Systems, apparatus, and methods for selective surface treatment

Abstract

A shielding system for use in a surface treatment process includes a first disk and a second disk. The first disk and the second disk are arranged substantially parallel to each other. The first disc comprises a slit-shaped opening, and the second disc comprises a plurality of openings; and the first disk and the second disk are arranged to move relative to each other about a common axis. Thus, the slit may be positioned at one or more of the plurality of openings to form a pathway through the shielding system.

Description

Technical Field

[0001] The present invention relates to a system, apparatus and method for selective surface treatment of a support surface. In particular, the present invention relates to a system for selective treatment of one or more burls on a surface arranged to support an object. Background Art

[0002] A lithographic apparatus is a machine configured to apply a desired pattern onto a substrate. For example, a lithographic apparatus may be used in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern (also often referred to as a "design layout" or "design") of a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) disposed on a substrate (e.g., a wafer).

[0003] As semiconductor manufacturing processes continue to advance, the number of functional elements (such as transistors) per device has been steadily increasing for decades while the size of circuit elements has continued to decrease, following a trend commonly referred to as "Moore's law". In order to keep up with Moore's law, the semiconductor industry is seeking technologies that can produce smaller and smaller features. In order to project a pattern onto a substrate, a lithography device can use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the features patterned on the substrate. Typical wavelengths currently used are 365nm (i-line), 248nm, 193nm, and 13.5nm. Lithography equipment using extreme ultraviolet (EUV) radiation (having a wavelength in the range of 4nm to 20nm, such as 6.7nm or 13.5nm) can be used to form smaller features on a substrate than lithography equipment using, for example, radiation with a wavelength of 193nm.

[0004] In a lithographic apparatus, a substrate is clamped to a substrate support when a pattern is transferred from a pattern forming device. The substrate support typically has a plurality of burls that support the substrate. The total area of ​​the burls that contact the substrate is small compared to the total area of ​​the substrate. Therefore, there is less likelihood of contaminant particles randomly located on the surface of the substrate or substrate support being caught between the burls and the substrate. Furthermore, in the manufacture of the substrate support, the tops of the burls can be made more precisely coplanar than large surfaces can be accurately flattened.

[0005] Additionally, the patterning device may be clamped to a mask support, the mask support comprising a plurality of burls at a clamping surface thereof.

[0006] Manufacturing tolerances, contamination and / or wear of the burl top surface may result in burl height inaccuracies. Any inaccuracies in the height of the burl may result in undesirable local deformation of an object (e.g., a substrate or a patterning device) clamped to the support (e.g., a substrate support or a mask support). Such local deformations may be a cause of IC manufacturing inaccuracies. Therefore, it is generally desirable to provide a system and method suitable for improving the surface characteristics of a support surface. Summary of the invention

[0007] According to a first aspect of the present invention, there is provided a shielding system for use in a surface treatment process. The shielding system comprises: a body for shielding a first area of ​​the surface from an environment (e.g., plasma) during the surface treatment process; and an opening through the body of the system for exposing a second area of ​​the surface during the surface treatment process. The shielding system may be referred to as a plasma shielding system.

[0008] According to a second aspect of the present invention, there is provided a shielding system comprising a first disc and a second disc. The first disc and the second disc are arranged parallel to each other with a common rotation axis. The first disc comprises a slit-shaped opening, and the second disc comprises a plurality of openings. The first disc and the second disc are arranged to move relative to each other around the common axis, whereby the slit can be positioned at one or more of the plurality of openings.

[0009] When provided in a system configured to perform a surface treatment process on a surface of an object, the shielding system is arranged between a radiation source (e.g., a plasma radiation source) and the surface of the object, a well-defined path for the plasma can be defined for treating selected areas at the surface and shielding the rest of the surface.

[0010] According to a third aspect of the present invention, there is provided a system configured to perform a plasma treatment process on a portion of a surface, the system comprising: a plasma source configured to generate a plasma environment (e.g., a plasma environment); and an arrangement according to the first aspect and / or the second aspect.

[0011] According to a fourth aspect of the present invention, a method for performing a plasma treatment process on a portion of a surface is provided. The method comprises: shielding a first area of ​​the surface from a plasma environment using a plasma shielding system according to the first aspect and / or the second aspect, and exposing a second area of ​​the surface to the plasma environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0013] Figure 1 A schematic overview of a lithographic apparatus is depicted;

[0014] Figure 2 schematically depicts a substrate holder for use in a lithographic apparatus;

[0015] Figure 3 schematically depicts a plurality of burls consisting of a substrate holder and a removable shielding system according to an embodiment;

[0016] Figure 4A and Figure 4B schematically depicts a shielding system according to an embodiment; and

[0017] Figure 5A and Figure 5B A shielding system according to an embodiment is schematically depicted. DETAILED DESCRIPTION

[0018] In this document, the terms "radiation" and "beam" are used to cover all types of electromagnetic radiation, including ultraviolet radiation (e.g., having a wavelength of 365nm, 248nm, 193nm, 157nm or 126nm) and EUV radiation (extreme ultraviolet radiation, e.g., having a wavelength in the range of about 5nm to 100nm).

[0019] The terms "reticle", "mask" or "patterning device" as used in the present invention may be broadly interpreted to refer to a general patterning device that can be used to impart a patterned cross-section to an incident radiation beam that corresponds to the pattern to be produced in a target portion of the substrate. In this context, the term "light valve" may also be used. In addition to classical masks (transmissive or reflective, binary, phase-shifting, hybrid, etc.), other examples of such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0020] Figure 1A lithographic apparatus LA is schematically depicted. The lithographic apparatus LA comprises an illumination system (also referred to as an illuminator) IL configured to condition a radiation beam B (e.g., UV radiation, DUV radiation, or EUV radiation), a mask support (e.g., a mask stage) MT configured to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA according to certain parameters, a substrate support (e.g., a wafer stage) WT configured to hold a substrate (e.g., a wafer coated with resist) W, connected to a second positioner PW configured to accurately position the substrate support according to certain parameters, and a projection system (e.g., a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g., a portion comprising one or more dies) of the substrate W.

