Classifications

• • 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
  • G03F7/708—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
• • 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
  • G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
  • G02B1/08—Optical elements characterised by the material of which they are made; Optical coatings for optical elements made of polarising materials
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B5/00—Optical elements other than lenses
  • G02B5/30—Polarising elements
  • G02B5/3083—Birefringent or phase retarding elements
• • 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
  • G03F7/70225—Optical aspects of catadioptric systems, i.e. comprising reflective and refractive elements
• • 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
  • G03F7/70241—Optical aspects of refractive lens systems, i.e. comprising only refractive elements
• • 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
• • 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
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S359/00—Optical: systems and elements
  • Y10S359/90—Methods

Definitions

• the invention relates to a lens according to the preamble of claim 1.
• Such projection lenses are known from US 6,201,634. It is disclosed there that in the manufacture of fluoride crystal lenses, the lens axes are ideally aligned perpendicular to the ⁇ 111 ⁇ crystal planes of the fluoride crystals in order to minimize stress birefringence. US Pat. No. 6,201,634 assumes that fluoride crystals have no intrinsic birefringence.
• Single crystals also have non-stress-induced, i.e. intrinsic birefringence.
• calcium fluoride has no intrinsic birefringence, as is also predicted by theory.
• the intrinsic birefringence is therefore strongly direction-dependent and increases significantly as the wavelength decreases.
• the indexing of the crystal directions is given below 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>, ⁇ 1 10>, ⁇ 1 10>, ⁇ 1 10>, ⁇ 1 10>,
• the main crystal directions ⁇ 100>, ⁇ 010>, ⁇ 001>, ⁇ 00>, ⁇ 010> and ⁇ 001> 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, the Prefix "(100) -" obtained. Crystal planes that are perpendicular to one of these main crystal directions are given the prefix "(100) -" accordingly.
• the main crystal directions ⁇ 110>, ⁇ 10>, ⁇ 10>, ⁇ ⁇ 0>, ⁇ 101>, ⁇ 10 ⁇ >, ⁇ T ⁇ l>, ⁇ 101>, ⁇ 011>, ⁇ 0 1 1>, ⁇ 01 1 > and ⁇ 01 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) - ".
• the main crystal directions ⁇ 111>, ⁇ T 1 1>, ⁇ I ⁇ 1>, ⁇ 1 1 T>, ⁇ 1 TT>, ⁇ T 11>, ⁇ 1 ⁇ 1> and ⁇ 11 1> are also equivalent to each other 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) -". Statements that are made below regarding one of the above-mentioned main crystal directions always apply to the equivalent main crystal directions.
• Projection objectives and microlithography projection exposure systems are known, for example, from the applicant's patent application PCT / EP00 / 13148 (WO 150171 AI) and the documents cited therein.
• the exemplary embodiments of this application show suitable 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.
• the rotation of lens elements to compensate for birefringence effects is also described in the patent application “Projection exposure system for microlithography, optical system and manufacturing method” (DE 10123725.1) with the file number of the applicant 01055P and the filing date May 15, 2001.
• the content of this application is also intended to be part of the present application Be registration.
• the object of the invention is to provide projection objectives for a microlithography projection exposure system in which the influence of birefringence, in particular intrinsic birefringence, is significantly reduced.
• a lens manufacturing method according to claim 56, 82 and 83, a method for manufacturing an optical blank according to claim 69 and an optical blank manufactured by this method according to claim 80.
• claim 1 proposes to align the lens axes in fluoride crystal lenses so that they coincide with the ⁇ 100> crystal direction. The lens axes then fall with one
• Main crystal direction together if the maximum deviation between the lens axis and the main crystal direction is less than 5 °. Not all fluoride crystal lenses of the objective need to have such an alignment of the crystal planes. Those lenses in which the lens axes are perpendicular to the ⁇ 100 ⁇ crystal planes are also referred to below as (100) lenses.
• the alignment of the lens axis in ⁇ 100> - The direction of the crystal has the advantage that the disruptive influence of the intrinsic birefringence, which occurs when light propagates in the ⁇ 110> crystal direction, only becomes noticeable at higher opening angles of the light beams than for an alignment of the lens axis in the ⁇ 111> crystal direction.
• the opening angle means the angle between a light beam and the optical axis outside a lens and between the light beam and the lens axis inside a lens. Only when the opening angles come into the range of the angle between the ⁇ 100> crystal direction and the ⁇ 110> ⁇ crystal direction, do the corresponding light beams feel the influence of birefringence.
• the angle between the ⁇ 110> crystal direction and the ⁇ 100> crystal direction is 45 °. If, on the other hand, the lens axis were oriented in the ⁇ 111> crystal direction, the disturbing influence of the intrinsic birefringence would be noticeable even at smaller opening angles, since the angle between the ⁇ 110> crystal direction and the ⁇ 111> crystal direction is only 35 °.
• the disclosed approaches can of course also be used to reduce the disruptive influence of the birefringence.
• the lens axis is given, for example, by an axis of symmetry of a rotationally symmetrical lens. If the lens has no 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 rays 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 the lens.
• the lens axis of a flat plate is perpendicular to the flat lens surfaces. However, the lenses are preferably rotationally symmetrical lenses.
• Lenses have an optical axis that runs from the object plane to the image plane.
• the (100) lenses are preferably constructed centered around this optical axis, so that the lens axes also coincide with the optical axis.
• the invention can advantageously be used in projection lenses for a microlithography projection exposure system, since extremely high demands are made on the resolution for these lenses.
• the influence of birefringence also has a disruptive effect on test lenses, for example with which lenses for projection lenses are tested by measuring wavefronts with a large aperture.
• opening angles which are greater than 25 °, in particular greater than 30 ° occur within the (100) lenses. It is precisely at these large opening angles that the invention comes into play in orienting the lens axes in the ⁇ 100> crystal direction. If the lens axes were oriented in the ⁇ 111> crystal direction, the light rays with opening angles greater than 25 °, in particular greater than 30 °, would feel the disruptive influence of birefringence more clearly if one of the correction measures described below is not used.
• NA denotes the numerical aperture on the south side
• np K is the refractive index of the fluoride crystal.
• Opening angle at which corresponds to the image-side numerical aperture within a fluoride crystal lens when the light beam is refracted at a flat interface becomes. This is achieved in that the lenses, which are arranged close to the image plane, have collecting lens surfaces, flat lens surfaces or at most slightly diverging lens surfaces if a more collecting lens surface follows in the light direction after the diverging lens surface.
• the (100) lenses should therefore preferably be used in the area of the field planes.
• the area in which the (100) lenses should be used can be determined via the ratio of the lens diameter to the diameter of the diaphragm.
• the lens diameter of the (100) lenses is preferably at most 85%, in particular at most 80% of the diaphragm diameter.
• the lens axis is preferably aligned in the direction of the ⁇ 100> crystal direction.
• the intrinsic birefringence of a fluoride crystal lens depends not only on the opening angle of a light beam, but also on the azimuth angle of the light beam.
• a birefringence distribution ⁇ ( ⁇ , ⁇ L ) can be assigned to each fluoride crystal lens, which is a function of the opening angle ⁇ on the one hand and a function of the azimuth angle OC L on the other.
• the value of the birefringence ⁇ n indicates the ratio of the optical path difference for two mutually orthogonal linear polarization states to the physical beam path covered in the fluoride crystal in the unit [nm / cm] for a beam direction determined by the aperture angle ⁇ L and the azimuth angle C.
