Lithographic apparatus, method of increasing plasma concentration and method of manufacturing device

Abstract

A lithographic apparatus (100) includes: a housing (400) defining an environment (401), where the environment surrounds a surface (402), where the housing is configured to contain a plasma; a microwave generator (410) configured to provide microwave radiation (411) into the housing; and a magnetic source (420) configured to generate a magnetic field adjacent to the surface, the magnetic field generating a plasma (432) by electron cyclotron resonance together with the microwave radiation, thereby increasing the concentration of the plasma adjacent to the surface.

Description

Technical Field

[0001] The present invention relates to lithographic apparatus, in particular to extreme ultraviolet (EUV) lithographic apparatus. Background Art

[0002] A lithographic apparatus is a machine that applies a desired pattern to a substrate (typically onto a target portion of the substrate). A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In this case, a patterning device (alternatively referred to as a mask or reticle) can be used to create the circuit pattern to be formed on a single layer of the IC. This pattern can be transferred to a target portion (e.g., a portion comprising a die, a die, or several dies) on a substrate (e.g., a silicon wafer). The pattern is typically transferred by imaging onto a layer of radiation-sensitive material (resist) disposed on the substrate. Typically, a single substrate will contain a grid of consecutively patterned adjacent target portions.

[0003] Photolithography is widely recognized as one of the key steps in the manufacture of ICs and other devices and / or structures. However, as the size of features manufactured using photolithography becomes smaller, photolithography becomes a more critical factor in enabling the manufacture of miniature ICs and other devices and / or structures.

[0004] The theoretical estimate of the limit of pattern printing can be given by the Rayleigh criterion of resolution, as shown in equation (1):

[0005] (1)

[0006] where λ is the wavelength of the radiation used, NA is the numerical aperture of the projection system used to print the pattern, k1 is a process-dependent adjustment factor (also known as the Rayleigh constant), and CD is the characteristic size (or critical dimension) of the printed feature. According to equation (1), a reduction in the minimum printable size of a feature can be achieved in three ways: by shortening the exposure wavelength λ, by increasing the numerical aperture NA, or by reducing the value of k1.

[0007] To shorten the exposure wavelength and thus reduce the minimum printable size, the use of extreme ultraviolet (EUV) radiation sources has been proposed. EUV radiation is electromagnetic radiation with a wavelength in the range of 10-20 nm (e.g., 13-14 nm). It has further been proposed that EUV radiation with a wavelength less than 10 nm could be used, for example, in the range of 5-10 nm (such as 6.7 nm or 6.8 nm). This radiation is known as extreme ultraviolet radiation or soft x-ray radiation. Possible sources include, for example, laser-generated plasma sources, discharge plasma sources, or sources based on synchrotron radiation provided by electron storage rings or free electron lasers.

[0008] Once the EUV radiation has been generated, it is directed through the lithographic apparatus by a plurality of mirrors to reach the patterned surface of the patterning device, which imparts the desired pattern to the EUV radiation.

[0009] The EUV generation process can deposit residues on various surfaces of the lithographic equipment, such as tin or hydrogen-induced outgassing (HIO) from the EUV light source. Another example of residue is water, which can form on surfaces when the lithographic equipment is taken out of vacuum, for example, for maintenance. The presence of such residues can degrade the performance of the lithographic equipment, for example, when they are present on optical surfaces. Such residues can be removed by contact with hydrogen plasma, which ionizes the residues. However, depending on the location of the surface within the lithographic equipment, it may be difficult to deliver a sufficient supply of hydrogen plasma to that surface to remove the residues. As a result, certain surfaces in the lithographic equipment may be affected by residue accumulation.

[0010] To clean these surfaces, the lithography equipment may need to be shut down for extended periods of time, which increases the downtime of the lithography equipment and reduces the manufacturing yield of the lithography equipment. Summary of the Invention

[0011] It is therefore an object of the present invention to provide a more efficient technique for increasing the plasma concentration in a lithographic apparatus, which technique may be used for cleaning surfaces and other purposes.

[0012] Another object of the present invention is to reduce the available costs associated with cleaning operations of EUV lithography equipment.

[0013] According to one aspect of the present invention, there is provided a lithographic apparatus, comprising:

[0014] an enclosure defining an environment, wherein the environment surrounds a surface, wherein the enclosure is configured to contain a plasma;

[0015] a microwave generator configured to provide microwave radiation into the enclosure;

[0016] A magnetic source is configured to generate a magnetic field adjacent to the surface, the magnetic field and the microwave radiation together generating additional plasma via electron cyclotron resonance, thereby increasing the concentration of plasma adjacent to the surface.

[0017] According to another aspect of the present invention, there is provided a method comprising:

[0018] providing microwave radiation from a microwave generator into an enclosure, wherein the enclosure defines an environment in the lithographic apparatus and the environment surrounds the surface; and

[0019] A magnetic field is generated adjacent the surface by a magnetic source, and the magnetic field and the microwave radiation together generate plasma by electron cyclotron resonance, thereby increasing the concentration of the plasma adjacent the surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, wherein corresponding reference numerals indicate corresponding parts.

[0021] Figure 1 A lithographic apparatus is schematically depicted.

[0022] Figure 2 A more detailed view of a lithographic apparatus is schematically depicted.

[0023] Figure 3 An EUV LPP source according to an embodiment is schematically depicted.

[0024] Figure 4 An EUV LPP source according to an embodiment is schematically depicted.

[0025] Figure 5 A MEMS device according to an embodiment is schematically depicted.

[0026] Figure 6 An illuminator according to an embodiment is schematically depicted.

[0027] Figure 7 A patterning device environment according to an embodiment is schematically depicted.

[0028] Figure 8 The provision of microwave radiation into multiple environments according to an embodiment is schematically depicted.

[0029] Figure 9 A second magnetic source according to an embodiment is schematically depicted.

[0030] Figure 10a and Figure 10b A housing with a plasma extractor according to an embodiment is schematically depicted.

[0031] Figure 11 A housing with multiple plasma extractors according to an embodiment is schematically depicted.

[0032] Figure 12 A small diameter housing with a plasma extractor is schematically depicted according to an embodiment.

[0033] Figure 13 A microwave coupler extending into a housing is schematically depicted according to an embodiment.

[0034] Figure 14a and Figure 14b A housing with a surrounding circular Halbach array according to an embodiment is schematically depicted.

[0035] The features shown in the figures are not necessarily drawn to scale, and the sizes and / or arrangements depicted are not limiting. It will be understood that the drawings include optional features that may not be essential to the present invention. In addition, not all features of the device are depicted in every drawing, and a drawing may only show some components relevant to describing a particular feature. DETAILED DESCRIPTION

[0036] Figure 1 A lithographic apparatus 100 comprising a radiation source SO according to an embodiment of the present invention is schematically depicted. The apparatus 100 comprises:

[0037] The illumination system (or illuminator) IL is configured to condition a radiation beam B (eg, EUV radiation).

[0038] a support structure (e.g., mask table) MT configured to support a patterning device (e.g., mask or reticle) MA and connected to a first positioner PM configured to accurately position the patterning device;

[0039] a substrate table (eg, wafer stage) WT configured to hold a substrate (eg, a resist-coated wafer) W and connected to a second positioning device PW configured to accurately position the substrate; and

[0040] A projection system PS (eg, a reflective projection system) is configured to project the pattern imparted to the radiation beam B by the patterning device MA onto a target portion C of the substrate W (eg, comprising one or more dies).

[0041] The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping or controlling the radiation.

[0042] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions (such as whether the patterning device is held in a vacuum environment). The support structure MT can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device MA. The support structure MT can be a frame or a table, for example, which can be fixed or movable as required. The support structure MT can ensure that the patterning device MA is in a desired position, for example relative to the projection system PS.

[0043] The term “patterning device” should be broadly interpreted as referring to any device that can be used to impart a pattern to the cross-section of a radiation beam B so as to create a pattern in a target portion C of a substrate W. The pattern imparted to the radiation beam B may correspond to a specific functional layer in a device being created in the target portion C, such as an integrated circuit.

[0044] Examples of patterning devices include masks, programmable mirror arrays, and programmable liquid crystal display (LCD) panels. Masks are well known in lithography and include 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 individually tilted to reflect an incident radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam that is reflected by the mirror matrix.

[0045] Like illumination system IL, projection system PS can include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types, or any combination thereof, as appropriate for the exposure radiation used, or for other factors, such as the use of a vacuum. It may be desirable to use a vacuum for EUV radiation because other gases may absorb too much radiation. Therefore, a vacuum environment can be provided throughout the beam path with the aid of vacuum walls and a vacuum pump.

[0046] As shown herein, the lithographic apparatus 100 is reflective (eg, employing a reflective mask).

[0047] The lithographic apparatus 100 may be of a type having two (dual stage) or more substrate tables WT (and / or two or more supports MT). In such a "multi-stage" lithographic apparatus, additional substrate tables WT (and / or additional supports MT) may be used in parallel, or preparatory steps may be performed on one or more substrate tables WT (and / or one or more supports MT) while one or more other substrate tables WT (and / or one or more other supports MT) are being used for exposure.

[0048] refer to Figure 1, the irradiation system IL receives an extreme ultraviolet radiation beam from a radiation source SO. The radiation source SO may be a laser produced plasma (LPP) source, a discharge produced plasma (DPP) source, a free electron laser (FEL), or any other radiation source capable of producing EUV radiation. Methods for producing EUV light include, but are not necessarily limited to, converting a material into a plasma state having at least one element (e.g., xenon, lithium, or tin) with one or more emission lines in the EUV range. In a laser produced plasma ("LPP"), the desired plasma may be produced by irradiating a fuel (such as a droplet, stream, or cluster of a material having the desired line-emitting element) with a laser beam. The radiation source SO may be a laser ( Figure 1 The laser source SO is a portion of an EUV radiation system (not shown) for providing a laser beam for excitation of the fuel. The resulting plasma emits output radiation, such as EUV radiation, which is collected using a radiation collector disposed in the radiation source SO. The laser and radiation source SO may be separate entities, for example when a CO laser is used to provide the laser beam for fuel excitation.

