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
  • G03F7/7095—Materials, e.g. materials for housing, stage or other support having particular properties, e.g. weight, strength, conductivity, thermal expansion coefficient
  • G03F7/70958—Optical materials or coatings, e.g. with particular transmittance, reflectance or anti-reflection properties
  • G03F7/70966—Birefringence
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B13/00—Machines or devices designed for grinding or polishing optical surfaces on lenses or surfaces of similar shape on other work; Accessories therefor
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
  • G02B1/02—Optical elements characterised by the material of which they are made; Optical coatings for optical elements made of crystals, e.g. rock-salt, semi-conductors
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B3/00—Simple or compound lenses
• • 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

Definitions

• the invention relates to a method for producing an optical blank from a crystal material and an optical blank.
• the optical blank serves as a preliminary stage for the production of a lens or a lens part.
• the invention thus also relates to a method for producing a lens or a lens part from a crystal material and a lens or a lens part.
• Such lenses or lens parts are used in objectives, in particular in projection objectives for microlithography.
• the invention thus also relates to objectives, in particular projection objectives for a microlithography projection exposure system.
• birefringent lenses result in an unpolarized beam being split into two beams, each with a different polarization state and different propagation speed and direction. If birefringent lenses are used in a lens, they lead to a reduction in the
• the birefringent effect in lenses can be caused, for example, by stress birefringence, which is caused by the manufacturing process or the mechanical stress on the lens.
• the birefringence plays a role particularly in crystal optics.
• Anisotropic crystals are birefringent.
• isotropic crystals such as cubic fluoride crystals also have an intrinsic birefringence, which is particularly noticeable at VUN wavelengths ( ⁇ 200nm).
• Cubic fluoride crystals such as calcium fluoride and barium fluoride are preferred lens materials for projection lenses with working wavelengths in this wavelength range. Therefore, the intrinsic birefringence of these crystals, which has a disruptive effect at these wavelengths, must be compensated for by suitable measures.
• the indexing of the crystal directions is given between the characters " ⁇ " and “>", the indexing of the crystal planes between the characters “ ⁇ ” and “ ⁇ ”.
• the crystal direction always indicates the direction of the surface normal of the corresponding crystal plane.
• the crystal direction ⁇ 100> points in the direction of the surface normal of the crystal plane ⁇ 100 ⁇ .
• the cubic crystals to which the fluoride crystals belong have the main crystal directions ⁇ 110>, ⁇ T l0>, ⁇ T T ⁇ >, ⁇ 101>, ⁇ l ⁇ T>, ⁇ T ⁇ l>, ⁇ T ⁇ T>, ⁇ T ⁇ T>,
• the main crystal directions ⁇ 100>, ⁇ 010>, ⁇ 001>, ⁇ 00>, ⁇ T ⁇ > and ⁇ O ⁇ T> are equivalent to each other due to the symmetry properties of the cubic crystals, so that in the following crystal directions, which point in one of these main crystal directions, that Prefix "(100) -" is obtained. Crystal planes perpendicular to one of these
• Main crystal directions are given the prefix "(100) -”. Lenses whose lens axes are parallel to one of these main crystal directions are given the prefix "(100) -".
• the main crystal directions ⁇ 110>, ⁇ T 10>, ⁇ T 10>, ⁇ T T ⁇ >, ⁇ 101>, ⁇ l ⁇ T>, ⁇ T ⁇ l>, ⁇ T ⁇ T>, ⁇ 011>, ⁇ 0 1 1>, ⁇ 01 T > and ⁇ 0 1 1> are also equivalent to each other, so that in the following crystal directions which point in one of these main crystal directions are given the prefix "(110) -". Crystal planes which are perpendicular to one of these main crystal directions are accordingly given the prefix " (110) - ". Lenses whose lens axes are parallel to one of these main crystal directions are given the prefix "(110) -" accordingly.
• the main crystal directions ⁇ 111>, ⁇ TIT>, ⁇ TT 1>, ⁇ T 1 T>, ⁇ 1 TT>, ⁇ T 11>, ⁇ 11 1> and ⁇ 11 1> are also equivalent to each other, so that in the following crystal directions which point in one of these main crystal directions are given the prefix "(111) -". Crystal planes which are perpendicular to one of these main crystal directions are accordingly given the prefix "(111) -”. Lenses whose lens axes are parallel to one of these main crystal directions are given the prefix "(111) -" accordingly.
• calcium fluoride has none intrinsic birefringence as predicted by theory. The intrinsic birefringence is therefore strongly direction-dependent and increases significantly as the wavelength decreases.
