WO2017102889A1 - Dispositif optique pour un appareil lithographique et appareil lithographique - Google Patents

Dispositif optique pour un appareil lithographique et appareil lithographique Download PDF

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Publication number
WO2017102889A1
WO2017102889A1 PCT/EP2016/081075 EP2016081075W WO2017102889A1 WO 2017102889 A1 WO2017102889 A1 WO 2017102889A1 EP 2016081075 W EP2016081075 W EP 2016081075W WO 2017102889 A1 WO2017102889 A1 WO 2017102889A1
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WIPO (PCT)
Prior art keywords
magnet
optical element
force
stiffness
mirror
Prior art date
Application number
PCT/EP2016/081075
Other languages
English (en)
Inventor
Yim-Bun Patrick Kwan
Jasper WESSELINGH
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
Priority to KR1020187019768A priority Critical patent/KR20180094032A/ko
Priority to JP2018531128A priority patent/JP6980660B2/ja
Publication of WO2017102889A1 publication Critical patent/WO2017102889A1/fr

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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
    • G03F7/70216—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
    • 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
    • G02B7/182—Mountings, adjusting means, or light-tight connections, for optical elements for prisms; for mirrors for mirrors
    • 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
    • G03F7/70825—Mounting of individual elements, e.g. mounts, holders or supports

Definitions

  • the present invention relates to an optical device for a lithography apparatus and to a lithography apparatus.
  • Microlithography is a process used in microfabrication to pattern parts of a thin film of the bulk of a substrate.
  • microlithography is used in the fabrication of integrated circuits.
  • the lithography process is carried out using a lithography apparatus comprising an illumination system and a projection system.
  • a geometric pattern is transferred using light from a reticle to a light- sensitive chemical layer known as photoresist on the substrate.
  • the reticle is illuminated by the illumination system.
  • the projection system projects the geometrical pattern onto the substrate which is located at the image plane of the projection system.
  • EUV lithography apparatuses which use light with a wavelength in the region of 5 nm to 30 nm, in particular 13.5 nm.
  • EUV denotes "Extreme Ultraviolet”.
  • reflective optical elements i.e. mirrors
  • refractive optical elements i.e. lenses
  • the mirrors in EUV lithography apparatuses may, for example, be fastened to a so-called force frame. Each mirror may be manipulated in up to six degrees of freedom.
  • DE 10151919 Al describes - see Figures 1 and 2 of said document - a mirror 1 comprising four posts 2.
  • An actuator 4 either pulls opposite posts 2 towards an optical axis 3 of the mirror 1, or pushes opposite posts 2 away from the optical axis 3. As a result, the optical element 1 is deformed.
  • JP 2013-106014 A discloses a deformable mirror 22 in Fig. 2.
  • Multiple mirror posts 24 are arranged on a rear face 22e of the mirror 22.
  • a load supply system 58 is configured to displace a tip of a respective mirror post 24 in order to induce a load into the rear face 22e of the mirror 22 and thus deform the reflective surface 22d of the mirror 22.
  • An object of the present invention is to provide an improved optical device for a lithography apparatus.
  • the optical element has a positive stiffness when deformed in at least one direction.
  • the actuator is configured for deforming the optical element in the at least one direction.
  • the compensation unit has a negative stiffness in the at least one direction at least partially compensating the optical element's positive stiffness.
  • Negative stiffness is defined as a stiffness producing a force or moment which tends to deform the optical element in the at least one direction, and increases (or remains constant) with increasing deformation of the optical element in the at least one direction. The negative stiffness thus counteracts the positive stiffness, therefore reducing (or even eliminating) the force required to deform the optical element.
  • Another characteristic of the negative stiffness is that it, preferably, does not require any external supply of energy. Rather, the negative stiffness relies on energy stored in a mechanical system or magnetic field and is
  • the quasi-static force is required to deform the optical element itself. It is noted that herein "deforming the optical element” is to say that either the entire optical element is deformed or one or multiple parts thereof are deformed.
  • the quasi- static force is mainly dependent on the optical element's (positive) stiffness. The stiffness is determined by the E-modulus of the material that the optical element is made of, e.g. glass or ceramics, as well as the optical element's geometry.
  • the dynamic force is required to accelerate the mass of the optical element. This force is mainly dependent on the density of the optical element, the geometrical deformation profile and the deformation trajectory as a function of time.
  • the dynamic force required is small.
  • the stiffness of the optical element is relatively large, thus requiring a quasi- static force for deforming the optical element which is much larger than the dynamic force.
  • the actuator With a (close to) zero stiffness arrangement as presently provided, the actuator now only needs to deliver the kinetic energy and the energy required to
  • the required negative stiffness to compensate the optical element's positive stiffness will typically be in the order of 10 5 to 10 6 N/m. For a l- ⁇ excursion, this will require a force of 1 N. In the present example, this corresponds to 100 times the required dynamic force, and is thus much larger.
