

[0075] As an example of temperatures TTH and TTL as indicated in FIG. 7, using tin as a target material which, as mentioned, has a melting temperature of about 232 °C, the high temperature TTH may be in a range, for example, of about 240 °C up to about 290 °C. The low temperature TTL may be in a range, for example, of about 225 °C down to 180 °C and even lower.

[0076] FIG. 8 is a flow chart describing an example of a method of controlling the temperature of a passageway in accordance with an aspect of an embodiment.. In a step S20 the passageway temperature is made to be less than the target material melting temperature. This may be accomplished, for example, by turning off a heater that is in thermal communication with the passageway. In a step S30 the source starts producing EUV radiation. In a step S40 the source discontinues production of EUV radiation. Then, in a step S50, the passageway temperature is made greater than the target material melting temperature. This may be for a time period having a predetermined duration. Step S50 may be accomplished, for example, by turning on a heater that is in thermal communication with the passageway. The process then reverts to step S20. This could be after a period of time of predetermined duration which is known to be sufficient to melt target material from the surface where it has accumulated. This could also be in response to a signal that it is necessary to make the source ready to resume production of EUV radiation.

[0077] As mentioned, other control procedures may be employed. FIG. 9 is a flow chart describing an example of a procedure in which the state of the source is based on whether the drive laser is on, that is, producing continuous or pulsed laser radiation, or off. In the flow chart of FIG. 9 steps which are essentially the same as those in the procedure described in connection with FIG. 8 have similar reference numbers.. In a step S35, however, the drive laser is turned on. Then, at a later time, ata step S45, the drive laser is turned off. Then in step S50 the passageway temperature is made greater than the target material melting temperature. This may be for a predetermined duration or may be until a signal is received indicating that the source is about to be placed back into operation.

