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WO2005050325A1 - Systeme d'eclairage optimisant la polarisation - Google Patents

Systeme d'eclairage optimisant la polarisation Download PDF

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Publication number
WO2005050325A1
WO2005050325A1 PCT/EP2004/012398 EP2004012398W WO2005050325A1 WO 2005050325 A1 WO2005050325 A1 WO 2005050325A1 EP 2004012398 W EP2004012398 W EP 2004012398W WO 2005050325 A1 WO2005050325 A1 WO 2005050325A1
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WIPO (PCT)
Prior art keywords
polarization
illumination system
light
rectifier
illumination
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Ceased
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PCT/EP2004/012398
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English (en)
Inventor
Jess Koehler
Damian Fiolka
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Carl Zeiss SMT GmbH
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Carl Zeiss SMT GmbH
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Publication of WO2005050325A1 publication Critical patent/WO2005050325A1/fr
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    • 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
    • G03F7/70058—Mask illumination systems
    • G03F7/70066—Size and form of the illuminated area in the mask plane, e.g. reticle masking blades or blinds
    • 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
    • G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
    • G03F7/7055—Exposure light control in all parts of the microlithographic apparatus, e.g. pulse length control or light interruption
    • G03F7/70566—Polarisation control

Definitions

  • the invention relates to an illumination system for a projection exposure system for microlithography, in particular for a wafer scanner, for illuminating an illumination field on an outlet plane of the illumination system with the light from a light source, and to a projection exposure installation equipped with an illumination system such as this.
  • the performance of projection illumination installations for microlithographic production of semiconductor components and other finely structured components is governed substantially by the imaging characteristics of the projection optics. Furthermore, the image quality and the wafer throughput which can be achieved with an installation are also governed substantially by characteristics of the illumination system upstream of the projection objective.
  • This illumination system must be able to prepare the light from a light source with as high an efficiency as possible and, in the process, to set a light distribution which can be defined accurately with regard to the position and shape of illuminated areas and in which the intensity distribution within illuminated areas is as uniform as possible.
  • a pupil forming unit allows a defined spatial light distribution to be set on a pupil plane in the illumination system and should satisfy the above requirements equally for all the illumination modes which can be selected, that is to say for example for conventional settings with different coherence degrees or for annular field, dipole or quadrupole illumination.
  • the last-mentioned, off-axis illumination modes represent one precondition for imaging of the reticle patterns with a high interference contrast.
  • One requirement which is becoming increasingly important for illumination systems is that they should be able to produce output light with a polarization state which can be defined as accurately as possible.
  • Linearly polarized input light allows, for example, catadioptric projection objectives with polarization beam splitters (beam splitter cube, BSC) to operate with a theoretical efficiency of 100% at the beam splitter.
  • BSC polarization beam splitters
  • a high degree of uniformity or homogeneity of the illumination falling on the photomask (reticle) can be achieved by homogenization of the light coming from a light source, by means of a homogenization device.
  • One widely used possible way to homogenize light is to use light mixing devices, which result in homogenization of the illumination of an illumination field on an intermediate plane in the illumination system, which is optically conjugated to the output plane of the illumination system.
  • a distinction is in this case drawn essentially between the light mixing devices with fly's eye integrators (honeycomb condensers) and light mixing devices with integrator rods or light mixing rods.
  • Systems with integrator rods are characterized by better transmission efficiency and are therefore frequently used in projection exposure installations for microlithography.
  • an integrator rod is composed of a material which is transparent for the light from the light source, with light with a given aperture passing through it, essentially along its longitudinal direction. The light passing through the integrator rod is subject to multiple total internal reflection on the lateral boundary surfaces, as in a kaleidoscope, so that it is possible to achieve virtually perfect mixing of light components which are not homogeneous.
  • integrator rods of this type has the disadvantage that their influence on the polarization state of the light passing through can be controlled only with difficulty.
  • Lasers are frequently used as the light source for the short wavelengths of about 248 nm, 193 nm or 157 nm that are used in microlithography, and emit light in an essentially linearly polarized form. If the pupil forming unit does not change the polarization state of the light, such that it falls in a linearly polarized form on the inlet surface of the integrator rod, it frequently emerges from the integrator rod again as light which is now only partially polarized.
  • the remaining polarization degree (proportion of the polarized light with respect to the total light) depends in particular on the orientation of the linear polarization at the rod inlet, the material quality with respect to stress birefringence, and the nature of the holder for the integrator rod. Initially, it is thus not possible to maintain the polarization state of the laser light as it passes through the illumination system when using an integrator rod as the homogenization device.
  • US 6,053,615 discloses an illumination system for an LCD projection installation, which has to produce light with a defined preferred polarization direction from the unpolarized light from a light source, in particular a halogen metal vapor lamp. This is because it is functionally necessary for LCD projection installations for the light to leave the illumination system with a defined polarization direction, since the liquid crystals in the LCD display connected downstream from the illumination system carry out their function only when illuminated with polarized light. Unpolarized light is converted to linearly polarized light by means of a polarization rectifier.
  • Japanese Patent Application JP 2002-116414 A and Patents US 6,154,320 or US 5,986,809 disclose other examples of illumination systems for projectors which are intended for producing uniformly polarized illumination light with a homogeneous intensity distribution from unpolarized light from a light source.
  • the invention is based on the object of providing an illumination system which is particularly suitable for use in a microlithographic projection exposure installation, transmits the light from an associated light source with high efficiency and allows the polarization state of the emerging light to be set in a defined manner, and of providing a projection exposure installation which is equipped with such an illumination system.