  • the actuator in accordance with the present invention only needs to provide the dynamic force, and, if at all, a small quasi-static force.
  • the total force provided by the actuator is significantly smaller compared to known solutions.
  • the actuator of the present invention is, preferably, a Lorentz actuator.
  • other types of actuators such as piezoelectric actuators or pneumatic actuators, may also be feasible in some applications.
  • Lorentz actuators are their small response time, which makes them particularly suitable for real-time optical error corrections, for example “die to die” or even “intra-die”.
  • Die to die refers to deforming the optical element in the time window between exposures of two consecutive dies on a single wafer.
  • Intra-die refers to deforming the optical element for optical correction in the time window during the scans of a single die.
  • Lorentz actuators compared to, e.g. piezoelectric actuators, is that they may be operated in an open-loop control system, since they exhibit less or no hysteresis, drift or other inaccuracies.
  • the compensation unit is configured to produce a first maximum force on the optical element in the at least one direction
  • the actuator is configured to produce a second maximum force on the optical element in the at least one direction, wherein a first maximum force is N times larger than the second maximum force, wherein N is > 5, preferably > 10 and more preferably > 50.
  • Maximum force refers to a maximum force found over the cycle of fabricating a single die or a complete wafer using the optical device. It was found that N > 5, preferably > 10 and more preferably > 50 gives a small enough actuator force, and, at the same time, good system stability for easy open-loop control.
  • the compensation unit is configured to produce a first force on the optical element in the at least one direction
  • the actuator is configured to produce a second force on the optical element in the at least one direction, wherein the first force had a first maximum time derivative, and the second force has a second maximum time derivative, wherein the second maximum time derivative is M times larger than the first maximum time derivative, wherein M is > 10, preferably > 100.
  • Maximum time derivative is the maximum derivative found over the cycle of fabricating a single die or a complete wafer using the optical device.
  • the given values of M were found to give highly dynamic deformation, while at the same time keeping the compensation unit simple.
  • the compensation unit's negative stiffness is 0.9 to 0.99 times the optical element's positive stiffness. This ratio of negative stiffness to positive stiffness was found to give a small actuator force and, at the same time, good dynamic stability. Ideally, one should wish to have 100% compensation, such that the ratio negative to positive stiffness should be equal to 1. In such case, the positive stiffness due to the optical element's elasticity is fully compensated by the negative stiffness of the compensation unit. However, this also means that the mirror is in force equilibrium at any deformed state, and will remain at such deformed state. This may not be desirable, since in case of a malfunction, one would wish to have the mirror returned to a specific original shape. Thus, it is desirable to have the negative stiffness compensation to be slightly less than 100%, e.g. 90% to 99%.
  • the difference between the optical element's positive stiffness and the compensation unit's negative stiffness is larger than zero.
  • the state of the optical element in particular its degree of deformation, is always defined.
  • the optical element will always return to its original shape.
  • the deforming of the optical element in the at least one direction is obtained by out-of-plane bending of the optical element.
  • Out-of-plane bending presently refers to bending about an axis perpendicular to the optical element's optical axis.
  • the compensation unit comprises magnets, in particular permanent magnets, or at least one spring.
  • the spring may be a mechanical spring such as a leaf or helical spring.
  • the compensation unit in particular the at least one spring, is configured to preload the optical element in plane. "In plane” is to say that the force generated by the compensation unit acts in a direction parallel to the optical element's plane of extension.
  • negative stiffness is obtained by using a buckling effect.
  • the optical device comprises a base, wherein the magnets are comprised of a first magnet fastened to the optical element and a second and a third magnet fastened to the base, respectively, the first magnet being movable between the second and third magnet.
  • the optical device comprises a base, wherein the magnets are comprised of a first magnet fastened to the optical element and a second magnet fastened to the base, wherein either the first magnet or the second magnet is formed as a ring magnet and the other magnet is movable along the ring magnet's central axis.
  • This embodiment describes a further configuration of magnets to obtain negative stiffness with a zero offset force. Again, the second magnet is stationary, and the first magnet moves along with a portion of the optical element as the optical element is deformed.
  • the optical device comprises an adjusting unit for adjusting the compensation unit's negative stiffness.
  • the adjusting unit allows the optical element to have its (normal) positive stiffness or at least a substantial positive stiffness, which will prevent damage to the optical element during transport or the like.
  • the adjusting unit may even adjust the negative stiffness in real time so as to keep the required actuator force at a minimum during operation of the optical device.
  • the adjusting unit may be configured to adjust the negative stiffness continuously.
  • the adjusting unit is configured for
  • a preload acting on the spring may be changed in order to adjust the negative stiffness.
  • Preloading may, for example, be performed by using a pneumatic cylinder.
