Optical elements and optical devices for reflecting VUV radiation

Abstract

To extend service life of an optical element for reflecting radiation in a VUV wavelength range.SOLUTION: The present invention relates to an optical element (4) for reflecting radiation in a VUV wavelength range, comprising: a substrate (41); and a reflective coating (42) which is applied to the substrate (41) and has at least one aluminium layer (43). At least one hydrogen-catalytic layer (45) for dissociation of molecular hydrogen is applied to the aluminium layer (43). The invention also relates to an optical device for the VUV wavelength range, comprising: an interior, in which at least one optical element is arranged, and at least one gas inlet for feeding a gas into the interior. The optical element (4) is designed as described above and the gas inlet serves to feed hydrogen into the interior. The optical device comprises a plasma-generating device for feeding a plasma gas through the gas inlet into the interior to generate an atmospheric-pressure plasma on at least one partial region of an optical surface of the optical element.SELECTED DRAWING: Figure 4a

Description

[Technical Field]

[0001] [Reference to Related Applications] This application is a continuation of German patent application DE 10 2018 221 191 filed on December 7, 2018. No. 4, the entire disclosure of which is incorporated herein by reference.

[0002] The present invention provides an optical element for reflecting radiation in the VUV wavelength range, the optical element comprising a substrate and a and a reflective coating having at least one aluminum layer. The present invention relates to an optical device for the VUV wavelength range, in particular a wafer inspection system or a VUV lithography system. A radiography device, comprising: an interior in which at least one optical element is disposed; and at least one gas inlet for supplying the gas. [Background technology]

[0003] In particular, the short wavelength range of approximately 100 nm to approximately 200 nm, also known as the vacuum ultraviolet wavelength range (VUV wavelength range), In the ultraviolet wavelength range, reflective optics are often used in addition to transmissive optics. Optical devices for radiation in the UV wavelength range are used, for example, to carry out optical inspection of wafers or masks or It can be used in the manufacture of semiconductor components.

[0004] Optical elements that reflect VUV radiation usually have a reflective coating. In certain applications, such as wafer inspection, large spots in the VUV wavelength range are required. Aluminum has high reflectivity in the VUV wavelength range. has a high reflectivity of about 0.9, or 90%, so such a reflective coating has one or possibly several aluminum layers as underlayer(s) It has been found to be advantageous.

[0005] When using an aluminum layer in the VUV wavelength range, the aluminum layer is exposed to the atmosphere or reflective optical elements. When it comes into contact with the surrounding atmosphere, it forms a layer of natural aluminum oxide with a thickness of about 2 nm to 3 nm. The problem is generally that a layer of aluminum (Al2O3) is formed immediately. Since the absorption in the VUV wavelength region is strong, the aluminum layer provides additional protection from oxidation. If this is not the case, it will not be attractive as a reflective layer for use in the VUV wavelength range.

[0006] In order to protect the aluminum layer from oxidation, for example, from the paper of Non-Patent Document 1, The aluminum layer may be provided with a metal fluoride, for example, MgF2, AlF3, or LiF. The protective layer or protective coating is made of these materials in the form of a three-layer protective coating. It is known that

[0007] However, there are some issues that may arise in lithography, particularly during mask and wafer inspection. At high radiation intensities, severe degradation of reflective optics occurs within hours or days, resulting in large reflections. It has been confirmed that there is a loss of emissivity associated with it. In fact, it provides very good protection against the environment. The protective layer made of the above-mentioned metal fluorides also prevents oxidation of the aluminum layer in case of irradiation. A significant decrease in reflectance can be prevented by reducing the oxygen or This was also observed when the water content was reduced.

[0008] In the case of optical devices for the VUV wavelength range, it is necessary to completely suppress unwanted gas components in the optical element environment. These gas components generally have the added problem of contaminating optical surfaces because they cannot be absorbed by the optical They deposit on the optical surface and are "burned in" there during irradiation. It exists not only for the optical surfaces of optical elements but also for the optical surfaces of transmissive optical elements. [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] "Protected and enhanced aluminum mirrors for the VUV" by S. Wilbrandt et al., Applied Optics, Vol. 53, No. 4, February 2014 Summary of the Invention [Problem to be solved by the invention]

[0010] The object of the present invention is to provide a light reflecting radiation in the VUV wavelength range that can extend its useful life. The present invention provides optical elements and optical devices for the VUV wavelength range. [Means for solving the problem]

[0011] The objective is to provide at least one hydrogen catalyst for the dissociation of (molecular) hydrogen (hydrogen-catalyst). This is achieved with optical elements of the type described above, in which a layer of aluminium is applied to the aluminium layer.

[0012] The inventors have recognized that certain materials are suitable for catalytic hydrogen cracking. This leads to the dissociation of molecular hydrogen (or hydrogen nitrating), which may occur in the form of compounds. When added to the optical element environment in a hydrogen-catalyst layer, the separation of hydrogen occurs in the material of the hydrogen catalyst layer, especially at high irradiation doses. Active hydrogen is formed by hydrogen radicals, hydrogen ions, and / or excited electrons. This active hydrogen is usually not amenable to high radiation intensities. Oxidation of the aluminum layer can be prevented or at least significantly slowed down.