  • An illumination system has a pupil forming unit for producing a light distribution which can be predetermined on a pupil plane of the illumination system, a homogenization unit for influencing the illumination of an illumination field on an intermediate field plane, which is optically conjugated with respect to the outlet plane, of the illumination system and an imaging objective for imaging the intermediate field plane on the outlet plane following the imaging objective.
  • At least one polarization conversion device having a large number of polarization rectifier elements is arranged in the imaging beam path of the imaging objective.
  • a polarization conversion device converts the incident light which is incident on it and is generally partially polarized or unpolarized to emitted light with a spatial distribution of polarization directions which can be predetermined. Only a small proportion of the light intensity is lost during this largely loss-free conversion process.
  • a polarization conversion device thus operates differently to a polarization filter which emits only a fraction of the light intensity again, in the form of polarized light, when partially polarized or unpolarized light is incident on it.
  • polarization conversion device in the illumination system thus makes it possible to ensure that the light emerging from the illumination system has a defined spatial distribution of polarization states, without a large proportion of the light intensity being lost during the production of this polarization state distribution.
  • a further advantage of polarization conversion without loss of light is the fact that there is no need to dissipate the component of the light, which could possibly fall on the sockets or the optics material, where it could cause damage.
  • One advantage of positioning the polarization conversion device in the imaging beam path of the imaging objective of the illumination system is that there are normally no more devices, or only a small number of devices, which greatly change the polarization in the light path downstream from the polarization conversion device.
  • the advantageous positioning of the polarization conversion device means that light with a defined polarization state can in any case be provided on the outlet plane of the illumination system.
  • the homogenization unit has at least one light mixing rod, then partially or completely unpolarized light frequently occurs owing to the depolarizing characteristics of this rod on the intermediate field plane, which is imaged by the imaging objective on the outlet plane of the illumination system.
  • the positioning of the polarization conversion device in the imaging beam path of the imaging objective, and thus in the light path downstream from the light mixing rod, has been found to be particularly advantageous in this case, in order to compensate for its partially uncontrollable polarization-changing effect independently of the selected illumination mode.
  • the homogenization unit need not necessarily have a light mixing rod or a fly's eye integrator arrangement. Particularly if the microlithography projection exposure installation is a wafer scanner, largely homogeneous illumination of the reticle can be achieved even with a suitable field trimming diaphragm unit, by using the integrating effect of the scanning process. Homogenization at right angles to the scanning direction may likewise be advantageous.
  • a laser for example an excimer laser with an operating wavelength of about 248 nm, about 193 nm or about 157 nm, then the light which is injected into the illumination system is essentially linearly polarized. If this polarization is to be maintained in the illumination system, then it has been found to be particularly advantageous to fit a polarization conversion device in the imaging objective, since any change in the polarization state produced by the illumination system upstream of the imaging objective can be effectively corrected by the use of this device.
  • a polarization conversion device which is configured overall as a polarization rectifier can be used to ensure that the emitted light beam has uniform polarization over its entire cross section, and at the same time also has a largely homogeneous intensity distribution. If the upstream elements in the light path are designed such that they produce partially polarized light, then it may be worthwhile positioning a separate depolarizer immediately in front of a polarization rectifier, in order to produce unpolarized incident light. This allows a polarization-maintaining illumination system to be created.
  • the polarization conversion device It has been found to be particularly advantageous to position the polarization conversion device on the pupil plane or in the vicinity of the pupil plane of the imaging objective, since the numerical aperture of the beam path is small there.
  • a parallel beam path for the light entering the polarization conversion device would be the ideal case, since such incidence would mean that there was no inhomogeneity in the angle distribution, so that the light produced by the polarization conversion device can have a polarization degree which is largely homogeneous over the entire outlet plane of the polarization conversion device.
  • the polarization conversion device has a length governed by the physical structure in the direction of the optical axis of the imaging objective, it is advantageous for the pupil plane to be located in the interior of the polarization conversion device.
  • the polarization conversion device may be advantageous to arrange the polarization conversion device in the vicinity of the outlet plane of the imaging objective, since in this case no optical elements, or only a very small number of optical elements, in the illumination system can change the polarization state produced by the polarization conversion device.
  • any small optical path differences which may occur when passing through lens systems owing to the birefringence of the lens material that is used can be compensated for again by skilful alignment of the crystal axes of the lens material that is used.
  • the polarization conversion device has a large number of polarization rectifier elements.
  • a polarization rectifier element is preferably designed such that the emerging light has a uniform polarization state, for example linear polarization, irrespective of the polarization state of the incident light.
  • Preferred polarization rectifier elements split the light striking them into partial beams with mutually orthogonal polarization directions, and then change the polarization direction of partial beams in such a way that only light with a single polarization direction now emerges from the polarization rectifier element. This is made possible by suitable retarder units.
  • the polarization direction of a first partial beam it has been found to be particularly advantageous for the polarization direction of a first partial beam to be aligned parallel to the polarization direction of a second partial beam by means of a ⁇ /2 plate or some other device with a comparable effect, for example a layer system or an optically active polarization rotator, which makes use of the optical activity of quartz.
  • Birefringent ⁇ /2 plates are preferably in the form of low-order delay plates, which are only slightly sensitive to angle.
  • the "polarization direction" is a specific oscillation direction of a component of the electrical field strength vector.