[0049] In this case, the laser is not considered to form part of the lithographic apparatus 100, and the radiation beam B is delivered from the laser to the radiation source SO by means of a beam delivery system comprising, for example, suitable steering mirrors and / or a beam expander. In other cases, the source may be an integral part of the radiation source SO, for example when the source is a discharge-produced plasma EUV generator (commonly referred to as a DPP source).

[0050] The illumination system IL can include an adjuster for adjusting the angular intensity distribution of the radiation beam. Typically, at least the outer and / or inner radial extent of the intensity distribution in a pupil plane of the illumination system IL (commonly referred to as σ-outer and σ-inner, respectively) can be adjusted. In addition, the illumination system IL can include various other components, such as a facet field and a pupil mirror arrangement. The illumination system IL can be used to adjust the radiation beam B to have a desired uniformity and intensity distribution in its cross-section.

[0051] A radiation beam B is incident on a patterning device (e.g., mask) MA, which is held on a support structure (e.g., mask table) MT, and is patterned by the patterning device MA. After reflecting from the patterning device (e.g., mask) MA, the radiation beam B passes through a projection system PS, which focuses the radiation beam B onto a target portion C of a substrate W. With the aid of a second positioner PW and a position sensor PS2 (e.g., an interferometer device, a linear encoder, or a capacitive sensor), the substrate table WT can be accurately moved, for example, to position a different target portion 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., mask) MA relative to the path of the radiation beam B. Mask alignment marks M1, M2 and substrate alignment marks P1, P2 can be used to align the patterning device (e.g., mask) MA and substrate W.

[0052] The controller 500 controls the overall operation of the lithographic apparatus 100, in particular, executing the operational processes described further below. The controller 500 may be embodied as a suitably programmed general-purpose computer, including a central processing unit, volatile and non-volatile storage devices, one or more input and output devices (such as a keyboard and screen), one or more network connections, and one or more interfaces to various components of the lithographic apparatus 100. It will be appreciated that a one-to-one relationship between the control computer and the lithographic apparatus 100 is not required. In embodiments of the present invention, a single computer may control multiple lithographic apparatuses 100. In embodiments of the present invention, multiple networked computers may be used to control a single lithographic apparatus 100. The controller 500 may also be configured to control one or more associated process devices and substrate handling devices within a lithocell or cluster of which the lithographic apparatus 100 forms a part. The controller 500 may also be configured to be subordinate to a supervisory control system of the lithocell or cluster and / or the overall control system of the factory.

[0053] Figure 2 The lithographic apparatus 100 is shown in greater detail and includes a radiation source SO, an illumination system IL, and a projection system PS. An EUV radiation-emitting plasma may be formed by the plasma source. The EUV radiation may be generated by a gas or vapor, such as Xe gas, Li vapor, or Sn vapor, wherein the radiation-emitting plasma is generated to emit radiation in the EUV range of the electromagnetic spectrum. In one embodiment, an excited tin (Sn) plasma is provided to generate EUV radiation.

[0054] The radiation source SO may include a radiation collector. Radiation passing through the radiation collector may be focused into a virtual source point IF. The virtual source point IF is often referred to as an intermediate focus, and the radiation source SO is arranged so that the virtual source point IF is located at or near the opening 221 in the enclosure 220. The virtual source point IF is an image of the radiation-emitting plasma.

[0055] The radiation then passes through an illumination system IL, which may include a faceted field mirror arrangement 22 and a faceted pupil mirror arrangement 24 arranged to provide a desired angular distribution of the unpatterned beam 21 at the patterning device MA, and a desired uniformity of radiation intensity at the patterning device MA. Upon reflection of the unpatterned beam 21 at the patterning device MA held by the support structure MT, a patterned beam 26 is formed, and the patterned beam 26 is imaged by the projection system PS via reflective elements 28, 30 onto a substrate W held by the substrate table WT. A pellicle 80 may be used to protect the patterning device from contaminants.

[0056] Typically, there may be more elements in the illumination system IL and the projection system PS than shown. Furthermore, there may be more mirrors than shown in the figures, e.g. Figure 2 As shown in FIG, there may be 1 to 6 additional reflective elements in the projection system PS.

[0057] Alternatively, the radiation source SO may be part of an LPP radiation system.

[0058] like Figure 1 As shown, in an embodiment, a lithographic apparatus 100 includes an illumination system IL and a projection system PS. The illumination system IL is configured to emit a radiation beam B. The projection system PS is separated from a substrate table WT by an intervening space. The projection system PS is configured to project a pattern imparted to the radiation beam B onto a substrate W. The pattern is EUV radiation from the radiation beam B.

[0059] The substrate W may include a previously formed pattern. In this case, the lithographic apparatus 100 aligns the image formed by the patterned EUV radiation beam B with the pattern previously formed on the substrate W.

[0060] The space between the projection system PS and the substrate table WT may be at least partially evacuated.The intervening space may be defined at the location of the projection system PS by a solid surface through which the employed radiation is directed towards the substrate table WT.

[0061] Both the patterning device MA and the support structure MT may be housed in a patterning device environment 90. The patterning device environment 90 may be isolated from the external environment surrounding the lithographic apparatus 100 and / or other components within the lithographic apparatus, thereby substantially preventing gases and contaminant particles from entering the patterning device environment 90.

[0062] The patterning device environment 90 can be partially evacuated of gas. That is, the pressure within the patterning device environment 90 can be less than ambient pressure. This is to limit the attenuation of EUV radiation as it passes through the patterning device environment 90. Even though the pressure within the patterning device 90 is less than ambient pressure, it is not a complete vacuum, and therefore gas particles may be present in the patterning device environment 90. Similarly, a relative vacuum, i.e., a small amount of gas (e.g., hydrogen) at a pressure significantly below atmospheric pressure, can be provided in the radiation source SO, illumination system IL, and / or projection system PS.

[0063] As described above, certain surfaces of the lithographic apparatus 100 may be susceptible to accumulation of residue. For example, tin vapor generated by EUV generation may deposit on certain surfaces of the lithographic apparatus 100. As another example, during a pumpdown operation of the lithographic apparatus, during which the pressure within the lithographic apparatus rises from a vacuum, water vapor may condense on certain surfaces of the lithographic apparatus 100. The presence of such residue may degrade the performance of the lithographic apparatus 100. In particular, the presence of residue on optical surfaces may reduce the reflectivity of the optical surfaces.

[0064] The present invention seeks to provide a technique for generating plasma via electron cyclotron resonance (ECR), which can be used to remove these residues. ECR is a well-known phenomenon in which, in the presence of an appropriate magnetic field and electromagnetic radiation, free electrons become excited by absorbing energy from the electromagnetic radiation. Generating plasma via ECR is well-established and widely used in various technologies. For example, in some ECR devices, microwave radiation is injected directly into a source chamber, which can be supplied with metal vapor or other gases. Preferably, the ion generator operates within the existing environment of a lithographic apparatus or other tool, such as a hydrogen atmosphere without an additional gas supply. Magnetic coils surround the source chamber and generate a magnetic field within it. Microwave absorption occurs where the magnetic field configuration matches the conditions for resonant electron absorption, resulting in plasma generation. The plasma is then ejected from the source chamber for further use. In addition to plasma, ECR generators can also generate electron or ion beams, depending on the specific application.

[0065] In theory, the plasma generated by known ECR devices can be used, for example, to remove residue from surfaces within the lithographic apparatus 100, or to control surface charge present on surfaces (such as the patterning device MA), or to control particle charge. However, in practice, given the complexity of the various components of the lithographic apparatus 100, there are often severe space limitations that make it impossible to place such ECR devices where they might be needed. This lack of space can be particularly severe near surfaces where residue deposition is most likely to occur. Additionally or alternatively, placement of such ECR devices at a desired location may be impossible due to obstructions to the optical path within the lithographic apparatus 100.

[0066] The inventive realization made by the present inventors is that the microwave source and the magnetic source can be decoupled and still generate sufficient plasma in the lithographic apparatus 100. That is, unlike some known ECR devices that tightly couple the microwave source and the magnetic source, in the lithographic apparatus, the microwave source can be positioned away from the magnetic source. As discovered by the inventors, this approach is particularly effective in the lithographic apparatus 100 due to the presence of plasma generated by EUV generation.

[0067] For example, in the aforementioned LPP apparatus, when EUV is generated by exciting tin vapor with a laser beam, hydrogen plasma is also generated. This hydrogen plasma, containing a mixture of free protons and free electrons, provides a base concentration of free electrons that can absorb energy from microwave radiation through electron cyclotron resonance. The excited electrons can then interact with other particles, including residual particles deposited on certain surfaces of the lithographic apparatus 100 and hydrogen (H2) present in the environment, generating even more plasma with additional free electrons capable of absorbing energy from microwave radiation. In other words, the presence of a base concentration of plasma generated by EUV facilitates plasma ignition, provided appropriate microwave radiation and a magnetic field are provided. More specifically, the presence of the EUV-generated plasma allows for ignition using microwave radiation of relatively low power and frequency (e.g., 2.45 GHz), which can offer the advantage of readily available equipment. However, plasma ignition may be easier at frequencies above 2.45 GHz. Higher frequencies can facilitate plasma ignition while requiring less power and allowing operation without an additional gas supply. Furthermore, higher-frequency microwaves can be propagated through smaller hollow waveguides (for example, hollow waveguides used at, for example, 2.45 GHz may be too large for applications in lithographic equipment or other tools using them), enabling the use of smaller devices. A simple device implemented in accordance with the present invention can be a hollow waveguide with several apertures / holes. This hollow waveguide can be considered a box with holes (similar to a multi-aperture extraction system) with a permanent magnet positioned near the box, eliminating the need for a bias voltage. This arrangement also enables the integration of unconventional geometries (for example, asymmetric devices) into limited available space. Thus, hollow waveguides allow for unconventional plasma chamber shapes to fill available space, which results in a larger plasma chamber within the available space with less stress on the material. Hollow waveguides also facilitate the use of dielectric liners and the use of dielectric surfaces to cover the interior of the plasma chamber. Furthermore, the use of higher microwave frequencies can potentially generate higher electron energies, making it easier to "extract" electrons with sufficient energy and current through the several apertures / holes in the waveguide when using low or even no bias voltage (zero bias voltage). Finally, if an additional gas supply may be required, "backflow" may be easily achieved using a hollow waveguide. In the absence of a base concentration of plasma, ignition of the plasma is still possible, but may require higher microwave power, or a significantly higher microwave frequency (e.g., above 2.45 GHz) and a correspondingly higher magnetic field strength. Once the plasma is ignited, it can be maintained by further reducing the microwave power.

