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
  • G03F7/70808—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
• • 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
  • G03F7/70008—Production of exposure light, i.e. light sources
  • G03F7/70041—Production of exposure light, i.e. light sources by pulsed sources, e.g. multiplexing, pulse duration, interval control or intensity control
• • 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

Definitions

• the invention relates to an optical device with a light source which emits light in the form of light pulses with a pulse frequency, and with at least one optical element.
• the invention also relates to a projection exposure apparatus having a pulsed light source and a projection objective, and to a method for correcting or improving the imaging behavior of such a device, in particular in a projection exposure apparatus.
• Optical devices may change their imaging properties during their operation for a variety of reasons. For example, material properties can change as a result of aging, as a result of temperature gradients or due to the influence of mechanical forces, for example due to the holder, deformations of the optical elements can occur. Exposure of optical devices to intense radiation for extended periods of time may also result in changes in imaging characteristics.
• the design of the optical system already takes into account the expected changes in the imaging properties.
• manipulators can be provided, which allow, for example, a lateral displacement of the optical element.
• a measuring device for example a wavefront sensor
• imaging aberrations resulting from aging effects or temporary effects such as local heating can thus be specifically compensated.
• Such a displacement of optical elements in the z-direction is described, for example, in US Pat. No. 2003/0063268 A1.
• No. 6,198,579 B describes a method for correcting non-rotationally symmetrical aberrations in an objective, in which a plurality of Peltier elements are arranged on at least one of the optical elements of the objective, which are distributed around its circumference, and which are driven differently to generate a temperature distribution in the optical element so as to correct aberrations.
• US Pat. No. 6,521,877 B describes an optical arrangement, in particular in a micro-lithographic projection exposure apparatus, in which aberrations are compensated for by targeted heating of optical elements by means of resistance heating.
• lens elements with a free-form surface provided specifically for the correction of aberrations of the objective.
• Such lens elements are referred to as correction spheres. They can already be used when adjusting the lens.
• interchangeable optical elements in the objective which can be replaced after some operating time by replacement elements with a freeform surface, the shape of which compensates for the aberration caused by aberration aberration.
• the object of the invention is to specify an optical device, in particular a projection exposure apparatus, in which image errors which arise in the course of the operating time, in particular image errors of a higher order, can be corrected with the simplest possible means.
• An optical device comprises a light source which emits light in the form of light pulses and an optical element which is connected to means for exciting a vibration of the optical element, wherein the oscillation of the optical element at a temporally periodic modulation at least one for the optical Image relevant parameter of the optical element, such as refractive index, polarization properties, density, shape, position or angle, leads, wherein the oscillation frequency by means of the devices for exciting a vibration of the optical element is adjustable so that they match the pulse frequency of the light source or a harmonic (integer multiple of the pulse rate) is synchronized.
• a clock is provided for the pulse frequency of the light pulses, wherein the clock is connected to at least one frequency multiplier whose output is connected to the means for generating a vibration.
• oscillation of the optical element means not only a local spatial excursion of the optical element but also sound waves, pressure waves, density waves, etc., which propagate within the optical element.
• a pulsed light source is understood to be any type of light source which emits light in the form of individual, temporally separated light pulses, such as a pulsed laser, but also a stroboscope.
• the light flux or the light intensity is periodically varied. This periodicity can, for. B. in pulsed lasers or other electronically switchable or controllable light sources, directly, for example by electronic circuitry, are set.
• the periodic light modulation can also be adjusted by one or more switchable elements downstream of the light source, such as diaphragms, chopper wheels, oscillating diaphragm segments or electronically controllable shutters, in particular LCD shutters, in transmission or in reflection, for example with a rotating periodically segmented mirror ,
• switchable elements downstream of the light source such as diaphragms, chopper wheels, oscillating diaphragm segments or electronically controllable shutters, in particular LCD shutters, in transmission or in reflection, for example with a rotating periodically segmented mirror
• Both the shape of the intensity profile of the light pulse and the pulse length and the duty cycle of the periodic variation can be adapted to the requirements by selecting the means. This can be done, for example, by designing the transmission properties of oscillating or rotating diaphragms or by adjusting the switching speed of electronically controllable diaphragms.
• a synchronization between the pulse frequency of the light source and the oscillation frequency of the optical element means that the frequency of the periodically varied irradiation and that of the oscillating element are matched to one another such that a quasi-static state sufficiently stable for the imaging or illumination purpose is reached.
• frequency this is the case when the frequency of the component oscillation is an integer multiple of the frequency of the illumination, so that applies
• V 0 E represents the oscillation frequency of the optical element
• v L the pulse frequency of the light source
• N an integer.
• a projection exposure apparatus for microlithography or an optical system in which dynamic forces are introduced into at least one optical element in order to compensate for aberration-induced image aberrations induced by voltage doubts.
• the dynamic forces are synchronized with a pulsed light source, so that at the time of influencing the light beam of the light source by the optical element optimal imaging conditions for the projection prevail.
• a diffraction grating as a reflection grating with a variable grating constant, wherein the variable grating constant is generated by surface waves on a surface of a surface acoustic wave device.
• the diffraction grating thus provided is used in a spectrometer for determining the wavelength of a radiation emitted by a radiation source to be measured.
• changes in the imaging properties of the optical device are compensated for over the course of the operating life, rather than being caused by static deformation of an optical element by means of an optical element which is set in oscillation, as in the prior art.
• the wavefront profile of the light pulses can be dynamically corrected or specifically influenced in order to improve the imaging quality of the optical device. It is also possible that through the vibrated optical element are induced in a targeted manner distortions of the wave front course of the light pulses, which then improve the imaging behavior of the optical devices.
• the oscillation frequency is selected according to the above equation such that the optical element is deflected at each instant that a light pulse is incident on that optical element so that the resulting shape of the optically active surface becomes one Has shape that causes a desired change of the wavefront.
