NL2022770A - Apparatus for and method of controlling debris in an euv light source - Google Patents

Abstract

Disclosed is an EUV system including measures to accumulate target material debris in a liquid form Where the target material is blocked from spitting onto optics and in which the target material may be caused to solidify and then conveyed to a location Where it can be melted and 5 permitted to drain away Without contaminating the collector.

Description

FIELD [00001] The present disclosure relates to apparatus for and methods of generating extreme ultraviolet (“EUV”) radiation from a plasma created through discharge or laser ablation of a target material in a vessel. In such applications optical elements are used, for example, to collect and direct the radiation for use in semiconductor photolithography and inspection.

BACKGROUND [00002] Extreme ultraviolet radiation, e.g., electromagnetic radiation having wavelengths of around 50 nm or less (also sometimes referred to as soft x-rays), and including radiation at a wavelength of about 13.5 nm, can be used in photolithography processes to produce extremely small features in substrates such as silicon wafers.

[00003] Methods for generating EUV radiation include converting a target material to a plasma state. The target material preferably 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 laser beam to irradiate a target material having the required line-emitting element.

[00004] One LPP technique involves generating a stream of target material droplets and irradiating at least some of the droplets with one or more laser radiation pulses. Such LPP sources 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.

[00005] For this process, the plasma is typically produced in a sealed vessel, e.g., a vacuum chamber, and the resultant EUV radiation is monitored using various types of metrology equipment. In addition to generating EUV radiation, the processes used to generate plasma also typically generate undesirable by-products in the plasma chamber which can include out-of-band radiation, high energy ions, and debris, e.g., atoms and/or clumps/microdroplets of residual target material.

[00006] The energetic 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 location. The collected radiation may then be relayed from the intermediate location to a set of optics, a reticle, detectors and ultimately to a silicon wafer.

[00007] In the EUV portion of the spectrum it is generally regarded as necessary to use reflective optics for the optical elements in the system including the collector, illuminator, and projection optics box. These reflective optics may be implemented as normal incidence optics as mentioned or as grazing incidence optics. At the wavelengths involved, the collector is advantageously implemented as a multi-layer mirror (“MLM”). As its name implies, this MLM is generally made up of alternating layers of material (the MLM stack) over a foundation or substrate. System optics may also be configured as a coated optical element even if it is not implemented as an MLM.

[00008] The optical elements and, in particular, the collector must be placed within the vessel with the plasma to collect and redirect the EUV radiation. The environment within the chamber is inimical to the optical elements and so limits their useful lifetime, for example, by degrading reflectivity. An optical element within the environment may be exposed to high energy ions or particles of target material. The particles of target material, which are essentially debris from the laser vaporization process, can contaminate the optical element’s exposed surface. Particles of target material can also cause physical damage to and localized heating of the MLM surface.

[00009] In some systems H? gas at pressures in the range of about 0.5 to about 3 mbar is used in the vacuum chamber as a buffer gas 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.

[00010] H2 gas is introduced into the vacuum chamber to slow down the energetic debris (ions, atoms, and clusters) of target material created by the plasma. The debris is slowed down by collisions with the gas molecules. For this purpose a flow of H2 gas is used which may also be counter to the debris trajectory and away from the collector. This serves to reduce the damage of deposition, implantation, and sputtering target material on the optical coating of the collector. [00011] Still, one of the most challenging problems in a source such as that described is management of residual target material. The process of transforming the target material into vapor and particles and deposits residual target material on every surface where 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. For example, if this gas is pumped across the top of vanes present in the chamber and to the mechanical pumps then soon the material is deposited on all of the cold metal parts. If the target material is tin, then this can lead to the growth of tin wool which can drop onto the collector optics and clog the exhaust paths.

