WO2023072745A1 - Projection exposure apparatus, method for operating the projection exposure apparatus - Google Patents

Projection exposure apparatus, method for operating the projection exposure apparatus Download PDF

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Publication number
WO2023072745A1
WO2023072745A1 PCT/EP2022/079334 EP2022079334W WO2023072745A1 WO 2023072745 A1 WO2023072745 A1 WO 2023072745A1 EP 2022079334 W EP2022079334 W EP 2022079334W WO 2023072745 A1 WO2023072745 A1 WO 2023072745A1
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WO
WIPO (PCT)
Prior art keywords
pressure
projection exposure
exposure apparatus
housing
pressure sensor
Prior art date
Application number
PCT/EP2022/079334
Other languages
French (fr)
Inventor
Dirk Ehm
Tobias Harter
Heiner Zwickel
Matthias Hillenbrand
Original Assignee
Carl Zeiss Smt Gmbh
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Carl Zeiss Smt Gmbh filed Critical Carl Zeiss Smt Gmbh
Publication of WO2023072745A1 publication Critical patent/WO2023072745A1/en

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Classifications

    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/708—Construction of apparatus, e.g. environment aspects, hygiene aspects or materials
    • G03F7/7085—Detection arrangement, e.g. detectors of apparatus alignment possibly mounted on wafers, exposure dose, photo-cleaning flux, stray light, thermal load
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L11/00—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00
    • G01L11/02—Measuring steady or quasi-steady pressure of a fluid or a fluent solid material by means not provided for in group G01L7/00 or G01L9/00 by optical means
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/708—Construction of apparatus, e.g. environment aspects, hygiene aspects or materials
    • G03F7/70808—Construction details, e.g. housing, load-lock, seals or windows for passing light in or out of apparatus
    • G03F7/70841—Constructional issues related to vacuum environment, e.g. load-lock chamber
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/708—Construction of apparatus, e.g. environment aspects, hygiene aspects or materials
    • G03F7/70858—Environment aspects, e.g. pressure of beam-path gas, temperature
    • G03F7/70883—Environment aspects, e.g. pressure of beam-path gas, temperature of optical system

Definitions

  • Projection exposure apparatus method for operating the projection exposure apparatus
  • the invention relates to a microlithographic projection exposure apparatus, in particular an EUV projection exposure apparatus, having a housing enclosing an interior space and at least one optical component arranged in the housing and also at least one pressure measurement unit arranged in the interior space.
  • the invention also relates to a method for operating the projection exposure apparatus.
  • Microlithographic projection exposure apparatuses are used to produce microstructured or nanostructured components for microelectronics or microsystems technology.
  • a corresponding projection exposure apparatus must be capable of imaging structures contained on a reticle exactly onto a substrate, for example a wafer.
  • a wavelength of 13.5 nm is used to achieve a corresponding resolution on the substrate. Due to a lack of suitable light-transmissive materials in this wavelength range, mirrors are used as optical components for the imaging process. Due to the low transmission of all gases at wavelengths in the range of 13.5 nm, it is necessary to operate projection exposure apparatuses of such designs at vacuum pressure conditions.
  • the optical elements or optical components, in particular mirrors, of the projection exposure apparatus have no contaminations or soiling on their active optical surfaces, if possible, in order to avoid limitations on the imaging quality caused by soiling.
  • a gas atmosphere in particular a hydrogen atmosphere, typically prevails in an EUV projection exposure apparatus.
  • Document WO 2008/034582 A2 describes a microlithographic projection exposure apparatus having a housing enclosing an interior space and at least one optical component arranged in the housing and also at least one pressure measurement unit arranged in the interior space.
  • the pressure measurement unit is embodied as a residual gas analyser, with which a pressure, in particular a hydrogen atmosphere pressure, is captured.
  • a pressure in particular a hydrogen atmosphere pressure
  • a pressure distribution in the interior space is typically determined by way of computer-assisted simulations, for example using the computational fluid dynamics (CFD) method, as it is known. Verification of the simulations by way of experimental measurements, in particular by using a multiplicity of residual gas analysers, is not possible, as described above.
  • CFD computational fluid dynamics
  • both the pressure, in particular the pressure of the gas atmosphere or hydrogen atmosphere, and changes in the pressure during operation of the projection exposure apparatus are not exactly determinable or ascertainable for every location of the projection exposure apparatus.
  • any knowledge relating to the pressure, in particular relating to pressure changes, in specific regions of the projection exposure apparatus is an important and critical piece of information, since the pressure has or can have a direct influence on the contamination of the optical components, a positioning accuracy of a respective optical component, a selection of a material of the optical component and/or a zero-crossing temperature of the respective optical component.
  • the pressure capture element is embodied in the form of a photonic pressure sensor.
  • “Photonic pressure sensor” in the present case is understood to mean a sensor unit that captures or ascertains a pressure on the basis of one or more pieces of light information. Said light information can be, for example, intensity information, phase information, polarization information and/or wavelength information.
  • the advantage here is that the photonic pressure sensor can be embodied to be particularly compact and space-saving. This ensures that a multiplicity of photonic pressure sensors are arrangeable in the interior space of the projection exposure apparatus and, in addition, that a particularly precise pressure determination is performable at in particular a plurality of, preferably at any desired number of, locations within the projection exposure apparatus.
  • the use of a plurality of photonic pressure sensors enables in particular continuous ascertainability of the pressure or a pressure distribution within the projection exposure apparatus.
  • By continuously ascertaining the pressure distribution it is possible to capture or ascertain dynamics, in particular pressure dynamics, during the operation of the projection exposure apparatus.
  • it is possible depending on the knowledge of those dynamics to take measures for counteracting a critical or contamination-promoting pressure or a correspondingly critical pressure change.
  • the fact that the photonic pressure sensor is able to be embodied in a compact and installation-space-saving manner additionally has the advantage that a contamination contribution by the pressure sensor itself is minimal.
  • Pressure in the present case is understood to mean an overall pressure composed of a plurality of partial pressures, or a specific partial pressure, for example a hydrogen partial pressure.
  • the projection exposure apparatus has at least one partial housing arranged in the housing, wherein this partial housing at least partially encloses the at least one optical component of the projection exposure apparatus, and wherein the photonic pressure sensor captures a pressure within the partial housing.
  • the pressure or partial pressure is capturable at a specifiable location in the vicinity or in the region of the optical component. This provides pressure information and, depending thereon, in particular also contamination information for the location or the component at which a contamination can have a particularly critical influence.
  • the pressure sensor is preferably arranged inside the partial housing, for example at a wall of the partial housing.
  • the projection exposure apparatus preferably has a plurality of partial housings, wherein each of the partial housings at least partially encloses an optical component in each case, and wherein at least one pressure sensor is arranged in each of the partial housings in each case. This ensures the ability to ascertain a pressure distribution within the projection exposure apparatus.
  • the partial housing preferably forms a vacuum partial environment, or what is known as a “mini environment”, around the respective optical component.
  • the photonic pressure sensor is arranged, or arrangeable, at the optical component.
  • the advantage in this case is that the pressure or partial pressure is capturable immediately or directly at the optical component. This ensures a particularly precise knowledge of the pressure or partial pressure at the location at which a contamination can have a particularly critical influence, in particular at the optical surface or on the light-reflective side of the optical component.
  • the photonic pressure sensor has at least one optical waveguide element and/or at least one optical sensor element.
  • the optical waveguide element is preferably formed from a glass material, polymer material and/or from silicon nitride.
  • the optical waveguide element serves to guide light or light radiation that has been coupled into the waveguide element.
  • the optical sensor element is in particular a photodetector or a 4-quadrant diode.
  • the photonic pressure sensor is based on a membrane, wherein the pressure sensor has a deformable membrane and wherein the membrane is deformed depending on the pressure.
  • membrane parameters in particular depending on a membrane material, a membrane material thickness or a membrane flexibility, it is possible to realize a specifiable response behaviour or a specifiable membrane sensitivity.
  • the membrane-based pressure sensor preferably has a substrate, in particular a semiconductor substrate, in which a cavity is formed that is covered or closed by the membrane.
  • the cavity preferably has a specifiable cavity pressure or reference pressure.
  • the membrane-based photonic pressure sensor is embodied such that the at least one optical waveguide element and/or the optical sensor element is coupled, or is able to be coupled, to the deformable membrane.
  • the advantage here is that the pressure or a pressure change is easily capturable. “Coupled” in the present case is understood to mean that an operative connection exists between the membrane and the waveguide element and/or between the membrane and the sensor element.
  • the operative connection is in particular an optical and/or mechanical operative connection.
  • the at least one optical waveguide element is additionally coupled, or able to be coupled, to at least one further optical waveguide element.