• paired (100), (111) and (110) lenses can reduce the optical path difference for two mutually orthogonal polarization states. Furthermore, the simultaneous use of calcium fluoride lenses and barium fluoride lenses also compensates for the disruptive influence of intrinsic birefringence, since, according to FIG. 2 of this article, the birefringence for comparable crystal directions for barium fluoride and calcium fluoride has opposite sign.
• Projection objectives and microlithography projection exposure systems are known, for example, from patent application WO 01/50171 AI (US Serial No. 10/177580) and known the writings cited therein.
• the exemplary embodiments of this application show purely refractive and catadioptric projection objectives with numerical apertures of 0.8 and 0.9, at an operating wavelength of 193 nm and 157 nm. Calcium fluoride is used as the lens material.
• the compensation methods described above for reducing the disruptive influence of birefringence are based, among other things, on the use of lenses rotated relative to one another about the lens axes.
• the angle of rotation between two lenses depends, for example, on the crystal direction in which the lens axis of a lens points. In the case of lenses which are produced using a method according to the previously described US Pat. No. 6,201,634, the lens axes point, for example, in the (111) crystal direction.
• a favorable angle of rotation of 60 ° between two (111) lenses results in accordance with the aforementioned.
• the angle of rotation relates to the crystal structures of the two lenses. However, the crystal structure of a lens cannot be viewed from the outside.
• the object of the invention is now to provide a production method for optical blanks from a crystal material as a preliminary stage for the production of lenses or lens parts, which takes into account that those subsequently produced from the optical blanks Lenses or lens parts can be rotated relative to one another with respect to their crystal structures when used in lenses.
• This object is achieved with a method for producing an optical blank from a crystal material according to claim 1 and an optical blank according to claim 13, a method for producing a lens or a lens part from a crystal material according to claim 16 and claim 18, and a lens or A lens part according to claims 28 and 32, a lens according to claims 33 and 37, a microlithography projection exposure system according to claim 39 and a method for producing semiconductor components according to claim 40.
• each lens or each lens part or its holding mounts has a marking which is in a defined connection to the crystal structure of the lens or the lens part.
• Lens parts are to be understood, for example, as individual lenses which are optically seamlessly joined to form a single lens by being wrung.
• lens parts refer to the building blocks of a single lens.
• Preferred starting materials for the optical blanks are cubic fluoride crystals such as calcium fluoride, barium fluoride or strontium fluoride. Until a lens or a lens part has its final shape, a large number of shape and surface processing steps are required. Since the lenses or lens parts consist of crystal material, a single-crystal ingot or single-crystal ingot, which can be produced, for example, by a method described in the aforementioned US Pat. No. 6,201,634, is generally used as the starting material. An optical blank is first produced from the single crystal block, for example by sawing and grinding. The preliminary stage of a lens or a lens part is referred to as an optical blank. One or more lenses or lens parts can be produced from the optical blank.
• the optical blank is cut into individual optical blanks by sawing, the individual optical blanks being ground and / or polished in a further processing step in order to carry out optical measurements on the surfaces thus prepared can.
• the optical blanks prepared in this way then form individual material disks in the form of cylinders.
• the optical blank is processed in such a way that it has an optical raw surface, the surface normal of which points in the direction of a first crystal direction that is defined within the crystal structure.
• This is advantageously a main crystal direction, for example the ⁇ 100>, ⁇ 111> or ⁇ 110> crystal direction. For this it is first necessary to determine the direction of the first one on the optical blank
• the optical blank is then processed by sawing and grinding in such a way that the first crystal direction is almost perpendicular to the optical raw surface.
• the angular deviation between the first crystal direction and the optical raw surface is preferably less than 5 °.
• the raw optical surface represents the front or back of the material disc.
• a marking is applied to the optical blank or its holding mount, which has a defined connection to a second crystal direction, which has an angle different from 0 ° to the first crystal direction.
• the second crystal direction can also be a main crystal direction or one that is oriented within the crystal structure
• Crystal direction for example the ⁇ 331> crystal direction or the ⁇ 511> crystal direction.
• the marking can be, for example, a dot-shaped or line-shaped engraving on the outer cylinder of the optical blank or on the holding mount which is firmly connected to the optical blank.
• the holder can be made of metal, ceramic or glass ceramic.
• the defined relationship between the second crystal direction and the marking can be established, for example, by the marking indicating a reference direction which is perpendicular to the first crystal direction and a projection of the second crystal direction into a plane whose surface normal points in the direction of the first crystal direction.
• the reference direction preferably intersects the axis of symmetry.
• the marking shows, for example, the point of intersection of the reference direction with the outer cylinder of the optical blank or with its holding mount.
