DE102011079451A1 - Optical arrangement, particularly projection exposure system for extreme ultraviolet lithography, has optical element with reflective coating, which has cover layer, on whose surface oxidic impurities are present - Google Patents

Optical arrangement, particularly projection exposure system for extreme ultraviolet lithography, has optical element with reflective coating, which has cover layer, on whose surface oxidic impurities are present

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Publication number
DE102011079451A1
DE102011079451A1 DE201110079451 DE102011079451A DE102011079451A1 DE 102011079451 A1 DE102011079451 A1 DE 102011079451A1 DE 201110079451 DE201110079451 DE 201110079451 DE 102011079451 A DE102011079451 A DE 102011079451A DE 102011079451 A1 DE102011079451 A1 DE 102011079451A1
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surface
18a
optical arrangement
arrangement according
cover layer
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DE201110079451
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German (de)
Inventor
Moritz Becker
Dirk Heinrich Ehm
Stefan-Wolfgang Schmidt
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Carl Zeiss SMT GmbH
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Carl Zeiss SMT GmbH
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Priority to DE201110079451 priority Critical patent/DE102011079451A1/en
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    • GPHYSICS
    • G03PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03FPHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70Exposure apparatus for microlithography
    • G03F7/70216Systems for imaging mask onto workpiece
    • G03F7/70316Details of optical elements, e.g. of Bragg reflectors or diffractive optical elements
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B5/00Optical elements other than lenses
    • G02B5/08Mirrors
    • G02B5/0816Multilayer mirrors, i.e. having two or more reflecting layers
    • G02B5/0825Multilayer mirrors, i.e. having two or more reflecting layers the reflecting layers comprising dielectric materials only
    • G02B5/0833Multilayer mirrors, i.e. having two or more reflecting layers the reflecting layers comprising dielectric materials only comprising inorganic materials only
    • GPHYSICS
    • G03PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03FPHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70Exposure apparatus for microlithography
    • G03F7/708Construction of apparatus, e.g. environment, hygiene aspects or materials
    • G03F7/70908Hygiene, e.g. preventing apparatus pollution, mitigating effect of pollution, removing pollutants from apparatus; electromagnetic and electrostatic-charge pollution
    • G03F7/70925Cleaning, i.e. actively freeing apparatus from pollutants

Abstract

The invention relates to an optical arrangement comprising:
at least one optical element (14) having a reflective coating (16) which has a cover layer (18) on the surface (18a) of which oxide contaminants are present, a gas supply device for supplying a reducing gas (CO) to the surface (18a) and an irradiation device (21) for irradiating radiation pulses (23) on the surface (18a), wherein a wavelength (λ S ) of the radiation pulses (23) is selected as a function of the material of the cover layer (18), typically in such a way in that a reaction rate of the oxidic impurities present on the surface (18a) of the covering layer (18) with the reducing gas (CO) is increased in the region of an impact point (P) of the radiation pulses (23) on the surface (18a). The invention also relates to associated method for removing oxide contaminants (O) from a surface (18a).

Description

  • Background of the invention
  • The invention relates to an optical arrangement, in particular a projection exposure apparatus for EUV lithography, and to a method for removing oxidic contaminants from optical elements.
  • In optical arrangements such. B. EUV lithography devices / projection exposure systems are typically used as optical elements reflective elements, since at the wavelengths used in the exposure mode, which are typically between 5 nm and 20 nm, no optical materials with a sufficiently large transmission are known. The optical elements used at wavelengths in the EUV range comprise a substrate and a reflective coating having a plurality of layers applied to the substrate.
  • Such a multilayer coating typically consists of alternating layers of high and low refractive index materials, e.g. B. alternating layers of molybdenum and silicon whose layer thicknesses are coordinated so that the coating performs its optical function and a high reflectivity is ensured. The multi-layer system typically has a cover layer covering the underlying layers e.g. B. should protect against oxidation and which usually consists of a metallic material, for. B. of ruthenium, rhodium or palladium.