[0013] In one embodiment, for the material of the hydrogen catalyst layer, this includes Ru, Pt, Pd, Ni, Rh. For these materials, particularly Ru and Pt, the residual gas atmosphere is used. By adding hydrogen to the atmosphere, oxidation can be virtually completely prevented. Ruthenium oxide formed in a vacuum environment is converted to ruthenium by subsequent hydrogenation. that it can be reduced to ruthenium, i.e., the oxidation reaction can be reversed, It is known from lithography in the EUV wavelength range.

[0014] In an advantageous embodiment, the hydrogen catalyst layer has a thickness of 0.1 nm to 3.0 nm, preferably 0.1 The hydrogen catalyst material specified above has a layer thickness of 1.0 nm to 1.0 nm. The hydrogen catalyst material is usually used in the VUV wavelength region. In this case, the reflectivity is too low or the absorption is too large, so a large layer thickness cannot be applied. Ru has a reflectivity well below 0.6 in the VUV wavelength range. A ruthenium layer with a thickness of only 3 nm reduces the overall reflectivity of the optical element by approximately 0.2. , which is generally unacceptable.

[0015] In yet another embodiment, the hydrogen catalyst layer does not completely cover the aluminum layer. Below a certain value, it is usually not possible to apply the layer in a completely sealed manner. For Ru as the layer material, this is the case for a layer thickness of about 1.0 nm or less. If the difference is below this value (which depends on the material), the hydrogen catalyst layer may not be applied. A portion of the surface of the aluminum layer is exposed, and native aluminum oxide may form on the exposed portion. However, the covered partial area(s) of the aluminum layer may be naturally Since an aluminum oxide layer cannot be formed, even a hydrogen catalyst layer that is not completely sealed can be easily irradiated. Furthermore, when hydrogen is added to the optical element's environment, In this case, the catalytic effect of the material of the hydrogen catalyst layer may cause the exposed surface area of ​​the aluminum layer to But oxidation cannot occur.

[0016] In a further development, the hydrogen catalyst layer is approximately 10% to 90%, preferably 30% to 70% covered. The coverage is the total surface area of ​​the aluminum layer (opposite to the substrate). This is understood to mean the ratio of the surface of the hydrogen catalyst layer to the total surface area. The coating is in the form of an accumulation of spaced apart islands of material, in this case of the hydrogen catalyst layer, on the aluminum layer. As in the case of a sealed hydrogen catalyst layer, (molecular) hydrogen is released between the aluminum and the hydrogen catalyst layer. The formation of bubbles that accumulate in between and usually lead to complete or partial delamination of the hydrogen catalyst layer. This is advantageous because it does not lead to the formation of bubbles or optical elements due to the action of hydrogen. To prevent the deterioration of the coating, the hydrogen atoms adsorbed on the surface of the upper layer of the coating were The top layer contains a hydrogen desorption material to convert the hydrogen atoms to molecular hydrogen and desorb it from the surface. It is known from DE 10 2017 222 690 A1.

[0017] In yet another embodiment, the reflective coating is applied to the aluminum layer and the hydrogen catalyst layer. For reflection reasons, the hydrogen catalyst layer does not completely cover the aluminum layer. When the native oxide layer is applied thinly, part of the surface of the aluminum layer is exposed. When formed on the exposed surface area of ​​the aluminum layer, this reaction is generally the reaction of aluminum with oxygen. The reaction enthalpy is relatively high, so the reaction cannot be reversed by adding hydrogen. Hydrogen is much more reactive than molecular hydrogen, but the above is This also applies to active hydrogen. However, the situation is different if the oxidation reaction has not yet occurred. The oxygen or hydroxide molecules are much more loosely bound to the surface before the reaction, and therefore It is easily reduced by hydrogen radicals, that is, the oxidation rate of aluminum is reduced in this case.

[0018] Therefore, the optical element should be stored until there is sufficient hydrogen in the environment to prevent oxidation. A protective layer is used to protect at least the surface area(s) not covered with the hydrogen catalyst layer. It is usually advantageous to protect the aluminum layer from oxidation by using a This is the case when a suitable hydrogen-containing environment is provided therein during operation of the optical element at room temperature.

[0019] The protective layer preferably forms a sealing layer. As mentioned above, the protective layer is preferably an aluminum layer. This is because the aluminum layer must cover at least the exposed surface area(s) of the This is usually achieved by applying a protective sealing layer to the hydrogen catalyst layer and partially covering it. Alternatively, it is understood that the protective layer may be applied only to the exposed surface area of ​​the aluminum layer. However, such a procedure is generally not practical due to the small thickness of the hydrogen catalyst layer. do not have.

[0020] The protective layer is made of a transparent, in particular fluoride material, for example a metal fluoride, for example A Preferably, it is made of 1F3. In this case, the protective layer is usually irreversible, i.e. i.e., permanently applied to the hydrogen catalyst layer.

[0021] In one embodiment, the protective layer is resistant to irradiation with radiation in the VUV wavelength range and / or exposure to hydrogen. In this embodiment, the protective layer is reversibly applied. That is, hydrogen is introduced anyway to protect the aluminum layer from oxidation during irradiation. The protective layer is then exposed to radiation in the VUV wavelength range. Since the optical element is exposed to light, the protective layer can be easily removed during operation of the optical element in an optical device. To make the protective layer peelable, the protective layer is usually the top layer of the reflective coating.