• the marking thus also defines an azimuth angle of the projected second crystal direction with respect to a coordinate system connected to the optical blank.
• the azimuth angle is defined as the angle between the reference direction and a coordinate axis which is perpendicular to the axis of symmetry and intersects the axis of symmetry.
• the optical blank When determining the first crystal direction, the optical blank can be illuminated with measurement radiation, in particular X-ray measurement radiation, from a defined direction.
• the measuring radiation is associated with the first crystal direction Crystal planes, for example the ⁇ 111 ⁇ crystal planes reflect and generate a corresponding Bragg reflex. Since the wavelength of the measuring radiation and the material of the optical blank are known, the target angle of the incident and outgoing measuring radiation with respect to the first crystal direction is known on the basis of the Bragg reflection law.
• the optical blank is now relative to the Bragg-
• the measuring arrangement is adjusted until the Bragg reflex for the first crystal direction is detected.
• the orientation of the first crystal direction with respect to the surface normal of the optical raw surface of the optical blank is now determined from the relative orientation of the measuring arrangement and the optical blank. If the surface normal of the optical raw surface does not match the first crystal direction, the optical blank is processed, for example by grinding, until the angular deviation is less than ⁇ 5 °.
• the optical blank is rotatably supported about an axis which is perpendicular to the raw optical surface of the optical blank.
• the Bragg reflexes are now determined for different angles of rotation, in the simplest case at 0 ° and at 90 °.
• the reference direction can also be determined by evaluating a Bragg reflex.
• the measurement radiation is reflected at the crystal planes assigned to the second crystal direction.
• the position of the reference direction can be determined using the Laue method.
• the reference direction in such a way that a light beam in the lens subsequently made from the optical blank experiences, for example, a maximum optical path difference for two mutually orthogonal linear polarization states due to the birefringence when the projection of this light beam into a plane which is perpendicular stands on the first crystal direction, runs parallel to the reference direction.
• the projection of the second crystal direction into a plane which is perpendicular to the first crystal direction is parallel to the projection of the ⁇ 110> crystal direction or an equivalent crystal direction in the same plane.
• Light rays that run parallel to the ⁇ 110> crystal direction or an equivalent crystal direction experience a maximum optical path difference for two mutually orthogonal polarization states in cubic fluoride crystals.
• first crystal direction points in the ⁇ 111> crystal direction or an equivalent crystal direction
• second crystal direction points in the ⁇ 331> - crystal direction or an equivalent crystal direction
• first crystal direction points in the ⁇ 100> crystal direction or an equivalent crystal direction
• second crystal direction points in the ⁇ 511> - crystal direction or an equivalent crystal direction
• an optical blank can advantageously be produced as a starting product for producing a lens or a lens part for a lens.
• the optical surfaces of the lens or the lens part are machined in such a way that the lens axis is aligned almost parallel to the direction of the first crystal direction or parallel to the surface normal of the raw optical surface ,
• the angular deviation between the first crystal direction and the lens axis is preferably less than 5 °.
• the curved lens surfaces of the lens are created by grinding and polishing the raw optical surfaces of the optical blank. If the surfaces are rotationally symmetrical, the lens axis is the axis of symmetry.
• the lens axis can be given by the center of an incident beam or by a straight line, with respect to which the beam angles of all light beams within the lens are minimal.
• refractive or diffractive lenses and correction plates with free-form correction surfaces can be used as lenses.
• Flat plates are also regarded as lenses if they are arranged in the beam path of a lens. The lens axis of a flat plate is perpendicular to the flat lens surfaces.
• the angular deviation between the lens axis and the first crystal direction plays a role, even if it is less than 5 °. It is therefore advantageous to determine this angular deviation very precisely.
• X-ray diffractometric methods are used.
• the orientation of the first crystal axis is also known. The orientation can be described by the direction of deviation. The direction of deviation is perpendicular to the lens axis and results as a projection of the first crystal direction into a plane perpendicular to the lens axis.
• the direction of deviation is then marked on the lens or the lens part, for example on the edge of the lens.
• the marking can also be applied to a holding frame of the lens or of the lens part.
• the signed angle between the reference direction and the direction of deviation can also be determined and assigned to the lens or the lens part.
• the angle value can be stored in a database in which the material data and production data of the lens or of the lens part are stored.
• the lens or the lens part can first be produced from an optical blank made of a crystal material and the marking for the second crystal direction can be applied.
• the lens is produced from an optical blank, for example by grinding and polishing the lens surfaces. The surfaces are processed in such a way that the lens axis is parallel to a first crystal direction, preferably a main crystal direction.