  • The EUV radiation, which is irradiated onto the optical elements in the exposure mode, can in the residual gas atmosphere in which the optical elements are operated form activated (atomic) oxygen, which is adsorbed on the surface of the cover layer and there to oxidative damage ("Oxidative damage") or leads to oxidic impurities. In particular, if the oxide contaminants penetrate deep into the multilayer coating, such damage is not with the help of conventional in-situ cleaning methods, eg. B. corrected by activated or atomic hydrogen. Furthermore, there is the problem with conventional cleaning methods that they can not usually be performed locally, but rather have a generally continuous distribution of the cleaning rate over the surface to be cleaned, whereas the contamination profiles are correlated with the illumination profiles of the optical elements. In addition, when using atomic hydrogen for cleaning, a hydrogen-induced outgassing effect on components present in the residual gas atmosphere can occur, which possibly leads to the formation of metallic deposits on the surface to be cleaned, which leads to a considerable reduction of the Reflectivity.
  • From the US 6,356,653 B2 For example, a method of removing particles from a surface has been disclosed in which focused radiant energy is radiated onto the particles to overcome the bonding energy between the surface and the particles. The particles dissolved from the surface can be removed from the surface by means of a directed gas flow. A laser can be used to generate the radiation energy. The amount of radiation used to detach the particles can be determined, for example, depending on the composition of the particles.
  • In the US 6,385,290 B1 is an exposure system with an x-ray source z. B. become known in the form of a plasma light source. In order to remove particles from the surfaces of the exposure system, there is proposed an additional light source, for. A laser, to generate radiation at a wavelength that is absorbed by the particles. In particular, it is proposed to use UV radiation which removes the bond between the carbon particles and the surface to remove impurities consisting essentially of carbon. If an oxygen or ozone atmosphere prevails in the exposure system, the released carbon can react with the oxygen to form (volatile) carbon dioxide.
  • From the US 6,538,722 B1 is a projection exposure system has become known in which a cleaning jet, z. As a pulsed laser beam, is used to clean optical elements of the exposure system in situ. For this purpose, the optical elements can be moved from a position in which they are arranged within the exposure beam path into a position within the cleaning beam path.
  • US 6,924,492 B2 describes an in-situ cleaning of optical components of a projection exposure apparatus in which the optical components are irradiated with microwave or UV radiation. It is proposed to use a frequency range during the irradiation, in which the optical component is only slightly heated. The particles or molecules present on the surfaces of the components can be excited, in particular, at frequencies at which they have a rotational or vibration frequency. For example, water should be removed or evaporated from the surfaces of the optical components in this way.
  • In the US 6,936,825 B2 For example, a method for removing contaminants from the surfaces of optical elements in a microlithography exposure apparatus has been disclosed in which UV exposure of an additional light source and a fluid for cleaning are used during exposure pauses. The fluid may contain oxygen and / or ozone gas.
  • The US 7,061,576 B2 describes an exposure apparatus having a housing with an inert gas supply and an oxygen and clean air supply to the housing. A control device controls the wavelength of the exposure radiation of a laser and the feeds for the optional exposure of a substrate or for cleaning an optical element. The US 7,119,878 B2 describes an exposure system in which a further housing is arranged in the housing, which receives a surface of the optical element. A feed device and a discharge device serve to supply and discharge of inert gas to the two housings.
  • The WO 94/23854 describes the removal of contaminants from a surface by irradiation of the surface with high energy radiation, the z. B. is supplied by a laser. During irradiation, a laminar flow of an inert gas is conducted along the surface. It is proposed to use high energy radiation at an energy level at least twice the binding energy between the contaminants and the surface.