• the invention is not limited to inducing vibrations in the optical element that result in a change in the shape or geometry of the optical element, but instead of or in addition to such transverse vibrations, longitudinal, in a suitably dimensioned optical element Vibrations are excited, leading to density variations, such as strains and compressions in the material of the optical element. Such density variations are associated with a local change in refractive index, i. When a longitudinal oscillation is excited, regions with different refractive indices are produced in the optical element, by means of which the desired optical effect can be achieved.
• Optical elements that are particularly suitable for excitation of longitudinal vibrations are gas or liquid-filled optical elements, as in these density variations with a pronounced amplitude can be adjusted. It is also possible in optical elements, which are formed as crystalline or amorphous solid, to induce longitudinal and transverse oscillations to change the imaging properties of the optical system.
• standing sound waves can be induced, which leads to pressure or density variations in the optical element.
• the optical element acts as a resonator for the induced vibrations, its shape, expansion and choice of material to the appropriate correction effect to be achieved the aberration of the optical device can be adjusted.
• the vibrations can propagate in two or three dimensions of the optical element.
• the evoked acoustic wave field leads to a location-dependent compression or elongation of the material of the optical element, which causes a location-dependent change in the refractive index of the optical element.
• the isotropic refractive index of the optical element can be varied, which leads, for example, to continuous influencing of the wavefront of the light pulse in the sense of a Grin lens which passes through the vibrated optical element. This is the case in particular for liquids of low viscosity or gases.
• the material of the optical element is an amorphous or crystalline solid, the sound pressure level can also translate into a local change in the birefringence properties of the optical element and change the polarization behavior, ie the polarization state and degree of polarization of the wavefront of the light pulse of the light source.
• the optical element can also be used as a spatially varying polarization-optical modulator with which the polarization state of the light can be manipulated in a spatially resolved manner.
• the ratio of the scalar refractive index change to the strength of induced birefringence can be controlled by the appropriate choice of medium.
• polarization aberrations of optical systems can be compensated. These occur, for example, for imaging systems or even illumination systems at short wavelengths in the DUV, since crystalline solids are used as optical materials having intrinsic birefringence (IDB).
• IDB intrinsic birefringence
• the resulting polarization aberrations affect the imaging properties in the system and therefore need to be corrected.
• Crystals eg CaF 2, quartz but also high-index materials such as spinel or luag, BaF 2 , BaLiF 3 , LiF
• the applied to the lenses optical layers (antireflection coatings, etc.) on a birefringent behavior are a manufacturing caused anisotropy of the layers by the sputtering process or introduced voltages in the multilayer systems. They usually provide a rotationally symmetric double computation. Also, the inhomogeneous radiation exposure during operation of an exposure system can lead to locally induced tension and therefore lead to registration of birefringence, which have an iA complicated course.
• the optical element is designed as a rectangular or circular plate with a suitable edge length or radius or as a lens and made of quartz glass, calcium fluoride, Luag or even suitable birefringent liquids.
• the light source has a corresponding trigger in the form of a clock, for example an optical switch, whereby the pulse frequency and the oscillation frequency of the optical element are synchronized ,
• the method according to the invention is not only designed to correct wavefront aberrations, but the correction effect can also relate to the intensity distribution and thus to the contrast of the image or, in the case of a projection exposure apparatus, to the structure width in the lacquer of the wafer.
• the correction may relate to the angular distribution of the intensity of the illumination.
• the angles of illumination in the object plane correspond to the locations of the pupil of the projection objective.
• the angular distribution of the illumination corresponds to the intensity distribution in the objective pupil.
• the important for the imaging intensity distribution in the exit pupil may vary undesirably, for example in the form of a static apodization, for example, by non-ideal, that is not homogeneous over all angles acting layers (usually transmission in lenses, reflection in mirrors), but also by temporal variation of the layer properties.
• the intensity distribution can be spatially modulated by the combination of a polarization-optical modulator in the sense described above with other polsarisationsoptischen elements (especially polarizers).
• a polarization-optical modulator in the sense described above with other polsarisationsoptischen elements (especially polarizers).
• the transmission behavior of the entire element can be spatially adjusted and changed similar to the principle of liquid displays.
• the elements used according to the invention in the illumination system make it possible to correct or optimize the imaging properties of the overall system, which can be adapted to the individual, possibly also temporally unstable transmission properties of the optics in the selected illumination settings and the structures to be imaged.
• the diffraction orders in the projection lens undergo different optical paths and, according to the local transmission properties / variations with different intensities, overlap / interference at the image location. Accordingly, the superimposed intensities determine the contrast of the image and thus the "width" of the structure depicted in the paint (threshold behavior of the paint) .
• the equality of the imaged feature widths over the entire image field (CD uniformity) is an important factor in addition to the resolution.
• the oscillation of the optical element is excited as a superimposition of oscillations with different integer multiples of the pulse frequency, so as to set periodically modulated imaging properties in the optical element which lead to a higher-order optical effect. Since each eigenmode of a vibration of an optical element has a characteristic eigenmode dependent only on the geometry of the optical element and the boundary conditions, this can be controlled by the excitation in its amplitude and phase, but not in its shape. In order to achieve the desired optical effect, it is possible to superpose several eigenmodes whose natural frequencies are integer multiples of the laser frequency with a suitable amplitude or phase in order to set the desired optical function.
• the desired optical function function is developed according to eigenmodes of the oscillation modes whose natural frequencies are harmonious with the pulse frequency.
• the geometry of the optical element so that the eigenmodes correspond to the required correction functions and whose natural frequencies coincide with the harmonics of the pulse frequency.
• each of the different integer multiples of the pulse rate is associated with an individual phase shift, wherein the phase shifts are preferably variably adjustable, and / or if each of the different integer multiples of the pulse rate is assigned its own oscillation amplitude, which also preferably is variably adjustable.
• the phase shifts and / or amplitudes, which are assigned to the different integer multiples of the pulse frequency may be different from each other and / or to the pulse frequency.
