DE10210782A1 - Lens with crystal lenses - Google Patents

Abstract

Objective, in particular projection objective for a microlithography projection exposure system with at least one fluoride crystal lens. A reduction in the disturbing influence of birefringence is achieved if this lens is a (100) lens with a lens axis which is approximately perpendicular to the {100} crystal planes or to the equivalent crystal planes of the fluoride crystal. In the case of lenses with at least two fluoride crystal lenses, it is expedient if the fluoride crystal lenses are arranged rotated relative to one another. In addition to the <100> crystal direction, the lens axes of the fluoride crystal lenses can also point in the <111> or <110> crystal direction. A further reduction in the disruptive influence of birefringence is achieved by the simultaneous use of groups with (100) lenses twisted against one another and groups with twisted (111) lenses or (110) lenses. A further reduction in the disruptive influence of birefringence is achieved by covering an optical element with a compensation coating.

Description

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 ideally, when producing fluoride crystal lenses, the lens axes are perpendicular to the {111} crystal planes of the fluoride crystals are aligned to the To minimize stress birefringence. US 6,201,634 assumes that Fluoride crystals have no intrinsic birefringence.

From the Internet publication "Preliminary Determination of an Intrinsic Birefringence in CaF2 "by John H. Burnett, Eric L. Shirley, and Zachary H. Levine, NIST Gaithersburg However, MD 20899 USA (distributed on May 7, 2001) is known that calcium fluoride Single crystals also have non-stress-induced, i.e. intrinsic birefringence. The measurements presented there show that with beam spreading in the <110> - Crystal direction has a birefringence of (6.5 ± 0.4) nm / cm at a wavelength of λ = 156.1 nm, from (3.6 ± 0.2) nm / cm at a wavelength of λ = 193.09 nm and from (1.2 ± 0.1) nm / cm occurs at a wavelength of λ = 253.65 nm for calcium fluoride. at a beam propagation in the <100> crystal direction and in the <111> crystal direction calcium fluoride, on the other hand, has no intrinsic birefringence, as is the case with the theory is predicted. The intrinsic birefringence is therefore strong depends on the direction and increases significantly with decreasing wavelength.

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>, < 11 0>, <101>, <10 1 >, < 1 01>, < 1 0 1 >, <011>, <0 1 1>, <01 1 >, <0 11 >, <111>, < 111 >, < 11 1>, < 1 1 1 >, <1 11 >, < 1 11>, <1 1 1>, <11 1 >, <100>, <010>, <001>, < 1 00>, <0 1 0> and <00 1 > on. The main crystal directions <100>, <010>, <001>, < 1 00>, <0 1 0> and <00 1 > are equivalent to one another 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 are given the prefix "(100) -". Crystal planes that are perpendicular to one of these main crystal directions are given the prefix "(100) -". The main crystal directions <110>, < 1 10>, < 1 10>, < 11 0>, <101>, <10 1 >, < 1 01>, < 1 0 1 >, <011>, <0 1 1>, <01 1 > and <0 11 > 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 that are perpendicular to one of these main crystal directions are given the prefix "(110) -". The main crystal directions <111>, < 111 >, < 11 1>, < 1 1 1 >, <1 11 >, < 1 11>, <1 1 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, get the prefix "(111) -". Crystal planes that are perpendicular to one of these main crystal directions are given the prefix "(111) -". Statements that are made below regarding one of the above-mentioned main crystal directions always also apply to the equivalent main crystal directions.

Projection lenses and microlithography projection exposure systems are available for example from the applicant's patent application PCT / EP 00/13148 and therein known writings known. The exemplary embodiments of this application show suitable ones Purely refractive and catadioptric projection lenses with numerical apertures from 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 in the patent application "projection exposure system of microlithography, Optical system and manufacturing process "(DE 101 23 725.1) with the file number of Applicant 01055P and the filing date May 15, 2001. The content of this Registration should also be part of the present application.

The object of the invention is to provide projection lenses for a microlithography To specify projection exposure equipment in which the influence of birefringence, in particular, the intrinsic birefringence is significantly reduced.

This object is achieved with a lens according to claim 1, 8 and 31, one Microlithography projection exposure apparatus according to claim 47, a method for Manufacture of semiconductor devices according to claim 48, a method for Production of lenses according to claim 49, a method for compensating Birefringence effects according to claim 53 and a lens manufacturing method according to Claim 54.

Advantageous refinements of the invention result from the features of dependent claims.