  • The WO 2010/043398 A1 The applicant describes an EUV lithography device with a processing device for preferably spatially resolved processing of an optical element at a processing position of the lithographic device. For activating at least one gas component of a gas stream supplied to the surface of the optical element by means of a gas nozzle, the processing device comprises a radiation source for generating radiation, for example a femtosecond laser. The gas constituent to be activated may be, for example, carbon monoxide, carbon dioxide, molecular hydrogen or nitrogen.
  • Object of the invention
  • An object of the invention is to provide an optical arrangement with reduced oxide contaminants on the optical surface of at least one optical element.
  • Subject of the invention
  • This object is achieved by an optical arrangement comprising: at least one optical element having a reflective coating, which has a cover layer on the surface of which oxide contaminants are present, a gas supply device for supplying a reducing gas to the surface, and an irradiation device for irradiating Radiation pulses to the surface, wherein a wavelength of the radiation pulses is selected depending on the material of the cover layer. The wavelength is typically selected or set such that a reaction rate of the oxidic impurities or particles present on the surface of the cover layer increases with the reducing gas in the region of impact of the radiation pulses on the surface (compared to the reaction rate at the remainder of the surface) is.
  • The inventors have recognized that the rate of reaction of the reducing gas with the oxide contaminants may be increased in a region of the surface where pulsed (laser) radiation impinges on the surface. However, this presupposes that the laser pulses have a suitable energy or wavelength at which the chemical reaction of the reducing gas with the oxidic impurities is favored. Since the chemical reaction occurs on the surface of the cover layer, the material of the surface or the cover layer has an influence on the chemical reaction, for example because the surface has a catalytic effect, so that the wavelength to be selected for the irradiation depends on the material of the cover layer , It is understood that the choice of a wavelength at which the reaction is favored may additionally depend on the nature of the reducing gas. The oxidic impurities are typically adsorbed on the surface (atomic) oxygen.
  • The material of the cover layer is typically a metallic material, for example ruthenium, rhodium, palladium, platinum, iridium, niobium, vanadium, chromium, zinc or tin. Metallic cover layers can be oxidized by the oxygen present in the residual gas atmosphere and possibly activated by the EUV radiation. It is understood that non-metallic materials may also be used as the cover layer, for example materials containing silicon and / or carbon and / or nitrogen and / or boron.
  • As reducing gases or as components of the reducing gas, carbon monoxide and hydrogen, in particular activated hydrogen, as well as hydrogen-containing compounds as favorable. In particular, carbon monoxide is a highly reducing gas that reacts with the oxide contaminants on the surface of the topcoat when irradiated with laser pulses of appropriate wavelength. In this case, the cover layer material may optionally act as a catalyst on the surface at which the chemical reaction takes place. For the purposes of this application, activated hydrogen is understood as meaning hydrogen which is not present in molecular form, ie in particular hydrogen radicals H, hydrogen ions (H + or H 2 + ) or hydrogen (H *) in an excited electronic state.
  • In one embodiment, the irradiation device has a radiation source for generating radiation pulses having a wavelength in the infrared wavelength range. Radiation pulses having such a wavelength have been found to be particularly favorable for converting (atomic) oxygen adsorbed on a metallic ruthenium layer with carbon monoxide adsorbed on the surface into carbon dioxide, cf. the article Bonn, et al., Science Vol. 285, no. 5430, pp. 1042-1045 , the contents of which are incorporated herein by reference. The article states that heating a ruthenium surface in which carbon monoxide and atomic oxygen are co-adsorbed, without irradiation with laser pulses, results almost exclusively in the desorption of carbon monoxide. For the purposes of this application, the infrared wavelength range is understood to mean a wavelength range between approximately 780 nm and approximately 1 mm, with wavelengths of less than approximately 50 μm, in particular wavelengths in the so-called near infrared range, typically up to approx 3 μm, in particular up to about 1 μm.