[0021] In operation, the illumination system IL receives a radiation beam from a radiation source SO, for example via a beam delivery system BD. The illumination system IL may include various types of optical components for directing, shaping and / or controlling the radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic and / or other types of optical components, or any combination thereof. The illuminator IL may be used to condition the radiation beam B to have a desired spatial and angular intensity distribution in its cross-section at the plane of the patterning device MA.

[0022] The term "projection system" PS as used in the present invention should be interpreted broadly to cover various types of projection systems suitable for the exposure radiation used and / or for other factors such as the use of immersion liquid or the use of vacuum, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems or any combination thereof. Any term "projection lens" used herein may be considered synonymous with the more general term "projection system" PS.

[0023] The lithographic apparatus LA may be of a type in which at least a portion of the substrate may be covered by an immersion liquid having a relatively high refractive index, such as water, so as to fill the space between the projection system PS and the substrate W - this is also known as immersion lithography. More information on immersion techniques is given in US 6952253, which is incorporated herein by reference.

[0024] The lithographic apparatus LA may also be of a type having two or more substrate supports WT (also referred to as a "dual stage"). In such a "multi-stage" machine, the substrate supports WT may be used in parallel and / or a substrate W on one of the substrate supports WT may be used for exposing a pattern on another substrate W while a step of preparing the substrate W for subsequent exposure is being performed on the substrate W on another substrate support WT.

[0025] In addition to the substrate support WT, the lithographic apparatus LA may also comprise a measurement platform. The measurement platform is arranged to hold sensors and / or cleaning means. The sensors may be arranged to measure properties of the projection system PS or properties of the radiation beam B. The measurement platform may hold a plurality of sensors. The cleaning means may be arranged to clean a part of the lithographic apparatus, for example a part of the projection system PS or a part of the system providing immersion liquid. The measurement platform may be moved under the projection system PS when the substrate support WT is away from the projection system PS.

[0026] In operation, the radiation beam B is incident on the patterning device (e.g. mask) MA held on the mask support T and is patterned by a pattern (design layout) present on the patterning device MA. Having traversed the mask MA, the radiation beam B passes through the projection system PS which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and the position measurement system IF, the substrate support WT can be accurately moved, for example in order to position different target portions C in the path of the radiation beam B in a focused and aligned position. Similarly, the first positioner PM and possibly another position sensor (in Figure 1 The patterning device MA (not explicitly depicted in the figure) can be used to accurately position the patterning device MA relative to the path of the radiation beam B. The patterning device MA and the substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2 occupy dedicated target portions as shown, the marks can be located in the space between target portions. When the substrate alignment marks P1, P2 are located between the target portions C, these substrate alignment marks are called scribe line alignment marks.

[0027] In order to illustrate the present invention, a Cartesian coordinate system is used. The Cartesian coordinate system has three axes, namely the x-axis, the y-axis and the z-axis. Each of the three axes is orthogonal to the other two axes. The rotation around the x-axis is called the Rx rotation. The rotation around the y-axis is called the Ry rotation. The rotation around the z-axis is called the Rz rotation. The x-axis and the y-axis define a horizontal plane, while the z-axis is in the vertical direction. The Cartesian coordinate system is not limited to the present invention and is only used for illustration. As an alternative, another coordinate system (such as a cylindrical coordinate system) can be used to illustrate the present invention. The direction of the Cartesian coordinate system can be different, for example, so that the z-axis has a component along the horizontal plane.

[0028] The substrate support WT (which may also be referred to as a substrate holder) is designed for accurate positioning of the substrate during exposure. The substrate holder typically comprises a solid body made of a rigid material and having in-plane XY dimensions similar to the production substrate W to be supported. The substrate-facing surface of the solid body is provided with a plurality of protrusions or projections referred to as burls. The distal surfaces of the burls conform to a substantially flat plane and support the substrate W. The burls provide several advantages: contaminant particles on the substrate holder or on the substrate may fall between the burls and thus do not cause deformation of the substrate; machining the burls makes it easier to conform the ends of the burls to a plane than flattening the surface of the solid body; and the height of some of the burls can be reduced. Reducing the height of some of the burls can improve the overall height profile of the burls, thereby improving how the substrate W is clamped.

[0029] Figure 2 A substrate holder 60 for use in a lithographic apparatus LA is schematically depicted, which may be a substrate support WT. The substrate holder 60 is used to support a substrate W. The substrate holder 60 comprises a body 21. The body 21 has a body surface 22. A plurality of burls 20 are arranged to protrude from the body surface 22. A distal surface of each burl 20 engages with the substrate W. The distal surfaces of the burls 20 are substantially coplanar, i.e. the distal surfaces of the burls 20 substantially conform to a support plane and support the substrate W. The body 21 may be formed of ceramic, such as SiC or SiSiC. The burl 20 may be formed of the same material as the body 21, or may include a different material, such as diamond-like carbon (DLC), diamond, boron-doped diamond (BDD), boron nitride, boron carbide, tungsten carbide, aluminum oxide, sapphire, titanium nitride, titanium carbonitride, titanium aluminum nitride or titanium carbide, such as disclosed in WO2020 / 135971, WO2020 / 221539, WO2021 / 249768.

[0030] The pitch of the burls 20 may be in the range of from about 0.5 mm to 3 mm, for example about 1.5 mm. The pitch of the burls 20 is the distance between the centers of two adjacent burls 20. The total area of ​​the distal surfaces of the burls 20 may be in the range of from 1% to 3% of the total area of ​​the substrate holder 60. The shape of the burls 20 may be a frustoconical shape, wherein the burl side surfaces are slightly inclined. Alternatively, the burl side surfaces may be vertical or even overhanging. The burls 20 may be circular in a plan view. Alternatively, the burls 20 may also be formed in other shapes if desired.

[0031] A plurality of through holes 89 may be formed in the body 21. The through holes 89 allow e-pins to protrude through the substrate holder 60 to receive the substrate W. The through holes 89 may also allow the space between the substrate W and the substrate holder 60 to be evacuated. If the space above the substrate W is also not evacuated, the evacuation of the space between the substrate W and the substrate holder 60 may provide a clamping force. The clamping force holds the substrate W in place. If the space above the substrate W is also evacuated, as would occur in a lithographic apparatus using EUV radiation, electrodes may be provided on the substrate holder 60 to form an electrostatic clamp.

