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
  • G03F7/70858—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
  • G03F7/70891—Temperature
• • 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
  • G03F7/70216—Mask projection systems
  • G03F7/70258—Projection system adjustments, e.g. adjustments during exposure or alignment during assembly of projection system
  • G03F7/70266—Adaptive optics, e.g. deformable optical elements for wavefront control, e.g. for aberration adjustment or correction
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
  • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
  • G02B26/0816—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements
  • G02B26/0825—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a flexible sheet or membrane, e.g. for varying the focus
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B7/00—Mountings, adjusting means, or light-tight connections, for optical elements
  • G02B7/18—Mountings, adjusting means, or light-tight connections, for optical elements for prisms; for mirrors
  • G02B7/181—Mountings, adjusting means, or light-tight connections, for optical elements for prisms; for mirrors with means for compensating for changes in temperature or for controlling the temperature; thermal stabilisation
• • 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

• the invention concerns an arrangement for the thermal actuation of a mirror, in particular in a microlithographic projection exposure apparatus.
• Microlithography is used for the production of microstructured components, such as for example integrated circuits or LCDs.
• the microlithographic process is carried out in what is known as a projection exposure apparatus, which has an illumination device and a projection lens.
• a projection exposure apparatus which has an illumination device and a projection lens.
• mirrors are used as optical components for the imaging process because of the lack of availability of suitable light-transmissive refractive materials.
• a problem that arises in practice is that, in particular as a result of absorption of the radiation emitted by the EUV light source, the EUV mirrors undergo heating and an accompanying thermal expansion or deformation, which in turn may have the consequence of impairing the imaging properties of the optical system.
• the heat inputs brought about by the EUV radiation can be varied over the optically effective cross section of mirrors close to the pupil, so that an inhomogeneous heat input into the mirror takes place.
• a problem that arises in practice in the thermal actuation or deformation of a mirror is that, on the one hand, for the introduction of deformations into the mirror substrate material by way of thermal expansion or contraction, there must in principle be sufficient sensitivity of the mirror substrate material to thermal loads but, on the other hand, sensitivities to the optical loads, and the associated temperature effects, occurring during the "normal" operation of the projection exposure apparatus, are desired.
• sensitivities to the optical loads, and the associated temperature effects, occurring during the "normal" operation of the projection exposure apparatus are desired.
• without further measures in the design of the mirror to obtain an increasing sensitivity to thermal loads introduced for the purpose of producing deformation there is an increasing occurrence of thermally induced aberrations during the operation of the projection exposure apparatus as a result of the unavoidable optical loads due to the (for example EUV) radiation that is used.
• An object of the present invention is to provide an arrangement for the thermal actuation of a mirror in an optical system that makes efficient thermal actuation possible with at the same time low sensitivity to the optical loads occurring during normal operation.
• the invention concerns an arrangement for the thermal actuation of a mirror in an optical system, in particular in a microlithographic projection exposure apparatus, the mirror having a mirror substrate and an optically effective surface and also at least one access channel extending from a surface of the mirror not corresponding to the optically effective surface in the direction of this effective surface,
• At least one heat source for coupling heating power that can be set variably into a region of the mirror substrate that is adjoining the optically effective surface is provided;
• the invention is based in particular on the concept of using cooling elements that are variable with regard to their cooling power in combination with a heat source that can be set variably with regard to its heating power to provide two degrees of freedom in the thermal actuation that can be set independently of one another in terms of automatic control.
• an entirely different temperature can be set in the region of the mirror substrate material that is more remote from the optically effective surface, a temperature at which a comparatively greater sensitivity to thermal loads is obtained for the material concerned, as is desired for specific thermal actuation or deformation.
• the present invention is based in particular on the concept of creating, using the independently realizable adjustability of the cooling power of a cooling element on the one hand and the heating power of at least one heat source on the other hand, a thermal flux between the optically effective surface and said surface of the mirror not corresponding to the optically effective surface (e.g. the backside of the mirror).
• This thermal flux results in a temperature gradient and a related local variation of a value of the coefficient of thermal expansion in the mirror substrate, which leads to a behaviour of said mirror substrate being comparable, in terms of thermal sensitivity or the locally varying coefficient of thermal expansion (CTE), to a bimetal.
• this behaviour makes it possible to maintain the optically effective surface of the mirror at a temperature for which the mirror material is substantially insensitive against thermal loads occurring during operation of the optical system (namely the so-called zero crossing temperature explained below in more detail), while at the same time enabling a region in the mirror substrate remote from said optically effective surface to be more sensitive or thermally actuable due to the different CTE-value in order to create a desired specific deformation of the mirror.
