EUV optical module for EUV projection exposure apparatus

Abstract

The invention relates to an EUV optical module (35) for an EUV projection exposure device (1), comprising at least one optical component (19, 21, 23, 7, M1 to M6, 13) having an optical surface for guiding used EUV radiation (16) from an EUV source (3) along an illumination and / or imaging beam path of the projection exposure device (1). The optical components (19, 21, 23, 7, M1 to M6, 13) are housed in the decompression chamber (36). A gas source (37) is fluidly connected to the reduced pressure chamber (36) via at least one valve. The gas source (37) is designed such that it provides at least the following gases: hydrogen. The result is an EUV optical module with a longer operating time.

Description

[0001] This patent application claims the priority of German patent application DE 10 2022 212 168.6, the content of which is incorporated herein by reference. Field of the Invention

[0002] The present invention relates to an EUV optical module for an EUV projection exposure apparatus. The present invention further relates to an optical system for an EUV projection exposure apparatus including such an EUV optical module, a projection exposure apparatus including such an optical system, a method of producing a microstructured or nanostructured component by means of such a projection exposure apparatus, and a microstructured or nanostructured component produced by such a method. Background Art

[0003] EUV optical modules for EUV projection exposure apparatuses having an EUV source for generating the EUV radiation used are known from, for example, US 7,598,508 B2. DE 10 2021 202 802 B3 discloses a projection exposure apparatus including means for determining the atomic hydrogen concentration. DE 10 2017 213 406 A1 discloses a reflective optical element for EUV lithography and a method of adjusting the geometry of a component. DE 10 2016 208 850 A1 discloses a projection exposure apparatus for semiconductor lithography having an element for plasma regulation. DE 10 2020 202 179 A1 discloses an optical arrangement for EUV lithography and a method of determining required values for target plasma parameters. US 2010 / 0071720 A1 discloses a method and system for removing contaminants from a surface. US 2011 / 0143288 A1 discloses a radiation source, a lithography system, and a method of producing a component. US2012 / 0086925 A1 discloses a method of avoiding contaminants and an EUV lithography system. US 2007 / 0012889 A1 discloses a gaseous spectral purity filter for EUV and an optical system including the same. Summary of the Invention

[0004] It is an object of the present invention to develop an EUV optical module of the type specified at the outset such that the operating time of an EUV projection exposure apparatus is increased.

[0005] According to the present invention, this object is achieved by an EUV optical module having the features as claimed in claim 1.

[0006] It has been found according to the present invention that hydrogen as the provided gas leads to the production of activated hydrogen specie. This can in particular be used to generate cleaning free radicals, which are used to effectively clean the optical surfaces of optical components. This increases the operating time of EUV optical modules. By defining the hydrogen partial pressure, the activated hydrogen specie can be produced as desired in a reduced pressure chamber. The gas source can also be used to provide additional gas species, such as oxygen or nitrogen, or a mixture of two or more gas species. The gas source can have a plurality of gas source units, each unit being used to provide a specific gas. The gas source can have at least one gas container. The gas source can have two or more gas containers containing different gases. Then, each of these gas containers can belong to a corresponding gas source unit. Isotopes of at least one of the provided gases can also be provided. In the case of hydrogen, these are D2HD, T2TD, HT (D is Deuterium; T is Tritium). By adding hydrogen isotopes, the effective cross-sectional area for dissociating to produce reactive hydrogen specie can be increased by up to three orders of magnitude, and thus the reactivity of hydrogen in the environment of gas injection can be adjusted. The reduced pressure chamber can accommodate a plurality of optical components, for which the corresponding activated hydrogen specie and / or nitrogen / oxygen specie are subsequently generated by means of the provided gas, which completes the effective cleaning and / or reaction of the optical surfaces of the optical components. In particular, those optical components closest to the projection exposure apparatus in the beam path of the EUV radiation used in the EUV source can thus achieve a longer operating time.

[0007] Isotopes of these gases or vapors can also be provided via the gas source, in particular at a controlled concentration. In each case, the addition of the gas can be controlled in an open loop, or the closed loop control of the partial pressure can be carried out.

[0008] The isotope content within the concentration range as claimed in claim 3 has been found to be particularly advantageous. Depending on the type of gas used, a favorable increase in the dissociation cross-sectional area can occur here, in particular a uniform ionization cross-sectional area. The isotope content can be within an isotope concentration range between 0.1% and 10%.

[0009] The isotope concentration can be controlled by closed loop control via the operating state as claimed in claim 4 using the operating states described above in relation to the control valve design of the EUV optical module.

[0010] The control valve according to claim 5 enables open-loop or even closed-loop control of at least one gas in a decompression chamber via a gas source. Two or more control valves of this kind can be provided. In that case, at least one of the control valves can be assigned to each of the gas source units or each of the gas containers of the gas source in each case. The open-loop / closed-loop control device can be designed such that the respective partial pressure of the at least one gas provided is defined according to the operating state of the EUV optical module or the projection exposure apparatus. This can be done using a look-up table. The operating state can be defined via measuring the gas composition (especially H2, N2, NH3, O2, H2O), and / or measuring the concentration of active substances (especially H, N, and O radicals or ions), and / or measuring the measured or calculated temperature of the optical element. In particular, the operating state can also be defined via measuring changes in the reflective layer of the optical element.

[0011] Using at least one pressure sensor according to claim 6 allows the definition of the partial pressure of the at least one gas provided under closed-loop control. The EUV optical module can have a plurality of such pressure sensors. In that case, at least one of these pressure sensors can be assigned to each gas species and / or each gas source unit and / or each gas container of the gas source. For example, if nitrogen and hydrogen are provided via a gas source, one of the pressure sensors can specifically measure the nitrogen partial pressure, and another of the pressure sensors can specifically measure the hydrogen partial pressure. The respective pressure sensors can in particular also be assigned to the respective optical components.

[0012] The design-optimized EUV optical module according to claim 7 functions in the environment of the optical surface of the optical component. In particular, the EUV optical module can then have a pressure sensor that ensures the measurement of the pressure in the environment of the optical surface of the optical component. Two or more such pressure sensors can also be assigned to exactly one optical surface or to more than one optical surface as part of the EUV optical module.

[0013] The hydrogen partial pressure according to claim 8 has been found to be particularly suitable for ensuring the function of the EUV optical module.