  • a polarization splitter layer for splitting the light which is incident on a polarization rectifier element into two partial beams with mutually orthogonal polarization directions, it has been found to be advantageous to arrange this layer at an angle of 45° ⁇ 5° with respect to the light striking the polarization rectifier element, since a large number of layer systems which are suitable for polarization splitting operate particularly effectively in this case.
  • a polarization splitter layer should be operated in the angle range of the associated Brewster angle.
  • the expression polarization splitter layer is used synonymously in the following text to the expression beam splitter layer.
  • a beam deflection surface is arranged parallel to each beam splitter layer. This aligns the partial beam reflected from the beam splitter layer parallel to the partial beam transmitted from the beam splitter layer. This means that the light emerging from the polarization rectifier element essentially comprises parallel partial beams, each with a defined polarization direction.
  • a spatial arrangement of polarization rectifier elements is used for polarization rectification, each of which is equipped with beam deflection surfaces and polarization splitter surfaces aligned parallel to one another, and with a retarder unit.
  • the polarization rectifier elements spatially such that they lie on a plane at right angles to the optical axis, with the beam splitter layers and hence also the beam deflection surfaces preferably being inclined at about 45° to the optical axis.
  • the spatial arrangement is also referred to in the following text as an "array”.
  • An array such as this may have a single row of polarization rectifier elements located alongside one another (linear array), or may have two or more rows and columns (two-dimensional array).
  • a focusing device is fitted in the light path in front of each polarization rectifier element, in order to focus the light that is incident on this element onto the polarization splitter surface provided in this element, so that all of the light which is incident on the polarization rectifier is passed to the polarization splitter surfaces.
  • the polarization conversion device virtually all of the light which is incident on the polarization conversion device is used for conversion to light with a desired spatial distribution of preferred polarization directions, so that the amount of light lost through the polarization conversion device is small. Due to the fact that the inlet surface of the polarization conversion device can be designed to be essentially the same size as its outlet surface, this can be incorporated in the imaging objective, without having to make any major physical changes.
  • At least one beam deflection surface is a mirror surface, which is advantageously in the form of a multilayer system with dielectric individual layers.
  • the layers which are required for production of such mirror surfaces can be produced at low cost.
  • polarization splitter surfaces as beam deflection surfaces may be advantageous since only a single type of optical element then need be manufactured for the purpose of beam splitting and beam deflection, which may contribute to reducing the costs for production of the polarization rectifier.
  • a ⁇ /2 delay unit for example a ⁇ /2 plate
  • a polarization rectifier element produces light which is polarized essentially parallel to the incidence plane of the polarization splitter surface, since a polarization splitter surface normally transmits light which is incident parallel to the incidence plane, but in contrast reflects light which is polarized at right angles to the incidence plane.
  • a polarization rectifier element essentially produces light which is polarized at right angles to the incidence plane of the polarization splitter surface.
  • the polarization conversion device has a linear small rod array comprising polarization rectifier elements, as well as a linear cylindrical lens array as a focusing device.
  • a linear array means an arrangement of elements (lenses and/or polarization rectifier elements) in a row alongside one another, with the long faces of the small rods or of the cylindrical lenses abutting against one another in the present case.
  • the distance between the cylindrical lens array and the polarization rectifier elements is in this case preferably chosen such that the polarization rectifier elements are arranged in the vicinity of the focal plane of the cylindrical lenses.
  • the projection exposure installation is a wafer scanner, and the long faces of the cylindrical lenses and of the small rods are fitted at right angles to the scanning direction of the wafer scanner.
  • a path length difference occurs between partial beams which are reflected and transmitted by the polarization splitter layer. If the light which strikes a polarization rectifier element is focused by means of a focusing device, this path length difference leads to the focal planes of the partial beams being axially offset with respect to one another, that is to say in the direction of the optical axis.
  • the reflected beam has a focal plane which is located in front of the focal plane of the transmitted beam in the light propagation direction. This means that the energy distribution in the pupil is offset in the scanning direction on the reticle plane, which corresponds to a telecentric error.
  • the length of the short faces of the polarization rectifier elements pointing in the scanning direction is thus in one particularly preferred embodiment short in comparison to the length of the overall light field in the scanning direction. This may be in the order of magnitude of 5%, 2%, 1% or less of this length.
  • Polarization conversion devices make it possible to set different spatial distributions, which can be predetermined, of the polarization state of the emitted light beam.
  • the polarization conversion device is in the form of a polarization rectifier for conversion of an incident light beam to an emitted light beam with a uniform polarization over its entire cross section. If required, this makes it possible to produce uniformly polarized light, for example linearly polarized light, from completely unpolarized light. In one preferred embodiment, this is achieved by all of the polarization rectifier elements in the polarization conversion device having a uniform orientation. Polarization rectifier elements with obliquely positioned polarization splitter surfaces may be provided for this purpose, with all of the polarization splitter surfaces being aligned parallel and offset with respect to one another.
  • illumination modes may be advantageous for illumination of a mask in a microlithography installation, in which a polarization distribution with a spatial variation in the polarization state is provided in the area of a pupil plane in the imaging system.
  • the polarization conversion device in preferred embodiments is designed to produce an emitted light beam with a predeterminable local variation of the polarization state over the cross section of the emitted light beam.
  • the polarization conversion device is designed as a tangential polarizer for conversion of an incident light beam to an emitted light beam with essentially tangential polarization.
  • the tangential polarization is characterized in that the locally occurring preferred polarization directions, that is to say the locally occurring main oscillation directions of the electrical field vector, are essentially aligned at right angles to a radial direction, with respect to the optical axis.