[0068] In some known ECR devices, the microwave source and magnetic source are tightly coupled due to a lack of a sufficient base concentration of free electrons. Typically, in these known ECR devices, free electrons initially exist due to cosmic radiation, but the number of free electrons generated in this manner is small and random. Therefore, in known ECR devices, igniting the plasma from this small initial concentration of free electrons requires either relatively high microwave power, or a relatively high microwave frequency and a correspondingly strong magnetic field. In some known ECR devices, particularly those using, for example, 2.45 GHz microwave radiation, to provide sufficient microwave power, microwave radiation must be injected directly from the microwave source into the location where the magnetic field is provided. Consequently, the magnetic and microwave sources are tightly integrated. This may also theoretically be due to the fact that longer wavelengths cannot propagate in overly small "waveguides" or confined spaces, and it is also more difficult to "focus" longer wavelength microwaves. In these known ECR devices, if the microwave source is separated from the magnetic field by a large distance, the microwave power generated by the microwave source must be significantly increased to compensate for the drop in microwave power at the location where the magnetic field is provided. For this reason, in these known ECR devices, it is impractical to physically separate the microwave source from the magnetic source.

[0069] Now refer to Figures 3 to 7 According to an embodiment of the present invention, a lithographic apparatus 100 is disclosed that includes a housing 400, a microwave generator 410, and a magnetic source 420. The housing 400 defines an environment 401. As will be further disclosed below, in some embodiments, the environment 401 can be an environment within the lithographic apparatus 100 in which a plasma generated by EUV generation is present. The environment 401 surrounds a surface 402, which can be a surface to be cleaned or, more generally, a surface that may need to be exposed to a plasma. The housing 400 can be configured to contain a plasma, including a base concentration of plasma 431 generated by EUV generation. As used herein, an "housing" need not be fluid-tight and can have holes and apertures through which fluids and / or light can pass. The microwave generator 410 is located outside the environment 401 and is configured to provide microwave radiation 411 into the housing 400. As shown, the location where the microwave radiation 411 is introduced into the housing 400 can be physically remote from the magnetic source 420. A microwave launcher (not shown) may be present at the point where microwave radiation 411 is introduced into enclosure 400. The microwave launcher may provide impedance matching for microwave radiation 411 entering enclosure 400.

[0070] Magnetic source 420 is configured to generate a magnetic field proximate to surface 402. Typically, because the magnetic field has a short range, magnetic source 420 can be positioned close to surface 402, resulting in a relatively high-intensity magnetic field proximate to surface 402. The magnetic field proximate to surface 402, along with the microwave radiation, generates additional plasma 432 through electron cyclotron resonance. As described above, a pre-existing base concentration of plasma 431 resulting from EUV generation can exist, and the microwave power required to ignite additional plasma 432 can be reduced without requiring high-frequency microwave radiation and a high-intensity magnetic field, thereby enabling microwave generator 410 to be positioned outside of environment 401. The generation of additional plasma 432 increases the concentration of plasma proximate to surface 402. The plasma can be used to remove residue from surface 402. The plasma can also be used for other purposes.

[0071] The plasma may include hydrogen plasma, i.e., a mixture of free protons and free electrons. This may be the case for plasma 431 generated by EUV generation, particularly when EUV is generated by exciting tin vapor. Similarly, additional plasma 432 may also include hydrogen plasma, which may be generated by ionization of hydrogen (H2) present in environment 401.

[0072] The enclosure 400 can be configured to contain hydrogen (H2) gas. This is because hydrogen may be present in many environments 401 within the lithographic apparatus 100. Compared to some conventional ECR devices, in the case of the lithographic apparatus 100, a dedicated gas supply into the enclosure 400 may not be necessary, as sufficient hydrogen may already be present in the environment 401 within the lithographic apparatus 100. Furthermore, not including a dedicated gas supply (e.g., hydrogen) has the advantage of allowing plasma generation without increasing the amount of hydrogen per volumetric space, thereby maintaining a high EUV transmission rate. Specifically, the enclosure can be configured to contain the hydrogen gas so that it does not reach the exterior of the enclosure 400. The hollow waveguide enables "backflow" away from the orifice from which the plasma / electrons / ions are extracted. This helps prevent particle contamination by inhibiting particle transport from within the plasma generator to sensitive surfaces intended to be kept clean by the plasma, electron beam, and / or ion beam.

[0073] As described above, various types of residues may be found on surface 402. For example, some tin vapor used in EUV generation may be deposited on surface 402. Another example is that the residue may include hydrogen-induced outgassing elements (e.g., tin, zinc, lead, or sulfur). Another example is that the residue may include water. Specifically, water may form when the lithographic apparatus 100 is taken out of vacuum for maintenance. When the vacuum is released, a monolayer of water may condense on surface 402. When the vacuum is subsequently restored during evacuation, most gases, such as hydrogen and nitrogen, will be evacuated, but the monolayer of water may remain adhered to surface 402. The presence of water may have harmful effects, such as when exposed to EUV radiation. EUV radiation can break water molecules into harmful particles, such as oxygen atoms. Plasma particles generated by electron cyclotron resonance may have sufficient kinetic energy to release water molecules from surface 402, allowing them to be expelled from environment 401 during evacuation.

[0074] Unlike some known ECR devices, the plasma generation method of the present invention does not require a dedicated plasma chamber. In some ECR plasma generators that do not require a plasma chamber, the plasma is generated near the microwave coupler. In contrast, in this embodiment, the additional plasma 432 is generated directly at the desired location. More specifically, the location where the additional plasma 432 is generated can be controlled by placing a magnetic source 420 in an appropriate position, so that a magnetic field is generated near the surface 402 where the additional plasma 432 is desired. The precise placement of the microwave generator 410 outside the environment may not be critical, as long as the microwave radiation 411 is provided within the housing 400 that defines the environment 401 within which the surface 402 is located. Compared to a complete ECR device, the magnetic source 420 can be more compact and can be located within the lithographic apparatus even when space is limited. Furthermore, the magnetic source 420 can be positioned where desired without obstructing the optical path. Furthermore, the magnetic source 420 can be relatively easily integrated into the lithographic apparatus 100 as needed. For example, because magnetic fields can penetrate some solid walls (unlike plasma), magnetic source 420 can provide the required magnetic field through the walls of enclosure 400, thereby avoiding the need for additional apertures in the walls.

[0075] Furthermore, by utilizing a base concentration of plasma 431 produced by EUV generation, the power and frequency of the microwave radiation 411 and the strength of the magnetic field required to ignite and subsequently sustain the additional plasma 432 can be lower.

[0076] As discovered by the present inventors, in one embodiment, a brief application of microwave radiation of about 1 ms to 100 ms is sufficient to ignite an additional plasma. Furthermore, the power of the microwave radiation required for ignition is comparable to the power levels required to maintain a plasma in known ECR devices. For example, in one embodiment, a power of less than 1 W / cm3 The ignition of the additional plasma is achieved with a microwave power density of about 1 / 30 to 1 / 10 of the microwave power density required for ignition. In this embodiment, once the additional plasma is ignited, the additional plasma can be maintained using a microwave power density of about 1 / 30 to 1 / 10 of the power density required for ignition. In other words, as discovered by the present inventors, even if the microwave generator 410 is located at a distance away from the magnetic source 420, due to the presence of the base concentration of plasma 431 generated by EUV generation, the microwave power required to ignite and maintain the generation of the additional plasma 432 can be significantly lower (e.g., an order of magnitude lower) than the microwave power required in some known ECR devices.

[0077] The magnetic source 420 can be of any type as long as it can generate the necessary magnetic field. For example, the magnetic source 420 can include a permanent magnet and / or an electromagnet. For example, the magnetic source 420 can be a neodymium magnet or a magnet made of any other magnetic material. In the case where the magnetic material is incompatible with the environment from the lithographic equipment, the magnet can optionally be encapsulated by a protective coating. Such a coating can help avoid degradation, such as embrittlement caused by a hydrogen atmosphere. Preferably, the magnetic source 420 is a magnet made of a material that is compatible with the environment present in the lithographic equipment. The use of permanent magnets can simplify the implementation of the lithographic equipment 100 because no power supply is required. In addition, the use of permanent magnets may also be beneficial in terms of thermal management because permanent magnets do not undergo Joule heating.

[0078] As described above, the magnetic source 420 can be placed at a location where additional plasma 432 is desired. In the simplest embodiment, the magnetic source 420 can include a single permanent magnet or a single electromagnet. However, depending on the shape and size of the surface 402 that is to be exposed to the additional plasma 432, it may be more appropriate to provide a magnetic source 420 that includes multiple permanent magnets and / or electromagnets. Figures 3 to 6 Each of the drawings depicts an arrangement that uses multiple magnets to provide a magnetic field to surface 402. It should be noted that although the figures depict magnetic source 420 using symbols typically associated with permanent magnets, magnetic source 420 can include one or more permanent magnets, or one or more electromagnets, or a combination of permanent magnets and electromagnets. By using multiple permanent magnets and / or electromagnets, a sufficient magnetic field can be generated adjacent to surface 402 even if surface 402 has a large area.

