Cleaning structural surfaces in EUV chambers

Abstract

In some general aspects, a surface of a structure within a chamber of an extreme ultraviolet (EUV) light source is cleaned using a method. The method includes generating a plasma state of the material present at a location adjacent the non-conductive body within the chamber. The generation of the plasma state of the material includes electromagnetically inducing an electrical current at a location adjacent the non-conductive body, thereby transitioning the material adjacent the non-conductive body from the first state to the plasma state. The plasma state of the material includes plasma particles, at least some of which are radicals of the material. The method further includes enabling plasma particles to pass through the surface of the structure to remove debris from the surface of the structure without removing the structure from the chamber of the EUV light source.

Description

[0001] Division Explanation

[0002] This application is a divisional application of the Chinese patent application with the application number 201980012976.1 and the title "Cleaning Structural Surfaces in an EUV Chamber" filed on February 12, 2019.

[0003] Cross - Reference to Related Applications

[0004] This application claims the priority of U.S. Application No. 62 / 630,036 filed on February 13, 2018 and U.S. Application No. 62 / 795,107 filed on January 22, 2019, the entire contents of which are incorporated herein by reference. Technical Field

[0005] The disclosed subject matter relates to a system and method for cleaning debris from the surface of a structure within a chamber of an extreme ultraviolet light source. Background Art

[0006] In a lithography process, extreme ultraviolet (EUV) light (e.g., electromagnetic radiation having a wavelength of about 50 nm or less (sometimes also referred to as soft x-rays) and including light having a wavelength of about 13 nm) can be used to create extremely small features in a substrate (e.g., a silicon wafer).

[0007] Methods for generating EUV light include, but are not limited to, converting a material having an element such as xenon, lithium, or tin whose emission line is in the EUV range into a plasma state. In one such method commonly referred to as laser-produced plasma ("LPP"), the required plasma can be generated by irradiating a target material in the form of, for example, a material droplet, plate, strip, stream, or cluster with an amplified light beam. For this process, the plasma is typically generated in a sealed container (e.g., a vacuum chamber) and monitored using various types of metrology equipment. Summary of the Invention

[0008] In some general aspects, a method is used to clean the surface of a structure within a chamber of an extreme ultraviolet (EUV) light source. The method includes generating a plasma state of a material present at a location of a non-conductor adjacent to the chamber. The generation of the plasma state of the material includes electromagnetic induction of a current at a location adjacent to the non-conductor, thereby transforming the material adjacent to the non-conductor from a first state to a plasma state. The plasma state of the material includes plasma particles, and at least some of the plasma particles are free radicals of the material. The method further includes enabling the plasma particles to pass over the structure surface to remove debris from the structure surface without removing the structure from the chamber of the EUV light source.

[0009] The implementation may include one or more of the following various ones. For example, the method may include maintaining the temperature of the structure below 50 °C.

[0010] The surface of the structure may be positioned to optically interact with the light present in the chamber and modify the light present in the chamber.

[0011] The plasma state of the material can be generated by generating the plasma state of the material in the absence of oxygen. The plasma state of the material can be generated without reducing the amount of the material flowing through the surface of the structure.

[0012] An electric current can be electromagnetically induced by passing an electric current through a conductive tube adjacent to a non-conductor. The electric current flowing through the conductive tube can be at radio frequency. The method may include: providing a cooling fluid through the interior of the conductive tube to maintain the temperature of the non-conductor or the structure below a threshold temperature.

[0013] The structure may include a non-conductor; and the plasma state of the material at a position adjacent to the surface of the structure can be generated by generating the plasma state of the material at a position adjacent to the non-conductor.

[0014] The structure may be different from the non-conductor. By causing plasma particles to move from a position near the non-conductor towards and across the surface of the structure, the plasma state of the material can be made to pass through the surface of the structure.

[0015] An electric current can be electromagnetically induced at a position adjacent to the non-conductor by generating a time-varying magnetic field near the non-conductor in the chamber; and a time-varying magnetic field can be generated in the chamber by passing a time-varying electric current through a conductor adjacent to the non-conductor.

[0016] The plasma particles may at least include ions, electrons and free radicals of the material. The material may include hydrogen.

[0017] Debris can be removed from the surface of the structure by causing the plasma particles to chemically react with the debris on the surface of the structure to form a chemical substance released from the surface of the structure. The method may further include removing the released chemical substance from the chamber. The material may include hydrogen, and the plasma particles may include free radicals of hydrogen. The debris on the surface of the substrate may include tin, and the released chemical substance may include tin hydride.

[0018] The chamber may be maintained at a pressure below atmospheric pressure.

[0019] The non-conductor may be made of a dielectric.

[0020] An electric current can be induced electromagnetically by generating microwave radiation at a non-conductor or causing an electromagnetic surface wave to propagate along the non-conductor.

[0021] An electric current can be induced electromagnetically by passing an electric current through a conductor adjacent to a non-conductor. By applying a first current at a first frequency and a second current at a second frequency different from the first frequency to the conductor, an electric current can be made to flow through the conductor. The first frequency can be a radio frequency and the second frequency can be lower than the radio frequency. The first current and the second current can be applied by applying a dual-frequency alternating current or a pulsating direct current to the conductor.

[0022] A first current at a first frequency can be applied to the conductor to transform a material adjacent to the non-conductor from a first state to a plasma state of the material including plasma particles. A second current at a second frequency can be applied to the conductor to inductively heat and evaporate debris on the surface of the structure.

[0023] In other general aspects, a device includes: an extreme ultraviolet (EUV) light source; a structure including an exposed surface within a chamber; and a cleaning device near the structure. The EUV light source includes: a chamber; and a target delivery system configured to direct a target to an interaction region in the chamber. The target includes a material that emits extreme ultraviolet light when converted to a plasma. The cleaning device is configured to remove target debris from the exposed surface of the structure without removing the structure from the chamber. The cleaning device includes a conductor that contacts a non-conductor. The cleaning device is configured to inductively generate an electric current at a location adjacent to the non-conductor to transform a material present in the chamber from a first state to a plasma state including plasma particles, where at least some of the plasma particles are free radicals and ions of the material. The non-conductor is configured relative to the structure such that the plasma particles contact debris on the exposed surface of the structure.

[0024] Implementation can include one or more of the following various aspects. For example, the device can include a temperature control system thermally coupled to the conductor.

[0025] The temperature control system can be configured to maintain the temperature of the structure adjacent to the cleaning device within a threshold range. The temperature control system can maintain the temperature of the structure adjacent to the cleaning device below a threshold maximum. The threshold maximum can be 50 °C. The temperature control system can include a fluid control system configured to feed a cooling fluid through an internal channel of the conductor.

[0026] The exposed surface can optically interact with light and modify the light. The light can be an amplified beam that interacts with the target or EUV light generated by the target.

[0027] The device may include a flow device configured to flow plasma particles from a position adjacent to the non-conductor towards and across the exposed surface.

[0028] A current can be electromagnetically induced by passing a current through an electrical conductor, and the current passing through the electrical conductor is at radio frequency.

[0029] The structure having the exposed surface and the non-conductor can be the same physical structure.

[0030] The structure having the exposed surface can be physically different from the non-conductor.

[0031] The non-conductor includes a shield that includes a passage for a target from a target delivery system to an interaction region or defines a passageway for a target from a target delivery system to an interaction region.

[0032] The structure having the exposed surface can be a condenser mirror of an EUV light source. The condenser mirror can be positioned to capture at least a portion of the EUV light emitted from the plasma, and the non-conductor can include a ring positioned around an outer surface of the condenser mirror.

[0033] The structure having the exposed surface can be the non-conductor. The EUV light source can include a liner located between the condenser mirror and an intermediate focus. The structure can include the liner, and an inner surface of the liner faces the EUV light reflected from the condenser mirror towards the intermediate focus and constitutes the exposed surface of the structure. If the outer surface of the liner is at a pressure different from the pressure at the inner surface, the electrical conductor can be positioned outside the outer surface of the liner, or if the outer surface of the liner is at the same pressure as the pressure at the inner surface, the electrical conductor can be embedded in the liner. The induced current can be at the inner surface of the liner. The liner can have a conical shape that smoothly tapers from a flat base positioned adjacent to the condenser mirror to a vertex opening towards the intermediate focus.

[0034] The non-conductor can be made of a dielectric. The dielectric can include a ceramic. The ceramic can include aluminum nitride or boron nitride.

[0035] The target can include tin, and the material can include hydrogen. The cleaning device can be configured to remove tin debris from the exposed surface of the structure in the absence of oxygen.

[0036] If the pressures on the first side and the second side of the non-conductor are equal, the conductor can be embedded in the non-conductor. Or, if the pressure on the first side of the non-conductor is different from the pressure on the second side of the non-conductor, the electrical conductor can be adjacent to the first side of the non-conductor and outside the first side.

[0037] The chamber can be maintained at a pressure below atmospheric pressure.

[0038] The device may include a power source configured to supply current to an electrical conductor. The device may include a control device to which the power source is connected, the control device being configured to send a signal to the power source to operate the cleaning device.

[0039] The device may include a fluid port configured to introduce a material into the chamber.

[0040] The cleaning device may be configured to: inductively generate an electric current at a location adjacent to a non-conductive body by causing an electromagnetic surface wave to propagate along the non-conductive body or by generating microwave radiation at the non-conductive body.

[0041] The cleaning device may include a power source electrically connected to supply current to an electrical conductor. The power source may be configured to supply a first current at a first frequency to the electrical conductor and to supply a second current at a second frequency to the electrical conductor, where the second frequency is different from the first frequency. The first frequency may be a radio frequency, and the second frequency may be less than the radio frequency. The power source may be configured to apply a dual-frequency alternating current or a pulsating direct current to the electrical conductor.

[0042] In other general aspects, a device includes: an extreme ultraviolet (EUV) light source including a chamber; and a shield within the chamber. The EUV light source includes a target delivery system configured to direct a target into an interaction region in the chamber. The target includes a material that emits extreme ultraviolet light when converted to a plasma. The shield defines a channel extending from the target delivery system to the interaction region, and an outer surface of the shield is exposed to debris generated by the target. The shield includes: a non-conductive body defining the channel, and an electrical conductor adjacent to the non-conductive body. The electrical conductor inductively generates an electric current at a location adjacent to the shield, thereby converting a material present in the chamber from a first state to a plasma state including plasma particles, at least some of the plasma particles being radicals and ions of the material. The electrical conductor is positioned relative to the non-conductive body such that the plasma particles chemically react with debris fixed to an exposed surface of the shield, thereby releasing the debris from the exposed surface of the shield.

[0043] Implementations may include one or more of the following. For example, the device may include a temperature control system thermally coupled to the electrical conductor. The temperature control system may be configured to keep the temperature of the surface of the channel below a threshold. The temperature control system may be configured to cool the surface of the channel to prevent debris from melting at the surface of the channel.

[0044] The electrical conductor may be embedded within the non-conductive body. The electrical conductor may be in contact with the non-conductive body.

[0045] The non-conductive body may be made of a dielectric.

