Apparatus and method for controlling debris in EUV light sources

Abstract

An EUV system is disclosed that includes provisions for accumulating target material fragments in liquid form, wherein the target material is blocked from being spit onto an optical element and wherein the target material can be caused to solidify and then transported to a location where the target material can be melted and allowed to drain away without contaminating a collector.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Application No. 62 / 648,505, filed on March 27, 2018, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to an apparatus and method for generating extreme ultraviolet ("EUV") radiation from a plasma generated by discharge or laser ablation of a target material in a container. In such applications, optical elements are used, for example, to collect and direct radiation for semiconductor lithography and inspection. Background Art

[0004] Extreme ultraviolet radiation (eg, electromagnetic radiation having a wavelength of about 50 nm or less (sometimes also referred to as soft X-rays), and including radiation having a wavelength of about 13.5 nm) can be used in photolithography processes to produce extremely small features in substrates such as silicon wafers.

[0005] Methods for generating EUV radiation include converting a target material into a plasma state. The target material preferably includes at least one element having one or more emission lines in the EUV portion of the electromagnetic spectrum, such as xenon, lithium, or tin. The target material may be a solid, liquid, or gas. In one such method, commonly referred to as laser produced plasma ("LPP"), the desired plasma may be produced by irradiating a target material having the desired line-emitting element with a laser beam.

[0006] One LPP technique involves generating droplets of a target material and irradiating at least some of the droplets with one or more pulses of laser radiation. Such an LPP source generates EUV radiation by coupling laser energy into a target material having at least one EUV emitting element, thereby producing a highly ionized plasma with an electron temperature of tens of eV.

[0007] For this process, the plasma is typically generated in a sealed container (e.g., a vacuum chamber), and the resulting EUV radiation is monitored using various types of metrology equipment. In addition to generating EUV radiation, the process used to generate the plasma typically generates undesirable byproducts within the plasma chamber, which may include out-of-band radiation, energetic ions, and fragments such as atoms and / or clumps / microdroplets of residual target material.

[0008] Energetic radiation is emitted from the plasma in all directions. In one common arrangement, a near-normal incidence mirror (often referred to as a "collector mirror" or simply "collector") is positioned to collect, direct, and in some arrangements focus at least a portion of the radiation to an intermediate location. The collected radiation can then be relayed from the intermediate location to a set of optical elements, a reticle, a detector, and ultimately to a silicon wafer.

[0009] In the EUV part of the spectrum, it is generally considered necessary to use reflective optics for the optics in a system comprising a collector, an illuminator and a projection optics box. These reflective optics can be implemented as normal incidence optics or grazing incidence optics as described above. At the wavelengths involved, the collector is advantageously implemented as a multilayer mirror ("MLM"). As the name suggests, this MLM typically consists of alternating layers of material (MLM stack) on a base or substrate. Even if the system optics are not implemented as MLMs, the system optics can be configured as coated optics.

[0010] Optical elements and especially collectors must be placed inside the container together with the plasma to collect and redirect EUV radiation. The environment inside the chamber is hostile to the optical elements and thus limits their service life, for example due to reduced reflectivity. The optical elements inside the environment may be exposed to energetic ions or particles of the target material. Particles of the target material (which are essentially debris generated during the laser vaporization process) can contaminate the exposed surfaces of the optical elements. Particles of the target material can also cause physical damage and local heating of the MLM surface.

[0011] In some systems, H2 gas at a pressure in the range of about 0.5 to about 3 mbar is used in the vacuum chamber as a buffer gas for debris reduction. Without the gas, it would be difficult to adequately protect the collector from target material debris ejected from the irradiation area at vacuum pressure. Hydrogen is relatively transparent to EUV radiation at a wavelength of about 13.5 nm and is therefore preferred over other candidate gases such as He, Ar, or other gases with higher absorption at about 13.5 nm.

[0012] H2 gas is introduced into the vacuum chamber to slow down the high-energy fragments (ions, atoms and clusters) of the target material generated by the plasma. The fragments are slowed down by collisions with gas molecules. For this purpose, a flow of H2 is used, which can also go against the trajectory of the fragments and away from the collector. This is used to reduce damage to the deposited, injected and sputtered target materials on the optical coating of the collector.