In order to minimize the influence of intrinsic birefringence, claim 1 proposes in the case of fluoride crystal lenses, align the lens axes so that they are aligned with the <100> Crystal direction collapse. The lens axes then fall with one Main crystal direction together when the maximum deviation between lens axis and the main crystal direction is less than 5 °. Not all fluoride crystal lenses need to be Objectives have such an alignment of the crystal planes. Those lenses where the lens axes are perpendicular to the {100} crystal planes are in Hereinafter also referred to as (100) lenses. The alignment of the lens axis in <100> - Crystal direction has the advantage that the disruptive influence of the intrinsic Birefringence, which results from light propagation in the <110> crystal direction, only at higher opening angles of the light rays than for an alignment of the Lens axis in <111> crystal direction. The opening angle is understood in this Relationship between the angle between a light beam and the optical axis outside a lens and between the light beam and the lens axis inside one Lens. Only when the opening angle in the range of the angle between the <100> - Crystal direction and the <110> crystal direction come, feel the corresponding Light rays the influence of birefringence. The angle between the <110> - The crystal direction and the <100> crystal direction is 45 °. Would be the lens axis oriented in the <111> crystal direction, the disruptive influence of the make intrinsic birefringence noticeable even at smaller opening angles, because the angle between the <110> crystal direction and the <111> crystal direction is only 35 ° is.

Is the angular dependence of the birefringence, for example, by the Manufacturing process of the fluoride crystal or the mechanical stress on the lens, voltage birefringence, in particular, so the disclosed Solution approaches, of course, also to reduce the disruptive influence of Birefringence can be applied.

The lens axis is, for example, an axis of symmetry given rotationally symmetrical lens. If the lens has no axis of symmetry, it can the lens axis through the center of an incident beam or through a straight line be given with respect to the beam angle of all light rays within the lens are minimal. Refractive or diffractive lenses, for example, come as lenses Correction plates with free-form correction surfaces in question. Flat sheets are also considered Lenses viewed, provided they are arranged in the beam path of the lens. The 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, which extends from the object plane to the image plane runs. The (100) lenses are preferably constructed centered around this optical axis, so that the lens axes coincide with the optical axis.

The invention can advantageously be used in projection objectives for microlithography Use a projection exposure system because the requirements for these lenses are extremely high to be resolved. But also with test lenses with which for example, lenses for projection lenses by measuring wavefronts with large opening are tested, the influence of birefringence is disruptive.

For lenses with large numerical apertures on the image side, in particular larger than 0.7, occur within the (100) lens opening angles that are greater than 25 °, in particular are greater than 30 °. The invention comes to fruition precisely at these large opening angles Wear to orient the lens axes in the <100> crystal direction. Would they be If the lens axes are oriented in the <111> crystal direction, the light rays would also Opening angles greater than 25 °, in particular greater than 30 ° more clearly the disturbing Feel the influence of birefringence if not one of those described below Corrective measures are applied.

On the other hand, since the disturbing influence of the intrinsic birefringence can be maximal at an aperture angle of 45 °, it is advantageous to design the projection lens so that all aperture angles of the light beams are less than 45 °, in particular less than or equal


where NA denotes the numerical aperture on the image side and n _FK the refractive index of the fluoride crystal. The expression


specifies the opening angle, which corresponds to the numerical aperture on the image side within a fluoride crystal lens when the light beam is refracted at a flat interface. 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.

Large opening angles occur mainly with lenses near field planes, especially the image plane. The (100) lenses should therefore preferably be in the range of the field levels are used. The area where the (100) lenses are used can be determined by the ratio of the lens diameter to the diameter determine the aperture. For example, the lens diameter of the (100) lenses is preferably a maximum of 85%, in particular a maximum of 80% of the diaphragm diameter.

In the case of projection lenses, the largest opening angles generally occur in that of Closest to the image plane. That is why this lens is preferred the lens axis is 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 Δn (α _L , θ _L ) can be assigned to each fluoride crystal lens, which is a function of the opening angle θ _L on the one hand and a function of the azimuth angle α _L on the other. The value of the birefringence Δn 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 θ _L and the azimuth angle α _L. 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 θ _L is determined between the beam direction and the lens axis, the azimuth angle α _L between the beam direction projected into the crystal plane perpendicular to the lens axis 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 ΔOPL (α _R , θ _R ) for two mutually orthogonal linear polarization states. The optical path differences ΔOPL are given as a function of the opening angle θ _R and the azimuth angle α _R. The opening angle θ _{R of} a beam is determined between the beam direction and the optical axis in the image plane, the azimuth angle α _R between the beam direction projected into the image plane and a fixed reference direction within the image plane. If the objective now has at least two lenses or lens parts made of fluoride crystal, it is advantageous if 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 ΔOPL ( α _R , θ _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. However, since the birefringence distributions of the lenses have an azimuthal dependency, the twisted arrangement of the lenses can reduce the maximum value of the distribution ΔOPL (α _R , θ _R ) by up to 20%, in particular by up to 25%, in comparison to an identically oriented installation become.