[0032] Other structures may be provided, for example for controlling the airflow and / or thermal conductivity between the substrate holder 60 and the substrate W. The substrate holder 60 may be provided with electronic components. The electronic components may include heaters and sensors. Heaters and sensors may be used to control the temperature of the substrate holder 60 and the substrate W.

[0033] The burls 20 of the substrate holder 60 wear during use, for example, due to repeated loading and unloading of substrates W. Furthermore, during use, the burls may be contaminated, for example, by particles or thin films of material. Wear and contamination of the burls 20 result in changes to the surface profile provided by the distal surfaces of the burls 20.

[0034] Any inaccuracies in the height of the burls may result in undesired local deformations of the substrate W clamped to the substrate holder 60. Such local deformations may be the cause of manufacturing inaccuracies.

[0035] It is known that the manufacture and / or maintenance of the burl 20 includes a cleaning and polishing process, for example by a system and method as disclosed in WO 2018 / 224303, and an ion beam forming (IBF) process.

[0036] A polishing process may be performed first.

[0037] A height profile of the distal surface of the burl 20 may then be generated by measuring the height using a sensor. Such height measurement may be accomplished using any of a variety of known techniques, such as using a non-contact sensor, such as an optical sensor or a contact sensor. The height profile may be determined, for example, by optical interferometer measurements. A height profile map, which may be referred to as a hitmap, may be generated to indicate burls or areas requiring surface treatment. The determined height profile may be relative to measurements of a clamped substrate W of known thickness.

[0038] An IBF process may then be performed based on the determined height profile. The IBF process uses a high energy ion beam, such as an argon ion beam, to remove material from the burls. The IBF process may reduce height variations in the burls as determined by the height profile measurements.

[0039] The problem with the IBF process is that it is a wide area process. That is, the IBF process can be used to reduce the height of all the multiple burls 20 in the area of ​​the substrate holder 60. The IBF process cannot reduce the height of only a single burl 20. Therefore, burls and areas that do not require surface treatment may be affected by the IBF process. In addition, the IBF process has an effect on the roughness and surface properties of the burls 20 (those burls to be treated and those burls that should not be treated). The IBF process may cause the burls 20 to have damaged layers or amorphous layers, which may increase the wear of the burls 20.

[0040] Embodiments provide a new technique for surface treatment of an area, especially a selected area. Embodiments use plasma (eg, hydrogen plasma) to treat a surface. An opening in a shielding system may define an area of ​​the surface that is treated with the aid of the plasma.

[0041] An exemplary application of an embodiment is a technique for treating the surface of a burl 20 or a support surface 22. The technique may be used to reduce the height of one or more burls 20. An embodiment may use plasma to reduce the height of one or more burls 20 without substantially affecting the surface topography at the nanoscale or larger scale. In particular, an embodiment includes using a shield to control which burls the hydrogen plasma is applied to. The shield may allow only a single burl 20 to be reduced in height. An embodiment may use plasma to treat an area of ​​the support surface 22 between burls 20 without substantially affecting the burls 20. This may be beneficial in removing contaminants on the area of ​​the support surface 22 between burls 20.

[0042] Reference below Figure 3 , Figure 4A , Figure 4B , Figure 5A and Figure 5BEmbodiments for varying the height profile of one or more of the plurality of burls 20 are described in further detail.

[0043] Figure 3 Schematically a cross-sectional view of a plurality of burls 20, 303 comprised by a substrate holder is shown. The substrate holder may be the same as the substrate holder 60 / substrate support WT described above for use in a lithographic apparatus LA. The substrate holder is for supporting a substrate W. The substrate holder comprises a body 21. The body 21 has a body surface 22. A plurality of burls 20, 303 protrude from the body surface 22. Figure 3 2. A removable shield 301 according to an embodiment is also shown. The shield 301 or shielding system is arranged to cover at least some of the burls 20, and preferably most of the burls. The shield 301 may be made of the same material as the substrate W. The shield 301 according to an embodiment is described in more detail later.

[0044] In order to provide a desired height profile of the burls 20, 303, a polishing process may be performed first. The polishing process may be performed when no burls 20, 303 are covered by the shield 301. The polishing process may be according to known techniques as used in wide area IBF processes.

[0045] The height profile of the distal surface of the burls 20, 303 may then be determined according to known techniques used in wide area IBF processes. These may include optical interferometer measurements as described above and / or determination of the height profile relative to measurements of a clamped substrate W of known thickness. Based on the height profile, a determination may be made to reduce the height of one or more of the burls 20, 303.

[0046] The embodiment differs from the known art in that the shield 301 is provided above the burls 20 of the substrate holder. The shield 301 may have been selected and / or configured such that the shield 301 comprises openings at the location of a single burl 303, or a selective surface at the support 22 for which a surface treatment, such as a height reduction, is required. The shield 301 may cover the distal surfaces of all the multiple burls 303 except the distal surface of a single burl 20. The shield 301 thus shields the distal ends of all the burls 20 and the area 22 between the burls from the environment 302 above the shield 301 except for the single exposed burl 303.

[0047] When the openings are provided at selected surface areas between the burls 20, the shield 301 thus shields the distal ends of all burls 20 and the area 22 between the burls from the environment 302 above the shield 301 except for the selected surface areas.

[0048] The shield 301 may include a plurality of coverable openings over the locations of the burls 20, 303. The shield 301 may be configured to cover all openings over the burls 20 that do not require height reduction, and not cover openings over a burl 303 or burls 303 that require surface treatment (e.g., height reduction).

[0049] The plasma treatment process can then be performed by providing a plasma environment above the shield 301. For example, a hydrogen plasma can be provided. The plasma environment can be generated using a variety of known techniques. These include the use of ion generators, electrodes, hot wires, and microwave generators. The plasma environment can be generated according to the techniques described in "Plasma generation and Plasma Sources" by H. Conrads and M. Schmidt, Plasma Sources Science and Technology, Vol. 9 (4), p. 441, 2000.