  • the photonic pressure sensor is embodied in a non- membrane-based manner and captures the pressure depending on a change in refractive index of a reference element that has a specified or specifiable reference refractive index.
  • the reference element in particular the reference element material, has a specified or specifiable refractive index or reference refractive index that changes or can change depending on a pressure change.
  • the reference element is in particular the waveguide element formed from glass material, polymer material and/or silicon nitride, preferably the cladding of the waveguide element.
  • the reference element, in particular the cladding of the waveguide element has a coating that is permeable to hydrogen or another element.
  • the mem- brane-based photonic pressure sensor is embodied to capture the pressure depending on a change in refractive index of a reference element that has a specified or specifiable reference refractive index.
  • the photonic pressure sensor is an integral part of an optical pressure capture unit, wherein the pressure capture unit has at least one light source and also at least one light capture element.
  • the light source serves for generating light, which is injected into the waveguide element of the pressure sensor and is guided through the waveguide element.
  • the light source is, for example, a laser or a laser diode, in particular a static or tunable laser.
  • the light source is a broadband light source.
  • the light capture element serves for capturing the light that is guided through the waveguide element.
  • the light capture element is, for example, a photodetector for capturing a light intensity or an interferogram, or a spectrometer for capturing a specifiable wavelength, in particular a resonance wavelength.
  • the pressure sensor is embodied to capture a pressure of at least 0.1 Pa and at most 1000 Pa, preferably at least 1 Pa and at most 200 Pa, with particular preference at least 1 Pa and at most 20 Pa.
  • the at least one optical component is arranged in a hydrogen atmosphere.
  • Figure 1 shows an EUV projection exposure apparatus with a photonic pressure sensor according to one exemplary embodiment
  • Figure 2 shows an EUV projection exposure apparatus with a plurality of photonic pressure sensor according to one exemplary embodiment
  • Figures 3A to 3G show various exemplary variants of a membrane-based photonic pressure sensor for use in a projection exposure apparatus
  • Figures 4A and 4B show various exemplary variants of a non-membrane-based photonic pressure sensor for use in a projection exposure apparatus
  • Figure 5 shows a schematic illustration of an optical pressure capture unit according to one exemplary embodiment.
  • FIG. 1 shows a simplified illustration of a microlithographic projection exposure apparatus 100, in particular a microlithographic EUV projection exposure apparatus.
  • the projection exposure apparatus 100 has a housing 101 enclosing an interior space, at least one, in the present case a plurality of, optical components 102 to 112, in particular mirrors, arranged in the housing 101 , and at least one pressure capture element 113 arranged in the housing 101 for capturing a pressure within the housing 101 .
  • the pressure capture element 113 is embodied in the form of a photonic pressure sensor 114.
  • the projection exposure apparatus 100 furthermore has, according to the exemplary embodiment, a radiation source 115, in particular an EUV light source, an illumination system 116 for illuminating an object field 117 in an object plane 118, and a projection system 119.
  • a reticle 120 which is arranged or arrangeable in the object field 117 and is held by a reticle holder 121 , is illuminated by the illumination system 116.
  • the projection system 119 serves for imaging the object field 117 into an image field 122 in an image plane 123.
  • a structure on the reticle 120 is imaged onto a light-sensitive layer of a wafer 124 which is arranged in the region of the image field 122 in the image plane 123 and is held by a wafer holder 125.
  • the wafer is formed in particular from a semiconductor material, for example from silicon.
  • the radiation source 115 emits EUV radiation 126, in particular in the range of between 5 nm and 30 nm, in particular 13.5 nm.
  • at least one of the optical components 102 to 112, in particular each of the optical components 102 to 112, is embodied to be controllable, in particular for the respective alignability or positionability.
  • the EUV radiation 126 generated using the radiation source 115 is aligned by means of a collector mirror (not illustrated here), which is integrated in the radiation source 115, in such a way that the EUV radiation 126 passes through an intermediate focus 127 in the region of an intermediate focal plane before the EUV radiation 126 is then incident on a first one of the optical components 102, in the present case a field facet mirror 128. Downstream of the field facet mirror 128, the EUV radiation 126 is guided onto a second one of the optical components 103, in the present case a pupil facet mirror 129. Next, the light is guided through the further optical components 104, 105, 106 to the object field 117.
  • the reticle 120 that is arranged or arrangeable in the object field 117 is, for example, a reflective photomask which has reflective and non-reflective, or at least less strongly reflective, regions for producing at least one structure to be imaged.
  • the reticle 120 is formed by a plurality of micro-mirrors which are arranged in a one-dimensional or multi-dimensional arrangement and are preferably movable about at least one axis.
  • the reticle 120 reflects some of the EUV radiation 126 coming from the illumination system 116 into the projection system 119 and shapes the light reflected into the projection system 119 in a manner such that the information relating to the structure of the reticle 120 is transferred to the image plane 123 by means of the projection system 119.
  • the projection lens 119 has, without being limited to this number, six optical components or optical elements 107 to 112.
  • the projection exposure apparatus 100 has at least one partial housing 130 arranged in the housing 101 , wherein this partial housing 130 at least partially encloses at least one optical component 102, according to the present exemplary embodiment the field facet mirror 128.
  • the partial housing 130 serves for avoiding or at least minimizing a contamination of the region at least partially enclosed by the partial housing 130, in particular a contamination of the optical component 102, 128.
  • a purge gas unit 131 is connected or connectable to the partial housing 130 to feed a purge gas 132, for example hydrogen (H2) or carbon monoxide (CO), to the interior space of the partial housing 130.
  • a purge gas 132 for example hydrogen (H2) or carbon monoxide (CO)
  • the purge gas 132 ensures that the optical component 102, 128, in particular the surface or light-reflective side of the optical component 102, 128, is arranged in a hydrogen atmosphere and is consequently protected against potential contaminants and/or is cleaned or can be cleaned to be free from said potential contaminants.
  • the pressure sensor is in particular embodied to capture a pressure of at least 0.1 Pa and at most 1000 Pa, preferably at least 1 Pa and at most 200 Pa, with particular preference at least 1 Pa and at most 20 Pa.
  • the photonic pressure sensor is arranged in particular directly at the optical component 102, in the present case the field facet mirror 128.
  • the photonic pressure sensor 114 is arranged or arrangeable at any desired location within the partial housing 130 or housing 101.
  • the projection exposure apparatus is embodied in the form of a DUV projection exposure apparatus, wherein the optical components in this case in particular take the form of lens elements and/or mirrors.
  • the illustration or positioning of the partial housing 130 in figure 1 should be understood to be by way of example.
  • the radiation source 115, the reticle holder 121 including the reticle 120 and/or the wafer holder 125 including the wafer 124 and/or the illumination system 116 and/or the projection system 119 are also at least partially enclosed or enclosable by a partial housing 130. This makes it possible to determine a pressure even at those locations by means of pressure sensors accordingly arranged in these partial housings.
  • the projection exposure apparatus has no partial housing 130, wherein the at least one photonic pressure sensor 114 is then arranged or arrangeable at any desired location within the housing 101 .
  • the at least one pressure capture element is a Pirani pressure sensor, in particular a miniature Pirani pressure sensor.
  • the Pirani pressure sensor is in particular an infrared sensor having at least one thermal column.
  • the thermal column serves for measuring a temperature of an object by capturing infrared radiation of the object.
  • the object is, for example, an optical component of the projection exposure apparatus.
  • FIG. 2 shows the projection exposure apparatus described in connection with Figure 1 , wherein according to the present exemplary embodiment the projection exposure apparatus has, in addition to the partial housing 130, further partial housings 133, 134, 135 and 136.
  • Each of the further partial housings 133, 134, 135, 136 is in the present case assigned to a respective one of the optical components 103, 104, 105, 106 of the illumination system 116.
  • each of the partial housings 133-136 has a respective photonic pressure sensor 137, 138, 139, 140, wherein in particular each of the pressure sensors 137-140 is arranged directly at the respective optical component 103, 104, 105 and 106. This ensures that precise and in particular continuous pressure ascertainment is performable for the entire illumination system 116 in particular during operation.
  • at least one of the further or each of the further partial housings has at least one purge gas unit connected thereto.
  • At least one partial housing 130 is assigned to at least one optical component 107, 108, 109, 110, 111 , 112, in particular to all optical components 107-112, of the projection system 119.
  • two partial housings that are adjacent in the beam path of the EUV radiation 126 are directly connected to each other.
  • two partial housings that are adjacent in the beam path of the EUV radiation 126 have a common opening for letting through EUV radiation 126 and/or purge gas. This ensures in particular a targeted distributability of the purge gas to contamination-critical locations, in particular to the light-reflective surfaces of the respective optical components of the illumination system 116 and/or of the projection system 119.