[0046] The electrical conductor may be wound around an outer surface of the non-conductive body, and the electrical conductor may be coated in a dielectric material. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1A is a block diagram of a cleaning device designed to clean debris from an exposed surface of a structure within a chamber of an extreme ultraviolet (EUV) light source;

[0048] Figure 1B is Figure 1A a block diagram of the cleaning device, wherein the cleaning device includes an electrical conductor in contact with a non-conductive body configured relative to the exposed surface of the structure;

[0049] Figure 2A and 2B is Figure 1A a block diagram of an implementation of the cleaning device, wherein the non-conductive body is different from the structure having the exposed surface;

[0050] Figure 2C is Figure 1A a block diagram of another implementation of the cleaning device, wherein the non-conductive body is different from the structure having the exposed surface;

[0051] Figure 3A and 3B is Figure 1A a block diagram of an implementation of the cleaning device, wherein the non-conductive body is the structure having the exposed surface;

[0052] Figure 4A is a schematic diagram showing an implementation of the cleaning device, wherein the electrical conductor is partially exposed and contacts the non-conductive body at multiple positions at the exposed surface of the non-conductive body;

[0053] Figure 4B is a schematic diagram showing an implementation of the cleaning device, wherein the electrical conductor is embedded within the non-conductive body at multiple positions;

[0054] Figure 4C is a schematic diagram showing an implementation of the cleaning device, wherein the electrical conductor is partially exposed and contacts the non-conductive body over a continuous spatial region of the exposed surface of the non-conductive body;

[0055] Figure 4D is a schematic diagram showing an implementation of the cleaning device, wherein the electrical conductor is embedded within the non-conductive body and continuously contacts the non-conductive body;

[0056] Figure 5 is a block diagram of an EUV light source in which the cleaning device is implemented;

[0057] Figures 6A - 6D shows a rear perspective view, a front perspective view, a side cross-sectional view, and a front plan view of an exemplary light collector that can be cleaned by the Figure 5 cleaning device;

[0058] Figure 7AIt is a block diagram of an EUV light source, where the cleaning device is implemented as cleaning a shield placed between the target delivery system and the interaction area;

[0059] Figure 7B It is a plan view taken along the XY plane Figure 7A of the implementation of the cleaning device and the shield to be cleaned in

[0060] Figure 7C It is a plan view taken along the XZ plane Figure 7B of the implementation of the cleaning device and the shield to be cleaned in

[0061] Figure 7D It is Figure 7A and 7B exploded perspective view of the implementation of the cleaning device and the shield, showing the placement of the electrical conductor inside the shield;

[0062] Figure 7E It is Figure 7A and 7B perspective view of the implementation of the cleaning device and the shield;

[0063] Figure 8A It is a block diagram of an EUV light source, where the cleaning device is implemented as a liner or sub-container located between the collector and the intermediate focus of the collector, where the electrical conductor is embedded in the liner body, and the liner body is conical in shape;

[0064] Figure 8B It is Figure 8A perspective view of the cleaning device where the liner is conical in shape;

[0065] Figure 9A It is a block diagram of an EUV light source, where the cleaning device is implemented as a liner or sub-container located between the collector and the intermediate focus of the collector, where the electrical conductor contacts the outer surface of the liner body, and the liner body is conical in shape;

[0066] Figure 9B It is Figure 9A perspective view of the cleaning device;

[0067] Figure 10A It is a block diagram of an EUV light source, where the cleaning device is implemented as cleaning the collector;

[0068] Figure 10B It is Figure 10A perspective view of the cleaning device;

[0069] Figure 10C It is Figure 10B side cross-sectional view of a part of the cleaning device;

[0070] Figure 10D It is Figure 10CClose-up side view cross-sectional view of a part of a cleaning device;

[0071] Figure 11 Is a flowchart of a process that is performed to clean the surface of a structure;

[0072] Figure 12 Is a flowchart of a process for inducing a current at a location adjacent to a non-conductor;

[0073] Figures 13A - 13C Is a perspective view of a shield, showing Figure 12 Steps of the process;

[0074] Figure 14 Is a block diagram of an EUV light source in which a cleaning device can be used;

[0075] Figure 15 Is a block diagram of an EUV light source and a lithography apparatus that receives EUV light from the EUV light source;

[0076] Figure 16A Is a plan view along the XY plane of Figure 7A Another implementation of the cleaning device and the shield to be cleaned in;

[0077] Figure 16B Is Figure 16A Perspective view of the cleaning device and the shield;

[0078] Figure 17A Is a perspective view of an implementation of the cleaning device and the tubular shield to be cleaned;

[0079] Figure 17B Is a perspective view of an implementation of the cleaning device and the hybrid (tubular and U-shaped) shield to be cleaned;

[0080] Figure 18A Is a diagram showing the supply of Figure 1A And 1B Block diagram of the implementation of a power supply that supplies a single current to the electrical conductors; and

[0081] Figure 18B Is a diagram showing the supply of Figure 1A And 1B Block diagram of the implementation of a power supply that supplies a first current and a second current to the electrical conductors. Detailed Description

[0082] Referring to Figure 1A And 1B The cleaning device 100 is designed to remove debris 105 from the exposed surface 110 of a structure 115 within a chamber 120 defined by a container 125 of an extreme ultraviolet (EUV) light source. Examples of EUV light sources are in Figure 5 、 7A, shown in FIGS. 8A, 9A, and 10A. The EUV light source also includes a target delivery system 130 configured to direct a stream 132 of the target 135 to an interaction region 140 within the chamber 120. The target 135 includes a material that emits EUV light 145 when converted to a plasma 150 (also referred to as a luminous plasma 150).

[0083] The debris 105 is at least partially generated by residual or remaining target material 155 within the chamber 120. In particular, the residual or remaining target material 155 can be target material within the interaction region 140 that is not converted to the plasma 150; and / or the residual or remaining target material 155 can be generated by the plasma 150 that reverts back to the target material 155. The process of generating the EUV light 145 relies on converting the material in many targets 135 into the plasma 150, and thus a large amount of residual or remaining target material 155 may be generated during this process. Different phases of the target material 155 tend to deposit on the surfaces of various objects inside the chamber 120. The residual or remaining target material 155 can travel through the chamber 120 and coat various objects such as the walls, optical elements, and components within the chamber 120. The debris 105 formed on the surfaces of these objects can include vapor residues, ions, particles, and / or clusters of the material formed by the target material 155.

[0084] The debris 105 can severely degrade the performance of the EUV light source by blocking the EUV light 145 or by contaminating the objects within the chamber 120. The debris 105 forms an effective coating on the surface 110 that blocks the surface 110. Thus, if the surface 110 is an optical surface intended to interact with the light within the chamber 120, its efficiency will decrease as it becomes coated with the debris 105. As another example, if the surface 110 is a non-optical surface (does not interact with light), the debris 105 coating the surface 110 can cause other serious problems within the chamber 120. The debris 105 can cause the surface 110 and the structure 115 to heat up, which may cause the debris 105 to be ejected from the surface 110 and onto other components within the chamber 120. The debris 105 may cause other problems, resulting in a reduction in the generation of the EUV light 145. For example, the debris 105 may flake, fall, shoot, or drip from the surface 110. In summary, the presence of such debris 105 reduces the performance of the surfaces within the chamber 120 and reduces the overall efficiency of the EUV light source and the generation of the EUV light 145. As described below, if the target 135 includes molten metal of tin, tin particles, tin clusters, tin residues, or tin ions may accumulate (or coat) on one or more structures within the chamber 120.

[0085] The debris 105 can be generated by materials other than the target material 155 present within the chamber 120. For example, the debris 105 can include carbon.

[0086] As Figure 1B shown, the cleaning device 100 is positioned within the chamber 120 and is close enough to the structure 115 such that debris 105 can be removed from the exposed surface 110, as described below. The cleaning device 100 includes an electrical conductor 160 that contacts a non-conductor 165. The electrical conductor 160 is configured to inductively generate an electric current at a location (which is a volume) 161 adjacent to the structure 115, thereby causing a material 170 present within the chamber 120 to transition from a first state of matter (e.g., vapor or liquid) to a plasma state of matter.

[0087] The material 170 can be present within the chamber 120 in such a manner that the material 170 is already present within the chamber 120 independent of the operation of the cleaning device 100. In a typical implementation, the chamber 120 is initially fabricated without introducing the material 170; then, subsequently, the material 170 is introduced before and / or during the operation of the chamber 120. Then, during the operation of the chamber 120, the material 170 is present within the chamber. Thus, it is not necessary to transport the material 170 from outside the chamber 120 into the chamber 120 prior to the operation of the cleaning device 100 because the material 170 is already present within the chamber 120 for the operation of the chamber 120. The material 170 can be transported into the chamber 120 via a fluid port in the container 125. For example, during the operation of an EUV light source, the material 170 can be supplied into the chamber 120 for other purposes, such as to provide a fluid flow pattern or to provide a buffer over the surfaces within the chamber 120.

[0088] The electrical conductor 160 acts as an inductively coupled plasma (ICP) tool that includes the electrical conductor 160 placed in contact with the structure 115 as a plasma generator. During the ICP process, a time-varying current (from a power source) flows through the electrical conductor 160, and the flow of the time-varying current generates a time-varying magnetic field in the vicinity of the electrical conductor 160. The generated time-varying magnetic field induces an electric field at a location 161 adjacent to the structure 115. The induced current is large enough to generate a plasma state of matter at the location 161 using the nearby material.

[0089] The plasma state of the material 170 includes the plasma particles 175 of the material 170, and these plasma particles 175 have considerable chemical reactivity. For example, the plasma particles 175 can include free radicals and / or ions of the material 170. The electrical conductor 160 is positioned such that the plasma particles 175 contact the debris 105 on the exposed surface 110. The plasma particles 175 chemically react with the deposited target material 155 of the debris 105 to form a new chemical substance 180, and this new chemical substance 180 is released from the exposed surface 110. For example, the new chemical substance 180 can be gaseous and thus becomes released from the exposed surface 110 upon formation. Then, this new chemical substance 180 in the gaseous state can be pumped out of the chamber 120 by the removal device 185.

[0090] The cleaning device 100 can be configured to operate even when exposed to molecular hydrogen present in the chamber 120 (i.e., to remove the debris 105 from the exposed surface 110). In addition, the cleaning device 100 can be configured to operate without the use or presence of oxygen; that is, oxygen is not required or not necessary for the operation and / or function execution of the cleaning device 100.

[0091] The cleaning device 100 is designed to remove the debris 105 from the exposed surface 110 of the structure 115 without the need to remove the structure 115 from the chamber 120. It is not necessary to stop the operation of the structure 115 within the chamber 120 in order to clean the exposed surface 110 of these structures 115, and this structure 115 contributes to the generation of EUV light 145 and / or maintains the operation of the chamber 120. Therefore, it is not necessary to stop or turn off the operation of the EUV light source in order for the cleaning device 100 to clean the surface 110. The cleaning device 100 is capable of removing most (if not all) of the debris 105 from the surface 110 within the chamber 120. The cleaning device 100 operates to prevent the debris 105 from being ejected from the exposed surface 110 (such as by sputtering, flaking, or dripping). In addition, the cleaning device 100 can be fluid-cooled, and thus, compared with previous designs that require heating components within the chamber 120 to reduce the harmful effects of the target material 155, it is more reliable thermally, less complex, and less expensive. For example, in existing designs where the structure 115 is heated to remove the debris 105, spattering of the debris 105 occurs. On the other hand, the cleaning device 100 does not heat the structure 115, and thus spattering is completely alleviated or avoided. In particular, the overall temperature of the chamber 120 is lower and the structure 115 is not heated, and the overall temperature of the structure 115 is lower than the melting point of the debris 105. In addition, the consumption of the material 170 is reduced or minimized because any plasma particles 175 that do not interact with the target material 155 in the debris 105 will reform into the material 170.

[0092] In some implementations, chamber 120 is maintained at atmospheric pressure. In other implementations, chamber 120 is maintained under vacuum, i.e., at a pressure below atmospheric pressure. For example, chamber 120 can be at a low pressure between about 0.5 Torr (T) and about 1.5 T (e.g., 1 T). A particular pressure can be suitable for most effectively generating EUV light 145. The cleaning device 100 is configured to operate in the environment of chamber 120, and thus, if chamber 120 is maintained at 1 T, the cleaning device 100 can operate at such a pressure.

[0093] Various parts of the target delivery system 130 can be located outside the container 125, in the wall of the container 125 (as Figure 1A shown), or inside the chamber 120. The target delivery system 130 delivers, controls, and guides the target 135 in the stream 132 towards the interaction region 140. The target 135 can be, for example, droplets of liquid or molten metal, a portion of a liquid stream, solid particles or clusters, solid particles contained in droplets, a form of the target material, or solid particles contained in a portion of a liquid stream. The target 135 can be any material that emits EUV light 145 when in a plasma state. That is, the target 135 is a substance that has emission lines in the EUV range when in a plasma state. For example, the target 135 can include water, tin, lithium, and / or xenon. The target 135 can be a target mixture that includes the target substance 155, as well as impurities such as non-target particles (which do not contribute to the generation of EUV light 145). As an example, the target 135 can be elemental tin, which can be used as pure tin (Sn); as a tin compound, such as SnBr4, SnBr2, SnH4; as a tin alloy, such as a tin-gallium alloy, a tin-indium alloy, a tin-indium-gallium alloy; or any combination of these alloys. In the absence of impurities, the target 135 includes only the target substance 155.