  • magnets to obtain negative stiffness repulsion and attraction forces between the magnets and thereby the negative stiffness may be changed by adjusting their relative position.
  • a set screw or the like may be used.
  • magnetic field coupling between the magnets can be changed by, for example, using a moving iron as a short circuit. For example, a horseshoe-type moving iron may be used.
  • electro-permanent magnets may be used.
  • An “electro-permanent magnet” is presently defined as a magnetic unit comprising at least a first magnet with an adjustable permanent magnetization and a means to adjust the permanent magnetization of at least one magnet.
  • the at least one magnet can be made of, for example, ferromagnetic or
  • Permanent magnetization is to say that the at least one magnet does not lose its magnetization (for example expressed as A/m) by more than 5%, preferably not more than 2% and even more preferably by not more than 0.5% per year, when the means for adjusting the permanent magnetization does not produce a magnetic field.
  • the permanent magnetization is adjustable. This is to say that, for example, the means for permanent magnetization of the at least one magnet is switchable between two states of magnetization. These two states may comprise, for example, one demagnetized (magnetization is zero) and one magnetized state. In other embodiments, this is to say that the means for permanent magnetization is switchable between more than two, preferably more than ten, states of
  • the means for permanent magnetization may be formed as a coil. By adjusting the current in the coil, the external field for magnetizing the at least one magnet may be adjusted.
  • the at least one magnet has a medium coercivity field strength.
  • “Coercive field strength” refers to the field strength required to fully demagnetize the magnetic material of the at least one magnet after magnetic saturation of said material.
  • Medium coercivity materials are known in the art and, for example, comprise iron, aluminium, cobalt, copper and/or nickel.
  • the medium coercivity field strength corresponds to a field strength of 10 to 300 kA/m, preferably 40 and 200 kA/m, more preferably 50 to 160 kA/m.
  • the material of medium coercivity is AlNiCo.
  • AlNiCo refers to an alloy of iron, aluminium, nickel, copper and cobalt.
  • the magnetic unit may comprise a further magnet whose permanent magnetization may not be changed by the means for changing the permanent magnetization.
  • This characteristic may be obtained by using a high- coercivity material for the further magnet (second magnet).
  • the first and the second magnet may together produce the negative stiffness required.
  • the first magnet alone produces the negative stiffness required.
  • the negative stiffness may be adjusted appropriately.
  • the optical element has a first positive stiffness when deformed in a first direction and a second positive stiffness when deformed in a second direction, wherein the actuator is configured for deforming the optical element in the first and second direction and wherein the
  • compensation unit has a first negative stiffness in the first direction at least partially compensating the optical element's positive stiffness in the first direction and a second negative stiffness in the second direction at least partially compensating the optical element's positive stiffness in the second direction.
  • the basic principle of the invention can be applied to systems with multiple axes.
  • the response of such systems may be described using a stiffness matrix where the non- diagonal terms describe the coupling between axes. If the system is significantly coupled, local negative stiffness as described in the previous paragraph will no longer suffice to compensate all stiffness forces and an equivalent negative stiffness matrix needs to be built to compensate the positive stiffness matrix. I.e. not only the diagonal (local) stiffness needs to be compensated, but also cross-talk between neighboring actuators. Depending on the geometry, the resulting mechanical system is usually a somewhat banded stiffness matrix, where actuators close together will have some coupling stiffness and actuators far apart will have (near) zero coupling stiffness.
  • a typical negative stiffness matrix is given in equation 1 below, where k p is the local actuator negative stiffness and k c is the coupling stiffness between the degrees of freedom, ⁇ ... 5i gives the deformation in a respective direction, and Fi...Fi gives the negative stiffness force produced by a respective actuator.
  • a negative stiffness matrix with properties as described in equation 1 may be obtained by using an appropriate topology of magnets.
  • the actuator is configured for deforming the optical element for optical correction.
  • optical correction may comprise any type of image error correction, in particular in overlay and/or in focus correction.
  • the optical element is a mirror, a lens, a grating or a lambda plate.
  • Lambda plates are also known as wave plates or retarders, i.e. optical devices which alter the polarization state of the light wave traveling through it.
  • the mirror may be plane or curved. Further, the mirror may be a facet of a mirror comprising multiple facets. Further, a lithography apparatus is provided comprising the optical device described above.
  • the lithography apparatus may be a EUV- or DUV lithography apparatus.
  • EUV stands for “Extreme Ultraviolet” and refers to a wavelength of the exposure light between 0.1 and 30 nm.
  • DUV stands for “Deep Ultraviolet” and refers to a wavelength of the exposure light between 30 and 250 nm.
  • the optical device may be integrated into an objective of the lithography apparatus.
  • the objective may be immersed in a fluid at least during exposure of the waver (immersion lithography).