  • To generate the radiation pulses, the irradiation device typically has a laser as the radiation source. A (pulsed) laser makes it possible to generate laser pulses with pulse lengths in the picosecond or femtosecond range, which are particularly advantageous for the present applications, since the pulsed operation can prevent the material of the cover layer in the irradiated region from being at least partially melted. This is particularly advantageous when the radiation pulses are focused, i. H. into a narrowly defined area (place of impact) at the surface.
  • In a development, the irradiation device is designed to vary a point of impact of the radiation pulses on the surface. The radiation pulses are typically radiated locally onto the surface, into a respective area of the surface where oxide contaminants are present. This may be z. B. to act areas where the impacting on the surface EUV radiation has a high intensity. The irradiation device may comprise suitable movement devices, in particular with translatory or rotary drives, in order to produce, for example, B. to move the beam source or to pivot and in this way to vary the point of impact on the surface. It is understood that for the localization of the oxide contaminants on the surface, if necessary, an inspection device, for. As a spatially resolving camera or the like, can be provided in the optical arrangement.
  • In a further embodiment, the processing device comprises an optical system for widening, focusing and / or for deflecting the radiation pulses. The electromagnetic radiation z. B. generated by a laser, can be deflected over conventional lenses or mirrors, widened or focused. The expansion / focusing is beneficial to adjust the size of the impact of the radiation on the surface as the increase in the reaction rate concentrates around the point of impact. By the deflection z. B. by means of a (scanner) mirror, it is easily possible to irradiate the radiation pulses in the desired surface area to be cleaned. When using two scanner mirrors or a scanner mirror with two rotational degrees of freedom for beam deflection, it is typically possible to scan each location on the surface of the cover layer with the radiation pulses when the radiation source is stationary. It is understood that, depending on the wavelength of the radiation pulses used, if appropriate, optical fibers can also be used to guide the (laser) radiation.
  • In one embodiment, the gas supply device has a gas inlet for introducing the reducing gas into a housing in which the optical element is arranged. The gas inlet may, for example, be provided on a housing of a projection system, an illumination system or a beam generation system of a projection exposure apparatus and connect the residual gas atmosphere present there to a gas reservoir. In this case, it has proved to be advantageous if a partial pressure of the reducing gas of typically between about 1 × 10 -3 mbar and 5 × 10 -2 mbar is achieved by the (optionally controlled) gas inlet or a correspondingly dimensioned supply line in the residual gas atmosphere , If appropriate,> 5 × 10 -2 mbar is generated.
  • Alternatively or additionally, the gas supply device may comprise at least one gas nozzle for supplying the reducing gas in a gas stream have on the surface. The gas stream is typically oriented at an angle to the surface and impinges on the surface at the point of impact of the radiation pulses. The gas stream may, in addition to the reducing gas or in addition to the reducing gas constituents, which undergo the chemical reaction with the oxidic impurities, optionally further gas constituents, for. B. inert gases.
  • In a further development, the gas supply device for supplying the gas flow to the surface with a flow rate between 1 and 100 mbar l / s is formed. It has been found that at such flow rates the surface treatment efficiency is particularly high.
  • In a further embodiment, the radiation pulses at the surface have an energy density between 1 μJ / mm 2 and 10 mJ / mm 2 . With such energy densities, on the one hand an effective increase of the reaction rate on the surface of the cover layer can take place and on the other hand it can be ensured that the surface is not damaged by the radiation pulses, in particular not locally melted.
  • In one embodiment, the reflective coating comprises a plurality of individual layers for reflection of EUV radiation. The individual layers are made of different materials, which are chosen so that the reflectivity of the optical element at a wavelength in the EUV range is maximum, which corresponds to the operating wavelength of the optical arrangement.
  • In one embodiment, the optical arrangement is designed as a projection exposure apparatus for microlithography, in particular for EUV lithography. The oxidic impurities on the optical elements of the projection exposure apparatus can be made in-situ, i. H. it is not necessary to remove the optical elements for the surface treatment from the projection exposure apparatus. Optionally, the treatment of the surface may also take place during the exposure operation. It goes without saying that other optical arrangements, for example devices for inspecting wafers and / or masks, can also be formed in the manner described above, in order to be able to perform effective cleaning on the optical elements provided there.