  • the polarization conversion device may be in the form of a radial polarizer, in order to use an incident light beam to produce an emitted light beam which is essentially polarized radially (oscillation direction of the electrical field vector essentially radially with respect to the optical axis) over the entire cross section.
  • a usable cross section of the polarization conversion device to be subdivided into two or more rectifier groups, each having one or more polarization rectifier elements, with the polarization rectifier elements in a rectifier group with two or more polarization rectifier elements each being configured to produce a uniform polarization within the partial beam of the emitted light produced by them, and the polarization rectifier elements in different rectifier groups having a different orientation, at least in some cases.
  • the shape and/or size of the effective cross section of the individual rectifier groups may be matched to the desired polarization distribution in the emitted light beam.
  • the polarization rectifier elements may be advantageous from the manufacturing point of view for all of the polarization rectifier elements to have the same cross- sectional size and/or the same design, it is also possible for the polarization rectifier elements to have a different cross-sectional size, in order to make it possible to set particular polarization distributions with a suitable spatial resolution.
  • a changeover device is provided for optional insertion, removal or replacement of polarization conversion devices into, from or in the beam path. If a polarization conversion device is in the form of a replaceable element, then the changeover device can be used to set suitable polarization distributions in the emitted light beam for different illumination modes (for example dipole illumination, conventional illumination of different coherence degrees, quadrupole illumination) (for example polarization in the x direction, polarization in the y direction, radial polarization or tangential polarization).
  • illumination modes for example dipole illumination, conventional illumination of different coherence degrees, quadrupole illumination
  • polarization in the x direction for example polarization in the x direction, polarization in the y direction, radial polarization or tangential polarization.
  • the polarization conversion device has an associated collimator device, which is arranged in the light path downstream from the polarization conversion device, for collimating the emitted light.
  • the collimator device preferably has a lens array with a large number of individual lenses, the number of which corresponds to the number of partial beams coming from the polarization conversion device.
  • each polarization rectifier element may be associated with two individual lenses in the collimator device, in order to collimate on the one hand the directly transmitted partial beam and on the other hand the partial beams which are initially reflected and are then deflected on the beam deflection surface, separately from one another. Since a path length difference may occur between the transmitted partial beam and the reflected partial beam when light passes through a polarization rectifier element, leading to different axial positions of the focal planes of the partial beams when there is an upstream focusing device, individual lenses which are adjacent in pairs in one development of the collimator device are offset at an axial distance from one another, with this axial distance corresponding to the axial distance between the focal planes of the partial beams.
  • the collimator unit may have individual lenses which are located alongside one another and have a different focal length, in order to achieve collimation for each partial beam, despite the focal planes being in different positions.
  • the diameters of the lenses would vary.
  • transparent material blocks may be provided between the polarization rectifier elements and the associated downstream individual lenses in the collimator device, in order to compensate for the optical path length differences of the partial beams.
  • Preferred variants of polarization conversion devices according to the invention produce a large number of secondary light sources, the number of which corresponds to the number of partial beams. In one preferred embodiment, this is made use of in order to use the polarization conversion device for the purpose of homogenization of the intensity of the beam by means of light mixing.
  • a field lens arrangement is for this purpose arranged in the light path downstream from the polarization conversion device such that partial beams which emerge from the polarization rectifier elements are at least partially superimposed on a plane which follows the field lens arrangement. This allows the polarization conversion device to be combined with an arrangement similar to a honeycomb condenser (a fly's eye integrator).
  • Figure 1 shows a schematic overview of one embodiment of an illumination system according to the invention for a projection installation for microlithography having a light mixing device as a homogenization unit;
  • Figure 2 shows a schematic overview of one embodiment of a polarization conversion device according to the invention, which is configured as a polarization rectifier;
  • Figure 3 shows a schematic overview of a further embodiment of an illumination system according to the invention for a wafer scanner
  • Figure 4 shows, schematically, in (a) an axial view of a pupil plane of an imaging objective having a polarization conversion device, which comprises two or more rectifier groups with different orientation, in order to produce emitted light with a tangential polarization, and in (b) a single polarization rectifier element;
  • Figure 5 shows, schematically, axial views of pupil planes of the imaging objective with various arrangements of rectifier groups in polarization conversion devices;
  • Figure 6 shows, schematically, an axial section through one embodiment of a polarization conversion device, which has an associated collimator device for collimation of the output radiation;
  • Figure 7 shows, schematically, an axial section through one embodiment of a polarization conversion device, which is combined with a light mixing device in the form of a fly's eye integrator.
  • Figure 1 shows one example of a projection exposure installation 1 for microlithography, which can be used for the production of semiconductor components and other finely structured components and operates with light from the deep ultraviolet band in order to achieve resolutions down to fractions of micrometers.
  • An F 2 excimer laser with an operating wavelength of about 157 nm is used as the light source 2, whose light beam is aligned coaxially with respect to the optical axis 3 of the illumination system.
  • Other UV light sources for example ArF excimer lasers with an operating wavelength of 193 nm, KrF excimer lasers with an operating wavelength of 248 nm, or mercury vapor lamps with an operating wavelength of 368 nm or 436 nm, or light sources with wavelengths below 157 nm are likewise possible.
  • the linearly polarized light from the light source 2 first of all enters a beam widener 4 which, for example, may be in the form of a mirror arrangement as claimed in DE 41 24 311 , and is used for coherence reduction and to enlarge the beam cross section.