Lens parts are to be understood, for example, as individual lenses which are caused by wringing optically seamless to be added to a single lens. Describe in general Lens parts are the building blocks of a single lens, with the lens axes of the lens parts each point in the direction of the lens axis of the individual lens.

By twisting the fluoride crystal lenses, the dependence of the distribution ΔOPL (α _R , θ _R ) on the azimuth angle α _{R can be} significantly reduced, so that there is an almost rotationally symmetrical distribution ΔOPL (α _R , θ _R ).

If the lens axis points in a main crystal direction, the birefringence distribution Δn (α _L , θ _L ) of the lens has a k-fold azimuthal symmetry. For example, the birefringence distribution of a (100) lens, in which the lens axis points in the <100> crystal direction, shows 4-fold azimuthal symmetry, the birefringence distribution in a (111) lens, in which the lens axis points in the <111> crystal direction, a 3-fold azimuthal symmetry, and the birefringence distribution of a (110) lens, in which the lens axis points in the <110> crystal direction, a 2-fold azimuthal symmetry. Depending on the count of the azimuthal 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 γ. The angles of rotation γ are measured between the reference directions of two lenses or lens parts. For the lenses of a group, the lens axes point in the same main crystal direction or an equivalent main crystal direction. The reference directions of the lenses of a group are associated with the lenses, that the birefringence distributions .DELTA.n (α _L θ, ₀₎ My 60 have a predetermined opening angle of the same azimuthal course. Thus, for all lenses in a group, the azimuthal areas with maximum birefringence occur at the same azimuth angles. For n lenses in a group, the angles of rotation between two lenses are given as follows:


k specifies the numeracy of the azimuthal symmetry, n the number of lenses in a group and m any integer. The tolerance of ± 10 ° takes into account the fact that the angles of rotation may 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 compensation of the optical path differences of the lenses of a group. However, this can be tolerated within certain limits.

For (100) lenses, the rotation angle is given as follows:

If the group comprises two (100) lenses, the angle of rotation between these two is Lenses ideally 45 °, or 135 °, 225 °. , ,

For (111) lenses, the rotation angle is given as follows:

For (110) lenses, the rotation angle is given as follows:

The distribution of the optical path differences ΔOPL _G (α _R , θ _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 an outermost one Aperture beam of a bundle of rays within each of these lenses is similar Has opening angle, advantageously the opening angle of the outermost Aperture beam within these lenses are greater than 15 °, in particular greater than 20 °. As outermost aperture beam is a beam that starts from an object point, whose beam height in the diaphragm plane corresponds to the radius of the diaphragm and which is therefore in the image plane has an angle according to the numerical aperture on the image side. The extreme aperture rays are used to define the groups because they usually have the largest opening 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 extreme aperture rays thus enables statements about the maximum disturbance of a Wavefront through birefringence.

Furthermore, it is advantageous if the outermost aperture beam has one in each of these lenses same beam path. These measures result in a good balance of the azimuthal contributions to the distribution of the optical path differences, which the individual lenses of a group are caused, so that the resulting distribution the optical path differences is almost rotationally symmetrical.

It is also advantageous if the outermost aperture beam in each lens of a group with the same orientation of the lenses similarly large optical path differences for two linear polarization states orthogonal to one another. If this condition is met, If these lenses are twisted, an optimal compensation of the azimuthal occurs Posts on.

In the case of plane-parallel adjacent (100) or (111) lenses of the same thickness or of four plane-parallel (110) lenses of the same thickness are obtained rotationally symmetrical distribution of the optical path differences ΔOPL by rotation of the lenses according to the formulas above. Even with lenses with curved surfaces by skillful selection of the lenses of a group or by an appropriate choice the thickness and the radii of the lenses by rotating two lenses one achieve approximately rotationally symmetrical distribution of the optical path differences. With (100) lenses or (111) lenses, it is advantageous if a group has two lenses having. With (110) lenses there is an approximately rotationally symmetrical one Distribution of optical path differences for four lenses in a group.

The rotation of the lenses becomes particularly effective when the lenses are adjacent are arranged. It is particularly advantageous to split a lens into two parts and the To twist lens parts against each other optically seamless, for example by Wringing.

In the case of a projection objective with a large number of lenses, it is expedient to form several groups of lenses. The lenses of a group are arranged rotated about the lens axes in such a way that the resulting distribution ΔOPL (α _R , θ _R ) is almost independent of the azimuth angle.