• a marking is applied to the lens or the lens part or its holding mount, which has a defined relationship to a second crystal direction, which has an angle different from 0 ° to the first crystal direction.
• the second crystal direction can likewise be a main crystal direction or a crystal direction defined within the crystal structure, for example the ⁇ 331> crystal direction if the lens axis points in the ⁇ 111> crystal direction, or the ⁇ 511> crystal direction if the lens axis in ⁇ 100 > -Crystalline direction.
• the marking can, for example, be a dot-shaped or line-shaped engraving on the outer cylinder of the lens or the lens part or on the one fixed to the lens or the Lens part connected holding frame.
• the holder can be made of metal, ceramic or glass ceramic.
• the defined relationship between the second crystal direction and the marking can be established, for example, by the marking indicating a reference direction which is perpendicular to the lens axis and a projection of the second crystal direction into a plane whose surface normal points in the direction of the lens axis.
• the reference direction preferably intersects the lens axis.
• the marking shows, for example, the point of intersection of the reference direction with the outer cylinder of the lens or the lens part or with its holding mount.
• the marking thus also defines an azimuth angle of the projected second crystal direction with respect to a coordinate system connected to the lens or the lens part.
• the methods already presented for the optical blank can be used to determine the reference direction.
• the position of the lens is adjustable so that the measuring radiation hits the curved lens surface at a defined location.
• the measuring radiation strikes the area of the lens apex.
• the second crystal direction in such a way that the incident measurement radiation and the reflected radiation, which is used to determine the first crystal direction or the reference direction, are not disturbed by the lens geometry.
• Cubic fluoride crystals such as calcium fluoride, barium fluoride or strontium fluoride are advantageous crystal materials for use in lenses with low wavelengths less than 200 nm.
• the intrinsic birefringence in cubic fluoride crystals only has such a great influence at wavelengths below 200 nm that suitable corrective measures are necessary.
• the determination of the reference direction and the possibly necessary determination of the direction of deviation is therefore primarily favorable for this application.
• Lenses or lens parts which have a marking of a reference direction and possibly a direction of deviation are advantageously used in lenses in which the disruptive influence of birefringence is reduced by mutual rotation of the lenses or lens parts about their lens axes.
• the marking which is dependent on the crystal orientation, considerably simplifies the targeted rotation of the individual lenses.
• angles of rotation between the individual lenses or lens parts of a lens can be determined in such a way that the disturbing influence of the birefringence on the imaging performance of a lens is significantly reduced.
• the sole determination and marking of the direction of deviation is advantageous if the optical effect of the lens or of the lens part essentially depends on the angular deviation between the first crystal direction and the lens axis.
• the effect on the imaging performance of a lens can then be influenced in such a way that a correction effect is produced by the interaction of a plurality of lenses or lens parts which are rotated relative to one another.
• Lenses or lens parts which have an angular deviation between the first crystal direction and the lens axis can thus also be used. This facilitates the manufacture of the lenses or lens parts made of crystal material considerably, since the manufacturing tolerances can be reduced.
• the objective can be a purely refractive projection objective, which consists of a plurality of lenses arranged rotationally symmetrically about the optical axis, or a projection objective of the catadioptric objective type.
• Such projection objectives can advantageously be used in microlithography projection exposure systems which, starting from a light source, incorporate an illumination system, a mask positioning system, and a structure-bearing mask
• Projection lens an object positioning system and a photosensitive substrate.
• This microlithography projection exposure system can be used to manufacture microstructured semiconductor components.
• Figure 1 shows a section through an optical blank in a schematic representation
• Figure 2 shows the optical blank of Figure 1 in plan view in a schematic representation
• Figure 3 shows a section through a mounted lens in a schematic representation
• Figure 4 shows the captured lens of Figure 3 in plan view in a schematic representation
• Figure 5 shows a section through another embodiment of a lens in a schematic representation
• Figure 6 shows the lens of Figure 5 in a plan view in a schematic representation
• FIG. 7 shows a lens in a schematic, perspective representation
• FIG. 8 shows a lens section of a projection objective
• FIG. 9 shows a projection exposure system in a schematic illustration.
• the production of calcium fluoride lenses is described as an exemplary embodiment.
• the manufacturing processes can also be applied to the manufacture of lenses from other crystal materials with a cubic crystal structure, such as barium fluoride or strontium fluoride.
• the lens axes can also point in the ⁇ 100> or the ⁇ 110> crystal direction.
• the method is suitable for the production of plane-parallel lenses as well as lenses or lens parts with curved surfaces.
• Figures 1 and 2 show a schematic representation of such an optical blank 1, which was produced with the method according to the invention.
• Figure 1 shows a section through the optical blank 1 along the line AA, which is shown in the plan view of Figure 2.