[0094] Free radicals (which can be at least one type of plasma particle 175 generated by the cleaning device 100) are atoms, molecules, or ions that have unpaired valence electrons or an open electron shell, and thus can be considered to have dangling covalent bonds. The dangling covalent bonds make free radicals highly chemically reactive, that is, free radicals can easily react with other substances. Due to their reactivity, free radicals are used to remove substances (such as debris 105) from objects such as the exposed surface 110. Free radicals remove the debris 105 by, for example, etching, burning, and / or reacting with the target substance 155 that forms the debris 105.

[0095] Plasma particles 175 (including free radicals) can be generated from material 170 in any suitable manner. For example, plasma particles 175 can be formed by decomposing larger molecules of material 170 that are located near non-conductor 165. The larger molecules are decomposed by a process that puts sufficient energy into these larger molecules, such as ionization radiation, heat, and discharge caused by the operation of electrical conductor 160. Specifically, the formation of plasma particles 175 involves supplying sufficient energy to the larger molecules of material 170 to break the bonds (usually covalent bonds) between the atoms of the larger molecules.

[0096] In some implementations, as described above, target 135 includes tin (Sn), and in these implementations, the target material 155 that forms debris 105 includes tin particles (e.g., tin or tin oxide). One of the materials 170 present and allowed in chamber 120 is molecular hydrogen (H2). In this case, plasma particles 175 are generated from molecular hydrogen. Plasma particles 175 can include free radicals and ions of hydrogen. An example of a simple free radical of hydrogen is a single hydrogen element (H*) with an unpaired valence electron. The chemical process that occurs due to the operation of cleaning device 100 is represented by the following chemical formula:

[0097] where g indicates that the chemical substance is in the gaseous state.

[0098] The generated hydrogen free radical H* binds to the tin particles in debris 105 and forms a new chemical substance 180, called tin hydride (SnH4), which is then released from exposed surface 110. This chemical process is represented by the following chemical formula:

[0099] where s indicates that the chemical substance is in the solid state.

[0100] In this way, the coating formed from debris 105 is etched or removed from exposed surface 110 at a rate of at least 10 nanometers per minute and up to 200 nm / min over the entire exposed surface 110 (not just in the area near cleaning device 100). This is because plasma particles 175 are generated as close as possible to or sufficiently close to exposed surface 110 such that the fluid flow within chamber 120 causes plasma particles 175 to move rapidly across exposed surface 110 before the plasma particles 175 recombine or revert back to material 170. This is important because the lifetime of hydrogen free radicals H* (and other free radicals) is short and they tend to recombine to reform molecular hydrogen. Cleaning device 100 is designed such that: before these plasma particles 175 have the opportunity to recombine with each other to reform material 170, the plasma particles 175 have the opportunity to react with the target material 155 of debris 105, and this enables the cleaning of exposed surface 110 without having to remove structure 115 from chamber 120.

[0101] H* is not the only radical or ion produced from molecular hydrogen H2 by the cleaning device 100. Due to the operation of the cleaning device 100, many other radicals and ions can be formed from molecular hydrogen H2. These other radicals and ions are also plasma particles 175. For example, deuterons H2+ and tritons H3+ can also react with tin and form gaseous tin hydride, although they are not the main ones.

[0102] The electrical conductor 160 can be made of any suitable conductive material, such as copper and copper alloys. The electrical conductor 160 is placed near (and in contact with) the non-conductive body 165, and thus the electrical conductor 160 should be appropriately sized so that it does not obstruct other components or elements of the chamber 120. The electrical conductor 160 can include multiple conductors that are placed such that they contact various parts of the non-conductive body 165. The electrical conductor 160 can be wound or coiled so that it contacts multiple regions of the non-conductive body 165. The electrical conductor 160 can extend so that it continuously contacts a large area of the non-conductive body 165. These different designs are discussed below.

[0103] In some implementations, the electrical conductor 160 approaches the non-conductive body 165 in such a way that there is a thermal coupling between the electrical conductor 160 and the non-conductive body 165. The non-conductive body 165 can have a high enough thermal conductivity to enable effective heat transfer between the non-conductive body 165 and the electrical conductor 160. This means that the temperature of the non-conductive body 165 is related to (and affected by) the temperature of the electrical conductor 160. The value of the thermal conductivity of the non-conductive body 165 depends on the thermal load applied to the non-conductive body 165; thus, if the thermal load is low, the thermal conductivity may be lower compared to the case where the thermal load on the non-conductive body 165 is high. For example, the thermal conductivity of the non-conductive body 165 can be about 70 watts per meter per Kelvin (W / m·K).

[0104] In these implementations, the cleaning device further includes a temperature control system 190 that is thermally coupled to the electrical conductor 160. And, since the non-conductive body 165 is thermally coupled to the electrical conductor 160, the temperature of the non-conductive body 165 can also be controlled by controlling the temperature of the electrical conductor 160. In other implementations, the structure 115 can also be thermally coupled to one or more of the electrical conductor 160 and the non-conductive body 165 (or the structure 115 and the non-conductive body 165 are the same component, as referenced Figure 2A and 2B discussed).

[0105] If structure 115 is thermally coupled to electrical conductor 160, temperature control system 190 can be configured to maintain the temperature of non-conductive body 165 and structure 115 below a threshold maximum or within a threshold range. Accordingly, temperature control system 190 can be used to cool non-conductive body 165 or both non-conductive body 165 and structure 115. For example, temperature control system 190 can be configured to cool non-conductive body 165 or both non-conductive body 165 and structure 115 to a temperature below the melting point of target material 155. Accordingly, if target material 155 includes tin, temperature control system 190 is configured to cool non-conductive body 165 or both non-conductive body 165 and structure 115 to below 50° C.

[0106] Although not required, electrical conductor 160 can be designed as a tube extending along a longitudinal direction, such a tube including a hollow longitudinal opening 195, as Figure 1B shown. The hollow opening 195 can be used as a conduit or internal channel as follows. In such an implementation, temperature control system 190 includes a fluid control system that feeds or supplies a cooling fluid (such as water) through the internal channel 195 to control the temperature of electrical conductor 160. In this example, the cooling of non-conductive body 165 is limited by the freezing temperature of the cooling fluid flowing through opening 195, and if the cooling fluid is water, the temperature of the water should be maintained above the freezing temperature of water at the pressure in opening 195.

[0107] Non-conductive body 165 is non-conductive. Accordingly, non-conductive body 165 is made of a dielectric. For example, suitable dielectrics are ceramics such as aluminum nitride, boron nitride, silicon carbide, aluminum oxide, boron carbide, and other composite ceramics. In other implementations, the dielectric can be glass, porcelain, mica, polyethylene, quartz, or sapphire.

[0108] Referring again to Figure 1A , cleaning device 100 can be coupled to power source 191, which is configured to supply current to electrical conductor 160. The current supplied to electrical conductor 160 can be in the radio frequency (RF) range. Radio frequency is an electromagnetic wave frequency that ranges from about 20 kilohertz (kHz) to 300 gigahertz (GHz).

[0109] In one implementation, the electric power supplied to the electrical conductor 160 can be on the order of several kilowatts (kW) or tens of kilowatts (kW). The electrical conductor 160 is a hollow tube made of copper with a diameter less than 1 / 2", through which 1 gallon of cooling water flows per minute through its internal channel 195. The RF frequency can be approximately 14 mHz, and the electric power supplied to the electrical conductor 160 can be approximately 1 - 3 kW. The chamber 120 can be maintained at approximately 140 pascals (Pa), which is approximately 1.05 T. The removal rate of debris 105 from the surface 110 can be at least 200 nanometers (nm) / minute across the entire surface 110.

[0110] In other implementations, the electrical conductor 160 can be implemented as part of a microwave plasma generator. For example, the current supplied to the electrical conductor 160 is in the range that generates microwave radiation. Microwave radiation is an electromagnetic wave with a frequency in the range from approximately 1 GHz to approximately 300 GHz. In such an implementation, the current induced at the location 161 can be along the surface of the structure 115 and can be considered a surface wave.

[0111] Additionally, the control device 192 can communicate with the cleaning device 100 and the power supply 191 to control the operation of the electrical conductor 160. The control device 192 can also communicate with the temperature control system 190 and control the operation of the temperature control system 190.

[0112] For example, the control device 192 can send a signal to the power supply 191 to supply current to the electrical conductor 160 and simultaneously send a signal to the temperature control system 190 to activate the temperature control of the non - conductor 165 or the structure 115. The control device 192 can include one or more modules. The various modules of the control device 192 can be independent modules because data does not transfer from one module to another. Or, one or more modules within the control device 192 can communicate with each other. The modules within the control device 192 can be physically located in the same place or separated from each other.

[0113] The control device 192 can include a memory, which can be a read - only memory and / or a random - access memory. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non - volatile memory, including for example semiconductor storage devices such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto - optical disks; and CD - ROM disks. The control device 192 can also include one or more input devices (such as a keyboard, touch screen, microphone, mouse, handheld input device, etc.) and one or more output devices (such as a speaker or a display).

[0114] The control device 192 includes one or more programmable processors, and one or more computer program products tangibly embodied in a machine-readable storage device for execution by the programmable processors. Each of the one or more programmable processors can execute an instruction program to perform a desired function by operating on input data and generating an appropriate output. Typically, a processor receives instructions and data from a memory. Any of the foregoing can be supplemented or incorporated by a specially designed ASIC (Application Specific Integrated Circuit).

[0115] Each module within the control device 192 can be a set of computer program products executed by one or more processors. Moreover, any module can access data stored in the memory. The connections between the controllers / functions / modules within the control device 192 and the connections between the controllers / functions / modules within the control device 192 and the components of the cleaning device 100 can be wired or wireless.

[0116] Reference Figure 2A , in some implementations, the non-conductor 165 is a different non-conductor 265 from the structure 215 having the exposed surface 210. In these implementations, the structure 215 and the non-conductor 265 can be configured to be close to or adjacent to each other. Alternatively, the structure 215 and the non-conductor 265 can be two parts of a larger object (e.g., the structure 215 is an area including the exposed surface 210, and the non-conductor 265 is remote from that area). The electrical conductor 260 is in contact with the non-conductor 265.

[0117] As Figure 2B shown, in these implementations, when the electrical conductor 260B electromagnetically induces a current at the position 261B adjacent to the non-conductor 265B, plasma particles 175 are generated near the non-conductor 265A. In these implementations, the non-conductor 265B is configured relative to the structure 215B such that the plasma particles 175 can contact debris 105 on the exposed surface 210B. For example, as Figure 2BAs shown, the non-conductor 265B can be physically positioned such that plasma particles 175 generated at position 261B are swept or pushed from the non-conductor 265B towards the exposed surface 210B. In this example, there is a fluid flow pattern 266 within the chamber 120, and this fluid flow pattern 266 provides the force needed to quickly sweep or push the plasma particles 175 towards the exposed surface 210B before the plasma particles 175 have a chance to recombine and revert to the target substance 155. The fluid flow pattern 266 can be a fluid flow of the material 170 across the exposed surface 210B for protecting the exposed surface 210B during operation. The fluid flow pattern 266 is the flow needed to transport the plasma particles 175 to one or more debris-contaminated surfaces 110. Additionally, the fluid flow pattern 266 can also provide the flow needed to transport a new substance 180 (such as tin hydride) from the surface 110 to the removal device 185. Another type of fluid flow pattern 266 is shown in Figure 10C and 10D . The fluid flow pattern 266 is the peripheral flow pattern 1066, which is an existing flow pattern configured to protect the reflective surface 1043 of the light collector 1042.

[0118] In other implementations, such as where the exposed surface 210C is near the non-conductor 265C and also near the position 261C where the plasma particles 175 are generated, as Figure 2C shown, ensuring that the plasma particles 175 reach the exposed surface 210C may not require the fluid flow pattern 266. Specifically, the exposed surface 210C is very close to the non-conductor 265C such that the position 261C where the plasma particles 175 are generated coincides with the exposed surface 210C.