[0014] The additional gas provided via the gas source according to claim 9 has likewise been found to be particularly suitable for realizing the function of the EUV optical module in order to increase the operating time of at least one optical component.

[0015] It is also possible to use an inert gas.

[0016] The advantages of the optical system according to claim 10 or 11, the projection exposure apparatus according to claim 12, the production method according to claim 13, and the microstructured or nanostructured component according to claim 14 correspond to those set forth above with reference to the EUV optical module.

[0017] The EUV light source of the projection exposure apparatus can be designed to result in a wavelength used, for example, of not greater than 13.5 nm, less than 13.5 nm, less than 10 nm, less than 8 nm, less than 7 nm, and 6.7 nm or 6.9 nm. A wavelength used of less than 6.7 nm is also possible, and in particular in the range of 6 nm.

[0018] In particular, the projection exposure apparatus can be used for producing semiconductor components, such as memory chips. Description of the Drawings

[0019] At least one working example of the present invention is described below with reference to the accompanying drawings. The drawings show:

[0020] Figure 1 A schematic diagram of a meridian section of a projection exposure apparatus for EUV projection lithography;

[0021] Figure 2 A correlation diagram of the effective cross-sectional area σ proportional to the light absorption at a specific wavelength of a specific particulate matter and its partial pressure p;

[0022] Figure 3 Results of model calculations of the relative transmission normalized by in-band transmission of various particulate matters for the first lowest partial pressure for various wavelength ranges;

[0023] Figures 4 to 6 Each is a presentation similar to Figure 3 of the relative transmission of these particulate matters, each at a partial pressure one order of magnitude higher than these particulate matters;

[0024] Figure 7 A correlation of the effective cross-sectional area σ of nitrogen (N2) adjacent to the surface of the mirror substrate and the nitrogen pressure p adjustable via a nitrogen source, where photoionization of nitrogen molecules is observed;

[0025] Figure 8 A correlation of the effective cross-sectional area σ of nitrogen (N2) adjacent to the surface of the mirror substrate and the partial pressure p of first various elemental vapors, where photodissociation of nitrogen molecules into two nitrogen atoms is observed;

[0026] Figure 9 A correlation of the effective cross-sectional area σ of nitrogen (N2) adjacent to the surface of the mirror substrate and the isotope concentration c of deuterium D2 in hydrogen H2 in the vacuum chamber of the projection exposure apparatus. Detailed Description

[0027] The following will first refer to Figure 1 to illustrate the basic components of the projection exposure apparatus 1 for microlithography. The description of the basic structure of the projection exposure apparatus 1 and its components should not be regarded as a limitation here.

[0028] A design of the illumination system 2 of the projection exposure apparatus 1 has, in addition to the light or radiation source 3, an illumination optical unit 4 for illuminating the object field 5 in the object plane 6. In an alternative specific embodiment, the light source 3 can also be provided as a module separate from the rest of the illumination system. In this case, the illumination system does not include the light source 3.

[0029] The mask reticle 7 disposed in the object field 5 is exposed. The mask reticle 7 is carried by a mask reticle carrier 8. The mask reticle carrier 8 can be displaced, in particular in the scanning direction, by a mask reticle shift drive 9.

[0030] Figure 1 By way of illustration, a Cartesian xyz coordinate system is shown. The x-direction extends perpendicular to the plane of the drawing. The y-direction extends horizontally, and the z-direction extends vertically. The scanning direction extends in the Figure 1 y-direction in. The z-direction extends perpendicular to the object plane 6.

[0031] The projection exposure apparatus 1 includes a projection optical unit 10. The projection optical unit 10 is used to image the object field 5 into the image field 11 in the image plane 12. The image plane 12 extends parallel to the object plane 6. Alternatively, an angle other than 0° between the object plane 6 and the image plane 12 is also possible.

[0032] The structures on the mask reticle 7 are imaged onto the photosensitive layer of the wafer 13 in a region of the image field 11 disposed in the image plane 12. The wafer 13 is carried by a wafer carrier 14. The wafer carrier 14 can be displaced, in particular in the y-direction, by a wafer shift drive 15. First, the mask reticle 7 can be displaced by the mask reticle shift drive 9, and second, the wafer 13 can be displaced by the wafer shift drive 15 to be synchronized with each other.

[0033] The radiation source 3 is an EUV radiation source or an EUV source. The radiation source 3 specifically emits EUV radiation 16, which is also referred to hereinafter as the used radiation, illumination radiation, or illumination light. In particular, the used radiation has a wavelength in the range between 5 nm and 30 nm. The radiation source 3 can be a plasma source, such as a laser produced plasma (LPP) source or a gas discharge produced plasma (GDPP) source. It can also be a synchrotron radiation source. The radiation source 3 can be a free electron laser (FEL).

[0034] The illumination radiation 16 emitted from the radiation source 3 is focused by the condenser 17. The condenser 17 can be a condenser having one or more elliptical and / or hyperbolic reflecting surfaces. The illumination radiation 16 can be incident on at least one reflecting surface of the condenser 17 at a grazing incidence (i.e., at an incident angle greater than 45°), or at a normal incidence (i.e., at an incident angle less than 45°). The condenser 17 can be structured and / or coated to first optimize its reflectivity for the used radiation and second to suppress stray light.

[0035] Downstream of the condenser 17, the illumination radiation 16 propagates through an intermediate focus in the intermediate focal plane 18. The intermediate focal plane 18 can represent the separation between the radiation source module having the radiation source 3 and the condenser 17 and the illumination optical unit 4.

[0036] The illumination optical unit 4 includes a deflecting mirror 19 and a first facet mirror 20 downstream thereof in the beam path. The deflecting mirror 19 can be a planar deflecting mirror, or alternatively, a mirror having a beam influencing effect beyond a pure deflecting effect. Alternatively or additionally, the deflecting mirror 19 can be designed as a spectral filter that separates the used light wavelength of the illumination radiation 16 from the stray light of the wavelengths deviated therefrom. If the first facet mirror 20 is arranged in the plane of the illumination optical unit 4 that is optically conjugate to the object plane 6 and serves as a field plane, it is also referred to as a field facet mirror. The first facet mirror 20 includes a plurality of individual first facets 21, which are also referred to hereinafter as field facets. Figure 1 Only some of the said facets 21 are illustrated by way of example.