[0022] The peelable protective layer is generally applied during or after the manufacture of the optical element before it is exposed to an air environment. In order to transfer the optical element into the optical device to be used, the protective layer is provided, and the optical element is then heated in an inert gas atmosphere. / Complex concepts of handling and transporting optical elements in nitrogen or possibly vacuum are required. When the optical device is serviced, the optical elements are exposed to the atmosphere, so aluminum There is sufficient hydrogen to prevent oxidation of the silicon layer, but if necessary, e.g., in a vacuum environment. Alternatively, a suitable substance may be added to the environment of the optical element, which may be an environment where a flushing gas is flowed. By doing so, the protective layer can be applied again.

[0023] In a further development, the protective layer is formed from carbon or at least one hydrocarbon. As mentioned above, it would be advantageous if the protective layer could be easily removed and reapplied. A thin protective layer containing carbon or carbohydrates that is reduced to carbon compound gases during operation of the optical element. The addition of carbon or hydrocarbons to the environment of the reflective optical elements of an optical device This allows a protective layer to be (re)deposited on the hydrogen catalyst layer. The hydrogen chloride can be, for example, a volatile alkane or alkene, which is then deposited on the surface. The polymer adheres to form a polymer layer.

[0024] A second aspect of the invention is that the optical element is designed as already described above and has a gas inlet (dispersion) inside. Optical devices of the aforementioned type, in particular wafers, designed or configured to supply hydrogen (in the form of hydrogen) The inspection system or VUV lithography equipment includes a flush gas inlet. The single gas can be supplied, and hydrogen is additionally supplied to the gas inlet. It is also possible to create a vacuum environment inside the chamber, and hydrogen is introduced into this vacuum environment through a gas inlet. To supply hydrogen to the inside, the gas inlet is used to store molecular hydrogen. It usually has a gas reservoir.

[0025] Forming active hydrogen on the hydrogen catalyst layer, thus protecting the aluminum layer from oxidation To achieve this, a sufficient amount of molecular hydrogen is supplied to the interior where the optical element is placed. The amount of oxidizing agent such as oxygen or water can be reduced in the ambient environment, i.e., in the surrounding flushing gas or vacuum. It should be understood that efforts should also be made to keep the amount of waste as low as possible. As a result, the oxidation rate of the aluminum in the aluminum layer is reduced to a level where the high reflectivity of the optical element is sufficient. can usually be reduced to such an extent that it is possible to ensure long exposure times. This minimizes the need to replace optical elements or renew reflective coatings. This minimizes the need for adjustments.

[0026] A further aspect of the invention may be designed according to the second aspect of the invention, but is not necessarily The optical device may be of the aforementioned type, which may or may not be an optical device. through a gas inlet to generate atmospheric pressure plasma in at least one partial region of The plasma generating device supplies plasma gas to the inside of the plasma generating device.

[0027] The optical element may be a reflective optical element for radiation in the VUV wavelength range, the reflective coating Alternatively, the optical element may be configured such that radiation in the VUV wavelength range is incident on the optical surface. In either case, the optical surface is a transmissive optical element that is part of the optical device. It is disposed at least partially in the beam path.

[0028] As already mentioned above, the reflecting optical elements and The problem with both optical and transmissive elements is that gaseous components that deposit on the optical surfaces of the optical elements can cause environmental The problem is that the optical elements become contaminated over time due to the presence of the optical elements in the optical system. In order to achieve this, in this aspect of the invention, atmospheric pressure plasma is used to treat an optical surface(s). It is recommended to remove unwanted deposits on the surface of the optical device, especially if the optical device is in a flushing gas atmosphere. It can operate in air and does not require a vacuum pump, so it can be used under vacuum conditions. Compared to atmospheric pressure plasma, i.e. above 100 mbar, preferably about 1 It has been found to be advantageous to use a plasma with a pressure of 1 bar. In this case, compressed air or another type of flushing gas, e.g. nitrogen and / or a noble gas, e.g. argon, in the plasma It can be used as a gas or as the main component of plasma gas. To enhance the effect of the plasma, reactive gases or species, such as hydrogen, oxygen, or water, are introduced into the plasma. In some cases, it can be added to the

[0029] In one embodiment, the plasma generating device generates a hydrogen plasma on the optical surface of the optical element. In this embodiment, hydrogen can be added to the plasma gas. The plasma gas is supplied to the interior through a gas inlet. Alternatively, the plasma gas and Hydrogen can be supplied to the interior through two or more separate gas inlets. It is important that the matrix is ​​formed in the environment of the optical surface.

[0030] Particularly advantageous use of hydrogen plasma for cleaning aluminum layers of reflective optical elements The exposed surface of the reflective optical element allows the hydrogen plasma to penetrate the aluminum layer. The natural Al2O3 layer already mentioned above is then heated by the excited hydrogen ions of the plasma. It is completely or partially reduced to aluminum, so that the reflectivity of the reflective optical element is The optical transmittance of the optical device is improved.

[0031] As already mentioned above, the reaction enthalpy of aluminum with oxygen is high, so hydrogen or Simply supplying activated hydrogen on the hydrogen catalyst layer does not convert aluminum oxide to aluminum. However, when cleaning with hydrogen plasma, such reduction is not possible. Such reduction reactions are possible and therefore the hydrogen catalysts already mentioned above for the dissociation of molecular hydrogen are The hydrogen plasma can be generated not continuously but with interruptions in operation. When the light is emitted intermittently, for example at predetermined time intervals, or when the reflectivity of the optical element is significantly In this case, the combination of hydrogen plasma generation and the hydrogen catalyst layer already mentioned above is advantageous. do.