• the orientation of the ⁇ 111> crystal direction 3 of the optical blank 1, in this case a calcium fluoride disk is determined.
• the ⁇ 111> crystal direction 3 is perpendicular to the ⁇ 111 ⁇ crystal planes 5, some of which are shown in FIG. 1.
• the determination can be carried out, for example, with high accuracy using crystallographic methods, such as, for example, by determining gap areas or producing etch pits.
• a suitable device is a goniometer arrangement using monochromatic X-rays.
• the occurrence of a Bragg reflex for the ⁇ 111 ⁇ crystal planes 5 is determined with the help of table values known from the literature.
• the table values indicate the required incidence angles depending on the reflex indexing.
• the calcium fluoride disk is rotated around an axis that is perpendicular to the calcium fluoride disk. This gives the deviation of the ⁇ 111> crystal direction from the surface normal of the calcium fluoride disk for different angles of rotation. It is favorable to determine the deviation in at least two rotational positions.
• the measurements are carried out at 0 ° and 90 °. In order to increase the measuring accuracy, the measurements can also be carried out at 180 ° and 270 ° or other intermediate angles.
• the calcium fluoride disk is processed in such a way that the surface normal of the calcium fluoride disk is parallel to the direction of the ⁇ 111> crystal direction 3, so that the ⁇ 111> crystal direction 3 is essentially perpendicular to the optical one Raw area 7 stands.
• the measured deviation serves as the basis for a targeted correction, i.e. a defined processing of the calcium fluoride disc by sawing or grinding.
• the surface normal of the calcium fluoride disk points in the ⁇ 111> crystal direction with a deviation of less than 5 °.
• a reference direction 9 is determined on the calcium fluoride disk, which has a defined relationship to a further crystal direction. Assigns the surface normal of the calcium fluoride disk to the ⁇ 111> - Crystal direction 3, it is favorable to know one of the three crystal directions ⁇ 110>, ⁇ 011> and ⁇ 101>, or ⁇ 100>, ⁇ 010> and ⁇ 001>, which is grouped in three-wave symmetry around the ⁇ 111> crystal direction are. This is interesting because a light beam experiences a maximum optical path difference for two mutually orthogonal linear polarization states due to intrinsic birefringence when it runs in a calcium fluoride lens in the ⁇ 110> crystal direction or an equivalent crystal direction.
• the three crystal directions ⁇ 110>, ⁇ 011> and ⁇ 101> each close an angle of 35 °, the three crystal directions ⁇ 100>, ⁇ 010> and ⁇ 001> an angle of 55 ° with the ⁇ 111> -Kri stable direction on.
• X-ray reflections of (110) or (100) crystal planes cannot be measured on crystals with a calcium fluoride structure. Therefore one has to use Bragg reflections from other crystal planes which are in a defined relationship to the (100) - or (110) -crystal planes.
• a (331) -Bragg reflex can be used.
• the three crystal directions ⁇ 331>, ⁇ 133> and ⁇ 313> each enclose an angle of 22 ° with the ⁇ 111> crystal direction.
• 1 shows the ⁇ 331> crystal direction 11 which is perpendicular to the ⁇ 331 ⁇ crystal planes 13, some of which are shown.
• the (331) -Bragg reflex appears for monochromatic copper kay radiation (8048 eV) with calcium fluoride below 38 °. This results in an angle of incidence of 16 ° and a
• Detector angle of 60 ° relative to the reference plane which is defined by the surface 7 of the calcium fluoride disk. If the disk is rotated 360 ° around the surface normal, Bragg reflections can be measured at three rotation angles. These indicate that one of the direction vectors of the three relevant (331) crystal planes lies in the plane of incidence of the Bragg measurement. The projections of these three (331) crystal directions on the reference plane.
• Disk surface 7 are parallel to the projections of the three crystal directions ⁇ 110>, ⁇ 011> and ⁇ 101>. If one determines the directions of the projections of the crystal directions ⁇ 331>, ⁇ 133> and ⁇ 313>, one also simultaneously determines the directions of the projections of the crystal directions ⁇ 110>, ⁇ 011> and ⁇ 101>. With a possible Deviation of the surface normal from the ⁇ 111> crystal direction must be adjusted accordingly source and detector.
• the reference direction 9 points in the direction of the projected ⁇ 331> crystal direction, which is projected in a plane perpendicular to the ⁇ 111> crystal direction.
• the reference direction also intersects the axis of symmetry 17 of the optical blank 1.
• the crystal orientations can also be determined using a Laue image.
• the Laue method uses "white", ie broadband X-ray light.