[0037] The first facets 21 can be embodied as macro facets, in particular bow-shaped facets or facets having an arched or partially circular edge profile. The first facets 21 can be in the form of planar facets or alternatively facets having a convex or concave curvature.

[0038] For example, it can be learned from DE 10 2008 009 600 A1 that each of the first facets 21 itself may also be composed of a plurality of individual mirrors, in particular a plurality of micromirrors. The first facet mirror 20 may in particular take the form of a microelectromechanical system (MEMS system). For more detailed information, reference is made to DE10 2020 212 351 A1, US 10,139,618, US 9,874,819, US 9,851,555 and DE 10 2008 009600 A1, which are hereby incorporated by reference.

[0039] The illumination radiation 16 travels horizontally between the condenser 17 and the deflection mirror 19, that is, in the y direction.

[0040] In the beam path of the illumination optical unit 4, the second facet mirror 22 is arranged downstream of the first facet mirror 20. If the second facet mirror 22 is arranged in the pupil plane of the illumination optical unit 4, it is also referred to as a pupil facet mirror. The second facet mirror 22 may also be arranged at a certain distance from the pupil plane of the illumination optical unit 4. In this case, the combination of the first facet mirror 20 and the second facet mirror 22 is also referred to as a mirror body. The mirror body can be learned from US 2006 / 0132747 A1, EP 1 614 008 B1 and US 6,573,978.

[0041] The second facet mirror 22 includes a plurality of second facets 23. In the case of a pupil facet mirror, the second facets 23 are also referred to as pupil facets.

[0042] The second facets 23 may likewise be macroscopic facets, which may for example have a circular, rectangular, or hexagonal boundary, or alternatively may be facets composed of micromirrors. Reference in this regard can be made to DE 10 2008 009 600 A1 and the references mentioned above.

[0043] The second facets 23 may have a planar reflective surface, or alternatively a reflective surface with convex or concave curvature.

[0044] Thus, the illumination optical unit 4 forms a two-facet system. This basic principle is also referred to as a compound eye integrator.

[0045] It may be advantageous not to set the second facet mirror 22 exactly in a plane optically conjugate to the pupil plane of the projection optical unit 10. In particular, the pupil facet mirror 22 may be arranged to be inclined with respect to the pupil plane of the projection optical unit 10, as illustrated for example in DE 10 2017 220 586 A1.

[0046] The separate first facet 21 is imaged into the object field 5 using the second facet mirror 22. The second facet mirror 22 is the last beam shaping mirror or indeed the last mirror in the beam path upstream of the object field 5 for the illumination radiation 16.

[0047] In a further specific embodiment (not illustrated) of the illumination optical unit 4, the transmission optical unit can be arranged in the beam path between the second facet mirror 22 and the object field 5 and in particular contributes to imaging the first facet 21 into the object field 5. The transmission optical unit can comprise exactly one mirror; or, alternatively, comprise two or more mirrors which are arranged successively in the beam path of the illumination optical unit 4. The transmission optical unit can in particular comprise one or two normal incidence mirrors (NI mirrors) and / or one or two grazing incidence mirrors (GI mirrors).

[0048] In Figure 1 In the illustrated design, the illumination optical unit 4 has exactly three mirrors downstream of the condenser 17, specifically the deflection mirror 19, the field facet mirror 20 and the pupil facet mirror 22.

[0049] The deflection mirror 19 can also be omitted in a further design of the illumination optical unit 4, and thus the illumination optical unit 4 may then have exactly two mirrors downstream of the condenser 17, specifically the first facet mirror 20 and the second facet mirror 22.

[0050] Imaging the first facet 21 into the object plane 6 by means of the second facet 23 or using the second facet 23 and the transmission optical unit is often only approximate imaging.

[0051] The projection optical unit 10 comprises a plurality of mirrors Mi which are successively numbered according to their arrangement in the beam path of the projection exposure apparatus 1.

[0052] In Figure 1 In the illustrated example, the projection optical unit 10 comprises six mirrors M1 to M6. There can equally be alternatives with four, eight, ten, twelve or any other number of mirrors Mi. The projection optical unit 10 is a two-mask optical unit. Each of the penultimate mirror M5 and the last mirror M6 has a through hole for the illumination radiation 16. The projection optical unit 10 has an image-side numerical aperture greater than 0.5 and can also be greater than 0.6 and can be, for example, 0.7 or 0.75.

[0053] The reflective surface of the mirror Mi can be designed as a free-form surface without rotational symmetry. Alternatively, the reflective surface of the mirror Mi can be designed as an aspherical surface with exactly one rotational symmetry of the reflective surface shape. Similar to the mirror of the illumination optical unit 4, the mirror Mi can have a highly reflective coating for the illumination radiation 16. These coatings can be designed as multilayer coatings, especially with alternating layers of molybdenum and silicon.

[0054] The projection optical unit 10 has a large object-image offset in the y-direction between the y-coordinate of the center of the object field 5 and the y-coordinate of the center of the image field 11. In the y-direction, this object-image offset can have a magnitude approximately the same as the z-distance between the object plane 6 and the image plane 12.

[0055] The projection optical unit 10 can in particular have a deformed form. In particular, it has different imaging ratios β in the x- and y-directions x , β y . The two imaging ratios β of the projection optical unit 10 x , β y are preferably (β x , β y ) = (+ / -0.25, + / -0.125). A positive imaging ratio β means imaging without image inversion. A negative sign of the imaging ratio β means imaging with image inversion.

[0056] The projection optical unit 10 thus causes a size reduction in the x-direction (i.e., in the direction perpendicular to the scanning direction) by a factor of 4:1.

[0057] The projection optical unit 10 causes a size reduction in the y-direction (i.e., in the scanning direction) by a factor of 8:1.

[0058] Other imaging ratios are equally possible. Imaging ratios with the same sign and the same absolute value in the x- and y-directions are also possible, for example with an absolute value of 0.125 or 0.25.

[0059] In the beam path between the object field 5 and the image field 11, the number of intermediate image planes in the x-direction and in the y-direction can be the same, or can be different depending on the design of the projection optical unit 10. Examples of projection optical units with different numbers of these intermediate images in the x- and y-directions can be found in US 2018 / 0074303 A1.

