Reflective mirrors for photolithography equipment

Abstract

A reflector comprises a body and a surface defined by the body. The body comprises a plurality of layers. When radiation having a first wavelength is incident on the surface, the plurality of layers are arranged to act as a multilayer Bragg reflector for radiation having the first wavelength. A local tangent plane of the surface is inclined at a non-zero angle relative to a local tangent plane of the plurality of layers.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to EP application 19175714.5 filed on May 21, 2019 and EP application 19184661.7 filed on July 5, 2019, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to a reflector, in particular, the reflector is suitable for extreme ultraviolet (EUV) radiation and can be used in an EUV lithography device. Background Art

[0004] A lithographic apparatus is a machine configured to apply a desired pattern to a substrate. A lithographic apparatus may be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern from a pattern forming device (e.g., a mask) onto a layer of radiation-sensitive material (resist) disposed on a substrate.

[0005] To project a pattern on a substrate, a lithography apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features that can be formed on a substrate. A lithography apparatus using extreme ultraviolet (EUV) radiation having a wavelength in the range of 4-20 nm, such as 6.7 nm or 13.5 nm, can be used to form smaller features on a substrate compared to a lithography apparatus using radiation having a wavelength of, for example, 193 nm.

[0006] A radiation source that generates EUV radiation to be used in a lithographic apparatus may also generate particulate matter and radiation having wavelengths that do not correspond to EUV ("out-of-band" radiation). Such particulate matter and out-of-band radiation may propagate through the lithographic apparatus and cause a number of problems.

[0007] For example, particulate matter propagating through a lithographic apparatus may cause damage or failure of a patterning device or other optical components, such as a mirror within the lithographic apparatus. Such particulate matter may also cause errors in the pattern transferred to the substrate. Out-of-band radiation propagating through a lithographic apparatus may cause an increase in the dose received by the substrate, which may cause errors in the pattern transferred to the substrate. Out-of-band radiation propagating through a lithographic apparatus may also cause an increase in the thermal load received by the substrate, which may cause thermal deformation of the substrate and subsequent errors in the pattern transferred to the substrate.

[0008] Embodiments of the present invention relate to a new design of mirrors that reduces (and may completely prevent) the propagation of particulate matter and out-of-band radiation through a lithographic apparatus. Summary of the invention

[0009] According to a first aspect of the present invention, there is provided a reflector. The reflector may comprise: a body comprising a plurality of layers; and a surface defined by the body. When radiation having a first wavelength is incident on the surface, the plurality of layers may be arranged to act as a multilayer Bragg reflector for radiation having the first wavelength. A local tangent plane of the surface may be inclined at a non-zero angle relative to a local tangent plane of the plurality of layers.

[0010] The radiation may be electromagnetic radiation, or may be referred to as light.

[0011] The reflector according to the first aspect of the invention may have a body comprising a plurality of individual layers arranged to act as a multilayer Bragg reflector for radiation having a first wavelength. The plurality of layers may comprise layers formed of a first material (the "first set" of layers) interlaced with layers formed of a second material (the "second set" of layers). Additional layers may be provided between the layers of the first set and the layers of the second set to prevent mixing of materials during production of the body.

[0012] The body may define an inclined surface. In particular, the plurality of layers may define an inclined surface.

[0013] Typically, when radiation having a first wavelength is incident on the surface, a portion of the radiation incident on each interface between adjacent layers of the plurality of layers may be reflected. It should be understood that for the plurality of layers acting as a multilayer Bragg reflector for radiation having the first wavelength, all such reflected portions may be in phase so as to interfere constructively.

[0014] The reflector according to the first aspect of the invention is advantageous because it can be used as a reflector for radiation having a first wavelength (using multiple layers as a multilayer Bragg reflector) and, further, because the local cut surface of the surface is inclined at a non-zero angle relative to the local cut surfaces of the multiple layers, the reflector can also be used to filter out particles and radiation having a different wavelength, as now discussed.

[0015] Radiation having a wavelength greater than the first wavelength may be referred to as radiation having a second wavelength. It may be that radiation having a wavelength greater than the first wavelength cannot resolve structures defined by interfaces between layers of the plurality of layers of the body. Thus, when radiation having a wavelength greater than the first wavelength is incident on a surface of the body, the primary interface experienced by the radiation may be the interface between the surface and the environment in which the reflector is disposed (i.e., the surface). Thus, radiation having the first wavelength will be primarily reflected from the layers of the body, while radiation having a wavelength greater than the first wavelength will be primarily reflected from the surface.

[0016] Particulate matter may be incident on the surface of the reflector. Particulate matter having collided with the reflector surface may then be deflected from the surface in a direction at least partially determined by a local facet of the surface. Thus, radiation having a first wavelength will be primarily reflected from the layer of the body, while the particulate matter will be reflected from the surface.

[0017] Radiation may be generated for many industrial applications (e.g., photolithography). A radiation source may generate radiation of multiple wavelengths (or wavelength ranges), of which only one wavelength (or wavelength range) is desired. The radiation may be directed in an apparatus using one or more reflectors. Particulate debris may be present near the one or more reflectors. Light of undesired wavelengths directed to certain components of the apparatus downstream of the light source may degrade performance of the apparatus and / or induce errors in the apparatus. Particulate matter directed to certain components of the apparatus downstream of the light source may degrade performance of the apparatus and / or induce errors in the apparatus.

[0018] Thus, it may be desirable to direct light of one wavelength to a first location, while directing light of another wavelength to a different second location. It may also be desirable to have a reflector that directs light to a first location without directing particulate matter to said first location. Advantageously, the reflector according to the first aspect of the invention is configured to direct light having a first wavelength in a first direction, while directing light having a second wavelength in another direction. Advantageously, the reflector according to the first aspect of the invention is configured to direct light having a first wavelength in a first direction, while directing particulate matter in another direction.

[0019] The plurality of layers of the body may be generally flat so as to form a reflector with no optical power for radiation having a first wavelength. For such an embodiment, the local facets of the plurality of layers are the same for all portions of the reflector. Alternatively, the plurality of layers may be curved (concave or convex) so as to form a reflector for radiation having a first wavelength with optical power (positive or negative). For such an embodiment, the local facets of the plurality of layers depend on the position on the reflector, such that the local facets of the plurality of layers are generally different for different portions of the reflector.

[0020] The first wavelength may correspond to extreme ultraviolet radiation.

[0021] The second wavelength may correspond to deep ultraviolet radiation.

[0022] The second wavelength may correspond to infrared radiation.

[0023] Particulate matter may refer to droplets of liquid tin.

[0024] The surface may be formed from a material that is transmissive to extreme ultraviolet radiation.

[0025] The surface may be formed from a material that transmits greater than 50% of incident extreme ultraviolet radiation.

[0026] The surface may be formed from one or more of a plurality of layers.

[0027] The body may further comprise a supplementary member. The supplementary member may be arranged on a plurality of layers. The surface may be defined by the supplementary member.

[0028] As described above, the body may define a surface. When a supplementary component is provided, the surface may not be defined by the plurality of layers, but by the supplementary component. That is, the supplementary component may define a surface whose local cross-section is inclined at a non-zero angle relative to the local cross-sections of the plurality of layers of the body.

[0029] The supplementary components may have dimensions that vary in at least one spatial dimension.

[0030] The supplemental member may not be conformal to the surface of the plurality of layers upon which the supplemental member may be disposed.

[0031] The supplemental member may be formed from a material that is transmissive to extreme ultraviolet radiation.

[0032] The supplemental member may be formed from a material that transmits greater than 50% of incident EUV radiation.

[0033] The complementary member may be formed at least partially by an element having an extinction coefficient less than or equal to 0.1 for extreme ultraviolet radiation.

[0034] The supplementary member may be formed of at least one of carbon (C), silicon (Si), niobium (Nb), molybdenum (Mo), ruthenium (Ru), or rhodium (Rh).

[0035] The local tangent plane of the surface may be inclined at a non-zero angle relative to the local tangent planes of the plurality of layers over a majority of the surface.

[0036] The plurality of layers and the surface may be arranged such that, when radiation having the second wavelength is incident on the surface, radiation having the second wavelength is preferentially reflected from the surface.

[0037] The body may be provided with a cap. The cap may be a conformal coating. The cap may be arranged substantially parallel to a main portion of the body. The cap may define a surface.