• the invention also circumvents or avoids the conflicting aspects that an actuator, which is desired to be insensitive against thermal loads, will also behave insensitive against thermal actuation.
• the heating power of the heat source may be reduced - with unchanged cooling power of the cooling element -, with the consequence that the thermal balance in the direct vicinity of the optically effective surface is preserved, whereas an efficient thermal actuation or deformation can take place in the region remote from the optically effective surface that is at a temperature well below the zero-crossing temperature, as a result of the greater, and no longer negligible, coefficient of linear expansion in this remote region.
• the temperature in the region remote from the optically effective surface can be specifically manipulated at any time, while the temperature in the direct vicinity of the optically effective surface is kept substantially constant (that is preferably at the aforementioned zero-crossing temperature).
• the sensitivity to changes in temperature that there consequently is in the region remote from the optically effective surface mirror deformations can be generated there, while at the same time in the region of the optically effective surface the mirror remains largely insensitive to the impinging electromagnetic radiation of unavoidable optical loads occurring during the operation of the optical system.
• the arrangement has a plurality of access channels.
• each of these access channels may in particular be respectively assigned a cooling element, the cooling elements preferably being able to be set independently of one another in their cooling power.
• the at least one cooling element has a tubular geometry.
• the heat source has at least one heat emitter for coupling heating radiation into the at least one access channel.
• each of the access channels may be respectively assigned a heat emitter, the heat emitters preferably being able to be set independently of one another in their heating power.
• the at least one heat emitter may be arranged in the end portion of the access channel that is facing the optically effective surface.
• the heat emitter may, for example, also be arranged in the region of the rear side of the mirror, in order to couple in the heating radiation by way of reflection along the access channel (preferably with what is known as a "grazing incidence").
• the heating radiation may, for example, have a wavelength of at least 2.5 ⁇ , in particular at least 5 ⁇ .
• the heat source may also have at least one heating wire or at least one heat-dissipating conductor track (for example in the form of a structured electrically conducting layer), which is arranged between the mirror substrate and the reflective coating of the mirror.
• the access channel extends from the surface of the mirror that is opposite from the optically effective surface in the direction of the optically effective surface.
• the mirror has a first mirror substrate region of a first mirror substrate material and a second mirror substrate region of a second mirror substrate material, different from the first mirror substrate material, the second mirror substrate region being more remote from the optically effective surface of the mirror than the first mirror substrate region.
• the first mirror substrate material preferably has a lower coefficient of linear expansion at a prescribed temperature than the second mirror substrate material.
• the described greater sensitivity of the mirror substrate material that is desired for the purpose of specific deformation is obtained in the region more remote from the optically effective surface not only because of the temperature gradient forming within the mirror substrate material but also because of the transition between different mirror substrate materials, which is of advantage in particular whenever the temperature gradient forming in the mirror substrate alone is not yet sufficient to achieve the sensitivity to thermal loads desired for the deformation while at the same time maintaining the zero- crossing temperature at the optically effective surface.
• the first mirror substrate material is a material with ultra-low thermal expansion "ultra-low expansion material", for example a titanium- silicate glass sold under the name ULETM by the company Corning Inc.
• the second mirror substrate material may, for example, be amorphous or crystalline quartz (S1O 2 ).
• the mirror has a reflective coating, an absorbent layer for the absorption of heating radiation that is coupled into the access channel being arranged between the mirror substrate and the reflective coating.
• the invention also concerns a method for the thermal actuation of a mirror, in particular in a microlithographic projection exposure apparatus, the mirror having a mirror substrate, an optically effective surface and at least one access channel extending from a surface of the mirror not corresponding to the optically effective surface in the direction of this effective surface and also a cooling element with a cooling power that can be set variably protruding into the at least one access channel,
• heating power is coupled into a region of the mirror substrate that is adjoining the optically effective surface
• This constant value preferably corresponds to the zero-crossing temperature of the mirror substrate material in the region concerned.
• the constant value lies, for example, in the range of 22°C to 55°C, in particular in the range of 22°C to 40°C.
• the variation of the heating power of the heat source may be performed in such a way that a heat input into the optically effective surface that is caused by optical loads during the operation of the projection exposure apparatus is at least partially compensated. In this way, the temperature of the optically effective surface can be kept constant even under variable optical loads.
• a deformation in that region of the mirror substrate facing away from the optically effective surface is effected, wherein said deformation mechanically transfers to the optically effective surface.