  • at least one photonic pressure sensor is positioned or positionable at a connecting point and/or in the region of the common opening. This is particularly advantageous in the regions or at the connecting points of the reticle holder 121 , of the wafer holder 125 and/or of the intermediate focus 127.
  • a partial housing at least partially encloses at least two optical components.
  • FIGS 3A to 3G show different variants of a membrane-based photonic pressure sensor.
  • Each of the membrane-based pressure sensors has a cavity which is formed in a substrate, in particular semiconductor substrate, of the pressure sensor.
  • the cavity is covered or closed by the membrane.
  • the cavity has a specifiable cavity pressure or reference pressure.
  • the membrane is deformable, wherein the membrane is deformed depending on a pressure P or a pressure change in the interior space of the housing and/or partial housing.
  • Figure 3A shows, according to a first exemplary embodiment, a membrane-based photonic pressure sensor 300a, which has at least one optical waveguide element 301 a, for example an optical fibre.
  • the optical waveguide element 301 a in the present case is connected to a light source (not illustrated here), through which light is radiated into the optical waveguide element 301 a.
  • the optical waveguide element 301 a of the pressure sensor 300a in the present case is coupled, in particular mechanically coupled, to a deformable membrane 302a in a manner such that the optical waveguide element 301 a is arranged in the membrane 302a.
  • the optical waveguide element 301 a is likewise deformed depending on a pressure-dependent deformation of the membrane 302a, in particular in relation to its geometric length, for example by stretching or compression.
  • a deformation of the membrane 302a influences the light guided through the waveguide element 301 a, in particular by changing total internal reflection properties of the waveguide element, in a manner such that a light intensity or a resonance wavelength of the light guided through the waveguide element 301 a changes or can change.
  • the light intensity is captured by means of a light capture element (not illustrated here), for example a photodetector or an interferometer.
  • the resonance wavelength is preferably captured by a spectrometer.
  • phase or a phase change brought about by a change in the geometric length of the waveguide element 301 a or a change in the time of flight of the light is captured.
  • the phase change or change in time of flight is capturable or ascertainable for example by way of an interferometer, in particular a Mach-Zehnder interferometer or multimode interferometer, or by way of a resonance arrangement, for example a ring resonator, a racetrack resonator or a Fabry-Perot resonator.
  • the pressure is ascertained in dependence on the captured light intensity or light intensity information, the captured resonance wavelength or wavelength information, the captured phase and/or phase information.
  • the pressure is captured or ascertained on the basis of a captured actual light intensity.
  • monitoring is preferably performed for a deviation of the captured actual light intensity from a specifiable target light intensity.
  • a pressure change is determined or ascertained.
  • the arrangement of the waveguide element 301 a in the membrane 302a has the advantage that the waveguide element is substantially shielded against external influences at least in the region of the membrane.
  • Figure 3B shows, according to a second exemplary embodiment, a membrane-based photonic pressure sensor 300b, which has at least one optical waveguide element 301 b.
  • the waveguide element 301 b in the present case is arranged on a bottom of a cavity 303b or of the pressure sensor 300b.
  • the waveguide element 301 b has a specifiable refractive index or reference refractive index that changes or can change depending on a pressure change. In the event that a hydrogen atmosphere is present in the interior space of the cavity 303b, the refractive index is changed in particular in dependence on a pressure-related increase or decrease of a hydrogen concentration on or in the cladding material of the waveguide element 301 b.
  • the reference refractive index is changed in dependence on another inert gas or element, for example nitrogen.
  • the change in refractive index influences the light guided through the waveguide element 301 b, in particular a light intensity which is captured or capturable by a light capture element.
  • the pressure or a pressure change is ascertained on the basis of the light intensity captured.
  • the change in refractive index influences a resonance wavelength of the light guided through the waveguide element, wherein the resonance wavelength is captured or capturable by a spectrometer.
  • the waveguide element 301 b in particular the cladding of the waveguide element 301 b, has a coating, for example a nanopore coating or an organometallic coating, which is permeable or transmissive to in particular hydrogen.
  • a coating for example a nanopore coating or an organometallic coating, which is permeable or transmissive to in particular hydrogen.
  • Figure 3C shows, according to a third exemplary embodiment, a membrane-based photonic pressure sensor 300c, which has two optical waveguide elements 301 c1 , 301 c2.
  • the two waveguide elements 301 c1 and 301 c2 are arranged at a distance from each other within an interior space 303c that is encapsulated by a membrane 302c and in the present case are coupled to each other for the transmission of light signals.
  • the waveguide elements 301 c1 and 301 c2 each have a specifiable refractive index or reference refractive index that changes or can change depending on a pressure change. The change in refractive index influences the light guided through the respective waveguide element.
  • a change in refractive index for light or a light component it is possible here in dependence on a change in refractive index for light or a light component to emerge from one of the waveguide elements 301 c1 and 301 c2 and penetrate into the other one of the waveguide elements.
  • the change in the light intensity in at least one of the two waveguide elements 301 c1 and 301 c2 is capturable or ascertainable by way of a light capture element (not illustrated here), in particular a photodetector or an interferometer.
  • a change in a resonance wavelength is captured by a spectrometer.
  • Figure 3D shows, according to a fourth exemplary embodiment, a membrane-based photonic pressure sensor 300d, which has two optical sensor elements 301 d1 and 301 d2 within an interior space 303d encapsulated by a membrane 302d which are each embodied, for example, as 4-quadrant diodes.
  • the optical sensor elements 301 d1 and 301 d2 are in the present case optically coupled to the deformable membrane 302d such that each of the sensor elements 301 d1 and 301 d2 captures a light intensity of light that is reflected at the membrane 302d.
  • the deformation of the membrane 302d or the pressure is then ascertained in dependence on the light intensity captured.
  • the light is radiated for example by a light source (not illustrated here) or measurement light source onto the membrane 302d.
  • the pressure sensor has only one optical sensor element.
  • the light intensity is measured by means of an interferometer.
  • Figure 3E shows, in accordance with a fifth exemplary embodiment 300e a membranebased photonic pressure sensor which has an optical sensor element 301 e1 , which is embodied for example as 4-quadrant diode, and a light source 301 e2 within an interior space 303e encapsulated by a membrane 302e.
  • the optical sensor element 301 e1 is in the present case coupled to the deformable membrane 302e such that the sensor element captures a light intensity of light that is reflected at the membrane 302e.
  • the light is radiated by the light source 301 e2 onto the membrane 302e.
  • the light intensity is measured by means of an interferometer.
  • Figure 3F and Figure 3G show, according to a sixth and seventh exemplary embodiment, in each case a membrane-based photonic pressure sensor 300f and 300g, which at least each have two optical waveguide elements 301f1 , 301f2 and 301 g1 , 301 g2, which are arranged such that they form a resonance arrangement.
  • the resonance arrangement is for example a ring resonator arrangement, a Bragg grating or a photonic crystal.
  • the resonance frequency or resonance wavelength of the resonance arrangement is changed in dependence on a deformation of a membrane 302f and 302g, respectively. This is capturable for example by a spectrometer.
  • the two waveguides are arranged next to each other such that they are in contact.
  • FIG 3G one of the waveguide elements is arranged on the bottom of the cavity 303g and, at a distance therefrom, the other of the waveguide elements is arranged on a lower side of the membrane.
  • Figure 4A shows, according to a first exemplary embodiment, a non-membrane-based photonic pressure sensor 400a, which has at least one optical waveguide element, in the present case two optical waveguide elements 401 a, 402a.
  • a first of these waveguide elements 401 a is at least substantially circular or annular, and a second of these waveguide elements 402a is at least substantially linear.
  • the first and the second waveguide element 401 a, 402a in the present case form a ring resonator.
  • At least one of the waveguide elements, in particular the cladding material thereof, preferably has a specifiable refractive index or reference refractive index that changes or can change depending on a pressure change.
  • the change in the refractive index takes place in particular in dependence on a pressure-related increase or decrease of a hydrogen concentration on or in the cladding material of the waveguide element.
  • the reference refractive index is changed in dependence on another inert gas or element, for example nitrogen.
  • the refractive index of the linear waveguide element in the present case changes, for pressure-related reasons, due to an accumulation of hydrogen on the surface of the linear waveguide element.
  • this causes a change in a light 403a which emerges from the linear optical waveguide 402a and couples in an intermediate region 404a with the annular waveguide element 401 a.
  • This change in the emerging light brings about a change in the coupling, in particular the resonance frequency of the ring resonator, or a change in an effective mode index.
  • the resonance frequency is preferably capturable by a detector 405a, in particular a spectrometer.