• white X-ray light Bragg reflections are obtained from various groups of crystals, so that the Laue is characteristic of the material
• a Laue image with triple symmetry is generated. If the ⁇ 111> crystal direction deviates by a few degrees from the normal to the pane, the result is a slightly distorted image
• Exact analysis of the Laue image for example using suitable software, can then be used to determine the deviation of the ⁇ 111> crystal direction from the normal to the disk.
• the evaluation of the image also allows the three-fold crystal directions ⁇ 110>, ⁇ 011> to be determined and ⁇ 101>, or ⁇ 100>, ⁇ 010> and ⁇ 001> and thus the orientation of the disc.
• a fourth step at least one marking 15, which marks the reference direction 9, is attached to the optical blank 1.
• the marking 15 is thus in a defined connection with the ⁇ 331> crystal direction 11.
• the marking 15 can be done, for example, by means of engraving, etching or labeling.
• the cylinder edge of the optical blank 1 lends itself to the marking 15.
• the marking can also be attached to a holder with which the optical blank 1 is firmly connected.
• a lens is manufactured from the optical blank 1.
• FIGS. 3 and 4 show in a schematic representation the lens 31 manufactured from the optical blank 1.
• the lens 31 is held by a holding frame 33.
• FIG. 3 shows the captured lens 31 in a section along the line BB, which is shown in the top view in FIG. 4.
• the lens 31 is manufactured in such a way that the lens axis 35 is parallel to the ⁇ 111> crystal direction 3.
• the previously applied marking 15 is not destroyed during the processing of the optical blank 1. This is possible because many processing steps such as grinding or polishing only affect the top and bottom of the lens, but not the edge of the cylinder. If, however, the edge of the calcium fluoride disc is also processed, for example rotated, it is necessary to transfer the marking to the holder of the calcium fluoride disc with sufficient accuracy and to put the marking back on the cylinder edge after processing.
• a marking 37 of the reference direction 9 is attached to the holding frame 33.
• a lens is produced from an optical blank made of cubic fluoride crystal, for example calcium fluoride, for which the ⁇ 111> crystal direction is already essentially perpendicular to the surface of the optical blank. The marking is then only applied after the lens has been produced.
• the lens is manufactured from the optical blank in such a way that the lens axis points in the ⁇ 111> crystal direction.
• a reference direction is determined in a second step.
• the same methods are used as described above for the production of the optical blank.
• it must be ensured that the height of the point of impact of the X-ray beam on the lens surface is set exactly.
• the height of the contact surface of the lens can therefore be adjusted. This allows the curved profile of the lens to be traversed if various points on the curved lens surface are measured.
• the curvature can shade the incoming or outgoing beam. Shading can be avoided by selecting a suitable Bragg reflex and the resulting measurement geometry.
• the method described can be applied at any point on the surface based on a goniometer structure.
• FIGS. 5 and 6 show a schematic illustration of a further exemplary embodiment of a lens 51 according to the invention.
• FIG. 5 shows the lens 51 in a section along the line C-C, which is shown in the top view in FIG. 6.
• the calcium fluoride lens 53 is not a (111) lens, but rather a (100) lens. However, the lens axis 53 does not point exactly in the ⁇ 100> crystal direction 55, but the deviation angle ⁇ occurs between the lens axis 53 and the ⁇ 100> crystal direction 55.
• the ⁇ 100> crystal direction 55 is perpendicular to the ⁇ 100 ⁇ crystal planes 57.
• the direction of deviation 63 is obtained as a projection of the ⁇ 100> crystal direction 55 into a plane which is perpendicular to the lens axis 53.
• the direction of deviation 63 preferably intersects the lens axis 53.
• the marking 65 is applied to the lens 51 to identify the direction of deviation 63.
• the marking can also be applied to a holding frame (not shown in FIGS. 5 and 6). In FIG. 6, the marking 65 indicates the point of intersection of the deviation direction 63 with the outer cylinder of the lens 51.
• the orientation of the ⁇ 100> crystal direction 55 to the lens axis 53 can be determined by determining the Bragg reflection of the ⁇ 100> crystal direction 55 for different rotational positions of the lens 51.
• the lens 51 is rotated about its lens axis 53. It is favorable to determine the deviation in at least two rotational positions.
• the measurements are carried out at 0 ° and 90 °. In order to increase the measuring accuracy, the measurements are also carried out at 180 ° and 270 °.
• the deviation between the ⁇ 100> crystal direction 55 and the lens axis 53 can also be determined using the Laue method, in that the incident measuring radiation is incident in the direction of the lens axis 53.
• the lens 51 also has the marking 67.