• the time phase such that the pulse hits the optical element at the point of reversal of the oscillation process, since the temporal Changing the eigenform over the pulse width is the smallest and thus the best approximation of a temporally stationary optical effect can be achieved.
• a clock for the pulse frequency of the light pulses is provided, which in turn is connected to at least one frequency multiplier and at least one phase shifter whose output is connected to the devices for exciting a vibration.
• the clock signal is first supplied to the frequency multiplier, which generates a signal which represents an integer multiple (for example, 1, 2, 3, 4, ... times) of the pulse frequency.
• the phase shifter adds a certain phase shift to the signal, which can also be zero.
• the variable gain member controls the amplitude of the oscillation, which may also be zero.
• the signal thus generated is then supplied to the devices for exciting a vibration of the optical element to excite the optical element corresponding to the vibration.
• a clock generator for the purposes mentioned, which generates a multiple of the light source clock frequency.
• the clock frequency for the light source and for the excitation of the optical elements is generated from one or more phase-synchronous frequency dividers and adjusted by adjustable phase shifters and amplifiers according to the requirements.
• a plurality of frequency multipliers and phase shifter members are connected to the clock having their outputs connected to a summer whose output is connected to the means for exciting a vibration.
• a plurality of frequency-multiplied and possibly phase-shifted signals of the clock generator are summed to a control signal, which is then used to excite the optical element in a desired manner to a vibration which is a superposition of Represents vibration eigenmodes with which the desired optical effect can be achieved.
• the optical element comprises birefringent material, whereby a degree of polarization and a polarization state of the wavefront of a light pulse passing through the vibrated optical element can be selectively influenced with a suitable synchronization of pulse frequency and oscillation frequency.
• the optical element may also have a multilayer structure in that, for example, the optical element has a liquid or gas layer between two solid-state layers, wherein the liquid or gas layer or at least one of the two solid-state layers can be excited to vibrate.
• the optical element is preferably arranged in the region of a field plane of the optical device.
• the optical element is provided in the region of a pupil plane of the optical device.
• the optical element in the projection objective can be provided for image aberration correction at all those positions at which correction elements can be provided. These are preferably pupil planes and field planes, but also positions between pupil and field plane.
• an optical element which can be excited into oscillations can be used for the purpose of deliberately changing intensity profiles.
• Such as means for generating elastic oscillations of the optical element are devices such as loudspeakers (voice coils, Lorenz motor), piezoactuators, electrostatic, magnetostatic actuators / drives (motors different types) or hydraulically or pneumatically controlled actuators.
• loudspeakers voice coils, Lorenz motor
• piezoactuators piezoactuators
• electrostatic, magnetostatic actuators / drives motors different types
• hydraulically or pneumatically controlled actuators are also suitable as several different means for generating elastic vibrations.
• shading region is here and hereinafter referred to that portion of the optical element to which no light of the light source falls during operation. In this way, the passage of the operating light - in a projection exposure system of the projection radiation - and accordingly the figure is not affected.
• Such a shading area may be the circumference of the optical element.
• the optical element may also have a central center hole in which further devices for generating vibrations are arranged. This makes it possible to excite an even higher number of vibration modes.
• Such a hole for attacking means for generating vibrations may also be arranged decentrally, that is with an offset relative to the optical axis.
• the decoupling can be effected by avoiding a mechanical connection between the oscillating optical elements and further static optical elements of the objective. This is possible, for example, by providing a first carrier structure for the static optical elements and a second separate from the first, or decoupled, carrier structure is provided for the oscillating optical elements.
• an undesired power transmission by the oscillating optical element to the environment is avoided by generating compensation oscillations.
• This can be effected, for example, by one or more compensating elements, which oscillate correspondingly in antiphase, so as to compensate for the oscillation of the oscillating optical element.
• the optical element to be excited to elastic vibrations may be a plane plate.
• the optical element is preferably mechanically rigid, that is to say thick, for example, since this makes it possible to find relatively simply high-frequency modes whose frequency is at the laser frequency or one of the multiples.
• the optical element can furthermore preferably be made thin.
• thin optical elements for example thin plates, it is primarily the relatively high-frequency longitudinal modes that are suitable for setting a large number of higher vibration modes and thus correcting higher-order aberrations.
• the optical element is preferably formed as at least a partial space of the optical device which is filled with gas or in general a fluid.
• the gas of the subspace is vibrated by the means for generating vibration in the form of sound generators (eg, microphones), whereby local density variations cause a local refractive index change of the gas. If a light pulse synchronized with the sound wave impinges on the subspace, the wavefront of the light pulse experiences a change which can lead to an improvement of the imaging behavior of the optical device.
• the optical device has at least two spaced-apart optical elements on, between which a gap with gas or liquid is arranged.
• one of the two optical elements, the two optical elements and / or the gap with gas or liquid to the vibration can be excited.
• a first optical element of the two optical elements is made electrically insulating and a second optical element of the two optical elements is electrically conductive, it is preferred that first charges be locally induced on the first optical element first, and then the gap with gas or liquid is excited to vibrate.
• the vibratable optical element is designed so that its elasticity properties are not constant over the entire optical element but vary locally.
• Elasticity properties are to be understood, for example, as stiffness or damping behavior of the optical element.
• This can be achieved, for example, in the case of a transmitting optical element in that the optical element has a locally locally varying thickness from its center to its edge.
• the thickness of an optical element is the distance between its two optical surfaces, the distance being measured parallel to the optical axis.
• Such a locally varying thickness have, for example, spherical or aspherical lenses or optical elements with free-form surface.
• locally varying elasticity properties can also be achieved by suitable material design of the optical element, for example by the optical element having a locally locally varying density from its center to its edge.
• the optical element can be held by a carrier device, wherein the carrier device has locally varying elasticity properties.
• an array of optical elements may be provided which are interconnected by means of connecting elements, wherein these connecting elements may each have different elasticity properties.
• the carrier element can be designed such that eigenmodes of the oscillations in the optically used region of the optical element have the desired shape.