• the intrinsic birefringence is therefore independent of the beam paths and the shape of the lens.
• the optical path difference for a beam is obtained accordingly by multiplying the birefringence by the beam path covered.
• the opening angle ⁇ L is determined between the beam direction and the lens axis, the azimuth angle OC L between that perpendicular to the lens axis Projected crystal plane and a reference direction firmly linked to the lens.
• the angular dependence of the birefringence distributions of the individual fluoride crystal lenses leads to the rays of a bundle of rays hitting a pixel in the image plane of the lens experiencing angle-dependent optical path differences ⁇ OPL (O. R , ⁇ R ) for two mutually orthogonal linear polarization states ,
• the optical path differences ⁇ OPL are given as a function of the opening angle ⁇ R and the azimuth angle ofo.
• the opening angle ⁇ R of a beam is determined between the beam direction and the optical axis in the image plane, the azimuth angle CC R between the beam direction projected into the image plane and a fixed reference direction within the image plane.
• the lens axes of these lenses or lens parts point in a main crystal direction and the lenses or lens parts are rotated relative to one another about the lens axes such that the distribution ⁇ OPL ( R , ⁇ R ) of the optical path differences has significantly reduced values compared to an arrangement in which the lens axes point in the same main crystal direction and the lenses or lens parts are installed with the same orientation.
• the twisted arrangement of the lenses can reduce the maximum value of the distribution ⁇ OPL ( R , ⁇ R ) by up to 20%, in particular by up to 25%, in comparison to an identically oriented installation ,
• Lens parts are to be understood, for example, as individual lenses which are optically seamlessly joined to form a single lens by means of wringing. Describe in general
• Lens parts are the building blocks of an individual lens, the lens axes of the lens parts each pointing in the direction of the lens axis of the individual lens.
• the dependence of the distribution ⁇ OPL (OC R , ⁇ R ) on the azimuth angle OC can be significantly reduced, so that there is an almost rotationally symmetrical distribution ⁇ OPL (OC R ,, R ).
• the optical path differences should advantageously vary for the same aperture angle ⁇ R by a maximum of 30%, in particular by a maximum of 20% based on the maximum value of the distribution ⁇ OPL (CX R , ⁇ R ).
• the birefringence distribution ⁇ n (ot L , ⁇ ) of the lens has a k-fold azimuthal symmetry.
• the birefringence distribution of a (100) lens in which the lens axis points in the ⁇ 100> crystal direction, shows a 4-fold azimuthal symmetry
• the birefringence distribution in a (III) lens in which the lens axis points in the ⁇ 111> crystal direction, a 3-fold azimuth symmetry
• the birefringence distribution of an (Il ⁇ ) lens in which the lens axis points in the ⁇ 110> crystal direction, a 2-fold azimuth symmetry.
• the individual lenses or lens parts of a group are now rotated relative to each other about the lens axes by a predetermined angle of rotation ⁇ .
• the angles of rotation ⁇ are determined or measured between the reference directions of two lenses or lens parts.
• the lens axes point in the same main crystal direction or an equivalent one
• the reference directions of the lenses of a group are linked to the lenses in such a way that the birefringence distributions ⁇ n ( ⁇ (, L, ⁇ 0 ) have the same azimuthal course for a given aperture angle ⁇ 0.
• the azimuthal areas with maximum for all lenses in a group Birefringence at the same azimuth angle, for n lenses in a group the angles of rotation are between two
• the tolerance of ⁇ 10 ° takes into account the fact that under certain circumstances the angles of rotation deviate from the theoretically ideal angles in order to be able to take other boundary conditions into account when adjusting the lens. A deviation from the ideal angle of rotation leads to a non-optimal azimuthal
• Lenses ideally 45 °, or 135 °, 225 ° ...
• the distribution of the optical path differences ⁇ OPL G (OR, ⁇ R) can also be specified for the influence of a single group of lenses by only considering these lenses in the birefringence evaluation and assuming the other lenses are not birefringent.
• the lenses of a group are determined, for example, by the fact that an outermost aperture beam of a bundle of rays has similar opening angles within these lenses.
• the opening angles advantageously vary by a maximum of 30%, in particular by a maximum of 20%, based on the maximum opening angle within the lenses of this group.
• the opening angles of the outermost aperture beam within these lenses are advantageously greater than 15 °, in particular greater than 20 °.
• the outermost aperture beam is a beam that originates from an object point proceeds, the beam height in the diaphragm plane corresponds to the radius of the diaphragm and which therefore has an angle in the image plane according to the numerical aperture on the image side.
• the outermost aperture rays are used to define the groups because they usually have the largest aperture angles within the lenses and thus experience the greatest interference from birefringence.
• the determination of the optical path difference for two mutually orthogonal linear polarization states for the outermost aperture rays thus enables statements to be made about the maximum interference of a wavefront by the birefringence.
• the outermost aperture beam covers a similarly large beam path in each of these lenses.
• the beam paths advantageously vary by a maximum of 30%, in particular a maximum of 20% based on the maximum beam path within the lenses of this group.
• the outermost aperture beam in each lens of a group experiences similarly large optical path differences for two mutually orthogonal linear polarization states with the same orientation of the lenses.
• the optical path differences advantageously vary by a maximum of 30%, in particular a maximum of 20%, based on the maximum optical path difference within the lenses of this group. If this condition is met, an optimal compensation of the azimuthal contributions occurs when these lenses are rotated.
• the rotation of the lenses becomes particularly effective when the lenses are arranged adjacent to one another. It is particularly advantageous to divide a lens into two parts and to join the lens parts in a visually seamless manner, for example by wringing.
• a subgroup has at least one lens, for example one, two or three lenses.
• the lenses of a subgroup are not rotated relative to one another except for an angular offset that is insignificant due to the azimuthal symmetry.
• ⁇ 1 ⁇ 10 °, where 1 is an integer and k indicates the numeracy k of the azimuthal symmetry of the birefringence distribution ⁇ n ( ⁇ L , ⁇ L ) of a lens.
• Rotating two lenses not to the desired generation of an almost rotationally symmetrical distribution of the optical path differences can be done by the Assignment of another lens to a sub-group achieve the desired distribution. This is possible if the distributions of the optical path differences caused by the individual subgroups have almost similar maximum values and distributions. The mutual rotation of the lenses of one subgroup to the lenses of another subgroup ultimately results in the almost rotationally symmetrical distribution of the optical path differences.
• a group formed in this way from subgroups always has n lenses, for their mutual lenses
• the projection lens has at least one group with (100) lenses and at least one group with (111)
• Has lenses A good compensation is also possible if a group with (HO) lenses is arranged inside the lens next to a group with (100) lenses.
• birefringence not only has an absolute value, but also a direction.
• the compensation of the disturbing influence of birefringence is optimal if the distribution of the optical path differences ⁇ OPL ⁇ OC J ⁇ R ), which is caused by the lenses or lens parts of all groups with (100) lenses, and the distribution of the optical path differences ⁇ OPL 2 (OCR, ⁇ R), which is caused by the lenses or lens parts of all groups with (111) lenses or (110) lenses, has similarly high maximum values.
• Another advantageous way of reducing the disruptive influence of birefringence is to cover an optical element of the projection objective with a compensation coating.