[0032] The plasma gas, or more precisely, the plasma gas ions generated during plasma formation, are The optical surface can be provided with the above-mentioned method.

[0033] In one embodiment, the gas inlet directs plasma gas to at least one subregion of the optical surface. In this case, the gas inlet is designed as a plasma nozzle supplying at least one The plasma gas may have an exit aperture, which directs the plasma gas flow to the optical surface or optical In this case, the gas inlet is designed to be directed into at least one partial area of ​​the optical surface. The plasma nozzle has a gas outlet, and the plasma nozzle or its outlet opening is connected to the optical surface. If the optical element can be moved, e.g. tilted and / or displaced, it can be directed or In the case of plasma nozzles, it can be directed e.g. in the form of oil-free compressed air or The plasma gas, typically in the form of a flushing gas, e.g., nitrogen or another inert gas, is The gas flows through the discharge where it is excited and converted into a plasma state. The plasma gas to which the active gas can be added is introduced into the interior from the plasma nozzle in a plasma state. The generation of an active gas jet that should be electrically neutral immediately after leaving the plasma nozzle An example of a plasma nozzle that allows this is described in DE 101 45 131 A1. and is incorporated herein by reference in its entirety.

[0034] Alternatively or additionally, the plasma generating device may be spaced apart from the optical surface and positioned to At least one electrode is provided for generating atmospheric pressure plasma in at least one partial region. The electrode(s) can be used to direct the plasma at the desired location inside the chamber. In this case, for example, the aluminum layer of the reflective coating or Another metal layer may act as a counter electrode or to provide a ground potential for the plasma electrode. The electrode(s) can, for example, ionize the plasma gas in the region of the electrode tip. or tapered to generate a plasma thereon that extends to a partial area of ​​the optical surface. It is possible.

[0035] In yet another embodiment, the plasma generating device has a variable optical surface area. It is designed to generate atmospheric pressure plasma. It is used to treat areas of optical surfaces that have previously been contaminated or oxidized. It has been found to be advantageous if the material is only exposed to the plasma to a limited extent. This is achieved by proper placement of the nozzle(s) and / or electrode(s). For example, electrodes and / or plasma nozzles can be arranged in a ring around the optical element. so that each electrode or plasma nozzle is assigned to a partial area of ​​the optical surface. Targeted activation of individual plasma nozzles or electrodes can produce a In particular, the atmospheric pressure plasma can be changed depending on the location. The time during which the electrode is activated for cleaning or reduction is determined, especially for each partial area of ​​the optical surface. It can also be set individually depending on the degree of contamination or oxidation of the area.

[0036] To determine the degree of contamination or oxidation of each partial area, an optical device, for example in the form of a camera, If a plasma is generated during a break in operation, oxidation or use a camera or another inspection device during interruptions in operation to obtain location-dependent information about contamination It can be installed internally.

[0037] In the examples already mentioned above, the plasma nozzle(s) or electrode(s) However, it is assumed that the detector is located outside the beam path of the optical system. The plasma nozzle(s) or electrode(s) are then guided through the beam of the optical system. It is also possible to introduce the gases into the pathway and remove them again. This can be particularly useful if the occurrence only occurs during interruptions in the operation of the optical device.

[0038] The cleaning or reducing effect of atmospheric pressure plasma already mentioned above reduces the reflectivity of optical elements. This allows for increased efficiency, i.e., the optical element does not need to be removed from the optical device. In addition, each optical element must be frequently removed from the optical device and replaced with a new, structurally identical optical element. or the reflective coating can be removed so that it does not need to be reapplied after removal. Cut.

[0039] Further features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments with reference to the accompanying drawings, in which: This is apparent from the description of exemplary embodiments of the invention and from the claims. Each of the features may be implemented alone or in any combination of several in one variant of the invention. It is possible.

[0040] Exemplary embodiments are shown in the schematic drawings and are described in detail below. [Brief explanation of the drawings]

[0041] [Figure 1] 1 shows a schematic diagram of an optical arrangement for the VUV wavelength range in the form of a VUV lithography apparatus. [Figure 2] 1 shows a schematic diagram of an optical apparatus in the form of a wafer inspection system. [Figure 3] 1 shows a schematic diagram of the wavelength-dependent reflectance of an unoxidized aluminum layer and an aluminum layer that has been oxidized upon irradiation. [Figure 4a] 1 shows a schematic diagram of an optical element with a reflective coating having an aluminum layer and a hydrogen catalyst layer applied to the aluminum layer. [Figure 4b] 1 shows a schematic diagram of an optical element with a reflective coating having an aluminum layer and a hydrogen catalyst layer applied to the aluminum layer. [Figure 5a] 1 shows a plasma generation device with six plasma nozzles for generating atmospheric pressure plasma at the optical surface of a reflective optical element. [Figure 5b] 1 shows a plasma generation device with six plasma nozzles for generating atmospheric pressure plasma at the optical surface of a reflective optical element. [Figure 6a] 1 shows a plasma generation device with six electrodes for generating atmospheric pressure plasma on the optical surface of a reflective optical element. [Figure 6b] 1 shows a plasma generation device with six electrodes for generating atmospheric pressure plasma on the optical surface of a reflective optical element. DETAILED DESCRIPTION OF THE INVENTION

[0042] In the following description of the drawings, identical or functionally identical components will be designated by the same reference numerals. There are.