• the marking 67 has a defined relationship to the ⁇ 511> crystal direction 59, which is perpendicular to the ⁇ 511 ⁇ crystal planes 61.
• the marking indicates the point of intersection of the reference direction 69 with the outer cylinder of the lens 51.
• the reference direction 69 is obtained as a projection of the ⁇ 511> crystal direction 59 in a plane perpendicular to the lens axis 53.
• the reference direction 69 intersects the lens axis 53.
• the ⁇ 511> - crystal direction 59 is used because the projection of the ⁇ 511>
• Crystal direction 59 runs in a plane perpendicular to lens axis 53 parallel to the corresponding projection of the ⁇ 011> crystal direction.
• the ⁇ 011> crystal direction is an excellent direction, since rays that pass through the lens 51 parallel to this direction experience a maximum optical path difference for two orthogonal polarization states due to the intrinsic birefringence.
• a single marking is sufficient. Since the lens 51 has the marking 67 of the reference direction 69, the angle between the reference direction 69 and the deviation direction 63 can alternatively be determined instead of the marking 65 of the deviation direction 63 and assigned to the lens. For example, this angle can be stored together with the deviation angle in a database in which, for example, the material and manufacturing data of the lens 51 are stored. This angle and the deviation angle are thus available for the optimization processes.
• Figure 7 shows a first embodiment of a lens 71 according to the invention in a schematic representation.
• the objective maps an object OB to an image IM.
• the lenses 73, 75, 77 and 79 are shown.
• the lens axes of the lenses 73, 75, 77 and 79 point in the direction of the optical axis OA.
• the lenses 73 and 75 are (111) lenses, the lenses 77 and 79 (100) lenses made of calcium fluoride.
• the lenses are each rotated about their lens axes, so that the difference in the optical path difference between two orthogonal polarization states of an outer aperture beam 81 and the corresponding optical path difference for a beam which runs along the optical axis OA is minimal is.
• the angle of rotation between the (111) lenses 73 and 75 is 60 °.
• the angle of rotation can be easily adjusted according to the invention, since the lenses 73 and 75 have the markings 83 and 85 which indicate the reference directions 87 and 89.
• the reference directions 87 and 89 represent projections of the respective ⁇ 331> crystal direction in planes which are perpendicular to the respective lens axes.
• the angle of rotation between the (100) lenses 77 and 79 is not exactly 45 °, since with these lenses the respective ⁇ 100> crystal direction does not point exactly in the direction of the respective lens axis.
• the directions of deviation 95 and 97 are indicated by the markings 91 and 93. The size and orientation of the deviation are taken into account when optimizing the angle of rotation between the lenses 77 and 79.
• the markings 99 and 101 indicate the reference directions 103 and 105, which represent projections of the respective ⁇ 511> crystal direction in planes which are perpendicular to the respective lens axes.
• the material orientation with respect to the coordinate system of a lens is also known.
• the birefringent properties can also be known from measurements on the lenses. Since the birefringent properties of the lenses and the optical design of the objective are known, the optical path difference for two mutually orthogonal linear polarization states, which a beam experiences within the objective, is known. In the following, this optical path difference serves as an optimization variable, the absolute value of which must be minimized. In a similar way, the optimization can also be carried out for an entire bundle of rays from individual rays.
• Possible degrees of freedom for this optimization are the angles of rotation of the individual lenses to one another and the orientation of the lens axes with respect to the main crystal directions. It is favorable if, on the one hand, the lens axes point in the main crystal directions and, on the other hand, the angles of rotation of the lenses to one another only assume discrete values depending on the direction of the respective lens axis.
• the lens axes can point in (100), (111) or (110) crystal direction.
• Lenses whose lens axes point in the same or an equivalent main crystal direction are combined into individual groups, each group having at least two lenses.
• the discrete angles of rotation of the lenses of a group depend on the orientation of the
• the angle of rotation between these two lenses is ideally 45 °, or 135 °, 225 ° ...
• Discrete rotation angles of the lenses with one another and discrete crystal orientations are thus available as degrees of freedom.
• FIG. 8 shows the lens section of a catadioptric projection objective 8 for the wavelength 157nm.
• the optical data for this lens are summarized in Table 1.
• the exemplary embodiment is taken from patent application WO 01/50171 AI (US Serial No. 10/177580) and corresponds there to FIG. 9 or Table 8.
• WO 01/50171 AI US Serial No. . 10/177580
• All lenses of this lens are made of calcium fluoride crystal.
• the numerical aperture of the objective on the image side is 0.8.