• lens arrays in other embodiments with flexible connecting elements it is also possible to provide arrays of mirrors or gratings or combinations of lenses and mirrors.
• an optical element in a further embodiment, it is also possible to design such an optical element as an array of flat, in particular plane-parallel, segment-wise and / or zonally-refractive lens segments.
• Such an array can be used as a Fresnel lens.
• the individual components of the array may have the same or different geometries. By providing different geometries of the individual components, the flexibility of the oscillating optical element with respect to image aberration correction or influencing the wavefront is further increased.
• the focus positions of the individual lenses are selectively influenced by selecting a suitable vibration mode.
• angles or intensities of the penetrating radiation beams can be influenced.
• a special application of such an angle-influencing oscillating lens array is possible in the illumination system of a projection exposure apparatus in order to set specific lighting settings.
• An illumination setting in a projection exposure apparatus is understood to mean the angular distribution of the intensities of the illumination beams when they hit the reticle, which corresponds to the angular distribution in a field plane.
• the adjustment of illumination settings with the aid of such an oscillating lens array has the advantage that by choosing different Licher vibration modes different lighting settings can be optionally set. Thus, no change of optical elements or insertion of screens or filters is required for a change of the lighting settings. Instead, it is sufficient to set a different vibration state.
• An oscillating lens array according to the invention can also be used to fine-tune a lighting setting which is adjusted by other means known in the art.
• the optical elements or arrays of optical elements which can be excited to oscillate here described can be used in an advantageous embodiment together with a control unit when used in an optical device, in particular in a projection exposure apparatus for photolithography.
• the control unit is equipped with a measuring system which locally determines predetermined control parameters of the oscillating optical element or of the array, for example the phase or the amplitude of the oscillation.
• the measuring system may comprise, for example, an interferometer with clocked illumination or an array of microphones or acceleration sensors which register spatially resolved the pressure fluctuations or acceleration of the optical surfaces.
• the measuring system in a preferred embodiment comprises individual sensors, for example focus sensors, which determine the focus position of the individual array components.
• the control unit also has an evaluation and control system, which controls the devices for exciting vibrations of the optical element based on the measured values recorded by the measuring system, if necessary by comparing these measured values with predetermined parameters from model calculations. In this way, the accuracy of the oscillation amplitude of the oscillating optical element or array and the corresponding synchronization with the pulsed light source can be set particularly precisely.
• Such a control unit may be provided for a single oscillating optical element, for a plurality of such elements simultaneously or for the entire optical device. Additionally or alternatively, a wavefront sensor can also be provided, which receives the wavefront of the entire optical system.
• the data determined by the wavefront sensor are also processed by the control unit and used for setting or adjusting the necessary for correcting vibration modes or vibration amplitudes of the optical element.
• a wavefront sensor or an interferometer is preferably used, preferably an interferometer with a plurality of parallel measuring channels for synchronous measurement at a plurality of field points, for example a multichannel shearing interferometer.
• an advantage of characterizing and controlling each of these elements is that individual deviations of the individual optical elements from model calculations based on an ideal optical element can be considered and compensated.
• a characterization and control is also advantageous in the overall system, since with the help of a sensor that detects the characteristics of the entire optical system, the interaction of the individual oscillating components can be determined and the desired effect can be set specifically in the overall system.
• control system further comprises a synchronization system for synchronizing the oscillation frequency of the optical element with the pulse frequency of the light source.
• the synchronization takes place on the basis of the parameters determined by the measuring and evaluation system for the vibration excitation and on the basis of the predetermined pulse frequency of the light source.
• further manipulatable optical elements can also be provided in an optical system according to the invention, in particular displaceable or tiltable as well as statically deformable optical elements.
• a control unit which has a measuring system which includes both sensors for determining parameters of the individual optical elements and sensors for determining parameters of the overall system.
• the intensity distribution in the exit pupil of the overall system of illumination system and imaging system can be measured instead of, for example, only separately measuring and separately correcting the intensity distribution of the illumination system.
• the correction values resulting from the measurement of the intensity distribution of the exit pupil then serve to correct the sum contributions from the illumination system and the imaging system, wherein the correction can then be carried out in the illumination system.
• the optical element is operated in reflection, it can be provided in a particularly advantageous embodiment to use a liquid medium having a reflective surface as a mirror.
• optical elements which can be excited to vibrate are provided in an optical device according to the invention, suitable positioning within the optical device and suitable adjustment and combination of the respectively excited vibration modes make it possible to compensate for even more complicated image defects than with only one oscillating optical element.
• Fig. 1 shows a schematic representation of a projection exposure apparatus with a projection lens
• Fig. 2 shows schematically the vibration of a thin plane plate with a simple vibration mode and with driving force at the place of fixation of the plane plate;
• Fig. 3 shows schematically the vibration of a thin plane plate with a simple vibration mode and with driving force outside the fixation
• Fig. 4 shows schematically a round optical element with 8 actuators
• Fig. 5 shows schematically a rectangular optical element with 12 actuators
• Fig. 6 shows schematically a central hole centered optical element and actuators at the periphery of the optical element and within the center hole;
• Fig. 7 shows schematically an embodiment of the optical element as
• Fig. 8 shows schematically an embodiment of the optical element as
• Fig. 9 shows schematically an embodiment of the optical element as
• Fig. 10 shows schematically an embodiment of the optical element as
• Fig. 11 shows schematically an embodiment with a lens array
• Fig. 12 shows schematically an embodiment with a lens array on a support
• Fig. 13 shows schematically an embodiment with a mirror array
• Fig. 14 shows schematically an embodiment with an array of mirrors and lenses
• Fig. 15 shows schematically an embodiment with a mirror
• Fig. 16 shows schematically a measurement and control concept for a single optical element
• Fig. 17 schematically shows an objective with a mechanical decoupling of vibratable optical elements and static optical elements
• Fig. 18 is a skeleton diagram of a control of the excitation of a vibration of the optical element in synchronization with the pulse frequency of a light source;
• Fig. 19 schematically shows another embodiment of the vibration-excitable optical element with lateral (longitudinal) vibration excitation
• Fig. 20 shows schematically a further optical element with transversal
• FIG. 21 schematically shows another embodiment of the optical element in the form of a gas resonator for exciting longitudinal vibration modes
• Fig. 22 shows schematically still another embodiment of the optical
• FIG. 23 shows the optical element in FIG. 22 with transverse vibrational excitation
• Fig. 24 shows schematically still another embodiment of the optical
• Fig. 25 shows schematically a still further embodiment of the optical
• Figs. 26A, 26B schematically show an arrangement of two optical elements between which a gas layer is interposed
• FIGS. 27A, 27B schematically show a still further embodiment of the optical element as a polarization-influencing plane parallel plate and its refractive index dependence on the radius.