[0079] The magnetic source 420 may operate within the plasma 432 but may be shielded from the outside or isolated from the outside. Figure 4As shown, the magnetic source 420 can be disposed behind the optical surface of the collector mirror CO. Additionally or alternatively, the magnetic source 420 can be coated or encapsulated. This can be advantageous because some types of magnetic sources 420 are incompatible with the plasma 432 and / or gases within the environment 401, which may contain H+ ions. For example, neodymium magnets may be incompatible with hydrogen due to embrittlement unless they are encapsulated with a protective coating.

[0080] exist Figure 4 In the example shown, the magnetic source 420 may be located within the environment 401. However, as Figure 3 As shown, the magnetic source 420 may alternatively be located outside of the housing 400. Thus, the plasma 432 may be separated from the magnetic source 420 by the walls of the housing 400. Thus, the magnetic source 420 may be further protected from the plasma 432 and / or gases within the environment 401.

[0081] As described above, microwave generator 410 is located outside of environment 401, and microwave generator 410 is configured to provide microwave radiation 411 into enclosure 400 defining environment 401. Figure 5 As shown in the example of FIG4 , a waveguide 404 may be provided to guide microwave radiation 411 from the microwave generator 410 into the housing 400. The use of the waveguide 404 may provide flexibility in the placement of the microwave generator 401 within the lithographic apparatus 100. In particular, the microwave generator 410 may be placed away from the environment 401, and due to the presence of the waveguide 404, the microwave radiation may still be effectively guided into the housing 400, and the microwave power may still be sufficient to ignite the plasma 432.

[0082] In particular, waveguide 404 can be a hollow waveguide. Using a hollow waveguide allows for a robust microwave launcher design because, in contrast to coaxial waveguides, microwave propagation in a hollow waveguide does not require electrical isolation of the center conductor, which is relevant when the coaxial coupler is exposed to plasma or metal vapor. The microwave launcher is a device (not shown) that provides impedance matching between hollow waveguide 404 and a larger space (e.g., environment 401). When using a hollow waveguide, a microwave window 405 may also be provided. Microwave window 405 allows microwave radiation to pass through while maintaining the continuity of the solid wall of enclosure 400, which may be required to maintain a pressure differential (e.g., vacuum inside enclosure 400, atmospheric pressure outside).

[0083] Alternatively, waveguide 404 may be a coaxial waveguide. In this case, a microwave feedthrough may be provided in place of microwave window 405. The microwave feedthrough may allow microwave radiation to be introduced into enclosure 400 while maintaining the continuity of the solid walls of enclosure 400.

[0084] In either case, the microwave window 405 or microwave feedthrough can be positioned outside the environment 401. This prevents the microwave window 405 or microwave feedthrough from coming into contact with additional plasma 432 and / or gases within the environment 401. For example, as a result of EUV generation, the environment 401 can contain a concentration of metal vapor, which could condense on the microwave window 405 or microwave feedthrough if the microwave window 405 or microwave feedthrough were positioned inside the environment 401. Therefore, by positioning the microwave window 405 or microwave feedthrough outside the environment, such condensation of metal vapor can be avoided or reduced.

[0085] In particular, the lithographic apparatus 100 can be configured to prevent the plasma 432 from flowing along a straight line between the surface 402 and the microwave window 405 or the microwave feedthrough. For example, a solid wall can be provided to interrupt the straight line path between the surface 402 and the microwave window 405 or the microwave feedthrough. In other words, the lithographic apparatus 100 can be configured to avoid any direct line of sight between the surface 402 and the microwave window 405 or the microwave feedthrough. For example, the solid wall can be part of the hollow waveguide 404 described above. In particular, the waveguide 404 can have a bend, such as to form an L-shape, as shown in FIG. Figure 5 It will be appreciated that the waveguide 404 may have more than one bend and may also have curved portions as required by space constraints within the lithographic apparatus 100 .

[0086] Furthermore, because microwave generator 410 is located outside of environment 401, microwave generator 410 can be replaced while lithographic apparatus 100 is operating to manufacture devices. This is because while lithographic apparatus 100 is operating to manufacture devices, surface 402 may not need to be cleaned, and therefore, microwave generator 410 may not need to be operated. Furthermore, because microwave generator 410 is located outside of environment 401, microwave generator 410 can be removed and / or installed without interrupting processes occurring within environment 401 during device manufacturing. More specifically, due to the flexibility of microwave generator 410 placement, microwave generator 410 can be placed within lithographic apparatus 100 in a location that is easily accessible to maintenance personnel even while lithographic apparatus 100 is operating to manufacture devices.

[0087] Since some environments 401 in the lithographic apparatus 100 may be under vacuum, if a hollow waveguide 404 is used, gate valves (not shown) may be provided at certain points along the waveguide 404. By closing the gate valves, the vacuum can be maintained while the microwave generator 410 is replaced. By maintaining the vacuum, any processes occurring within the environment 401 can continue without interruption. However, preferably, the microwave generator is placed outside the vacuum and separated by a vacuum window, which is arranged so that microwaves pass through it. This arrangement has the advantage that the microwave generator can be replaced at any time without affecting the vacuum.

[0088] Therefore, if microwave generator 410 fails, microwave generator 410 can be replaced with a new microwave generator without interrupting manufacturing operations. This can increase the availability of lithographic apparatus 100 because the downtime associated with replacing microwave generator 410 can be reduced or completely eliminated. By comparison, the time it takes to replace a component in the environment within lithographic apparatus 100 can be a day or more.

[0089] Due to the flexibility provided by the present invention, the additional plasma 432 can be provided at any location within the lithographic apparatus 100 where it is needed, as long as there is a sufficient base concentration of plasma 431 generated by EUV. This can cover various environments 401 within the lithographic apparatus 100.

[0090] For example, Figure 3 and Figure 4 As shown, surface 402 may be a surface within EUV laser produced plasma (LPP) source vessel 212. For example, Figure 4 As shown, the surface 402 may include the surface of the collector reflector CO within the container 212, and in particular the optical surface of the collector reflector CO. The surface of the collector reflector CO may be particularly susceptible to the accumulation of, for example, tin residue. Therefore, an additional plasma 432 may be usefully generated near the surface of the collector reflector CO in order to ionize and remove the residue. For example, the additional plasma 432 may facilitate tin etching. As shown, the magnetic source 420 may include a magnetic source 420 embedded in the collector reflector CO. More specifically, the magnetic source 420 may be disposed behind the optical surface 402 of the collector reflector CO. The magnetic source 420 may be completely encapsulated within the bulk material of the collector reflector CO, which may further reduce or eliminate the amount of plasma that comes into contact with the magnetic source 420. The magnetic source 420 may generate a magnetic field adjacent to the surface of the collector reflector CO such that the magnetic field may generate the additional plasma 432 together with the microwave radiation 411 provided to the container 212. As described above, the magnetic source 420 may include a plurality of magnets, such as Figure 4Furthermore, multiple portions of the surface 402 of the collector mirror CO may be cleaned. This may be achieved by providing a magnetic source 420 corresponding to each portion of the surface 402 so as to generate a magnetic field adjacent to each portion of the surface 402.

[0091] Alternatively or additionally, the surface 402 may include an inner wall of the container 212 of the EUV LPP source, such as Figure 3 As shown. Figure 3 In the example shown, the magnetic source 420 can be placed outside the housing 400 (i.e., the wall of the container 212). As described above, this arrangement can shield the magnetic source 420 from the plasma 432. In addition, to provide cleaning of the inner wall of the container 212 (which can be generally conical in shape), the magnetic source 420 can include an array of magnets arranged to follow the shape of the container 212. The magnetic field generated by the magnetic source 420 can be strong enough to penetrate the housing 400 and provide the necessary strength of the magnetic field adjacent to the inner wall 402 to generate additional plasma 432.

[0092] like Figure 3 and Figure 4 As shown, the container 212 of the EUV LPP source may include an exhaust 403 that may be used to remove gases and / or contaminants from the environment 401. In this arrangement, microwave radiation 411 may be provided into the container 212 via the exhaust 403. Figure 3 and Figure 4 As shown, drain 403 may include an opening through which microwave radiation 411 from microwave generator 410 may enter drain 403 and ultimately enter container 212. As described above, it may be desirable to avoid a direct line of sight between surface 402 and microwave window 405 or microwave feedthrough. By placing the introduction point of the microwave radiation along drain 403 and by positioning microwave window 405 or microwave feedthrough a distance away from drain 403, any direct line of sight between surface 402 and microwave window 405 or microwave feedthrough may be avoided. A microwave launcher (not shown) may be provided to introduce microwave radiation into drain 403. The microwave launcher may be used to provide impedance matching for the microwave radiation entering drain 403.

[0093] The microwave generator 410 may be connected to the discharge portion 403 via a waveguide. As described above, the waveguide may include bends and / or curved portions as needed. Figure 3 and Figure 4 As shown, the container 212 may include a narrow opening at the imaginary source point IF. In order to prevent leakage of the microwave radiation 411 , the IF opening may be sufficiently small compared to the wavelength of the microwave radiation 411 .

[0094] Alternatively or additionally, the surface 402 may comprise an optical surface of a MEMS mirror device 22, 24, such as Figure 5 As shown in the figure, the MEMS mirror device 22, 24 may include an array of MEMS mirrors, each of which may be actuated by a control and sensing mechanism 251. In addition, in the control base of the MEMS mirror device 22, 24, wiring 252 may be present behind the optical surface 402 and the control and sensing mechanism 251. Because components such as the control and sensing mechanism 251 and the wiring 252 may reflect or absorb electromagnetic waves, the microwave radiation 411 may be advantageously provided on the mirror side of the MEMS mirror device 22, 24, as shown in the figure. Figure 5 As shown, the magnetic source 420 can still be disposed on the opposite side of the optical surface 402 of the MEMS mirror device 22, 24. As described above, the magnetic field from the magnetic source 420 can pass through the sensing mechanism 251, the wiring 252, the control base, etc. to reach the optical surface 402 of the MEMS mirror device 22, 24. With this arrangement, additional plasma 432 can be generated adjacent to the optical surface 402 of the MEMS mirror device 22, 24 without obstructing the optical path to and from the MEMS mirror device 22, 24.