  • Fig. 1A shows a schematic view of an EUV lithography apparatus
  • Fig. IB shows a schematic view of a DUV lithography apparatus
  • Fig. 2 shows a perspective view of an optical device integrated into the
  • FIG. 3 shows schematically a section IITIII from Fig. 2!
  • FIG. 3A showing a force diagram pertaining to Fig. 3!
  • Fig. 4A shows a diagram illustrating a force vs. displacement diagram for the optical device of Fig. 3 according to a first embodiment
  • Fig. 4B illustrates a force vs. displacement diagram for the optical device of Fig. 3 according to a second embodiment
  • Figs. 5A - 5C illustrate, in a schematic side view respectively, an optical device using a mechanical compensation system to obtain negative stiffness
  • Fig. 6A shows, in a schematic side view, an optical device using a magnetic compensation system to obtain negative stiffness!
  • Fig. 6B shows a variation of the embodiment of Fig. 6A!
  • Figs. 7A - 7D illustrate different embodiments to obtain an optical device having an adjustable negative stiffness!
  • Fig. 8 illustrates in a schematic side view an optical device comprising negative stiffness compensation along multiple axes.
  • like reference numerals designate like or functionally equivalent elements, unless otherwise indicated.
  • Fig. 1A shows a schematic view of an EUV lithography apparatus 100A
  • EUC Extreme Ultraviolet
  • the illumination system 102 and the projection system 104 are integrated into a vacuum housing evacuated by means of an evacuation device (not shown).
  • the vacuum housing is enclosed by a machinery room (not shown).
  • the machinery room includes devices for
  • the machine room may include control devices and other electrical equipment.
  • the EUV lithography apparatus 100A comprises an EUV light source 106A.
  • the EUV light source 106A may be formed as a plasma source or synchrotron emitting light 108A in the EUV range, for example light at a wavelength between 0.1 nm to 30 nm.
  • the EUV light 108A is bundled inside the illumination system 102, and the desired operational wavelength is filtered out.
  • the EUV light 108A has a low transmissivity in air which is why the illumination system 102 and the projection system 104 are evacuated.
  • the illumination system 102 shown in Fig. 1A has, for example, five mirrors 110, 112, 114, 116, 118. After passing through the illumination system 102, the EUV light 108A is guided onto a reticle 120.
  • the reticle 120 is also configured as a reflective optical element and may be arranged outside the systems 102, 104. Further, the EUV light 108A may be directed towards the reticle 120 using a mirror 126 outside either of the systems 102, 104.
  • the reticle 120 comprises a structure, a much smaller image of which is projected onto a waver 122 or the like by the projection system 104.
  • the projection system 104 may comprise, for example, six mirrors Ml— M6, for projecting the structure onto the waver 122. Some of the mirrors Ml - M6 of the projection system 104 may be arranged symmetrically with respect to the optical axis 124 of the projection system 104.
  • the number of mirrors of the EUV lithography apparatus 100A is not limited to the number shown in Fig. 1A, of course. Further, the mirrors may be of different shapes, for example some may be formed as curved mirrors, while others may be formed as facet mirrors.
  • Fig. IB shows a schematic view of a DUV lithography apparatus 100B, also comprising an illumination system 102 and a projection system 104.
  • DUV refers to "Deep Ultraviolet" and designates a wavelength of the exposure light between 30 and 250 nm.
  • the illumination system 102 and the projection system 104 may — as explained with reference to Fig. 1A— be arranged in a vacuum housing and/or machine room.
  • the DUV lithography apparatus 100B comprises a DUV light source 108B.
  • the DUV light source 108B may be configured as an ArF excimer laser emitting light 108b at, for example, 193 nm wavelength.
  • the illumination system 102 guides the DUV light 108B onto a reticle 120.
  • the reticle 120 is configured as a transmissive optical element and may be arranged outside the systems 102, 104, respectively. Again, the reticle 120 has a structure, a much smaller image of which is projected onto a waver 122 or the like by the projection system 104.
  • the projection system 104 may comprise multiple lenses 132 and/or mirrors 134 for projecting the structure of the photomask 120 onto the waver 122.
  • the lenses 132 and/or mirrors 134 may be arranged symmetrically with respect to an optical axis 124 of the projection system 104.
  • the number of lenses or mirrors of the DUV lithography apparatus 100B is not limited to the number of lenses and mirrors shown in Fig. IB.
  • Fig. 2 illustrates, in a perspective view, an optical device 200 comprising a base 202 supporting an optical element 204 which may be formed as a mirror, for example.
  • the optical device 200 may be integrated into one of the lithography apparatuses shown in Fig. 1A and Fig. IB.
  • the optical element 204 may correspond to, for example, one of the mirrors Ml - M6 (Fig. 1A) or one of the lenses or mirrors 132, 134 (Fig. IB). In other embodiments (not shown), the optical element 204 is configured as an optical grid or lambda plate.