  • the pressure is ascertained or captured on the basis of the resonance frequency captured.
  • a light intensity of the light guided through one of the waveguides is captured by means of a photodetector or interferometer.
  • the pressure is ascertained or captured on the basis of the light intensity captured.
  • the refractive index of the ring-shaped waveguide element 401 a changes, for pressure-related reasons, due to an accumulation of hydrogen on the surface of the ring-shaped waveguide element. This also brings about a change in the emerging light 403a and thus a change in the coupling, in particular the resonance frequency of the ring resonator, or a change in an effective mode index.
  • a Bragg grating what is known as a distributed feedback grating (DFB grating), a photonic crystal or a grating having a grating period that is smaller than a specifiable light wavelength, for example the measurement light wavelength.
  • feedback loops for example a Pound-Drever-Hall loop
  • the presence of gas can also change absorption of light capturable by a photodetector within the waveguide element.
  • the spectrometer has integrated spectral filters, for example arranged waveguide element gratings, Vernier filters, multimode interference filters and/or cascaded interferometers.
  • a change in a propagation coefficient brought about by a change in the emerging light is captured.
  • the change in the propagation coefficient is preferably captured by an interferometer.
  • the pressure is ascertained or captured on the basis of the propagation coefficient captured.
  • At least one of the waveguide elements has an oxide cladding.
  • the waveguide element that forms a reference arm of the interferometer has the oxide cladding. In this way, particularly small pressure changes are capturable or ascertainable.
  • Figure 4B shows the non-membrane-based photonic pressure sensor from Figure 4A with the difference that, in the present case, one of the two waveguide elements 401 b, 402b has at least in part a coating that is permeable or transmissive to in particular hydrogen.
  • the ring-shaped waveguide element 401 b in particular the cladding of the waveguide element, has this coating, which is for example a nanopore coating or an organometallic coating.
  • the coating is embodied as what is known as surface anchored metal organic frameworks (SURMOF).
  • SURMOF surface anchored metal organic frameworks
  • the pressure or partial pressure can be locally increased due to selectively reducing intermolecular interactions and thus a sensitivity can be improved.
  • the waveguide element has at least one binding site for hydrogen.
  • the coating and/or the binding site brings about a targeted binding of hydrogen 406b. This ensures an improvement and a settability of a selectivity or a sensitivity for hydrogen.
  • Light 403b emerging from the linear waveguide element 402b couples to the ring- shaped waveguide element 401 b in an intermediate region 404b, which is able to be registered by a detector 405b.
  • Figure 5 shows a schematic illustration of an optical pressure capture unit 500 according to one exemplary embodiment.
  • the pressure capture unit in the present case is arranged at an optical component 501 of a projection exposure apparatus 502, wherein the optical component 501 is at least partially enclosed by a partial housing.
  • the pressure capture unit 500 in the present case has a plurality of integral parts. It has a membrane-based photonic pressure sensor 503 with a membrane and a circular waveguide element 504.
  • the pressure sensor 503 is in particular embodied such that a cavity formed in a substrate of the pressure sensor is covered or closed by the membrane.
  • the pressure capture unit furthermore has at least one light source 505, an inlet waveguide element 506, a first waveguide coupling element 507, a linear waveguide element 508, a second waveguide coupling element 509, an outlet waveguide element 510 and a light capture element 511 .
  • the circular waveguide element 504 forms a measurement arm and the linear waveguide element 508 forms a reference arm of an interferometer, wherein the light capture element 511 is embodied to capture an interferogram.
  • the light capture element 511 is embodied to capture an interferogram.
  • all integral parts of the pressure capture unit 500 are arranged on the optical component 501 , that is to say on the light-reflective side or front side of the optical component 501.
  • all integral parts are formed on a substrate of the pressure capture unit 500.
  • the integral parts of the pressure capture unit 500 are arranged on the light-reflective side of the optical component 501 .
  • the remaining integral parts are preferably arranged on the non-reflective side, or a rear side, of the optical component 501 .
  • the remaining integral parts are arrangeable at any desired location in the interior space of the housing and/or of the partial housing. Independently of their arrangement, the integral parts are connected to one another for signal transmission, in particular with respect to both optical signals and electrical signals.
  • the pressure sensor 503 or the pressure measurement unit 500 has in particular an area of one or more square millimetres.
  • the ability of the photonic pressure sensor 503 or the pressure measurement unit 500 to have a compact design has the advantage that a contamination contribution by the pressure sensor 503 itself is minimal.
  • the pressure capture unit 500 has a light source 505, a light capture element 511 and a pressure sensor 503.
  • the pressure capture unit 500 has a plurality of pressure sensors 503. It is advantageous here that a plurality of pressure sensors 503, in particular the waveguide elements 504 of the respective pressure sensors 503, are supplied with light by way of one and the same light source 505 and are or can be optically read by one and the same light capture element 511 .
  • the use of a plurality of pressure sensors 503 has the advantage that a pressure range that is specifiable in its broadness is capturable, wherein each individual one of the plurality of pressure sensors 503 is settable in terms of its sensitivity to a specifiable partial region of said pressure range.
  • a settability is brought about in the membrane-based pressure sensor in particular in dependence on a corresponding realization of specific membrane properties of the respective mem- brane-based pressure sensor, for example by a formation with a specifiable membrane thickness, a specifiable membrane material and/or a specifiable geometric dimension.
  • the light source 505 of the pressure capture unit 500 is an in particular broadband light source.
  • a plurality of pressure sensors 503 that are separated spectrally in terms of their respective response behaviour can be combined with one another.
  • the advantage here is that the number of light sources 505, light capture elements 511 and connecting waveguide elements within the projection exposure apparatus can be greatly reduced.
  • An optional implementation of a plurality of pressure sensors are fibre Bragg grating sensors (FBG sensors) with different grating periods (or other dispersive properties, such as the resonance frequency of a ring resonator), which are connected sequentially by waveguide elements (or are arranged at different locations of a waveguide element).
  • the FBG sensors are read in particular in parallel using a detector with a high spectral bandwidth.
  • the individual FBG sensors are assigned non-overlapping spectral partial bands. Each FBG sensor produces a spectral peak or trough in the transmitted or reflected signal.
  • the deformation information of the plurality of FBG sensors are acquired from the spectral positions of the peaks or troughs in the reflected or transmitted signal. In this way, the number of the sources and detectors and in particular the required number of waveguide elements in the projection exposure apparatus can be reduced.
  • wavelength-addressable photonic pressure sensors or ring resonators are also utilizable.
  • the pressure sensor 503 or the pressure capture unit 511 has at least one photonic temperature measurement unit, for example a temperature sensor.
  • the temperature measurement unit is preferably connected to a separate electronic circuit for signal transmission, in particular in order to ascertain measurement data from the temperature measurement unit.
  • the electronic circuit is a circuit of the pressure capture unit. This ensures that the number of waveguide elements in the projection exposure apparatus is as small as possible.

Abstract

Microlithographic projection exposure apparatus (100), in particular EUV projection exposure apparatus, having a housing (101) enclosing an interior space and at least one optical component (102, 128) arranged in the housing (101) and at least one pressure capture element (113), arranged in the housing, for capturing a pressure within the housing (101). Provision is made for the pressure capture element (113) to be a photonic pressure sensor (114, 503).

Description

Projection exposure apparatus, method for operating the projection exposure apparatus
Field of the invention
The invention relates to a microlithographic projection exposure apparatus, in particular an EUV projection exposure apparatus, having a housing enclosing an interior space and at least one optical component arranged in the housing and also at least one pressure measurement unit arranged in the interior space.
The invention also relates to a method for operating the projection exposure apparatus.
Background of the invention
Microlithographic projection exposure apparatuses are used to produce microstructured or nanostructured components for microelectronics or microsystems technology. In order to be able to exactly produce components with structures with extremely small dimensions in the nanometre and micrometre ranges, a corresponding projection exposure apparatus must be capable of imaging structures contained on a reticle exactly onto a substrate, for example a wafer.
In projection exposure apparatuses designed for the EUV range, typically a wavelength of 13.5 nm is used to achieve a corresponding resolution on the substrate. Due to a lack of suitable light-transmissive materials in this wavelength range, mirrors are used as optical components for the imaging process. Due to the low transmission of all gases at wavelengths in the range of 13.5 nm, it is necessary to operate projection exposure apparatuses of such designs at vacuum pressure conditions.
Due to the required resolution for EUV projection exposure apparatuses, it is necessary that the optical elements or optical components, in particular mirrors, of the projection exposure apparatus have no contaminations or soiling on their active optical surfaces, if possible, in order to avoid limitations on the imaging quality caused by soiling.