[0060] In each case, one of the pupil facets 23 is assigned to one of the field facets 21 to form an illumination channel for illuminating the object field 5 in each case. This can in particular result in illumination according to the Köhler principle. The far field is deconstructed into a plurality of object fields 5 by means of the field facets 21. The field facets 21 produce a plurality of images of the intermediate foci on the pupil facets 23 assigned to them respectively.

[0061] The field facets 21 are each imaged onto the mask reticle 7 via the assigned pupil facets 23 in such a way that they overlap for the illumination object field 5. The illumination of the object field 5 is in particular as uniform as possible. It preferably has a uniformity error of less than 2%. The field uniformity can be achieved by superimposing different illumination channels.

[0062] The illumination of the entrance pupil of the projection optical unit 10 can be geometrically defined by the configuration of the pupil facets. The intensity distribution in the entrance pupil of the projection optical unit 10 can be set by selecting illumination channels, in particular a subset of the pupil facets guiding the light. This intensity distribution is also referred to as the illumination setting or illumination pupil filling.

[0063] Similarly good pupil uniformity can be achieved in the regions of the individual segments of the illumination pupil of the illumination optical unit 4 illuminated in the defined manner by redistributing the illumination channels.

[0064] Further aspects and details of the illumination of the object field 5 and in particular of the entrance pupil of the projection optical unit 10 are described below.

[0065] The projection optical unit 10 can in particular have a concentric entrance pupil. The latter can be accessible. It can also be inaccessible.

[0066] The entrance pupil of the projection optical unit 10 usually cannot be fully illuminated by means of the pupil facet mirror 22. When imaging the projection optical unit 10 which images the center telecentric of the pupil facet mirror 22 onto the wafer 13, the aperture rays often do not intersect at a single point. However, a region can be found in which the spacing of the pairwise determined aperture rays becomes minimal. This region represents the entrance pupil or the region in the real space conjugate thereto. In particular, this region has a finite curvature.

[0067] It is possible that the projection optical unit 10 has different poses of the entrance pupil for the tangential beam path and the sagittal beam path. In this case, imaging elements (in particular the optical component parts of the transmission optical unit) should be arranged between the second facet mirror 22 and the mask reticle 7. By means of this optical element, the different poses of the tangential entrance pupil and the sagittal entrance pupil can be taken into account.

[0068] In Figure 1 In the illustrated configuration of the components of the illumination optical unit 4, the pupil facet mirror 22 is arranged in the region conjugate to the entrance pupil of the projection optical unit 10. The field facet mirror 20 is arranged inclined with respect to the object plane 6. The first facet mirror 20 is arranged inclined with respect to the configuration plane defined by the deflection mirror 19.

[0069] The first facet reflector 20 is arranged to be inclined with respect to the arrangement plane defined by the second facet reflector 22 .

[0070] In source operation of the EUV source 3, the used EUV radiation 16 is emitted by a source region 25. This source region 25, the condenser 17 and the components of the EUV source 3 are accommodated in a reduced pressure chamber 26 of an EUV source module 27 of the projection exposure apparatus 1. A part of the EUV source module 27 is the EUV source 3.

[0071] EUV source module 27 is a gas source 29 fluidly connected to decompression chamber 26 via valve group 28. Gas source 29 has a plurality of gas source units. In the design shown, there are four gas source units 301, 302, 303, and 304. Valve group 28 has valves assigned to the corresponding gas source units 30. i Each of the actuable source valves 31 i And the main valve 32. The main valve 32 is connected to all source valves 31 via a fluid conduit. i Fluid connection. The main valve 32 is set at the source valve 31 i Between the decompression chamber 26. Corresponding gas source unit 30 i By the corresponding source valve 31 i The main valve 32 is fluidically connected to the decompression chamber 26 via the main valve 32 arranged in series therewith.

[0072] The gas source unit 30 i Each may have a corresponding gas container containing the gas to be provided.

[0073] The gas source 29 is designed so that it passes through the gas source unit 30 i At least one of the following gases is provided: nitrogen, hydrogen, oxygen, water vapor, CH4, NH3, metal vapor based on, for example, tin (Sn), zinc (Zn), ruthenium (Ru), or iron (Fe), volatile metal hydrides such as SnH4, ZnH2, or PbH4, or volatile metal oxides such as RuO4, IrO4, or volatile metal fluorides such as MoF6, IrF6, WF6, ReF6. Inert gases may also be used. Other gaseous substances may also be provided via the gas source 29 of the reduced pressure chamber 26. Lead (Pb) and / or molybdenum may also be provided as metal vapor. If metal vapor is provided, this may be accomplished by means of, for example, an evaporator using a spirally wound filament.

[0074] Isotopes forming the aforementioned gases may also be provided, namely in the case of hydrogen (H2), D2, HD, T2, TD, HT (D: deuterium; T: tritium).

[0075] Valve 31 i Each of and 32 is a control valve having a signal connection to a closed-loop control device 33 of the EUV source module 27 .

[0076] The closed-loop control device 33 can be designed to define the gas or the specific partial pressures of two or more gases provided by the gas source 29 in each case depending on the operating state of the EUV source module 27 or the projection exposure apparatus 1. In this case, the closed-loop control device 33 can refer to a stored look-up table in which the partial pressure values of the (plural) gases that can be provided by the gas source 29 in each case are assigned as a function of the corresponding operating state of the projection exposure apparatus 1.

[0077] The operating state can be defined via measuring the gas composition (in particular H2, N2, NH3, O2, H2O), and / or measuring the concentration of active substances (in particular H, N, and O radicals or ions), and / or measuring the measured or calculated temperature of the optical components. In particular, the operating state can also be defined via measuring changes in the reflective layer of the optical components.

[0078] In one design of the EUV source module 27, it has at least one pressure sensor 34 for measuring the partial pressure of at least one gas provided by the gas source 29 in the decompression chamber 26. In Figure 1 the design shown, there are two such pressure sensors 341, 342. These pressure sensors 34 i are arranged in the decompression chamber 26, close to the intermediate focus in the intermediate focal plane 18, that is, measuring the partial pressure of at least one gas provided close to this intermediate focus.

[0079] The pressure sensor 34 i can measure the partial pressure of each of the gases provided via the gas source unit 30 i provided.