• Figures 1 -2 show schematic representations for explaining the structure of an arrangement according to the invention for the thermal actuation of a mirror in a first embodiment of the invention
• Figure 3 shows a diagram in which the temperature dependence of the coefficient of linear expansion for different mirror substrate materials is plotted;
• Figures 4a-b show schematic representations for explaining the structure of an arrangement according to the invention for the thermal actuation of a mirror in a further exemplary embodiment of the invention;
• Figures 5a-b show schematic representations of further embodiments of the invention;
• Figure 6 shows a schematic representation of a projection lens of a microlithographic projection exposure apparatus designed for operation in EUV, in which the invention can be realized for example;
• Figure 7 shows a schematic representation illustrating a concept of the present invention.
• the mirror 100 has a plurality of access channels 1 10, 1 1 1 , 1 12,..., which extend from the rear side of the mirror (i.e. the side of the mirror 100 that is opposite from the optically effective surface 101 ) through the mirror substrate denoted by "102" into the vicinity of the optically effective surface 101 , the access channels 1 10, 1 1 1 , 1 12,... according to Fig. 1 being in a matrix-like arrangement.
• Fig. 2a-b only one access channel 1 10 is shown in section, the mirror 100 and the other access channels 1 1 1 , 1 12,... being configured in an analogous way.
• a cooling element 120 of a tubular geometry in the exemplary embodiment extends into the access channel 1 10, this cooling element 120 being able to be set variably in its cooling power (by connection to a controllable cooler that is not shown).
• the arrangement also has a heat source in the form of a heat emitter 130, which in the exemplary embodiment is arranged in the end portion of the access channel 1 10 that is facing the optically effective surface 101 and has a heating power that can likewise be set variably.
• the heat emitter 130 may also be arranged in a different region of the access channel 1 10, in particular also in the region of the rear side of the mirror, in order in this case to couple in the heating radiation by way of the access channel 1 10 or reflection on the side walls of the access channel 1 10, preferably sufficiently shallow reflection angles with what is known as "grazing incidence”.
• the heat source may also be configured in the form of at least one heating wire.
• the electromagnetic radiation that is radiated - once again with reference to Fig. 1 and 2a, b - by way of the heat emitter 130 and coupled into the mirror substrate material may, for example, have a wavelength of at least 2.5 ⁇ , more particularly a wavelength of at least 5 ⁇ , as may be realized for instance by way of what is known as a low-temperature emitter at temperatures of up to 400°C, in particular in the range up to 200°C.
• a high-temperature emitter such as for example a spiral-wound filament (with an operating temperature of typically up to 3000°C) may also be used.
• heating radiation for example infrared radiation
• the combined use of the cooling element 120, on the one hand, and the heat emitter 130, on the other hand, allows the temperature of the mirror substrate material in the region of the optically effective surface 101 to be kept constantly at a value that corresponds substantially to the zero-crossing temperature of the mirror substrate material concerned (for example when there is an increasing optical load in the region of the optically effective surface 101 as a result of the impinging electromagnetic (EUV) radiation during the operation of the projection exposure apparatus).
• EUV impinging electromagnetic
• a temperature that deviates from the zero-crossing temperature and makes sufficient sensitivity of the mirror substrate material to thermal loads possible, and consequently specific thermal actuation or deformation of the mirror 100 can be set in a region remote therefrom (that is in the "lower" region in Fig. 2a-b).
• the temperature set in the region of the optically effective surface 101 may be 30°C and in the region remote from the optically effective surface 101 may be -15°C, in which case there is already a significant change in the coefficient of linear expansion depending on the mirror substrate material.
• the inventive concept in particular involves creating, using the independently realizable adjustability of the cooling power of a cooling element on the one hand and the heating power of at least one heat source on the other hand, a thermal flux between the optically effective surface and said surface of the mirror not corresponding to the optically effective surface (e.g. the backside of the mirror).
• the access channel 1 10 and the created temperature gradient between the optically effective surface 101 and the backside of the mirror 100 makes it possible to maintain the optically effective surface 101 of the mirror 100 at a temperature for which the mirror material is substantially insensitive against thermal loads occurring during operation of the optical system (namely the so-called zero crossing temperature), while at the same time enabling a region in the mirror substrate remote from said optically effective surface to be more sensitive or thermally actuable due to the different CTE-value in order to create a desired specific deformation of the mirror.