[00012] Still using tin as an example of a target material, one technique for controlling tin dispersal involves capturing tin from vapor or particles on a surface heated to above the meting point of tin. There the tin melts (or remains molten) and is caused to flow to a capture receptacle. Fiquid tin, however, tends to erupt or “spit” in the presence of hydrogen radicals such as are found in an EUV chamber, and this ejected tin can strike the collector. This is a major contributor to collector degradation. Second, the liquid tin typically does not flow as intended. For example, structures within the chamber such as vanes and a gutter for a scrubber provided to remove some or all of the tin vapor in the chamber may drip liquid tin onto the collector. Also the scrubber gutter may overflow and liquid tin may run down the back of the vanes creating a thermal short (i.e., an unintended heat conductive path) and clogging the flow path to the capture receptacle. In addition liquid tin is highly corrosive and leads to failures of, for example, the electrical heaters used to maintain the collection surfaces above the meting point of tin. Also, the flow restriction caused by tin accumulation leads to the gas finding a path through smaller spaces in the vanes and collector causing significantly increased collector degradation by tin deposition. [00013] As mentioned, a scrubber may be added to areas such as the top of the vanes to capture entrained tin by precipitating it out of the vapor. The scrubber surface may be maintained above the melting point of tin so that liquid tin may flow down the vanes and into a receptacle. Fiquid tin in the scrubber may, however, still spit onto the collector and drip from the gutter onto the collector again, increasing the collector degradation. There are also challenges in maintaining the scrubber above the melting point of tin. When the temperature of the scrubber is below the melting point of tin the tin solidifies and clogs the scrubber. Altering the scrubber geometry by, for example, changing the size and tilt of the scrubber vanes, may improve performance but cannot entirely eliminate the tendency of the scrubber to spit on the collector or onto a cold surface and clogging the exhaust.

[00014] The process of generating EUV light may also cause target material to be deposited on the walls of the vessel. Controlling target material deposition on the vessel walls is important for achieving an acceptably long lifetime of EUV sources placed in production. Also, managing target material flux from the irradiation site is important for ensuring that the waste target material mitigation system works as intended.

SUMMARY [00015] The following presents a simplified 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 key or critical elements of all embodiments nor set limits 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 the more detailed description that is presented later.

[00016] According to one aspect, different tin management techniques are used for different portions of the “tin path,” that is, the path from the chamber liner to the imaging relay mirrors that redirect light leaving the chamber. A combination of solid and liquid tin techniques is used together with an exhaust manifold to manage the dispersal and collection of tin. Zones in the exhaust stream are identified and the proper technique for handling the exhaust gas stream is used in each of these zones based upon their differing requirements.

[00017] According to another aspect of an embodiment, there is disclosed an apparatus for generating EUV radiation comprising a vessel and a residual target material collection surface having a first position at which the residual target material collection surface is arranged to collect residual target material from an irradiation region and a second position occluded from an interior of at least a portion of a wall of the vessel at which the residual target material collection surface is arranged to release residual target material collected at the first position, and a temperature controller 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. The residual target material collection surface may comprise a surface of a belt. The belt may cooled in the first position and heated in the second position. The apparatus may further comprise at least one scrubber positioned adjacent the belt in the second position and arranged to remove residual target material from the belt. The at least one scrubber may be positioned so that residual target material removed from the belt flows by force of gravity to a receptacle. The apparatus may further comprise a chamber exhaust manifold in fluid communication with the chamber. The chamber exhaust manifold may have a liner and at least part of the liner may be heated. The residual target material collection surface may comprise a shield. The shield may be cooled in the first position and heated in the 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 molten residual target material flows from the shield by force of gravity to a receptacle. The apparatus may further comprise a chamber exhaust manifold in fluid communication with the chamber. The chamber exhaust manifold may have a liner and at least part of the liner may be heated.

[00018] According to one aspect of an embodiment, there is disclosed a method of controlling residual target material in an apparatus for generating EUV radiation, the method comprising the steps of accumulating residual target material on a surface at a first position, the surface being at a temperature below a melting temperature of the target material, moving the surface to a second position at which the surface is at a temperature above a 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 comprise scraping the melted residual target material from the surface. The step of removing the melted residual target material from the surface may comprise causing the melted residual target material to flow from the surface. There may be a step after the removing step of causing the removed melted residual target material to flow to a receptacle. [00019] Further embodiments, features, and advantages of the present invention, as well as the structure and operation of the various embodiments are described in detail below with reference to accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING [00020] FIG. 1 is a schematic, not-to-scale view of an overall broad conception for a laserproduced plasma EUV radiation source system according to an aspect of the present invention. [00021] FIG. 2 is a not-to-scale diagram showing a possible arrangement of a vessel and exhaust systems used in a laser-produced plasma EUV radiation source system according to an aspect of the present invention.

[00022] FIG. 3 is a not-to-scale view showing a possible arrangement of a target material control system for a vessel used in a laser-produced plasma EUV radiation source system according to an aspect of the present invention.