[0095] like Figure 6 As shown, the MEMS mirror arrangement 22, 24 may be part of the illuminator IL of the lithographic apparatus 100. As shown, two MEMS mirror arrangements 22, 24 may be provided in the illuminator IL. The MEMS mirror arrangement may comprise the faceted field mirror arrangement 22 and the faceted pupil mirror arrangement 24 described above. As described above, after evacuation of the lithographic apparatus 100, surfaces in the illuminator IL may be particularly susceptible to accumulation of water molecules. Because the optical surface 402 of the MEMS mirror arrangement 22, 24 is exposed to EUV radiation, any water molecules present on the optical surface 402 may be decomposed by the EUV radiation into harmful particles as described above. Therefore, it may be beneficial to use an additional plasma 432 to remove these water molecules. It may be necessary to have a plasma 432 below 10 - 7 mbar, preferably about 10 -8 mbar water vapor pressure.

[0096] Because water molecules can be efficiently released from the optical surface 402 of the MEMS mirror device 22, 24, the pump-down time can be reduced. For example, a tenfold reduction in pump-down time can be achieved. A shorter pump-down time may be desirable because it can reduce damage to the capping or underlying layers of the MEMS mirror device 22, 24 due to deep oxidation during startup. This is particularly true because MEMS illuminators may be particularly susceptible to deep oxidation.

[0097] As described above, according to the present invention, additional plasma 432 may be provided in various environments 401 within the lithographic apparatus 100, particularly in the presence of a sufficient concentration of plasma 431 resulting from EUV generation. Figure 7 As shown, additional or alternatively, additional plasma 432 can be provided to various surfaces 402 within patterning device environment 90. As another example, not shown in the figures, surface 402 can include a window for measurement. In particular, magnetic source 420 can be embedded within the window, blocking only a small portion of the window's cross-section. With this arrangement, the material used for the window can be selected to facilitate chemical compatibility (e.g., with hydrogen plasma) without affecting the cleaning function of the present invention.

[0098] As described above, multiple surfaces 402 within an environment 401, 90 may be exposed to the additional plasma 432 generated using microwave radiation 411 from a microwave generator 410. Additionally or alternatively, the same microwave generator 410 may provide microwave radiation 411 to several environments 401, 90. Each of these environments 401, 90 may in turn house one or more surfaces 402 that need to be exposed to the additional plasma 432. Figure 8 As shown, as an example, microwave generator 410 can provide microwave radiation 411 to two environments 401. Microwave radiation 411 can be provided via waveguide 404, one end of which is connected to microwave generator 410 and branches into the two environments 401 as shown. In addition, the wavelength of microwave radiation 411 can be varied for each environment 401 so that the conditions for electron cyclotron resonance are met at the location where additional plasma 432 is required.

[0099] Typically, microwave generator 410 can be continuously activated, for example, if continuous generation of plasma 432 is desired. Similarly, magnetic source 420 can also be continuously activated. However, in some embodiments, microwave generator 410 can be selectively activated (i.e., when needed). Similarly, magnetic source 420 can be selectively activated. For example, when there are few contaminants that can form residues on surface 402, generation of additional plasma 432 may not be necessary. More generally, in some embodiments, prolonged exposure to additional plasma 432 may damage surface 402. Therefore, in some embodiments, it may be desirable to activate generation of additional plasma 432 only when cleaning of surface 402 is desired.

[0100] refer to Figure 9To further protect the surface 502 from exposure to plasma (eg, the base concentration of plasma 431 generated by EUV radiation), a second magnetic source 520 may be provided. The second magnetic source 520 may be configured to generate a magnetic field adjacent to and parallel to the second surface 502. The second surface 502 may be surrounded by an environment 401. As discovered by the present inventors, the magnetic field The plasma potential can be reversed (i.e., a negative potential difference between the plasma and the surface 502). In one experimental setup, it has been found that the plasma potential can be reversed by applying a magnetic field of approximately 20-30 Gauss (2-3 mT). This negative potential difference can cause the surface 502 to repel ions, thereby protecting the surface 502 from damage.

[0101] Certain surfaces within the lithographic apparatus 100 can particularly benefit from this protection. For example, multilayer mirrors can be used to transmit light through the lithographic apparatus 100. These mirrors may be exposed to the hydrogen plasma (ionized gas) produced by EUV generation. A positive potential difference (plasma potential) can accumulate between the plasma and the mirrors, which can accelerate ions with energies up to 25 eV from the plasma toward the mirrors. These high-energy ions are primarily generated during and immediately after the EUV pulse; lower-energy ions are generated later (>1 μs). Therefore, while these ions certainly help keep the optics clean, long-term exposure can cause damage (primarily due to the high-energy ions).

[0102] In the foregoing disclosure, in general, first surface 402 and second surface 502 may be different surfaces within environment 401. In some cases, first surface 402 and second surface 502 may overlap, or may be the same surface. First surface 402 and second surface 502 may be coincident.

[0103] The second magnetic source 520 can be selectively activated (eg, when it is desired to protect the surface 502). The second magnetic source 520 can be an electromagnet, which can allow for selective activation.

[0104] As described above, the first magnetic source 420 can also be selectively activated, allowing additional plasma 432 to be generated when needed. The second magnetic source 520 can achieve the opposite effect, repelling plasma ions for the purpose of protecting the surface 502. The lithographic apparatus 100 can selectively activate either the first magnetic source 420 or the second magnetic source 520 at any given time. The lithographic apparatus 100 can be configured so that the first magnetic source 420 and the second magnetic source 520 are not activated simultaneously. In particular, by selectively activating / deactivating the first magnetic source 420 and the second magnetic source 520, an amount of plasma sufficient for cleaning can be applied to the surface 402 / 502 while limiting damage to the surface 402 / 502. The first magnetic source 420 and the second magnetic source 520 can also be controlled synchronously with the EUV pulse. For example, the second magnetic source 520 can be activated when the energy is highest (during and shortly thereafter the EUV pulse), which results in the greatest damage.

[0105] As described above, the additional plasma 432 can be generated adjacent to the surface 402. This can be useful for cleaning the surface 402. In other words, the additional plasma 432 can be said to be generated in situ (i.e., generated where the additional plasma is used). However, the additional plasma 432 can also be extracted from the environment 401 for other uses.

[0106] refer to Figure 10a , a plasma extractor 69 may be provided to extract at least a portion of the additional plasma 432 from within the environment 401 to the outside of the environment 49. As shown, microwave radiation 411 may enter the environment 401 and propagate primarily in the longitudinal direction of the housing 400. The plasma extractor 69 may be positioned opposite the entry point of the microwave radiation 411 and may be aligned with the longitudinal direction. As shown, the extracted plasma 632 may flow substantially in the longitudinal direction.

[0107] Additionally or alternatively, such as Figure 10b As shown, the plasma extractor 69 may not be aligned with the direction of propagation of the microwave radiation 411. For example, the plasma extractor 69 may be positioned on a side of the housing 400 so that the direction of flow of the extracted plasma 632 is not in the longitudinal direction. For example, the plasma extractor 69 may be positioned so that the extracted plasma 632 flows in a direction substantially orthogonal to the direction of propagation of the microwave radiation 411.

[0108] like Figure 10a and Figure 10bAs shown, plasma extractor 69 may include aperture 691. Aperture 691 may allow additional plasma 432 to pass through for extraction. At the same time, aperture 691 may induce an impedance change that prevents at least a portion of microwave radiation 411 within environment 401 from escaping through aperture 691. Instead, due to the impedance change, microwave radiation 411 may be reflected back into environment 401. This may reduce the microwave power emitted to the exterior of environment 49. This may also more efficiently utilize microwave radiation 411 provided to enclosure 400.

[0109] Magnetic source 420 can provide a static magnetic field within housing 400, which can promote resonant absorption of microwave power within housing 400. Magnetic source 420 can include a symmetrical or asymmetrical arrangement of magnets, such as a simple dipole. Magnetic source 420 can surround housing 400. Magnetic source 420 can be a permanent magnet and / or an electromagnet.

[0110] refer to Figure 11 , plasma extractor 69 can include more than one aperture 691. Multiple apertures 691 can be provided. As previously described, each aperture 691 can allow plasma to be extracted therethrough. Each aperture 691 can cause an impedance change that prevents at least a portion of microwave radiation 411 within environment 401 from escaping through aperture 691. This can allow for the extraction of additional plasma 432 at a greater rate while preventing microwave radiation 411 from being emitted outside of environment 49.

[0111] exist Figure 11 In the illustrated arrangement, the housing 400 is elongated and the plurality of apertures 691 are arranged along the longitudinal axis of the housing 400. However, it will be appreciated that other arrangements of the plurality of apertures 691 may be employed as desired.

[0112] Additional plasma 432 may be generated by a single magnetic source 420, such as Figure 10a and Figure 10b Additionally or alternatively, as Figure 11 As shown, each of the plurality of apertures 691 can be associated with a separate magnetic source 420 for plasma generation. Specifically, as shown, each magnetic source 420 can be integrated with a corresponding aperture 691. That is, each aperture 691 can be formed in a corresponding magnetic source 420. In this arrangement, plasma 632 can be extracted once generated. Furthermore, the plurality of magnetic sources 420 can operate in different modes (e.g., plasma, electron beam, and / or ion beam). For example, plasma generation near a particle beam can be used to compensate for the space charge of the extracted charged particle beam.