• each optical coating for example antireflection or mirror coatings, in addition to its properties with regard to reflection and transmission, also always entails optical path differences for two mutually orthogonal linear polarization states. These are different for s- and p-polarized light and also depend on the angle of incidence of the beam on the layer. So you have birefringence dependent on the angle of incidence. For a bundle of rays whose center beam strikes the compensation coating with an incidence angle of 0 °, the birefringence values and directions are rotationally symmetrical with respect to the center beam. The angle of incidence gives the angle between the light beam and the surface normal at the intersection of the
• the compensation coating is now constructed in such a way that, with regard to the amount of birefringence, it exhibits a predetermined behavior as a function of the opening angle of the rays of a beam.
• the distribution of the optical path differences ⁇ OPL (OCR, ⁇ R) for two mutually orthogonal linear polarization states for a bundle of rays in the image plane of the projection lens is determined.
• the opening angle ⁇ R of a beam is determined between the beam direction and the optical axis in the image plane, the azimuth angle OC between the beam direction projected into the image plane and a fixed reference direction within the image plane.
• the distribution of the optical path differences ⁇ OPL (OC R , ⁇ R ) for two mutually orthogonal linear polarization states describes all influences by intrinsic birefringence of fluoride crystal lenses, voltage birefringence, covering the optical elements with antireflection layers of lenses or mirror layers.
• the effective birefringence distribution of the compensation coating is determined from the distribution of the optical path differences ⁇ OPL (OCR, ⁇ R).
• OLR optical path differences
• Refractive or diffractive lenses, plane plates or mirrors, for example, are used as optical elements.
• the optical surfaces of the optical element are given by the optically used areas, that is to say usually the front and rear surfaces.
• the element axis is given, for example, by an axis of symmetry of a rotationally symmetrical lens. If the lens has no axis of symmetry, the element 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 rays within the lens are minimal.
• the effective birefringence values depend on azimuth angles OC F , which are related to a reference direction perpendicular to the element axis, and on opening angles ⁇ p, which are also related to the element axis.
• a pair of values (, ⁇ R ) of a beam in the image plane corresponds to a pair of values (OCF, ⁇ p) on the optical element.
• Compensation coating is significantly reduced compared to the distribution without the compensation coating.
• the maximum value of the distribution ⁇ OPL (OC R , ⁇ R ) is reduced by up to 20%, in particular by up to 25%, compared to a lens without a compensation coating.
• the effective birefringence distribution can be influenced by the choice of material, the thickness curves and the vapor deposition angle for the individual layers of the compensation coating.
• the layer design and the process parameters result from the use of weak design computer programs, which result from the effective birefringence distribution, the specification of the materials and the geometry of the optical element determines the thickness curves of the individual layers and the process variables.
• the compensation coating can also be applied to several optical elements. This increases the degrees of freedom in the determination of the compensation layers, which in addition to the compensation should also ensure a high transmission of the coating.
• the invention can advantageously be used in that the optical element with the compensation coating is an exchangeable element.
• the optical element closest to the image plane is advantageously used.
• the method provides that in a first step the distribution of the optical path differences ⁇ OPL (OC R , ⁇ R ) for two mutually orthogonal linear polarization states for a bundle of rays in the image plane is determined.
• the influence of all optical elements of the lens including coatings is taken into account.
• the optical element, which is coated with the compensation coating in a subsequent step, is also in the beam path of the beam.
• a second step the method described above is used to determine the effective birefringence distribution of a compensation coating and the resulting thickness profiles of the individual layers and the process parameters for producing the individual layers.
• the optical element is removed from the beam path and coated with the compensation coating. If the optical surface of the optical element was already occupied, this layer is removed before the renewed covering.
• the optical element with the compensation coating is reattached to the original location within the lens.
• Calcium fluoride is preferably used as the material for the lenses in projection lenses, since calcium fluoride, when used together with quartz, is particularly suitable for color correction at a working wavelength of 193 nm, or provides sufficient transmission at a working wavelength of 157 nm.
• the statements made here also apply to the fluoride crystals strontium fluoride or barium fluoride, since they are crystals of the same cubic crystal type.
• the disruptive influence of intrinsic birefringence is particularly noticeable when the light rays within the lenses have large opening angles. This is the case for projection lenses that have a numerical aperture on the image side that is greater than 0.7, in particular greater than 0.8.
• the intrinsic birefringence increases significantly as the working wavelength decreases.
• the intrinsic birefringence at a wavelength of 193nm is more than twice as large, at a wavelength of 157nm more than five times as large as at a wavelength of 248nm.
• the invention can therefore be used particularly advantageously if the light beams have wavelengths of less than 200 nm, in particular less than 160 nm.
• 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 lenses can advantageously be used in microlithography projection exposure systems which, starting from the light source, comprise an illumination system, a mask positioning system, a structure-bearing mask, a projection lens, an object positioning system and a light-sensitive substrate.
• microstructured semiconductor components can be produced.
• the invention also provides a suitable method for manufacturing lenses.
• lenses or lens parts made of fluoride crystal, the lens axes of which point in a main crystal direction are arranged rotated about the lens axes in such a way that the distribution ⁇ OPL (OC R , ⁇ R ) has significantly reduced values in comparison to a lens arrangement in which the Lens axes of the fluoride crystal lenses point in the same main crystal direction and in which the lenses are arranged in the same orientation.
• the method further provides for groups with (100) lenses and groups with (111) lenses or (110) lenses to be formed and these to be used in parallel.
• the method is used, for example, in the case of a projection objective which comprises at least two fluoride crystal lenses in the ⁇ 100> orientation and at least two lenses in the ⁇ 111> orientation.
• the position of the reference directions is also known from these lenses.
• the method uses the inventive knowledge that by rotating the fluoride crystal lenses around the optical axis
• the maximum value of the distribution ⁇ OPL ( ⁇ R , ⁇ R ) can be reduced by up to 30%, in particular up to 50%, in comparison to a projection objective in which the fluoride crystal lenses are arranged in the same orientation.
• the optimization process can also have an intermediate step. In this intermediate step, groups with lenses are formed from the fluoride crystal lenses, the lenses of a group for an outermost aperture beam with a similarly oriented arrangement of the lenses producing a similar optical path difference between two mutually orthogonal linear polarization states. In the subsequent optimization step, the lenses are then only rotated within the groups in order to reduce the optical path differences. First, the (100) lenses can be rotated in such a way that the optical path differences caused by the (100) lenses be reduced.
• the distribution of the fluoride crystal lenses on lenses with (100) -orientation and (III) -orientation must be such that the resulting (100) - distribution ⁇ OPL 10O (OC R , ⁇ R ) and the resulting (111) - Compensate for the distribution ⁇ OPL ⁇ I (OC R , ⁇ R ) to a large extent.
• the invention also relates to a manufacturing method for a lens, in which in a first step a plurality of fluoride crystal plates are optically seamlessly joined to form a blank, and in a second step the lens is worked out of the blank by known manufacturing methods. As previously described for lenses or lens parts, the plates are arranged rotated relative to one another about the surface normal.
• Plates whose surface normals point in the same main crystal direction or in an equivalent main crystal direction advantageously have the same axial thickness.
• the ratio of the sum of the thicknesses of the (lll) panels to the sum of the thicknesses of the (lOO) panels should be 1.5 ⁇ 0.2.
• the ratio of the sum of the thicknesses of the (110) panels to the sum of the thicknesses of the (100) panels should be 4.0 ⁇ 0.4.
• the invention also provides a method for producing lenses or lens parts made of crystal material with a cubic crystal structure, which can advantageously be used in the lenses described above to reduce the disruptive influence of birefringence.