[0038] As described above, the surface of the body may be defined by multiple layers of the body (in which case the main part of the body may include only the multiple layers). Alternatively, the body may include a supplementary component and the surface may be defined by the supplementary component (in which case the main part of the body may include multiple layers and the supplementary component). For either type of embodiment, the cap may be provided as a coating on the main part of the body. Therefore, the cap may also be described as defining a surface whose local tangent plane is inclined at a non-zero angle relative to the local tangent plane of the multiple layers of the body. That is, the cap may define a surface.

[0039] One embodiment of a reflector may comprise a plurality of layers (constituting a substantial portion of a body) and a cap, wherein the plurality of layers define a surface, and wherein the cap is provided as a coating on said surface defined by the plurality of layers. The cap may correspond to an outer surface of the body. The cap may define a surface. That is, the cap may be tilted at a non-zero angle relative to a local tangent plane of the plurality of layers.

[0040] Another embodiment may include a plurality of layers and a supplementary member (which together form a major portion of the body) and a cap, wherein the supplementary member defines a surface, and wherein the cap is provided as a coating on said surface defined by the supplementary member. The cap may correspond to an outer surface of the body. The cap may define a surface. That is, the cap may be inclined at a non-zero angle relative to a local section of the plurality of layers.

[0041] The reflector may be disposed in an environment where it is exposed to substances that corrode or otherwise damage the reflector. For example, the reflector may be exposed to hydrogen or hydrogen plasma. Advantageously, providing a cap may protect the body from exposure to, for example, hydrogen or hydrogen plasma. This may increase the life of the reflector relative to an arrangement where no cap is provided.

[0042] The cap may be formed from a material that transmits extreme ultraviolet radiation.

[0043] The cap may be formed from a material that transmits greater than 50% of incident EUV radiation.

[0044] The cap may be formed at least in part from an element having an extinction coefficient less than or equal to 0.1 for extreme ultraviolet radiation.

[0045] The cap may be formed of at least one of: zirconium (Zr), yttrium (Y), ruthenium (Ru), or rhodium (Rh); any oxide, nitride, or boride ceramic formed of zirconium (Zr), yttrium (Y), ruthenium (Ru), or rhodium (Rh); or any combination thereof.

[0046] The cap may be configured such that when radiation having the second wavelength is incident on the cap, radiation having the second wavelength is preferentially reflected from the cap.

[0047] The mirror may form part of an optical system within a lithographic apparatus.

[0048] The mirror may form part of a faceted mirror device.

[0049] The reflector may form part of an optical system within the radiation source.

[0050] The reflector may have optical power.

[0051] The reflector may be curved.

[0052] The composite reflector may be formed from an array of elements. Each element of the composite reflector may correspond to a reflector having any combination of the above-mentioned features.

[0053] It will be appreciated that adjacent elements within an array of elements may be formed continuously. This may make the manufacture of the composite reflector simpler and cheaper. Alternatively, each individual element within the array of elements may be separate. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0055] - Figure 1 A lithography system including a lithography apparatus and a radiation source is depicted;

[0056] - Figure 2 depicts a reflector according to an embodiment of the present invention;

[0057] - Figure 3 A reflector according to an embodiment of the present invention is depicted, showing Figure 2 Modifications of the depicted reflector design;

[0058] - Figure 4 Depicts a reflector according to an embodiment of the invention, wherein a supplementary member is provided;

[0059] - Figure 5 A reflector according to an embodiment of the invention is depicted, wherein a cap is provided;

[0060] - Figure 6 depicts a reflector according to an embodiment of the invention, wherein a supplementary member and a cap are provided;

[0061] - Figure 7 A reflector according to an embodiment of the present invention is depicted, wherein the reflector is formed by an array of elements, each element corresponding to Figure 5 The reflector depicted;

[0062] - Figure 8 Depicted are cross-sectional and plan views of the mirror and the effect of a droplet impinging on the mirror surface;

[0063] - Fig. 9Depicted are cross-sectional and plan views of a reflector and the effect of a droplet impinging on the reflector surface when an obstacle is placed on the reflector surface. DETAILED DESCRIPTION

[0064] Figure 1 A lithographic system is shown comprising a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an EUV radiation beam B and to provide the EUV radiation beam B to the lithographic apparatus LA. The lithographic apparatus LA comprises an illumination system IL (which may alternatively be referred to as an illuminator), a support structure MT configured to support a patterning device MA (e.g. a mask), a projection system PS, and a substrate table WT configured to support a substrate W.

[0065] For example, Figure 1 The radiation source SO shown is of a type that may be referred to as a laser produced plasma (LPP) source. A laser system 1, which may, for example, include a CO2 laser, is arranged to deposit energy into a fuel, such as tin (Sn), provided, for example, from a fuel emitter 3, via a laser beam 2. The laser beam 2 may include infrared (IR) radiation. Although tin is mentioned in the following description, any suitable fuel may be used. The fuel may, for example, be in liquid form and may, for example, be a metal or an alloy. The fuel emitter 3 may include a nozzle configured to direct tin (for example, in the form of droplets) along a trajectory toward a plasma formation region 4. The laser beam 2 is incident on the tin at the plasma formation region 4. The deposition of laser energy into the tin generates a tin plasma 7 at the plasma formation region 4. During recombination and de-excitation of electrons with ions of the plasma 7, radiation including EUV radiation is emitted from the plasma 7. Deep ultraviolet (DUV) radiation may also be emitted during recombination and de-excitation of electrons with ions of the plasma 7.

[0066] EUV radiation from the plasma is collected and focused by a collector 5. The collector 5 comprises, for example, a near normal incidence radiation collector 5 (sometimes more generally referred to as a normal incidence radiation collector). The collector 5 may have a multilayer mirror structure arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength such as 13.5 nm). The collector 5 may have an ellipsoidal structure with two focal points. The first focal point may be at the plasma formation region 4, and the second focal point may be at an intermediate focus 6, as described below. With this arrangement, an image of the plasma at the first focal point may be formed at the second focal point.

[0067] The laser system 1 may be spatially separated from the radiation source SO. In this case, the laser beam 2 may be delivered from the laser system 1 to the radiation source SO by means of a beam delivery system (not shown) comprising, for example, suitable directional mirrors and / or beam expanders and / or other optical devices. The laser system 1, the radiation source SO and the beam delivery system may together be considered a radiation system.

[0068] The radiation reflected by the collector 5 forms an EUV radiation beam B. The EUV radiation beam B is focused at an intermediate focus 6 to form an image of the plasma present at the plasma formation region 4 at the intermediate focus 6. The image at the intermediate focus 6 acts as a virtual radiation source for the illumination system IL. The radiation source SO is arranged such that the intermediate focus 6 is located at or near an opening 8 in an enclosure 9 of the radiation source SO.

[0069] although Figure 1 The radiation source SO is depicted as a laser produced plasma (LPP) source, but any suitable source, such as a discharge produced plasma (DPP) source or a free electron laser (FEL), may be used to produce EUV radiation.

[0070] The illumination system IL is configured to condition the EUV radiation beam B before it is incident on the patterning device MA. In particular, the illumination system IL comprises optics arranged to provide control of the spatial and angular intensity distribution of the EUV radiation beam B in the plane of the patterning device MA.

[0071] The EUV radiation beam B enters the illumination system IL through the opening 8 (adjacent to the intermediate focus 6). The illumination system IL includes a faceted field reflector device 10 and a faceted pupil reflector device 11. The EUV radiation beam B is reflected by the faceted field reflector device 10 toward the faceted pupil reflector device 11, and then subsequently reflected by the faceted pupil reflector device 11 toward the pattern forming device MA. Each of the faceted field reflector device 10 and the faceted pupil reflector device 11 includes a reflector array (also referred to herein as a multi-faceted reflector and a faceted reflector). Each of the individual faceted reflectors of the faceted field reflector device 10 and the faceted pupil reflector device 11 can be flat or can have some curvature. For example, in one embodiment, the field facets (mirrors) of the faceted field reflector device 10 can be curved, and each pupil facet (mirror) of the faceted pupil reflector device 11 can be flat. The orientation of each field facet can be independently controlled. This allows each field facet to direct a portion of EUV radiation beam B incident thereon to any one of a plurality of pupil planes. The selected orientations of all the field facets determine the pupil shape for illumination of the patterning device MA (i.e. the angular intensity distribution of EUV radiation beam B in the plane of the patterning device MA).

[0072] The illumination system IL may include other mirrors or devices in addition to or instead of the faceted field mirror device 10 and the faceted pupil mirror device 11 .