[0013] Nonetheless, one of the most challenging issues in sources such as the one described is the management of residual target material. The process of converting the target material into vapor and particles deposits the residual target material wherever there is an unobstructed path between the radiation site and the surface and on every surface in the exhaust path entraining the residual target material. For example, if such a gas is pumped across the tops of the vanes in the chamber and to the mechanical pump, material will soon be deposited on all the cold metal parts. If the target material is tin, this will result in the growth of tin wool, which will fall onto the collector optics and block the exhaust path.

[0014] Still using tin as an example of a target material, a technique for controlling tin diffusion involves capturing tin from vapor or particles on a surface heated above the melting point of tin. The tin melts here (or remains molten) and is caused to flow to a capture container. However, liquid tin tends to erupt or "spit" in the presence of hydrogen radicals (such as those found in EUV chambers), and this ejected tin can hit the collector. This is a major factor in the degradation of collector performance. Secondly, liquid tin does not usually flow as expected. For example, structures within the chamber (such as blades and grooves of a scrubber for removing some or all of the tin vapor in the chamber) can cause liquid tin to drip onto the collector. In addition, the scrubber grooves may overflow, and the liquid tin may flow down the back of the blades, causing a thermal short circuit (i.e., an unintended heat conduction path) and blocking the flow path to the capture container. In addition, liquid tin is highly corrosive and causes, for example, failure of an electric heater used to keep the collection surface above the melting point of tin. Furthermore, the flow restrictions caused by tin accumulation cause the gas to find its way through smaller spaces in the vanes and collector, greatly increasing collector degradation due to tin deposition.

[0015] As described above, scrubbers can be added to areas such as the tops of blades to capture the carried tin by precipitating it from the steam. The scrubber surface can be kept above the melting point of tin so that the liquid tin can flow down the blades and into the receiver. However, the liquid tin in the scrubber may still be spit onto the collector and drip onto the collector from the grooves again, thereby exacerbating collector degradation. In addition, it is difficult to keep the scrubber above the melting point of tin. When the temperature of the scrubber is lower than the melting point of tin, the tin solidifies and blocks the scrubber. Changing the geometry of the scrubber by, for example, changing the size and inclination of the scrubber blades can improve performance, but the tendency of the scrubber to spit on the collector or onto a cold surface and block the exhaust cannot be completely eliminated.

[0016] The process of generating EUV light may also cause the target material to be deposited on the walls of the container. Controlling the deposition of target material on the walls of the container is important to achieve an acceptable long lifetime of EUV sources placed in production. Likewise, managing the flux of target material from the radiation site is also important to ensure that the waste target material mitigation system works as expected. Summary of the invention

[0017] A simplified overview of one or more embodiments is given below to provide a basic understanding of the embodiments. This overview is not an exhaustive overview of all contemplated embodiments, and is not intended to identify key or important elements of all embodiments, nor is it intended to set limitations on the scope of any or all embodiments. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to a more detailed description presented later.

[0018] According to one aspect, different tin management techniques are used for different portions of the "tin path" (i.e., the path from the chamber liner to the imaging relay mirror that redirects light out of the chamber). A combination of solid and liquid tin techniques are used with the exhaust manifold to manage tin distribution and collection. Zones in the exhaust gas stream are identified, and appropriate techniques for treating the exhaust gas stream are used in each of these zones according to their different requirements.

[0019] According to another aspect of the embodiment, an apparatus for generating EUV radiation is disclosed, the apparatus comprising: a container and a residual target material collection surface having a first position and a second position, at the first position, the residual target material collection surface is arranged to collect residual target material from the irradiation area, the second position is shielded between the interior of at least a portion of the wall of the container, and at the second position, the residual target material collection surface is arranged to release the residual target material collected at the first position; and a temperature controller, arranged to maintain the residual target material collection surface below the melting temperature of the target material at the first position and above the melting temperature of the target material at the second position. The residual target material collection surface may include a surface of a belt. The belt may be cooled at the first position and heated at the second position. The apparatus may also include at least one scrubber, at least one scrubber positioned adjacent to the belt at the second position and arranged to remove residual target material from the belt. The at least one scrubber may be positioned so that the residual target material removed from the belt flows to a receiver by gravity. The apparatus may also include a chamber exhaust manifold in fluid communication with the chamber. The chamber exhaust manifold may have a liner, and at least a portion of the liner may be heated. The residual target material collection surface may include a shield. The shield may be cooled in a first position and heated in a second position. The shield may be arranged to pivot to move from the first position to the second position. The shield may be arranged to move laterally from the first position to the second position. The second position may be selected so that the molten residual target material flows from the shield to the receiver by gravity. The apparatus may also include a chamber exhaust manifold in fluid communication with the chamber. The chamber exhaust manifold may have a liner, and at least a portion of the liner may be heated.