• FIG. 1 schematically shows a microlithographic projection exposure apparatus 1, which is provided for the production of highly integrated semiconductor components by means of photolithography.
• the projection exposure apparatus 1 comprises a pulsed excimer laser 3 with a working wavelength of 193 nm as the light source.
• light sources of other operating wavelengths for example 248 nm or 157 nm or a plasma source of the wavelength 13.4 nm could also be used, with a wavelength of 13.4 nm only mirrors instead of lenses.
• a downstream lighting system 5 generates in its exit plane or object plane 7 a large, sharply delimited, very homogeneously illuminated and adapted to the Telezentrieer Dunisse the downstream projection lens 11 illumination field.
• the illumination system 5 has means for controlling the pupil illumination and setting a predetermined polarization state of the illumination light.
• a device is provided which polarizes the illumination light in such a way that the oscillation plane of the electric field vector runs parallel to the structures of the mask 13.
• a device for holding and moving a mask 13 is arranged such that it lies in the object plane 7 of the projection lens 11 and can be moved in a departure direction 15 in this plane for scanning operation.
• the substrate 19 is arranged so that the planar substrate surface coincides with the resist 21 substantially with the image plane 23 of the projection lens 11.
• the substrate is held by a device 17 which includes a drive to move the substrate 19 in synchronism with the mask 13.
• the device 17 also includes manipulators to move the substrate 19 both in the z direction parallel to the optical axis 25 of the projection lens 11, and in the x and y directions perpendicular to this axis.
• a tilting device with at least one tilting axis running perpendicular to the optical axis 25 is integrated.
• the device 17 (wafer stage) provided for holding the substrate 19 may be constructed for use in immersion lithography.
• a liquid is introduced into the intermediate space between the last optical element of the projection objective 11 and the substrate 19.
• projection exposure equipment devices for supplying and discharging the immersion liquid and a liquid-tight receptacle for fixing the liquid between the substrate 19 and the last optical element provided.
• the projection objective 11 comprises optical elements 27, 29, which are subjected to asymmetric radiation.
• the non-rotationally symmetric irradiation of the optical elements leads to a change in the imaging properties of the optical elements 27, 29 and corresponding to the entire objective in the course of the operating time.
• an optical element 31 is provided in the projection lens 11, which can be set into elastic oscillations by means of a series of piezoactuators 33 which are arranged on the circumference of the optical element 31.
• a control unit 35 is provided for controlling the piezo actuators 33.
• pneumatically or hydraulically controlled actuators can be used to excite the optical element 31, and an acoustic excitation is also possible.
• a sensor 55 is arranged, which receives the wavefront of the entire system.
• This sensor 55 is preferably designed as a wavefront sensor or as an interferometer.
• This interferometer has several parallel measuring channels for synchronous measurement at several field points.
• the measurement results are transmitted to a control computer 51 via data lines 53. From the measured data, this control computer 51 determines the image errors arising during the operating time and uses this information to determine a vibration mode for the optical element 31, which leads to an optimum compensation of the image errors. Via data lines 53, the control computer is connected to the control unit 35 for the optical element and to the light source 3.
• Fig. 2 shows schematically the operation of the vibrating optical element 231.
• the optical element 231 consists of a thin plane plate or a membrane. This membrane is vibrated by drives 233 arranged at the attachment points of the optical element 231.
• the drives can be arranged, for example, such that a cylindrical deformation of the optical element 231 occurs during the oscillation.
• the optical element 231 has the same shape every time a light pulse strikes. In effect, this corresponds to a static optical element with a corresponding cylindrical shape.
• the strength of the optical effect can be adjusted substantially by two effects, namely by the oscillation amplitude of the optical element 231 and the phase difference between the pulse frequency and the oscillation frequency of the optical element 231. If the light pulses each meet at the time of maximum deflection, the optical Effect of a maximum curved static optical element. If the light pulses each arrive at a different time at which the oscillating optical element 231 is less strongly deflected, the optical effect corresponds to a correspondingly less strongly curved optical element.
• the effect of an optical element with a curvature of opposite sign can be achieved by the phase shift between pulse frequency and oscillation frequency of the optical element is chosen to be greater than half a period of oscillation.
• the driving force can alternatively be introduced outside the fixation of the optical element 227. This is shown schematically in FIG.
• optical element 3331 By the shape of the optical element 331, by arrangement, number and position of the support points 332 and the actuators 333, as well as by the excitation frequency different eigenmodes and thus different deformations of the optical element 331 can be set.
• FIGS. 4 to 6 exemplarily show various shapes of the vibratable optical element 431.
• FIG. 4 shows a round optical element 431 with eight actuators 433 arranged along its circumference.
• the eigenmodes of circular plates or membranes, their calculation and modeling are known to those skilled in the art. It will therefore not be discussed further here.
• Fig. 5 shows another embodiment of the optical element 531 as a rectangular plane plate with 12 actuators 533, which are arranged along its circumference.
• the optical use region 537 lies in the center of the rectangular plane plate.
• the actuators 533 are arranged so that the useful range is not restricted.