[0043] FIG. 1 shows a VUV lithography system, particularly for wavelengths in the range of 100 nm to 200 nm or 190 nm. The VUV lithography device 1 includes the following essential components: As components, it has two optical systems in the form of an illumination system 12 and a projection system 14. The imaging apparatus 1 comprises a radiation source 10 for carrying out an exposure process, which may be, for example, a An exciter that emits radiation 11 with a wavelength in the VUV wavelength range of 93 nm, 157 nm, or 126 nm. It may be a simmer laser and may be an integral part of the VUV lithography apparatus 1 .

[0044] The radiation 11 emitted by the radiation source 10 is projected onto a mask 1, also called a reticle, by means of an illumination system 12. In the example shown in FIG. 1, the illumination system 12 is adjusted to fully illuminate the light source 3. For example, a transmissive optical element 12 that focuses radiation 11 0 and a reflective optical element 121 that deflects the radiation 11 are representatively shown in FIG. As such, various transmissive, reflective, or other optical elements may be used in any desired configuration. They can be combined with one another in the illumination system 12 in complex ways.

[0045] The mask 13 is exposed using a projection system 14 as part of the manufacture of a semiconductor component. The mask 1 has on its surface a structure to be transferred onto an element 15, for example a wafer. In an alternative embodiment, the mask 13 is embodied as a reflective optical element. Projection system 14 may also be embodied as an optical element. In the illustrated example, two transmissive optical elements 140 and 141 are shown as representative examples. These are used to, for example, scale the structures on the mask 13 to the size desired for exposure of the wafer 15. The projection system 14 may also be provided with, inter alia, reflective optical elements, and may be used to reduce any light The optical elements can be combined with each other in any known manner. It is also noted that the apparatus can also be used for VUV lithography.

[0046] FIG. 2 shows a schematic diagram of an exemplary embodiment of an optical device in the form of a wafer inspection system 2. The following description applies equally to inspection systems for mask inspection.

[0047] The wafer inspection system 2 includes a radiation source 20, whose radiation 21 is directed by an optical system 22. For this purpose, radiation 21 is directed from a concave mirror 220 to the wafer 25. In the case of the mask inspection system 2, the mask to be inspected is reflected instead of the wafer 25. The radiation reflected, diffracted, and / or refracted by the wafer 25 may also be A further concave mirror 221 associated with the optical system 22 provides the light to a detector 23 for further evaluation. By way of example, the radiation source 20 may be configured to provide a substantially continuous radiation spectrum. For this purpose, there may be only one radiation source or a combination of several individual radiation sources. Therefore, one or more narrowband radiation sources 20 may be used. Preferably, the radiation source 20 is The wavelength or wavelength band of the generated radiation 21 is 100 nm to 200 nm, particularly preferably 11 It is in the range of 0nm to 190nm.

[0048] For example, the VUV lithography apparatus 1 from FIG. 1 or the wafer or mask inspection system from FIG. During operation of an optical device such as the stem 2, the reflective optical surfaces 121, 220, and 221 of the reflective optical elements 121, 220, and 221 Oxidation of the reflective optical elements 121, 220, 221a, and 222a may occur. can have a metallic mirror layer that reflects VUV radiation 11, and the aluminum layer For example, it is a metal mirror layer that has high reflectivity in a wide wavelength range of 100 nm to 200 nm. It is known that...

[0049] As an example, the reflectance R of such an aluminum layer is set to be about 120 nm to about 280 nm. wavelengths that encompass almost the entire VUV wavelength range, i.e., from about 100 nm to 200 nm 3 as a function of wavelength λ in the wavelength range shown. The total corresponds to a reflectivity R of the non-oxidized aluminum layer of more than 0.9.

[0050] The solid curves in Figure 3 show the oxidized carbon nanotubes oxidized by irradiation with VUV wavelength radiation 11 and 21. The reflectance R of the aluminum layer is shown here for wavelengths λ less than about 200 nm. The reflectance R drops significantly, specifically to values ​​below 0.1 at wavelengths λ below about 140 nm. Using the reflectivity R curve shown in Figure 3, we can see that the To avoid oxidation of the aluminum layer when it is used to reflect radiation in the VUV wavelength range, It is quite clear that it should.

[0051] 4a and 4b are embodied to reflect radiation 11 in the VUV wavelength range, and are not shown in FIG. 1 or 2. The optical element 4 may for example form one of the reflecting optical elements 121, 220, 221 of the The optical element 4 shown in FIGS. 4a and 4b is a mirror having a substrate 41. In the illustrated example, quartz (glass), particularly titanium-doped quartz glass, ceramic, or glass A reflective coating 42 is applied to the substrate 41, which may be ceramic. The lid has a continuous aluminum layer 43 which acts as a metallic mirror layer. 4a and 4b, the adhesion promoting layer 44 can be applied directly to the substrate 41. A functional layer of this type is applied between the aluminum layer 43 and the substrate 41. The material of the adhesion promoting layer 44 is Although a number of materials can be selected, it is preferable that both the substrate 41 and the aluminum layer 43 are sufficiently thick. Care should be taken to ensure adequate adhesion. Other functional layers, such as smoothing and / or polishing layers, may be provided between the aluminum layer 43 and the substrate 41 .