[0020] According to one aspect of one embodiment, a method of controlling residual target material in an apparatus for generating EUV radiation is disclosed, the method comprising the steps of accumulating residual target material on a surface at a first position, the temperature of the surface being below the melting temperature of the target material, moving the surface to a second position, at the second position, the temperature of the surface being above the melting temperature of the residual target material to melt the residual target material, and removing the melted residual target material from the surface. The step of removing the melted residual target material from the surface may include scraping the melted residual target material from the surface. The step of removing the melted residual target material from the surface may include causing the melted residual target material to flow from the surface. The step of causing the removed melted residual target material to flow to a receiver may also be present after the removing step.

[0021] Further embodiments, features, and advantages of the present invention as well as the structure and operation of various embodiments are described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1is a schematic, non-scale illustration of the overall broad concept of a laser produced plasma EUV radiation source system according to one aspect of the present invention.

[0023] Figure 2 is a non-scale view showing a possible arrangement of a container and exhaust system for use in a laser produced plasma EUV radiation source system according to one aspect of the present invention.

[0024] Figure 3 is a non-scale view showing a possible arrangement of a target material control system for a container used in a laser produced plasma EUV radiation source system according to one aspect of the present invention.

[0025] Figure 4A is a non-scale view showing a possible arrangement of a target material control system for a throat of a vessel used in a laser produced plasma EUV radiation source system according to one aspect of an embodiment of the present invention.

[0026] Figure 4B is a non-scale view showing another possible arrangement of a target material control system for a throat of a vessel used in a laser produced plasma EUV radiation source system according to an aspect of an embodiment of the present invention.

[0027] Figure 5A is a non-scale view showing another possible arrangement of target material control system elements for a throat of a vessel used in a laser produced plasma EUV radiation source system according to an aspect of an embodiment of the present invention.

[0028] Figure 5B yes Figure 5A A top view of the arrangement.

[0029] Figure 6 is a non-scale view showing other elements of a target material control system element of a throat of a vessel used in a laser produced plasma EUV radiation source system according to an aspect of an embodiment of the present invention.

[0030] Other features and advantages of the present invention and the structure and operation of various embodiments of the present invention are described in detail below with reference to the accompanying drawings. Note that the present invention is not limited to the specific embodiments described herein. Such embodiments are proposed herein for illustrative purposes only. Based on the teachings contained herein, other embodiments will be clear to those skilled in the relevant art. DETAILED DESCRIPTION

[0031] Various embodiments are now described with reference to the accompanying drawings, wherein like reference numerals are used to refer to like elements throughout the text. In the following description, for the purpose of explanation, many specific details are set forth to facilitate a thorough understanding of one or more embodiments. However, it may be clear in some or all cases that any of the embodiments described below may be practiced without adopting the specific design details described below. In other cases, well-known structures and devices are shown in block diagram form to facilitate description of one or more embodiments.

[0032] However, before describing such embodiments in more detail, an example environment in which embodiments of the present invention may be implemented is exemplarily presented. In the following description and in the claims, terms such as "upper", "lower", "top", "bottom", "vertical", "horizontal", etc. may be used. Unless otherwise indicated, these terms are intended to show only relative orientations, not any orientation relative to gravity.

[0033] First reference Figure 1 , shows a schematic diagram of an exemplary EUV radiation source (e.g., a laser-generated plasma EUV radiation source 10) according to one aspect of an embodiment of the present invention. As shown, the EUV radiation source 10 may include a pulsed or continuous laser source 22, which may be, for example, a pulsed gas discharge CO2 laser source that produces a 10.6 μm or 1 μm radiation beam 12. The pulsed gas discharge CO2 laser source may have a DC or RF excitation that operates at high power and high pulse repetition rate.