• the eigenmodes of rectangular plates or membranes, their calculation and modeling are also known to those skilled in the art.
• FIG. 6 shows a further embodiment of the optical element 631 with a central center hole 639.
• actuators 633 are arranged both on the circumference of the optical element 631 and on the center hole 639. The number and arrangement of the actuators 633 determines the number of modes that can be excited.
• the actuators 633 are connected to compensation elements 641, which oscillate in phase opposition to the excitation of the optical element 631. This serves to decouple the actuators 633 from the socket of the optical element 631 or from the entire frame structure of the optical device. In this way it is avoided that the forces applied to excite the vibration of the optical element 631 are registered in the socket and cause adjacent optical elements to vibrate.
• the compensation elements 641 are designed so that the forces occurring are compensated exactly. Such compensating elements can be self- Of course, be provided for all other embodiments of the invention given here.
• a liquid medium may be provided as optical element 731, 831.
• the vibrating optical element 731 is operated here in reflection.
• the liquid may itself be reflective, such as mercury.
• the liquid may also be coated with a reflective thin elastic layer, for example with a gold foil. Deformations of the liquid surface then transfer to this film.
• the liquid is held by a liquid-tight container 743.
• the vibration excitation is carried out by means of acoustic stimuli through speakers 733, which are mounted on the circumference of the liquid container 743.
• a liquid optical element operated in transmission is also called a liquid lens.
• a liquid lens is shown.
• the liquid is contained in a liquid container 843, whose base consists of a transparent plane plate 845, for example made of quartz glass, and on whose circumference loudspeakers for acoustic excitation of the liquid are attached.
• Suitable liquids are, for example, distilled water, sulfuric acid, perfluorinated ethers or cyclohexane.
• the shape of the liquid container 843 may be designed such that the base of the container is designed as a further optical element, for example as a plano-concave or plano-convex lens.
• a closed embodiment as shown in Fig. 9 is particularly advantageous.
• the optical device can be kept free from contamination by evaporating liquid molecules.
• no contamination particles from the environment can enter the liquid.
• the liquid lens 931 in FIG. 9 is surrounded by a liquid container 943 whose base consists of a transparent plane plate 945, for example of quartz glass.
• the liquid keits responsible for a Plankenonvexlinse 951 completed.
• a liquid inlet and outlet 947 is provided.
• a vent 949 provides pressure equalization.
• speakers 933 are provided for vibrational excitation of the liquid lens.
• lattice-type periodic structures can also be produced with correspondingly high vibration modes.
• phase gratings can be generated as linear sine gratings, cross gratings or even radial gratings.
• 10 shows a rectangular optical element 1031 with a reflective surface, on the circumference of which a plurality of actuators 1033 are mounted, wherein a lattice-like structure was generated in the optical element 1031 by vibration excitation.
• FIGS. 11 to 14 Another embodiment of the vibrating optical element is shown in various configurations in FIGS. 11 to 14.
• the optical element is here designed as an array of individual optical components, for example in the form of a lens (FIGS. 11 and 12) or mirror array (FIG. 13) or else as an array of lenses and mirrors (FIG. 14).
• FIG. 11 shows a vibratable lens array 1131 in which the single lenses 1161 are connected to each other by flexible connecting members 1163.
• the individual lenses 1163 are arranged as a planar lens array 1131.
• the array need not be flat, but may be arranged in an uneven, z-shaped preformed matrix.
• the amplitude of a possible oscillation of the lens array 1131 are shown by arrows.
• FIG. 12 shows a lens array 1231 with individual lenses 1261 on a common carrier 1265.
• This carrier may be made of a material which has a different density locally, for example the density may be from the center of the Remove the carrier continuously towards the edge.
• the oscillation amplitude is locally influenced, so that the effective optically active form of the synchronized with the pulse frequency of the light source oscillating optical element, instead of basically assume a sinusoidal shape in cross section, is freely designed by the locally different density.
• FIG. 13 shows a mirror array 1331 with flexible connecting elements 1363 and 1367 between the individual mirrors 1369.
• the connecting elements 1363 and 1367 each have a different rigidity.
• FIG. 14 shows an array 1431 of individual lenses 1461 and individual mirrors 1469, which are connected to one another by connecting elements 1463.
• the local phase and amplitude of the individual elements can be controlled by means of focus sensors. This is shown in FIG.
• the operating radiation 1575 is reflected at the individual mirrors 1569, while the individual lenses 1561 focus the operating radiation 1575 at the point 1571.
• the focus sensors 1573 can be used for a control loop for the actuators 33, which excite the optical element 31 to vibrate. Such a control loop can be used not only for arrays of individual components, but also for a single oscillating optical element according to FIGS. 1 to 10.
• a measuring system 1655 serves to characterize the generated deformation of the optical element.
• the measuring system 1655 may include, for example, an interferometer with clocked illumination for measuring the surface, or else an arrangement. have microphones that record the pressure fluctuations of the optical surfaces spatially resolved. It is also possible for the measuring system 1655 to have an arrangement of acceleration sensors which register the acceleration fluctuations of the optical surfaces in a spatially resolved manner. Via data lines 1653, the measured values can be forwarded to an evaluation and control system 1651, which records and processes the measured values, in particular also stores them.
• the measured values can be compared with ideal values, for example with an ideal amplitude, obtained for the oscillation of an ideal optical element from model calculations.
• the deviations from the ideal state are determined, and the movement of the actuators 1633 for vibration excitation is optionally adjusted so that the vibration characteristic of the optical element 1631 comes close to the ideal state.
• the adjustment of the actuator movement is likewise carried out by the evaluation and control system 1651 via a data line 1653 which is connected to the actuator 1633.
• the evaluation and control system 1651 also serves to synchronize the oscillation frequency of the optical element 1631 with the pulse frequency of the light source (not shown in FIG. 16). For this purpose, the evaluation and control system 1651 is connected to the light source.
• FIG. 17 shows an embodiment of a lens with such decoupling.