• the reduction in the disruptive influence of birefringence according to the invention is based on the mutual rotation of lenses within a group, the lens axes of the lenses pointing in the same crystal direction, preferably in the same main crystal direction.
• a reference direction should be known for each lens. In the following, methods are described how a suitable reference direction is determined and marked on the lens or the lens part.
• the lenses or lens parts consist of crystal material
• a single crystal block is generally used as the starting material, from which an optical blank is first produced, 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. If several lenses or lens parts are manufactured from an 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.
• it is first necessary to determine the direction of the first crystal direction on the optical blank. This determination can be made on the optical blank before the optical blank is divided into individual optical blanks. It is also possible to carry out the division first and then to carry out the determination on the individual optical blanks.
• the optical blank will Now processed by sawing and grinding in such a way that the first crystal direction is almost perpendicular to the raw optical surface. A deviation of ⁇ 5 ° is tolerable.
• the raw optical surface represents the front or back of the material disc.
• a reference direction is determined which is perpendicular to the first crystal direction.
• the reference direction represents a projection of a second crystal direction into a plane whose surface normal points in the direction of the first crystal direction.
• the angle between the first crystal direction and the second crystal direction has a value different from 0 °.
• the crystal direction can also be a main crystal direction or a crystal direction defined within the crystal structure, for example the ⁇ 331> crystal direction.
• the reference direction is marked on the optical blank, for example on the outer cylinder, by engraving. It is also possible that the optical blank is firmly connected to a holding frame and the marking is attached to the holding frame.
• the optical blank When determining the first crystal direction, the optical blank can be marked with a
• Measurement radiation can be illuminated from a defined direction.
• the measurement radiation is reflected at the crystal planes assigned to the first crystal direction, for example the ⁇ 111 ⁇ crystal planes, and generates a corresponding Bragg reflex. Since the incidence angle of the measuring radiation and the material of the optical blank are known, the theoretical target angle of the Bragg reflex by applying the Bragg reflection law is also known. Only when the surface normal of the optical raw surfaces coincides with the first crystal direction is the reflected measurement radiation detected at the predetermined target angle. If necessary, the optical blank is processed, for example by grinding, in such a way that the surface normal of the raw optical surface corresponds to the first crystal direction.
• 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 experiences, due to the birefringence, for example a maximum optical path difference for two mutually orthogonal linear polarization states if the projection of this light beam into a plane which is perpendicular to the first crystal direction, runs parallel to the reference direction. If one uses the compensation methods described above, i.e. the mutual turning of lenses, it is easy to set the prescribed rotation angles on the basis of this marking rule. It is also possible to mark the reference direction for which a light beam experiences a minimal optical path difference if its projection into a plane that is perpendicular to the first crystal direction runs parallel to the reference direction.
• Crystal direction or in a crystal direction equivalent to these crystal directions it is advantageous if the projection of the second crystal direction in a plane which is perpendicular to the first crystal direction parallel to the projection of the ⁇ 110> crystal direction or an equivalent crystal direction in the same Level is. Light rays that run parallel to the ⁇ 110> crystal direction or an equivalent crystal direction experience a maximum optical path difference.
• first crystal axis 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
• the measuring radiation for determining the Bragg reflections can lead to material damage in the area of the optical raw surfaces, it is expedient to remove those material areas of the optical blank by grinding or polishing that have been penetrated by the measuring radiation.
• an optical blank can advantageously be produced as a starting product for producing a lens or a lens part for a lens.
• the lens axis is aligned almost parallel to the direction of the first crystal axis, or parallel to the surface normal of the raw optical surface, when processing the optical surfaces of the lens or the lens part.
• the deviation should be less than + 5 °.
• the curved lens surfaces of the lens are created by grinding and polishing the optical raw surfaces of the optical blank. If the surfaces are rotationally symmetrical, the lens axis is the axis of symmetry.
• the reference direction can also be determined and marked on the lens or the lens part.
• the lens is produced from an optical blank made of crystal material with a cubic crystal structure, 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. In the case of lenses with rotationally symmetrical lens surfaces, the Axis of symmetry the lens axis.
• a reference direction is now determined on the lens or the lens part.
• the reference direction is perpendicular to the first crystal direction and is a projection of a second crystal direction into a plane perpendicular to the first crystal direction.
• the first and the second crystal direction enclose an angle different from 0 °.
• the reference direction is now marked on the lens or the lens part. If the lens is firmly connected to a holder, the marking can also be attached to this holder.
• 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 measurement 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.
• Lenses or lens parts which have a marking of a reference direction are advantageously used in lenses in which the disruptive influence of birefringence is reduced by rotating the lenses or lens parts against one another. With the marking, the targeted rotation of the individual lenses is considerably simplified. The invention is explained in more detail with reference to the drawings.
• Figure 1 shows a section through a fluoride crystal block perpendicular to the ⁇ 100 ⁇ -
• FIG. 2A-C each show a plane-parallel (100), (111) and (HO) lens in a schematic three-dimensional representation;
• Figure 3 shows a coordinate system for defining the opening angle and the
• FIGS 6A-G show the birefringence distribution for (HO) lenses in different
• FIG. 7 shows the lens section of a refractive projection objective
• FIG. 8 shows the lens section of a catadioptric projection objective
• FIG. 9 shows a microlithography projection exposure system in schematic form
• Figure 1 shows schematically a section through a fluoride crystal block 3.
• the section is chosen so that the ⁇ 100 ⁇ crystal planes 5 can be seen as individual lines, so that the ⁇ 100 ⁇ crystal planes 5 are perpendicular to the paper plane ,
• the fluoride crystal block 3 serves as a blank or starting material for the (100) lens 1.
• the (100) lens 1 is a biconvex lens with the lens axis EA, which at the same time Axis of symmetry of the lens is.
• the lens 1 is now worked out of the fluoride crystal block in such a way that the lens axis EA is perpendicular to the ⁇ 100 ⁇ crystal planes.
• FIG. 2A illustrates with a three-dimensional representation how the intrinsic birefringence is related to the crystal directions when the lens axis EA points in the ⁇ 100> crystal direction.
• a circular, plane-parallel plate 201 made of calcium fluoride is shown.
• the lens axis EA points in the ⁇ 100> crystal direction.
• the ⁇ 101>, ⁇ 1 10>, ⁇ 101> and ⁇ 110> crystal directions are also shown as arrows.
• the intrinsic birefringence is schematically represented by four "lobes" 203, the surfaces of which indicate the amount of intrinsic birefringence for the respective beam direction of a light beam.
• the maximum intrinsic birefringence results in the ⁇ 101> -, ⁇ 1 10> -, ⁇ 10 1> - and ⁇ 110> - crystal directions, i.e. for light rays with an opening angle of 45 ° and an azimuth angle of 0 °, 90 °, 180 ° and 270 ° inside the lens.
• azimuth angles of 45 °, 135 °, 225 ° and 315 ° there are minimal values of the intrinsic birefringence.
• the intrinsic birefringence disappears for an opening angle of 0 °.
• FIG. 2B shows with a three-dimensional representation how the intrinsic birefringence is related to the crystal directions when the lens axis EA points in the ⁇ 111> crystal direction.
• a circular, plane-parallel plate 205 made of calcium fluoride is shown.
• the lens axis EA points in the ⁇ 111> crystal direction.
• the ⁇ 011>, ⁇ 101> and ⁇ 110> crystal directions are also shown as arrows.