[0034] The EUV radiation source 10 also includes a target delivery system 24 for delivering a target material in the form of droplets or a continuous liquid stream. In this example, the target material is a liquid, but it can also be a solid or a gas. The target material can be made of tin or a tin compound, although other materials can be used. In the depicted system, the target material delivery system 24 introduces droplets 14 of the target material into the interior of the vacuum chamber 26 to the irradiation area 28, in which the target material can be irradiated to produce a plasma. The vacuum chamber 26 can be provided with a lining. In some cases, an electric charge is placed on the target material to allow the target material to be turned toward or away from the irradiation area 28. It should be noted that, as used herein, an irradiation area is an area where irradiation of the target material can occur or is expected to occur, and is an irradiation area even when irradiation does not actually occur. The EUV light source may also include a beam steering system 32.

[0035] In the system shown, the components are arranged so that the droplet 14 travels substantially horizontally. The direction from the laser source 22 to the irradiation area 28 (i.e., the nominal propagation direction of the beam 12) can be referred to as the Z-axis. The path of the droplet 14 from the target material delivery system 24 to the irradiation area 28 can be referred to as the X-axis. Figure 1 The view is thus perpendicular to the XZ plane. As shown, preferably, the orientation of the EUV radiation source 10 is rotated relative to gravity, with arrow G showing a preferred orientation downward relative to gravity. This orientation applies to the EUV source, but does not necessarily apply to optically downstream components such as scanners. Moreover, although a system is shown in which the droplets 14 travel substantially horizontally, one of ordinary skill in the art will understand that other arrangements may be used in which the droplets travel vertically or at some angle between 90 degrees (horizontal) and 0 degrees (vertical), inclusive, relative to gravity.

[0036] The EUV radiation source 10 may also include an EUV light source controller system 60, a laser emission control system 65, and a 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 indicating an absolute position or relative position of a target droplet (e.g., relative to the irradiation area 28) and provide the output to the target position detection feedback system 62.

[0037] like Figure 1 As shown, the target material delivery system 24 may include a target delivery control system 90. The target delivery control system 90 may be operative in response to a signal (e.g., the target error described above or some amount derived from the target error provided by the system controller 60) to adjust the path of the target droplet 14 through the irradiation area 28. This may be accomplished, for example, by repositioning the position at which the target delivery mechanism 92 releases the target droplet 14. For example, the droplet release position may be repositioned 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 preferably supplied with a target material and a gas source from the outside to place the target material under pressure in the target delivery mechanism 92.

[0038] continue Figure 1, the radiation source 10 may also include one or more optical elements. In the following discussion, the collector 30 is used as an example of such an optical element, but the discussion is also applicable to other optical elements. The collector 30 may be, for example, a normal incidence reflector implemented as an MLM with an additional thin barrier layer such as B4C, ZrC, Si3N4 or C deposited at each interface to effectively prevent thermally induced interlayer diffusion. Other substrate materials such as aluminum (Al) or silicon (Si) may also be used. The collector 30 may be in the form of a prolate ellipsoid having a central hole to allow the laser radiation 12 to pass through and reach the irradiation area 28. The collector 30 may be, for example, in the shape of an ellipse with a first focus at the irradiation area 28 and a second focus at a so-called intermediate point 40 (also referred to as intermediate focus 40), where EUV radiation can be output from the EUV radiation source 10 and input into, for example, an integrated circuit lithography scanner 50, which uses the radiation 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 integrated circuit devices.

[0039] Figure 1 The arrangement also includes a temperature sensor 34 , such as a thermocouple located within the chamber 26 for measuring the local temperature of the gas within the chamber 26 (ie, the temperature at the sensor). Figure 1 One temperature sensor is shown, but it is apparent that additional temperature sensors may be used. The temperature sensor 34 generates a signal indicative of the measured temperature and provides this as an additional input to the controller 60. The controller 60 bases the control signal it provides to the beam steering system 32 at least in part on the temperature signal.