• Threshold acceptance (threshold accepting)
• FGH 1 (111) lens with an angle of rotation of 0 °
• FGH 2 (111) lens with an angle of rotation of 60 °
• FGH 3 (100) lens with 0 ° rotation angle
• FGH 4 (100) lens with 45 ° rotation angle
• the angles of rotation for the individual lenses each relate to a fixed reference direction in the object plane O.
• the Monte Carlo search and the specification of the four degrees of freedom FGH1 to FGH4 were used to determine the optimal crystal orientations of the lens axes and the angles of rotation ⁇ , of the lenses L801 to L817 with respect to a fixed reference direction in the object plane O.
• Table 2 shows the crystal directions of the lens axes and the angles of rotation ⁇ L for the lenses L801 to L817.
• the optical path difference for two mutually orthogonal polarization states for the top and bottom outermost aperture beam is also given for each lens.
• the two outermost aperture rays start from an object point in the center of the object field and each have an angle in the image plane O 'with respect to the optical axis OA, which corresponds to the numerical aperture on the image side.
• the maximum resulting optical path difference is 5nm.
• Table 2 Additional degrees of freedom for optimization can be obtained by assigning the lenses to individual groups.
• the lens axes of the lenses of a group point in the same main crystal direction.
• the lenses are now rotated relative to one another such that the distribution of the optical path differences for two mutually orthogonal linear polarization states, which is caused by a group, is almost rotationally symmetrical.
• the angles of rotation between the individual groups can now be set as desired in order to use these additional degrees of freedom to correct, for example, production-related additional aberrations.
• the lenses L801 and L814 form a first group with (100) lenses, the two lenses being arranged rotated relative to one another by the angle of rotation 45 °.
• the lenses L802, L804, L807 and L812 form a second group with (111) lenses.
• the lenses L803, L805 and L815 form a third group with (100) lenses.
• the lenses L808, L809 and L811 form a fourth group with (100) lenses.
• the lenses L816 and L817 form a fifth group with (111) lenses, the two lenses being rotated relative to one another by the angle of rotation 60 °.
• optimization process can also be carried out with finer discretized angles of rotation.
• the natural number m can be used as a degree of freedom in the optimization.
• the natural number m can assume the values 1, 2 and 3. Since the direction of deviation and the reference direction are marked, the rotation angle determined in this way can be set exactly.
• the objective function is calculated for a lens in which the birefringent properties of the lenses are known.
• the objective function gives a measure of the disturbing influence of birefringence.
• the optical path difference for two mutually orthogonal linear polarization states of an outermost aperture beam can serve as a target function.
• the angles of rotation of the lenses, the crystal orientations and the target function for this objective state are stored.
• the process is terminated. If the threshold is not fallen below, the third step follows.
• the process begins again with the first step, the number of loops being run through being determined. If the number of loops passed exceeds a maximum number, the method also terminates.
• the method therefore terminates when a certain threshold is undershot or a predetermined number of loops is exceeded. If the maximum number of loops is exceeded, a ranking list can be created, for example, in which the individual lens states are specified with the associated target function.
• the projection exposure system 111 has a light source 113, an illumination device 115, a structure-bearing mask 117, a projection lens 119 and a substrate 121 to be exposed.
• Illumination device 115 collects the light from light source 113, for example, depending on the working wavelength, a KrF or an ArF laser and illuminates mask 117. A homogeneity of the illumination distribution, which is predetermined by the exposure process, and a predetermined illumination of the entrance pupil of objective 119 are provided.
• the mask 117 is held in place by means of a mask holder 113
• Such masks 113 used in microlithography have a micrometer-nanometer structure.
• a controllable micro-mirror array or a programmable LCD array can alternatively be used as the structure-bearing mask.
• the mask 117, or a partial area of the mask is imaged on the substrate 121 positioned by a substrate holder 125 by means of the projection objective 119.
• the projection objective 119 is, for example, the catadioptric objective shown in FIG. 8.
• the individual lenses 127 of the projection objective are arranged rotated relative to one another in order to minimize the disruptive influence of birefringence or other effects.
• the substrate 121 is typically a silicon wafer, which is provided with a light-sensitive coating, the so-called resist. Semiconductor components are then produced from the exposed substrates in further processing steps.

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• 2002
  • 2002-11-13 KR KR10-2004-7017804A patent/KR20050003410A/ko active IP Right Grant
  • 2002-11-13 JP JP2004504053A patent/JP2005524985A/ja active Pending
  • 2002-11-13 WO PCT/EP2002/012690 patent/WO2003096124A1/de active Application Filing
  • 2002-11-13 AU AU2002356590A patent/AU2002356590A1/en not_active Abandoned
  • 2002-11-13 CN CNB02828920XA patent/CN1327294C/zh not_active Expired - Fee Related

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