[0050] The object holder (e.g., the substrate support WT or the mask support T) can be moved into an apparatus for generating the plasma environment. The apparatus may include a plasma source, such as a hydrogen plasma source. The plasma source is preferably located directly above the center of the object holder so that any object deformation caused by changes in the etching rate due to the location of the plasma source is bowl-shaped and can thus be easily corrected. During the plasma treatment process, the object holder (e.g., substrate support) can be grounded. The ion energy during the plasma treatment process is preferably at least 2 eV so that a suitable etching rate is achieved. If the ion energy during the plasma treatment process is too high, the ions may damage the exposed structure. The ion energy during the plasma treatment process is preferably less than 15 eV, more preferably less than 10 eV, and even more preferably less than 6 eV.

[0051] A control unit or controller may be provided to set and control the ion energy of the plasma. This may be the energy of a hydrogen plasma. In addition, the controller may be arranged to control the ratio between ions and free radicals in the plasma. This may be the ratio between hydrogen ions and hydrogen free radicals in the plasma. Control of the energy and / or ratio is advantageous for efficient treatment of surfaces.

[0052] During the plasma treatment process, the plasma radiation can etch the distal end of a single exposed burl 303. The plasma radiation can be used to etch away a definable amount of material. The etching process can reduce the height of the exposed burl 303 without causing any substantial damage to the exposed burl 303. The etching process can reduce the height of the exposed burl 303 at a rate of about 5 to 25 nm / hour. The rate of the etching process can depend on the applied gas or ion pressure and the distance from the plasma source. The duration of the etching process can be used to control the treatment applied to the surface and thus control the reduction in the height of the burl 303. The exposed surface can remain uniform and clean. The etching process can be independent of the roughness of the etched surface, i.e., the etching process can be uniform. All burls 20 whose distal surfaces are covered by the shield 301 can be substantially unaffected by the plasma environment.

[0053] All processes can be automatically controlled by the processing system. In particular, the processing system can receive a height profile map of the surface of interest. The processing system can be manually controlled or can be automatically operated to determine which areas and / or burls require selective surface treatment. In addition, the processing system can (automatically) configure the shield 301 based on the selected area and automatically control the plasma treatment process to treat the selected area, for example, burl 303.

[0054] Thus, embodiments allow the selected surface to be treated in a controlled manner. In particular, embodiments allow the height of a single burl 303 to be reduced in a controlled manner. By repeating the process with different burls 20 (or different selected areas), the height of a plurality of burls 20 can be reduced. The burl height reduction can be performed accurately and in accordance with the determined height profile of the burls. Embodiments thereby improve the height profile of the burls 20. The use of plasma according to embodiments allows the height reduction of one or more burls without a substantial impact on the surface topography at the nanoscale or larger. This is an advantage over known IBF techniques, in which high energy sputtering causes surface sputtering.

[0055] Embodiments include other techniques for exposing one or more of the burls 303 for plasma processing while shielding (ie, masking) the burls 20. Alternatively or additionally, a removable coating may be used to shield the burls 20.

[0056] It will be appreciated by those skilled in the art that the same plasma treatment using a shield as disclosed above may be applicable for selective surface treatment of the mask support T. The mask support T may include burls for supporting the patterning device MA.

[0057] Those skilled in the art will appreciate that the shield 301 as disclosed above can be used in a selective surface treatment system and / or process using radiation, wherein the radiation is provided as one of laser radiation, electron beam and ion beam. The use of laser radiation in combination with the shield 301 will allow for selective surface treatment of an object by laser ablation. The laser radiation may be radiation having a wavelength in the spectral range of visible light and / or (extreme) ultraviolet light. The wavelength may be selected depending on the material deposited on the surface to be treated (e.g., contaminant material) or the base material of the surface (e.g., the material composition of the burl 303).

[0058] Figure 4A and Figure 4B Another shielding system 400 according to an embodiment is schematically illustrated. Figure 4A is an exploded view of the shielding system 400 . Figure 4B The assembled shielding system 400 is shown.

[0059] The shielding system 400 includes a first plate 401 and a second plate 402. The present embodiment is described with the first plate 401 being a first disk 401 and the second plate 402 being a second disk 402. However, the embodiment also includes a first plate 401 and a second plate 402 having other shapes than a disk. For example, both the first plate 401 and the second plate 402 may be substantially rectangular.

[0060] Both the first disk 401 and the second disk 402 are substantially planar. The diameter of each of the first disk 401 and the second disk 402 may be substantially the same as each other and substantially the same as or slightly larger than the diameter of the region of the substrate holder covered by the burls.

[0061] The first disc 401 and / or the second disc 402 may comprise mechanical means for reinforcing said discs. Thus, deformation of one or both discs may be prevented or limited.

[0062] The first disk 401 may include a slit opening 404 or a first opening. Figure 4A and Figure 4BIn the figure, the slit opening 404 is shown as a wedge-shaped opening. However, the slit opening 404 can alternatively be rectangular in shape, or have an irregular shape. The slit opening 404 can be set from the center of the disk towards the edge of the disk. Alternatively, the slit opening does not continue to the edge, but a portion of the disk material closes the slit opening at the edge of the disk. Therefore, the disk forms a closed loop at the periphery of the disk, i.e., the circumference. This can be beneficial to avoid plasma reaching the surface of the object that needs to be shielded during the surface treatment process. In particular, the surface area at the edge of the object under the shielding system.

[0063] The second disk 402 includes a plurality of openings 403 or second openings. Each opening 403 may be circular, square, rectangular or oval. Preferably, the shape of each (second) opening 403 is circular. Each opening 403 may be located at different radial and axial positions as viewed from the midpoint of the second disk 402. The size of each opening 403 is suitable for exposing only a single burl. Each opening 403 may have different sizes. The sizes of the openings 403 may be similar. The diameter of each opening 403 is preferably greater than the diameter of each burl 20. When the burl 20 has a diameter of approximately 200 µm and a pitch of approximately 1.5 mm, the diameter of each opening 403 may be approximately 200 µm to 1300 µm, and preferably approximately 400 µm to 1100 µm. When the burls 20 have a diameter of about 350 μm and a pitch of 2.5 mm, the diameter of each opening 403 may be about 350 μm to 2150 μm, and preferably about 550 μm to 1950 μm.