[00023] FIG. 4A is a not-to-scale view showing a possible arrangement of a target material control system for the throat portion of a vessel used in a laser-produced plasma EUV radiation source system according to an aspect of an embodiment of the present invention. [00024] FIG. 4B is a not-to-scale view showing another possible arrangement of a target material control system for the throat portion of a vessel used in a laser-produced plasma EUV radiation source system according to an aspect of an embodiment of the present invention. [00025] FIG. 5A is a not-to-scale view showing another possible arrangement of a target material control system element for the throat portion of a vessel used in a laser-produced plasma EUV radiation source system according to an aspect of an embodiment of the present invention. [00026] FIG. 5B is a top view of the arrangement of FIG, 5A.

[00027] FIG. 6 is a not-to-scale view showing additional elements of a target material control system element for the throat portion of a vessel used in a laser-produced plasma EUV radiation source system according to an aspect of an embodiment of the present invention. [00028] Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. It is noted that the invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art based on the teachings contained herein.

DETAILED DESCRIPTION [00029] 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. [00030] Before describing such embodiments in more detail, however, it is instructive to present an example environment in which embodiments of the present invention may be implemented. In the description that follows and in the clauses 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.

[00031] 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 of the present invention. As shown, the EUV radiation source 10 may include a pulsed or continuous laser source 22, which may for example be a pulsed gas discharge CO2 laser source producing a beam 12 of radiation at 10.6 pm or 1 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.

[00032] The EUV radiation source 10 also includes a target 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 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. In some cases, an electrical charge is placed on the target material to permit the target material to be steered toward or away from the irradiation region 28. It should be noted that as used herein an irradiation region is a region where target material irradiation may or is intended to occur, and is an irradiation region even at times when no irradiation is actually occurring. The EUV light source may also include a beam steering system 32.

[00033] In the system shown, the components are arranged so that the droplets 14 travel substantially horizontally. The direction from the laser source 22 towards the irradiation region 28, that is, the nominal direction of propagation of the beam 12, may be taken as the Z axis. The path the droplets 14 take from the target material delivery system 24 to the irradiation region 28 may be taken as the X axis. The view of FIG. 1 is thus normal to the XZ plane. The orientation of the EUV radiation source 10 is preferably rotated with respect to gravity as shown, with the arrow G showing the preferred orientation with respect to gravitationally down. This orientation applies to the EUV source but not necessarily to optically downstream components such as a scanner and the like. Also, 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).

[00034] The EUV radiation source 10 may also include an EUV light source controller system 60, a laser firing control system 65, along with the beam steering system 32. The EUV radiation source 10 may also include a detector such as a target position detection system which may include one or more droplet imagers 70 that generate an output indicative of the absolute or relative position of a target droplet, e.g., relative to the irradiation region 28, and provide this output to a target position detection feedback system 62.

[00035] 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 target 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 target 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 preferably externally supplied with target material and a gas source to place the target material in the target delivery mechanism 92 under pressure.

[00036] 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 B4C, ZrC, SÏ3N4or C, deposited at each interface to effectively block thermally-induced interlayer diffusion. Other substrate materials, such as aluminum (Al) or silicon (Si), can also be used. The collector 30 may be in the form of a prolate ellipsoid, with a central aperture to allow the laser radiation 12 to pass through and reach the irradiation region 28. The collector 30 may be, e.g., in the shape of a ellipsoid that has a first focus at the irradiation region 28 and a second focus at a so-called intermediate point 40 (also called the intermediate focus 40) 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.

[00037] The arrangement of FIG. 1 also includes a temperature sensor 34, e.g., a thermocouple positioned within the chamber 26 to measure the local temperature, i.e., temperature at the sensor, of the gas within the chamber 26. FIG. 1 shows one temperature sensor but it will be apparent that additional temperature sensors may be used. The temperature sensor 34 generates a signal indicative of the measured temperature and supplies it as an additional input to the controller 60. The controller 60 bases the control signal it supplies to the beam steering system 32 at least in pail on this temperature signal.

[00038] Target material debris accumulation on the vessel walls directly above the collector creates the risk that target material will drip onto the collector. The solid double arrow in FIG. 2 shows the direction of debris propagation. The outline arrows show a preferred arrangement for causing H2 to flow away from the collector 30. Elements 42 are scrubbers for removing contaminants from the H2. Arrow G indicates the direction of gravity. Also shown is a line 13 demarking a division between the source 10 and the scanner 50.

[00039] FIG. 3 shows a chamber design having asymmetrical exhaust with a large throat area. The design of FIG. 3 has two exhaust ports 60 In this design, large amounts of tin may be deposited at the location 70 on the wall of the exhaust manifold, opposite of this large throat. If this surface is maintained at a temperature above the melting point of tin, then molten tin may spit onto the collector.