To avoid contaminations, a gas atmosphere, in particular a hydrogen atmosphere, typically prevails in an EUV projection exposure apparatus.
Regarding the use of pressure sensors within apparatus housings of projection exposure apparatuses, reference is made to documents US 2002/0051124 A1 and US 2003/0020888 A1. Documents US 2008/0087094 A1 , US 2012/0120380 A1 and US 2019/0086202 A1 furthermore disclose pressure sensors as part of distance sensors for the application of projection exposure apparatuses in microlithography.
Document WO 2008/034582 A2 describes a microlithographic projection exposure apparatus having a housing enclosing an interior space and at least one optical component arranged in the housing and also at least one pressure measurement unit arranged in the interior space. The pressure measurement unit is embodied as a residual gas analyser, with which a pressure, in particular a hydrogen atmosphere pressure, is captured. However, due to installation space restrictions regarding the projection exposure apparatus, such residual gas analysers are usable for capturing pressure only in very limited numbers and only in few specific regions of the projection exposure apparatus, in particular not directly at the optical components. Since a pressure is captured using the residual gas analyser only in the immediate environment of the residual gas analyser itself and the number of residual gas analysers is limited for installation space reasons, a pressure distribution in the interior space is typically determined by way of computer-assisted simulations, for example using the computational fluid dynamics (CFD) method, as it is known. Verification of the simulations by way of experimental measurements, in particular by using a multiplicity of residual gas analysers, is not possible, as described above.
For this reason, both the pressure, in particular the pressure of the gas atmosphere or hydrogen atmosphere, and changes in the pressure during operation of the projection exposure apparatus are not exactly determinable or ascertainable for every location of the projection exposure apparatus. However, any knowledge relating to the pressure, in particular relating to pressure changes, in specific regions of the projection exposure apparatus is an important and critical piece of information, since the pressure has or can have a direct influence on the contamination of the optical components, a positioning accuracy of a respective optical component, a selection of a material of the optical component and/or a zero-crossing temperature of the respective optical component.
It is therefore the object of the invention to provide an apparatus for capturing the pressure within the projection exposure apparatus that is space-saving, robust and suitable for the operating conditions of the projection exposure apparatus.
This object is achieved in accordance with the features of the independent patent claims.
Disclosure of the invention
According to the invention, the pressure capture element is embodied in the form of a photonic pressure sensor. “Photonic pressure sensor” in the present case is understood to mean a sensor unit that captures or ascertains a pressure on the basis of one or more pieces of light information. Said light information can be, for example, intensity information, phase information, polarization information and/or wavelength information. The advantage here is that the photonic pressure sensor can be embodied to be particularly compact and space-saving. This ensures that a multiplicity of photonic pressure sensors are arrangeable in the interior space of the projection exposure apparatus and, in addition, that a particularly precise pressure determination is performable at in particular a plurality of, preferably at any desired number of, locations within the projection exposure apparatus. In particular the use of a plurality of photonic pressure sensors enables in particular continuous ascertainability of the pressure or a pressure distribution within the projection exposure apparatus. By continuously ascertaining the pressure distribution, it is possible to capture or ascertain dynamics, in particular pressure dynamics, during the operation of the projection exposure apparatus. Furthermore, it is possible depending on the knowledge of those dynamics to take measures for counteracting a critical or contamination-promoting pressure or a correspondingly critical pressure change. The fact that the photonic pressure sensor is able to be embodied in a compact and installation-space-saving manner additionally has the advantage that a contamination contribution by the pressure sensor itself is minimal. “Pressure” in the present case is understood to mean an overall pressure composed of a plurality of partial pressures, or a specific partial pressure, for example a hydrogen partial pressure.
According to one embodiment, the projection exposure apparatus has at least one partial housing arranged in the housing, wherein this partial housing at least partially encloses the at least one optical component of the projection exposure apparatus, and wherein the photonic pressure sensor captures a pressure within the partial housing. The advantage in this case is that the pressure or partial pressure is capturable at a specifiable location in the vicinity or in the region of the optical component. This provides pressure information and, depending thereon, in particular also contamination information for the location or the component at which a contamination can have a particularly critical influence. The pressure sensor is preferably arranged inside the partial housing, for example at a wall of the partial housing. The projection exposure apparatus preferably has a plurality of partial housings, wherein each of the partial housings at least partially encloses an optical component in each case, and wherein at least one pressure sensor is arranged in each of the partial housings in each case. This ensures the ability to ascertain a pressure distribution within the projection exposure apparatus. The partial housing preferably forms a vacuum partial environment, or what is known as a “mini environment”, around the respective optical component.
According to one embodiment, the photonic pressure sensor is arranged, or arrangeable, at the optical component. The advantage in this case is that the pressure or partial pressure is capturable immediately or directly at the optical component. This ensures a particularly precise knowledge of the pressure or partial pressure at the location at which a contamination can have a particularly critical influence, in particular at the optical surface or on the light-reflective side of the optical component.
According to one development, the photonic pressure sensor has at least one optical waveguide element and/or at least one optical sensor element. The optical waveguide element is preferably formed from a glass material, polymer material and/or from silicon nitride. The optical waveguide element serves to guide light or light radiation that has been coupled into the waveguide element. The optical sensor element is in particular a photodetector or a 4-quadrant diode.
According to one embodiment, the photonic pressure sensor is based on a membrane, wherein the pressure sensor has a deformable membrane and wherein the membrane is deformed depending on the pressure. A pressure change in the interior space, in particular within the housing and/or partial housing, consequently leads to a capturable or ascertainable deformation or deformation change of the membrane. Depending on membrane parameters, in particular depending on a membrane material, a membrane material thickness or a membrane flexibility, it is possible to realize a specifiable response behaviour or a specifiable membrane sensitivity. The membrane-based pressure sensor preferably has a substrate, in particular a semiconductor substrate, in which a cavity is formed that is covered or closed by the membrane. The cavity preferably has a specifiable cavity pressure or reference pressure.
According to one embodiment, the membrane-based photonic pressure sensor is embodied such that the at least one optical waveguide element and/or the optical sensor element is coupled, or is able to be coupled, to the deformable membrane. The advantage here is that the pressure or a pressure change is easily capturable. “Coupled” in the present case is understood to mean that an operative connection exists between the membrane and the waveguide element and/or between the membrane and the sensor element. The operative connection is in particular an optical and/or mechanical operative connection. Optionally, the at least one optical waveguide element is additionally coupled, or able to be coupled, to at least one further optical waveguide element.
According to one development, the photonic pressure sensor is embodied in a non- membrane-based manner and captures the pressure depending on a change in refractive index of a reference element that has a specified or specifiable reference refractive index. The reference element, in particular the reference element material, has a specified or specifiable refractive index or reference refractive index that changes or can change depending on a pressure change. The reference element is in particular the waveguide element formed from glass material, polymer material and/or silicon nitride, preferably the cladding of the waveguide element. Optionally, the reference element, in particular the cladding of the waveguide element, has a coating that is permeable to hydrogen or another element. Alternatively or additionally, the mem- brane-based photonic pressure sensor is embodied to capture the pressure depending on a change in refractive index of a reference element that has a specified or specifiable reference refractive index.
According to one development, the photonic pressure sensor is an integral part of an optical pressure capture unit, wherein the pressure capture unit has at least one light source and also at least one light capture element. The light source serves for generating light, which is injected into the waveguide element of the pressure sensor and is guided through the waveguide element. The light source is, for example, a laser or a laser diode, in particular a static or tunable laser. Optionally, the light source is a broadband light source. The light capture element serves for capturing the light that is guided through the waveguide element. The light capture element is, for example, a photodetector for capturing a light intensity or an interferogram, or a spectrometer for capturing a specifiable wavelength, in particular a resonance wavelength.
According to one development, the pressure sensor is embodied to capture a pressure of at least 0.1 Pa and at most 1000 Pa, preferably at least 1 Pa and at most 200 Pa, with particular preference at least 1 Pa and at most 20 Pa.
According to one development, the at least one optical component is arranged in a hydrogen atmosphere.
The method according to the invention for operating the projection exposure apparatus is characterized by the features of Claim 12. The advantages already mentioned are evident therefrom. Further advantages and preferred features are evident from the description above and from the claims.
The invention will be explained in greater detail below with reference to the drawings.
In this respect: Figure 1 shows an EUV projection exposure apparatus with a photonic pressure sensor according to one exemplary embodiment,
Figure 2 shows an EUV projection exposure apparatus with a plurality of photonic pressure sensor according to one exemplary embodiment,
Figures 3A to 3G show various exemplary variants of a membrane-based photonic pressure sensor for use in a projection exposure apparatus,
Figures 4A and 4B show various exemplary variants of a non-membrane-based photonic pressure sensor for use in a projection exposure apparatus, and
Figure 5 shows a schematic illustration of an optical pressure capture unit according to one exemplary embodiment.