[0064] A plurality of openings 403 (or second openings) may be provided in a spiral arrangement to the second disk 402. The second disk 402 may be provided with openings 403 arranged in one or more spirals. The openings 403 may be arranged in a phyllochronous spiral.

[0065] When assembling the shielding system 400, as shown in FIG. Figure 4B As shown in FIG. 4 , the first disk 401 may be arranged close to or in contact with the second disk 402. The plane of the first disk 401 may be parallel to the plane of the second disk 402, and the spacing between the first disk 401 and the second disk 402 is less than 100 μm. The midpoints of the first disk 401 and the second disk 402 may be aligned with each other on a line orthogonal to the planes of the first disk 401 and the second disk 402. When the shielding system 400 is arranged above the burl 20 of the substrate holder, the second disk 402 is preferably closer to the substrate holder than the first disk 401.

[0066] The thickness of each of the first disk 401 and the second disk 402 may be less than 2 mm. The shielding system 400 is preferably as thin as possible. The thickness of the shielding system 400 is preferably less than twice the diameter of one of the (second) openings 403, more preferably less than the diameter of one of the openings 403, and even more preferably less than half the diameter of one of the openings 403.

[0067] The shielding system 400 may include a rotary joint 405 for supporting the relative axial rotation of the first disk 401 and the second disk 402. The relative axial rotation of the first disk 401 and the second disk 402 may be controlled by the operation of a motor. The motor may be arranged to rotate the first disk 402 while the second disk 401 remains stationary, to rotate the second disk 402 while the first disk 401 remains stationary, or to rotate both the first disk 401 and the second disk 402 in opposite directions. The motor may also be arranged to axially rotate the entire shielding system 400, wherein no relative axial rotation occurs between the first disk 401 and the second disk 402. The motor may be arranged above the shielding system 400 or at the side of the shielding system 400. The use of the rotary joint 405 is optional, and in particular when the motor is arranged to the side of the shielding system 400, the axis of rotation may not be fixed. The relative movement of the first disk 401 and the second disk 402 may also be only linear movement without rotational movement.

[0068] When the first disk 401 and the second disk 402 are axially rotated relative to each other, the slit opening 404 (first opening) of the first disk 401 can move over any one of the openings 403 (second opening). The slit opening 404 can be shaped so that the first disk 401 can cover all of the openings 403 except for a single opening 406, over which the slit opening 404 is located. At all locations along its length, the width of the slit opening 404 can be less than the spacing between adjacent openings 403, so that there is no position of the slit opening 404 that causes more than one opening 403 to be exposed.

[0069] Thus, only a single opening 406 of the plurality of openings 403 may provide a passage through the shielding system 400. A passage through the shielding system 400 is defined by one of the openings 403 that is covered by the slit opening 404. By rotating the first disk 401 relative to the second disk 402, a different one of the openings 403 may define a passage through the shielding system 400.

[0070] The position of the slit in the first disk 401 and the orientation of the second disk 402 (where one of the plurality of openings 403 is arranged) may be set and controlled by a control unit (eg a controller). The controller may determine the position and orientation of the two disks based on a height profile or hitmap.

[0071] All burls 20 may be arranged on the substrate holder in a plurality of concentric circles with different radii. The radial position of each burl opening in the second disk 402 may be arranged so that when the shielding system 400 is positioned over the burls 20, there is an opening 403 that can be aligned with each burl only by axial rotation of the second disk 402. Thus, rotation of the first disk 401 relative to the second disk 402 and rotation of the shielding system 400 may be used to provide a passage through the shielding system 400 over any burl 20 on the substrate holder (except for the center burl 20). Thus, the shielding system 400 may be configured so that a specific one of the burls 20 is exposed.

[0072] If the substrate holder includes a central burl 20, to expose the central burl 20, the shield system 400 may be moved horizontally so that the passage therethrough is aligned with the central burl 20. Alternatively, a separate shield may be used for exposing the central burl 20.

[0073] The shielding system 400 can be used in the plasma treatment process described above according to an embodiment. During the surface treatment process (e.g., plasma treatment process), both the first disk 401 and the second disk 402 can be grounded. Preferably, the object to be treated (e.g., substrate support or mask support) is grounded during the surface treatment process.

[0074] By controlling the relative rotation of the first disk 401 and the second disk 402 and / or the overall rotation of the shield system 400, the shield system 400 can be reconfigured during the plasma treatment process. This allows more than one burl 20, or selected areas between multiple burls, to be exposed during the same plasma treatment process.

[0075] The shield system 400 can be arranged to seat on the burl 20 during the plasma treatment process. The shield system 400 can be lifted so that it is not seated on the burl 20 during rotation to provide for reconfiguration of the shield system 400 for changing the exposed burl 303 to avoid damage to the burl and / or the shield system 400.

[0076] Alternatively, the shield system 400 may be held slightly above the burl 20 during the plasma treatment process. The space between the shield system 400 and the burl 20 should be large enough to avoid problems with any sagging of the shield system 400 leading to collisions between the shield system 400 and the burl 20. Mechanical means may be provided to one or both disks to prevent sagging. However, the space between the shield system 400 and the burl 20 is preferably as small as possible after providing a tolerance for sagging. The space between the shield system 400 and the burl 20 is preferably less than the Debye length of the plasma, which is approximately 100 μm.

[0077] The determination of the height profile, the configuration of the shielding system 400, and the operation of the entire plasma treatment process can be automatically controlled by one or more processing systems. In particular, the controller can receive data about one or more burls 20, or areas at the support surface that should be processed, and automatically configure the shielding system 400 based on the received data.

[0078] Thus, embodiments provide techniques for improving the height profile of burls 20. The height of each burl 20 can be individually changed. The height of each burl can also be accurately changed. The exposure time of the plasma source, i.e., the exposure time, can be controlled with millisecond accuracy, i.e., precision. Using a plasma process that provides an etch rate of about 5 to 25 nm / hour, the reduction in the height of the burl 20 can be controlled to the picometer level.