  • the base 202 may be fastened to a stationary structure of the lithography apparatus 100A, 100B, for example, to a force frame (not shown). To this end, the base 202 may be equipped with fastening holes 206 or the like.
  • the base 202 may comprise a rectangular or any other suitable shape.
  • the mirror 204 (reference is made to a mirror hereinafter in order to facilitate understanding— this is not to be construed as a limitation to only a mirror but any other suitable optical element may be used) reflects incoming light 108A, 108B.
  • a corresponding optical axis of the mirror 204 is designated with reference numeral 208.
  • At least the front face 210 at which the light 108A, 108b is reflected, or the entire mirror 204, may be curved (as shown) or straight.
  • Fig. 3 shows a section IITIII from Fig. 2.
  • the mirror 204 is depicted in an undeformed state (solid line) and in a deformed state (dot- dash line).
  • the mirror 204 is shown to have a planar shape in its undeformed state.
  • the mirror 204 may have any shape— for example a curved shape— in its undeformed state.
  • the mirror 204 may be supported, for example, at two locations, for example by supports 300, 302.
  • the supports 300, 302 may support the mirror 204 or a portion thereof at its rear face 304.
  • the support 300 may be configured so as to allow relative rotation of the mirror 204, yet fixedly connects the mirror 204 to the base 202 in a direction perpendicular to the optical axis 208.
  • the support 302 allows for relative rotation of the mirror 204, and allows movement of the mirror 204 perpendicularly with respect to the optical axis 208.
  • Perfectdicular as used herein may include deviations from exactly perpendicular of up to 10°, preferably up to 5° and more preferably up to 1°.
  • the mirror 204 may be supported at more than two locations, for example five, ten or twenty or more locations. Further, the supports may be configured for producing a force or moment or both at the locations where they connect to the mirror 204.
  • the optical device 200 comprises an actuator 306.
  • the actuator 306 is configured to deform the optical element 204 (or a portion thereof) between the two states shown in Fig. 3.
  • the actuator 306 is, on the one hand, fastened to the mirror 204 and, on the other hand, to the base 202 or any other suitable reference.
  • the actuator 306 may, for example, be configured as a Lorentz-type actuator, i.e.
  • a voice coil (not shown) and a magnet (not shown) to produce a resulting force F r (see Fig. 3A showing a force diagram pertaining to Fig. 3) on the mirror 204 for deforming the same.
  • the direction in which the force F r acts is designated with ⁇ .
  • any other actuator for example a piezoelectric actuator or a pneumatic actuator, may be used.
  • Lorentz actuator specifically when used in an open-loop control system, may provide a system of low complexity which may be cost-effective.
  • the magnet When a Lorentz actuator is used, the magnet may be fastened to the mirror 204, specifically to its rear side 304, and the voice coil may be fastened to the base 202.
  • the voice coil 306 is fastened to the mirror 204, and the magnet is fastened to the base 202 are also conceivable.
  • the actuator 306 may be controlled by a controller 308.
  • the controller 308 may be configured to control the actuator 306 so as to deform the mirror 204 to provide optical correction. I.e., by deforming the mirror 204, the angle of incidence of the light 108A, 108B is changed.
  • Optical corrections may comprise image error corrections, such as in overlay or in focus corrections. "Image” refers to the image projected onto the waver 122 (see Figs. 1A and IB).
  • the controller 308 may be configured to deform the mirror 204 in real time, for example inside the time window between exposing two different dies on the wafer 122 or even intra-die, i.e. during scans of a single die on the wafer 122. Scanning of respective dies on the wafer 122 may take place at, for example, 30 Hz. Thus, the time window for changing the deformation of the mirror 204 may be smaller than l/30 th of a second.
  • deforming the mirror 204 in the direction ⁇ is obtained by out-of-plane bending of the mirror 204.
  • This is a result of the actuator 306 acting on the mirror 204 at a location between the two supports 300, 302 in the direction ⁇ parallel to the optical axis 208.
  • "Parallel" may include deviations from exactly parallel of up to 10°, preferably up to 5° and more preferably up to 1°.
  • This quasi- static force is a function of the E-modulus of the material of the mirror 204 as well as its geometry, thus corresponding to the (positive) stiffness of the mirror 204.
  • the force will be made of a dynamic force FD required to accelerate the mass of the mirror 204.
  • This dynamic force depends on the density of the mirror 204, the geometrical deformation profile, and the deformation trajectory (as a function of time).
  • the mirror's positive stiffness is paired with a corresponding negative stiffness.
  • the optical device 200 comprises a compensation unit 310 having a negative stiffness in the direction ⁇ at least partially compensating the positive stiffness of the mirror 204.