  • a beam widener 4 which, for example, may be in the form of a mirror arrangement as claimed in DE 41 24 311 , and is used for coherence reduction and to enlarge the beam cross section.
  • the imaging objective 15 contains a first lens group 17, a pupil intermediate plane 18, a second and a third lens group 19 and 20, respectively, and, in between them, a deflection mirror 21 , which allows the large illumination device (with a length of approximately 3 m) to be installed horizontally, and allows the reticle 50 to be mounted horizontally.
  • a polarization conversion device 22 is arranged in the vicinity of the pupil plane 18, is in the form of a polarization rectifier overall, and its design will be described in more detail in conjunction with Figure 2.
  • a device 52 for holding and manipulating the reticle 50 is arranged behind the illumination system, such that the reticle is located on the object plane of a projection objective 51 , and can be moved on this plane for scanner operation in a scanning direction (y direction), with the aid of a scanning drive.
  • the mask plane 53 is followed by the projection objective 51 , which acts as a reduction objective and produces an image of a pattern which is arranged on the mask on a reduced scale, for example on a scale of 1 :4 or 1 :5, on a wafer 54 which is covered with a photoresist layer and is arranged on the image plane 55 of the reduction objective.
  • a reduced scale for example on a scale of 1 :4 or 1 :5
  • a wafer 54 which is covered with a photoresist layer and is arranged on the image plane 55 of the reduction objective.
  • Other reduction scales for example greater reductions down to 1 :20 or 1 :200, are possible.
  • the wafer 54 is held by a device 56 which comprises a scanner drive in order to move the wafer in synchronism with the reticle 50, and parallel to it. All the systems are controlled by a control unit 57.
  • the small rod array 24 is arranged in the vicinity of the focal plane of the cylindrical lens array 23.
  • the cylindrical lenses 39 are joined together to form an array in such a way that each individual cylindrical lens abuts against the adjacent cylindrical lenses.
  • the entire array can be thought of as being formed by translation of a single cylindrical lens with an integer multiple of the diameter of a cylindrical lens in the scanning direction.
  • the small rod array can likewise be thought of as being formed by translation by an integer multiple of the length of a single polarization rectifier element 36 in the scanning direction.
  • the cylindrical lenses 39 and the polarization rectifier elements 36 each extend in the x direction over the entire illuminated width of the imaging system.
  • Each polarization rectifier element 36 has two identically constructed small polarization splitter rods 37, 38 which are directly adjacent to one another.
  • Each of the two small polarization splitter rods 37, 38 has a square base area and has a polarization splitter layer 31 , 32.
  • This polarization splitter layer 31 , 32 is arranged between two triangular prisms 40, 41 with a rectangular equilateral base surface, such that two triangular prisms 40, 41 abut against one another along their hypotenuse face, with the polarization splitter layer 31 , 32.
  • a ⁇ /2 plate 33 is wrung against the light outlet surface of the first small polarization splitter rod 37.
  • the short face, pointing in the scanning direction, of a triangular prism 41 acts as the light outlet surface for the small polarization splitter rod.
  • the polarization splitter layers 31 , 32 are each tilted at an angle of 45° with respect to the optical axis of the illumination system.
  • the incident light should strike them at an incidence angle range of 45° ⁇ 5°. This is possible in the vicinity of the pupil plane 18 of the imaging objective, since the light here comprises partial beams which run approximately parallel to the optical axis and diverge at most about 1 ° from the direction of the optical axis 3; this arrangement of the polarization rectifier 22 results in the essentially parallel beam path of the light entering the polarization rectifier 22 being changed to an essentially parallel beam path of the light emerging from the polarization rectifier 22.
  • a typical order of magnitude for the lens cross sections in the exemplary embodiment described here is from 120 mm to 4 mm; a typical order of magnitude for such cross sections for the small polarization splitter rods is from 120 mm to 2 mm, and the order of magnitude of the distance between the lens array and the polarization splitter small rod array, that is to say the focal length of the lenses, is about 50 mm.
  • the splitting of the light in the polarization splitter small rod array 24 results in the introduction of a light transmission level in the scanning direction which is additionally increased by the cylindrical lens array.
  • the incidence angle range of the light striking the polarization splitter layer is about 45° ⁇ 3°, and is thus within the interval of 45° ⁇ 5° which is advantageous for the operation of the polarization splitter layer.
  • Each polarization splitter layer 31 breaks down the incoming light beams into light which is polarized at right angles (s) and parallel (p) to the incidence plane.
  • the p-polarized partial beam is transmitted by the polarization splitter layer 31 , and continues essentially parallel to the optical axis of the imaging objective, while the s-polarized partial beam is reflected on the polarization splitter layer 31 , and continues essentially at right angles to the optical axis of the illumination system.
  • the s-polarized partial beam thus strikes a second polarization splitter layer 32, which acts as a beam deflection device, in a second small beam splitter rod 38, which is adjacent to the first small beam splitter rod 37.
  • the ⁇ /2 plate 33 which is fitted to the light outlet surface of the first small polarization splitter rod 37 rotates the polarization direction of the first partial beam from p polarization to s polarization, so that essentially only s-polarized light emerges from the polarization rectifier 22. If the incident light striking the field arrangement 24 is completely unpolarized or is circular-polarized, then the light intensities in the partial beams are the same, so that the intensity distribution behind the small rod array 24 is homogeneous.
  • the intensities which emerge from the beam splitter elements 37 and 38 are different.