[0079] The design of the substrate holder, and in particular the typical height of each burl 20 on the substrate holder, varies between the processes for which the substrate holder is to be used. For example, the typical burl height of a substrate holder designed for a photolithography process may be in the range of about 10 μm to about 200 μm. For burls having a height of about 10 μm, embodiments may be used to reduce their height by less than about 1 nm, or more than 1 nm if desired. For burls having a height of about 200 μm, embodiments may be used to reduce their height by up to about 10 nm, or more than 10 nm if desired.

[0080] Embodiments include numerous modifications and variations of the techniques described above.

[0081] Embodiments include using shields that expose more than one burl 20 simultaneously. For example, the shield system may include a single opening that is large enough to expose multiple burls 20. The height of multiple burls 20 may be reduced simultaneously. Then, if desired, a different shield system may be used to individually reduce the height of one or more of the burls 20. This may be a faster process than only reducing the height of the burls 20 individually.

[0082] Embodiments also include using a shielding system that includes more than one opening for exposing more than one burl 20 simultaneously.

[0083] It should be noted that although the distal surfaces of the burls 20 may conform substantially to a plane, the preferred height profile of the burls 20 may be the same as the profile of the substrate W clamped to the substrate holder. Thus, if the substrate has a slight bowl-shaped deformation, the preferred profile provided by the distal surfaces of the burls 20 will be of a slightly convex form so that the end of each burl is flush with the surface of the substrate.

[0084] Embodiments include the height profile provided by the distal surface of the burl 20 being altered so that it better fits the overall shape of a substrate W clamped to the substrate holder 60. The height profile provided by the distal surface of the burl 20 may not be flat.

[0085] Embodiments are not limited to the specific application of reducing the height of burls.Embodiments more generally include treating a surface using a plasma, wherein openings in a shielding system define areas of the surface being treated.

[0086] Shield systems according to embodiments are not limited to circular disks. Embodiments include using shields of any shape as long as the shield defines a first area of ​​the surface that is not exposed to the plasma environment and at least one opening in the shield defines a second area of ​​the surface that is exposed to the plasma environment.

[0087] A person skilled in the art will appreciate that the shielding system 400 as disclosed above can be used in a selective surface treatment system and / or process using radiation, wherein the radiation is provided as one of laser radiation, electron beam and ion beam. The use of laser radiation in combination with the shielding system 400 will allow for selective surface treatment of an object by laser ablation. The laser radiation may be radiation having a wavelength in the spectral range of visible light and / or (extreme) ultraviolet light. The wavelength may be selected depending on the material deposited on the surface to be treated (e.g., contaminant material) or the base material of the surface (e.g., the material composition of the burl).

[0088] Embodiments include a shielding system 500 that includes a plurality of movable plates or blades. For example, the shielding system 500 may include a first layer having a first pair of plates 501 that are substantially rectangular, such as Figure 5A and Figure 5B Schematically shown in . Figure 5A An exploded view of the shielding system 500 is depicted. Figure 5B An assembly diagram of the shielding system 500 is depicted. The first pair of plates 501 can be separated from each other so that there is a first linear opening 504, such as a first slit opening, between them. The shielding system 500 can also include a second layer having a second pair of plates 502 that is substantially rectangular. The second pair of plates 502 can be separated from each other so that there is a second linear opening 503, such as a second slit opening, between them. The first pair of plates 501 and the second pair of plates 502 can be oriented so that the first linear opening 504 and the second linear opening 503 (or slit opening) are substantially orthogonal to each other. Then, at the location where the first linear opening and the second linear opening overlap each other, there will be a rectangular or square opening 506 through the shield. The size and location of the opening 506 can be changed by changing the location and spacing of the first pair of plates 501 and the second pair of plates 502.

[0089] At the opening 506, an auxiliary element may be provided, which is arranged to move with the opening. The auxiliary element may have a central circular opening so that the passage through the shielding system 500 matches the base diameter of the burl. When treating cylindrical burls according to an aspect of the present invention, it is preferred that the passage 506 in the shielding system 500 has a similar shape and size. Thereby, unintended treatment of the area around the burl of interest is minimized or can be prevented.

[0090] The first pair of plates 501 and the second pair of plates 502 are sized so that they at least partially, preferably completely, shield the surface of the object that is subjected to selective surface treatment by means of plasma. Both the first pair of plates 501 and the second pair of plates 502 are similar in size to a substrate support WT or a mask support T as used in a lithographic apparatus.

[0091] The shielding device 500 including the first pair of plates and the second pair of plates may be preferably used for surface treatment of an object including burls arranged in non-concentric circles (eg, arranged in a linear configuration).

[0092] The positions of the first slit opening 504 and the second slit opening 503 whereby the opening or passage 506 is arranged may be set and controlled by a control unit (eg a controller). The controller may determine the positions of the two slit openings based on a height profile map or hitmap.

[0093] During a surface treatment process, such as a plasma treatment process, both the first pair of plates 501 and the second pair of plates 502 may be grounded. Preferably, the object to be treated, such as a substrate support or a mask support, is grounded during said surface treatment process.

[0094] According to an embodiment, a device for adjusting a component of a lithographic device is provided. The device includes a housing configured to contain plasma (e.g., hydrogen plasma), wherein the plasma is provided by a plasma generator. A support device is provided to support an object to be processed using the plasma. A shielding system 301, 400, 500 is arranged between a plasma source and the support device to shield at least a portion of a surface of the object, wherein the device is configured to control at least one of a ratio of ions (e.g., hydrogen ions) to radicals (e.g., hydrogen radicals) in the plasma, an energy of the plasma, and a position of a passage or opening through the shielding system for selective surface treatment of the object.

[0095] Embodiments include moving the substrate support to a specific device for performing a plasma treatment process. Alternatively, the plasma treatment process may be performed in the same device as used for a lithography or metrology process (in-situ). The device may already include a plasma source for generating a plasma environment (e.g., hydrogen plasma) with appropriate ion energy. Alternatively, a new plasma source may be included in the device.

[0096] Embodiments are not limited to surface treatments of substrate holders. Embodiments include treatments of the surface of any structure. The applied surface treatment also need not change the surface profile and may, for example, simply clean the surface. Embodiments particularly include surface treatments of mask / reticle / patterning device support structures (which may also include burls). Embodiments may be used to clean and / or change the profile of the burls.