[0119] Referring to Figure 3A , in other implementations, the non-conductor 165 is the structure 110. Thus, the structure 110 and the non-conductor 165 are one and the same structure 312. In these implementations, the electrical conductor 160 is directly coupled to the structure 312. That is, the electrical conductor 160 contacts at least some parts or regions of the structure 312. Additionally, the structure 312 has all the properties of the non-conductor 165, which means that the structure 312 is non-conductive and can be made of a dielectric such as ceramic. For example, as Figure 3B shown, the electrical conductor 360B is placed adjacent to the structure 312B (or embedded therein, as Figure 3B shown) such that the electrical conductor 360B is configured to electromagnetically induce a current at the position 361B adjacent to the structure 312B to transform the existing material 170 into plasma particles 175. Since the plasma particles 175 are generated at the structure 312B, no fluid flow pattern 266 is needed to transport the plasma particles 175.

[0120] As described above, the electrical conductor 160 contacts the non-conductive body 165. Refer to Figures 4A - 4D , the electrical conductor 160 can contact the non-conductive body 165 in different ways, depending on the geometry of the non-conductive body 165 and also on the relative pressure between two surfaces of the non-conductive body 165. The non-conductive body 165 needs to be made of a dielectric in order to induce a current at position 161 due to the current flowing through the electrical conductor 160. Additionally, although the following examples discuss the non-conductive body 165, it should be noted that in each of these examples, the non-conductive body 165 can also be the structure 110. Each of these examples will be discussed next.

[0121] As Figure 4A shown, the electrical conductor 460A contacts the non-conductive body 465A at multiple positions on a first surface 4621_A held at a first pressure P1_A. A second surface 4622_A (which is adjacent to the position 461A where the current is induced) is held at a second pressure P2_A. In this example, the second pressure P2_A is different from the first pressure P1_A. For example, the second pressure P2_A can be a vacuum pressure, while the first pressure P1_A can be an atmospheric pressure. In this case, at least a portion of the electrical conductor 460A is exposed to the first pressure P1_A. Exposing the electrical conductor 460A to the atmospheric pressure (to reduce cost and design steps) is safe because at these pressures, the plasma particles 175 generated by the cleaning device 100 will not be ignited and there is little chance of damaging the electrical conductor 460A.

[0122] As Figure 4B shown, the electrical conductor 460B contacts the non-conductive body 465B at multiple positions. Additionally, the first surface 4621_B is held at a first pressure P1_B. The second surface 4622_B (which is adjacent to the position 461B where the current is induced) is held at a second pressure P2_B. In this example, the second pressure P2_B is the same as the first pressure P1_B. For example, both the second pressure P2_B and the first pressure P1_B can be vacuum pressures. In this case, the entire electrical conductor 460B is embedded within the non-conductive body 465B such that the conductor 460B is not exposed to the first pressure P1_B. In this example, since the pressure P1_B is at a vacuum pressure, the plasma particles 175 will have the opportunity to be ignited and cause damage to the exposed electrical conductor 460B. Therefore, in this case, the electrical conductor 460B is protected from plasma attack by being embedded within the non-conductive body 465B, which is a non-conductive material such as a dielectric.

[0123] As Figure 4CAs shown, the electrical conductor 460C contacts the non-conductive body 465C above a continuous spatial region at a first surface 4621_C, and the first surface 4621_C is maintained under a first pressure P1_C. A second surface 4622_C (which is adjacent to the location 461C where current is induced) is maintained under a second pressure P2_C. In this example, the second pressure P2_C is different from the first pressure P1_C. For example, the second pressure P2_C can be a vacuum pressure, while the first pressure P1_C can be an atmospheric pressure. In this case, the electrical conductor 460C is exposed to the first pressure P1_C.

[0124] As Figure 4D shown, the electrical conductor 460D continuously contacts the non-conductive body 465C. In addition, a first surface 4621_D is maintained under a first pressure P1_D. A second surface 4622_D (which is adjacent to the location 461D where current is induced) is maintained under a second pressure P2_D. In this example, the second pressure P2_D is the same as the first pressure P1_D. For example, both the second pressure P2_D and the first pressure P2_D can be vacuum pressures. In this case, the entire electrical conductor 460D is embedded within the non-conductive body 465D such that the conductor 460D is not exposed to the first pressure P1_D.

[0125] Referring Figure 5 , a cleaning device 500 in the implementation of an EUV light source 502 is shown. In this implementation, the cleaning device 500 is shown adjacent to a structure 515 to clean the exposed surface of the structure. Other components of the EUV light source 502 are discussed next. The EUV light source 502 includes a target delivery system 530 that directs a stream 532 of a target 535 towards an interaction region 540 in a chamber 520. The interaction region 540 receives an amplified beam 541, which can be a series of amplified light pulses. As described above, the target 535 includes a material that emits EUV light 545 when converted into a luminous plasma 550. The interaction between the material within the target 535 and the amplified beam 541 at the interaction region 540 converts at least some of the material in the target 535 into a luminous plasma 550, and the luminous plasma 550 emits EUV light 545. The luminous plasma 550 has elements with emission lines in the EUV wavelength range. The luminous plasma 550 has certain characteristics that depend on the composition of the target 535. These characteristics include the wavelength of the EUV light 545 generated by the luminous plasma 550.

[0126] The luminous plasma 550 can be considered as a highly ionized plasma with an electron temperature of several tens of electron volts (eV). For clarity, as described below, the luminous plasmas 150, 550 generated from the targets 135, 535 are different from the plasma particles 175 in the plasma state of the material 170. The luminous plasmas 150, 550 are generated due to the interaction between the targets 135, 535 and the amplified beam 541. In addition, the luminous plasmas 150, 550 of the targets 135, 535 are the materials for generating EUV light 145. In contrast, the plasma particles 175 are generated from the material 170 found within the chambers 120, 520. Neither the material 170 nor the plasma particles 175 contribute to the generation of the EUV light 145, 545. In addition, the plasma particles 175 are not generated by any interaction between the material 170 and the amplified beam 541.

[0127] Using fuel materials (target 535) such as terbium (Tb) and gadolinium (Gd) other than tin, higher energy EUV light 545 can be generated. The high-energy radiation (EUV light 545) generated during the de-excitation and recombination of ions is emitted from the luminous plasma 550, and at least a portion of the EUV light 545 is collected by the optical element 542. The optical element 542 can be a light collector in which the surface 543 interacts with at least a portion of the emitted EUV light 545. The surface 543 of the optical element 542 can be a reflective surface that can be positioned to receive a portion of the emitted EUV light 545 and direct the collected EUV light 544 for use outside the EUV light source 502. The reflective surface 543 directs the collected EUV light 544 to the secondary focal plane, where the EUV light 544 is then captured for use by a tool 546 (such as a lithography apparatus) outside the EUV light source 502. Refer to Figure 14 and 15 discuss exemplary lithography apparatuses.

[0128] The reflective surface 543 is configured to reflect light within the EUV wavelength range and can absorb, diffuse, or block light outside the EUV wavelength range. The light collector 542 also includes a hole 547 that allows the amplified beam 541 to pass through the light collector 542 towards the interaction region 540.

[0129] As Figures 6A - 6D shown, for example, the light collector 542 can be an elliptical mirror having a primary focus at the interaction region 540 and an auxiliary or intermediate focus IF at the secondary focal plane. This means that the plane section (such as the plane section C-C) is elliptical or circular. Thus, the plane portion C-C cuts through the reflective surface 543 and is formed by a portion of the ellipse. The light collector 542 (Figure 6D ) shows that the edges of the reflective surface 543 are rounded.

[0130] Reference again Figure 5 , the EUV light source 502 includes an optical system 551 that generates an amplified light beam 541 due to a population inversion in one or more gain media of the optical system 551. The optical system 551 may include at least one light source that generates the light beam, and a beam delivery system that manipulates and modifies the light beam and also focuses the light beam to the interaction region 540. The light source in the optical system 551 includes one or more optical amplifiers, lasers, and / or lamps for providing one or more main pulses that form the amplified light beam 541. And, in some cases, the optical system 551 may also provide one or more pre-pulses (not shown) that form a pre-amplifier beam that interacts with the target 535 before the interaction between the amplified light beam 541 and the target 535. Each optical amplifier includes: a gain medium that is capable of optically amplifying a desired wavelength with high gain; an excitation source; and internal optical devices. The optical amplifier may or may not have a laser mirror or other feedback device that forms a laser cavity. Therefore, even without a laser cavity, the optical system 551 generates an amplified light beam 541 due to a population inversion in the gain medium of the amplifier. Furthermore, the optical system 551 can generate the amplified light beam 541 as a coherent laser beam if a laser chamber is present to provide sufficient feedback to the optical system 551. Thus, the term "amplified light beam" encompasses one or more of: light from the optical system 551 that is merely amplified and not necessarily coherent laser oscillation; and light from the optical system 551 that is amplified and is also coherent laser oscillation.

[0131] The optical amplifier used in optical system 551 can include a gas including carbon dioxide (CO2) as a gain medium and can amplify light having a wavelength between about 9100 and 11000 nanometers (nm), and for example, about 10600 nm, with a gain greater than or equal to 100. Suitable amplifiers and lasers for use in optical system 551 include pulsed laser devices, such as pulsed gas discharge CO2 laser devices that generate radiation at about 9300 nm or 10600 nm, for example, using DC or RF excitation, operating at relatively high powers (e.g., 10 kW or more) and higher pulse repetition frequencies (e.g., 40 kHz or more).

[0132] The EUV light source 502 further includes a control device 552 that communicates with one or more controllable components or systems of the EUV light source 502. The control device 552 communicates with the optical system 551 and the target delivery system 530. In addition, the control device 552 may include or may communicate with a control device 192 that operates a power supply 191 that supplies power to the cleaning device 500. The target delivery system 530 may operate in response to signals from one or more modules within the control device 552. For example, the control device 552 may send a signal to the target delivery system 530 to modify the release point of the target 535 to correct an error in the target 535 arriving at the interaction region 540. The optical system 551 may be operable in response to signals from one or more modules within the control device 552. The various modules of the control device 552 may be independent modules, as data does not transfer from one module to another. Alternatively, one or more modules within the control device 552 may communicate with each other.

[0133] One or more modules within the control device 552 may be located in the same location. Alternatively, one or more modules within the control device 552 may be physically separated from each other. For example, the module that controls the target delivery system 530 may be located in the same location as the target delivery system 530, while the module that controls the optical system 551 may be located in the same location as the optical system 551.

[0134] The EUV system 502 further includes a removal or evacuation device 585 that is configured to remove the released chemical species 580 and other gaseous by-products that may form within the EUV chamber 520. As described above, the released chemical species 580 are formed by the interaction of plasma particles 575 (produced from the material 570) with the target material 555 that has been deposited on the exposed surface of the structure 515. The removal device 585 may be a pump that removes the released chemical species 580 from the EUV chamber 520. The removal device 585 may include a gas port that is in fluid communication with the EUV chamber 520 such that the released new chemical species 580 are transported from the region near the structure 515 towards the gas port, passed through the gas port, and out of the EUV chamber 520. For example, once the new chemical species 580 are formed, they are released from the exposed surface of the structure 515, and since the new chemical species 580 are volatile, they are drawn into the removal device 585, which removes the new chemical species 580 from the EUV chamber 520.

[0135] For example, other components of the EUV light source 502 (not shown) include a detector for measuring parameters associated with the generated EUV light 545. The detector can be used to measure the energy or energy distribution of the amplified beam 541. The detector can be used to measure the angular distribution of the intensity of the EUV light 545. The detector can measure the timing of the pulses of the amplified beam 541 or the error of the focus. The outputs of these detectors are provided to a control device 552, which includes modules for analyzing the outputs and adjusting aspects of other components of the EUV light source 502, such as the optical system 551 and the target delivery system 530.