  • The invention also relates to a method of removing oxide contaminants from a surface of a cover layer of a reflective coating of an optical element, comprising: supplying a reducing gas to the surface, and irradiating radiation pulses to the surface, wherein a wavelength of the radiation pulses is dependent on the material the cover layer is selected. As described above, the wavelength is typically chosen such that a reaction rate of the oxidic impurities present on the surface with the reducing gas is increased in the region of impact of the radiation pulses on the surface (compared to the reaction rate at the remainder of the surface).
  • Further features and advantages of the invention will become apparent from the following description of embodiments of the invention, with reference to the figures of the drawing, which show details essential to the invention, and from the claims. The individual features can be realized individually for themselves or for several in any combination in a variant of the invention.
  • drawing
  • Embodiments are illustrated in the schematic drawing and will be explained in the following description. It shows
  • 1 a schematic representation of an optical arrangement in the form of an EUV lithography system,
  • 2 a schematic representation of an optical element of the EUV lithography of 1 , such as
  • 3 a schematic representation of a radiation-induced reaction of a surface of a cover layer of the optical element of 2 adsorbed reducing gas with there adsorbed (atomic) oxygen.
  • In 1 is schematically a projection exposure system 1 shown for EUV lithography. The projection exposure machine 1 has a beam generating system 2 , a lighting system 3 and a projection system 4 accommodated in separate vacuum housings and consecutively in one of an EUV light source 5 of the beam-forming system 2 outgoing beam path 6 are arranged. As an EUV light source 5 For example, a plasma source or a synchrotron can serve. The from the light source 5 Exiting radiation in the wavelength range between about 5 nm and about 20 nm is first in a collimator 7 bundled. With the help of a subsequent monochromator 8th By varying the angle of incidence, as indicated by a double arrow, the desired operating wavelength λ B is filtered out, which in the present example is approximately 13.5 nm. The collimator 7 and the monochromator 8th are designed as reflective optical elements.
  • The in the beam generation system 2 radiation treated in terms of wavelength and spatial distribution is introduced into the lighting system 3 introduced, which a first and second reflective optical element 9 . 10 having. The two reflective optical elements 9 . 10 direct the radiation onto a photomask 11 as a further reflective optical element having a structure formed by the projection system 4 on a smaller scale on a wafer 12 is shown. These are in the projection system 4 a third and fourth reflective optical element 13 . 14 intended.
  • The reflective optical elements 9 . 10 . 11 . 13 . 14 each have an optical surface, the EUV radiation 6 the light source 5 is exposed. The optical elements 9 . 10 . 11 . 13 . 14 are operated under vacuum conditions in a residual gas atmosphere, in which a small proportion of oxygen is present. As the interior of the projection exposure system 1 can not heat out, the presence of residual gas components in the vacuum environment can not be completely avoided.
  • To oxidic impurities or particles from the surfaces of the optical elements 9 . 10 . 11 . 13 . 14 to remove, points the projection exposure system 1 a gas supply device 19 with a supply channel 20 which is connected to a (not shown) gas reservoir and for supplying a reducing gas, in the present example of carbon monoxide CO, in the vacuum environment or residual gas atmosphere of the projection system 4 serves. It is understood that corresponding supply channels also in the lighting system 3 and / or in the beam generating system 2 may be provided or a central supply channel for the entire projection exposure system 1 can be provided. A control device (not shown) serves to control the gas supply device 19 as well as the control of further functions of the projection exposure apparatus 1 ,
  • By the supply of carbon monoxide to oxidic impurities from the surfaces of the optical elements 13 . 14 in the projection system 4 be removed. To explain this process, will be related to 2 the structure of the second optical element 14 of the projection system 4 described in detail.