[0052] In the examples shown in Figures 4a and 4b, the dissociation of molecular hydrogen H2 in active hydrogen or hydrogen radicals A hydrogen catalyst layer 45 is applied to the aluminum layer 43. The material of the hydrogen catalyst layer 45 is: For example, it can be Ru, Pt, Pd, Ni, or Rh.

[0053] The above materials have a relatively low reflectivity for radiation 11 in the VUV wavelength range. This results in a thickness D of the hydrogen catalyst layer 45, which is less than 1.0 nm in the example shown in FIGS. 4a and 4b. It is beneficial for the hydrogen catalyst layer 45 to be as thin as possible. It cannot be applied over the aluminum layer 43, i.e. in the form of a sealing layer, as shown in FIG. 4b, the hydrogen catalyst layer 45 is formed by islands of spaced apart material accumulations on the aluminum layer. Formed on 43.

[0054] The coverage of the aluminum layer 43 with the hydrogen catalyst layer 45 is about 10% to about 90%, preferably is 30% to 70%, which makes it possible to realize a hydrogen catalyst layer 45 having a small thickness D. The reflectivity R of the optical element 5 does not decrease too much and, moreover, the optical element 5 is This allows the dissociation effect of the hydrogen catalyst layer 45 to be sufficient to prevent oxidation of the aluminum layer 43 .

[0055] The necessary condition for the protective effect of the hydrogen catalyst layer 45 is that molecular hydrogen H2 is generated in the environment of the reflecting optical element 4. The molecular hydrogen H in the VUV lithography system 1 shown in FIG. 2 is supplied with a reflective optical element through a gas inlet 123 formed in a housing 122 of the illumination system 12. The gas is supplied to the interior 122a of the housing 122 in which the element 121 is arranged. The inlet 123 has a gas reservoir (not shown) containing molecular hydrogen H2. If molecular hydrogen H2 is present in the environment of the reflecting optical element 121, this will 5 can be converted into active hydrogen, thus protecting the aluminum layer 43 from oxidation. do.

[0056] When placed inside 122a of housing 122 of illumination system 12, reflective optical element 121 , generally exposed to the atmosphere, which can irreversibly damage the hydrogen catalyst layer 45 or aluminum layer 43. This can lead to possible oxidation. Therefore, as shown for example in Figure 4b, It is advantageous to apply a protective layer 46 to the layer 45. The protective layer 46 protects the aluminum layer 43 and the water The protective layer 46 should form a sealing layer that covers both the hydrogen catalyst layer 45 and the hydrogen catalyst layer 45. In this case, the material of the protective layer 46 is well suited to the aluminum layer 43. In this case, the material of the protective layer 46 should be transparent, for example, It may be a fluoride material, for example a metal fluoride, for example in the form of AlF3.

[0057] Alternatively, the protective layer 46 may be reversibly applied to the hydrogen catalyst layer 45 and the aluminum layer 43. In this case, the protective layer 46 is formed on the surface of the reflective optical element 121 when the reflective optical element 121 is introduced into the illumination system 122. For this purpose, irradiation with radiation 11 in the VUV wavelength range and A material that is stripped when in contact with hydrogen and / or (molecular) hydrogen H2 is used for the protective layer 46. The material of the protective layer 46 that can be stripped due to irradiation is carbon or at least one hydrocarbon, For example, it can be parylene.

[0058] An aluminum layer 43, a hydrogen catalyst layer 45 applied thereto, and a hydrogen catalyst layer 46 possibly applied thereto. The protective layer 46 is preferably deposited by atomic layer deposition, which is particularly useful for depositing thin, flat, This allows for the deposition of smooth layers and thus reduces the loss of reflectivity due to absorption and scattering. Besides atomic layer deposition, other coating processes, e.g. magnetron Also suitable are ion-assisted deposition, plasma-enhanced deposition, thermal evaporation, and the like.

[0059] The reflective optical elements 220 and 221 of the wafer inspection system 2 shown in FIG. 2 are also shown in FIGS. 4a and 4b. The optical system 22 of the wafer inspection system 2 can be designed as described in connection with The optical system has a housing 24, and two reflecting optical elements 220 and 221 are arranged in an interior 24a thereof. A gas inlet capable of supplying molecular hydrogen H2 to the interior 24a of the housing 24 is provided. A port 26 is formed in the housing 24 .

[0060] 5a and 5b are designed to reflect radiation 11, 21 in the VUV wavelength range, and are similar to those of FIG. may form, for example, one of the reflective optical elements 121, 220, 221 of FIG. 5a and 5b show a reflective optical element 5. The reflective optical element 5 of FIG. 5a and FIG. 5b is substantially the same as the reflective optical element 5 of FIG. 4a and FIG. 4b. It is designed like the optical element 4, but does not have the hydrogen catalyst layer 45 or the protective layer 36, i.e. That is, the aluminum layer 43 is directly exposed to the environment, and the upper part thereof forms the reflective optical surface 5a.