[0073] After being so adjusted, the EUV radiation beam B interacts with the patterning device MA. In particular, the EUV radiation beam B may interact with only a portion of the patterning device MA. The portion of the patterning device MA that interacts with the EUV radiation beam B can be controlled by controlling the position of the patterning device relative to the EUV radiation beam B. The portion of the patterning device MA that interacts with the EUV radiation beam B can be further controlled by a shutter system 15. The shutter system 15 may include movable blades, and the position of these movable blades may control which portion of the patterning device MA receives energy from the EUV radiation beam B. As a result of the interaction of the EUV radiation beam B with the patterning device MA, a patterned EUV radiation beam B' is generated. The projection system PS is configured to project the patterned EUV radiation beam B' onto a substrate W. For this purpose, the projection system PS may include a plurality of mirrors 13, 14, which are configured to project the patterned EUV radiation beam B' onto a substrate W held by a substrate table WT. In this way, a typical diffraction limited image of the patterning device MA is formed on the substrate W. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B' so as to form an image having features that are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 may be applied. Figure 1 The projection system PS is shown with only two mirrors 13, 14, but the projection system PS may comprise a different number of mirrors (eg six or eight mirrors).

[0074] The substrate W may include a previously formed pattern. In this case, the lithographic apparatus LA is operable to align an image formed by the patterned EUV radiation beam B′ with a pattern previously formed on the substrate W.

[0075] A relative vacuum, ie a small amount of gas (eg hydrogen) at a pressure well below atmospheric pressure, may be provided in the radiation source SO, illumination system IL and / or projection system PS.

[0076] Figure 2 A cross section of a reflector 200 according to an embodiment of the present invention is shown. The reflector 200 comprises: a body 202; and a surface 204.

[0077] The body 202 may be referred to as a mirror body.

[0078] The body 202 includes a plurality of layers arranged to act as a multilayer Bragg reflector for radiation having a first wavelength (e.g., EUV radiation) when the radiation having the first wavelength is incident on the surface 204. The plurality of layers includes layers formed of a first material (a "first set" of layers) interleaved with layers formed of a second material (a "second set" of layers). The first set and the second set are arranged to act as a multilayer Bragg reflector for radiation having a first wavelength when the radiation having the first wavelength is incident on the surface 204. Figure 2 This is schematically illustrated by light and dark horizontal lines within the body 202.

[0079] Surface 204 includes two portions, each portion being inclined at a non-zero angle relative to the plane of the plurality of layers. A local tangent plane of surface 204 may be considered to be inclined at a non-zero angle relative to the plane of the plurality of layers (which is flat in this embodiment).

[0080] Mirror 200 is advantageous because it can act as a reflector for radiation having a first wavelength (using the multiple layers as a multilayer Bragg reflector), and further, because the local cut surface of surface 204 is inclined at a non-zero angle relative to the plane of the multiple layers, mirror 200 is also used to filter out particles and radiation having wavelengths different from the first wavelength, as discussed in more detail below.

[0081] The material forming the first group has a different refractive index than the material forming the second group. The first group can be formed of molybdenum (Mo). The second group can be formed of silicon (Si). Additional layers can be provided between the layers of the first group and the layers of the second group. These additional layers can prevent mixing of the material forming the first group and the material forming the second group during the production process of the body 202.

[0082] The first and second groups of layers within the body 202 are arranged to function as a multilayer Bragg reflector. In particular, the first and second groups of layers within the body 202 are arranged to function as a multilayer Bragg reflector for radiation having a wavelength equal to about 13.5 nm (corresponding to EUV radiation). This wavelength may be described as a first wavelength.

[0083] The surface 204 is defined by the body 202. The surface 204 can be described as an inclined surface. In particular, a local section of the surface 204 is inclined at a non-zero angle relative to a local section of a plurality of layers within the body 202.

[0084] When radiation having a first wavelength, such as EUV radiation, is incident on the surface 204 , the first and second sets of layers within the body 202 are arranged to act as a multilayer Bragg reflector for radiation having the first wavelength.

[0085] In use, radiation having a first wavelength may be incident on the surface 204. The radiation having the first wavelength will propagate at least partially into the layers within the body 202. The propagation of the incident radiation having the first wavelength is Figure 218a. A portion of radiation 18a incident on each interface between adjacent layers of the plurality of layers will be reflected. It will be appreciated that for a plurality of layers acting as a multilayer Bragg reflector for radiation having a first wavelength, all such reflected portions may be in phase so as to interfere constructively. Thus, the dimensions of the first set of layers and the second set of layers are designed such that portions of radiation 18a reflected from interfaces between adjacent layers are in phase so as to interfere constructively. The reflected radiation having the first wavelength is Figure 2 This is schematically depicted by arrow 18b.

[0086] Radiation having a wavelength greater than the first wavelength (eg, IR radiation or DUV radiation) may be referred to as radiation having a second wavelength. In use, radiation having the second wavelength may be incident on the surface 204. The propagation of the incident radiation having the second wavelength is Figure 2 204. The reflected radiation 19a is generally not able to resolve structures defined by interfaces between layers within the body 202. Therefore, when this radiation 19a is incident on the surface 204, the main interface experienced by the radiation 19a is the interface between the surface 204 and the environment in which the reflector 200 is arranged. Therefore, the radiation 19a is reflected from the surface 204 in a direction determined at least in part by the local cut surface of the surface 204. The reflected radiation having the second wavelength is at Figure 2 This is schematically indicated by arrow 19b.

[0087] Thus, radiation having a first wavelength will be primarily reflected from the layers of body 202 (see arrows 18a, 18b), whereas radiation having a wavelength greater than the first wavelength (eg radiation having a second wavelength) will be primarily reflected from surface 204 (see arrows 19a, 19b).

[0088] In use, particulate matter may be incident on the surface 204. The trajectory of the incident particulate matter is Figure 2 The particulate matter 19a that collides with the surface 204 may then be deflected from the surface 204 in a direction at least partially determined by a local section of the surface 204. The deflected particulate matter Figure 2 This is schematically indicated by arrow 19b.

[0089] Thus, radiation having the first wavelength will be primarily reflected from the layers of body 202 (see arrows 18a, 18b), whereas particulate matter will be reflected from surface 204 (see arrows 19a, 19b).

[0090] It will be appreciated that the optical properties of the reflector 200 (for radiation having the first wavelength) are defined by the geometry of the layers in the body 202. The layers in the body 202 may be generally flat (eg, Figure 2) so as to form a reflector with no optical power (for radiation having a first wavelength). For such an embodiment, the local facets of the multiple layers are the same for all portions of the reflector. Alternatively, the multiple layers can be curved (concave or convex) so as to form a reflector with positive or negative optical power (for radiation having a first wavelength). For example, reflector 200 can be one of the field facet mirrors of the faceted field reflector device 10. For such an embodiment, the local facets of the multiple layers depend on the position on the reflector, so that the local facets of the multiple layers are generally different for different portions of the reflector 200.

[0091] In contrast, the optical properties of mirror 200 for radiation not having the first wavelength are defined by the geometry of surface 204 .

[0092] Radiation may be generated for many industrial applications (e.g., lithography). The radiation source may generate radiation of multiple wavelengths (or wavelength ranges), of which only one wavelength (or wavelength range) may be required. The radiation may be directed in an apparatus using one or more mirrors. Reflectors may be particularly beneficial if the radiation is well absorbed by materials such as EUV radiation (for which the use of refractive lenses may be impractical). Particulate matter may be present in the vicinity of the one or more mirrors. Radiation of undesirable wavelengths directed to certain components of an apparatus downstream of the radiation source may degrade the performance of the apparatus and / or induce errors in the apparatus. Particulate matter directed to certain components of an apparatus downstream of the radiation source may degrade the performance of the apparatus and / or induce errors in the apparatus.

[0093] Laser 2 is incident on source SO (see Figure 1 ) (which may be referred to as a "LPP tin target") may not be completely converted into plasma 7. After receiving energy from the laser beam 2, tin droplets that are not completely converted into plasma 7 may be scattered from the plasma formation region 4. When interacting with surfaces within the source SO, the scattering of particulate matter (especially scattered liquid tin balls) can be approximated as ray reflection. This approximation may be valid due to the surface tension of the particulate matter upon impact and the recoil of the particulate matter after impact, which can demonstrate a certain degree of energy conservation and momentum conservation upon collision with the surface. Therefore, tin droplets that are not completely converted into plasma 7 may bounce and / or propagate along the inner wall of the enclosure 9 of the radiation source SO. In addition, tin droplets that are not completely converted into plasma 7 may be reflected by the collector 5.