Figure 1 shows a simplified illustration of a microlithographic projection exposure apparatus 100, in particular a microlithographic EUV projection exposure apparatus. The projection exposure apparatus 100 has a housing 101 enclosing an interior space, at least one, in the present case a plurality of, optical components 102 to 112, in particular mirrors, arranged in the housing 101 , and at least one pressure capture element 113 arranged in the housing 101 for capturing a pressure within the housing 101 . The pressure capture element 113 is embodied in the form of a photonic pressure sensor 114.
The projection exposure apparatus 100 furthermore has, according to the exemplary embodiment, a radiation source 115, in particular an EUV light source, an illumination system 116 for illuminating an object field 117 in an object plane 118, and a projection system 119. A reticle 120, which is arranged or arrangeable in the object field 117 and is held by a reticle holder 121 , is illuminated by the illumination system 116. The projection system 119 serves for imaging the object field 117 into an image field 122 in an image plane 123. A structure on the reticle 120 is imaged onto a light-sensitive layer of a wafer 124 which is arranged in the region of the image field 122 in the image plane 123 and is held by a wafer holder 125. The wafer is formed in particular from a semiconductor material, for example from silicon. The radiation source 115 emits EUV radiation 126, in particular in the range of between 5 nm and 30 nm, in particular 13.5 nm. For controlling the radiation path of the EUV radiation 126, preferably at least one of the optical components 102 to 112, in particular each of the optical components 102 to 112, is embodied to be controllable, in particular for the respective alignability or positionability.
The EUV radiation 126 generated using the radiation source 115 is aligned by means of a collector mirror (not illustrated here), which is integrated in the radiation source 115, in such a way that the EUV radiation 126 passes through an intermediate focus 127 in the region of an intermediate focal plane before the EUV radiation 126 is then incident on a first one of the optical components 102, in the present case a field facet mirror 128. Downstream of the field facet mirror 128, the EUV radiation 126 is guided onto a second one of the optical components 103, in the present case a pupil facet mirror 129. Next, the light is guided through the further optical components 104, 105, 106 to the object field 117.
The reticle 120 that is arranged or arrangeable in the object field 117 is, for example, a reflective photomask which has reflective and non-reflective, or at least less strongly reflective, regions for producing at least one structure to be imaged. Alternatively, the reticle 120 is formed by a plurality of micro-mirrors which are arranged in a one-dimensional or multi-dimensional arrangement and are preferably movable about at least one axis.
The reticle 120 reflects some of the EUV radiation 126 coming from the illumination system 116 into the projection system 119 and shapes the light reflected into the projection system 119 in a manner such that the information relating to the structure of the reticle 120 is transferred to the image plane 123 by means of the projection system 119.
In the present exemplary embodiment, the projection lens 119 has, without being limited to this number, six optical components or optical elements 107 to 112. The projection exposure apparatus 100 has at least one partial housing 130 arranged in the housing 101 , wherein this partial housing 130 at least partially encloses at least one optical component 102, according to the present exemplary embodiment the field facet mirror 128. The partial housing 130 serves for avoiding or at least minimizing a contamination of the region at least partially enclosed by the partial housing 130, in particular a contamination of the optical component 102, 128.
According to the present exemplary embodiment, a purge gas unit 131 is connected or connectable to the partial housing 130 to feed a purge gas 132, for example hydrogen (H2) or carbon monoxide (CO), to the interior space of the partial housing 130. The purge gas 132 ensures that the optical component 102, 128, in particular the surface or light-reflective side of the optical component 102, 128, is arranged in a hydrogen atmosphere and is consequently protected against potential contaminants and/or is cleaned or can be cleaned to be free from said potential contaminants.
The pressure sensor is in particular embodied to capture a pressure of at least 0.1 Pa and at most 1000 Pa, preferably at least 1 Pa and at most 200 Pa, with particular preference at least 1 Pa and at most 20 Pa.
In the exemplary embodiment shown in Figure 1 , the photonic pressure sensor is arranged in particular directly at the optical component 102, in the present case the field facet mirror 128. Alternatively, the photonic pressure sensor 114 is arranged or arrangeable at any desired location within the partial housing 130 or housing 101.
Alternatively, the projection exposure apparatus is embodied in the form of a DUV projection exposure apparatus, wherein the optical components in this case in particular take the form of lens elements and/or mirrors.
The illustration or positioning of the partial housing 130 in figure 1 should be understood to be by way of example. Optionally, the radiation source 115, the reticle holder 121 including the reticle 120 and/or the wafer holder 125 including the wafer 124 and/or the illumination system 116 and/or the projection system 119 are also at least partially enclosed or enclosable by a partial housing 130. This makes it possible to determine a pressure even at those locations by means of pressure sensors accordingly arranged in these partial housings. Optionally, the projection exposure apparatus has no partial housing 130, wherein the at least one photonic pressure sensor 114 is then arranged or arrangeable at any desired location within the housing 101 .
As an alternative to the photonic pressure sensor, the at least one pressure capture element is a Pirani pressure sensor, in particular a miniature Pirani pressure sensor. The Pirani pressure sensor is in particular an infrared sensor having at least one thermal column. The thermal column serves for measuring a temperature of an object by capturing infrared radiation of the object. The object is, for example, an optical component of the projection exposure apparatus.
Figure 2 shows the projection exposure apparatus described in connection with Figure 1 , wherein according to the present exemplary embodiment the projection exposure apparatus has, in addition to the partial housing 130, further partial housings 133, 134, 135 and 136. Each of the further partial housings 133, 134, 135, 136 is in the present case assigned to a respective one of the optical components 103, 104, 105, 106 of the illumination system 116. Preferably, each of the partial housings 133-136 has a respective photonic pressure sensor 137, 138, 139, 140, wherein in particular each of the pressure sensors 137-140 is arranged directly at the respective optical component 103, 104, 105 and 106. This ensures that precise and in particular continuous pressure ascertainment is performable for the entire illumination system 116 in particular during operation. Optionally, at least one of the further or each of the further partial housings has at least one purge gas unit connected thereto.
In addition or alternatively, at least one partial housing 130 is assigned to at least one optical component 107, 108, 109, 110, 111 , 112, in particular to all optical components 107-112, of the projection system 119.
Preferably, two partial housings that are adjacent in the beam path of the EUV radiation 126 are directly connected to each other. Optionally, two partial housings that are adjacent in the beam path of the EUV radiation 126 have a common opening for letting through EUV radiation 126 and/or purge gas. This ensures in particular a targeted distributability of the purge gas to contamination-critical locations, in particular to the light-reflective surfaces of the respective optical components of the illumination system 116 and/or of the projection system 119. In the case of two adjacent partial housings, preferably at least one photonic pressure sensor is positioned or positionable at a connecting point and/or in the region of the common opening. This is particularly advantageous in the regions or at the connecting points of the reticle holder 121 , of the wafer holder 125 and/or of the intermediate focus 127. Optionally, a partial housing at least partially encloses at least two optical components.
Figures 3A to 3G show different variants of a membrane-based photonic pressure sensor. Each of the membrane-based pressure sensors has a cavity which is formed in a substrate, in particular semiconductor substrate, of the pressure sensor. The cavity is covered or closed by the membrane. The cavity has a specifiable cavity pressure or reference pressure. The membrane is deformable, wherein the membrane is deformed depending on a pressure P or a pressure change in the interior space of the housing and/or partial housing.
Figure 3A shows, according to a first exemplary embodiment, a membrane-based photonic pressure sensor 300a, which has at least one optical waveguide element 301 a, for example an optical fibre. The optical waveguide element 301 a in the present case is connected to a light source (not illustrated here), through which light is radiated into the optical waveguide element 301 a. The optical waveguide element 301 a of the pressure sensor 300a in the present case is coupled, in particular mechanically coupled, to a deformable membrane 302a in a manner such that the optical waveguide element 301 a is arranged in the membrane 302a. The optical waveguide element 301 a is likewise deformed depending on a pressure-dependent deformation of the membrane 302a, in particular in relation to its geometric length, for example by stretching or compression. A deformation of the membrane 302a influences the light guided through the waveguide element 301 a, in particular by changing total internal reflection properties of the waveguide element, in a manner such that a light intensity or a resonance wavelength of the light guided through the waveguide element 301 a changes or can change. The light intensity is captured by means of a light capture element (not illustrated here), for example a photodetector or an interferometer. The resonance wavelength is preferably captured by a spectrometer. Optionally or alternatively, a phase or a phase change brought about by a change in the geometric length of the waveguide element 301 a or a change in the time of flight of the light is captured. The phase change or change in time of flight is capturable or ascertainable for example by way of an interferometer, in particular a Mach-Zehnder interferometer or multimode interferometer, or by way of a resonance arrangement, for example a ring resonator, a racetrack resonator or a Fabry-Perot resonator.