  • the intensities of the partial beams which are transmitted directly through the beam splitter layers are greater than the intensities of those partial beams which do not emerge from the small rod array 24 until they have been reflected twice.
  • the intensity distribution behind the small rod array is thus inhomogeneous, with areas of relatively strong and relatively weak intensity being located alongside one another, alternately.
  • a possibly replaceable depolarizer 26 can optionally be introduced into the beam path of the illumination system upstream of the polarization conversion device 22 ( Figure 1 ).
  • the depolarizer which may be positioned near the field plane 6, for example, may include a wedge of birefringent material.
  • the offset between the focal planes corresponds precisely to the path length difference which the beam reflected by the polarization splitter layer 31 travels over between this and the beam deflection surface 32, but this path length difference corresponds essentially to half the length of a polarization rectifier element in the scanning direction, at least 50 polarization rectifier elements should thus be used for an offset of less than 1/100 of the pupil diameter.
  • the use of light with a defined polarization state as the illumination light for the projection objective 51 in the projection exposure installation 1 can be implemented in various ways.
  • the use of illumination light with linear polarization is advantageous, since the polarization beam splitter can in this case be operated with very high efficiency. No polarization-changing element is thus required for this purpose behind the polarization rectifier 22.
  • a suitable delay element for example a ⁇ /4 plate, may be used to convert the linearly polarized light in the beam path downstream from the polarization rectifier 22 to circular-polarized light before the reticle plane 53, and this has a particularly advantageous effect on the avoidance of structure- direction-dependent resolution differences (H-V differences or CD variations) in the imaging of the reticle 50 on the wafer 54.
  • Polarization-changing devices for example as described in DE 101 24 803 (which corresponds to US 2002/0176166 A1 ) may of course also be fitted permanently or replacably in the illumination beam path downstream from the polarization rectifier, if required, in order to produce radially or tangentially polarized illumination light.
  • FIG 3 shows a schematic overview of one embodiment of an illumination system according to the invention for a wafer scanner, which operates without a rod integrator.
  • the illumination system 101 shown in Figure 3 has all of the elements of the illumination system 1 shown in Figure 1 except for the light mixing device (rod integrator) 12.
  • the same reference symbols, increased by 100, are therefore used for corresponding elements. Since the light mixing device 12 is not included in the illumination system shown in Figure 3, the planes 11 and 13 from Figure 1 coincide on a plane 113.
  • the input optics 110 thus transmit the light directly to the field intermediate plane 113.
  • Homogenization can be achieved by the raster element 109 being modified in comparison to the raster element 9 shown in Figure 1 such that a sufficiently uniform intensity distribution is produced in the imaging plane 113 of the input optics, which is at the same time the object plane of the objective 115.
  • the illumination can also be homogenized by means of a diaphragm unit, which is positioned in the vicinity of the field intermediate plane 113, offset slightly axially with respect to the REMA system 114, and which is designed or can be adjusted such that it shields specific edge areas of the light distribution in such a way that, in conjunction with the integrating effect of the scanning process, this allows largely homogeneous illumination of the reticle 50. Dispensing with an integrator rod makes it possible to save material and space.
  • the polarization conversion device is in the form of a polarization rectifier, in order to produce an emitted light beam with linear polarization that is uniform over the entire cross section.
  • illumination modes with uniform polarization illumination modes with a local polarization distribution of different polarization states in the area of the pupil plane of the respective objective 15 or 115 are also frequently desirable for illumination of a mask in a microlithography installation.
  • Figure 4(a) illustrates, schematically, a polarization conversion device 422 in an axial view of the pupil surface 118 of the embodiment shown in Figure 3, which is designed to produce an emitted light beam with tangential polarization and with no significant losses from largely linearly polarized incident light, which is incident in the form of a quadrupole light distribution.
  • the polarization conversion device 422 has a large number of polarization rectifier elements 436 ( Figure 4(b)) each of which has two polarization splitter cubes 437, 438, which are directly adjacent to one another and have a respective polarization splitter layer 431 , 432.
  • a ⁇ /2 plate 433 is wrung onto the light outlet surface of a first polarization splitter cube 437.
  • the ⁇ /2 plates may be held in a separate socket, for example as a grid or raster of ⁇ /2 plates which are held in a network-like mesh and are positioned a short distance away from the prism array.
  • a raster device which is separate from the prism array is provided with a large number of retarder elements 433, then it is also possible to move the ⁇ /2 plates collectively from the beam splitter cubes 437 to the beam splitter cubes 438 (or vice versa), for example by translation of the retarder unit array through the width of one cube.
  • s-polarized or p-polarized are understood relative to the incident plane associated with the respective polarization splitter surface.
  • a microlens 439 is arranged in the light path upstream of the polarization splitter cubes in order to focus incident light onto the polarization splitter surface 431 of the first polarization splitter cube 437.
  • the polarization rectifier element 436 together with the upstream microlens 439 may be regarded as a minimal unit of the polarization conversion device 422, which contains a large number of identically constructed minimal units.
  • these are each illustrated in the form of pairs of squares located alongside one another, with the squares that are shown darkened in each case representing the delay plates 433 in which the position of the fast crystal axis of the birefringent material is illustrated schematically by means of arrows 402, 403.
  • twelve identical polarization rectifier elements with the same orientation and with a uniform alignment of the fast axis of the ⁇ /2 plate are in each case combined in a 6-2 arrangement to form a rectifier group 450, each of which produces a uniform output polarization, in the form of a polarization rectifier, via that subarea of the pupil plane which is covered by the rectifier group.