[0113] To further enhance the extraction of plasma, e.g. Figure 10a 、 Figure 10b and Figure 11As shown, the plasma extractor 69 may also include an extraction electrode 692. The extraction electrode 692 may be used to generate a voltage bias, which may facilitate extraction of the plasma 632. In embodiments, the extraction electrode 692 may be configured to extract the plasma 632 as an ion beam. A power supply may be connected to the extraction electrode 692 to maintain the voltage bias. Alternatively, a diode may be utilized to maintain the bias voltage for the extraction electrode 692, thereby eliminating the need for a power supply or cables. Cables leading to a power supply may not always be easily accessible to narrow sections where bias is required. Surfaces exposed to the plasma without being grounded or connected to any other reference potential may "float" at an uncontrolled potential. By using, for example, Zener diodes, they can be used to bias surfaces in lithographic equipment or other tools in spaces that cannot be easily reached by cables. Zener diodes can also be used to bias objects or surfaces exposed to a plasma or charged particle beam (electron or ion beam) in a controlled manner, thereby avoiding the need for a power supply and cables to provide the bias voltage. In an embodiment, pellicle 80 can be biased relative to the reticle front side by electrically isolating pellicle 80 from the reticle front side and establishing contact with the reticle front side via a Zener diode. The Zener diode can also be a load-bearing part of the pellicle support structure (i.e., the pellicle frame that connects the pellicle film to the reticle front side). Additionally, electrodes of a plasma generator in an EUV scanner, or the plasma generator itself, can be biased using a Zener diode.

[0114] In some arrangements, several extraction electrodes 692 may be provided to achieve space charge compensation and / or beam focusing. Furthermore, using several extraction electrodes 692 can help reduce (potentially unavoidable) electrode corrosion. Furthermore, the extraction electrodes 692 can be asymmetric, which can be used to steer the beam or compensate for effects due to (asymmetric) stray magnetic fields. Furthermore, fins can be positioned between the extraction electrodes 692. These fins can be used to block cross-field-promoted discharges. Cross-field drift can also be used to extract the charged particle beam and / or avoid or prevent corrosion of the extraction electrodes 692.

[0115] In an embodiment, the extraction electrode 692 can be omitted. That is, the plasma (or electrons) can be extracted without the need for a bias voltage, for example by using a waveguide with an aperture. This can reduce the size of the plasma extractor 69.

[0116] refer to Figure 12 , the housing 400 can be elongated and can have a cross-sectional area smaller than that required for microwave radiation 411 to propagate as electromagnetic waves. Alternatively, the microwave energy can penetrate into the housing 400 as an evanescent wave. The evanescent wave, together with the magnetic field provided by the magnetic source 420, can enable the generation of additional plasma 432. Using a housing 400 with a small cross-section can reduce the size of the housing 400.

[0117] The housing 400 can be made of a material with a low sputtering yield. The housing 400 can be covered with a dielectric coating or liner (e.g., a low sputtering yield material such as yttrium oxide). The plasma-surface interaction at the plasma impact point can be managed by various additional features, such as thicker materials, low-sputtering materials, small wells or "beam dumps" or openings (to move the impact point to the outside of the housing 400, which provides geometric shielding from material emission from the impact point area).

[0118] like Figure 11 and Figure 12 As shown, there may be a microwave coupler 61, an antenna 611 that provides microwave radiation, and a microwave window 405. The antenna 611 may be disposed at a first end of the microwave coupler 61. The second end of the microwave coupler 61 may be coupled to the housing 400 at a joint. The microwave window 405 may be located at the joint and may allow microwave radiation 411 to pass through while fluidly isolating the microwave coupler 61 from the environment 401 surrounded by the housing 400. This may allow the environment 401 to be maintained at a different pressure than within the microwave coupler 61. Furthermore, the microwave window 405 may be used to shield the antenna 611 from additional plasma 432 generated within the housing 400.

[0119] refer to Figure 13 The second end of the microwave coupler 61 can extend into the housing 400. Furthermore, the second end of the microwave coupler 61 can be suspended within the housing 400 to allow relative movement between the second end of the microwave coupler and the housing. For example, the microwave coupler 61 can be suspended within the housing 400 without direct mechanical contact. The housing 400 surrounding the microwave coupler 61 can be slightly larger than sufficient to accommodate the microwave coupler 61, so that the impedance change from the microwave coupler 61 into the housing 400 can be kept small. This can reduce the amount of reflected microwave radiation 411.

[0120] Figure 10a and Figure 10b Also shown is an optional waveguide 62, which can be part of the housing 400. The waveguide 62 can transmit microwave radiation 411 from the microwave coupler 61 to a location within the housing 400 where a magnetic field provided by the magnetic source 420 is present. As described above, a microwave window 405 can be provided. The waveguide 62 can be shaped (not shown) such that the microwave window 405 is not within the line of sight of the additional plasma 432. In addition, the interior volume of the waveguide 62 can have various cross-sectional shapes, such as circular, oval, square, rectangular, C-shaped, or H-shaped.

[0121] As described above, the magnetic source 420 can have various shapes or arrangements. Figure 14aand Figure 14b As shown, the magnetic source 420 may include a circular Haugh array surrounding the housing 400. As shown, an antenna 611 may be provided to direct microwave radiation 411 into the housing 400. The antenna 611 may extend into the housing 400 along a longitudinal axis. The antenna 611 may be coextensive with the housing 400 in the longitudinal direction. The Haugh array may be substantially concentric with the antenna 611 and may have a longitudinal extent that overlaps with the antenna 611. For example, the Haugh array may be coextensive with the antenna 611 in the longitudinal direction. In other words, the housing 400 and the antenna 611 may together form a coaxial plasma chamber. Different configurations of the circular Haugh array may be used. For example, the circular Haugh array may be a quadrupole, a sextupole, or an octupole. With this arrangement, microwaves of all frequencies may propagate within the housing 400, regardless of the size of the housing 400. This may enable the housing 400 to be miniaturized.

[0122] As shown, one or more holes 691 can be provided to extract plasma from within the housing 400. The one or more holes 691 can be offset from the longitudinal axis of the antenna 611. The off-axis holes 691 can prevent corrosion of the antenna 611.

[0123] Where the foregoing disclosure refers to a "plasma," it will be understood that electrons (which are also charged particles) may be generated instead. Thus, where the foregoing disclosure refers to extracting a plasma as an "ion beam," it will be understood that in embodiments configured to generate electrons, an electron beam will be produced.

[0124] In one embodiment, the above components and methods (including Figure 6 、 Figure 8 、 Figure 9 Figure 10 Figure 11 、 Figure 12 、 Figure 13 and the embodiment shown in Figure 14) are implemented in other equipment than the lithographic equipment, optionally in a metrology equipment, and optionally in an inspection equipment. In one embodiment, these embodiments are implemented in an SXR device. An SXR device is a device comprising a source that emits SXR and / or EUV radiation. Optionally, these embodiments are implemented in an SXR metrology device and / or an SXR inspection device. An example of an SXR device is as described in WO2023165783A1, which is incorporated herein by reference in its entirety. Ions may be generated in the flushing environment around the SXR optical elements (e.g. the illumination system / optics and / or filtering device in WO2023165783A1) and, depending on the choice of flushing gas, they may damage the coatings of the SXR optical elements. In one embodiment, Figure 9The surface 502 in FIG. 5 is the surface of the illumination system / optical device and / or the surface of the filter device in the measurement / inspection equipment. In one embodiment, the filter device includes a zirconium film. In one embodiment, the filter device is a surface film. In one embodiment, Figure 9 Surface 502 in WO2023165783A1 is any surface exposed to the plasma, as described in WO2023165783A1. In one embodiment, the illumination optic is a mirror, optionally a curved mirror, and optionally a toroidal mirror. Optionally, the mirror includes a diffraction element, such as a grating, in its reflective surface. Optionally, the mirror is a toroidal mirror with a grating. Ions can be induced by SXR radiation, and due to the presence of ions, some gas must be excluded from the flushing gas of the device. The embodiments mentioned in the above paragraphs can enable the use of gas. A magnetic field can be applied to the surface of the SXR optic (optionally parallel to the surface) to deflect electrons and thereby change the plasma potential to the point of potential reversal (i.e., achieving a reversal of the plasma potential). A negative potential difference between the plasma and the surface can be achieved because the positive ions have already charged the surface. In addition to devices with high harmonic generation (HHG) sources, the above embodiments are also applicable to devices with other light sources, such as laser-produced plasma (LPP) sources, discharge-produced plasma (DPP) sources, and free-electron laser (FEL) sources. Adapting the magnetic field strength to the specific situation can also enable the identification of a beneficial field strength for specific optical devices, where the specific optical device is cleaned without being damaged. In another embodiment, the housing mentioned in the above embodiments is replaced by a container.

[0125] Although specific reference may be made herein to the use of lithographic apparatus in IC manufacturing, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), pellicle heads, and the like.

[0126] Where the context permits, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented by instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read-only memory (ROM); random-access memory (RAM); magnetic storage media; optical storage media; flash memory devices; electrical, optical, acoustic, or other propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.). Furthermore, firmware, software, routines, and instructions may be described herein as performing certain actions. However, it should be understood that such descriptions are for convenience only, and that such actions are actually performed by a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc., and in doing so, may cause actuators or other devices to interact with the physical world.

[0127] Although specific reference may be made herein to embodiments of the present invention in the context of lithographic apparatus, embodiments of the present invention may be used in other apparatus. Embodiments of the present invention may form part of mask inspection equipment, metrology equipment, or any apparatus that measures or processes objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatuses may generally be referred to as lithographic tools.

[0128] In one embodiment, the metrology device is configured to measure a parameter of interest of a process other than a photolithography process. For example, the metrology device is configured to measure a parameter of an etching process.

[0129] Although specific reference has been made above to embodiments of the invention being used in the context of optical lithography, it will be appreciated that the invention is not limited to optical lithography where the context permits.

[0130] Various aspects of the invention are described in the following numbered clauses.