  • The optical element 14 has a substrate 15 of a material with a low coefficient of thermal expansion, which is typically less than 100 ppb / K at 22 ° C or over a temperature range of about 5 ° C to about 35 ° C. A material exhibiting these properties is titania-doped silicate glass, which typically has a silicate glass content of greater than 90%. Such available on the market silicate glass is sold by the company. Corning Inc. under the trade name ULE ® (ultra low expansion glass). Another group of materials which has a very low coefficient of thermal expansion are glass-ceramics in which the ratio of the crystal phase to the glass phase is adjusted so that the thermal expansion coefficients of the different phases almost cancel each other out. Such glass ceramics are z. B. under the trade name Zerodur ® from the company. Schott AG or under the trade name Clearceram ® from the company Ohara Inc. offered.
  • On the substrate 15 is a reflective coating 16 applied, which has a plurality of individual layers 17a . 17b has, which consist of different materials. In the present case, the individual layers consist alternately of materials with different refractive indices. If the operating wavelength λ B is about 13.5 nm, as in the present example, the individual layers are usually made of molybdenum and silicon. Other material combinations such. As molybdenum and beryllium, ruthenium and beryllium or lanthanum and B 4 C are also possible. In addition to the individual layers described, the reflective coating 16 also include interlayers to prevent diffusion. On the representation of such auxiliary layers in the figures has been omitted.
  • The reflective coating 16 has a cover layer 18 to oxidize the underlying monolayers 17a . 17b to prevent. The cover layer 18 consists in the present example of ruthenium. It is understood that other materials, in particular metallic materials such as rhodium, palladium, platinum, iridium, niobium, vanadium, chromium, zinc or tin as cover layer materials. It is understood that the top coat 18 for the EUV radiation 6 is permeable.
  • The optical element 14 has a flat surface in the illustrated embodiment. This was chosen only to simplify the presentation, ie the optical element 14 may also have a curved surface shape, wherein z. B. concave surface shapes or convex surface shapes are possible, which may be formed both spherical and aspherical.
  • By existing in the residual gas atmosphere, by the EUV radiation 6 activated oxygen becomes the ruthenium material of the topcoat 18 , more specifically, the ruthenium material on the surface 18a the topcoat 18 oxidized (Ru + O x -> RuO x ), ie at the surface 18a the topcoat 18 (atomic) oxygen is adsorbed.
  • To remove these oxidic impurities from the surface 18a is in the projection exposure machine 1 an irradiation device 21 intended. The irradiation device 21 include a femtosecond laser 22 for generating ultrashort radiation pulses 23 (with pulse durations in the femtosecond range), which has a deflection mirror 24 on the surface 18a be steered and hit there at an impact point P. In the femtosecond laser 22 it is an infrared laser with a wavelength λ S in the infrared range, z. B. a CO 2 laser having a wavelength λ S of about 10.6 microns to a helium-neon laser, which is operated at a wavelength λ S of 1152.3 nm, or a Ti: sapphire Laser, which is operated at a wavelength λ S of about 800 nm. The laser can be used to generate ultrashort pulses 22 be stimulated pulsed. Typically, the laser points 22 but a Q-switching (eg, using a Pockels cell) on the ultrashort radiation pulses 23 to create.
  • The radiation pulses 23 lead to a local increase in a reaction rate of the surface 18a adsorbed (atomic) oxygen O with there also adsorbed carbon monoxide CO, carbon dioxide CO 2 forms, which from the surface 18a is desorbed, as in 3 is shown.
  • The radiation pulses 23 lead here to an excitation of the material of the cover layer 18 , which contributes to the adsorbed oxygen O and the adsorbed carbon monoxide CO to CO 2 in the irradiated area. The ruthenium material of the surface 18a has a catalytic effect for this reaction, as described in detail in the article "Phonon-Versus Electron-Mediated Desorption and Oxidation of CO to Ru" cited above. The reaction occurring in this case can be described by the following reaction equation: Ru x O + y CO -> x Ru + y CO 2 , wherein by the radiation pulses 23 (hv) the Reakitonsgleichgewicht is shifted to the reaction products, ie, the reaction rate is in the region of the impact point P by the radiation pulses 23 elevated.