[0040] Accumulation of target material fragments on the vessel wall directly above the collector creates a risk of target material dripping onto the collector. Figure 2 The solid double arrows in show the direction of debris propagation. The outline arrows show the preferred arrangement for causing H2 to flow away from the collector 30. Element 42 is a scrubber for removing contaminants from the H2. Arrow G indicates the direction of gravity. Line 13 is also shown, marking the separation between the source 10 and the scanner 50.

[0041] Figure 3 A chamber design with asymmetric exhaust and a large throat area is shown. Figure 3 The design has two exhaust ports 60. In this design, a large amount of tin can be deposited on the wall of the exhaust manifold opposite the large throat at a location 70. If the temperature of this surface is maintained above the melting point of tin, the molten tin may be spit onto the collector.

[0042] In a system according to one aspect of one embodiment of the present invention, the tin is melted or maintained in liquid form at a location where liquid tin cannot or is unlikely to be ejected into the chamber interior or onto a collector. High conductivity can be maintained and exhaust gas is purified. According to another aspect, the tin can be discharged in situ while the source is operating.

[0043] An example of such a system is Figure 4A . Tin fragments from the irradiation area 28 are captured by two heated scrubbers 80. These scrubbers 80 are located in respective hot zones which are fully shielded to prevent spitting back into the inner surface 84 of the chamber 26, including spitting onto the liner 84 which at least partially covers the exhaust chamber wall 86. The portion 88 of the liner 84 adjacent to the scrubber 80 may be heated above melting to "drip out" excess solid tin. These surfaces are again shielded to prevent spitting onto the collector.

[0044] Likewise, if Figure 4A As shown, the arrangement includes an annular belt 90 covering a portion of the rear or outer wall 94 of the exhaust chamber. The belt 90 has a cold (e.g., water-cooled) plate 92 sandwiched therebetween, in contact or near contact with the plate 92 to keep the surface below the melting temperature of the tin. Thus, any solid tin particles impinging on this area will remain solid, while any tin vapor impinging on this area will become solid.

[0045] The belt 90 may be continuously, intermittently moved, periodically forwardly mounted with ratchets or the like, to bring the solid tin to the hot scrubber 80. Where the endless belt 90 meets the hot scrubber 80, there may be a heated scraper to melt the tin and scrape the belt 90 clean, thereby allowing the belt 90 to return to the deposition area to be ready to collect more tin. This arrangement ensures that the tin cannot be spit onto the collector or liner. The belt 90 is preferably placed in an area where the greatest amount of tin deposition can be expected, such as in the throat area.

[0046] Another example of such a system is Figure 4B Likewise, tin fragments from the irradiation area 28 are captured by two heated scrubbers 80 located in respective hot zones which are fully shielded from spitting back into the inner surface 84 of the liner 86 and the collector. Figure 4BAs shown, the arrangement includes a wedge-shaped diverter 96 located on the wall of the exhaust chamber (plenum) at the throat outlet. The diverter 96 forces the debris from the debris irradiation area 28 (open arrows) to flow into the portion of the exhaust manifold (curved arrows) shielded from the irradiation area 28. The spit direction of any entrained / deposited molten tin will tend to be toward the scrubber 80, rather than back into the interior of the vacuum vessel. By its shape, the diverter 94 directs the exhaust flow and entrained debris to change direction at the throat outlet to leave the rear wall and be directed more directly into the scrubber. The diverter 96 is typically cooled to below the melting point of the target material, but can be heated to above the melting temperature of tin to cause the accumulated solid tin on the diverter 96 to flow away and flow downward toward the tin discharge port. The tin spits mostly perpendicular to the surface of the diverter 96 facing away from the interior of the chamber 26, which greatly limits the amount of spits that may reach the optical elements in the tool.

[0047] Special care must be taken with the roof portion of the liner at the opening of the large throat. These roof and floor areas are usually sloped and recessed to protect as much of the collector / liner as possible.

[0048] Other high deposition areas can be covered by water-cooled shields that are hinged to allow them to rotate behind the opening to drip off. Figure 5A and 5B Such an arrangement is shown in . Figure 5A The throat area is shown with a shutter 110. The shutter 110 is connected to the wall of the throat by a hinge 112 so that the shutter 110 can be pivoted behind the opening to a position (shown in phantom) where it can be heated and the tin allowed to drip. Figure 5B yes Figure 5A 1, showing the rotation of the shield 110 about the hinge 112. These shields 110 can be positioned to minimize any adverse effects on conductance and so that any spitted liquid tin has no unimpeded path to the collector or liner.