[0131] 1. A lithographic apparatus (100), comprising:

[0132] an enclosure (400) defining an environment (401), wherein the environment surrounds a surface (402), wherein the enclosure is configured to contain a plasma;

[0133] a microwave generator (410) configured to provide microwave radiation (411) into the housing;

[0134] A magnetic source (420) is configured to generate a magnetic field adjacent to the surface, the magnetic field, together with the microwave radiation, generating plasma (432) by electron cyclotron resonance, thereby increasing the concentration of the plasma adjacent to the surface.

[0135] 2. The lithographic apparatus of clause 1, wherein:

[0136] The microwave generator is located outside the environment; and

[0137] The enclosure is configured to contain a base concentration plasma (431) generated by EUV radiation.

[0138] 3. The lithographic apparatus of clause 1 or clause 2, wherein the housing is configured to contain hydrogen gas.

[0139] 4. The lithographic apparatus of any preceding clause, wherein the plasma comprises hydrogen plasma.

[0140] 5. The lithographic apparatus of any preceding clause, wherein the magnetic source comprises a permanent magnet and / or an electromagnet.

[0141] 6. The lithographic apparatus of any preceding clause, wherein the magnetic source comprises a plurality of permanent magnets and / or a plurality of electromagnets.

[0142] 7. The lithographic apparatus of any preceding clause, wherein the magnetic source is separated from the plasma shield.

[0143] 8. The lithographic apparatus of any preceding clause, wherein the magnetic source is located external to the housing.

[0144] 9. The lithographic apparatus of any preceding clause, further comprising a waveguide (404) configured to guide the microwave radiation from the microwave generator into the housing.

[0145] 10. The lithographic apparatus of any preceding clause, configured to prevent the plasma from flowing along a straight line between the surface and a microwave window (405) through which microwave radiation from the microwave generator passes into the housing.

[0146] 11. The lithographic apparatus of any preceding clause, wherein the microwave generator is replaceable while the lithographic apparatus is operating to manufacture a device.

[0147] 12. The lithographic apparatus of any preceding clause, wherein the surface comprises a surface within an EUV laser generated plasma source vessel (212).

[0148] 13. The lithographic apparatus of clause 12, wherein the surface comprises a surface of a collector mirror (CO) within the container.

[0149] 14. The lithographic apparatus of clause 13, wherein the magnetic source comprises a magnetic source embedded in the collector mirror.

[0150] 15. The lithographic apparatus of any of clauses 12 to 14, wherein the surface comprises an inner wall of the container.

[0151] 16. The lithographic apparatus of any of clauses 12 to 15, wherein the container comprises a drain (403), and the microwave radiation is provided into the container via the drain.

[0152] 17. The lithographic apparatus of any preceding clause, wherein the surface comprises a window for metrology.

[0153] 18. The lithographic apparatus of clause 17, wherein the magnetic source comprises a magnetic source embedded in the window.

[0154] 19. The lithographic apparatus of any preceding clause, wherein the surface comprises an optical surface of a MEMS mirror arrangement (22, 24).

[0155] 20. The lithographic apparatus of clause 19, wherein the MEMS mirror arrangement is part of an illuminator (IL) of the lithographic apparatus.

[0156] 21. The lithographic apparatus of any preceding clause, comprising a plurality of said environments, wherein the microwave generator is configured to provide microwave radiation into each of the plurality of environments.

[0157] 22. The lithographic apparatus of any preceding clause, further configured to selectively activate the microwave generator.

[0158] 23. The lithographic apparatus of any preceding clause, further configured to selectively activate the magnetic source.

[0159] 24. The lithographic apparatus of any preceding clause, further comprising a second magnetic source (520) configured to generate a magnetic field adjacent to and parallel to a second surface (502) surrounded by the environment .

[0160] 25. The lithographic apparatus of clause 24, wherein the second magnetic source comprises an electromagnet.

[0161] 26. The lithographic apparatus of clause 24 or clause 25, wherein the first surface and the second surface are coincident.

[0162] 27. The lithographic apparatus of any of clauses 24 to 26, further configured to selectively activate the second magnetic source.

[0163] 28. The lithographic apparatus of any of clauses 24 to 26, further configured to selectively activate either the first magnetic source or the second magnetic source at a time, rather than activating both the first magnetic source and the second magnetic source simultaneously.

[0164] 29. The lithographic apparatus of any preceding clause, further comprising a plasma extractor (69) configured to extract at least a portion of the plasma from within the environment to outside the environment (49).

[0165] 30. A lithographic apparatus as described in item 29, wherein the plasma extractor includes an aperture (691) configured to allow plasma to be extracted through the aperture and to cause an impedance change that prevents at least a portion of microwave radiation within the environment from escaping through the aperture.

[0166] 31. A lithographic apparatus as described in item 29, wherein the plasma extractor includes a plurality of holes (691), each hole (691) being configured to allow plasma to be extracted through the hole and to cause an impedance change that prevents at least a portion of microwave radiation within the environment from escaping through the hole.

[0167] 32. The lithographic apparatus of clause 31 , wherein the housing is elongate and the plurality of apertures are arranged along a longitudinal axis of the housing.

[0168] 33. The lithographic apparatus of clause 31 or clause 32, wherein each of the plurality of apertures is associated with a separate magnetic source for plasma generation.

[0169] 34. The lithographic apparatus of any of clauses 24 to 33, wherein the plasma extractor further comprises an extraction electrode (692).

[0170] 35. The lithographic apparatus of any of clauses 24 to 34, wherein the housing is elongate and has a cross-sectional area that is smaller than required for propagation of the microwave radiation as an electromagnetic wave, such that microwave energy penetrates into the housing as an evanescent wave.

[0171] 36. The lithographic apparatus of any one of clauses 30 to 35, further comprising a microwave coupler (61), an antenna (611) for providing said microwave radiation, and a microwave window (405), wherein:

[0172] The antenna is disposed at the first end of the microwave coupler;

[0173] A second end of the microwave coupler is coupled to the housing at a joint; and

[0174] The microwave window is located at the junction and is configured to allow the microwave radiation to pass therethrough while isolating the microwave coupler from the ambient fluid surrounded by the housing.

[0175] 37. The lithographic apparatus of clause 36, wherein the second end of the microwave coupler extends into the housing.

[0176] 38. The lithographic apparatus of clause 37, wherein the second end of the microwave coupler is suspended within the housing so as to allow relative movement between the second end of the microwave coupler and the housing.

[0177] 39. The lithographic apparatus of any of clauses 34 to 38, wherein the extraction electrodes have an asymmetric arrangement.

[0178] 40. The lithographic apparatus of any of clauses 24 to 39, wherein the second magnetic source has an asymmetric arrangement.

[0179] 41. The lithographic apparatus of clause 30 or clause 31, further comprising an antenna (611), the microwave radiation being provided into the housing via the antenna (611); wherein:

[0180] the antenna extending into the housing along a longitudinal axis; and

[0181] The magnetic source includes a circular Hall array surrounding the housing, the Hall array being substantially concentric with the antenna and having a longitudinal extent overlapping the antenna.

[0182] 42. The lithographic apparatus of clause 41, wherein one or more apertures are offset from a longitudinal axis of the antenna.

[0183] 43. The lithographic apparatus of clause 41 or clause 42, wherein the circular Haugh array is a quadrupole, a hexapole, or an octupole.

[0184] 44. A method comprising:

[0185] providing microwave radiation (411) by a microwave generator (410) into an enclosure (400), wherein the enclosure defines an environment (401) in the lithographic apparatus (100), and the environment surrounds a surface (402); and

[0186] A magnetic field is generated adjacent the surface by a magnetic source (420), and the magnetic field and the microwave radiation together generate plasma (432) by electron cyclotron resonance, thereby increasing the concentration of the plasma adjacent the surface.

[0187] 45. The method of clause 44, wherein:

[0188] The microwave generator is located outside the environment; and

[0189] The housing contains a base concentration plasma (431) generated by EUV radiation.

[0190] 46. ​​The method of clause 44, wherein the housing contains hydrogen gas.

[0191] 47. The method of any one of clauses 44 to 46, wherein the plasma comprises hydrogen plasma.

[0192] 48. The method of any one of clauses 44 to 47, wherein the magnetic source comprises a permanent magnet and / or an electromagnet.

[0193] 49. The method of any one of clauses 44 to 48, wherein the magnetic source comprises a plurality of permanent magnets and / or a plurality of electromagnets.

[0194] 50. The method of any one of clauses 44 to 49, wherein the magnetic source is separated from the plasma shield.

[0195] 51. The method of any one of clauses 44 to 50, wherein the magnetic source is located external to the housing.

[0196] 52. The method of any one of clauses 44 to 51, wherein providing the microwave radiation comprises directing the microwave radiation from the microwave generator into the enclosure via a waveguide (404).

[0197] 53. The method of any one of clauses 44 to 52, wherein the plasma is prevented from flowing along a straight line between the surface and a microwave window (405) through which microwave radiation from the microwave generator travels into the enclosure.

[0198] 54. The method of any one of clauses 44 to 53, wherein the surface comprises a surface within an EUV laser generated plasma source vessel (212).

[0199] 55. The method of clause 54, wherein the surface comprises a surface of a collector mirror (CO) within the container.

[0200] 56. The method of clause 55, wherein the magnetic source comprises a magnetic source embedded in the collector mirror.

[0201] 57. The method of any one of clauses 54 to 56, wherein the surface comprises an interior wall of the container.

[0202] 58. The method of any one of clauses 54 to 57, wherein the container comprises a drain (403), and the microwave radiation is provided into the container via the drain.

[0203] 59. The method of any one of clauses 44 to 58, wherein the surface comprises a window for measurement.

[0204] 60. The method of clause 59, wherein the magnetic source comprises a magnetic source embedded in the window.

[0205] 61. The method of any one of clauses 44 to 60, wherein the surface comprises an optical surface of a MEMS mirror device (22, 24).

[0206] 62. The method of clause 61, wherein the MEMS mirror arrangement is part of an illuminator (IL) of a lithographic apparatus.

[0207] 63. The method of any one of clauses 44 to 62, further comprising providing microwave radiation into a plurality of said environments using said microwave generator.