  • In order to achieve this, it is necessary to use the photon energy or the wavelength λ s of the radiation pulses 23 suitable to choose what is achieved in the present combination of top layer material and carbon monoxide CO as a reducing gas in that a wavelength λ s in the infrared wavelength range, in particular in the so-called NIR range is selected, for. B. a wavelength of about 800 nm. Be other, especially metallic materials for the cover layer 18 used, the wavelength of the radiation pulses must be 23 optionally adapted to the respective cover layer material, wherein also in other metallic materials, the wavelength of the radiation pulses 23 typically in the IR (or NIR) range. It will be appreciated that such an adaptation may also be necessary if instead of carbon monoxide CO, another strongly reducing gas is used, for example hydrogen, in particular activated hydrogen, or if the reducing gas comprises both carbon monoxide CO and hydrogen or hydrogen-containing compounds Contains gas components.
  • As in 2 Also shown, to enhance the above-described chemical reaction, may be the optical element 14 a gas nozzle 25 which are used to generate one on the surface 18a directed gas flow 26 serves, with the carbon monoxide CO on the surface 14a of the optical element 14 is applied. The gas nozzle 25 is here outside the beam path 6 arranged the EUV radiation and at an angle α to the surface 18a aligned, which is chosen so that the gas flow 26 at least partially in the same surface area or impact point P as the radiation pulses 23 on the surface 18a incident. By supplying additional carbon monoxide CO to the surface 18a it can be ensured that the above-described reaction of the oxidized ruthenium takes place sufficiently. It has proved to be favorable when the flow rate of the gas stream 26 between 1 and 100 mbar l / s. It is understood that, if necessary, on the gas nozzle 25 can be omitted or that if necessary when using the gas nozzle 25 no additional introduction of the reducing gas via the supply line 20 must be done.
  • At the radiation pulses 23 it is laser radiation of high intensity or power on the part to be processed or the point of impingement P of the optical element 14 is focused there to produce an energy density typically in the range between about 1 μJ / mm 2 and about 10 mJ / mm 2 . To oxidic contaminants from the entire surface 18a or from the subregions of the surface 18a in which these are present, remove, the entire irradiation device 21 ie the laser 22 as well as the deflection mirror 24 together by means of a in 2 indicated by a double arrow movement device comprising three conventional linear drives, along the three axes of the XYZ coordinate system of the projection exposure system 1 to be moved. It is understood that alternatively or additionally, the deflection mirror 24 relative to the laser 22 or the laser 22 relative to the deflection mirror 24 can be moved, for. B. by a Shifting or tilting is done to the radiation pulses 23 to a desired area of the surface 18a to steer and so a local processing of the surface 18a to enable.
  • It is understood that the irradiation device 21 additionally or alternatively to the deflection mirror 24 Also, other optics or optical elements may have a deflection, focusing and / or widening or shaping of the laser radiation or the radiation pulses 23 produce. The focusing or widening can take place here to the size of the point of impact 23 and thus the energy density of the radiation pulses 23 on the surface 18a suitable to choose. It is understood that for localization of the oxide particles or impurities optionally an inspection device in the projection exposure system 1 may be provided, which includes, for example, a spatially resolving camera and an associated evaluation device to detect the oxide contaminants on the surface.
  • QUOTES INCLUDE IN THE DESCRIPTION
  • This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.