• the intrinsic birefringence is schematically represented by three "lobes" 207, the surfaces of which indicate the amount of intrinsic birefringence for the respective beam direction of a light beam.
• the maximum intrinsic birefringence arises in the ⁇ 011> -, ⁇ 101> - and ⁇ 110> - crystal directions, i.e. for light rays with an opening angle of 35 ° and an azimuth angle of 0 °, 120 ° and 240 ° within the lens. For azimuth angles of 60 °, 180 ° and 300 ° each result in minimal values of the intrinsic birefringence. The intrinsic birefringence disappears for an opening angle of 0 °.
• Figure 2C illustrates a three-dimensional representation, related how the intrinsic birefringence with Kris tallraumen 'when the lens axis EA points in the ⁇ 110> crystal.
• a circular, plane-parallel plate 209 made of calcium fluoride is shown.
• the lens axis EA points in the ⁇ 110> crystal direction.
• the ⁇ 01 1>, ⁇ 101>, ⁇ 101> and ⁇ 011> crystal directions are also shown as arrows.
• the intrinsic birefringence is schematically represented by five "lobes" 211, the surfaces of which indicate the amount of intrinsic birefringence for the respective beam direction of a light beam.
• the maximum intrinsic birefringence results on the one hand in the direction of the lens axis EA, and on the other hand in each case in the ⁇ 01 1>, ⁇ 101> -, ⁇ 101> - and ⁇ 011> crystal direction, i.e. for light beams with an aperture angle of 0 °, or with an opening angle of 60 ° and the four azimuth angles, which result from the projection of the ⁇ 01 1>, ⁇ 101>, ⁇ 101> and ⁇ 011> crystal directions into the ⁇ 110 ⁇ crystal plane.
• Such high opening angles do not occur in crystal material, however, since the maximum opening angles are limited to less than 45 ° by the refractive index of the crystal.
• the definition of the opening angle ⁇ and azimuth angle ⁇ is shown in FIG. 3.
• the z-axis points in the ⁇ 100> crystal direction, the x-axis in the direction which results from projecting the ⁇ 110> crystal direction into the ⁇ 100 ⁇ crystal plane.
• the z axis is the lens axis and the x axis is the reference direction.
• the curve shape was determined according to the formulas known from crystal optics.
• Azimuth angle for the opening angle ⁇ 45 ° for a (100) lens.
• the fourfold azimuthal symmetry is obvious.
• FIG. 4C shows the birefringence distribution ⁇ n ( ⁇ , ⁇ ) for individual beam directions in the ( ⁇ , ⁇ ) angular space for a (100) lens.
• Each line represents the magnitude and direction for a beam direction defined by the opening angle ⁇ and the azimuth angle ⁇ .
• the length of the lines is proportional to the amount of birefringence or the difference in the main axis lengths of the cutting ellipse, while the direction of the lines indicates the orientation of the longer main axis of the cutting ellipse.
• the cut ellipse is obtained by cutting the index ellipsoid for the beam of direction ( ⁇ ,) with a plane that is perpendicular to the beam direction and passes through the center of the index ellipsoid. Both the directions and the lengths of the lines show the four-fold distribution. The length of the lines and thus the birefringence is maximal at the azimuth angles 0 °, 90 °, 180 ° and 270 °.
• FIG. 4D now shows the birefringence distribution ⁇ n ( ⁇ , ⁇ ) which results when two adjacent plane-parallel (100) lenses of the same thickness are arranged rotated by 45 °.
• the resulting birefringence distribution ⁇ n ( ⁇ , ⁇ ) is independent of the azimuth angle.
• the longer main axes of the cutting ellipses are tangential.
• the resulting optical path differences between two mutually orthogonal polarization states are obtained by multiplying the birefringence values by the physical path lengths of the beams within the plane-parallel (100) lenses.
• Rotationally symmetrical birefringence distributions are obtained if n plane-parallel (100) lenses of the same thickness are arranged in such a way that the following applies to the angle of rotation ß between two lenses:
• the maximum value of the lens can be compared to an equally oriented arrangement of the lenses
• An almost rotationally symmetrical distribution of the optical path differences for two mutually orthogonal linear polarization states also results for any lenses if all beams of a bundle of rays in the lenses each have similarly large angles and cover similarly large path lengths within the lenses.
• the lenses should therefore be grouped together in such a way that the rays meet the previously specified condition as well as possible.
• the intrinsic birefringence is independent of the azimuth angle ⁇ .
• the curve was determined according to the formulas known from crystal optics.
• Azimuth angle ⁇ for the opening angle ⁇ 35 ° for an (III) lens.
• the threefold azimuthal symmetry is obvious.
• FIG. 5C shows the birefringence distribution ⁇ n ( ⁇ , ⁇ ) for individual beam directions in the ( ⁇ ,) angular space for a (111) lens in the representation already introduced with FIG. 4C. Both the directions and the lengths of the lines show the threefold distribution. The length of the lines and thus the birefringence is maximum at the azimuth angles 0 °, 120 ° and 240 °. In contrast to a (100) lens, the orientation of the birefringence rotates by 90 ° if a beam passes through a lens instead of an azimuth angle of 0 ° with an azimuth angle of 180 °. Thus, for example, the birefringence can be compensated for by two identically oriented (III) lenses.
• Refractive projection lenses have several lens groups with positive and negative refractive powers. In particular in lens groups with positive refractive power there is often a maximum of the tuft diameter, in lens groups with negative refractive power there is a minimum of the tuft diameter.
• a typical microlithography projection objective has, for example, a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, a fourth lens group with negative refractive power and a fifth lens group with positive refractive power.
• a first lens group with positive refractive power there is a maximum of the tuft diameter
• the second lens group a minimum of the tuft diameter
• the third lens group a maximum of the tuft diameter
• within the fourth lens group a minimum of the tuft diameter and within the fifth lens group a maximum of the tuft diameter.
• FIG. 5D now shows the birefringence distribution .DELTA.n (.theta., .Alpha.) which results when two adjacent plane-parallel (III) lenses of the same thickness are arranged rotated by 60.degree.
• the resulting birefringence distribution ⁇ n ( ⁇ , ⁇ ) is independent of the azimuth angle.
• the longer main axes of the cutting ellipses run radially.
• the resulting optical path differences of two mutually orthogonal polarization states are obtained by using the birefringence values with the multiplied physical path lengths of the rays within the (III) lenses. Rotationally symmetrical birefringence distributions are also obtained if n are plane-parallel
• Opening angle ⁇ for the azimuth angle ⁇ 0 ° for the two adjacent plane-parallel (111) lenses of the same thickness shown in FIG. 5D.
• the intrinsic birefringence is independent of the azimuth angle ⁇ .
• the curve shape was determined according to the formulas known from crystal optics.
• FIG. 6B shows the amount of the intrinsic birefringence as a function of the
• the two-fold azimuthal symmetry is obvious.
• FIG. 6D now shows the birefringence distribution ⁇ n ( ⁇ ,) which results when two adjacent plane-parallel (110) lenses of the same thickness are arranged rotated by 90 °. The resulting birefringence distribution ⁇ n ( ⁇ , ⁇ ) now has a fourfold azimuthal symmetry.
• FIG. 6E now shows the birefringence distribution .DELTA.n (.theta.,) which results when the two plane-parallel (110) lenses of the same thickness in FIG. 6C are combined with two further plane-parallel (110) lenses of the same thickness.
• the angle of rotation between two of the (HO) lenses is 45 °.