• the oscillating optical elements 1731 are arranged in a first carrier structure 1783, while the static optical elements 1727 are arranged in a second carrier structure 1781.
• Both support structures 1781 and 1783 are mechanically separated from each other.
• the inner support structure 1781 has recessed ring segments, similar to a crown.
• the outer support structure 1783 engages with transverse arms 1787 through the recesses of the inner support structure 1781. It is also possible to provide more than two separate support structures. For example a separate carrier structure can be provided for each oscillating optical element.
• FIG. 18 shows a schematic diagram of an optical device 1810, which may be, for example, the projection exposure layer 1 in FIG. 1.
• Optical device 1810 includes a light source 1812, such as a laser.
• the optical device 1810 further comprises an optical element 1814, which may be, for example, the optical element 31 in the projection objective 11 of the projection exposure apparatus 1 in FIG. It is understood, however, that the optical element 1814 may also be an optical element of the illumination system 5 in FIG. 1.
• the light emitted by the light source 1812 is shown in FIG. 18 with an arrow 1816 and is directed through the optical element 1814.
• the optical element 1814 can be excited to vibrate as described in the previous exemplary embodiments, for which purpose devices 1818 for exciting a vibration, for example in the form of a piezoactuator, are assigned to the optical element 1814.
• the light source 1812 is associated with a clock 1820 (clock), which supplies the light source 1812 with a clock signal at the pulse frequency f pu i S e, so that the light source 1812 emits pulsed light with the pulse frequency f pu ise.
• clock which supplies the light source 1812 with a clock signal at the pulse frequency f pu i S e, so that the light source 1812 emits pulsed light with the pulse frequency f pu ise.
• a plurality of frequency-locked (phase locked loop (pH)) circuits 1822i 1,..., N) are connected to the clock generator 1820.
• Each of the frequency multipliers 1822i generates an integer multiple of the pulse frequency f pu ise.
• the frequency multiplier 1822 3 generates a signal having a frequency which is 3 times the pulse frequency f pu ise.
• a phase shifter 1824 which shifts or leaves unchanged the respective phase of the frequency-multiplied signal by an adjustable value (phase shift zero).
• phase shifter members 1824 is followed by an amplitude amplifier member 1826, which adjusts the signal amplitude appropriately by a factor less than or equal to 1.
• All signals processed in this way are fed to a summing element 1828 and summed up by it.
• the output of the summer 1828 is then connected to a signal amplifier 1838 whose output is connected to the devices 1818 for exciting a vibration of the optical element 1814.
• the vibration exciting devices 1818 which are applied with the amplified sum signal, excite the optical element 1814 in accordance with the sum signal.
• the light pulses of the light source 1812 are in phase synchronization with the modulation frequencies of the optical element 1814, they always sense the same state of the periodically excited optical element 1814.
• the periodically modulated imaging properties thus look temporally quasi stationary for the light pulses, similar to a stroboscope.
• an optical element 1910 is shown, which is formed as a transparent flat plate.
• the optical element 1910 may also be formed as a lens, mirror and the like.
• devices 1912, 1914 for exciting vibrations of the optical element 1910 are arranged.
• the devices 1912, 1914 are, for example, piezoelectric elements. With the devices 1912, 1914 predominantly lateral, ie longitudinal, eigenmodes of the optical element 1910 can be excited resonantly.
• the refractive index or birefringence is also locally modulated with a vibration amplitude that can be set by the excitation.
• the direction of excitation is illustrated by arrows 1916, 1918.
• the modulation of the refractive index then serves to achieve the desired optical effect.
• vibration isolation means 1920, 1922 are arranged on the optical element 1910 for vibration-decoupling the optical element 1910 from other optical elements of the optical system in which the optical element 1910 is present.
• FIG. 20 shows an optical element 2010 comparable to the optical element 1910, in which devices 2012, 2014 act to excite vibrations transversely on the optical element 2010 in order to excite transverse vibrational modes of the optical element 2010.
• the longitudinal vibration modes of the optical element 1910 in Fig. 19 do not or substantially do not change the shape of the surfaces of the optical element 1910
• the transverse vibrations of the optical element 10 result in a shape variation resulting in an optical effect.
• the modulated optical effect is predominantly based on a modulated distribution of the refractive index in the optical element 1910.
• Fig. 21 shows an optical element 2110 having a gas-filled or liquid-filled space 2116 between two plates 2112 and 2114.
• suitable devices for exciting a vibration longitudinal vibration modes are excited in the gas, which manifest themselves in a modulated density distribution and thus a location-dependent modulated refractive index.
• the higher density and lower density regions 2118-2122 and 2124-2130 are at the same time regions of higher pressure and lower pressure, respectively.
• a pressure difference of, for example, 28 Pa between the higher pressure regions and the lower pressure regions a refractive index difference ⁇ n of approximately 8.3 x 10 6 .
• the gas-filled space 2116 of the optical element 2110 may be adjusted in terms of modulation frequencies, and the higher-density and lower-density regions 2118-2122 and 2124-2130 may also be locally displaced by an appropriate choice of vibration excitation.
• Longitudinal vibration modes may be excited in different directions, for example, as shown in FIG. 21, in the direction of light transmission, transverse thereto, or simultaneously in the two aforementioned directions.
• FIG. 22 shows another optical element 2210 that has a liquid layer, for example a water layer 2216, between two solid state layers 2212 and 2214.
• the solid state layers 2212, 2214 are configured, for example, as transparent planar plates.
• the liquid layer 2216 can be excited to oscillate, either via the density-dependent refractive index of the liquid and / or via the thickness variation of the liquid layer 2216 due to pressure variations in the liquid and the compliance of the solid state layers 2212, 2214 to achieve an optical effect.
• FIG. 23 shows the optical element 2210 in FIG. 22, wherein, unlike FIG. 22, devices 2318, 2320 for exciting a vibration of the optical element 2210 engage transversely on the optical element 2310.