[0078] FIG. 10 is a flow chart showing an example of a procedure in which the state of the source is based on whether the drive laser is on or off as in the procedure of FIG. 9. Thus, in a step S35, the drive laser is turned on. Then, at a later time, at a step S45, the drive laser is turned off. In a step S47, however, it is determined whether the drive laser has been off formore than a predetermined period of time. Alternatively or in addition it may be determined in step S47 whether the laser-off period is likely to be long enough to permit melting and clearing of target material on the passageway. This may be a signal explicitly indicating that the laser-off period will be of sufficient duration or may be based on other signals from which the likely duration of the machine laser-off period may be inferred. This prevents needless cycling of the heaters or needless prolongation of source downtime. Then in step S50 the passageway temperature is made greater than the target material melting temperature. This may be for a predetermined duration or may be until a signal is received indicating that the source should be placed in a state of readiness for continued operation.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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 implementationsdescribed 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] The implementations can be further described using the following clauses.1. Apparatus for generating extreme ultraviolet radiation by irradiating a target material, the apparatus comprising: a chamber; a gas flow system arranged to cause a flow of gas through a portion of the chamber, the gas flow system having at least one exhaust outlet positioned in a wall of the chamber, the gas carrying target material as the gas passes through an exhaust outlet; a passageway arranged around at least part of an inner surface of the exhaust outlet; and a heater in thermal communication with the passageway.2. The apparatus of clause 1 further comprising a controller arranged to control a temperature of the heater in which the apparatus has a first state and a second state, the controller controlling the heater so that the passageway assumes a first temperature below the melting temperature of the target material when the apparatus is in the first state and so that the passageway assumes a second temperature above the melting temperature of the target material when the apparatus is in the second state.3. The apparatus of clause 2 wherein the first state is a plasma on state in which target material is irradiated at the irradiation site to generate extreme ultraviolet radiation and the second state is a plasma off state in which no target material is irradiated at the irradiation site.4. The apparatus of clause 2 further comprising a drive laser for irradiating the target material and wherein the first state is a drive laser on state in which the drive laser generates continuous or pulsed laser radiation and the second state is a drive laser off state in which the drive laser does not generate continuous or pulsed laser radiation.5. The apparatus of clause 1 further comprising a gas channel in thermal communication with the passageway.6. The apparatus of clause 1 wherein the heater comprises at least one electrically resistive in thermal communication with the passageway.7. The apparatus of clause 6 wherein the at least one electrically resistive wire is wound around an outer periphery of the passageway.8. The apparatus of clause 6 wherein the at least one electrically resistive wire is arranged in a serpentine pattern around an outer periphery of the passageway.9. The apparatus of clause 6 wherein a lateral spacing of adjacent portions of the at least one electrically resistive wire around that outer periphery of the passageway is varied.10. Apparatus for generating extreme ultraviolet radiation by irradiating a target material, the apparatus having a first state and a second state, the apparatus comprising: a chamber;a gas flow system arranged to cause a flow of gas through a portion of the chamber, the gas flow system having at least one exhaust outlet positioned in a wall of the chamber, the gas carrying target material as the gas passes through an exhaust outlet; a passageway arranged around at least part of an inner surface of the exhaust outlet; a gas channel in thermal communication with the passageway; a heater in thermal communication with the passageway, the heater comprising at least one electrically resistive in thermal communication with the passageway; and a controller arranged to control a temperature of the heater, the controller controlling the heater so that the passageway assumes a first temperature below the melting temperature of the target material when the apparatus is in the first state and so that the passageway assumes a second temperature above the melting temperature of the target material when the apparatus is in the second state.11. The apparatus of clause 10 wherein the first state is a plasma on state in which target material is irradiated at the irradiation site to generate extreme ultraviolet radiation and the second state is a plasma off state in which no target material is irradiated at the irradiation site.12. The apparatus of clause 10 further comprising a drive laser for irradiating the target material and wherein the first state is a drive laser on state in which the drive laser generates continuous or pulsed laser radiation and the second state is a drive laser off state in which the drive laser does not generate continuous or pulsed laser radiation.13. The apparatus of clause 12 wherein the at least one electrically resistive wire is arranged as windings around an outer periphery of the passageway.14. The apparatus of clause 13 wherein a density of the windings varies so that positions on the passageway acquiring greater amounts of target material are provided with more heat than positions on the passageway acquiring lower amounts of target material.15. The apparatus of clause 12 wherein the at least one electrically resistive wire is arranged in a serpentine pattern on an internal surface of the passageway.16. The apparatus of clause 15 wherein a spacing of turns of the electrically resistive wire in the serpentine pattern varies so that positions on the passageway acquiring greater amounts of target material are provided with more heat than positions on the passageway acquiring lower amounts of target material.17. A method of removing debris generated in a radiation source vessel having an exhaust outlet and a passageway, the method comprising: controlling a temperature of at least part of the passageway to be below a melting temperature of the debris is in a first state; and controlling the temperature of the at least part of the passageway to be above the melting temperature of the debris at least part of a time when the radiation source vessel is in a second state.18. The method of clause 17 wherein the first state is a plasma generation state in which target material is irradiated to generate extreme ultraviolet radiation at an irradiation site and the second state is a plasma non-generation state in which the target material is not irradiated.19. The method of clause 17 in which the radiation source vessel is coupled to a drive laser for irradiating the target material and wherein the first state is a drive laser on state in which the drive laser generates continuous or pulsed laser radiation and the second state is a drive laser off state in which the drive laser does not generate continuous or pulsed laser radiation.20. 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 gas flow system arranged to cause a flow of gas through a portion of the chamber, the gas flow system having at least one exhaust outlet positioned in a wall of the chamber, the gas carrying target material as the gas passes through an exhaust outlet, a passageway arranged around at least part of an inner surface of the exhaust outlet, and a heater in thermal communication with the passageway 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.

[0093] The above-described implementations and other implementations are within the scope of the following claims.

Claims

CLAIMS1. A radiation source comprising: a source vessel; a gas flow system having at least one exhaust outlet positioned in a wall of the source vessel; a passageway arranged around at least part of an inner surface of the exhaust outlet; and a heater in thermal communication with the passageway.

2. The radiation source of claim 1 further comprising a controller arranged to control a temperature of the heater in which the radiation source has a first state and a second state, the controller controlling the heater so that the passageway assumes a first temperature below a melting temperature of target material when the radiation source is in the first state and so that the passageway assumes a second temperature above the melting temperature of the target material when the radiation source is in the second state.