[0094] The radiation constituting the laser beam 2 may be IR radiation. IR radiation from the laser beam 2 may be reflected by tin droplets that are not fully converted into the plasma 7. IR radiation may be reflected by the collector 5. DUV radiation may be emitted during recombination and de-excitation of electrons with ions of the plasma 7. This DUV radiation may be reflected by the collector 5.

[0095] Therefore, particulate matter (particularly tin droplets) may propagate from the source SO through the opening 8 in the enclosure 9 into the illumination system IL. The particulate matter propagating from the source SO into the illumination system IL may consist mainly of the material forming the LPP tin target (i.e., molten tin). The particles constituting this particulate matter may have a diameter of the order of 1 μm and may be formed at a rate of 10 ms. -1 IR radiation may also propagate from source SO through opening 8 in enclosure 9 into illumination system IL. DUV radiation may also propagate from source SO through opening 8 in enclosure 9 into illumination system IL.

[0096] UV entering the illumination system IL may propagate through the lithographic apparatus LA and subsequently degrade the performance of the lithographic apparatus LA and / or induce errors in the lithographic apparatus LA. IR and / or DUV radiation entering the illumination system IL may propagate through the lithographic apparatus LA and subsequently degrade the performance of the lithographic apparatus LA and / or induce errors in the lithographic apparatus LA.

[0097] Thus, it may be desirable to direct radiation of one wavelength (e.g., EUV radiation) to a first location while directing radiation of other wavelengths (e.g., IR and DUV radiation) to a different second location. It may also be desirable to direct radiation of one wavelength (e.g., EUV radiation) to a first location while not directing particulate matter (e.g., tin droplets) to the first location.

[0098] Reference again Figure 2 Advantageously, the mirror 200 is configured to direct radiation having a first wavelength 18a (e.g. EUV radiation) in a first direction 18b while directing radiation having a second wavelength 19a (e.g. IR and DUV radiation) in another direction 19b. Advantageously, the mirror 200 is configured to direct radiation having a first wavelength 18a (e.g. EUV radiation) in a first direction 18b while directing particulate matter 19a (e.g. tin droplets) in another direction 19b. To mitigate issues with tin and radiation having a second wavelength propagating through the lithographic apparatus LA, one or more mirrors within the lithographic apparatus LA may be of the type of the mirror 200.

[0099] Reference Figure 1Different optical requirements and / or tolerances may exist for the propagation of radiation wavefronts of a radiation beam propagating through the illumination system IL (e.g., EUV radiation beam B) and a radiation beam propagating through the projection system PS (e.g., patterned EUV radiation beam B'). In particular, tighter optical requirements (e.g., lower tolerances) may exist in the projection system PS compared to the illumination system IL. Therefore, when incorporating the mirror 200 into a lithographic apparatus, it may be desirable to modify optical elements within the illumination system IL (e.g., in order to incorporate the mirror 200) rather than optical elements within the projection system PS.

[0100] Each of the faceted field mirror device 10 and the faceted pupil mirror device 11 (both disposed within the illumination system IL) comprises individual facets (individual mirrors). To mitigate the problem of tin and radiation having a second wavelength propagating through the lithographic apparatus LA, one or more facets of the faceted field mirror device 10 and / or the faceted pupil mirror device 11 may be of the type of mirror 200. Such use of the mirror 200 is now described.

[0101] As described above, the dimensions of the first and second groups of layers within the body 202 are designed such that the mirror 200 acts as a multilayer Bragg reflector for EUV radiation. Furthermore, each mirror 200 included in the lithographic apparatus LA may be arranged such that the above-mentioned “first direction” (for each mirror 200) corresponds to the above-mentioned first direction as described with reference to Figure 1 The EUV radiation propagating through the illumination system IL and the projection system PS of the lithographic apparatus LA is described (i.e., in an intended manner). That is, each mirror 200 included in the lithographic apparatus LA may be arranged such that the "first direction" corresponds to EUV radiation propagating through the lithographic apparatus LA, as schematically depicted by the beams B, B'. It should be understood that, as used herein, for Figure 2 For curved reflectors of the type shown (ie having curved layers), the term first direction may be intended to denote the direction of a chief ray of a portion of the radiation beam B scattered from the curved reflector.

[0102] The patterning device MA may form part of a patterning device assembly, which may include: a structural support MT; a patterning device MA; and a protective film, which may be referred to as pellicle 17. Tin droplets entering the illumination system IL may propagate through the illumination system IL so as to be incident on the patterning device assembly MT, MA, 17. This may result in errors in the pattern being transferred to the patterned EUV radiation beam B' and subsequently to the substrate W. Furthermore, if tin reaches the patterning device assembly MT, MA, 17, at least a portion of the patterning device assembly MT, MA, 17 may be damaged. This may ultimately result in failure of at least a portion of the patterning device assembly MT, MA, 17.

[0103] The substrate W may have a photoresist coating (a substance that undergoes a chemical reaction when receiving a nominal dose of radiation). The photoresist may be configured so as to undergo the chemical reaction for a predetermined length of time when receiving EUV radiation (via the patterned EUV radiation beam B'). DUV radiation propagating through the lithographic apparatus LA may propagate so as to be incident on the substrate W. This may increase the dose received by the substrate W. This may result in errors in the pattern transferred to the substrate W (e.g., which may affect critical dimension uniformity).

[0104] An integrated circuit may be formed from a substrate W. In order to form the integrated circuit from the substrate W, patterned radiation (via a patterned EUV radiation beam B') may be provided to the substrate W multiple times. Therefore, the substrate W may be described as comprising layers. It is desirable to ensure that all these layers are well aligned. The misalignment of the pattern projected onto the substrate W relative to the pattern of the layer exposed to the substrate W that has been formed (or is to be formed) may be referred to as "overlay". Overlay generally has an adverse effect on lithographic performance. An increase in overlay may correspond to a reduction in the quality of the integrated circuit produced using the lithographic apparatus LA, or even a failure. IR radiation propagated through the lithographic apparatus LA may propagate so as to be incident on the substrate W. This may result in a thermal load on the substrate W. This may result in thermal deformation of the substrate W. This may increase overlay.

[0105] IR and / or DUV radiation propagating through the lithographic apparatus LA may propagate so as to be incident on the patterning device assembly MT, MA, 17. This may result in thermal loading on the pellicle 17. This may reduce the lifetime of the pellicle 17 or cause the pellicle 17 to fail.

[0106] Each mirror 200 included in the lithographic apparatus LA may be arranged such that tin droplets entering the illumination system IL and incident on a surface 204 of the mirror 200 (which may constitute a facet of the faceted field mirror device 10 and / or the faceted pupil mirror device 11) are deflected from the mirror 200 in a direction that does not correspond to the direction of the EUV radiation beam B within the illumination system IL. That is, the "second direction" (the direction in which the incident tin droplets may be deflected) does not correspond to the direction of the EUV radiation beam B within the illumination system IL. Thus, advantageously, the tin droplets are not directed towards the patterning device MA.

[0107] Each mirror 200 included in the lithographic apparatus LA may be arranged such that IR and / or DUV radiation entering the illumination system IL and incident on a surface 204 of the mirror 200 (which may constitute a facet of the faceted field mirror device 10 and / or the faceted pupil mirror device 11) is deflected from the mirror 200 in a direction that does not correspond to the direction of the EUV radiation beam B within the illumination system IL. That is, the "second direction" (the direction in which the incident IR and / or DUV radiation may be deflected) does not correspond to the direction of the EUV radiation beam B within the illumination system IL. Thus, advantageously, the IR and / or DUV radiation is not incident on the patterning device MA (or any other component of the lithographic apparatus LA downstream of the illumination system IL, including the substrate W).

[0108] The propagation of IR and / or DUV radiation within the illumination system IL can be determined from Figure 1 The propagation direction of the EUV radiation beam B shown is offset so that the IR and / or DUV radiation is incident on the blades of the shutter system 15 while the EUV radiation beam B propagates through the aperture of the shutter system 15 (defined by the blades). The propagation of the IR and / or DUV radiation within the illumination system IL can be further offset so that the IR and / or DUV radiation is incident on a portion 16 of the wall of the illumination system IL. The portion 16 of the wall of the illumination system IL can be shaped to have a relatively large surface area. For example, the portion 16 of the wall of the illumination system IL may include grooves and / or fins. The portion 16 of the wall of the illumination system IL may include a heat sink. This is advantageous for dissipating the heat load received by the portion 16 of the wall of the illumination system IL from the IR and / or DUV radiation.