• devices 2318, 2320 for exciting a vibration of the optical element 2210 engage transversely on the optical element 2310.
• the solid state layer 2212 is excited, while the solid state layer 2214 is sufficiently rigid due to its greater thickness, so that the transverse oscillation modes of the solid state layer 2312 do not transfer to the solid state layer 2214 via the liquid layer 2216.
• FIG. 24 shows another embodiment of an optical element 2130, which is designed as a mirror 2132.
• Disposed on the mirror 2132 are devices 2133 for generating a vibration of the optical element 2130, which engage longitudinally on a mirror substrate 2135.
• the mirror substrate 2135 is vibrated so that a reflecting mirror surface 2137 oscillates in time, whereby a desired optical correction effect of the wavefront of a light pulse striking the mirror 2132 is achieved.
• a temporal variation of the reflecting mirror surface 2137 is meant, for example, a local density variation of the mirror surface 2137 or a spatial displacement of local points of the mirror surface 2137.
• an optical element 2140 is shown, which is formed as a subspace 2142 of an optical device 2143 (see dashed lines in Fig. 25).
• devices 2147 for generating an acoustic oscillation of the gas of the subspace 2142 which in the exemplary embodiment shown are designed as sound generators or microphones. By means of the devices 2147, a temporally modulated sound wave is generated in the gas of the subspace 2142, whereby a local density change in the closed subspace 2142 is induced.
• the sound wave is on reflected the sides of the subspace 2142.
• the oscillation frequency is synchronized with the pulse frequency of the light pulses, so that the light pulse passes through the subspace 2142 at a defined point in time at which the gas has a specific density pattern. This allows a targeted influencing of the wave front course of the light pulse.
• damping elements may further be arranged, which dampen the generated sound wave suitable, so that the wavefront second consecutive light pulses can be changed differently.
• the configuration of the optical element 2140 as a gas-filled subspace 2142 of the optical device 2143 advantageously enables a particularly simple, cost-effective improvement of the imaging behavior of the optical device 2143 that can be carried out in operation of the optical optical device 2143.
• the optical element 2140 may also be formed as the entire interior of the optical device 2143 or as a disk-shaped volume, for example in the region of the light passage of the optical device 2143.
• Fig. 26A shows an optical device 2150 in which two vibratable optical elements 2152, 2154 are accommodated.
• the two optical elements 2152, 2154 may, for example, be two spaced-apart circular plane-parallel plates or also a pellicle and a mask or a lens.
• the two optical elements 2152, 2154 are interconnected via elastic sidewalls 2156, with a gap 2158 filled with a gas, such as argon.
• the first optical element 2152 which is located upstream in the light propagation direction of the light pulses, is excited to transverse vibration by means of devices 2160. This leads to a location-dependent deflection of the pellicle or optical element, which is shown schematically exaggerated by the dashed lines in FIG. 26A.
• the gas is given a certain topology, which in addition leads to a density and thus to a refractive index variation of the gas. This leads to a targeted influencing of the wavefront of the light pulses.
• the two optical elements 2152, 2154 can be excited to a transverse vibration.
• a device 2162 for generating a vibration is also arranged on the optical element 2154.
• the oscillation frequencies of the two optical elements 2152, 2154 may be offset, for example, by 180 ° to each other phases.
• the gas in the intermediate space 2158 undergoes a density and refractive index variation, which changes the wavefront of a temporally suitably timed light pulse and specifically minimizes its error course.
• the gas in the gap 2158 is directly excited by means of a sound generator 2164 to an acoustic oscillation. As described above, a desired optical correction effect can thus be achieved.
• Fig. 26B shows the two optical elements 2152, 2154 of Fig. 26A, which are formed here as a plane-parallel plate and as a lens.
• the first optical element 2152 has a high resistance, i. it is electrically insulating, and the second optical element 2154 disposed in the light passing direction downstream of the optical element 2152 is electrically conductive. Inducing electric charges on the first optical element 2152 by means of a charged rod results in a repulsion of local areas of the optical element 2152 from the second optical element 2154.
• the gas in the gap 2158 undergoes a corresponding density modulation ,
• the gas of the gap 2158 is vibrated by the device 2164 disposed on the gap 2158.
• the density variation of the gas results in a local change in the refractive index of the gas, as a result of which a wavefront curve of a suitably clocked light pulse which passes through the gas can be influenced in a targeted manner.
• FIG. 27A shows a top view of an optical element 2170, which is designed as a circular quartz plate 2172 with radius R and is accommodated, for example, in the projection objective of the projection exposure apparatus.
• the optical element 2170 can likewise be accommodated in the illumination optics of the projection exposure apparatus.
• the optical element 2170 is oscillatable by means of a sound generator 2173, whereby a sound wave propagates in the optical element 2170.
• This acoustic wave results in longitudinal density waves that propagate in the optical element 2170 and produce a directional stress field, which in turn locally affects the birefringence properties of the optical element.
• the resultant double-pincushion of the optical element having the radius r of the circular disk decreases radially outward toward the edge of the optical element 2170 (see Fig. 27B).
• the major axes of birefringence are oriented radially and tangentially.
• the optical element 2170 can act as a depolarizer for the polarization state of the wavefront of the light pulses of the light source.
• the optical element 2170 acts as a rapidly switchable ⁇ / 2 plate which changes or tilts the polarization state by 90 ° between two laser pulses.
• the laser pulses fall alternately to a minimum and a maximum of the voltage field in the material of the optical element 2170.
• both the lighting mode and the imaging properties of the projection exposure apparatus can be dynamically influenced and selectively changed in order to improve their imaging quality and to correct aberrations that occur.
• aberrations of the wavefront profile of the light pulses of the light source can be compensated, or else the image contrast can be compensated by adapting the (local) polarization state to the image to be imaged Structure to be optimized.
• Use of the optical element 2170 in the illumination makes it possible, for example, to generate rotationally symmetrical illumination modes of the projection objective and to manipulate the coherence properties and the polarization of the light pulses of the light source.

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