• the resulting birefringence distribution ⁇ n ( ⁇ , ⁇ ) is independent of the azimuth angle ⁇ .
• the longer main axes of the cutting ellipses run radially, that is to say similar to the distribution of FIG.
• the resulting optical path differences of two mutually orthogonal polarization states are obtained by multiplying the birefringence values by the physical path lengths of the beams within the (HO) lenses. Also rotationally symmetrical birefringence distributions are obtained if 4-n plane-parallel ( ⁇ l ⁇ ) lenses of the same thickness are arranged in such a way that for the angle of rotation ß
• the intrinsic birefringence is independent of the azimuth angle ⁇ .
• FIG. 7 shows the lens section of a refractive projection objective 611 for the wavelength 157 nm.
• the optical data for this lens are in Table 1 compiled.
• the exemplary embodiment is taken from the applicant's patent application PCT / EP00 / 13148 (WO 150171 AI) and corresponds there to FIG. 7 or Table 6.
• PCT EP00 / 13148 WO 150171 AI
• All lenses of this lens are made of calcium fluoride crystal.
• the numerical aperture of the lens on the image side is 0.9.
• the imaging performance of this lens is corrected so well that the deviation from the wavefront of an ideal spherical wave is less than 1.8m ⁇ in relation to the wavelength of 157nm. Especially with these high-performance lenses, it is necessary to reduce interfering influences such as that of intrinsic birefringence as much as possible.
• the opening angles ⁇ and beam paths RL L of the outermost aperture beam 609 were calculated for the individual lenses L601 to L630.
• the outermost aperture beam 609 is used because it results in almost the maximum opening angle within the lenses.
• Table 2 In addition to the opening angles ⁇ and the path lengths RL L for the outermost aperture beam, Table 2 shows the optical path differences for two mutually orthogonal linear polarization states for different lens orientations.
• the optical path differences are compiled for (III) lenses, (100) lenses and (HO) lenses, the azimuth angle L of the outermost marginal ray within the lenses for a (111) lens 0 ° and 60 °, for a (100 ) Lens is 0 ° and 45 ° and for a (110) lens it is 0 °, 45 °, 90 ° and 135 °.
• Table 2 shows that the opening angles ⁇ for the lenses L608, L617, L618, L619, L627, L628, L629 and L630 are greater than 25 °, for the lenses L618, L627, L628, L629 and L630 even greater than 30 ° are.
• the lenses L627 to L630 closest to the image plane are particularly affected by high opening angles.
• the design of the projection lens ensures that the maximum opening angle of all light rays is less than 45 °.
• the maximum opening angle for the outermost aperture beam is 39.4 ° for the L628 lens.
• the use of two thick planar lenses L629 and L630 directly in front of the image plane was helpful.
• the diameter of the aperture which is located between the lenses L621 and L622, is 270mm.
• the diameter of the lens L618 is 207mm and the diameter of the lenses L627 to L630 are all less than 190mm.
• the diameters of these lenses, which have high opening angles, are therefore less than 80% of the diaphragm diameter.
• Table 2 shows that it is favorable for individual lenses with large opening angles to orient them in the (100) direction since the birefringence values are lower overall. This is due to the fact that with (100) lenses the influence of the ⁇ 110> crystal directions can only be felt at larger angles than with (III) lenses. For example, with lenses L608, L609 and L617, the optical path differences are more than 30% lower.
• both lenses have the same opening angle for the outermost aperture beam of 35.3 ° and similar beam paths of 27.3mm or 26.0mm. If both lenses were installed as (100) lenses with the same orientation, there would be an optical path difference of 30.7 nm. However, if you twist the two (100) lenses mutually by 45 °, the optical path difference is reduced to 20.9nm, i.e. by 32%. If both lenses were installed as (111) lenses with the same orientation, there would be an optical path difference of 34.6nm. However, if you twist the two (111) lenses mutually by 60 °, the optical path difference is reduced to 13.6nm, i.e. by 61%.
• the lens L629 into the lenses L6291 and L6292 and the lens L630 into the lenses L6301 and L6302 are split, the lens L6291 a (100) lens with a thickness of 9.15mm, the lens L6292 with a (III) lens with a thickness of 13.11mm, the lens L6301 with a (100) lens with a thickness of 8.33mm and the lens L6302 is a (111) lens 12.9mm thick.
• the lenses L6291 and L6301 are rotated against each other by 45 °, the lenses L6292 and L6302 by 60 °. In this case, the resulting maximum optical path difference is 0.2 nm.
• the lenses L6291 and L6292, as well as the lenses L6301 and L6302 can be joined optically seamlessly, for example by starting.
• This principle can also be used if the projection lens contains only one crystal lens. This is then broken down into at least two lenses, which are arranged rotated relative to one another. The assembly is possible by starting. Another possibility is to first connect individual plates of the desired crystal orientation optically seamless and in a further process step to manufacture the lens from the plates joined together.
• lens L629 and L630 Another way to reduce the disruptive influence of intrinsic birefringence through lenses L629 and L630 is to insert lens L629 into the lenses L6293 and L6294 and the lens L630 are split into the lenses L6303 and L6304, the lens L6293 then a ( ⁇ l ⁇ ) lens with a thickness of 11.13mm, the lens L6294 with a (110) lens with a thickness of 11.13mm, the lens L6303 with a lens (110) lens 10.62mm thick and lens L6304 is a (110) lens 10.62mm thick.
• the lenses L6293 and L6294, as well as the lenses L6303 and L6304, are each rotated against one another by 90 °, the angle of rotation between the lenses L6293 and L6303 being 45 °.
• the resulting maximum optical path difference in this case is 4.2nm.
• the lenses L6293 and L6294 like the lenses L6303 and L6304, can be joined optically seamlessly as lens parts, for example by means of wringing.
• the optical path differences for two mutually orthogonal linear polarization states are almost completely compensated for, which is caused by the highly stressed lenses L629 and L630 when the lens L629 is in the three lens parts L6295, L6296 and L6297 and the lens L630 in the lens parts L6305, L6306 and L6307 are split, the lens L6295 then being a (100) lens with a thickness of 4.45 mm, the lenses L6296 and L6297 (110) lenses with a thickness of 8.90 mm, the lens L6305 being a (100) lens with a thickness of 4.25 mm and L6306 and L6307 (HO) lenses are 8.49mm thick.
• the lenses L6294 and L6304 are rotated against each other by 45 °, two of the lenses L6295, L6297, L6306 and L6307 by 45 °. In this combination, the resulting maximum optical path difference is reduced to less than 0.1 nm.
• the lenses L6295 to L6297 like the lenses L6305 to L6307, can be joined optically seamlessly as lens parts, for example by cracking.
• a further possibility to reduce the disturbing influence of the intrinsic birefringence by the lenses L629 and L630 is to combine two (HO) lenses with one (100) lens.
• the two (110) lenses are to be installed rotated by 90 ° to each other, while the angle of rotation between the (100) lens and the (HO) lenses is 45 ° + m-90 °, where m is an integer.
• the lens L629 is split into the lenses L6298 and L6299 and the lens L630 into the lenses L6308 and L6309, the lens L6298 then a (HO) lens with a thickness of 17.40 mm, the lens L6299 is a (110) lens with a thickness of 4.87mm, lens L6308 is a (110) lens with a thickness of 12.53mm and lens L6309 is a (100) lens with a thickness of 8.70mm.
• the resulting maximum optical path difference is 3.1 nm.