[0049] Variations of the above embodiments can still achieve the spirit of the present disclosure. According to one aspect of the disclosed embodiment, a solid tin temperature surface is presented to an area that may be spit into the liner and collector. The tin can then be removed by any of several methods, including temperature cycling of the surface, that is, temporarily raising the temperature of the surface to above the melting point of tin. Alternatively or additionally, the surface can be moved to a shielded position for dripping, or the surface can be covered during dripping. According to another aspect, liquid tin is recovered (washed) from the gas flow and transported to a suitable isolated location (e.g., without a clear path to the collector or liner) for discharge. The wall upstream of the scrubber can be maintained at a temperature from which tin can drip. According to another aspect, for areas with very high deposition, temperature cycling, moving liner components to a safe position for dripping, generating ions for cleaning and keeping them clean, or using partial coverage during dripping can be used.

[0050] Figure 6 An embodiment is shown in which the throat 100 has been moved to the highest possible position in the chamber to limit the amount of debris overshoot between turning the plasma on and off (i.e., when plasma is being generated or not being generated). This improves the efficiency of debris removal and limits the amount of debris deposited on the inner wall surfaces. In this embodiment, a Figure 4A The annular belt 90 of the embodiment of the present invention may be provided, or a heating plate may be placed at the outlet of the throat 100. The exhaust manifold may be made circular (tubular) and therefore have a circular scrubber 110 instead of a rectangular scrubber. The tin drainer 115 collects the molten tin and then passes it to a tin drum or tin receiver 117. The freezing valve 119 allows the tin receiver 117 to be discharged through the conduit 121 without interrupting the operation of the source. The tin drainer may be placed on both sides of the source.

[0051] The above description includes examples of one or more embodiments. Of course, for the purpose of describing the aforementioned embodiments, it is not possible to describe every possible combination of parts or methods, but those of ordinary skill in the art will recognize that many other combinations and arrangements of various embodiments are possible. Therefore, the described embodiments are intended to cover all such changes, modifications and variations that fall within the spirit and scope of the appended claims. In addition, to the extent that the term "includes" is used in the specific embodiments or claims, the term is intended to be inclusive in a manner similar to the term "comprising" because when used as a transitional term in the claims, it is interpreted as "comprising". In addition, although the elements of the described aspects and / or embodiments can be described or claimed in the singular, the plural form can be imagined unless the limitation to the singular form is explicitly stated. In addition, unless otherwise stated, all or part of any aspect and / or embodiment can be used together with all or part of any other aspect and / or embodiment.

[0052] Further aspects of the invention are set out in the following numbered clauses.

[0053] 1. An apparatus for generating EUV radiation, the apparatus comprising:

[0054] container;

[0055] a residual target material collection surface having a first position, wherein the residual target material collection surface is arranged to collect residual target material from the irradiated area, and a second position, wherein the residual target material collection surface is shielded from the interior of at least a portion of the wall of the container, and wherein the residual target material collection surface is arranged to release residual target material collected at the first position; and

[0056] A temperature controller is arranged to maintain the residual target material collection surface below a melting temperature of the target material in the first position and above a melting temperature of the target material in the second position.

[0057] 2. An apparatus according to clause 1, wherein the residual target material collection surface comprises a surface of a belt.

[0058] 3. Apparatus according to clause 2, wherein the belt is cooled in the first position and heated in the second position.

[0059] 4. The apparatus of clause 2, further comprising: at least one scrubber positioned adjacent the belt at a second location and arranged to remove residual target material from the belt.

[0060] 5. Apparatus according to clause 4, wherein the at least one scrubber is positioned so that residual target material removed from the belt flows by gravity to a receiver.

[0061] 6. The apparatus of clause 1, further comprising: a chamber exhaust manifold in fluid communication with the chamber.

[0062] 7. The apparatus of clause 6, wherein the chamber exhaust manifold has a liner, and wherein at least a portion of the liner is heated.