[0109] By Figure 2 A mirror in the form of the mirror 200 shown is incorporated into a lithographic apparatus LA (e.g., as described above) to reduce or prevent tin droplets from propagating through the lithographic apparatus LA. Advantageously, problems associated with tin droplets propagating toward the patterning device assembly MT, MA, 17 (e.g., errors transferred to the patterned EUV radiation beam B' and subsequently to the substrate W; damage to at least a portion of the patterning device assembly MT, MA, 17; failure of at least a portion of the patterning device assembly MT, MA, 17) are mitigated.

[0110] By Figure 2A reflector in the form of the reflector 200 shown is incorporated into the lithographic apparatus LA (e.g., as described above) to reduce or prevent the propagation of IR and DUV radiation through the lithographic apparatus LA. Advantageously, problems associated with DUV radiation incident on the substrate W are mitigated (e.g., increasing the dose received by the substrate W, which may result in errors in the pattern transferred to the substrate W). Advantageously, problems associated with IR radiation incident on the substrate W are mitigated (e.g., increasing the heat load received by the substrate W, which may result in thermal deformation and subsequently increased overlay of the substrate W). Advantageously, problems associated with IR and DUV radiation incident on the thin film 17 are mitigated (e.g., increasing the heat load on the thin film 17, which may reduce the lifetime of the thin film 17 or result in failure of the thin film 17).

[0111] Figure 2 The mirror in the form of the mirror 200 shown may be incorporated into the lithographic apparatus LA as described in detail above (by forming part or all of one or more facets of the faceted field mirror device 10 or the faceted pupil mirror device 11). However, it will be appreciated that the mirror 200 may be incorporated into the lithographic system in another arrangement. For example, the mirror 200 may form part of the collector 5. Alternatively, the mirror 200 may be incorporated into the lithographic system in another arrangement. It will also be appreciated that the mirror 200 may be incorporated into a completely different apparatus.

[0112] The reflector 200 may provide advantages in any optical system where particulate matter is present.The reflector 200 may provide advantages in any optical system where multiple wavelengths of radiation are present and where only a subset of the multiple wavelengths of radiation are desired.

[0113] Figure 3 A cross section of a reflector 300 according to an embodiment of the present invention is shown. The reflector 300 comprises: a body 302; and a surface 304.

[0114] The body 302 may be referred to as a mirror body.

[0115] Ontology 302( Figure 3 ) is usually composed of the main body 202 ( Figure 2 ) are formed of the same material. That is, the body 302 includes a first group and a second group of layers arranged to function as a multilayer Bragg reflector.

[0116] The surface 304 is formed by the body 302 ( Figure 3 ) is defined similarly to how surface 204 is defined by body 202 ( Figure 2 ) is defined. Surface 304 can be described as an inclined surface similar to surface 204, but the shapes of surfaces 204, 304 are different. However, the local section of each surface 204, 304 is inclined at a non-zero angle relative to the local section of the multiple layers within each body 202, 302, respectively.

[0117] In use, the reflector 300 ( Figure 3 ) is provided with the reflector 200 ( Figure 2 ) provides functional behavior similar to that provided by .

[0118] Radiation having a first wavelength may be incident on surface 304. The incident radiation having the first wavelength propagates at Figure 3 The propagation of the reflected radiation having the first wavelength is schematically depicted by arrow 18a. Figure 3 This is schematically indicated by arrow 18b.

[0119] Radiation having a second wavelength may be incident on surface 304. The propagation of incident radiation having a second wavelength is Figure 3 The propagation of the reflected radiation having the second wavelength is schematically depicted by arrow 19a. Figure 3 This is schematically indicated by arrow 19b.

[0120] Particulate matter may be incident on surface 304. The trajectory of the incident particulate matter is Figure 3 The propagation of the deflected particulate matter is schematically depicted by arrow 19a. Figure 3 This is schematically indicated by arrow 19b.

[0121] Thus, the mirror 300 is configured to direct radiation having a first wavelength 18a (e.g., EUV radiation) in a first direction 18b while directing radiation having a second wavelength 19a (e.g., IR and DUV radiation) in another direction 19b. The mirror 300 is also configured to direct radiation having a first wavelength 18a (e.g., EUV radiation) in a first direction 18b while directing particulate matter 19a (e.g., tin droplets) in another direction 19b. Thus, the mirror 300 ( Figure 3 ) is provided with the reflector 200 ( Figure 2 ) has the same advantageous features as those provided by

[0122] Reflector 300 is included as an exemplary embodiment of the present invention to demonstrate an alternative design of reflector that provides similarity to the above referenced embodiments. Figure 2 The reflector 200 has the same advantageous features as those described in detail.

[0123] Figure 4 A cross section of a reflector 400 according to an embodiment of the present invention is shown. The reflector 400 comprises: a body 402; a surface 404; and a supplemental member 406.

[0124] The body 402 may be referred to as a mirror body, and the supplementary member 406 may be referred to as an auxiliary layer.

[0125] Ontology 402( Figure 4 ) is usually composed of the main body 202 ( Figure 2 That is, the body 402 includes a first group and a second group of layers arranged to function as a multilayer Bragg reflector.

[0126] The supplementary member 406 is disposed on the body 402. The cross-section of the supplementary member 406 is generally triangular. Supplementary members of different shapes may be used in alternative embodiments, but the size of the supplementary member will generally vary in at least one spatial dimension. The supplementary member 406 can be described as not conforming to the surface of the plurality of layers on which the supplementary member is disposed.

[0127] The supplemental member 406 may be formed of a material having a relatively low extinction coefficient (e.g., less than or equal to 0.1) and a low refractive index for radiation of a first wavelength. The supplemental member 406 may be formed of a material having a relatively high transmittance (e.g., 50% or more) for EUV radiation. The supplemental member 406 may be formed of a material having a relatively high reflectivity for radiation of a second wavelength. The supplemental member 406 may be formed of a material having a relatively high reflectivity for IR and / or DUV radiation. The supplemental member 406 may be formed of at least one of carbon (C), silicon (Si), niobium (Nb), molybdenum (Mo), ruthenium (Ru), or rhodium (Rh).

[0128] The surface 404 of the body 402 is defined by the surface of the supplemental member 406. The surface 404 can be described as an inclined surface. In particular, a local section of the surface 404 is inclined at a non-zero angle relative to a local section of the plurality of layers within the body 402.

[0129] In use, the reflector 400 ( Figure 4 ) is provided with the reflector 200 ( Figure 2 ) provides functional behavior similar to that provided by .

[0130] In reflector 400, a surface inclined at a non-zero angle relative to a local tangent plane of multiple layers within body 402 is defined by surface 404 of supplemental member 406. In some cases, body 402 may be described as including multiple layers of body 402 and supplemental member 406.

[0131] Radiation having a first wavelength may be incident on surface 404. The incident radiation having the first wavelength propagates at Figure 4 4. As the supplementary member 406 has a relatively high transmittance for radiation of the first wavelength, incident radiation having the first wavelength 18a generally propagates through the supplementary member 406 toward the multiple layers of the body 402. The incident radiation having the first wavelength 18a is then reflected by the multiple layers of the body 402 acting as a multilayer Bragg reflector. The propagation of the reflected radiation having the first wavelength is Figure 4This is schematically indicated by arrow 18b.

[0132] Radiation having a second wavelength may be incident on surface 404. The propagation of incident radiation having a second wavelength is Figure 4 Since the supplementary member 406 has a relatively high reflectivity for radiation of the second wavelength, incident radiation having the second wavelength 19a is generally reflected from the supplementary member 406. The propagation of the reflected radiation having the second wavelength is Figure 4 Note that any (small) portion of incident radiation having a second wavelength that propagates into the supplementary member 406 will generally not be well reflected by the multiple layers of the body 402, as this is specifically tuned to act as a multilayer Bragg reflector for the first wavelength (rather than the second wavelength).

[0133] Particulate matter may be incident on surface 404. The trajectory of the incident particulate matter is Figure 4 Since the supplementary member 406 is solid, incident particulate matter will generally be deflected from the supplementary member 406. The propagation of the deflected particulate matter is Figure 4 This is schematically indicated by arrow 19b.