[0080] In a design having at least one pressure sensor 34, the closed-loop control device 33 can be designed such that a target value is defined for the corresponding partial pressure of at least one gas provided depending on the corresponding operating state of the EUV source module 27 or the projection exposure apparatus 1, and this gas is then provided in a controlled manner in the decompression chamber 26 via the gas source 29 by appropriately actuating first the assigned source valve 31 i and secondly the main valve 32, with the actual partial pressure value in the decompression chamber 26, using the corresponding pressure sensor 34 i as well.

[0081] Alternatively, the corresponding pressure sensor 34 can also be arranged in the environment of the source region 25, as Figure 1 shown, where it can measure the corresponding partial pressure of at least one gas provided.

[0082] The pressure sensors 34, 34 i can in principle be designed as optical sensors.

[0083] The partial pressure of at least one gas provided can be maintained within a defined pressure range by means of the open-loop / closed-loop pressure control system described above, for example in the source region 25. This can be ensured by monitoring in the environment of the source region 25 by means of a pressure sensor 34.

[0084] Alternatively or additionally, the partial pressure of at least one gas provided can also be maintained within a defined pressure range in the region of the intermediate focus in the intermediate focal plane 18 by means of the open-loop / closed-loop control system described above. Compliance with this partial pressure can be monitored here by measuring the pressure by means of pressure sensors 341, 342 in the region of the intermediate focus in the intermediate focal plane 18.

[0085] In one design of the gas source 29 (not shown), this has an injection nozzle for controllably injecting at least one of the plurality of gases provided into the decompression chamber 26 in the environment of the intermediate focus in the intermediate focal plane 18. Then, the amount of gas injected in each case can be monitored by means of pressure sensors 341, 342 in the environment of the intermediate focus in the intermediate focal plane 18.

[0086] The corresponding gas can also be supplied to the decompression chamber 26 by means of at least one purge conduit.

[0087] If nitrogen is to be provided, the nitrogen partial pressure in the decompression chamber 26 in the range between 10 Pa and 100 Pa can be maintained via the open-loop / closed-loop control system described above. If hydrogen is to be provided as the gas in the decompression chamber 26, the hydrogen partial pressure can generally be maintained in the range between 30 Pa and 300 Pa.

[0088] Figure 2 Shows the correlation of the effective cross-sectional area σ of different particulate substances with their partial pressure p. This effective cross-sectional area is proportional to the absorption of the corresponding particulate substance at a specific wavelength of light or radiation. Additionally, Figure 2 The obliquely descending curves shown are the transmissions of 1e-06 (solid line) and 1e-03 (dashed line). Shown in solid / dashed / dashed and dotted / dotted form respectively are H2, H2O, N, N2, NH, NH + , NH2, NH3, O, O2, O2 + , O3, OH, and OH + 's effective cross-sectional area. Due to the relatively large effective cross-sectional areas of hydrogen and nitrogen, transmissions of 1e-06 and 1e-03 are found for relatively low partial pressures in the range of 10 -2 Pa. For other particulate substances, these two 1e-03 transmission values are only found at higher partial pressures, for example at 10 0in the range of Pa(H2O) or even higher partial pressures (e.g., O2).

[0089] In order to have a significant interaction of, for example, hydrogen or nitrogen with EUV radiation 16 at the intermediate focus in, for example, the source region 25 or in the intermediate focal plane 18, a partial pressure of at least 1e-03 must be defined. For other particle substances, a correspondingly higher partial pressure p must be defined, as is evident from the Figure 2 diagram.

[0090] NH3 gas can in particular bind nitrogen ions.

[0091] Figures 3 to 6 The wavelength dependence of the relative transmission T of a specific particle substance is shown, for the "in-band", "vacuum ultraviolet (VUV)", and "deep ultraviolet (DUV)" wavelength bands.

[0092] "In-band" here refers to the used EUV wavelength of 13.5 nm.

[0093] "VUV" refers to the wavelength range between 70 nm and 130 nm.

[0094] "DUV" refers to the wavelength range between 130 nm and 400 nm.

[0095] Figure 3 The wavelength dependence of the relative transmission of a specific particle substance is shown, for various wavelength ranges and a corresponding partial pressure of 0.001 Pa. The relative transmissions of the particle substances tin metal vapor, nitrogen, iron metal vapor, and zinc metal vapor are shown, which can be provided in the vacuum chamber 26 by appropriately assembling the gas source unit 30 of the gas source 29 i as described above.

[0096] According to Figure 3 the relative transmission values are normalized to the transmission in the in-band wavelength range.

[0097] In this pressure range, the VUV transmission is slightly higher than the in-band transmission and is approximately 1.1. At a partial pressure of 0.001 Pa, the DUV transmission of all these particle substances is approximately 1.4.

[0098] Figure 4 The ratio at a partial pressure of 0.01 Pa of the particle substance is shown, i.e., Figure 3 ten times the median. Compared to the relative transmission values according to Figure 3 there is hardly any change. It can thus be concluded that the corresponding particle substances still have no real influence on the relative transmission of EUV radiation 16.

[0099] Figure 5The relative transmission values at a partial pressure of the particulate matter of 0.1 Pa are again more than tenfold. Compared to Figure 3 and Figure 4 for the particulate matter of tin metal vapor and zinc metal vapor, the relative transmission in the DUV wavelength range has increased slightly, and at a partial pressure value of 0.1 Pa in Figure 5 it is approximately 1.5 for tin metal vapor and approximately 1.45 for zinc metal vapor.

[0100] Figure 6 The relative transmission values of the same particulate matter at a partial pressure of 1.0 Pa are again more than tenfold. In particular, compared to the lower partial pressure values, the relative transmission in the DUV wavelength range has now increased for the particulate matter of tin metal vapor, nitrogen, and zinc metal vapor. For a partial pressure of 1.0 Pa, the relative transmission is now approximately 2.3 for tin metal vapor, approximately 1.75 for zinc metal vapor, and approximately 1.5 for nitrogen. The relative transmission in the VUV wavelength range has also increased for tin metal vapor and for zinc metal vapor on the one hand, and is now approximately 1.2 for tin metal vapor and approximately 1.3 for zinc metal vapor.

[0101] Therefore, tin metal vapor and / or zinc metal vapor can be used as effective wavelength filters in the DUV range and the VUV range, especially in a partial pressure-dependent manner.