• a temperature variation is created in a region of the mirror substrate facing away from the optically effective surface (e.g. at the backside of the mirror) such that, due to the thermal sensitivity achieved by the value of the coefficient of thermal expansion in that region of the mirror substrate, a deformation in the mirror substrate is effected, said deformation being mechanically transferred to the optically effective surface (having a substantially constant temperature close to the zero crossing temperature).
• the corresponding impact matrices (and the resultant temperature base functions and deformation base functions) can be suitably combined to set a desired (as homogeneous as possible) temperature profile and also a desired deformation profile.
• the region of the mirror substrate 102 in the vicinity of the optically effective surface 101 is at this zero-crossing temperature, optical loads caused by the electromagnetic radiation impinging on the optically effective surface 101 during the operation of the projection exposure apparatus do not result in any deformation, since the coefficient of linear expansion of the mirror substrate material is equal to zero.
• Fig. 3 when there is a deviation from this temperature, there is an increasing sensitivity of the respective mirror substrate material to temperature changes, which can be used for the thermal actuation or deformation of the mirror 100 that is described above.
• the embodiment according to Fig. 4 differs from that according to Fig. 2 in that the mirror substrate 202 is produced from two different mirror substrate materials, the mirror 200 is therefore formed as a "composite mirror".
• the mirror substrate 202 has a first mirror substrate region 202a and a second mirror substrate region 202b, which is more remote in relation thereto from the optically effective surface
• the mirror substrate regions 202a, 202b being produced from different materials.
• the mirror substrate material of the first mirror substrate region is ULETM and the mirror substrate material of the second mirror substrate region 202b is quartz glass (S1O2).
• the invention is not restricted to these materials, so that in further embodiments the mirror substrate regions 202a, 202b may also be produced from different mirror substrate materials, the mirror substrate material in the second mirror substrate region 202b in each case having a coefficient of linear expansion that is greater in terms of the absolute amount at a prescribed temperature than the mirror substrate material in the first mirror substrate region.
• the desired greater sensitivity of the mirror substrate material that is described above and is desired for the purpose of specific deformation is obtained in the region more remote from the optically effective surface 201 not only because of the temperature gradient forming within the mirror substrate material but also because of the transition between different mirror substrate materials, so that the embodiment according to Fig. 4 is suitable in particular in situations in which the said temperature gradient alone is not yet sufficient to achieve the sensitivity to thermal loads desired for the deformation while at the same time maintaining the zero-crossing temperature at the optically effective surface.
• Fig. 5a and 5b serve for explaining further embodiments of the invention.
• an absorbent layer 530 for the at least partial absorption of the heating radiation that is coupled into the access channel 1 10 is arranged between the mirror substrate 102 and the reflective coating 550.
• an arrangement 540 of heating wires is provided as the heat source, by which the region between the mirror substrate 102 and the reflective coating 550 can be heated directly with heating power that can be set variably.
• An arrangement according to the invention for the thermal actuation of a mirror may be used both in conjunction with a mirror in the illumination device and in conjunction with a mirror in the projection lens of a microlithographic projection exposure apparatus.
• FIG. 6 shows merely as an example of an application the path of rays of a projection lens 600, which is disclosed in US 2008/0170310 A1 (see Fig. 2 there).
• the projection lens 500 is designed for operation in EUV and has six mirrors M1 to M6.
• the mirrors M2 and M6 that are respectively close to the pupil or else another of the mirrors according to one of the embodiments described above may be configured as thermally actuable.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Optics & Photonics (AREA)
• Engineering & Computer Science (AREA)
• Environmental & Geological Engineering (AREA)
• Epidemiology (AREA)
• Public Health (AREA)
• Toxicology (AREA)
• Atmospheric Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Exposure And Positioning Against Photoresist Photosensitive Materials (AREA)
• Exposure Of Semiconductors, Excluding Electron Or Ion Beam Exposure (AREA)
• Optical Elements Other Than Lenses (AREA)
• Mechanical Light Control Or Optical Switches (AREA)
• Mounting And Adjusting Of Optical Elements (AREA)

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• 2013
  • 2013-03-14 DE DE102013204427.5A patent/DE102013204427A1/de not_active Withdrawn
• 2014
  • 2014-03-07 JP JP2015562046A patent/JP6483626B2/ja active Active
  • 2014-03-07 WO PCT/EP2014/054487 patent/WO2014139896A2/en not_active Ceased
  • 2014-03-07 KR KR1020157026654A patent/KR102211633B1/ko active Active
  • 2014-03-07 CN CN201480014966.9A patent/CN105190443B/zh active Active
• 2015
  • 2015-09-09 US US14/848,593 patent/US9798254B2/en active Active

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