[0061] In order to protect the aluminum layer 43 of the reflecting optical element 5 from oxidation, the reflecting optical element 5 shown in FIGS. 5a and 5b is The optical devices 1 and 2 in which the reflective optical element 5 is disposed are large on the reflective optical surface 5a of the reflective optical element 5. The plasma generating device 50 generates atmospheric plasma 51. The plasma generation device 50 has six gas inlets in the form of plasma nozzles 52a to 52f, These are distributed uniformly around the optical surface 5a, which is circular in top view, specifically It is positioned outside the beam path 53 of the VUV radiation 11, 21 shown in dashed lines in Figure 5b.

[0062] The plasma nozzles 52a to 52f respectively emit plasma gases 54a to 54f in the form of plasma gas flows. 5a and 5b, each plasma is designed to supply 4f to the optical surface 5a. The gas flows 54a to 54f are arranged on the optical surface 5a, which is circular in top view, and form arcs around the optical surface 5a. The light is supplied to one of the six partial regions 5a to 5f of the reflective optical element 5. As can be seen in FIG. 5b, each plasma nozzle 52a to 52f has a As a result, the plasma gas flows 54a to 54f are also directed obliquely with respect to the optical surface 5a.

[0063] In the illustrated example, the plasma generating device 50 is designed to generate a hydrogen plasma 51. For this purpose, plasma gas flows 54a to 54f are emitted from the plasma nozzles 52a to 52f. 4f in addition to a flushing gas in the form of, for example, nitrogen, a noble gas, or a mixture of the above gases. The plasma gas 54a to 54f contains a relatively low proportion of hydrogen. By adding the atmospheric pressure plasma 51, the cleaning effect of the atmospheric pressure plasma 51 is improved, and the optical surface 5 The thin aluminum oxide layer formed on a is reduced back to aluminum.

[0064] As discussed above in connection with FIG. 3, this significantly increases the reflectivity R of the reflective optical element 5. The reflecting optical element 5 is also positioned in each of the interiors 122a, 24a. By using the plasma nozzles 54a to 54f, molecular water is formed in the interiors 122a and 24a. The gas inlets 123, 26 shown in Figures 1 and 2 for supplying hydrogen H2 can be omitted.

[0065] 6a and 6b are designed to reflect radiation 11, 21 in the VUV wavelength range, and are similar to those of FIG. may form, for example, one of the reflective optical elements 121, 220, 221 from FIG. A plasma generator is used to generate atmospheric pressure plasma 61 on the optical surface 6a of the optical element 6. 6a and 6b show the plasma generating device 60. The plasma generating device 60 of FIG. 6a and FIG. 6b is similar to that of FIG. 5a and FIG. 5b. 1. The difference from the plasma generating device 50 shown in FIG. 1 is that the optical surface 6a of the reflecting optical element 6 is an atmospheric pressure plasma. Six pointed electrodes 62a to 62f are provided to generate the stimuli 61. The six electrodes 62a to 62f are It is positioned outside the beam path 63 .

[0066] The plasma generating device 60 is connected to the electrodes 62a to 62f in the illustrated example, which are kept at a predetermined potential. A potential difference is generated between the optical surface 6a of the aluminum layer 54 connected to the ground potential, and as a result As a result, atmospheric pressure plates extending to the optical surface 6a are formed between the electrodes 62a to 62f and the optical surface 6a. In the plasma generating device 60 shown in FIGS. 6a and 6b, each electrode 62a 62f are assigned to the partial regions 65a to 65f of the optical surface 6a that form an arc. The plasma gas 64 is supplied to the associated interior 122a, 24a from FIG. The gas is supplied to the environment of the optical surface 6a through respective gas inlets 123, 26. As shown in FIG. 2, molecular hydrogen is introduced into the interiors 122a and 24a through gas inlets 123 and 26. Additional H2 can be supplied, but this is generally in the form of a small admixture. It is added to Plasma Gas 64.

[0067] The plasma generating device 50 shown in FIGS. 5a and 5b and the plasma generating device 51 shown in FIGS. 6a and 6b are In both the optical devices 60, the atmospheric pressure plasmas 51 and 61 on the optical surfaces 5a and 6a are For this purpose, the plasma nozzles 52a to 52f or the electrodes 62a to 62f may be changed depending on the location. 2f can be controlled individually. For example, the plasma generation device shown in Fig. 5a and Fig. 5b In the plasma nozzle 50, the flow passing through each plasma nozzle 52a to 52f and / or the plasma gas flow 54 a to 54f flowing to each of the partial regions 55a to 55f of the optical surface 5a individually. In response to this, hydrogen plaques generated in the partial regions 65a to 65f of the optical surface 6a can be In order to change the intensity of the lens 61, the electrodes 62a to 62f and the optical element 6 or the aluminum layer The potential or potential difference between 43 can also be changed.

[0068] In this way, the plasma generating devices 50 and 60 are used to generate the following of the optical surfaces 5a and 6a: Plasma is generated as intended in the previously oxidized or contaminated partial regions 55a to 55f, 65a to 65f. Cleaning can be performed on the respective related partial areas 55a to 55c of the optical surfaces 5a and 6a. Plasma nozzles 52a to 52f or electrodes 62a in locations not belonging to 55f, 65a to 65f Even with ~62f, (not very strong) atmospheric pressure plasmas 51 and 61 are generated, so All the plasma nozzles 52a to 52f or all the electrodes 62a to 62f are activated to generate atmospheric pressure plasma. It is not necessary to generate the plasma 51, 61. The number of the six plasma nozzles 52a to 52f or the six electrodes 62a to 62f shown in FIG. 6b is , are merely examples, i.e., the plasma generating devices 50, 51 may be configured to have fewer or more plasmas. It may also have plasma nozzles 52a to 52f or electrodes 62a to 62f.