[0102] This is used, for example, in a projection exposure apparatus to selectively filter out unwanted wavelengths or wavelength ranges from the radiation components of different wavelengths included in the EUV radiation 16 used, which causes unwanted photoreactions of the particles present below the beam path of the EUV radiation 16. Such unwanted reactions are especially those reactions that result in reaction products that damage or deteriorate the optical surfaces of the components of the projection exposure apparatus 1 that guide the EUV radiation 16 used. Reactions that result in products with unwanted absorption at the wavelength of the EUV radiation 16 used are also corresponding unwanted reactions.

[0103] Alternatively or additionally, filtration by means of the provided gas can be used to avoid unwanted photocurrents that would otherwise be generated in the exposed optical components of the projection exposure apparatus 1 by exposure to the wavelengths or wavelength ranges to be filtered out. This especially allows for an improvement in the performance of the optical components because these, in whole or in their individual components (for example, in the form of a single mirror), are held in place by means of a holding current. Then, any unwanted effects of the generated photocurrents on such components can be avoided. An example of such a component is a MEMS mirror system having a plurality of individual single mirrors held in a corresponding tilted position by means of a holding current.

[0104] The interaction of at least one gas provided in the vacuum chamber 26 via the gas source 29 further generates a wavelength distribution of radiation including radiation in the beam path of the used EUV radiation 16 below the beam path of the used EUV radiation 16, which reduces or completely avoids corresponding unwanted reactions and / or photocurrents. As a result, the attenuation of the corresponding absorption lines of the overall radiation spectrum emitted from the source region 25 occurs. Then, the wavelength range of this overall radiation spectrum corresponding to the attenuation by the gas provided in the vacuum chamber 26 is no longer available for causing unwanted degradation and / or is no longer available for causing unwanted power reduction, due to the photo-induced misalignment of the optical components downstream in the beam path of the used EUV radiation 16. In particular, it is possible to reduce or completely avoid the N2-induced and / or H2-induced degradation of the optical coatings on the optical surfaces of these optical components, and / or the unwanted photo-induced misalignment of the optical components. In addition, the N2 / N ion / H2-induced coating degradation will be caused by the radiation in these wavelength ranges through photoionization, and / or in addition, the photo-induced misalignment will be caused by the radiation in these wavelength ranges through photocurrent. Then, the attenuation of these wavelength ranges results in a reduction or complete avoidance of such photoionization. By defining, for example, the corresponding H2 partial pressure, it is possible to avoid, for example, the unwanted generation of a hydrogen plasma further below the beam path of the used EUV radiation 16.

[0105] In principle, there are two different ways to avoid this unwanted reaction product in the at least one gas provided:

[0106] First, a corresponding photoionization reaction can be induced in the vacuum chamber 26 of the EUV source module 27 by adding an appropriate gas partial pressure, such that the radiation wavelengths used in these destructive photoionization processes are no longer further available below the beam path of the used EUV radiation 16. By inducing a destructive reaction in the beam path before the intermediate focus in the intermediate focal plane 18, the reaction in the beam path downstream of the intermediate focus in the intermediate focal plane 18 is subsequently reduced or completely avoided in a desired manner. An example of this controlled-induced reaction is the photoionization process for nitrogen particle species and / or hydrogen particle species.

[0107] Second, if the unwanted reactions (especially photoionization) for generating unwanted reaction products are known to occur or the radiation wavelengths for which unwanted photocurrents are known to be generated, they can be attenuated by a filter used in a controlled manner (especially a band-pass filter formed by the at least one gas provided), such that this destructive photoionization / photocurrent wavelength is no longer available for generating unwanted reaction products in the beam path of the used EUV radiation 16 downstream of the intermediate focus in the intermediate focal plane 18. An example of such a band-pass filter is based on tin, zinc, or iron, or nitrogen, as described above, for example, regarding Figures 3 to 6The described metal vapor. Nitrogen and hydrogen gas substances can be used, for example, as line filters. With the aid of such band-pass filters, it is possible, in particular, to suppress entirely or partly the wavelength range between 40 nm and 170 nm, which has been found to be problematic in the generation of unwanted photocurrents.

[0108] Figure 7 Shows the correlation of the effective cross-sectional area σ of the optical surface of the optical component downstream of the intermediate focus in the vicinity of the intermediate focal plane 18 with the nitrogen partial pressure p in the environment of the source region 25 and / or in the evacuated chamber 26 in the environment of the intermediate focus in the intermediate focal plane 18. Above and higher than 10 1 Pa of nitrogen partial pressure, a distinct reduction in this effective N2 dissociation effective cross-sectional area is found, which drops by more than one order of magnitude between 10 Pa and 100 Pa.

[0109] This effective cross-sectional area σ is expressed in arbitrary units (a.u.).

[0110] In Figure 7 For higher N2 partial pressures, the decrease in the effective cross-sectional area σ results in a corresponding reduction, for example, in the generation of nitrogen ions N2 + And the corresponding reduction in the destructive photoionization of nitrogen to electrons. If this photoionization reaction is reduced or completely avoided in the environment of the optical surface of the optical component, then N2 + Ions cannot cause degradation of the optical surface.

[0111] Figure 8 Shows the corresponding correlation of the effective cross-sectional area with the partial pressure for the photodissociation of nitrogen molecules close to the optical surface into two nitrogen atoms or two nitrogen ions.

[0112] The effective cross-sectional areas of the respective elemental substances considered are in units of m 2 Is shown in Figure 8 In.

[0113] Above 10 -2 Pa of nitrogen partial pressure p in the evacuated chamber 26, for this photodissociation, there is a decrease in the N2 effective cross-sectional area σ by more than one order of magnitude.

[0114] The reduction in the effective N2 effective cross-sectional area for this photodissociation results in a corresponding reduction in the destructive nitrogen atoms or nitrogen ions in the region of the optical surface of the optical component in the beam path of the EUV radiation 16 downstream of the intermediate focus in the intermediate focal plane 18.

[0115] In this way, it is possible to reduce or completely avoid the degradation thereof or to improve the performance of the optical component, firstly the optical components of the illumination optical unit 4 and / or secondly the optical components of the projection optical unit 10, namely the mirror M i .