• the lenses L6298 and L6299, as well as the lenses L6308 and L6309, can be joined optically seamlessly as lens parts, for example by cracking.
• FIG. 8 shows the lens section of a catadioptric projection objective 711 for the wavelength 157nm.
• the optical data for this lens are summarized in Table 3.
• the exemplary embodiment is taken from the applicant's patent application PCT / EP00 / 13148 (WO 150171 AI) and corresponds there to FIG. 9 or Table 8.
• PCT / EP00 / 13148 WO 150171 AI
• All lenses of this lens are made of calcium fluoride crystal.
• the numerical aperture of the objective on the image side is 0.8.
• the opening angles ⁇ and beam paths RL of the upper outermost aperture beam -113 and the lower outermost aperture beam 715 were calculated for the individual lenses L801 to L817.
• the upper and lower outermost aperture beams were calculated because the object field is remote from the axis and therefore the aperture beams are not symmetrical to the optical axis, as was the case for the outermost aperture beam of the exemplary embodiment in FIG. 7.
• Table 4 shows the data for the top outermost aperture beam and in Table 5 for the bottom outermost aperture beam.
• the optical path differences for two mutually orthogonal linear polarization states for different lens orientations are compiled in Table 4 and Table 5; for (111) lenses,
• Table 4 and Table 5 show that the opening angles ⁇ for the lenses L815 to L817 are greater than 25 °. In this exemplary embodiment, too, the lenses L815 to L817 closest to the image plane have large opening angles. The design of the lenses L815 to L817 ensures that the maximum
• Opening angle is less than or equal to.
• the maximum Opening angle for the outermost aperture beam is 30.8 ° for the L817 lens.
• the diameter of the aperture, which is located between the lenses L811 and L812, is 193mm.
• the diameters of the lenses L815 to L817 are all less than 162mm. The diameters of these lenses, which have high opening angles, are therefore less than 85% of the diaphragm diameter.
• the following is intended to show how the intrinsic birefringence can be largely compensated for by the parallel use of groups with mutually rotated (100) lenses and groups with mutually rotated (III) lenses.
• all calcium fluoride is installed in (III) orientation without mutually twisting the (III) lenses.
• the maximum optical path difference can be reduced to approx. 38 nm by turning the (III) lenses.
• the lenses L801 and L804 are combined into one group and the lenses L802 and L803 into another group, the angle of rotation between the lenses in each case being 60 °.
• the lenses L808, L809 and L810, as well as the lenses L815, L816 and L817 are combined to form a group of three, the rotation angle between two of these lenses being 40 °.
• the lenses L811, L812, L813 and L814 are combined into a group of four with a mutual rotation angle of 30 °.
• the lenses L801 and L804 are combined into one group and the lenses L802 and L803 into another group, the angle of rotation between the lenses in each case being 45 °.
• the lenses L808, L809 and L810 and the lenses L815, L816 and L817 are combined to form a group of three, the angle of rotation between two of these lenses being 30 °.
• the lenses L811, L812, L813 and L814 are combined in a group of four with a mutual rotation angle of 22.5 °.
• a maximum optical path difference for two mutually orthogonal linear polarization states of only 7 nm is obtained if groups with (100) lenses are now combined with groups with (111) lenses.
• the lenses L801 and L804 are combined into a group of (III) lenses, the angle of rotation between the lenses being 60 °.
• the lenses L802 and L803 are combined into a group of (100) lenses, the angle of rotation between the lenses being 45 °.
• the lenses L808, L809 and L810 are combined to form a group of three (100) lenses, the angle of rotation between two of these lenses being 30 °.
• the lenses L815, L816 and L817 are combined to form a group of three (III) lenses, the angle of rotation between two of these lenses being 40 °.
• the lenses L811, L812, L813 and L814 are combined into a group of four (100) lenses with an angle of rotation of 22.5 °.
• the lens axes of the lenses L805 and L807 which are not combined into a group are oriented in the ⁇ 111> crystal direction, while the lens axis of the lens L806 is oriented in the ⁇ 100> crystal direction.
• the groups can be arranged mutually rotated around the optical axis. These degrees of freedom of rotation can be used to compensate for non-rotationally symmetrical aberrations, which are generated, for example, by the mounting of the lenses.
• a further method is described below as to how the groups can be determined using (100), (111) or (110) lenses. This is based on a lens with a well-known optical design. Several lenses of this lens are made of birefringent fluoride crystal, with the birefringent properties of the lenses are known. For example, the influence of intrinsic birefringence as a function of the beam's opening angle and azimuth angle can be predicted theoretically. The birefringent properties can also be known from measurements on the lenses. Since the birefringent properties of the lenses are known, the optical path difference for two mutually orthogonal is linear
• this optical path difference serves as an optimization variable, the absolute value of which must be minimized.
• 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
• the lens axes can point in (100), (111) or ( ⁇ l ⁇ ) 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 angle of rotation between these two is
• Lenses 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.
• Threshold acceptance (threshold accepting)
• FGH 1 (111) lens with 0 ° rotation angle
• FGH 2 (111) lens with rotation angle 60 °
• FGH 3 (100) lens with 0 ° swivel
• FGH 4 (100) lens with 45 ° rotation angle
• the angles of rotation each relate to a fixed reference direction in the
• the optimal crystal orientations of the lens axes and the angles of rotation ⁇ L of the lenses with respect to a fixed reference direction in the object plane were determined using the Monte Carlo search and the specification of the four degrees of freedom FGH1 to FGH4.
• Table 6 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 orthogonal linear polarization states for the uppermost and lowermost outermost aperture beam is also given for each lens.
• the maximum resulting optical path difference is 5nm.
• 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 rotated relative to one another by the angle of rotation 45 °.
• the lenses L802, L804, L807 and L812 form a second group with (III) 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 °.
• FGH 1 (111) lens with 0 ° rotation angle
• FGH 2 (11 D lens with 60 ° rotation angle
• FGH 3 (100) lens with 0 ° rotation angle
• FGH 4 (100) lens with 45 ° rotation angle
• FGH 5 (HO) lens with 0 ° rotation angle
• FGH 6 (HO) lens with 90 ° rotation angle
• FGH 7 (110) lens with 45 ° rotation angle
• FGH 8 (HO) lens with a rotation angle of 135 °
• Measurement data relating to voltage birefringence, the surface data of the lenses or mirrors and / or material inhomogeneities of the lenses can also be taken into account in the optimization. In this way, all disturbance variables that occur are detected and the lens state that delivers a good overall image quality is determined with the aid of the degrees of freedom.
• 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.
• a threshold for the objective function below which the disruptive influence of birefringence can be tolerated.
• the angles of rotation of the lenses with respect to one another and the crystal orientations within the objective are changed in accordance with the specified degrees of freedom, one of the previously described methods, for example the Monte Carlo method, being used.
• 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 result, for example, in which the individual lens states are specified with the associated objective function.
• the refractive objective 611 is intended to show in the following how the disruptive influence of birefringence effects can be significantly reduced by covering an optical element with a compensation coating 613.
• the two lenses L629 and L630 which consist of calcium fluoride and thus show intrinsic birefringence, should be considered.
• the two lenses have an (11 l) orientation and are rotated by 60 ° against each other. This results in an almost rotationally symmetrical distribution of the optical path differences ⁇ OPL.
• the maximum optical path difference ⁇ OPL is between 13.6 nm and 14.6 nm, depending on the azimuth angle ⁇ R.