[0134] Thus, the mirror 400 is configured to direct radiation having a first wavelength 18a (e.g., EUV radiation) in a first direction 18b while directing radiation having a second wavelength 19a (e.g., IR and DUV radiation) in another direction 19b. The mirror 400 is also configured to direct radiation having a first wavelength 18a (e.g., EUV radiation) in a first direction 18b while directing particulate matter 19a (e.g., tin droplets) in another direction 19b. Thus, the mirror 400 ( Figure 4 ) is provided with the reflector 200 ( Figure 2 ) has the same advantageous features as those provided by

[0135] Reflector 400 is included as an exemplary embodiment of the present invention to demonstrate an alternative design of reflector that provides similarity to the above referenced embodiments. Figure 2 The reflector 200 has the same advantageous features as those described in detail.

[0136] Figure 5 A cross section of a reflector 500 is shown according to an embodiment of the present invention. The reflector 500 includes: a body 502; a surface 504; and a cap 508.

[0137] The body 502 may be referred to as a mirror body.

[0138] Figure 5 The body 502 and the surface 504 are Figure 2The body 202 and the surface 204 are the same. Therefore, Figure 5 The reflector 500 may be described as comprising: Figure 2 : reflector 200; and cap 508.

[0139] Cap 508 is disposed on body 502. Cap 508 generally conforms to the shape of surface 504. Cap 508 may be described as a coating that coats surface 504. Cap 508 may be described as conforming to surface 504. Cap 508 may be described as being substantially parallel to surface 504. Cap 508 may have a thickness of less than 100 nm. Cap may have a thickness of less than 10 nm. It should be understood that for purposes of illustration, Figure 5 The thickness of cap 508 shown in FIG. 5 may be exaggerated relative to the components of reflector 500 .

[0140] Cap 508 is formed of a material having a relatively low extinction coefficient (e.g., less than or equal to 0.1) and a low refractive index for radiation of a first wavelength. Cap 508 is formed of a material having a relatively high transmittance for radiation of a first wavelength. Cap 508 may be formed of a material having a relatively high transmittance for EUV radiation (e.g., 50% or more). Cap 508 is formed of a material having a relatively high reflectivity for radiation of a second wavelength. Cap 508 may be formed of a material having a relatively high reflectivity for IR and / or DUV radiation. Cap 508 may be formed of a metallic material, such as ruthenium (Ru) or rhodium (Rh). Cap 508 may be formed of a stable oxide of a EUV-transparent metal, such as zirconium oxide (ZrO2) or yttrium oxide (Y2O3). Cap 508 may be formed of a ceramic material, such as a metal nitride, boride, or oxide. Cap 508 may be formed of any combination of the example materials given.

[0141] Surface 504 may be described as an inclined surface. In particular, a local cross-section of surface 504 is inclined at a non-zero angle relative to a local cross-section of multiple layers within body 502. Because cap 508 generally follows the shape of surface 504, outer surface 510 of cap 508 may also be described as an inclined surface. Outer surface 510 of cap 508 may be substantially parallel to surface 504. In particular, a local cross-section of surface 510 is inclined at a non-zero angle relative to a local cross-section of multiple layers within body 502. Therefore, both surface 504 and outer surface 510 are inclined at a non-zero angle relative to a local cross-section of multiple layers.

[0142] In reflector 500, a surface inclined at a non-zero angle relative to a local tangent plane of the layers within body 502 is defined by outer surface 510 of cap 508. In some cases, body 502 may be described as including the layers of body 502 and cap 508.

[0143] In use, the reflector 500 ( Figure 5 ) is provided with the reflector 200 ( Figure 2 ) provides functional behavior similar to that provided by .

[0144] Radiation having a first wavelength may be incident on the outer surface 510 of the cap 508. The propagation of the incident radiation having the first wavelength is Figure 5 18a. Since the cap 508 has a relatively high transmittance for radiation of the first wavelength, incident radiation having the first wavelength 18a generally propagates through the cap 508 towards the body 502. The incident radiation having the first wavelength 18a is then reflected by the body 502 acting as a multilayer Bragg reflector. The propagation of the reflected radiation having the first wavelength is Figure 5 This is schematically indicated by arrow 18b.

[0145] Radiation having a second wavelength may be incident on the outer surface 510 of the cap 508. The propagation of the incident radiation having the second wavelength is Figure 5 A portion of the incident radiation having the second wavelength 20a is reflected from the outer surface 510 of the cap 508. A portion of the incident radiation having the second wavelength 20a is transmitted by the cap 508 and subsequently impinges on the surface 504. The propagation of the portion of the radiation having the second wavelength reflected from the outer surface 510 of the cap 508 is Figure 5 The propagation of the portion of radiation having the second wavelength transmitted by the cap 508 is schematically depicted by arrow 20b. Figure 5 504. The transmitted portion of radiation having the second wavelength 20c is generally not able to resolve structures defined by interfaces between layers within body 502 (since the second wavelength is greater than the spacing between layers within body 502). Therefore, the primary interface experienced by the transmitted portion of radiation having the second wavelength 20c is surface 504. Therefore, the transmitted portion of radiation having the second wavelength 20c is generally reflected from surface 504. The propagation of the portion of radiation having the second wavelength reflected from surface 504 is Figure 5 This is schematically indicated by arrow 20d.

[0146] Particulate matter may be incident on the outer surface 510 of the cap 508. The trajectory of the incident particulate matter is Figure 5 Since cap 508 is solid, incident particulate matter will generally be deflected from cap 508. The propagation of the deflected particulate matter is Figure 5 This is schematically indicated by arrow 20b.

[0147] Thus, the mirror 500 is configured to direct radiation having a first wavelength 18a (e.g., EUV radiation) in a first direction 18b while directing radiation having a second wavelength 20a (e.g., IR and DUV radiation) in another direction 20b, 20d. The mirror 500 is also configured to direct radiation having a first wavelength 18a (e.g., EUV radiation) in a first direction 18b while directing particulate matter 20a (e.g., tin droplets) in another direction 20b. Thus, the mirror 500 ( Figure 5 ) is provided with the reflector 200 ( Figure 2 ) has the same advantageous features as those provided by

[0148] Surface 504 and outer surface 510 are configured to provide at least Figure 2 The same advantages as surface 204.

[0149] The reflector may be exposed to substances that corrode or otherwise damage the reflector. For example, the reflector may be exposed to hydrogen or hydrogen plasma. Advantageously, the reflector 500 includes a cap 508 that can protect the body 502 of the reflector 500 from exposure to, for example, hydrogen or hydrogen plasma. This can increase the life of the reflector 500 (relative to an arrangement where the cap 508 is not provided).

[0150] As described above, incident radiation having the second wavelength 20a is partially reflected by the outer surface 510 of the cap 508, while radiation having the second wavelength 20c that is transmitted by the cap 508 is generally reflected by the surface 504 of the body 202. Thus, there are two surfaces 504, 510 from which radiation having the second wavelength can be reflected. This can result in a relatively high proportion of radiation having the second wavelength being reflected in the second direction 20b, 20d. In particular, compared to a body that does not include a cap (e.g. Figure 5 The cap 508) of the reflector (eg Figure 2 The use of reflector 500 may result in a higher proportion of radiation having the second wavelength being reflected in the second direction than reflector 200 (e.g., without a cap). Figure 5 The cap 508) of the reflector (eg Figure 2 Compared to the reflector 200 of FIG. 5 , the reflector 500 can provide better effective filtering of the radiation beam including the radiation having the first and second wavelengths. That is, the reflector 500 can better reflect the radiation having the first wavelength and the radiation having the second wavelength in different directions.

[0151] Reflector 400( Figure 4 ) and reflector 500( Figure 5 ) can be described as providing an object between the incident radiation and the plurality of layers. Specifically, the reflector 400 ( Figure 4) provides a supplementary member 406 between the incident radiation 18a, 19a and the layers of the body 402, and the reflector 500 ( Figure 5 ) A cap 508 is provided between the incident radiation 18a, 20a and the plurality of layers of the body 502. As described above, each of the supplemental member 406 and the cap 508 is formed of a material that exhibits a high transmittance to EUV radiation. The supplemental member 406 is typically thicker than the cap 508. Therefore, it may be particularly important to select a material to form the supplemental member 406 that is highly transmissive to EUV radiation. In other words, in order to achieve the same nominal level of transmittance to EUV radiation for the supplemental member 406 and the cap 508, the cap 508 may be formed of a material that is less transmissive to EUV radiation than the material selected to form the supplemental member 406.

[0152] It will be appreciated that a cap (e.g. Figure 5 The cap 508) can be set on any reflector (in particular, Figure 5 The reflector 500 corresponds to the one provided with a cap. Figure 2 Other reflectors (for example, Figure 3 , 4 reflectors 300, 400) provide caps.