The pressure is ascertained in dependence on the captured light intensity or light intensity information, the captured resonance wavelength or wavelength information, the captured phase and/or phase information.
According to one exemplary embodiment, the pressure is captured or ascertained on the basis of a captured actual light intensity. In this case, monitoring is preferably performed for a deviation of the captured actual light intensity from a specifiable target light intensity. In the event that the captured actual light intensity deviates from the target light intensity by more than a specifiable limit deviation, or in the event that the actual light intensity is not equal to the target light intensity, a pressure change is determined or ascertained.
The arrangement of the waveguide element 301 a in the membrane 302a has the advantage that the waveguide element is substantially shielded against external influences at least in the region of the membrane.
Figure 3B shows, according to a second exemplary embodiment, a membrane-based photonic pressure sensor 300b, which has at least one optical waveguide element 301 b. The waveguide element 301 b in the present case is arranged on a bottom of a cavity 303b or of the pressure sensor 300b. The waveguide element 301 b has a specifiable refractive index or reference refractive index that changes or can change depending on a pressure change. In the event that a hydrogen atmosphere is present in the interior space of the cavity 303b, the refractive index is changed in particular in dependence on a pressure-related increase or decrease of a hydrogen concentration on or in the cladding material of the waveguide element 301 b. Alternatively or additionally, the reference refractive index is changed in dependence on another inert gas or element, for example nitrogen. The change in refractive index influences the light guided through the waveguide element 301 b, in particular a light intensity which is captured or capturable by a light capture element. The pressure or a pressure change is ascertained on the basis of the light intensity captured. Alternatively, the change in refractive index influences a resonance wavelength of the light guided through the waveguide element, wherein the resonance wavelength is captured or capturable by a spectrometer.
Optionally, the waveguide element 301 b, in particular the cladding of the waveguide element 301 b, has a coating, for example a nanopore coating or an organometallic coating, which is permeable or transmissive to in particular hydrogen.
Figure 3C shows, according to a third exemplary embodiment, a membrane-based photonic pressure sensor 300c, which has two optical waveguide elements 301 c1 , 301 c2. The two waveguide elements 301 c1 and 301 c2 are arranged at a distance from each other within an interior space 303c that is encapsulated by a membrane 302c and in the present case are coupled to each other for the transmission of light signals. The waveguide elements 301 c1 and 301 c2 each have a specifiable refractive index or reference refractive index that changes or can change depending on a pressure change. The change in refractive index influences the light guided through the respective waveguide element. For example, it is possible here in dependence on a change in refractive index for light or a light component to emerge from one of the waveguide elements 301 c1 and 301 c2 and penetrate into the other one of the waveguide elements. The change in the light intensity in at least one of the two waveguide elements 301 c1 and 301 c2 is capturable or ascertainable by way of a light capture element (not illustrated here), in particular a photodetector or an interferometer. Alternatively, a change in a resonance wavelength is captured by a spectrometer.
Figure 3D shows, according to a fourth exemplary embodiment, a membrane-based photonic pressure sensor 300d, which has two optical sensor elements 301 d1 and 301 d2 within an interior space 303d encapsulated by a membrane 302d which are each embodied, for example, as 4-quadrant diodes. The optical sensor elements 301 d1 and 301 d2 are in the present case optically coupled to the deformable membrane 302d such that each of the sensor elements 301 d1 and 301 d2 captures a light intensity of light that is reflected at the membrane 302d. The deformation of the membrane 302d or the pressure is then ascertained in dependence on the light intensity captured. The light is radiated for example by a light source (not illustrated here) or measurement light source onto the membrane 302d. Alternatively, the pressure sensor has only one optical sensor element. According to an alternative embodiment, the light intensity is measured by means of an interferometer.
Figure 3E shows, in accordance with a fifth exemplary embodiment 300e a membranebased photonic pressure sensor which has an optical sensor element 301 e1 , which is embodied for example as 4-quadrant diode, and a light source 301 e2 within an interior space 303e encapsulated by a membrane 302e. The optical sensor element 301 e1 is in the present case coupled to the deformable membrane 302e such that the sensor element captures a light intensity of light that is reflected at the membrane 302e. In the present case, the light is radiated by the light source 301 e2 onto the membrane 302e. According to an alternative embodiment, the light intensity is measured by means of an interferometer.
Figure 3F and Figure 3G show, according to a sixth and seventh exemplary embodiment, in each case a membrane-based photonic pressure sensor 300f and 300g, which at least each have two optical waveguide elements 301f1 , 301f2 and 301 g1 , 301 g2, which are arranged such that they form a resonance arrangement. The resonance arrangement is for example a ring resonator arrangement, a Bragg grating or a photonic crystal. The resonance frequency or resonance wavelength of the resonance arrangement is changed in dependence on a deformation of a membrane 302f and 302g, respectively. This is capturable for example by a spectrometer. In Figure 3F, the two waveguides are arranged next to each other such that they are in contact. In Figure 3G, one of the waveguide elements is arranged on the bottom of the cavity 303g and, at a distance therefrom, the other of the waveguide elements is arranged on a lower side of the membrane. Figure 4A shows, according to a first exemplary embodiment, a non-membrane-based photonic pressure sensor 400a, which has at least one optical waveguide element, in the present case two optical waveguide elements 401 a, 402a. A first of these waveguide elements 401 a is at least substantially circular or annular, and a second of these waveguide elements 402a is at least substantially linear. The first and the second waveguide element 401 a, 402a in the present case form a ring resonator.
At least one of the waveguide elements, in particular the cladding material thereof, preferably has a specifiable refractive index or reference refractive index that changes or can change depending on a pressure change. The change in the refractive index takes place in particular in dependence on a pressure-related increase or decrease of a hydrogen concentration on or in the cladding material of the waveguide element. Alternatively or additionally, the reference refractive index is changed in dependence on another inert gas or element, for example nitrogen.
The refractive index of the linear waveguide element in the present case changes, for pressure-related reasons, due to an accumulation of hydrogen on the surface of the linear waveguide element. In the present case, this causes a change in a light 403a which emerges from the linear optical waveguide 402a and couples in an intermediate region 404a with the annular waveguide element 401 a. This change in the emerging light brings about a change in the coupling, in particular the resonance frequency of the ring resonator, or a change in an effective mode index. The resonance frequency is preferably capturable by a detector 405a, in particular a spectrometer. The pressure is ascertained or captured on the basis of the resonance frequency captured.
Alternatively or additionally, a light intensity of the light guided through one of the waveguides, for example the linear waveguide 402a, is captured by means of a photodetector or interferometer. The pressure is ascertained or captured on the basis of the light intensity captured.
Additionally or alternatively, the refractive index of the ring-shaped waveguide element 401 a changes, for pressure-related reasons, due to an accumulation of hydrogen on the surface of the ring-shaped waveguide element. This also brings about a change in the emerging light 403a and thus a change in the coupling, in particular the resonance frequency of the ring resonator, or a change in an effective mode index.
As an alternative to the ring resonator, other resonance structures are also usable for pressure determination, for example a Bragg grating, what is known as a distributed feedback grating (DFB grating), a photonic crystal or a grating having a grating period that is smaller than a specifiable light wavelength, for example the measurement light wavelength. Alternatively, feedback loops (for example a Pound-Drever-Hall loop) can be used to fix a laser at a resonance wavelength or resonance frequency and then measure a resulting frequency. Optionally, the presence of gas can also change absorption of light capturable by a photodetector within the waveguide element. Preferably, the spectrometer has integrated spectral filters, for example arranged waveguide element gratings, Vernier filters, multimode interference filters and/or cascaded interferometers.
Alternatively, a change in a propagation coefficient brought about by a change in the emerging light is captured. The change in the propagation coefficient is preferably captured by an interferometer. The pressure is ascertained or captured on the basis of the propagation coefficient captured.
According to one embodiment, at least one of the waveguide elements has an oxide cladding. Preferably the waveguide element that forms a reference arm of the interferometer has the oxide cladding. In this way, particularly small pressure changes are capturable or ascertainable.
Figure 4B shows the non-membrane-based photonic pressure sensor from Figure 4A with the difference that, in the present case, one of the two waveguide elements 401 b, 402b has at least in part a coating that is permeable or transmissive to in particular hydrogen.