[00040] In a system according to one aspect of an embodiment of the invention, tin is melted or maintained in a liquid state in locations where the liquid tin cannot or is unlikely to spit onto the interior of the chamber or onto the collector. High flow conductance may be maintained and the exhaust gases are scrubbed. According to another aspect, tin can drain in situ and while the source is operating.

[00041] An example of such a system is shown in FIG. 4A. Tin debris from an irradiation region 28 is captured by the two heated scrubbers 80. These scrubbers 80 are located in respective hot zones that that are fully shielded from spitting back into the inner surface 84 of the chamber 26 including onto a liner 84 at least partially covering the an exhaust plenum wall 86. The portion 88 of the liner 84 adjacent the scrubbers 80 can be heated above melting to “drip off' excess solid tin. These surfaces are again shielded from spitting on the collector.

[00042] Also as shown in FIG. 4A, the arrangement includes an endless belt 90 covering a portion of the back or outside wall 94 of the exhaust plenum. This belt 90 has sandwiched between it cold (e.g., water cooled) plates 92, either touching or near touching to keep the surface well below the melting temperature of tin. Thus any solid tin particles impinging on this areas will remain solid and any tin vapor impinging on this area to become solid.

[00043] The belts 90 may be moved continuously, intermittently, ratchetted ahead periodically, etc. to carry the solid tin to the hot scrubbers 80. Where the endless belt 90 meets the hot scrubbers 80, there may be a heated doctor blade to melt the tin and scrape the belt 90 clean, allowing the belt 90 to return to the deposition area ready to collect more tin. This arrangement ensures that no tin will be able to spit onto the collector or liner. The belt 90 is preferably placed in areas where the largest amounts of tin deposition may be expected such as the throat area.

[00044] Another example of such a system is shown in FIG. 4B. Again, tin debris from an irradiation region 28 is captured by the two heated scrubbers 80 located in respective hot zones that that are fully shielded from spitting back into the inner surface 84 of the liner 86 and the collector. Also as shown in FIG, 4B, the arrangement includes a wedge-shaped diverter 96 positioned on the wall of the exhaust plenum at the throat exit. The diverter 96 forces the flow of debris from the irradiation region 28 (open arrow) into portions of the exhaust manifold shielded from the irradiation region 28 (curved arrows). The spitting direction of any entrained / deposited molten tin will tend to be towards the scrubbers 80 and not back towards the interior of the vacuum vessel. By its shape, diverter 94 redirects the flow of exhaust gas and the entrained debris away from the back wall at the exit of the throat and directed more directly into the scrubbers. Diverter 96 is normally cooled to below the melting point of the target material but can be heated to above tin melting temperatures to permit the solid accumulated tin on the diverter 96 to flow away way and down a tin drain. Tin mostly spits perpendicular to the surface of the diverter 96 facing away from the interior of the chamber 26, which greatly limits the amount of spitting that could find its way to the optics in the tool.

[00045] Some care must be used in the roof sections of the liner at the opening to the large throat. These roof and floor areas will typically be tilted and recessed to protect the collector/liner as much as possible.

[00046] Other areas of high deposition may be covered with water cooled shields which are hinged to allow them to rotate to behind the opening for drip off. Such an arrangement is shown in FIGS. 5A and 5B. FIG. 5A shows a throat area with a shield 110. The shield 110 is connected to the wall of the throat with a hinge 112 so it can be pivoted behind the opening to a position (shown in phantom) where it can be heated and the tin allowed to drip off. FIG. 5B is a top view of the arrangement of FIG. 5 A showing rotation of the shield 110 around the hinge 112. These shields 110 may be positioned so as to minimize any adverse impact on conductance and so that any spitting liquid tin does not have a clear path to the collector or liner.

[00047] Variations on the above embodiments which nevertheless capture the spirit of this disclosure are possible. According to one aspect of a disclosed embodiment, a solid tin temperature surface is presented to areas that could spit into the liner and collector. The tin may then be removed by any one of several methods, including temperature cycling of the surface,

i.e., temporarily raising the temperature of the surface to above the melting point of tin. Alternatively or in addition, the surface may be moved to a shielded location for drip off, or covered during drip off. According to another aspect, liquid tin is recovered (scrubbed) from the gas stream and delivered to a suitable isolated location (e.g., no clear path to collector or liner) to drain. The walls upstream of the scrubbers may be maintained at a temperature that tin can drip off of them. According to another aspect, for areas of very high deposition, temperature cycling, moving a liner part to a safe location for drip off, ion generation for cleaning and keeping clean, or a partial cover during drip off may be used.