  • Cited patent literature
    • US 6356653 B2 [0005]
    • US 6385290 B1 [0006]
    • US 6538722 B1 [0007]
    • US 6924492 B2 [0008]
    • US 6936825 B2 [0009]
    • US 7061576 B2 [0010]
    • US 7119878 B2 [0010]
    • WO 94/23854 [0011]
    • WO 2010/043398 A1 [0012]
  • Cited non-patent literature
    • Bonn, et al., Science Vol. 285, no. 5430, pp. 1042-1045 [0018]

Claims (14)

  1. Optical arrangement ( 1 ), comprising: at least one optical element ( 14 ) with a reflective coating ( 16 ), which a cover layer ( 18 ), on the surface ( 18a ) oxide contaminants (O) are present, a gas supply device ( 19 ) for supplying a reducing gas (CO) to the surface ( 18a ), as well as an irradiation device ( 21 ) for irradiating radiation pulses ( 23 ) on the surface ( 18a ), wherein one wavelength (λ S ) of the radiation pulses ( 23 ) depending on the material of the cover layer ( 18 ) is selected.
  2. An optical arrangement according to claim 1, wherein the material of the cover layer ( 18 ) is selected from the group comprising: ruthenium, rhodium, palladium, platinum, iridium, niobium, vanadium, chromium, zinc or tin.
  3. An optical arrangement according to claim 1 or 2, wherein the reducing gas contains at least one constituent selected from the group comprising: carbon monoxide and hydrogen, in particular activated hydrogen, or hydrogen-containing compounds.
  4. Optical arrangement according to one of the preceding claims, in which the irradiation device ( 21 ) a radiation source ( 22 ) for generating radiation pulses ( 23 ) having a wavelength (λ S ) in the infrared wavelength range.
  5. Optical arrangement according to one of the preceding claims, in which the irradiation device ( 21 ) for generating the radiation pulses ( 23 ) a laser ( 22 ) as a radiation source.
  6. Optical arrangement according to one of the preceding claims, in which the irradiation device ( 21 ) is formed, an impingement point (P) of the radiation pulses ( 23 ) on the surface ( 18a ) to vary.
  7. Optical arrangement according to one of the preceding claims, in which the irradiation device ( 21 ) an optic ( 24 ) for widening, focusing and / or redirecting the radiation pulses ( 23 ) having.
  8. Optical arrangement according to one of the preceding claims, in which the gas supply device comprises a gas inlet ( 20 ) for introducing the reducing gas (CO) into a housing ( 4 ), in which the optical element ( 14 ) is arranged.
  9. Optical arrangement according to one of the preceding claims, in which the gas supply device ( 19 ) at least one gas nozzle ( 25 ) for supplying the reducing gas (CO) in a gas stream ( 26 ) on the surface ( 18a ) having.
  10. Optical arrangement according to Claim 9, in which the gas supply device ( 19 ) for supplying the gas stream ( 26 ) is formed to the surface at a flow rate between 1 and 100 mbar l / s.
  11. Optical arrangement according to one of the preceding claims, in which the radiation pulses ( 23 ) on the surface ( 18a ) have an energy density between 1 μJ / mm 2 and 10 mJ / mm 2 .
  12. Optical arrangement according to one of the preceding claims, in which the reflective coating ( 16 ) a plurality of individual layers ( 17a . 17b ) for reflection of EUV radiation ( 6 ) having.
  13. Optical arrangement according to one of the preceding claims, which is used as a projection exposure apparatus ( 1 ) is designed for microlithography.
  14. Process for removing oxidic impurities (O) from a surface ( 18a ) a cover layer ( 18 ) of a reflective coating ( 16 ) of an optical element ( 14 ), comprising: supplying a reducing gas (CO) to the surface ( 18a ), as well as radiation of radiation pulses ( 23 ) on the surface ( 18a ), wherein one wavelength (λ S ) of the radiation pulses ( 23 ) depending on the material of the cover layer ( 18 ) is selected.
DE201110079451 2011-07-20 2011-07-20 Optical arrangement, particularly projection exposure system for extreme ultraviolet lithography, has optical element with reflective coating, which has cover layer, on whose surface oxidic impurities are present Withdrawn DE102011079451A1 (en)

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