3. The radiation source of claim 2 wherein the first state is a plasma on state in which the target material is irradiated at an irradiation site to generate extreme ultraviolet radiation and the second state is a plasma off state in which no target material is irradiated at the irradiation site.

4. The radiation source of claim 2 further comprising a drive laser for irradiating the target material and wherein the first state is a drive laser on state in which the drive laser generates continuous or pulsed laser radiation and the second state is a drive laser off state in which the drive laser does not generate continuous or pulsed laser radiation.

5. The radiation source of claim 1 further comprising a gas channel in thermal communication with the passageway.

6. The radiation source of claim 1 wherein the heater comprises at least one electrically resistive in thermal communication with the passageway.

7. The radiation source of claim 6 wherein the at least one electrically resistive wire is wound around an outer periphery of the passageway.

8. The radiation source of claim 6 wherein the at least one electrically resistive wire is arranged in a serpentine pattern around an outer periphery of the passageway.

9. The radiation source of claim 6 wherein a lateral spacing of adjacent portions of the at least one electrically resistive wire around that outer periphery of the passageway is varied.

10. Apparatus for generating extreme ultraviolet radiation by irradiating a target material, the apparatus having a first state and a second state, the apparatus comprising: a source vessel; a gas flow system arranged to cause a flow of gas through a portion of the source vessel, the gas flow system having at least one exhaust outlet positioned in a wall of the source vessel, the gas carrying debris as the gas passes through an exhaust outlet; a passageway arranged around at least part of the source vessel; a gas channel in thermal communication with the passageway; a heater in thermal communication with the passageway, the heater comprising at least one electrically resistive in thermal communication with the passageway; and a controller arranged to control a temperature of the heater, the controller controlling the heater so that the passageway assumes a first temperature below a melting temperature of the target material when the apparatus is in the first state and so that the passageway assumes a second temperature above the melting temperature of the target material when the apparatus is in the second state.

11. The apparatus of claim 10 wherein the first state is a plasma on state in which the target material is irradiated at an irradiation site to generate the extreme ultraviolet radiation and the second state is a plasma off state in which no target material is irradiated at the irradiation site.

12. The apparatus of claim 10 further comprising a drive laser for irradiating the target material and wherein the first state is a drive laser on state in which the drive laser generates continuous or pulsed laser radiation and the second state is a drive laser off state in which the drive laser does not generate continuous or pulsed laser radiation.

13. The apparatus of claim 12 wherein the source vessel includes a liner coupled to the passageway, and a portion of the liner is separate from a portion of the passageway.

14. The apparatus of claim 13 wherein the gas channel is defined between the portion of the liner and the portion of the passageway.

15. The apparatus of claim 13 wherein the portion of the liner is separate from the portion of the passageway in a range from about 3 millimeters (mm) to about 8 mm.

16. The apparatus of claim 15 further comprising a drain coupled to the passageway.

17. A method of removing debris generated in a radiation source vessel having an exhaust outlet and a passageway, the method comprising: controlling a temperature of at least part of the passageway to be below a melting temperature of the debris is in a first state; and controlling the temperature of the at least part of the passageway to be above the melting temperature of the debris at least part of a time when the radiation source vessel is in a second state.

18. The method of claim 17 wherein the first state is a plasma generation state in which target material is irradiated to generate extreme ultraviolet radiation at an irradiation site and the second state is a plasma non-generation state in which the target material is not irradiated.

19. The method of claim 17 in which the radiation source vessel is coupled to a drive laser for irradiating target material and wherein the first state is a drive laser on state in which the drive laser generates continuous or pulsed laser radiation and the second state is a drive laser off state in which the drive laser does not generate continuous or pulsed laser radiation.

20. 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 gas flow system arranged to cause a flow of gas through a portion of the chamber, the gas flow system having at least one exhaust outlet positioned in a wall of the chamber, the gas carrying target material as the gas passes through an exhaust outlet, a passageway arranged around at least part of an inner surface of the exhaust outlet, and a heater in thermal communication with the passageway 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.

Images