[0136] In summary, the amplified beam 541 is generated by the optical system 551 and is directed along a beam path to irradiate the target 535 at the interaction region 540 to convert the material within the target 535 into a plasma 550 that emits light in the EUV wavelength range. The amplified beam 541 operates at a specific wavelength (source wavelength), which is determined based on the design and characteristics of the optical system 551 and the characteristics of the target 535.

[0137] Although only one cleaning device 500 is explicitly shown in the EUV chamber 520 of Figure 5 , multiple cleaning devices 500 can be configured throughout the EUV chamber 520. Other possible and exemplary (but not limited to) locations of the cleaning device 500 are marked by the fork-shaped icon 511 shown in Figure 5 . For example, the cleaning device 500 can be positioned next to any element that includes a surface that may potentially interact with the target substance 555 during the operation of the EUV light source 502 and thus potentially become coated with debris. Thus, one or more cleaning devices 500 can be positioned next to the light collector 542; alternatively, next to any wall within the EUV chamber 520; or next to the target delivery system 530, or along the path between the target delivery system 530 and the interaction region 540. One or more cleaning devices 500 can be positioned near the removal device 585 to clean the surface of the port of the removal device 585. Thus, in various implementations, additional electrical conductors 160 can be deployed to induce a current at a location adjacent to one or more surfaces of the removal device 585.

[0138] Next, various implementations of the cleaning device 500 and their uses are discussed.

[0139] Referring to Figures 7A to 7E , the cleaning device 500_7 (not visible in Figure 7A but shown in Figures 7B to 7E ) is associated with Figure 3A and 3BThe cleaning device 100 shown is similarly configured in that the structure with the exposed surface is the same as that of the non-conductor. The cleaning device 500_7 includes a shield 512_7 placed between the target delivery system 530 and the interaction region 540. The shield 512_7 can be considered a solid (usually lacking internal cavities) and rigid body that provides a semi-protected or fully protected passage 701 for the target 535 as the target 535 travels from the target delivery system 530 towards the interaction region 540. The shield 512_7 is configured to reduce the impact of the turbulence within the chamber 520 on the target 535 as the target 535 travels along the path to the interaction region 540. The shield 512_7 is positioned to extend across the light collector 542 and is so close to the interaction region 540 that the shield 512_7 is liable to be exposed to the target material 555 generated at the interaction region 540, and thus debris 505_7 from the target material 555 forms on the surface of the shield 512_7. Accordingly, the cleaning device 500_7 is designed to clean the surface of the shield 512_7.

[0140] In this case, the shield 512_7 is a structure with an exposed surface to provide a semi-protected passage 701. The shield 512_7 is also a non-conductor, and thus the shield 512_7 serves as a self-cleaning device. Accordingly, the shield 512_7 is made of a non-conductive material. For example, the shield 512_7 can be made of a dielectric such as ceramic. In addition, the cleaning device 500_7 includes an electrical conductor 560_7 that extends through the body of the shield 512_7. The electrical conductor 560_7 electromagnetically induces a current at positions 561_7 (similar to position 361B) adjacent to all of the outer surfaces of the shield 512_7.

[0141] Since all of the outer surfaces of the shield 512_7 are maintained at the same pressure, i.e., the pressure within the chamber 520_7, the electrical conductor 560_7 is routed through the body of the shield 512_7 so as to be embedded within the shield 512_7, similar to Figure 4D the general design shown. In addition, the region between the electrical conductor 560_7 and any of the outer surfaces of the shield 512_7 is a solid region without cavities.

[0142] The cleaning device 500_7 may further include a temperature control system 590_7 configured to control the temperature of the electrical conductor 560_7 and thus also the temperature of the shield 512_7. The temperature control system 590_7 can be a cooling fluid (such as water) flowing adjacent to the surface of the electrical conductor 560_7. For example, the electrical conductor 560_7 can be designed as a hollow tube through which the cooling fluid can flow to cool the electrical conductor 560_7 and thus also cool the shield 512_7.

[0143] As Figure 7DAs shown, the shield 512_7 can be made of two solid pieces 712A, 712B, which are complementarily shaped and each solid piece includes complementary grooves 713A, 713B. The groove 713A in the solid piece 712A is formed on the side of the solid piece 712A facing the solid piece 712B, while the groove 713B in the solid piece 712B is formed on the side of the solid piece 712B facing the solid piece 712A. Thus, when the solid pieces 712A, 712B are placed together, the grooves 713A, 713B form an opening that is sized to accommodate the electrical conductor 560_7. Accordingly, the electrical conductor 560_7 is sandwiched between the grooves 713A, 713B, and the solid pieces 712A, 712B can be bonded together. The electrical conductor 560_7 can be made of a conductive material such as copper or a copper alloy. The solid pieces 712A, 712B of the shield 512_7 are made of a dielectric (such as ceramic) having a thermal conductivity sufficient to effectuate efficient heat transfer from the shield 512_7 to the cooling fluid flowing through the electrical conductor 560_7. An example of a suitable ceramic that can be used in the solid blocks 712A, 712B is boron nitride, but aluminum nitride can be used.

[0144] In Figures 7A - 7E 's design, the cleaning device 500_7 is integrated within a structure having a surface to be cleaned (similar to Figure 3A and 3B 's design). In this way, the structure itself becomes a conduit that is capable of electromagnetically inducing a current at location 561_7 due to current flowing through the electrical conductor 560_7.

[0145] In other implementations, the cleaning device 500_7 can be designed separately from or remotely from the shield 512_7 (similar to Figure 2A and 2B 's design). Accordingly, the cleaning device 500_7 can be configured to induce a current at a location adjacent to a non-conductor (such as non-conductor 265B), and then the fluid flow pattern 266 can be provided or used to push the generated plasma particles 175 across one or more surfaces of the shield 512_7.

[0146] Referring to Figure 8A and 8B , in another implementation, the cleaning device 500_8 is implemented as a liner or sub-container 512_8 placed between the light collector 542 and the intermediate focus IF. The cleaning device 500_8 includes the liner 512_8, which is both a non-conductor and a structure having an exposed surface. The cleaning device 500_8 includes an electrical conductor 560_8 embedded within the liner 512_8 and a temperature control system 590_8 in thermal contact with the electrical conductor 560_8. Accordingly, the cleaning device 500_8 is associated withFigure 3A and 3B The cleaning device 100 shown is similarly configured because the structure with the exposed surface is the same as that of the non-conductor (which is the liner 512_8). Therefore, the liner 512_8 is made of a non-conductive material such as a dielectric (which can be ceramic). The liner 512_8 is shaped to allow EUV light 545 to be transmitted from the collector 542 to the intermediate focus IF without being blocked. A suitable shape for the liner 512_8 is conical, which smoothly tapers from a flat base FB located adjacent to the collector 542 to a vertex AP leading to the intermediate focus IF. In other implementations, the liner 512_8 is cylindrical and its axis extends from the flat base FB to the intermediate focus IF. In other implementations, the liner 512_8 has the same shape as the container 525, except that it is fitted inside the container 525.

[0147] Because the pressure at all surfaces of the liner 512_8 has the same value (which is the value at which the chamber 520 is maintained), the electrical conductor 560_8 extends through and is embedded within the body of the liner 512_8, similar to Figure 4B the general design shown. The electrical conductor 560_8 extends in a helical shape from the flat base FB to the intermediate focus IF. The electrical conductor 560_8 electromagnetically induces a current at a position 561_8 adjacent to the inner surface of the liner 512_8.

[0148] The cleaning device 500_8 is designed to accommodate the target substance 555 within the internal volume of the liner 512_8. In addition, by accommodating the target substance 555, the cleaning device 500_8 can more effectively clean debris from all surfaces within the chamber 520. All components of the EUV light source 502 that contribute to the generation of EUV light 545 are accommodated within the liner 512_8 such that all these components will also receive cleaning benefits from the liner 512_8.

[0149] The liner 512_8 can also be extended to wrap around the non-reflective side of the collector 542 to further enable the removal of debris from the exposed surface of the collector 542.

[0150] Since the inner liner 512_8 acts as a non-conductor and is also a structure to be cleaned, the material of the inner liner 512_8 is made of one or more dielectrics to allow the current from the electrical conductor 560_8 to inductively generate a current at position 561_8. Additionally, since a temperature control system 590_8 can be implemented to cool the conductor 560_8 as well as the inner liner 512_8, the inner liner 512_8 can be made of a highly thermally conductive material (e.g., with a thermal conductivity of at least 100 W / m·K) to enable efficient heat transfer between the inner liner 512_8 and the conductor 560_8. In one example, the inner liner 512_8 is made of a ceramic material and the electrical conductor 560_8 is made of copper or a copper alloy.

[0151] In this way, the cleaning device 500_8 serves at least two purposes. First, the cleaning device 500_8 generates plasma particles 175 at position 561_8 adjacent to the exposed surface of the inner liner 512_8. Second, the cleaning device 500_8 cools the wall of the inner liner 512_8 to ensure a high removal rate of debris on the surface of the inner liner 512_8 and also prevent the target substance 555 from splashing from the surface of the inner liner 512_8. The cleaning device 500_8 further includes a removal device 585_8 that is used to discharge new chemical substances 580 from the interior of the inner liner 512_8 and keep the new chemical substances 580 away from all components of the EUV light source 502 exposed to the target substance 555.

[0152] Reference Figure 9A and 9B In another implementation, the cleaning device 500_9 is implemented as the inner liner 512_9. The inner liner 512_9 provides a new design for the container 925. In Figure 9A and 9B example, the EUV chamber 920 is defined by the interior of the inner liner 512_9. The inner liner 512_9 is placed between the light collector 542 and the intermediate focus IF. The cleaning device 500_9 includes the inner liner 512_9, an electrical conductor 560_9 adjacent to and in contact with the outer surface of the inner liner 512_9, and a temperature control system 590_9 in thermal contact with the electrical conductor 560_9. The inner liner 512_9 is both a non-conductor and a structure with an exposed surface. Thus, the cleaning device 500_9 is similar to Figure 3A and 3BThe cleaning device 100 shown is similarly configured in that the structure with the exposed surface is the same as that of the non-conductor, which is the liner 512_9. Thus, the liner 512_9 is made of a non-conductive material such as a dielectric (such as ceramic). Similar to the liner 512_8, the liner 512_9 is shaped to allow the EUV light 545 to pass from the light collector 542 to the intermediate focus IF without being blocked. A suitable shape for the liner 512_9 is conical, which smoothly tapers from a flat base FB located adjacent to the light collector 542 to a vertex AP leading to the intermediate focus IF.

[0153] Since the pressure at the outer surface of the liner 512_9 is different from the pressure on the inner surface of the liner 512_9, which is the value at which the chamber 920 is maintained, the electrical conductor 560_9 is not embedded within the body of the liner 512_9 but, similar to Figure 4A the general design shown, is placed on and in contact with the outer surface. The electrical conductor 560_9 extends in a helical shape from the flat base FB to the intermediate focus IF. The electrical conductor 560_9 electromagnetically induces a current at a location 561_9 adjacent to the inner surface of the liner 512_9.

[0154] The cleaning device 500_9 is designed to accommodate the target substance 555 within the internal volume of the liner 512_9. By accommodating the target substance 555, the cleaning device 500_9 can more effectively clean debris from all surfaces within the chamber 920. All components of the EUV light source 902 that contribute to the generation of the EUV light 545 are accommodated within the liner 512_9 such that all these components will also receive cleaning benefits from the liner 512_9.

[0155] Since the liner 512_9 is a new design of the container 925, it is configured to wrap around the non-reflective side of the light collector 542 to further enable the removal of debris from the exposed surface of the light collector 542. Since the liner 512_9 serves as a non-conductor and also as the structure to be cleaned, the material of the liner 512_9 is dielectric to allow the current from the electrical conductor 560_9 to electromagnetically induce a current at the location 561_9. Additionally, since a temperature control system 590_9 can be implemented to cool the conductor 560_9 as well as the liner 512_9, the liner 512_9 can be made of a highly thermally conductive material to enable efficient heat transfer between the liner 512_9 and the conductor 560_9. In one example, the liner 512_9 is made of a ceramic material and the electrical conductor 560_9 is made of copper or a copper alloy.