[00048] FIG. 6 shows an embodiment in which the throat 100 has been moved to the uppermost position possible of the chamber to limit the amount of debris overshoot between on and off plasma, i.e., when plasma is or is not being created. This increases the efficiency of debris exhaust and limits the amount of debris deposited on the internal wall surfaces. In this embodiment, the endless belt 90 of the embodiment of FIG. 4A may be used, or a heated plate may be placed at the output of the throat 100. The exhaust manifold can be made circular (pipe like) and thus have round scrubbers 110 instead of the rectangular scrubbers. Tin drain 115 collects the molten tin and passes it to a tin bucket or receptacle 117. A freeze valve 119 permits draining of the tin receptacle 117 through conduit 121 without interrupting operation of the source. Tin drains may be placed on both sides of the source.

[00049] The above description includes examples of one or more embodiments. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the aforementioned embodiments, but one of ordinary skill in the ail may recognize that many further combinations and permutations of various embodiments are possible. Accordingly, the described embodiments are intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended clauses. Furthermore, to the extent that the term includes is used in either the detailed description or the clauses, 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 clause. Furthermore, although elements of the described aspects and/or embodiments may be described 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.

[00050] Other aspects of the invention are set out in the following numbered clauses.

1. Apparatus for generating EUV radiation, the apparatus comprising:

a vessel;

a residual target material collection surface having a first position at which the residual target material collection surface is arranged to collect residual target material from an irradiation region and a second position occluded from an interior of at least a portion of a wall of the vessel at which the residual target material collection surface is arranged to release residual target material collected at the first position; and a temperature controller 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.

2. Apparatus as in clause 1 wherein the residual target material collection surface comprises a surface of a belt.

3. Apparatus as in clause 2 wherein the belt is cooled in the first position and heated in the second position.

4. Apparatus as in clause 2 further comprising at least one scrubber positioned adjacent the belt in the second position and arranged to remove residual target material from the belt.

5. Apparatus as in clause 4 wherein the at least one scrubber is positioned so that residual target material removed from the belt flows by force of gravity to a receptacle.

6. Apparatus as in clause 1 further comprising a chamber exhaust manifold in fluid communication with the chamber.

7. Apparatus as in clause 6 wherein the chamber exhaust manifold has a liner and wherein at least part of the liner is heated.

8. Apparatus as in clause 1 wherein the residual target material collection surface comprises a shield.

9. Apparatus as in clause 8 wherein the shield is cooled in the first position and heated in the second position.

10. Apparatus as in clause 8 wherein the shield is arranged to pivot from the first position to the second position.

11. Apparatus as in clause 8 wherein the shield is arranged to move laterally from the first position to the second position.

12. Apparatus as in clause 8 wherein the second position is selected so that molten residual target material flows from the shield by force of gravity to a receptacle.

13. Apparatus as in clause 8 further comprising a chamber exhaust manifold in fluid communication with the chamber.

14. Apparatus as in clause 13 wherein the chamber exhaust manifold has a liner and wherein at least part of the liner is heated.

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

accumulating residual target material on a surface at a first position, the surface being at a temperature below a melting temperature of the target material;

moving the surface to a second position at which the surface is at a temperature above a melting temperature of the residual target material to melt the residual target material; and removing the melted residual target material from the surface.

16. The method as in clause 15 wherein the step of removing the melted residual target material from the surface comprises scraping the melted residual target material from the surface.

17. The method as in clause 15 wherein the step of removing the melted residual target material from the surface comprises causing the melted residual target material to flow from the surface.

18. The method as in clause 15 further comprising a step after the removing step of causing the removed melted residual target material to flow to a receptacle.

Claims (2)

CONCLUSION A lithography apparatus comprising: an illumination device adapted to provide a radiation beam; 5 a carrier constructed for supporting a patterning device, which patterning device is capable of applying a pattern in a section of the radiation beam to form a patterned radiation beam; a substrate table constructed to support a substrate; and a projection device adapted to project the patterned radiation beam onto a target area of the substrate, characterized in that the substrate table is adapted to position the target area of the substrate in a focal plane of the projection device. 1/8 2/8 4/8 FIG. 4A 5/8 FIG. 4B 6/8 FIG. 5A 7/8 FIG. 5B 8/8 Ï-— O *