[0208] 64. The method of any one of clauses 44 to 63, further comprising selectively activating the microwave generator.

[0209] 65. The method of any one of clauses 44 to 64, further comprising selectively activating the magnetic source.

[0210] 66. The method of any of clauses 44 to 65, further comprising generating, by a second magnetic source, a magnetic field adjacent to and parallel to a second surface enclosed by the environment.

[0211] 67. The method of clause 66, wherein the second magnetic source comprises an electromagnet.

[0212] 68. The method of clause 66 or clause 67, wherein the first surface and the second surface are coincident.

[0213] 69. The method of any of clauses 66 to 68, further comprising selectively activating the second magnetic source.

[0214] 70. The method of any of clauses 66 to 69, further configured to selectively activate either the first magnetic source or the second magnetic source at a time, rather than activating both the first magnetic source and the second magnetic source simultaneously.

[0215] 71. The method of any of clauses 66 to 69, further comprising extracting at least a portion of the plasma from within the environment to outside of the environment using a plasma extractor.

[0216] 72. The method of clause 71, wherein the plasma extractor comprises an aperture that allows the plasma to be extracted through the aperture, and wherein the aperture causes an impedance change that prevents at least a portion of the microwave radiation within the environment from escaping through the aperture.

[0217] 73. The method of clause 71, wherein the plasma extractor comprises a plurality of apertures, wherein each of the apertures allows extraction of the plasma through the aperture and causes an impedance change that prevents at least a portion of the microwave radiation within the environment from escaping through the aperture.

[0218] 74. The method of clause 73, wherein the housing is elongated and the plurality of apertures are arranged along a longitudinal axis of the housing.

[0219] 75. The method of clause 73 or clause 74, wherein each of the plurality of apertures is associated with a separate magnetic source for plasma generation.

[0220] 76. The method of any one of clauses 66 to 75, wherein the plasma extractor further comprises an extraction electrode.

[0221] 77. The method of any one of clauses 66 to 76, wherein the housing is elongated and has a cross-sectional area smaller than that required for propagation of the microwave radiation as an electromagnetic wave, such that microwave energy penetrates into the housing as an evanescent wave.

[0222] 78. The method of any of clauses 72 to 77, further comprising providing microwave radiation via an antenna, the microwave radiation passing through a microwave window and into the housing; wherein:

[0223] The antenna is disposed at the first end of the microwave coupler;

[0224] A second end of the microwave coupler is coupled to the housing at a joint; and

[0225] The microwave window is located at the junction and allows the microwave radiation to pass through while isolating the microwave coupler from an ambient fluid surrounded by the housing.

[0226] 79. The method of clause 78, wherein the second end of the microwave coupler extends into the housing.

[0227] 80. The method of clause 79, wherein the second end of the microwave coupler is suspended within the housing so as to allow relative movement between the second end of the microwave coupler and the housing.

[0228] 81. The lithographic apparatus of any of clauses 76 to 80, wherein the extraction electrodes have an asymmetric arrangement.

[0229] 82. The lithographic apparatus of any of clauses 66 to 81 , wherein the second magnetic source has an asymmetric arrangement.

[0230] 83. The method of clause 72 or clause 73, further comprising providing the microwave radiation into the housing via the antenna; wherein:

[0231] The antenna extends into the housing along a longitudinal axis; and

[0232] The magnetic source includes a circular Hall array surrounding the housing, the Hall array being substantially concentric with the antenna and having a longitudinal extent overlapping the antenna.

[0233] 84. The method of clause 83, wherein one or more apertures are offset from a longitudinal axis of the antenna.

[0234] 85. The method of clause 83 or clause 84, wherein the circular Haugh array is a quadrupole, a hexapole, or an octupole.

[0235] 86. A method of manufacturing a device using the method of any of clauses 44 to 85.

[0236] 87. The method of clause 86, further comprising replacing the microwave generator while the lithographic apparatus is operating to fabricate the device.

[0237] 88. A measuring or inspection device comprising:

[0238] a source emitting SXR and / or EUV radiation,

[0239] a container or enclosure defining an environment, wherein the environment surrounds a surface, wherein the container or enclosure is configured to contain a plasma generated by the SXR and / or EUV radiation; and

[0240] A first magnetic source is configured to generate a first magnetic field adjacent to the surface.

[0241] 89. The measurement or inspection apparatus of clause 88, wherein the first magnetic source comprises a permanent magnet and / or an electromagnet.

[0242] 90. The measurement or inspection apparatus of clause 88 or 89, wherein the first magnetic source comprises a plurality of permanent magnets and / or a plurality of electromagnets.

[0243] 91. The metrology or inspection apparatus of any of clauses 88 to 90, wherein the first magnetic source is separated from the plasma shield.

[0244] 92. A measurement or inspection apparatus as described in any of clauses 88 to 91, wherein the first magnetic source is located outside the container or housing.

[0245] 93. The metrology or inspection apparatus of any of clauses 88 to 92, further configured to selectively activate the first magnetic source.

[0246] 94. The metrology or inspection apparatus of any of clauses 88 to 93, wherein the first magnetic source is configured to generate the first magnetic field adjacent and parallel to the surface.

[0247] 95. The metrology or inspection apparatus of any of clauses 88 to 94, further comprising a second magnetic source configured to generate a second magnetic field adjacent a second surface surrounded by the environment.

[0248] 96. The metrology or inspection apparatus of any of clauses 88 to 95, further comprising a plasma extractor configured to extract at least a portion of the plasma from within the environment to outside of the environment.

[0249] 97. A measurement or inspection device as described in item 95, wherein the first magnetic source and / or the second magnetic source have an asymmetric arrangement.

[0250] 98. The metrology or inspection apparatus of any of clauses 88 to 97, wherein the source is a high harmonic generation (HHG) source.

[0251] 99. The metrology or inspection apparatus of any of clauses 88 to 97, wherein the source is a laser produced plasma (LPP) source.

[0252] 100. The metrology or inspection apparatus of any of clauses 88 to 99, wherein the surface is a reflective surface of a mirror.

[0253] 101. The metrology or inspection apparatus of clause 100, wherein the mirror is a curved mirror.

[0254] 102. The metrology or inspection apparatus of clause 101, wherein the mirror is a toroidal mirror.

[0255] 103. The metrology or inspection apparatus of any of clauses 100 to 102, wherein the reflective surface comprises a diffractive element.

[0256] 104. The metrology or inspection apparatus of any of clauses 88 to 99, wherein the surface is a surface of a filtering device.

[0257] 105. A metrology or inspection apparatus as described in any of clauses 88 to 99, wherein the filtering device comprises a zirconium film.

[0258] While specific embodiments of the invention have been described above, it will be apparent that the invention may be practiced otherwise than as described.

[0259] The above description is intended to be illustrative rather than restrictive. It will therefore be apparent to those skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set forth below.

Claims

1. A lithographic apparatus (100), comprising: an enclosure (400) defining an environment (401), wherein the environment surrounds a surface (402), wherein the enclosure is configured to contain a plasma; a microwave generator (410) configured to provide microwave radiation (411) into the housing; A magnetic source (420) is configured to generate a magnetic field adjacent to the surface, the magnetic field, together with the microwave radiation, generating plasma (432) by electron cyclotron resonance, thereby increasing the concentration of the plasma adjacent to the surface.

2. The lithographic apparatus according to claim 1 , wherein: The microwave generator is located outside the environment; and The enclosure is configured to contain a base concentration plasma (431) generated by EUV radiation.

3. The lithographic apparatus of claim 1 or claim 2, wherein the housing is configured to contain hydrogen gas.

4. The lithographic apparatus of any preceding claim, wherein the plasma comprises hydrogen plasma.

5. The lithographic apparatus of any preceding claim, wherein the magnetic source comprises a permanent magnet and / or an electromagnet.

6. The lithographic apparatus of any preceding claim, wherein the magnetic source comprises a plurality of permanent magnets and / or a plurality of electromagnets.

7. The lithographic apparatus of any preceding claim, wherein the magnetic source is spaced apart from the plasma shield.

8. The lithographic apparatus of any preceding claim, wherein the magnetic source is located external to the housing.

9. The lithographic apparatus according to any one of the preceding claims, further comprising a waveguide (404) configured to guide the microwave radiation from the microwave generator into the housing.

10. The lithographic apparatus of any preceding claim, configured to prevent the plasma from flowing along a straight line between the surface and a microwave window (405) through which microwave radiation from the microwave generator passes into the housing.

11. The lithographic apparatus of any preceding claim, wherein the microwave generator is replaceable while the lithographic apparatus is operating to manufacture a device.

12. The lithographic apparatus of any preceding claim, wherein the surface comprises a surface within an EUV laser generated plasma source vessel (212).

13. The lithographic apparatus of claim 12, wherein the surface comprises a surface of a collector mirror (CO) within the container.

14. The lithographic apparatus of claim 13, wherein the magnetic source comprises a magnetic source embedded in the collector mirror.

15. The lithographic apparatus according to any one of claims 12 to 14, wherein the surface comprises an inner wall of the container.

16. The lithographic apparatus according to any one of claims 12 to 15, wherein the container comprises a drain (403), and the microwave radiation is provided into the container via the drain.

17. The lithographic apparatus of any preceding claim, wherein the surface comprises a window for metrology.

18. The lithographic apparatus of claim 17, wherein the magnetic source comprises a magnetic source embedded in the window.

19. The lithographic apparatus of any preceding claim, wherein the surface comprises an optical surface of a MEMS mirror arrangement (22, 24).

20. A method comprising: providing microwave radiation (411) by a microwave generator (410) into an enclosure (400), wherein the enclosure defines an environment (401) in the lithographic apparatus (100), and the environment surrounds a surface (402); and A magnetic field is generated adjacent the surface by a magnetic source (420), which, together with the microwave radiation, generates plasma (432) by electron cyclotron resonance, thereby increasing the concentration of the plasma adjacent the surface.

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