  • the resultant preferred polarization direction is in each case symbolized by double-headed arrows 460 alongside the rectifier groups.
  • Figure 4 shows one embodiment of a polarization conversion device, which is designed to produce tangentially polarized output light with an illumination setting with quadrupole illumination.
  • the intensity distribution of the illumination light which is set by means of the pupil forming unit (arranged between the light source and the polarization conversion device) in the illumination system, has four illumination spots, which are located at a distance away from the optical axis 103 and are offset on the one hand along the y axis and on the other hand along the x axis with respect to the optical axis.
  • the preferred polarization direction (double- headed arrow) is in each case aligned at right angles to the straight line connecting the centroid of the illumination spot and the optical axis, that is to say at right angles to a radial direction of the illumination system.
  • This is achieved by suitable alignment of the complete rectifier units relative to one another.
  • the rectifier units 451 and 452 are rotated through 90° with respect to one another in order to produce linearly polarized light rotated through 90°.
  • a corresponding situation applies, for example, to the rectifier units 450, 453.
  • the relative rotation can be seen in Figure 4(a) from the fact that the fast crystal axes of the rectifier units (rotated with respect to delay plates) are rotated by 90° with respect to one another.
  • any desired arrangements of the minimal units mentioned above may be used.
  • the size and/or the shape of the minimal units may also be varied.
  • preferred embodiments of polarization conversion devices are designed in the form of replaceable elements, and can be selectively inserted into the beam path, or removed from it, by means of a suitable changeover device 160 ( Figure 3), depending on the illumination mode and/or the desired polarization distribution.
  • the changeover device 160 and the variable elements of the pupil forming unit which are used to set different illumination modes (for example the objective 107 and the element 105) are driven in a coordinated manner by the control device 157.
  • Figure 5 shows different polarization conversion devices 510, 520, 530, which may be provided as replaceable elements in a changeover device.
  • the polarization conversion device 510 has a single rectifier group 511 , which comprises twelve identical polarization rectifier elements and is arranged concentrically with respect to the optical axis. It is thus possible to produce linearly polarized output light with conventional illumination settings with low coherence levels, whose preferred polarization direction runs parallel to the x axis in the illumination system.
  • the resultant preferred polarization direction is in the y direction.
  • the embodiments 520, 530 are each designed for dipole illumination, in order in each case to produce dipole illumination with tangential polarization.
  • two rectifier groups 521 , 522 and 531 , 532 are in each case arranged diametrically opposite with respect to the optical axis so that, when dipole illumination is selected, the light from the illumination poles in the pupil surface of the imaging objective falls on the respective rectifier group, which converts it to linearly polarized light with a preferred polarization direction running at right angles to the radial direction.
  • Figure 6 shows, schematically, another embodiment of a polarization conversion device 622, which is designed to produce collimated output light with a defined spatial distribution of polarization states over the cross section of the emitted light beam. Like the embodiment shown in Figure 2, it may be arranged in the area of the pupil plane of an imaging objective, although it can likewise be used at a different point in an illumination system.
  • the part which influences the polarization comprises a two-dimensional field arrangement (array) 624 with polarization rectifier elements 636 located directly alongside one another and one above the other.
  • Each polarization rectifier element comprises two identical polarization splitter cubes 637, 638, which each have a polarization splitter surface 631 , 632 positioned at an angle of 45° with respect to the inlet surface.
  • a ⁇ /2 plate 633 is wrung onto the outlet surface of one of the polarization splitter cubes.
  • Each polarization rectifier element is associated with a lens 639 (which is located in front of it in the light path) in a round lens array 623, which is used as a focusing device in order to inject essentially all of the incident light into that polarization splitter cube 637 which is used for injection of light in the field arrangement 624.
  • a lens 639 which is located in front of it in the light path
  • a round lens array 623 which is used as a focusing device in order to inject essentially all of the incident light into that polarization splitter cube 637 which is used for injection of light in the field arrangement 624.
  • a collimator device 650 is arranged in the light path downstream of the array arrangement 624 of polarization rectifier elements, and is in the form of a two- dimensional lens array with a large number of individual lenses 651 , 652, the number of which corresponds to the number of beam splitter cubes in the arrangement 624.
  • the diameter of each of the individual lenses 651 , 652 corresponds to 50% of the diameter of the individual lenses 639 in the focusing lens array 623.
  • Each of the individual lenses 651 , 652 has a short focal length and is arranged at such a distance downstream from the associated polarization splitter cube that the front focal plane of the individual lenses coincides with the focus plane 634, 635 of that partial beam which emerges from the associated polarization splitter cube. Since these focus planes are offset axially with respect to one another owing to the different optical path length difference, the individual lenses 651 , 652 in the collimator device are also offset axially and at the same distance in pairs in this embodiment.
  • FIG. 7 shows, schematically, one embodiment of a polarization conversion device 722, whose design in terms of the polarization rectifier elements 736 and the upstream focusing lenses 723 corresponds to the design of the system shown in Figure 6. Reference symbols for corresponding elements have accordingly been increased by 100.
  • a lens array 750 formed by individual lenses 751 , 752 which are offset axially with respect to one another in pairs and have a structure corresponding to the collimator device 650 is arranged in the light path downstream from the field arrangement 724, which is composed of polarization rectifier elements.
  • the axial distance to the polarization rectifier elements has been shortened such that the focal points 734, 735 of the partial beams emerging from the polarization splitter cubes each coincide approximately with the main planes of the individual lenses 751 , 752.