[0116] In addition, Figure 8 the effects of iron metal vapor (Fe) first and zinc metal vapor (Zn) second on the photodissociation of nitrogen molecules into two nitrogen atoms or nitrogen ions are shown, again close to the optical surface of the optical component to be protected. Depending on the iron partial pressure, above 10 0 there is a decrease in the effective cross-sectional area σ of N2 for an iron metal vapor partial pressure of, starting from approximately 8 × 10 -24 m 2 to a value of less than 4 × 10 -24 m 2 , i.e., more than twice. Correspondingly, when such metal vapors with these partial pressures are used in the vacuum chamber 26, for example, in the environment of the source region 25 or close to the intermediate focal point in the intermediate focal plane 18, the result is a desired reduction of this dissociation reaction in the beam path of the EUV radiation 16 used downstream of the intermediate focal point in the intermediate focal plane 18, and correspondingly protects the downstream optical components of the illumination optical unit 4 and the projection optical unit 10.

[0117] When using zinc metal vapor, above 10 0 Pa for the corresponding Zn metal vapor partial pressure, there is an increase in the effective cross-sectional area of N2 for this dissociation reaction. In the case of a Zn metal vapor partial pressure of 10 1 Pa, an effective cross-sectional area of N2 greater than 5 × 10 -23 m 2 is achieved.

[0118] When using hydrogen vapor, no significant correlation between the effective cross-sectional area of N2 and the H2 partial pressure is found.

[0119] A similar behavior can be found when using tin metal vapor (Sn). In that case, above 10 0 Pa for the Sn metal vapor partial pressure, an increase in the effective cross-sectional area of N2 is found, again starting from approximately 8 × 10 -24 m 2 to more than 2 × 10 -23 m 2 .

[0120] In particular, tin metal vapor effectively suppresses the wavelength range between 80 nm and 160 nm.

[0121] In a further design of the projection exposure apparatus 1 for the EUV source module 27 used alternatively or additionally with the gas source 29 and / or the sensor 34 in the vacuum chamber, the EUV optical module 35 described below is used.

[0122] The EUV optical module 35 has a vacuum chamber 36 housing the illumination optical unit 4 and the projection optical unit 10.

[0123] The pressure reduction is generated in the pressure reduction chambers 26 and 36 by means of at least one pressure reduction source (such as Figure 1 a vacuum pump not shown in

[0124] The pressure reduction chamber 36 includes all the optical components of the projection exposure apparatus 1, which guide the used EUV radiation 16 downstream of the intermediate focus in the intermediate focal plane 18. In the beam path of the used EUV radiation 16 downstream of the intermediate focus in the intermediate focal plane 18, there are optical components 19, 21, 23, mask blank 7, M1 to M6, and wafer 13.

[0125] Each of these optical components has an optical surface for guiding the used EUV radiation 16 from the EUV source module 27 including an EUV source along the illumination and / or imaging beam path of the used EUV radiation 16 within the projection exposure apparatus 1.

[0126] The optical components may be of a temperature - controllable design.

[0127] The EUV optical module 35 also has a gas source 37 fluid - connected to the pressure reduction chamber 36 via at least one valve 32a. The gas source 37 has at least one gas source unit 30 i and has a valve group 28a including a source valve 31 i (each source valve is assigned to the gas source unit 30 i and a main valve 32a), and the structure of the valve group 28a corresponds to the structure of the gas source 29 described above with respect to the EUV source module 27.

[0128] The gas source 37 is designed such that it supplies at least hydrogen as a gas to the pressure reduction chamber 36. Other gases, such as oxygen and / or nitrogen, may also be supplied via the gas source 37, especially also in the form of vapor, as described above with respect to the EUV source module 27.

[0129] The gas source 37 may have gas nozzles or injection nozzles directed onto the respective optical surfaces of the optical components 19, 21, 23, 7, M1 to M6, 13. This ensures that activated hydrogen species are generated at the optical surfaces of the respective optical components where they are used for cleaning. It is also possible to provide a number of corresponding gas nozzles for each optical surface of the optical components ( Figure 1 not shown in

[0130] Hydrogen provided by the gas source 37 causes the generation of at least one activated hydrogen species in the decompression chamber 36, which is used to react with unwanted contaminant components in the decompression chamber 36, in particular for cleaning the optical surfaces of the optical components 19, 21, 23, 7, M1 to M6, and 13. In this way, the corresponding optical surfaces are effectively cleaned. The definition of the hydrogen partial pressure in the decompression chamber 36 enables the desired generation of the activated hydrogen species therein.

[0131] Other gases (such as oxygen and / or nitrogen) that can be introduced into the decompression chamber 36 via the gas source 37 in addition to hydrogen can also be used to generate, for example, cleaning radicals for cleaning the optical surfaces of the optical components of the illumination optical unit 4 and / or the projection optical unit 10, and / or can be used to filter the radiation included in the EUV light radiation 16 similar to the previous description regarding the EUV source module 27, which reduces or completely avoids the generation of unwanted reaction components that may otherwise cause deterioration of the optical surfaces.

[0132] One option is to operate the EUV optical module 35 entirely by means of the control of the open-loop / closed-loop control device 33, that is, by means of a look-up table depending on, for example, the operating state of the EUV optical module 35 or the overall projection exposure apparatus 1. Alternatively or additionally, the gas source 37 can also be operated under closed-loop control. For this closed-loop control operation, the EUV optical module 35 further has a pressure sensor 38 i , which is Figure 1 indicated in 11 as the pressure sensors 381 to 38 to be assigned to the optical surfaces of the optical components 19, 21, 23, 7, M1 to M6, and 13 i . Furthermore, these pressure sensors 38 i signally connected to the open-loop / closed-loop control device 33 have a function corresponding to that of the pressure sensor 34 of the EUV source module 27.

[0133] In particular, by means of the pressure sensor 38 i , the hydrogen partial pressure can be measured.

[0134] The partial pressure measured by means of the corresponding pressure sensor 38, as described above regarding the EUV source module 27, can in particular be maintained within the defined pressure range by means of the open-loop / closed-loop control device 33.

[0135] The hydrogen partial pressure in the decompression chamber 36 can be maintained within a range, for example, between 0.2 Pa and 20 Pa.

[0136] Isotopes of the corresponding gas (especially hydrogen isotopes) can be allowed to enter the decompression chamber 36 and, if necessary, also enter the decompression chamber 26 of the EUV source module 27 via the corresponding gas source 37 or 29.