[0156] In this manner, the cleaning device 500_9 serves two purposes. First, the cleaning device 500_9 generates plasma particles 175 at a position 561_9 that is adjacent to the exposed (inner) surface of the liner 512_9. Second, the cleaning device 500_9 cools the walls of the liner 512_9 to ensure a high removal rate of debris on the surface of the liner 512_9 and also to prevent the target material 555 from splashing from the surface of the liner 512_9.

[0157] The cleaning device 500_9 further includes a removal device 585_9 that is configured to discharge a fresh chemical 580 from the interior of the liner 512_9 and to keep the fresh chemical 580 away from all components of the EUV light source 902 that are exposed to the target material 555.

[0158] In the cleaning devices 500_7, 500_8, and 500_9 described above, the surface of the debris to be cleaned is a wall that does not optically interact with light to cause the generation of EUV light 545. As will be discussed next with reference to Figures 10A to 10D the cleaning device 500_10 is designed to clean the reflective surface 1043 of the light collector 1042. As described above, the reflective surface 1043 of the light collector 1042 collects at least a portion of the EUV light 545 emitted from the emitting plasma 550 that is generated due to the interaction between the target 535 and the amplified beam 541.

[0159] Because the reflective surface 1043 of the light collector 1042 is made of several layers of different kinds of metals, it is not feasible or practical to make an electrical conductor contact the back side of the light collector 1042 because the current conducted through such an electrical conductor cannot effectively induce a current at a position adjacent to the reflective surface 1043. Accordingly, the cleaning device 500_10 is designed similarly to the cleaning devices described in Figure 2A and 2B where an electrical conductor 560_10 is positioned inside a non-conductor 1065 and plasma particles 575 are generated at a position 561_10 near the non-conductor 1065. These generated plasma particles 575 are swept or pushed towards the exposed reflective surface 1043 by a fluid flow pattern 1066 that passes through the position 561_10 and moves towards and across the reflective surface 1043.

[0160] The non-conductive body 1065 is a ring circumferentially positioned around the outer surface of the light collector 1042, and the electrical conductor 560_10 is a copper tube embedded within the ring and extending along the perimeter of the outer surface of the light collector 1042. The cleaning device 500_10 may further include a temperature control system 590_10 configured to control the temperature of the electrical conductor 560_10 and thus also the temperature of the non-conductive body 1065. The temperature control system 590_10 may be a cooling fluid (such as water) flowing adjacent to the surface of the electrical conductor 560_10. For example, the electrical conductor 560_10 may be designed as a hollow tube through which the cooling fluid may flow to cool the electrical conductor 560_10 and thus also cool the non-conductive body 1065.

[0161] An opening 1067 (shown in Figure 10D ) between the ring 1065 and the outer surface of the light collector 1042 defines a location 561_10 where plasma particles 575 are generated as long as the material 570 flows through the opening via a fluid flow pattern 1066. In this case, hydrogen as the material 570 flows through the opening and the location 561_10 via the fluid flow pattern 1066 and then flows across the reflective surface 1043 of the light collector 1042. The ring 1065 is made of a dielectric such as a ceramic (such as aluminum nitride). The shield 1012 is also shown in Figure 10B and 10C ; the shield 1012 operates to provide a passage for the target 535 between the target delivery system 530 and the interaction region 540. The shield 1012 may be designed similar to the shield 512_7 such that it is self-cleaning (using the cleaning device 500_7).

[0162] Referring to Figure 11 , a process 1100 is performed to clean the surface 110 of the structure 115. The process 1100 is performed by any one of the cleaning devices 100, 500, 500_7, 500_8, 500_9, or 500_10 described above. In the most basic description, the cleaning device 100 of Figure 1A and 1B is referred to, and a specific example of the cleaning device 500_7 is discussed with reference to the process 1100.

[0163] The process 1100 begins with generating a plasma state (1105) of a material 170 at a location 161 adjacent to the non-conductive body 165. The plasma state of the material 170 includes plasma particles 175, at least some of which are free radicals or ions of the material 170. The process 1100 further includes enabling these plasma particles 175 to cross the exposed surface 110 of the structure 115 to remove debris 105 from the exposed surface 110 without having to remove the structure 115 from the chamber 120 (1115).

[0164] A plasma state (1106) of a material 170 is generated (1105) by electromagnetic induction of a current at a location 161 adjacent to a non-conductor 165. Thereby, the induced current (1106) transforms nearby material 170 from its first physical state, which can be liquid, gas, or solid, into a plasma state (1116).

[0165] Next, referring to Figure 12 , a current (1106) can be induced at a location adjacent to the non-conductor 165 using process 1206. Specifically, a time-varying current flows through a conductor 160 (1207) adjacent to the non-conductor 165. The current flowing through the conductor 160 can be at radio frequency. The flow of the current through the conductor 160 (1207) thereby generates a time-varying magnetic field (1208) in the chamber 120 near the non-conductor 165. The generated time-varying magnetic field (1208) electromagnetically induces a current (1106) at the location 161.

[0166] Process 1100 can also include using a temperature control system 190 to maintain the temperature of the structure 115 and the exposed surface 110 within a temperature range. For example, the temperature of the structure 115 and the exposed surface 110 can be maintained below 50 °C but above the freezing temperature of the cooling fluid flowing through the internal channel 195 of the conductor 160. Thus, process 1100 can also include flowing a cooling fluid (such as water) through the interior of the conductor 160, which can be a conductive tube defining an interior, or providing a cooling fluid (such as water) through the interior of the conductor 160, which can be a conductive tube defining an interior.

[0167] Processes 1100, 1105, and 1206 can be performed in the absence of oxygen.

[0168] As shown in the implementation of Figures 2A to 2C , the non-conductor 165 can be different from the structure 115 having the exposed surface 110. In these implementations, plasma particles 175 can then be enabled to cross the exposed surface 110 of the structure 115 to remove debris 105 (1115) from the exposed surface 110 by moving the plasma particles 175 from a location 161 near the non-conductor 165 toward the exposed surface 110 and across the exposed surface 110 (e.g., using a fluid flow pattern 266). Figures 10A - 10D The cleaning device 500_10 of

[0169] As in Figures 3A - 3BAs shown in the implementation of, the non-conductive body 165 can be the same as the structure 115 with the exposed surface 110 and can be referred to as the structure 312. In these implementations, then, the position 161 of the plasma state of the generating material 170 adjacent to the non-conductive body 165 is actually adjacent to the exposed surface 110 of the structure 115, and the plasma particles 175 can cross the exposed surface 110 to remove the debris 105 when it is generated (1115). Figures 7A - 7E The cleaning device 500_7 is an example of such an implementation; Figure 8A and 8B The cleaning device 500_8 is another example of such an implementation; Figure 9A and 9B The cleaning device 500_9 is yet another example of such an implementation.

[0170] The removal of the debris (1115) can be carried out by causing the plasma particles 175 (which cross the exposed surface 110) to undergo a chemical reaction with the debris 105 to form a new chemical substance 180, which is released from the exposed surface 110. Thus, the process 1100 can also include removing the released new chemical substance 180 from the chamber 120.

[0171] Reference Figures 13A to 13B , an example of the process 1100 is discussed with reference to the shield 512_7. Initially, as Figure 13A shown, the debris 105 has formed on the exposed surface of the shield 512_7. In this example, only a small amount of debris 105 is shown, but the debris 105 can form on all the exposed surfaces of the shield 512_7. As described above, the debris 105 is formed from the remaining or residual target substance 555. In Figure 13A , the cleaning device 500_7 has not been opened and thus the process 1100 has not started. Next, as Figure 13B shown, the plasma state (which includes the plasma particles 575) is generated by the material 570 near the shield 512_7 and located within the chamber 520. Thus, in Figure 13B , the plasma particles 575 have been generated. As Figure 13C shown, the plasma particles 575 can cross the exposed surface of the shield 512_7 to remove the debris 105 (which is released from the exposed surface as a new chemical substance 580).

[0172] Reference Figure 14, in some implementations, the cleaning device 100 (or 500, 500_7, 500_8, 500_9 or 500_10) is implemented within the EUV light source 1400 that supplies EUV light 1484 to the lithographic apparatus 1485. The lithographic apparatus 1485 includes: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., EUV light 1484); a support structure (e.g., a mask table) MT configured to support a patterning device (e.g., a mask or reticle) MA and connected to a first positioner PM configured to accurately position the patterning device; a substrate table (e.g., a wafer table) WT configured to hold a substrate (e.g., a wafer coated with resist) W and connected to a second positioner PW configured to accurately position the substrate; and a projection system (e.g., a reflective projection system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., including one or more dies) of the substrate W.

[0173] The illumination system IL may include various types of optical components for guiding, shaping, or controlling the radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof. The support structure MT holds the patterning device MA in a manner depending on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions (such as, for example, whether the patterning device is held in a vacuum environment). The support structure MT may use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device. The support structure MT may be, for example, a frame or a table, which may be fixed or movable as required. The support structure MT may ensure that the patterning device is, for example, in a desired position relative to the projection system PS.

[0174] The term "patterning device" should be interpreted broadly as referring to any device that can be used to impart a pattern to a cross-section of a radiation beam to create a pattern in a target portion of a substrate. The pattern imparted to the radiation beam may correspond to a particular functional layer in a device created in a target portion such as an integrated circuit. The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography and include mask types such as binary, alternating phase shift, and attenuated phase shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be tilted individually to reflect an incident radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam reflected by the mirror matrix.

[0175] Like the illumination system IL, the projection system PS can include various types of optical components such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, that are suitable for the exposure radiation being used or other factors such as the use of a vacuum. Since other gases may absorb too much radiation, it may be desirable to use a vacuum for EUV radiation. Thus, with the aid of a vacuum wall and a vacuum pump, a vacuum environment can be provided for the entire optical path.

[0176] As depicted herein, the device is of the reflective type (e.g., employing a reflective mask).

[0177] The lithographic apparatus can be of the type having two (dual-stage) or more substrate tables (and / or two or more patterning device tables). In such a “multi-stage” machine, other worktables can be used in parallel, or preparation steps can be carried out on one or more worktables while using one or more other worktables for exposure.

[0178] Also refer to Figure 15 , the illuminator IL receives an extreme ultraviolet radiation beam (EUV light 1575) from an EUV light source 1400. Methods for generating EUV light include, but are not limited to, converting a material into a plasma state having at least one element (e.g., xenon, lithium, or tin) whose one or more emission lines are in the EUV range. In one such method, commonly referred to as laser-produced plasma (“LPP”), the desired plasma can be generated by irradiating a fuel (such as droplets, streams, or clusters of a material having the desired line-emitting element) with a laser beam. The EUV light source 1400 can be designed like the EUV light source 502 or 902. As described above, the resulting plasma emits output radiation, e.g., EUV radiation, which is collected using an optical element 542 (or radiation collector).

[0179] The radiation beam B is incident on a patterning device (e.g., a mask) MA, which is held on a support structure (e.g., a mask table) MT and patterned by the patterning device. After reflection from the patterning device (e.g., a mask) MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. By means of a second positioner PW and a position sensor PS2 (e.g., an interferometer, a linear encoder, or a capacitive sensor), for example, the substrate table WT can be accurately moved so as to position different target portions C in the path of the radiation beam B. Similarly, a first positioner PM and another position sensor PS1 can be used to accurately position the patterning device (e.g., a mask) MA with respect to the path of the radiation beam B. Patterning device alignment marks M1, M2 and substrate alignment marks P1, P2 can be used to align the patterning device (e.g., a mask) MA and the substrate W.

[0180] The described device can be used in at least one of the following modes:

[0181] 1. In the step mode, the support structure (e.g., mask table) MT and the substrate table WT remain substantially stationary, while the entire pattern given to the radiation beam is projected onto the target portion C at once (i.e., single static exposure). Then, the substrate table WT is moved in the X and / or Y directions so that different target portions C can be exposed.

[0182] 2. In the scan mode, the support structure (e.g., mask table) MT and the substrate table WT are scanned synchronously, while the pattern given to the radiation beam is projected onto the target portion C (i.e., single dynamic exposure). The speed and direction of the substrate table WT relative to the support structure (e.g., mask table)

[0183] MT can be determined by the (reduction) magnification and image inversion characteristics of the projection system PS.