  • Fig. 3A shows a schematic diagram of the forces acting on the mirror 204 at the location of the actuator 306 and the compensation unit 310.
  • the mirror's positive stiffness k p results in a positive force F p when the mirror 204 is deformed in the direction ⁇ .
  • Fig. 4A showing a diagram of force F vs. deformation ⁇ .
  • the negative stiffness of the compensation unit 310 results in a force F n , as the mirror is deformed in the direction ⁇ which opposes the force F p .
  • the resulting force is the force FQ which is the quasi-static force required to deform the mirror 204 in the direction ⁇ .
  • the actuator 306 needs to exert the dynamic force FD on the mirror 204 to accelerate the same.
  • the sum of the forces FQ and FD equals the resulting force F r exerted by the actuator 306. Since F n and F p are much larger than FQ, FD and F r , they are not drawn to scale in Fig. 3A which is indicated by a dotted line respectively.
  • the dynamic force FD required is small in comparison to the quasi-static force FQ.
  • the forces F p , F n , FD may vary over time as a die or a wafer is produced. Yet, the forces will typically show to be cyclic over the fabrication of a single die or an entire waver.
  • the system can be designed such that the negative stiffness force F n has, when looking at a single cycle, a maximum which is N times larger than the maximum resulting force F r that needs to be produced by the actuator 306, where N is preferably > 5, more preferably > 10 and even more preferably > 50.
  • This kind of system design gives an actuator 306 with low energy consumption. This in turn makes corresponding heat losses small, thus avoiding thermal expansion problems and corresponding cooling issues.
  • the "large" forces F p and F n may be designed to change little compared to the "small" dynamic force FD.
  • a maximum time derivative of the dynamic force FD over one cycle may be M times larger than the maximum time derivative of the negative stiffness force F n , wherein M is preferably larger than 1, more preferably larger than 2 and even more preferably larger than 10.
  • the actuator 306 may be designed so as to recover the dynamic energy in the mirror 204. In other words, when the mirror 204 needs to be slowed down, the work done by the mirror 204 on the actuator 306 is transformed into electrical energy, which is returned to an electrical energy storage. Thus, heat losses of the actuator 306 can be reduced even more.
  • the positive stiffness force F p , the negative stiffness force F n and the resulting force F r are respectively dependent on the stiffnesses k p (positive stiffness), k n (negative stiffness), k r (resulting stiffness) and the deformation ⁇ .
  • the resulting stiffness k r and the corresponding resulting force F r are designed to be positive and unequal to zero.
  • the negative stiffness k n may equal to 0.9 to 0.99 times the positive stiffness k p .
  • Fig. 4B shows a force vs. deformation diagram according to another embodiment of the optical device 200.
  • the negative stiffness force F n may be switched on or off, as will be explained in more detail referring to Figs. 7A to 7D hereinafter.
  • the resulting stiffness will correspond to the positive stiffness k p which is large enough to prevent, for example, damage to the mirror 204 during transport due to
  • the resulting stiffness k r during normal operation of the optical device 200 can be designed to be even smaller (or equal zero) than in the embodiment described in Fig. 4A.
  • the negative stiffness k n may be designed to be 0.99 to 0.999 times the positive stiffness k p .
  • the corresponding dynamic force FD thus equals 10 mN which can be delivered by Lorentz actuator with under 1 mW power dissipation.
  • the required negative stiffness k n to compensate the mirror's positive stiffness k p will be of the order of 10 5 to 10 6 N/m. For a 1 ⁇ excursion, this will thus require a negative stiffness force F n of 1 N. This corresponds to 100 times the dynamic force FD. TO get into the same order of magnitude of the dynamic force FD, the negative stiffness force F n needs to be very accurate.
  • the negative stiffness force can be adjusted in real time, i.e. dynamically during operation of the optical device 200. Ways of adjusting the negative stiffness will be explained with regard to Figs. 7A to 7D hereinafter.
  • the compensation unit 310 of Fig. 5A includes, for example, a mechanical spring 500, for example, a leaf or helical spring, and a preloading unit 502, for example, a pneumatic cylinder, configured to preload the spring 500.
  • the spring 500 acting, for example, on the side 504 of the mirror 204, is preferably configured to be fairly long.
  • a long spring 500 ensures a more or less constant preloading force Fc as the mirror 204 is deformed since this deformation will also causes the mirror 204 to move laterally, i.e. in a direction normal to the optical axis 208.
  • the spring 500 could, in its
  • the force F c may be exerted directly (without using a mechanical spring) by a pneumatic cylinder or using magnets, for example.
  • the mirror 204 of Fig. 5A is preloaded in plane, i.e. at right angles to the optical axis 208, with the compensation force F c .
  • the force F c tends to buckle the mirror 204, and thus bend the same out of plane.
  • This force F c may be exerted, for example, by a mechanical spring 500.