  • a condenser lens 760 which occupies the entire cross section of the device, is arranged at a distance downstream from the lens array 750, such that the lenses in the lens array 750 are essentially located on the front focal plane of the condenser lens 760.
  • the condenser lens 760 allows all of the partial beams emerging from the individual lenses 751 , 752 to be superimposed on a field plane 770 which follows the condenser lens 760 and is located in the area of the rear focal plane of the condenser lens 760.
  • a field plane 770 which follows the condenser lens 760 and is located in the area of the rear focal plane of the condenser lens 760.
  • the arrangement shown in Figure 7 can be installed in the area of a pupil plane of an illumination system, for example instead of the polarization conversion device 122 in Figure 3.
  • the entire arrangement can also advantageously be used in the area of another pupil plane of the illumination system, for example in the area of the pupil plane 108 in Figure 3 instead of the raster element 109 shown there.
  • the arrangement shown in Figure 7 may be used as a single homogenization device in an illumination system.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Polarising Elements (AREA)
  • Exposure Of Semiconductors, Excluding Electron Or Ion Beam Exposure (AREA)
  • Exposure And Positioning Against Photoresist Photosensitive Materials (AREA)

Abstract

L'invention concerne un système d'éclairage destiné à un dispositif d'exposition par projection pour microlithographie, et notamment à un dispositif de balayage de plaquettes, permettant d'éclairer un champ d'éclairage sur un plan de sortie (53) du système d'éclairage au moyen d'une lumière provenant d'une source de lumière (2). Ce système comprend, dans un système d'imagerie (15) générant des images d'un plan de champ intermédiaire (13) sur le plan de sortie (53), un dispositif de conversion de polarisation (22) possédant un grand nombre d'éléments redresseurs de polarisation destinés à produire un état de polarisation défini pour la lumière sortant du système d'éclairage. L'utilisation du dispositif de conversion de polarisation (22) permet de régler l'état de polarisation de la lumière d'éclairage sur l'état de polarisation requis dans l'objectif de projection aval (51) sans perte d'une proportion importante de la lumière injectée à partir de la source de lumière dans le système d'éclairage pendant la production de cet état de polarisation.
PCT/EP2004/012398 2003-11-05 2004-11-03 Systeme d'eclairage optimisant la polarisation Ceased WO2005050325A1 (fr)

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DE10352717.6 2003-11-05
DE10352717 2003-11-05

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WO2005050325A1 true WO2005050325A1 (fr) 2005-06-02

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008009353A1 (fr) * 2006-07-15 2008-01-24 Carl Zeiss Smt Ag Système d'éclairage d'un équipement d'éclairage par projection microlithographique
DE102008040058A1 (de) 2007-07-18 2009-01-22 Carl Zeiss Smt Ag Mikrolithographische Projektionsbelichtungsanlage
CN103869626A (zh) * 2012-12-11 2014-06-18 上海微电子装备有限公司 超高数值孔径光刻成像偏振补偿装置及方法

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Publication number Priority date Publication date Assignee Title
US6077631A (en) * 1995-12-15 2000-06-20 Canon Kabushiki Kaisha Photomask and scanning exposure apparatus and device manufacturing method using same
JP2003015084A (ja) * 2001-06-28 2003-01-15 Nagano Kogaku Kenkyusho:Kk 偏光光源装置
WO2003067334A2 (fr) * 2002-02-08 2003-08-14 Carl Zeiss Smt Ag Systeme d'eclairage a polarisation optimisee

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6077631A (en) * 1995-12-15 2000-06-20 Canon Kabushiki Kaisha Photomask and scanning exposure apparatus and device manufacturing method using same
JP2003015084A (ja) * 2001-06-28 2003-01-15 Nagano Kogaku Kenkyusho:Kk 偏光光源装置
WO2003067334A2 (fr) * 2002-02-08 2003-08-14 Carl Zeiss Smt Ag Systeme d'eclairage a polarisation optimisee

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PATENT ABSTRACTS OF JAPAN vol. 2003, no. 05 12 May 2003 (2003-05-12) *

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008009353A1 (fr) * 2006-07-15 2008-01-24 Carl Zeiss Smt Ag Système d'éclairage d'un équipement d'éclairage par projection microlithographique
DE102008040058A1 (de) 2007-07-18 2009-01-22 Carl Zeiss Smt Ag Mikrolithographische Projektionsbelichtungsanlage
US7817250B2 (en) 2007-07-18 2010-10-19 Carl Zeiss Smt Ag Microlithographic projection exposure apparatus
US8395753B2 (en) 2007-07-18 2013-03-12 Carl Zeiss Smt Gmbh Microlithographic projection exposure apparatus
DE102008040058B4 (de) 2007-07-18 2018-10-25 Carl Zeiss Smt Gmbh Mikrolithographische Projektionsbelichtungsanlage und Verfahren zur mikrolithographischen Herstellung mikrostrukturierter Bauelemente
DE102008040058B9 (de) 2007-07-18 2019-01-10 Carl Zeiss Smt Gmbh Mikrolithographische Projektionsbelichtungsanlage und Verfahren zur mikrolithographischen Herstellung mikrostrukturierter Bauelemente
CN103869626A (zh) * 2012-12-11 2014-06-18 上海微电子装备有限公司 超高数值孔径光刻成像偏振补偿装置及方法
CN103869626B (zh) * 2012-12-11 2016-12-07 上海微电子装备有限公司 超高数值孔径光刻成像偏振补偿装置及方法

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