[0184] 3. In another mode, the support structure (e.g., mask table) MT remains substantially stationary to hold the programmable patterning device, and the substrate table WT is moved or scanned while the pattern given to the radiation beam is projected onto the target portion. In this mode, a pulsed radiation source is typically employed, and the programmable patterning device is updated as needed after each movement of the substrate table WT or between consecutive radiation pulses during the scan. This operating mode can be easily applied to maskless lithography using a programmable patterning device, such as the programmable mirror array of the type described above.

[0185] Combinations and / or variations of the above usage modes or completely different usage modes can also be employed.

[0186] Figure 15 An implementation of a lithographic apparatus 1585 including an EUV light source 1500, an illumination system IL, and a projection system PS is shown in more detail. When describing the EUV light source 502 or 902, the EUV light source 1500 is constructed and arranged as described above.

[0187] The systems IL and PS are also contained in their own vacuum environments. The intermediate focus (IF) of the EUV light source 1500 is arranged such that it is at or near the aperture in the enclosed structure. The virtual source point IF is an image of the radiation-emitting plasma (e.g., EUV light 145 or 545).

[0188] A radiation beam passes through an illumination system IL from an aperture at an intermediate focus IF. In this example, the illumination system IL includes a multifaceted field mirror device 1522 and a multifaceted pupil mirror device 1524. These devices form a so-called "fly's eye" illuminator, which is arranged to provide a desired angular distribution of the radiation beam 1521 at the patterning device MA, and a desired radiation intensity uniformity at the patterning device MA (as shown by reference numeral 1560). When the beam 1521 is reflected at the patterning device MA held by a support structure (mask table) MT, a patterned beam 1526 is formed, and the patterned beam 1526 is imaged by a projection system PS via reflection elements 1528, 1530 onto a substrate W held by a substrate table WT. To expose a target portion C on the substrate W, synchronous movements are performed on the substrate table WT and the patterning device table MT to generate radiation pulses while scanning the pattern on the patterning device MA through an illumination slit.

[0189] Each of the systems IL and PS is arranged within its own vacuum or near-vacuum environment, which is defined by an enclosed structure similar to the EUV chamber 520. There may typically be more elements in the illumination system IL and the projection system PS than shown. Additionally, there may be more mirrors than shown. For example, in addition to Figure 15 those shown, there may be 1 to 6 additional reflection elements in the illumination system IL and / or the projection system PS.

[0190] Referring again to Figure 5 , the target delivery system 530 may include a droplet generator that is arranged within the EUV chamber 520 and is arranged to emit a high-frequency stream 532 of droplets (targets 535) towards an interaction region 540. Accordingly, an amplified beam 541 is delivered synchronously with the operation of the droplet generator to deliver radiation pulses to convert each droplet (each target 535) into a glowing plasma 550. The delivery frequency of the droplets may be several kilohertz, for example 50 kHz.

[0191] In some implementations, the energy from the amplified beam 541 is delivered in at least two pulses: namely, a prepulse with limited energy is delivered to the droplet before it reaches the interaction region 540 to vaporize the fuel material into a small cloud, and then the main energy pulse is delivered to the cloud at the interaction region 540 to generate the glowing plasma 550. A trap (e.g., it may be a container) is provided on the other side of the EUV chamber 520 to capture the fuel (i.e., the target material 555 or the target 535) that for whatever reason does not turn into a plasma.

[0192] The droplet generator in the target delivery system 530 includes a container that holds a fuel liquid (e.g., molten tin), as well as a filter and a nozzle. The nozzle is configured to eject droplets of the fuel liquid toward the interaction region 540. Droplets of the fuel liquid can be ejected from the nozzle by a combination of pressure within the container and vibrations applied to the nozzle by a piezoelectric actuator (not shown).

[0193] Other implementations are within the scope of the appended claims.

[0194] For example, although the light collector 542 shown herein is a single curved mirror, it can take other forms. For example, the light collector 542 can be a Schwarzschild collector having two radiation collection surfaces. In another implementation, the light collector 542 is a grazing incidence collector that includes a plurality of substantially cylindrical reflectors nested within one another.

[0195] As another example, the shield 512_7 can have a different geometric design than that Figures 7A - 7E shown. For example, as Figure 16A and 16B shown, the shield 512_7 can be shaped as a hollow cylinder 1612_7 that extends axially from the target delivery system 530 to the interaction region 540. The target 535 axially passes through the opening of the hollow cylinder. In this case, the shield 1612_7 shaped as a hollow cylinder provides a fully protected passage 1601.

[0196] As another example, the shield 512_7 can be shaped as a flat plate that serves as a barrier that disrupts the target 535 for turbulence along one direction of the path from the target delivery system 530 toward the interaction region 540.

[0197] Referring Figure 17A , in some implementations, the shield 512_7 is designed as a hollow cylinder 1712_7A similar to the hollow cylinder 1612_7. The shield 512_7 is made of a dielectric material. However, similar to the Figure 4A general design shown, the electrical conductor 1760_7A is not embedded within the body of the shield 1712_7A, but is placed around the outer surface. The electrical conductor 1760_7A extends helically along the longitudinal axis of the shield 1712_7A, which is generally aligned with the -X direction.

[0198] Referring Figure 17B , in other implementations, the shield 512_7 is designed as a hybrid structure 1712_7B that includes a tubular portion TS (similar to the shield 1712_7A) and a U-shaped portion US (similar to the shield 512_7), with an electrical conductor 1760_7B wound around the U-shaped portion US.

[0199] In some implementations, the electrical conductors 1760_7A, 1760_7B are electrically insulated by low-pressure hydrogen H2 surrounding the electrical conductors. Additionally, the electrical conductors 1760_7A, 1760_7B do not need to contact the body of the shield 512_7, which is made of a dielectric material. In some implementations, the electrical conductors 1760_7A, 1760_7B are coated with a dielectric material.

[0200] Reference Figure 18A , in some implementations, the power supply 191 is configured to supply a single current 1893 (shown as a dashed line) to the electrical conductor 160.

[0201] In other implementations, as Figure 18B shown, the power supply 191 is configured to supply a first current 1893_1 at a first frequency to the electrical conductor 160, and to supply a second current 1893_2 at a second frequency to the electrical conductor 160. The second frequency is different from the first frequency. In such an implementation, the cleaning device 100 can perform two functions.

[0202] As described above, the first function is to remove debris 105 from the exposed surface 115. To perform this first function, a first current 1893_1 at a first frequency is supplied to the electrical conductor 160. The first frequency is selected to achieve this first function of removing debris 105 from the exposed surface 115. Thus, as described above, the first frequency can be a radio frequency. For example, the first frequency can be in the range of 500 kHz to 3 GHz.

[0203] The second function is to directly couple heat to the debris 105 (by inductive heating) without heating the non-conductor 165 and / or the structure 115. That is, thereby, the second current 1893_2 at the second frequency applied to the electrical conductor 160 inductively heats and evaporates the debris 105 on the surface of the structure. To perform the second function, a second current 1893_2 is supplied to the electrical conductor 160. The second frequency can be less than the radio frequency. For example, the second frequency can be below 500 kHz or in the range of 100 Hz to 200 kHz. The use of the second current 1893_2 avoids or reduces the amount of resistive heating applied to the non-conductor 165 and / or the structure 115.

[0204] The second frequency 1893_2 should be sufficiently different from the first frequency such that the two frequencies can be applied simultaneously or alternately in time. For example, the second frequency 1893_2 can be less than 200 kHz. The second current 1893_2 can be supplied simultaneously with, separately from, or alternately with the first current 1893_1. The power supply 191 can provide the first current 1893_1 and the second current 1893_2 as alternating current (AC) or pulsating direct current (DC). For example, the power supply 191 can be configured to apply a dual-frequency alternating current to the electrical conductor 160. As another example, the power supply 191 can be configured to apply a pulsating direct current to the electrical conductor 160.

[0205] The embodiments can be further described using the following clauses:

[0206] 1. A method of cleaning a surface of a structure within a chamber of an extreme ultraviolet (EUV) light source, the method comprising:

[0207] generating a plasma state of a material present at a location adjacent to a non-conductive body within the chamber, the generating comprising:

[0208] electromagnetically inducing a current at the location adjacent to the non-conductive body, thereby transforming the material adjacent to the non-conductive body from a first state to the plasma state, wherein the plasma state of the material comprises plasma particles, and at least some of the plasma particles are free radicals of the material; and

[0209] enabling the plasma particles to pass over the surface of the structure to remove debris from the surface of the structure without removing the structure from the chamber of the EUV light source.

[0210] 2. The method according to clause 1, further comprising maintaining the temperature of the structure below 50 °C.

[0211] 3. The method according to clause 1, wherein the surface of the structure is positioned to optically interact with light present in the chamber and modifies the light present in the chamber.

[0212] 4. The method according to clause 1, wherein generating the plasma state of the material comprises: generating the plasma state of the material in the absence of oxygen.

[0213] 5. The method according to clause 1, wherein generating the plasma state of the material comprises: generating the plasma state of the material without reducing the amount of material flowing over the surface of the structure.

[0214] 6. The method according to clause 1, wherein inducing the current by electromagnetic induction includes: passing an electric current through a conductive tube adjacent to the non-conductive body.

[0215] 7. The method according to clause 6, wherein the current passing through the conductive tube is at radio frequency.

[0216] 8. The method according to clause 1, wherein inducing the current by electromagnetic induction includes: generating microwave radiation at the non-conductive body or causing an electromagnetic surface wave to propagate along the non-conductive body.

[0217] 9. The method according to clause 6, further comprising providing a cooling fluid through the interior of the conductive tube to keep the temperature of the non-conductive body or the structure below a threshold temperature.

[0218] 10. The method according to clause 6, wherein:

[0219] the structure includes the non-conductive body; and

[0220] generating the plasma state of the material at the location adjacent to the non-conductive body includes: generating the plasma state of the material at the location adjacent to the surface of the structure.

[0221] 11. The method according to clause 6, wherein the structure is different from the non-conductive body.

[0222] 12. The method according to clause 11, wherein enabling the plasma state of the material to pass over the surface of the structure includes: causing the plasma particles to move from a location near the non-conductive body towards and across the surface of the structure.

[0223] 13. The method according to clause 1, wherein:

[0224] inducing the current by electromagnetic induction at the location adjacent to the non-conductive body includes generating a time-varying magnetic field near the non-conductive body within the chamber; and

[0225] generating the time-varying magnetic field within the chamber includes passing a time-varying current through a conductor adjacent to the non-conductive body.

[0226] 14. The method according to clause 1, wherein the plasma particles at least include ions, electrons and free radicals of the material.

[0227] 15. The method according to clause 1, wherein the material includes hydrogen.

[0228] 16. The method according to clause 1, wherein removing debris from the surface of the structure includes: causing the plasma particles to chemically react with the debris on the surface of the structure to form a chemical substance released from the surface of the structure.

[0229] 17. The method according to clause 16, further comprising removing the released chemical substance from the chamber.

[0230] 18. The method according to clause 16, wherein:

[0231] the material includes hydrogen, and the plasma particles include hydrogen radicals.

[0232] the debris on the surface of the substrate includes tin or carbon; and

[0233] if the debris includes tin, the released chemical substance includes tin hydride, and if the debris includes carbon, the released chemical substance includes methane.

[0234] 19. The method according to clause 1, wherein the chamber is maintained at a pressure below atmospheric pressure.

[0235] 20. The method according to clause 1, wherein the non-conductor is made of a dielectric.

[0236] 21. The method according to clause 1, wherein inducing the current by electromagnetic induction includes: causing a current to flow through a conductor adjacent to the non-conductor, and causing the current to flow through the conductor includes: applying a first current at a first frequency to the conductor and applying a second current at a second frequency different from the first frequency to the conductor.

[0237] 22. The method according to clause 21, wherein the first frequency is a radio frequency and the second frequency is lower than the radio frequency.

[0238] 23. The method according to clause 21, wherein applying the first current and the second current includes applying a dual-frequency alternating current or a pulsating direct current to the conductor.