  • the mirror 204 is symmetrical, half of the mirror 204 can be considered as a simple cantilever subjected to a force at its end as shown in Fig. 5B.
  • L corresponds to the width of the mirror 204 between the supports 300, 302 as shown in Fig. 5A
  • F p corresponds to the positive stiffness force required to overcome the mirror's positive stiffness 204
  • E corresponds to the E-modulus of the material of the mirror 204 (for example glass or ceramics)
  • I corresponds to the moment of inertia (which depends on the geometry of the cross- section of the mirror 204).
  • the positive stiffness k p of the mirror 204 is given by:
  • a constant preload force F c is suitable to provide a negative or near negative stiffness which will compensate the positive stiffness of the mirror 204.
  • the near constant compensation force F c may be provided by a long spring 500 which is preloaded.
  • Figs. 6A and 6B illustrate a first and a second embodiment of a compensation unit 310 comprising magnets.
  • the compensation 310 of Fig. 6A comprises a first magnet 600 fastened to the mirror 204 to produce the negative stiffness force F n .
  • a connection between the first magnet 600 and the mirror 204 is indicated at 602.
  • the magnet 600 is arranged between a second and a third magnet 604, 606 which are stationary. To this end, the second and third magnet 604, 606 may be fastened to the base 202.
  • the first magnet 600 may be guided mechanically in the direction ⁇ .
  • the magnets 600, 604, 606 may be configured as block magnets, and may have the same polarization (indicated by "N" for North, and "S" for South) with respect to the direction ⁇ .
  • the first magnet 600 when the first magnet 600 is positioned halfway between the second and third magnet 604, 606, the first magnet 600 produces a zero offset force on the mirror 204. Also, as the deformation of the mirror 204 increases in the direction ⁇ , the force F n increases accordingly. Thus, the negative stiffness k n is produced.
  • the compensation 310 comprises a first magnet 600 connected to the mirror 204 by a connection 602. Further, the compensation unit 310 comprises a second magnet 604 configured as a ring magnet.
  • the ring magnet 604 has a central axis 608.
  • the first magnet 600 is, for example, mechanically guided to move along the central axis 608 as the mirror 204 is deformed in the direction ⁇ .
  • the first magnet 600 and the second magnet 604 have an opposed polarity along the axis 608.
  • the first magnet 600 is arranged on the axis of symmetry 610 of the second magnet 604 along the axis 608, the first magnet 600 produces a zero offset force on the mirror 204.
  • Fig. 7A to 7D illustrate four different embodiments of an adjusting unit 700.
  • the adjusting unit has a pneumatic cylinder 700 configured to be switched on or off. In the "off state, the pneumatic cylinder 700 does not produce the preload force F c on the spring 500.
  • a controller 702 may be provided configured to control the preload force F c (even continuously) based on input to the controller 702.
  • a sensor 704 may be provided, sensing an optical error requiring correction.
  • the controller 702 may receive a corresponding input signal from the sensor 704 and control the pneumatic cylinder 700 to produce a preload force F c which will result in a deformation of the mirror 204 leading to appropriate optical correction.
  • Setting of a desired preload force F c by the controller 702 may be performed by measuring e.g. the current of the (Lorentz) actuator 306 during a slow
  • Figs. 7B to 7D may also include a controller 702 and, as the case may be, also a sensor 704. They merely differ in the way in which the negative stiffness force F n is adjusted.
  • the adjusting unit 700 may comprise mechanical means, for example a set screw, to move the second magnet 604 along the central axis 608 from an initial position PI to a position P2, in which the first magnet 600 produces an initial offset force on the mirror 204.
  • electromagnetic means may be used to adjust the position of the second magnet 604, for example.
  • the adjusting unit 700 is configured to adjust the magnet field coupling between the first magnet 600 and the second magnet 604.
  • the adjusting unit 700 may comprise a, e.g. U-shaped, mover magnet which is moved perpendicular to the central axis 608 to change the field coupling between the magnets 600, 604.
  • the magnets 600, 604 are arranged inside the mover magnet 700.
  • the mover magnet 700 is moved to a position with the magnets 600, 604 arranged outside the mover magnet 700.
  • the adjusting unit 700 comprises an electro-permanent magnet 706.
  • the electro-permanent magnet 706 is comprised of at least a first magnet 708 made of a medium coercivity material and a coil 710 configured to change the magnetization of the magnet 708 depending on, for example, an input signal received from the controller 702 (see Fig. 7A).
  • the adjusting unit 700 may comprise a second magnet 712 of a high coercivity material, and, in addition or intratly, an iron core 714 to increase overall field strength.
  • the magnet 708 and, if provided, the magnet 712 form the second magnet 604 described in Fig. 6B.
  • FIG. 8 shows an optical device 200 having multiple axes 51, 52, 53 along which deformation may take place.