[0063] 8. The apparatus of clause 1, wherein the residual target material collection surface comprises a shield.

[0064] 9. The apparatus of clause 8, wherein the shield is cooled in the first position and heated in the second position.

[0065] 10. The device according to clause 8, wherein the shield is arranged to pivot from the first position to the second position.

[0066] 11. The apparatus of clause 8, wherein the shield is arranged to move laterally from the first position to the second position.

[0067] 12. The apparatus of clause 8, wherein the second position is selected so that molten residual target material flows from the shutter to a receiver by gravity.

[0068] 13. The apparatus of clause 8, further comprising: a chamber exhaust manifold in fluid communication with the chamber.

[0069] 14. The apparatus of clause 13, wherein the chamber exhaust manifold has a liner, and wherein at least a portion of the liner is heated.

[0070] 15. A method of controlling residual target material in an apparatus for generating EUV radiation, the method comprising the steps of:

[0071] accumulating residual target material on a surface at a first location, the surface having a temperature below a melting temperature of the target material;

[0072] moving the surface to a second position where the temperature of the surface is above the melting temperature of the residual target material to melt the residual target material; and

[0073] The melted residual target material is removed from the surface.

[0074] 16. The method of clause 15, wherein removing the melted residual target material from the surface comprises scraping the melted residual target material from the surface.

[0075] 17. The method of clause 15, wherein removing the melted residual target material from the surface comprises causing the melted residual target material to flow from the surface.

[0076] 18. The method of clause 15, further comprising: a step, after the removing step, of causing the removed molten residual target material to flow to a receiver.

Claims

1. An apparatus for generating EUV radiation, the apparatus comprising: a container, including a chamber located therein; a chamber exhaust manifold in fluid communication with the chamber, wherein the exhaust manifold is provided with a residual target material collection surface having a first position, wherein the residual target material collection surface is arranged to collect residual target material from the irradiated area, and a second position, wherein the first position is shielded from the interior of at least a portion of the wall of the container, and wherein the residual target material collection surface is arranged to release residual target material collected at the first position; and A temperature controller is arranged to maintain the residual target material collection surface below a melting temperature of the target material in the first position and arranged to maintain the residual target material collection surface above a melting temperature of the target material in the second position.

2. The apparatus of claim 1, wherein the residual target material collection surface comprises a surface of a belt.

3. The apparatus of claim 2, wherein the belt is cooled in the first position and heated in the second position.

4. The apparatus according to claim 2, further comprising: At least one scrubber is positioned adjacent the belt at a second location and is arranged to remove residual target material from the belt.

5. The apparatus of claim 4, wherein the at least one scrubber is positioned so that residual target material removed from the belt flows by gravity to a receiver.

6. The apparatus of claim 1, wherein the chamber exhaust manifold has a liner, and wherein at least a portion of the liner is heated.

7. The apparatus of claim 1, wherein the residual target material collection surface comprises a shield.

8. An apparatus according to claim 7, wherein the shield can be pivoted or laterally moved from its cooled position to its heated position.

9. The apparatus of claim 7, wherein the second position is selected so that molten residual target material flows from the shield to a receiver by gravity.

10. The apparatus of claim 1, wherein the chamber exhaust manifold has a liner, and wherein at least a portion of the liner is heated.

11. A method of controlling residual target material in an apparatus for generating EUV radiation according to claim 1, the method comprising the steps of: accumulating residual target material on the residual target material collection surface at the first location, the residual target material collection surface having a temperature below a melting temperature of the target material; moving the residual target material collecting surface to the second position, at which the temperature of the residual target material collecting surface is higher than the melting temperature of the residual target material to melt the residual target material; as well as The melted residual target material is removed from the residual target material collecting surface.

12. The method of claim 11, wherein the step of removing the melted residual target material from the residual target material collection surface comprises: The melted residual target material is scraped from the residual target material collecting surface.

13. The method of claim 11, wherein the step of removing the melted residual target material from the residual target material collection surface comprises: The melted residual target material is caused to flow from the residual target material collecting surface.

14. The method according to claim 11, further comprising: The removing step is followed by a step of causing the removed molten residual target material to flow to a receiver.

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