In the present case, the ring-shaped waveguide element 401 b, in particular the cladding of the waveguide element, has this coating, which is for example a nanopore coating or an organometallic coating. In particular, the coating is embodied as what is known as surface anchored metal organic frameworks (SURMOF). In particular by using SURMOF, the pressure or partial pressure can be locally increased due to selectively reducing intermolecular interactions and thus a sensitivity can be improved. Alternatively or additionally, the waveguide element has at least one binding site for hydrogen.
The coating and/or the binding site brings about a targeted binding of hydrogen 406b. This ensures an improvement and a settability of a selectivity or a sensitivity for hydrogen. Light 403b emerging from the linear waveguide element 402b couples to the ring- shaped waveguide element 401 b in an intermediate region 404b, which is able to be registered by a detector 405b.
Figure 5 shows a schematic illustration of an optical pressure capture unit 500 according to one exemplary embodiment. The pressure capture unit in the present case is arranged at an optical component 501 of a projection exposure apparatus 502, wherein the optical component 501 is at least partially enclosed by a partial housing.
The pressure capture unit 500 in the present case has a plurality of integral parts. It has a membrane-based photonic pressure sensor 503 with a membrane and a circular waveguide element 504. The pressure sensor 503 is in particular embodied such that a cavity formed in a substrate of the pressure sensor is covered or closed by the membrane. The pressure capture unit furthermore has at least one light source 505, an inlet waveguide element 506, a first waveguide coupling element 507, a linear waveguide element 508, a second waveguide coupling element 509, an outlet waveguide element 510 and a light capture element 511 .
In the present case, the circular waveguide element 504 forms a measurement arm and the linear waveguide element 508 forms a reference arm of an interferometer, wherein the light capture element 511 is embodied to capture an interferogram. This ensures that it is possible to ascertain or capture a pressure or a pressure change on the basis of pressure-related phase shifts or changes in times of flight. Alternatively, the pressure or the pressure change is ascertained or captured on the basis of intensity information.
In the present case, all integral parts of the pressure capture unit 500 are arranged on the optical component 501 , that is to say on the light-reflective side or front side of the optical component 501. Preferably, all integral parts are formed on a substrate of the pressure capture unit 500.
Alternatively, only some of the integral parts of the pressure capture unit 500, in particular the pressure sensor 503, the membrane and at least one of the waveguide elements of the pressure sensor 503, are arranged on the light-reflective side of the optical component 501 . This ensures minimization of any possible contaminations on the light-reflective side of the optical component 501 that are produced or can be produced by the integral parts of the pressure capture unit 500. In this case, the remaining integral parts are preferably arranged on the non-reflective side, or a rear side, of the optical component 501 . Alternatively, the remaining integral parts are arrangeable at any desired location in the interior space of the housing and/or of the partial housing. Independently of their arrangement, the integral parts are connected to one another for signal transmission, in particular with respect to both optical signals and electrical signals.
The pressure sensor 503 or the pressure measurement unit 500 has in particular an area of one or more square millimetres. The ability of the photonic pressure sensor 503 or the pressure measurement unit 500 to have a compact design has the advantage that a contamination contribution by the pressure sensor 503 itself is minimal.
According to the present exemplary embodiment, the pressure capture unit 500 has a light source 505, a light capture element 511 and a pressure sensor 503. Alternatively, the pressure capture unit 500 has a plurality of pressure sensors 503. It is advantageous here that a plurality of pressure sensors 503, in particular the waveguide elements 504 of the respective pressure sensors 503, are supplied with light by way of one and the same light source 505 and are or can be optically read by one and the same light capture element 511 . The use of a plurality of pressure sensors 503 has the advantage that a pressure range that is specifiable in its broadness is capturable, wherein each individual one of the plurality of pressure sensors 503 is settable in terms of its sensitivity to a specifiable partial region of said pressure range. A settability is brought about in the membrane-based pressure sensor in particular in dependence on a corresponding realization of specific membrane properties of the respective mem- brane-based pressure sensor, for example by a formation with a specifiable membrane thickness, a specifiable membrane material and/or a specifiable geometric dimension.
According to an embodiment, the light source 505 of the pressure capture unit 500 is an in particular broadband light source. As a result, a plurality of pressure sensors 503 that are separated spectrally in terms of their respective response behaviour can be combined with one another. The advantage here is that the number of light sources 505, light capture elements 511 and connecting waveguide elements within the projection exposure apparatus can be greatly reduced. An optional implementation of a plurality of pressure sensors are fibre Bragg grating sensors (FBG sensors) with different grating periods (or other dispersive properties, such as the resonance frequency of a ring resonator), which are connected sequentially by waveguide elements (or are arranged at different locations of a waveguide element). The FBG sensors are read in particular in parallel using a detector with a high spectral bandwidth. The individual FBG sensors are assigned non-overlapping spectral partial bands. Each FBG sensor produces a spectral peak or trough in the transmitted or reflected signal. The deformation information of the plurality of FBG sensors are acquired from the spectral positions of the peaks or troughs in the reflected or transmitted signal. In this way, the number of the sources and detectors and in particular the required number of waveguide elements in the projection exposure apparatus can be reduced. As an alternative to the FBG sensor, wavelength-addressable photonic pressure sensors or ring resonators are also utilizable.
In accordance with one embodiment, the pressure sensor 503 or the pressure capture unit 511 has at least one photonic temperature measurement unit, for example a temperature sensor. The temperature measurement unit is preferably connected to a separate electronic circuit for signal transmission, in particular in order to ascertain measurement data from the temperature measurement unit. Optionally, the electronic circuit is a circuit of the pressure capture unit. This ensures that the number of waveguide elements in the projection exposure apparatus is as small as possible.

Claims

Claims:
1. Microlithographic projection exposure apparatus (100), in particular EUV projection exposure apparatus, having a housing (101 ) enclosing an interior space and at least one optical component (102, 128) arranged in the housing (101 ) and at least one pressure capture element (113), arranged in the housing (101 ), for capturing a pressure within the housing (101 ), characterized in that the pressure capture element (113) is a photonic pressure sensor (114, 503).
2. Projection exposure apparatus according to Claim 1 , characterized by at least one partial housing (130) arranged in the housing (101 ), wherein this partial housing (130) at least partially encloses the at least one optical component (102, 128) of the projection exposure apparatus, and wherein the photonic pressure sensor (114, 503) captures a pressure within the partial housing (130).
3. Projection exposure apparatus according to Claim 1 or 2, characterized in that the photonic pressure sensor (114, 503) is arranged or arrangeable at the optical component (102, 128, 501 ).
4. Projection exposure apparatus according to any of the preceding claims, characterized in that the photonic pressure sensor (114, 503) has at least one optical waveguide element (504) and/or at least one optical sensor element.
5. Projection exposure apparatus according to any of the preceding claims, characterized in that the photonic pressure sensor (114, 503, 300a-300g) is embodied in a mem- brane-based manner, wherein the pressure sensor has a deformable membrane (302a-302g) and wherein the membrane is deformed in dependence on the pressure.
6. Projection exposure apparatus according to Claim 5, characterized in that the mem- brane-based photonic pressure sensor (300a-300g) is embodied such that the at least one optical waveguide element and/or the at least one optical sensor element (301 a- 301 g) is coupled or able to be coupled to the deformable membrane (302a-302g).
7. Projection exposure apparatus according to Claim 1 -4, characterized in that the photonic pressure sensor (114, 503, 400a, 400b) is embodied in a non-membrane-based manner and captures the pressure in dependence on a change in refractive index of a reference element that has a specified or specifiable reference refractive index.
8. Projection exposure apparatus according to any of the preceding claims, characterized in that the photonic pressure sensor (114, 503) is an integral part of an optical pressure capture unit (500), wherein the pressure capture unit (500) has at least one light source (505) and at least one light capture element (511 ).
9. Projection exposure apparatus according to any of the preceding claims, characterized in that the pressure sensor (503) is embodied to capture a pressure of at least 0.1 Pa and at most 1000 Pa, preferably at least 1 Pa and at most 200 Pa, with particular preference at least 1 Pa and at most 20 Pa.
10. Projection exposure apparatus according to any of the preceding claims, characterized in that the at least one optical component (501 ) is arranged in a hydrogen atmosphere.
11. Method for operating a microlithographic projection exposure apparatus (100), in particular EUV projection exposure apparatus, having a housing (101 ) enclosing an interior space and at least one optical component (102, 128) arranged in the housing (101 ) and at least one pressure capture element (113), arranged in the housing (101 ), through which a pressure within the housing (101 ) is captured, characterized in that a photonic pressure sensor (114, 503) is used as pressure capture element (113).
PCT/EP2022/079334 2021-10-25 2022-10-21 Projection exposure apparatus, method for operating the projection exposure apparatus WO2023072745A1 (en)

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