• the compensation coating 613 described in Table 7 is applied to the optical surface of the lens L630 facing the image plane O '.
• the compensation coating 613 consists of 15 individual layers made of the materials magnesium fluoride (MgF2) and lanthanum fluoride (LaF3).
• n and k in Table 7 indicate the real and imaginary parts of the refractive index.
• the layer thicknesses are homogeneous and have no lateral thickness curve.
• the evaporation angles during the coating are perpendicular to the optical surface of the L630 lens.
• the resulting optical path difference is 1.1 nm for the two lenses L629 and L630 and is therefore significantly reduced compared to a lens without compensation coating.
• An analogous procedure is also possible if the entire lens is viewed instead of the last two lenses.
• compensating the birefringence with only one optical element with a compensation coating it is also possible to cover several optical elements with compensation coatings.
• the method can also be used to compensate for birefringence in an overall system, the causes of this birefringence being stress birefringence, intrinsic birefringence and birefringence through the remaining layers.
• the distribution of the optical path differences ⁇ OPL for one or more tufts of rays in the image plane is determined.
• the necessary compensation layer is then calculated using a program for optimizing layers and applied, for example, to the system area closest to the image plane. It is advantageous if the optical element closest to the image plane can be exchanged. This also allows birefringence effects that only arise when the lens is in operation to be corrected.
• the orientation is selected according to the rules described above.
• Blanks are specified as exemplary embodiments, from which, for example, the lens L816 for the projection objective of FIG. 8 can be manufactured.
• the lens L816 has a convex aspherical front surface with the apex radius 342.13mm and a concave spherical back surface with the apex radius 449.26mm.
• the axial thickness is 37.3mm.
• the lens material is calcium fluoride.
• the lens diameter is 141mm.
• the blank from which the lens is to be worked out requires at least a total thickness of 45mm and a diameter of 150mm.
• the blank can consist of two (100) plates rotated by 45 ° (100) and two (13) plates rotated by 13 ° (13.5 mm), which are optically seamless.
• the (100) plates and the (III) plates should each be arranged adjacent to one another.
• six plates (lOO) of 3.0 mm thickness rotated relative to each other by 45 ° and six plates rotated relative to each other by 60 ° (HD plates 4.5 mm thick) are joined optically seamless, two after each of two (lOO) plates (11 D plates follow.
• Thickness 2.25 is optically seamless, with four (HO) plates each followed by two (100) plates.
• the following describes methods with which corresponding markings can be made on the lenses or lens parts or their holding frames.
• the production of calcium fluoride lenses, the lens axes of which point in the ⁇ 111> crystal direction, 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 both plane-parallel and gel-curved lenses or lens parts.
• the orientation of the ⁇ 111> crystal direction of an optical blank in this case a calcium fluoride disk, is determined.
• This can be done, for example, with high accuracy using crystallographic methods, such as, for example, by determining gap areas or producing etch pits.
• This direction determination can be improved with X-ray diffractometric methods.
• a suitable device is one
• the measurements are carried out at 0 ° and 90 °. To the To increase measuring accuracy, the measurements can also be carried out at 180 ° and 270 °.
• 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.
• the measured deviation serves as the basis for a targeted correction, i.e. a defined processing of the calcium fluoird 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 is determined on the calcium fluoride disk. If the surface normal of the calcium fluoride disk points in the ⁇ 111> crystal direction, it is advantageous to assign one of the three crystal directions ⁇ 110>, ⁇ 011> and ⁇ 101>, or ⁇ 100>, ⁇ 010> and ⁇ 001> know, which are grouped in three-wave symmetry around the ⁇ 111> crystal direction. 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. If the light beam runs in the ⁇ 100> crystal direction or an equivalent crystal direction, it experiences no optical path difference.
• the three crystal directions ⁇ 110>, ⁇ 011> and ⁇ 101>, or ⁇ 100>, ⁇ 010> and ⁇ 001> know, which are grouped in three-wave symmetry around the ⁇ 111> crystal direction. This is interesting because a light beam experiences
• Crystal directions ⁇ 110>, ⁇ 011> and ⁇ 101> each include an angle of 35 °
• the three crystal directions ⁇ 100>, ⁇ 010> and ⁇ 001> include an angle of 55 ° with the ⁇ 111> crystal direction.
• X-ray reflections from (110) or (100) crystal planes cannot be measured. Therefore, one has to use Bragg reflections from other crystal planes that are in a defined relationship to the (100) or (HO) 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.
• the (331) -Bragg reflex appears for monochromatic copper K ⁇ radiation (8048 eV) with calcium fluids below 38 °. This results in an angle of incidence of 16 ° and a detector angle of 60 ° relative to the reference plane defined by the surface 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 wafer surface are parallel to the projections of the three crystal directions ⁇ 110>, ⁇ 011> and ⁇ 101>.
• 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 marking is applied to the calcium fluoride disk, which indicates the direction of one of the projected crystal directions ⁇ 110>, ⁇ 011> and ⁇ 101>, or ⁇ 100>, ⁇ 010> and ⁇ 001>.
• the marking can be done, for example, by means of engraving, etching or labeling.
• For marking offers the cylinder edge of the calcium fluoride disc.
• the marking can also be attached to a holder with which the calcium fluoride disk is firmly connected.
• a lens is removed from the calcium fluoride disk in such a way that the lens axis is parallel to the ⁇ 111> crystal direction.
• the marking made previously is not destroyed when processing the calcium fluoride disc. 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 lens is produced from a calcium fluoride disc, the lens axis of which already points in the ⁇ 111> crystal direction. The marking is applied after the lens has been manufactured.
• the lens is manufactured from the calcium fluoride disk in such a way that the lens axis points in the ⁇ 111> crystal direction.
• the reference direction is determined in a second step.
• the same procedures are used as previously described for the calcium fluoride disk.
• 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. In the case of plane-parallel plates, the method described can be applied at any point on the surface based on a goniometer structure.
• Irradiation of calcium fluoride with X-rays can produce color centers.
• the penetration depth of Cu-K ⁇ radiation for calcium fluoride is approx. 30 ⁇ m.
• the projection exposure system 81 has an illumination device 83 and a projection lens 85.
• the projection objective 85 comprises a lens arrangement 819 with an aperture diaphragm AP, an optical axis 87 being defined by the lens arrangement 89. Exemplary embodiments for the lens arrangement 89 are given in FIGS. 7 and 8.
• a mask 89 is arranged between the illumination device 83 and the projection lens 85 and is held in the beam path by means of a mask holder 811. Such in the
• Masks 89 used in microlithography have a micrometer-nanometer structure, which is imaged on the image plane 813 by means of the projection objective 85, for example reduced by a factor of 4 or 5.
• a light-sensitive substrate 815 or a wafer positioned by a substrate holder 817 is held in the image plane 813.
• the minimum structures that can still be resolved depend on the wavelength ⁇ of the light used for the illumination and on the numerical aperture of the projection objective 85 on the image side, the maximum achievable resolution of the projection exposure system 81 with decreasing wavelength ⁇ the Illumination device 83 and with increasing numerical aperture of the projection objective 85 increases.
• resolutions of less than 150 nm can be realized. For this reason, effects such as Intiinsic birefringence must also be minimized.
• the invention has succeeded in greatly reducing the disruptive influence of intrinsic birefringence, particularly in the case of projection objectives with large numerical apertures on the image side.
• Wavelength and refractive index are given in relation to vacuum.

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