[0137] Figure 9 Show the correlation of the effective cross-section σ for the photodissociation of molecular hydrogen species (H2 and / or D2) with the isotope concentration c of deuterium D2 in hydrogen H2 for a specific ratio of D2 / H2 in the decompression chamber 36 or 26. Figure 9 The correlation shown therein is valid here, especially for the D2 / H2 partial pressure in the decompression chamber 36 or 26 between 0.2 - 20 Pa.

[0138] Shown as solid circles is the correlation of this effective dissociation cross-section σ with the concentration c (D2 / H2), presented in relative units [r.u.], based on exactly 1 dissociation cross-section for pure hydrogen (c (D2 / H2) = 0).

[0139] Furthermore, shown as open circles is the relative effective cross-section σ for the photoionization of molecular hydrogen species (H2 and / or D2). I Shown here is the ionization cross-section σ with respect to exactly 1 value for pure hydrogen content (c (D2 / H2) = 0). I .

[0140] Above a relative concentration c of 0.01, the dissociation cross-section σ rises rapidly by several orders of magnitude and exceeds 100 at a concentration c (D2 / H2) of 10%. At this concentration, the ionization cross-section σ I shows almost no reduction and is essentially constant for concentrations c in the range between 0.001% and 1%.

[0141] Figure 9 The correlation in shows that adding, for example, 10% or 25% deuterium causes a rapid and favorably rising dissociation cross-section, while there is no unwanted decrease in the ionization cross-section. Thus, this corresponding addition of deuterium allows, for example, an increase in the proportion of active hydrogen species in the decompression chamber 36 or 26, which enables more effective cleaning and / or reaction of the optical surfaces of optical components. The favorable isotope concentration fraction c (D2 / H2) is in the range between 0.02% and 25%, and for example, in the range between 0.1% and 10%.

[0142] In the design according to Figure 1 the decompression chamber 36 encloses both the illumination optical unit 4 and the projection optical unit 10. Alternatively, the decompression chamber 36 may also be subdivided into a first sub-chamber that encloses only the illumination optical unit 4 and a second sub-chamber that encloses only the projection optical unit 10. Thus, if the EUV optical module 35 is connected to one of these sub-chambers, it can be used as part of the illumination optical unit 4 and / or as part of the projection optical unit 10.

[0143] In order to produce microstructured or nanostructured components, the projection exposure apparatus 1 is used as follows: First, a reflective mask 7 or a mask master and a substrate or wafer 13 are provided. Subsequently, the structures on the mask master 7 are projected onto the photosensitive layer of the wafer 13 by means of the projection exposure apparatus 1. Then, the microstructures or nanostructures on the wafer 13 and thus the microstructured components are produced by developing the photosensitive layer.

Claims

1. An EUV optical module (35) for an EUV projection exposure apparatus (1) - comprising at least one optical component (19, 21, 23, 7, M1 to M6, 13) having an optical surface for guiding the used EUV radiation (16) from an EUV source (3) along an illumination and / or imaging beam path of the projection exposure apparatus (1), - comprising a vacuum chamber (36) housing the optical component (19, 21, 23, 7, M1 to M6, 13); - comprising a gas source (37) fluidly connected to the vacuum chamber (36) via at least one valve, - wherein the gas source (37) is designed such that it provides at least the following gases: - hydrogen, - wherein the gas source (37) is designed such that it adds at least one of its isotopes to at least one of the provided gases at a controlled concentration.

2. The EUV optical module according to claim 1, wherein The gas source (37) is designed such that adding hydrogen isotopes increases the effective cross-sectional area of the gas used to dissociate and generate active hydrogen species by a factor of approximately three orders of magnitude.

3. The EUV optical module according to claim 2, wherein, The proportion of the isotope corresponds to 0.02 - 25% of the at least one provided gas.

4. The EUV optical module according to claim 2 or 3, characterized in that, The concentration of the isotope in the provided gas is controlled via the operating state of the machine.

5. The EUV optical module according to any one of claims 1 to 4, characterized in that The valve is a control valve having a signal connection to an open-loop / closed-loop control device (33) for the EUV optical module (35).

6. The EUV optical module according to claim 5, wherein At least one pressure sensor (38 i ) is used to measure the partial pressure of the at least one gas provided in the decompression chamber (36) via the gas source (37), wherein the pressure sensor (38) has a signal connection to the control valve via the open-loop / closed-loop control device (33).

7. The EUV optical module according to any one of claims 1 to 6, characterized in that, Designed such that the partial pressure of the at least one provided gas is maintained within a defined pressure range in the environment of the optical surface of the optical component (19, 21, 23, 7, M1 to M6, 13).

8. The EUV optical module according to any one of claims 1 to 7, characterized in that Designed such that the partial pressure of hydrogen within the range between 0.2 Pa and 20 Pa is maintained in the vacuum chamber (36).

9. The EUV optical module according to any one of claims 1 to 8, characterized in that, The gas source (37) is designed such that it provides at least one of the following additional gases: - oxygen and / or - water vapor and / or - nitrogen and / or - CH4 and / or - NH3 and / or - CO and / or - CO2.

10. An optical system for an EUV projection exposure apparatus, comprising: - the EUV optical module (35) according to any one of claims 1 to 9, as part of an illumination optical unit (4) for illuminating the object field (5) of the projection exposure apparatus, in which an object (7) to be imaged can be arranged, - an imaging optical unit (10) for imaging the object field (5) in an image field (11) of the projection exposure apparatus, in which a wafer (13) can be arranged.

11. An optical system for an EUV projection exposure apparatus, comprising: - an illumination optical unit (4) for illuminating the object field (5) of the projection exposure apparatus, in which an object (7) to be imaged can be arranged, - the EUV optical module (35) according to any one of claims 1 to 9, as part of an imaging optical unit (10) for imaging the object field (5) in an image field (11) of the projection exposure apparatus, in which a wafer (13) can be arranged.

12. A projection exposure apparatus having an optical system as claimed in claim 10 or 11 and having an EUV light source (3).

13. A method for producing a structured component, comprising the following method steps: - Providing a mask blank (7) and a wafer (13); - Projecting the structures on the mask blank (7) onto the photosensitive layer of the wafer (13) by means of a projection exposure apparatus as claimed in claim 12; - Producing microstructures or nanostructures on the wafer (13).

14. A structured component produced by the method as claimed in claim 13.

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