[0153] Any reflector provided with a cap, in particular a reflector including an inclined surface, may be provided using the above reference Figure 5 Some or all of the advantages of the cap described above. As an example, Figure 6 A cross section of a reflector 600 according to an embodiment of the present invention is shown. The reflector 600 includes: a body 602; a surface 604; a supplemental member 606; and a cap 608. The surface 604 may be described as an inclined surface. The body 602 may be referred to as a mirror body. Figure 6 The body 602, the surface 604 and the supplementary member 606 are Figure 4 The body 402, surface 404 and supplementary member 406 are identical. Therefore, Figure 6 The reflector 600 may be described as comprising: Figure 4 and a cap 608. Cap 608 ( Figure 6 ) and cap 508( Figure 5 ) are the same, and therefore provide at least the same advantages. In use, the reflector 600 ( Figure 6 ) provides a reflector 400 ( Figure 4 ) but with reference cap 508 ( Figure 5 ) other advantages described.

[0154] In reflector 600, surfaces inclined at non-zero angles relative to local tangent planes of multiple layers within body 602 are defined by an outer surface of cap 608. In some cases, body 602 may be described as including multiple layers of body 602, supplemental member 606, and cap 608.

[0155] Figure 7 A reflector 700 comprising an array of elements is shown. The reflector 700 may be referred to as a composite reflector. The reflector 700 may be considered to comprise a plurality of elements (although the plurality of elements may be formed continuously with one another, such as Figure 7 Each element of reflector 700 generally corresponds to that of reflector 500 ( Figure 5 ). In use, radiation 702 is typically incident on the outer surface of the cap of each element of the reflector. The reflector 700 may provide the same Figure 5 All of the same advantages as described for reflector 500. However, reflector 700 ( Figure 7 ) also provides further advantages, which are now described.

[0156] The spacing 704 between the repeating peaks or valleys on the radiation-facing surface of the reflector 700 defines a reflective diffraction grating. The spacing 704 may be referred to as the "pitch" of the reflective diffraction grating. Thus, an incident radiation beam 702 may interact with the reflector 700 such that there is a zero-order diffracted beam 706, first-order diffracted beams 708a, 708b, and possibly more diffracted beams (not shown).

[0157] The reflective diffraction grating diffracts radiation of different wavelengths in different directions upon interaction with the radiation-facing surface of the reflector 700. The spacing 704 between the elements of the reflector 700 can be configured such that upon interaction with the radiation-facing surface of the reflector 700, the EUV radiation is diffracted in a direction different from the direction in which the DUV and / or IR radiation is diffracted. In other words, relative to using a reflector corresponding to the reflector 500 ( Figure 5 ), the spacing 704 of the elements of the mirror 700 can be configured to further filter out radiation having a second wavelength (eg, DUV and / or IR radiation) from radiation having a first wavelength (eg, EUV radiation).

[0158] It is known to include a reflective diffraction grating on a reflector (e.g., in the form of grooves). Reflector 700 schematically depicts how such a known arrangement may be implemented while also employing the principles of the invention disclosed herein (i.e., by using any of the reflectors 200, 300, 400, 500, 600).

[0159] Adjacent elements within an array of elements may be formed continuously. This may make the composite reflector simpler and cheaper to manufacture. Alternatively, each individual element within the array of elements may be separate.

[0160] Figure 8 A cross section through a reflector 800 is schematically shown and illustrates the effect of a droplet 901 when it impacts a substantially flat surface of the reflector. The reflector 800 comprises a body 801 and a complementary member 802 arranged on the body 801. In the embodiment shown, the body 801 is arranged on a substrate 803. The body 801 may be referred to as a mirror body. The complementary member 802 may be referred to as an auxiliary layer, which may be, for example, a cap layer or a covering layer.

[0161] The main body 801 can be composed of the main body 202 ( Figure 2 ) or main body 402( Figure 4 That is, the body 801 may include a first group and a second group of layers arranged to function as a multilayer Bragg reflector.

[0162] When such a mirror is used in an EUV lithography apparatus, in which EUV radiation is generated by a laser beam impinging on tin droplets, the apparatus - and in particular the mirrors used in the apparatus - may be contaminated by tin droplets and propagate through the apparatus as described above. When considering the typical outer surface of a mirror used in an EUV lithography apparatus, it can be pointed out that the curvature of such a mirror (for example a mirror used in the illumination system (or illuminator) of the apparatus) will be significantly larger than the diameter of the incident droplet. In this case, the reflection of the droplet will follow the light optics. In Figure 8 On the left side of the figure, this is illustrated by a droplet 901 having a diameter D, which upon impact with the surface of the complementary member 802 of the reflector 800 will flatten into droplet 902 and subsequently bounce off the surface, whereby the angle of incidence of the droplet (denoted as A) will substantially correspond to the angle of reflection A of a reflective droplet 903 having a diameter D, which moves away from the surface of the complementary member 802.

[0163] With regard to the properties of tin droplets that may occur at or near an optical device used in an EUV lithography apparatus, the following can be stated: Tin droplets propagating through the apparatus, for example through the illuminator of the apparatus, are expected to have a diameter in the range of 3-30 μm. Such particles may travel at a speed in the range of 10-50 m / s. When the droplet impacts a surface (essentially a flat surface), it will flatten out, then it retracts and bounces off the surface again. When balancing the surface energy and the kinetic energy of such a droplet, it can be shown that a flat droplet on a mirror surface may have a diameter in the range of 10-100 μm, such as Figure 8 The thickness of this flat droplet (in Figure 8The H_p in FIG. 4 may be, for example, in the range of 0.2 to 2 μm. Figure 8 The right side of FIG. 8 shows the location 810 of the incident droplet on the surface of component 802 , and the maximum spread 912 of the flat droplet.

[0164] It is an object of the present invention to reduce or mitigate the propagation of particles, such as tin droplets, through a photolithographic apparatus. Figures 2 to 7 As shown, this can be achieved by taking measures to ensure that local facets of the mirror surface are inclined at a non-zero angle relative to local facets of the layers of the mirror body.

[0165] exist Fig. 9 Alternative measures or measures which can be applied additionally are schematically shown in FIG. Fig. 9 A cross-sectional view of a reflector 900 according to the present invention is schematically shown, and the reflector 900 includes a body 801 and a supplementary member 802, wherein the body 801 can be similar to or identical to the body 801 of the reflector 800, and the supplementary member 802 can be similar to or identical to the supplementary member 802 of the reflector 800. In addition, the reflector 900 includes a plurality of obstacles 1000, which are arranged on the surface of the supplementary member 802, and these obstacles can be affected by particles such as tin droplets. According to an embodiment of the present invention, the obstacles can be small structures distributed across the surface (i.e., the outer surface of the reflector 900). According to the present invention, these obstacles are configured to interrupt the diffusion and contraction of the tin droplet flow that impacts the surface. In other words, the obstacles or structures 1000 provided on the surface are provided to disrupt the reference Figure 8 The process described, whereby droplet 901 strikes a surface, flattens into a flat droplet 902, shrinks again and is reflected into droplet 903, which has substantially the same size as droplet 901 and has a reflection angle substantially equal to the angle of incidence.

[0166] To interrupt this process, the obstacles or structures 1000 are distributed and sized in such a way that when a droplet hits a surface and flattens, it will encounter at least one obstacle or structure during the flattening process. Fig. 9 On the right side of FIG. 1 , the distribution of obstacles 1000 is shown, along with the expected flow or expansion 1011 of a droplet 1010 that impacts the surface and expands into a flat droplet with diameter D_p. Fig. 9 In the diagram, the height of a structure or obstacle is indicated as H_o, while D_o represents the width or diameter of the structure or obstacle. The distance S is used to represent the distance between Fig. 9 The distance between adjacent obstacles in the cross-sectional view on the left. As the expanding droplets encounter one or more obstacles 1000, the droplets are stimulated to scatter or break up. As a result, the rebound of the droplets will no longer be symmetrical, that is, the scattered or broken droplets will be reflected by the surface at a reflection angle different from the incident angle. In particular, Fig. 9As shown on the left side of FIG. 1 , due to the interaction of the expanding droplet with obstacle 1000, the initial droplet 1001 may break up into various small or smaller droplets, such as droplets 1003 and 1004, which bounce off the surface at different reflection angles, such as angle B, compared to the incident angle A of droplet 1001. Fig. 9 In , D represents the diameter of the droplet 1001, i.e. the droplet that hits the surface, and d represents the smaller diameter of the droplet 1003 that is reflected by the surface. In order for the obstacles to effectively scatter or break up the incident droplets, it may be advantageous to choose the height H_o of the obstacles to be in the same range as the expected height of the thinned or flattened droplets, i.e. H_o in the range of 0.1 to 1 μm. Preferably, the obstacles may be distributed on the surface in such a way that the average distance between the obstacles is less than the diameter D_p of the droplet when the droplet is allowed to fully flatten or expand. See Fig. 9 On the right side of the figure, the distance S or W between adjacent obstacles should therefore be less than 100 μm, preferably less than 30 μm, for example in the range of 3 to 30 μm. In a preferred embodiment, the size D_o of the obstacles can be in the range of 0.1 to 1 μm. By keeping the size of the obstacles small, the scattering or transmission losses of the reflector can be kept low. In this regard, it can be pointed out that the scattering or transmission losses are proportional to the ratio of the integrated obstacle area to the reflector area, and therefore, for example, as (D_o / S) 2 Proportional.