[0239] 24. The method according to clause 21, wherein:

[0240] applying the first current at the first frequency to the conductor, thereby transforming the material adjacent to the non-conductor from a first state to a plasma state of the material including the plasma particles; and

[0241] applying the second current at the second frequency to the conductor, thereby inductively heating and evaporating the debris on the surface of the structure.

[0242] 25. A device, comprising:

[0243] An extreme ultraviolet (EUV) light source, comprising:

[0244] A chamber; and

[0245] A target delivery system configured to direct a target to an interaction region in the chamber, the target comprising a material that emits extreme ultraviolet light when converted to a plasma;

[0246] A structure within the chamber, comprising an exposed surface;

[0247] A cleaning device, near the structure and configured to remove target debris from the exposed surface of the structure without removing the structure from the chamber, the cleaning device comprising:

[0248] An electrical conductor in contact with a non-conductor,

[0249] wherein the cleaning device is configured to inductively generate an electric current at a position adjacent to the non-conductor, thereby transforming a material present in the chamber from a first state to a plasma state comprising plasma particles, wherein at least some of the plasma particles are radicals and ions of the material, and

[0250] wherein the non-conductor is configured relative to the structure such that the plasma particles contact the debris on the exposed surface of the structure.

[0251] 26. The device according to clause 25, further comprising a temperature control system thermally coupled to the electrical conductor, wherein the temperature control system is configured to maintain the temperature of the structure adjacent to the cleaning device within a threshold range.

[0252] 27. The device according to clause 26, wherein the temperature control system maintains the temperature of the structure adjacent to the cleaning device below a threshold maximum.

[0253] 28. The device according to clause 27, wherein the threshold maximum is 50 °C.

[0254] 29. The device according to clause 25, wherein the temperature control system comprises a fluid control system configured to feed a cooling fluid through an internal channel of the electrical conductor.

[0255] 30. The device according to clause 25, wherein the exposed surface optically interacts with light and modifies the light.

[0256] 31. The apparatus according to clause 30, wherein the light is an amplified beam that interacts with the target, or EUV light generated by the target.

[0257] 32. The apparatus according to clause 25, further comprising a flow device configured to cause the plasma particles to flow from the position adjacent to the non-conductor towards and across the exposed surface.

[0258] 33. The apparatus according to clause 25, wherein inducting the current electromagnetically includes: passing a current through the electrical conductor, and the current passing through the electrical conductor is at radio frequency.

[0259] 34. The apparatus according to clause 25, wherein the structure having the exposed surface and the non-conductor are the same physical structure.

[0260] 35. The apparatus according to clause 25, wherein the structure having the exposed surface is physically different from the non-conductor.

[0261] 36. The apparatus according to clause 25, wherein the non-conductor includes a shield, and the shield includes a passage for the target from the target delivery system to the interaction region.

[0262] 37. The apparatus according to clause 25, wherein the structure having the exposed surface is a condenser mirror of the EUV light source, the condenser mirror is positioned to capture at least a portion of the EUV light emitted from the plasma, and the non-conductor includes a ring positioned around an outer surface of the condenser mirror.

[0263] 38. The apparatus according to clause 25, wherein:

[0264] The structure having the exposed surface is the non-conductor.

[0265] The EUV light source includes a liner located between the condenser mirror and the intermediate focus; and

[0266] The structure includes the liner, and an inner surface of the liner faces the EUV light reflected from the condenser mirror towards the intermediate focus and constitutes the exposed surface of the structure.

[0267] 39. The apparatus according to clause 38, wherein if an outer surface of the liner is at a pressure different from a pressure at the inner surface, the electrical conductor is positioned outside the outer surface of the liner, or if the outer surface of the liner is at the same pressure as the pressure at the inner surface, the electrical conductor is embedded in the liner; and

[0268] The induced current is at the inner surface of the liner.

[0269] 40. The device according to clause 38, wherein the liner has a conical shape that smoothly tapers from a flat base located adjacent to the condenser to a vertex leading to the intermediate focus opening.

[0270] 41. The device according to clause 25, wherein the non-conductor is made of a dielectric.

[0271] 42. The device according to clause 41, wherein the dielectric includes ceramics.

[0272] 43. The device according to clause 41, wherein the ceramics include aluminum nitride or boron nitride.

[0273] 44. The device according to clause 25, wherein the target includes tin and the material includes hydrogen, and the cleaning device is configured to: in the absence of oxygen, remove one or more of tin fragments and carbon fragments from the exposed surface of the structure.

[0274] 45. The device according to clause 25, wherein:

[0275] if the pressures on the first and second sides of the non-conductor are equal, the conductor is embedded within the non-conductor; or

[0276] if the pressure on the first side of the non-conductor is different from the pressure on the second side of the non-conductor, the electrical conductor is adjacent to and outside of the first side of the non-conductor.

[0277] 46. The device according to clause 25, wherein the chamber is maintained at a pressure below atmospheric pressure.

[0278] 47. The device according to clause 25, further comprising a power source configured to supply current to the electrical conductor.

[0279] 48. The device according to clause 47, further comprising a control device to which the power source is connected, the control device being configured to send a signal to the power source to operate the cleaning device.

[0280] 49. The device according to clause 25, further comprising a fluid port configured to introduce the material into the chamber.

[0281] 50. The device according to clause 25, wherein the cleaning device is configured to: inductively electromagnetically induce a current at a location adjacent to the non-conductor by causing an electromagnetic surface wave to propagate along the non-conductor or generating microwave radiation at the non-conductor.

[0282] 51. The apparatus according to clause 25, wherein the cleaning device includes a power source electrically connected to supply current to the electrical conductor,

[0283] wherein the power source is configured to supply a first current at a first frequency to the electrical conductor and supply a second current at a second frequency to the electrical conductor, wherein the second frequency is different from the first frequency.

[0284] 52. The apparatus according to clause 51, wherein the first frequency is a radio frequency and the second frequency is less than the radio frequency.

[0285] 53. The apparatus according to clause 51, wherein the power source is configured to apply a dual-frequency alternating current or a pulsating direct current to the electrical conductor.

[0286] 54. An apparatus, comprising:

[0287] An extreme ultraviolet (EUV) light source, comprising:

[0288] A chamber; and

[0289] A target delivery system configured to direct a target to an interaction region in the chamber, the target comprising a material that emits extreme ultraviolet light when converted to a plasma; and

[0290] A shroud within the chamber defining a channel extending from the target delivery system to the interaction region, an outer surface of the shroud being exposed to debris generated by the target, wherein the shroud comprises:

[0291] A non-conductor defining the channel, and

[0292] An electrical conductor adjacent to the non-conductor;

[0293] wherein the electrical conductor inductively generates a current at a position adjacent to the shroud, thereby transforming a material present within the chamber from a first state to a plasma state comprising plasma particles, at least some of the plasma particles being free radicals and ions of the material; and

[0294] wherein the electrical conductor is positioned relative to the non-conductor such that the plasma particles chemically react with debris fixed to an exposed surface of the shroud, thereby releasing the debris from the exposed surface of the shroud.

[0295] 55. The apparatus according to clause 54, further comprising a temperature control system thermally coupled to the electrical conductor, wherein the temperature control system is configured to maintain the temperature of a surface of the channel below a threshold.

[0296] 56. The device according to clause 55, wherein the temperature control system is configured to cool the surface of the channel so as to prevent the debris from melting at the surface of the channel.

[0297] 57. The device according to clause 54, wherein:

[0298] the electrical conductor is embedded in the non-conductive body; and / or

[0299] the electrical conductor is in contact with the non-conductive body.

[0300] 58. The device according to clause 54, wherein the non-conductive body is made of a dielectric.

[0301] 59. The device according to clause 54, wherein the electrical conductor is wound around the outer surface of the non-conductive body, and the electrical conductor is coated with a dielectric material.

Claims

1. A radiation source, comprising: A container having at least one inner liner and at least one optical element; An exhaust device coupled to the container; A power supply coupled to the container and configured to operate in a frequency range from kilohertz (kHz) to gigahertz (GHz); A fluid supply coupled to the container and configured to introduce an air flow into the container; And A cleaning device located inside the container, wherein a conductor of the cleaning device is coupled to the power supply to generate an electromagnetic wave propagating along a dielectric of the cleaning device, thereby converting the air flow into a plasma state including reactive species, and the reactive species are configured to selectively react with debris on the at least one inner liner or the at least one optical element to form a compound to be discharged from the container through the exhaust device.

2. The radiation source according to claim 1, wherein the cleaning device is configured to generate reactive species that selectively react with the debris without stopping or shutting down the operation of the radiation source.

3. The radiation source according to claim 1, wherein the cleaning device is configured to generate reactive species that selectively react with the debris without changing the pressure of the radiation source.

4. The radiation source according to claim 1, wherein the power supply is configured to inductively generate a current in the conductor of the cleaning device at a microwave frequency or a radio frequency (RF) frequency.

5. The radiation source according to claim 1, further comprising: Fluid flow within the container configured to sweep or push the reactive species towards the at least one inner liner or the at least one optical element.

6. The radiation source according to claim 1, wherein the dielectric of the cleaning device is positioned adjacent to the at least one inner liner or the at least one optical element.

7. The radiation source according to claim 1, wherein the reactive species include at least one of free radicals and ions generated from the air flow.

8. The radiation source according to claim 1, wherein the cleaning device includes a temperature control system having a cooling fluid configured to flow near the surface of the conductor.

9. A method of cleaning a surface of an optical element in a radiation source, comprising: Introducing an air flow into a container of the radiation source; Generating an electromagnetic wave propagating along a dielectric of a cleaning device using a power supply operating in a frequency range from kilohertz (kHz) to gigahertz (GHz); Converting the air flow into a plasma state including reactive species; Selectively reacting the reactive species with debris on the surface of the optical element to form a compound; And Discharging the compound from the container through an exhaust device.

10. The method according to claim 9, wherein introducing an air flow into the container includes introducing hydrogen molecules near a plasma generation region of the radiation source.

11. The method according to claim 9, wherein the operation of selectively reacting the reactive species with the debris is performed without stopping or shutting down the radiation source.

12. The method according to claim 9, wherein generating the electromagnetic wave includes electromagnetically inducing a current in a conductor of the cleaning device at a microwave frequency or a radio frequency (RF) frequency.

13. The method according to claim 9, wherein generating the electromagnetic wave comprises: The current is alternately electromagnetically induced at a first frequency and a second frequency, and the first frequency is different from the second frequency.

14. The method according to claim 9, further comprising: Maintaining the temperature of the dielectric or the cleaning device below a threshold temperature using fluid cooling.

15. The method according to claim 9, further comprising: Transporting the reactive material and the new material to the surface of the optical element through a fluid flow pattern.

16. A cleaning device, comprising: A conductor coupled to a power source operating in a frequency range from kilohertz (kHz) to gigahertz (GHz); And A dielectric coupled to the conductor, wherein the power source electromagnetically induces a current, thereby generating a time-varying magnetic field and generating an electromagnetic wave propagating along the surface of the dielectric, the electromagnetic wave converting an air flow into a plasma state including a reactive material, and the reactive material passes over the surface of an element in a radiation source container to remove debris from the surface of the element by causing the reactive material to propagate along the surface of the element without etching the element and without stopping or shutting down the operation of the radiation source container.

17. The cleaning device according to claim 16, wherein the cleaning device is a shield configured to define a path of a target material projected from a target delivery system in the radiation source container.

18. The cleaning device according to claim 16, wherein the dielectric is an annular structure disposed around the circumference of a reflective surface of a condenser lens, and the conductor is an annular structure embedded in the dielectric.

19. The cleaning device according to claim 18, wherein an opening is defined between the dielectric and the condenser lens, the air flow passes through the opening and flows toward the reflective surface of the condenser lens, and the reactive material is generated near the edge of the condenser lens.

20. The cleaning device according to claim 18, wherein the reactive material passes over the surface of a lining in the radiation source container to remove debris from the surface of the lining by causing the reactive material to propagate along the surface of the lining without etching the lining and without stopping or shutting down the operation of the radiation source container.

Images