[0069] Using the plasma generating devices 50 and 60 shown in FIGS. 5a, 5b and 6a, 6b, Atmospheric pressure plasmas 51 and 61 are generated on the front reflecting surfaces 5a and 6a of the reflecting optical elements 5 and 6. In addition, it is possible to use a transmissive optical element, such as the two transmissive optical elements of the projection system 14 shown in FIG. The elements 140 and 141 can also generate atmospheric pressure plasmas 51 and 61. , and atmospheric pressure plasma 51, 61 is used to remove contaminants from each of the transmissive optical surfaces 140a, 140b, 140c. 41a, 141b. To enhance the cleaning effect, reactive Gas components, such as the aforementioned hydrogen or possibly oxygen or water, are introduced into atmospheric pressure plasma 51, 61 This is possible because oxygen The aluminum layer 43 or any other material that may be damaged by the thermal decomposition effect. This is because no reflective optical elements having layers are disposed in projection system 14 .

[0070] The measures already mentioned above prevent the reflection of the reflective optical elements 121, 220, This can suppress the decrease in reflectivity R of 221. Hydrogen plasma 51, 72 is generated at atmospheric pressure. By allowing the oxidation reaction of the aluminum layer 54 to occur, the oxidation reaction of the aluminum layer 54 can be further reversed. That is, the aluminum oxide that has already formed can be re-reduced to metallic aluminum. The action of the atmospheric pressure plasma 51, 61 causes the optical surfaces 140 of the transmitting optical elements 140, 141 to a, 140b, 141a, and 141b can also be cleaned by removing contaminants. do.

Claims

1. An optical element (4) in the form of a mirror for reflecting radiation (11, 21) in the VUV wavelength range, a substrate (41); and a reflective coating (42) applied to the substrate (41) and having at least one aluminum layer (43) for reflecting radiation (11, 21) in the VUV wavelength range; In an optical element (4) comprising: Molecular hydrogen (H ２ At least one hydrogen catalyst layer (45) for the dissociation of hydrogen is applied to said aluminum layer (43), and at least one protective layer (46) applied to the aluminum layer (43) and the hydrogen catalyst layer (45). The optical element, wherein the protective layer is made of a fluoride material.

2. An optical element as described in claim 1, wherein the hydrogen catalyst layer (45) completely covers the aluminum layer (43).

3. 3. The optical element according to claim 1, wherein the material of the hydrogen catalyst layer (45) is selected from the group consisting of Ru, Pt, Pd, Ni, and Rh.

4. 3. The optical element according to claim 1, wherein the hydrogen catalyst layer (45) has a layer thickness (D) of 0.1 nm to 3.0 nm.

5. 5. The optical element according to claim 1, wherein the hydrogen catalyst layer (45) is a continuous layer.

6. 2. The optical element according to claim 1, wherein said protective layer (46) forms a sealing layer.

7. 7. The optical element according to claim 1 or 6, wherein the protective layer (46) is made of a transparent material.

8. 1. An optical device for use in the VUV wavelength range, comprising: an interior (122a, 24a) in which at least one optical element (121, 220, 221; 140, 141; 4, 5, 6) is arranged; Gas (H ２ at least one gas inlet (123, 26) supplying In an optical device comprising: The optical element (121, 220, 221, 4) is designed as claimed in any one of claims 1 to 7, and the gas inlet (123, 26) is adapted to introduce hydrogen (H ２ ) .

9. 9. The optical device according to claim 8, a plasma generation device (50, 60) for supplying plasma gas (54a to 54f, 64) to the interior (122a, 24a) via the gas inlet (123, 26) to generate atmospheric pressure plasma (51, 61) in at least one partial region (55a to 55f, 65a to 65f) of the optical surface (5a, 6a) of the optical element (5, 6); An optical device comprising:

10. 10. The optical arrangement according to claim 9, wherein the plasma generation device (50, 60) is designed to generate a hydrogen plasma (51, 61) at the optical surface (5a, 6a) of the optical element (5, 6).

11. 11. The optical device according to claim 9 or 10, wherein the gas inlet is designed as a plasma nozzle (52a-52f) for supplying the plasma gas (54a-54f) to at least one partial region (55a-55f) of the optical surface (5a).

12. 12. The optical apparatus according to claim 9, wherein the plasma generating device (60) comprises at least one electrode (62a-62f) spaced apart from the optical surface (6a) to generate the atmospheric pressure plasma (61) in the at least one partial region (65a-65f) of the optical surface (6a).

13. 13. The optical arrangement according to any one of claims 9 to 12, wherein the plasma generation device (50, 60) is designed to generate a spatially variable atmospheric pressure plasma (51, 61) at the optical surface (5a, 6a).

14. Optical device according to any one of claims 9 to 13, configured as a wafer inspection system (2) or as a VUV lithography device (1).

Images