[0097] Embodiments are not limited to surface treatment by means of plasma (e.g., hydrogen plasma). Embodiments include treating the surface by radiation (e.g., laser radiation, electron beam, or ion beam). For example, when using the laser radiation (e.g., high energy photons or high beam intensity), the technician can position the shielding system to select specific areas on the surface for treatment using the laser radiation. With the aid of the laser radiation, laser ablation can be initiated at selected surface areas or zones. Thus, the top surface at the burl, for example, can be treated. That is, the height of the burl can be reduced and / or contaminants at the burl can be removed by means of laser-induced surface treatment (e.g., laser ablation).

[0098] By means of the aforementioned shielding system, precise selection of the area or zone to be treated by radiation (plasma radiation, laser radiation, electron beam or ion beam) can be achieved.

[0099] Embodiments include the following numbered aspects:

[0100] 1. A shield for use in a plasma treatment process for a surface, the shield comprising: a body for shielding a first area of ​​the surface from the effects of the plasma treatment process; and an opening through the body of the shield for exposing a second area of ​​the surface during the plasma treatment process.

[0101] 2. The shield of aspect 1, wherein: the plasma treatment process is used to reduce the height of at least one burl; the body of the shield is arranged to shield a plurality of burls in the first region from the plasma treatment process; and

[0102] The opening through the body of the shield is arranged to expose at least one burl in the second region during the plasma treatment process.

[0103] 3. The shield of aspect 2, wherein the opening is configured to expose only a single burl of the plurality of burls.

[0104] 4. A shielding member according to aspect 2 or 3, wherein the shielding member comprises: a first plate having a slit opening; and a second plate having a plurality of burl openings; wherein: the first plate and the second plate are capable of rotating relative to each other; the opening passing through the shielding member is one of the burl openings; and the burl opening provided in the opening passing through the shielding member depends on the relative rotational position of the slit opening and the burl opening.

[0105] 5. An arrangement comprising: a structure having a surface; and a shield for covering at least some of the surface; wherein the shield is a shield according to any one of aspects 1 to 4.

[0106] 6. An arrangement according to aspect 5, wherein: the structure comprises a plurality of burls; and the shield is arranged to cover at least some of the burls.

[0107] 7. An arrangement according to clause 6, wherein the structure is a substrate holder.

[0108] 8. A system configured to perform a plasma treatment process on a portion of a surface, the system comprising: a plasma source configured to generate a plasma environment; and an arrangement according to any one of aspects 5 to 7.

[0109] 9. The system of aspect 8, wherein the system is configured to perform a plasma treatment process on one or more of the plurality of burls.

[0110] 10. The system of aspect 8 or 9, wherein the plasma source is configured to generate ions having an energy of preferably at least 2 eV, and preferably less than 15 eV, and more preferably less than 10 eV, and even more preferably less than 6 eV.

[0111] 11. The system according to any one of clauses 8 to 10, wherein the system is further configured to perform a lithography process and / or a metrology process.

[0112] 12. A method of performing a plasma treatment process on a portion of a surface, the method comprising: shielding a first region of the surface from a plasma environment; and exposing a second region of the surface to the plasma environment.

[0113] 13. The method of aspect 12, wherein: the surface comprises a plurality of burls;

[0114] The plasma treatment process is used to reduce the height of at least one burl; a plurality of burls in the first region are shielded from the plasma treatment process; and at least one burl in the second region is exposed during the plasma treatment process.

[0115] 14. The method of aspect 13, further comprising: determining a height profile of the plurality of burls; and performing the shielding according to the height profile.

[0116] 15. A method according to aspect 13 or 14, wherein the shielding leaves only one burl exposed.

[0117] 16. The method according to any one of aspects 13 to 15 further includes: changing the exposed burls during the exposure process by reconfiguring the shielding of the multiple burls during the exposure process; and / or repeating the exposure process with different shielding configurations so as to change the exposed burls in each exposure process.

[0118] 17. The shield of any one of aspects 1 to 4 or the system of any one of aspects 8 to 11 or the method of any one of aspects 12 to 16, wherein the plasma treatment process is a hydrogen plasma treatment process.

[0119] 18. A shielding system for use in a surface treatment process, comprising a first disk and a second disk;

[0120] The first disk and the second disk are arranged substantially parallel to each other; the first disk has a slit-shaped opening; the second disk includes a plurality of openings; and

[0121] Wherein the first and second discs are arranged to move relative to each other about a common axis, whereby the slit can be positioned at one or more of the plurality of openings to form a passage through the shielding system.

[0122] 19. The shielding system of aspect 18, wherein the passageway is configured to expose only selected areas on the surface of the object undergoing surface treatment.

[0123] 20. The shielding system according to aspect 18 or 19, wherein the passage is configured to expose only one burl among a plurality of burls included on the surface of the object subjected to the surface treatment.

[0124] 21. The shielding system of any of aspects 18 to 20, wherein the plurality of openings are arranged at the second disk along one or more spiral arrangements.

[0125] 22. A shielding system for use in a surface treatment process, comprising a first layer and a second layer, the first layer and the second layer being arranged substantially parallel to each other;

[0126] The first layer includes a first pair of plates, a first slit opening being provided between the first pair of plates;

[0127] The second layer includes a second pair of plates, a second slit opening is provided between the second pair of plates; and wherein the first slit opening and the second slit opening are substantially orthogonal to each other and an opening through the shield is provided according to the relative positions of the first slit opening and the second slit opening.

[0128] 23. A shielding system according to any one of aspects 18 to 22, wherein the shielding system is arranged to shield a first area of ​​the surface of an object from radiation during the surface treatment process and expose a second area of ​​the surface of the object to the radiation via the passage in the shielding system.

[0129] 24. The shielding system of aspect 23, wherein the radiation is plasma, laser radiation, electron beam, or ion beam.

[0130] 25. The shielding system of any one of aspects 18 to 24, wherein the first and second disks or the first and second layers are grounded during the surface treatment process.