  • the mirror 204 is connected through, for example, three connectors 602a, 602b, 602c to first magnets 600a, 600b, 600c, respectively.
  • the first magnet 600a, 600b, 600c are respectively arranged between first and second magnets 604a, 604b, 604c and 606a, 606b, 606c.
  • Each first, second and third magnet 604a...606c associated with a respective connector 602a, 602b, 602c forms a compensation sub unit 310a, 310b, 310c. Together, the compensation sub unit 310a, 310b, 310c form the compensation unit 310.
  • the negative stiffness of the compensation unit 310 of Fig. 8 is described by the negative stiffness matrix given below ⁇
  • the stiffness matrix should be built not only to produce the required diagonal (local) stiffness, but also needs to compensate cross-talk terms of the mirror 204 by generating the appropriate negative crosstalk between neighboring magnets 604a...606c.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Health & Medical Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Environmental & Geological Engineering (AREA)
  • Epidemiology (AREA)
  • Public Health (AREA)
  • Exposure And Positioning Against Photoresist Photosensitive Materials (AREA)
  • Mounting And Adjusting Of Optical Elements (AREA)

Abstract

La présente invention concerne un dispositif optique (200) pour un appareil lithographique (100A, 100B), comprenant : un élément optique (204) présentant une rigidité positive (kp) lorsqu'il est déformé dans au moins une direction (δ), un actionneur (306) servant à déformer l'élément optique (204) dans la au moins une direction (δ) et une unité de compensation (310) présentant une rigidité négative (kn) dans la au moins une direction (δ) compensant au moins partiellement la rigidité positive (kp) de l'élément optique.
PCT/EP2016/081075 2015-12-15 2016-12-14 Dispositif optique pour un appareil lithographique et appareil lithographique WO2017102889A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
KR1020187019768A KR20180094032A (ko) 2015-12-15 2016-12-14 리소그래피 장치용 광학 디바이스 및 리소그래피 장치
JP2018531128A JP6980660B2 (ja) 2015-12-15 2016-12-14 リソグラフィ装置用の光学デバイス及びリソグラフィ装置

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DEDE102015225263.9 2015-12-15

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DE102017216458A1 (de) * 2017-09-18 2019-03-21 Carl Zeiss Smt Gmbh Verfahren zur Herstellung eines Spiegels als optischer Komponente für ein optisches System einer Projektionsbelichtungsanlage für die Projektionslithographie
KR102548949B1 (ko) * 2020-12-14 2023-06-29 한국기계연구원 마스크 정렬을 위한 Z/Tilt 스테이지 및 제어 시스템

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US20030155882A1 (en) * 2002-02-19 2003-08-21 Nikon Corporation Anti-gravity mount with air and magnets
US20060232866A1 (en) * 2005-04-14 2006-10-19 Canon Kabushiki Kaisha Optical unit and exposure apparatus having the same
US20150123417A1 (en) * 2013-11-01 2015-05-07 Sabanci University Variable Negative Stiffness Actuation
US20150261093A1 (en) * 2012-10-15 2015-09-17 Asml Netherlands B.V. Actuation Mechanism, Optical Apparatus, Lithography Apparatus and Method of Manufacturing Devices

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JP2002323584A (ja) * 2001-02-22 2002-11-08 Nikon Corp アクチュエータ、ステージ、露光装置、デバイスの製造方法、及び免震装置
TWI250387B (en) * 2002-09-30 2006-03-01 Asml Netherlands Bv Lithographic apparatus and device manufacturing method
EP1403713A1 (fr) * 2002-09-30 2004-03-31 ASML Netherlands B.V. Appareil lithographique et méthode de fabrication d'un dispositif
WO2012097163A1 (fr) * 2011-01-14 2012-07-19 The Board Of Trustees Of The University Of Illinois Réseau de composants optiques ayant une courbure réglable
JP5848052B2 (ja) * 2011-07-21 2016-01-27 日本電産サンキョー株式会社 振れ補正機能付き光学ユニット

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20030155882A1 (en) * 2002-02-19 2003-08-21 Nikon Corporation Anti-gravity mount with air and magnets
US20060232866A1 (en) * 2005-04-14 2006-10-19 Canon Kabushiki Kaisha Optical unit and exposure apparatus having the same
US20150261093A1 (en) * 2012-10-15 2015-09-17 Asml Netherlands B.V. Actuation Mechanism, Optical Apparatus, Lithography Apparatus and Method of Manufacturing Devices
US20150123417A1 (en) * 2013-11-01 2015-05-07 Sabanci University Variable Negative Stiffness Actuation

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TWI712831B (zh) 2020-12-11
JP2019500648A (ja) 2019-01-10
JP6980660B2 (ja) 2021-12-15
TW201732345A (zh) 2017-09-16

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