[0167] In one embodiment, obstacles or structures 1000 may be arranged in a regular grid or array, a quasi-regular grid or array, or an irregular array. It may also be noted that the height of the obstacles need not be the same for all obstacles. Height variations of + / - 50% of the average height are acceptable. In other words, there are no strict tolerances on the height or relative position of the obstacles.

[0168] In one embodiment, the barrier 1000 may be made of a material that is resistant to EUV or hydrogen plasma. Thus, suitable materials may be Ru, Zr, ZrO(x), Mo, MoO(x), Fe, Ni, other metals, metal oxides, metal nitrides or metal borides, or mixtures of these materials. Where a supplementary member such as the supplementary member 802 is used, it may be preferred to select a material that is also compatible with the material of the member (e.g., Ru, Zr, ZrO(x), Mo, MoO(x)) during manufacture or use.

[0169] As shown, the use of obstacles or structures 1000 on the surface of a mirror used in an EUV lithography apparatus can change the trajectory of particles (e.g., tin droplets) applied to the mirror. By doing so, the propagation of such particles in the apparatus can be limited or hindered. In particular, the application of the obstacles is configured to at least partially scatter or decompose particles, such as tin droplets, that impact the outer surface of the mirror.

[0170] exist Fig. 9 In the embodiment shown, the plurality of obstacles are applied to a supplementary component 802 of the reflector. Such an auxiliary component 802 may be, for example, a cover layer of the reflector. However, it may be pointed out that, without such a supplementary component 802, the plurality of obstacles may also be arranged directly on the outer surface of the body 801 of the reflector.

[0171] It can also be pointed out that the measure of applying the plurality of obstacles to the outer surface of the mirror can be applied as an independent measure to limit or hinder the propagation of particles in the EUV lithography apparatus. In another embodiment, the application of the plurality of obstacles can also be combined with the measure of ensuring that the local cut surface of the mirror surface is inclined at a non-zero angle relative to the local cut surface of the plurality of layers of the mirror body.

[0172] The above has described in detail how to place the reflector 200 ( Figure 2 ) into a lithography system and the advantages that such an arrangement would provide. The same applies Fig. 9 Specifically, the reflector 200 or the reflector 900 may form one or more facets of the faceted field reflector device 10 or the faceted pupil reflector device 11. Figure 3 , 4, 5, 6 and 7) reflectors 300, 400, 500, 600, 700 show the reflectors 200 ( Figure 2 ) that provide at least the same general advantages as those provided by reflector 200. Thus, it should be understood that ( Figure 3 Any of the reflectors 300, 400, 500, 600, 700 in FIG. 4, 5, 6 and 7 may be used in conjunction with the above reference reflector 200 ( Figure 2 ) can be incorporated into a lithography system in a manner similar to that described above and will provide at least the same general advantages as those provided by mirror 200 (discussed in the context of a lithography system).

[0173] The term "radiation having a first wavelength" (or variations thereof) is generally used herein to refer to EUV radiation. It should be understood that in other embodiments, "radiation having a first wavelength" may refer to radiation of other wavelengths.

[0174] The term "radiation having a second wavelength" (or variations thereof) is generally used herein to refer to IR radiation or DUV radiation or both. It should be understood that in other embodiments, "radiation having a second wavelength" may refer to radiation of other wavelengths.

[0175] The term "particulate matter" (or variations thereof) is generally used herein to refer to tin droplets or molten tin. It should be understood that in other embodiments, "particulate matter" may refer to other substances.

[0176] Features described in the context of the embodiments disclosed herein may be combined while remaining within the scope of the invention as set forth in the claims. Features described in the context of the embodiments disclosed herein may be used in configurations different from those presented herein while remaining within the scope of the invention as set forth in the claims.

[0177] 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.

[0178] Although embodiments of the invention may be specifically referred to herein in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatuses. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrate) or a mask (or other pattern forming device). These apparatuses are generally referred to as lithographic tools. Such lithographic tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0179] Although specific embodiments of the present invention have been described above, it should be understood that the present invention may be implemented in a manner other than that described. The above description is intended to be illustrative rather than limiting. Therefore, it will be apparent to those skilled in the art that modifications may be made to the described invention without departing from the scope of the claims set forth below.

Claims

1. A reflector, comprising: A body including multiple layers; as well as a surface defined by the body; wherein the plurality of layers are arranged to: act as a multilayer Bragg reflector for radiation having a first wavelength when radiation having the first wavelength is incident on the surface; wherein a local tangent plane of the surface is inclined at a non-zero angle relative to a local tangent plane of the plurality of layers; wherein the surface is provided with a plurality of obstacles configured to at least partially scatter or break up particles that impinge on the surface of the reflector; and The height of the obstacles in the plurality of obstacles is in the range of 0.1 μm to 1 μm, the size of the obstacles in the plurality of obstacles is in the range of 0.1 μm to 1 μm, and the average distance between adjacent obstacles in the plurality of obstacles is less than 100 μm.

2. The reflector of claim 1, wherein the obstacle is configured to at least partially scatter or break up the particle into a plurality of particles, the plurality of particles reflecting off the surface at an angle different from an angle of incidence of the particle. 3 . The reflector of claim 1 , wherein an average distance between adjacent obstacles in the plurality of obstacles is less than 30 μm. 4 . The reflector of claim 1 , wherein an average distance between adjacent obstacles in the plurality of obstacles is in a range of 3 μm to 30 μm.

5. The reflector according to any one of claims 1 to 4, wherein the plurality of obstacles are formed of Ru, Zr, Mo, Fe, Ni, metal oxides, metal nitrides, or metal borides, or a combination thereof, wherein the metal oxides include ZrOx and MoOx.

6. A reflector according to any one of claims 1 to 4, wherein the surface is formed from a material that transmits greater than 50% of incident EUV radiation.

7. A reflector according to any one of claims 1 to 4, wherein the surface is formed by one or more of the plurality of layers.

8. The reflector according to any one of claims 1 to 4, wherein the body further comprises a complementary member disposed on the plurality of layers, and wherein the surface is defined by the complementary member.

9. The reflector of claim 8, wherein the complementary member has a size that varies in at least one spatial dimension.

10. A reflector according to any one of claims 1-4 and 9, wherein the local facets of the surface are inclined at a non-zero angle relative to the local facets of the plurality of layers over a majority of the surface.

11. A reflector according to any one of claims 1-4 and 9, wherein the plurality of layers and the surface are arranged such that when radiation having a second wavelength is incident on the surface, the radiation having the second wavelength is preferentially reflected from the surface.

12. A reflector according to any one of claims 1-4 and 9, wherein the body is provided with a cap, the cap being a conformal coating, the conformal coating being arranged substantially parallel to a main portion of the body, and wherein the cap defines the surface.

13. The reflector of any one of claims 1-4 and 9, wherein the reflector has optical power.

14. A reflector, comprising: A body including multiple layers; as well as a surface defined by the body; wherein the surface is provided with a plurality of obstacles configured to at least partially scatter or break up particles that impinge on the surface of the reflector; The height of the obstacles in the plurality of obstacles is in the range of 0.1 μm to 1 μm, the size of the obstacles in the plurality of obstacles is in the range of 0.1 μm to 1 μm, and the average distance between adjacent obstacles in the plurality of obstacles is less than 100 μm.

15. A composite reflector formed from an array of elements, wherein each element of the composite reflector corresponds to a reflector according to any preceding claim.

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