[0131] 26. An apparatus for conditioning a component of a lithographic apparatus, comprising: a housing configured to contain a plasma; a plasma generator for providing the plasma;

[0132] a support device configured to support the component to be treated with the plasma; a shielding system according to any one of aspects 18 to 25, the shielding system being arranged between the plasma source and the support device to shield at least a portion of a surface of the component; and

[0133] Wherein the apparatus is configured to control at least one of a ratio of ions to radicals in the plasma, an energy of the plasma, and a position of the opening through the shielding system for selective surface treatment of the component.

[0134] 27. A method of performing a surface treatment process on a portion of a surface, the method comprising: shielding a first area of ​​the surface from radiation; and exposing a second area of ​​the surface to the radiation to perform a selective surface treatment.

[0135] 28. The method of clause 27, wherein the radiation is plasma, laser radiation, electron beam or ion beam.

[0136] 29. The method of aspect 27 or 28, wherein: the surface comprises a plurality of burls;

[0137] The surface treatment process is used to surface treat at least one burl; the plurality of burls in the first region are shielded from the surface treatment process; and at least one burl in the second region is exposed during the surface treatment process.

[0138] 30. The method of any of aspects 27 to 29, further comprising: determining a height profile of the plurality of burls; and performing the shielding according to the height profile.

[0139] 31. The method of any of aspects 27 to 30, wherein the shielding system leaves only one burl exposed.

[0140] 32. The method according to any one of aspects 27 to 31 further includes: changing the exposed burls during the exposure process by reconfiguring the shielding of the multiple burls during the exposure process; and / or repeating the exposure process with different shielding configurations so as to change the exposed burls in each exposure process.

[0141] 33. The shielding system of any one of aspects 18 to 25, wherein the position of the slit in the first disk, and the orientation of the second disk or the first and second slit openings are set and controlled by a controller.

[0142] 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), thin film magnetic heads, etc.

[0143] Although specific reference is made herein to embodiments of the invention in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus for measuring or processing an object such as a wafer (or other substrate) or a mask (or other pattern forming device). These apparatuses may generally be referred to as lithographic tools. Such lithographic tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0144] Although specific reference has been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention is not limited to optical lithography and may be used in other applications, such as imprint lithography, where the context permits.

[0145] Where 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 as instructions stored on a machine-readable medium that can 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 that can be read by a machine (e.g., a computing device). For example, a machine-readable magnetic storage medium may include a read-only memory (ROM); a random access memory (RAM); a magnetic storage medium; an optical storage medium; a flash memory device; an electrical, optical, acoustic, or other form of propagation signal (e.g., a carrier wave, an infrared signal, a digital signal, etc.), etc. In addition, herein, firmware, software, routines, instructions may be described as performing certain actions. However, it should be understood that such descriptions are for convenience only, and that these actions are actually generated by a computing device, a processor, a controller, or other device that executes firmware, software, routines, instructions, etc., and in doing so may cause an actuator or other device to interact with the physical world.

[0146] Although specific embodiments of the present invention have been described above, it will be appreciated that the present invention may be practiced in a manner different from that described. The above description is intended to be exemplary and not restrictive. Therefore, it will be appreciated by those skilled in the art that modifications may be made to the present invention as described without departing from the scope of the claims set forth below.

Claims

1. A shielding system for use in a surface treatment process of an object, comprising a first disc and a second disc; The first and second disks are arranged substantially parallel to each other; The first disk has a slit-shaped opening; The second disk includes a plurality of openings; wherein the first and second disks are arranged to move relative to each other about a common axis whereby the slit can be positioned at one or more of the plurality of openings to form a passage through the shielding system; and Wherein the passages are configured to expose only selected areas on the surface of the object undergoing the surface treatment process.

2. The shielding system according to claim 1, wherein: The passage is configured to expose only one of a plurality of burls included on the surface of the object subjected to the surface treatment.

3. The shielding system according to claim 1 or 2, wherein: The plurality of openings are arranged at the second disk along one or more spiral arrangements.

4. The shielding system according to any one of claims 1 to 3, wherein: The shielding system is arranged to shield a first area of ​​a surface of an object from radiation during the surface treatment process and to expose a second area of ​​the surface of the object to the radiation via the passage in the shielding system.

5. The shielding system according to claim 4, wherein: The radiation is plasma, laser radiation, electron beam or ion beam.

6. The shielding system according to any one of claims 1 to 5, wherein: The first disk and the second disk are grounded during the surface treatment process.

7. The shielding system according to any one of claims 1 to 6, wherein: The first disk and the second disk are positioned and controlled by a controller.

8. An apparatus for adjusting a component of a lithographic apparatus, comprising: a housing configured to contain radiation; a radiation generator, the radiation generator being used to provide the radiation; a support device arranged to support the component to be treated with the radiation; The shielding system according to any one of claims 1 to 7, the shielding system being arranged between the radiation source and the support device to shield at least a portion of the surface of the component; The radiation is plasma; and Wherein the apparatus is configured to control at least one of a ratio of ions to radicals in the plasma, an energy of the plasma, and a position of the opening through the shielding system for selective surface treatment of the component.

9. A method of performing a surface treatment process on a selected area of ​​a surface of an object, the method comprising: Selecting a region to be processed on the surface of the object; shielding a first area of ​​the surface that is not a selected area of ​​the surface from radiation by using the shielding system according to any one of claims 1 to 7; and The selected areas of the surface are exposed to the radiation to perform a selective surface treatment.

10. The method according to claim 9, wherein: The radiation is plasma, laser radiation, electron beam or ion beam.

11. The method according to claim 9 or 10, wherein: The surface includes a plurality of burls; The surface treatment process is used to treat the surface of at least one burl; A plurality of burls in the first region are shielded from the surface treatment process; and at least one burl in the selected region is exposed during the surface treatment process.

12. The method according to any one of claims 9 to 11, further comprising: determining a height profile of the plurality of burls; And the shielding is performed according to the height profile map.

13. The method according to any one of claims 9 to 12, wherein: The shielding system leaves only one burl exposed.

14. The method according to any one of claims 9 to 13, further comprising: changing the exposed burls during the surface treatment process by reconfiguring the shielding system for the plurality of burls during the surface treatment process; and / or repeating the surface treatment process with different shielding configurations so as to change the exposed burls in each surface treatment process.

15. The method according to claim 10, wherein: The plasma is hydrogen plasma.

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