While the distributions ΔOPL _G (α _R , θ _R ) caused by the individual groups are almost independent of the azimuth angle due to the mutual rotation of the lenses of a group, the maximum value of the total distribution ΔOPL (α _R , θ _R ) of the entire objective can thereby become clear reduced that the projection lens has both at least one group with (100) lenses and at least one group with (111) lenses. Good compensation is also possible if a group with (110) lenses is arranged inside the lens next to a group with (100) lenses.

Compensation is possible because 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 ΔOPL ₁ (α _R , θ _R ), which is caused by the lenses or lens parts of all groups with (100) lenses, and the distribution of the optical Path differences ΔOPL ₂ (α _R , θ _R ), which are caused by the lenses or lens parts of all groups with (111) lenses or (110) lenses, have similarly high maximum values.

Another advantageous way to avoid the disruptive influence of birefringence reduce, is an optical element of the projection lens with a Compensation coating to document. It is based on the knowledge that any optical coating, for example anti-reflective or mirror coatings, in addition their properties with regard to reflection and transmission are always optical Path differences for two mutually orthogonal linear polarization states bring. These are different for s- and p-polarized light and also depend on Angle of incidence of the beam on the layer. So you have an angle of incidence dependent Birefringence. For a bundle of rays whose center beam with an incidence angle of 0 ° on the Compensation coating meets the birefringence values and directions rotationally symmetrical with respect to the center beam. The compensation coating is now constructed in such a way that it specifies a predetermined amount of birefringence Behavior as a function of the opening angle of the rays of a beam shows.

The distribution of the optical path differences ΔOPL (α _R , 6 _R ) for two linear polarization states orthogonal to one another for a bundle of rays in the image plane of the projection lens is first determined. The opening angle θ _{R of} a beam is determined between the beam direction and the optical axis in the image plane, the azimuth angle α _R 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 ΔOPL (α _R , θ _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, which is applied to an optical element with an element axis, is determined from the distribution of the optical path differences ΔOPL (α _R , θ _R ). For example, refractive or diffractive lenses, plane plates or mirrors 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 α _F , which are related to a reference direction perpendicular to the element axis, and on opening angles θ _F , which are also related to the element axis.

A pair of values (α _R , θ _R ) of a beam in the image plane corresponds to a pair of values (α _F , θ _F ) on the optical element.

The effective birefringence distribution of the compensation coating is now like this determines that the distribution of optical path differences for two to each other orthogonal linear polarization states for the entire system included Compensation coatings are significantly reduced compared to the distribution without the Compensating coating.

The effective birefringence distribution can be determined by the choice of material Thickness profiles and the evaporation angles for the individual layers of the compensation Affect coating. The layer design and the process parameters result thereby by using layer design computer programs, which from the effective birefringence distribution, the specification of the materials and the geometry of the optical element, the thickness curves of the individual layers and the process variables certainly.

The compensation coating can also be used on several optical elements be attached. This increases the degrees of freedom in determining the Compensation layers, which in addition to the compensation also a high transmission of the Should ensure coating.

Typical distributions of the optical path differences ΔOPL (α _R , θ _R ) for two mutually orthogonal linear polarization states have small path differences for the aperture angle θ _R = 0 °. It is therefore beneficial if the birefringent effect of the compensation coating for the opening angle θ _F = 0 ° almost disappears. This is achieved if no high evaporation angles are used in the production of the compensation coating. Therefore, the optical surface of the optical element to which the compensation coating is applied advantageously has the least possible curvature.

By rotating lenses with (100) or (111) orientation relative to one another, as described above, an approximately rotationally symmetrical distribution of the optical path differences ΔOPL (α _R , θ _R ) is obtained in the image plane, which depends only on the aperture angle θ _R. The optical path differences can be reduced even further with the compensation coating of an optical element, the effective birefringence distribution of which primarily depends only on the aperture angle θ _F. This is achieved in that the layer thicknesses of the individual layers of the compensation coating are homogeneous over the optical element and have no thickness curves.

The invention can be used advantageously by using the optical element with the Compensation coating as an interchangeable element.

The optical element closest to the image plane is advantageous used.

The method provides that in a first step distribution of the optical path differences ΔOPL (α _R , θ _R ) for two mutually orthogonal linear polarization states for a bundle of rays is determined in the image plane. 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.

In a second step, the method already described becomes effective Birefringence distribution of a compensation coating and the resulting one resulting thickness curves of the individual layers and the process parameters Production of the individual layers determined.

In a third step, the optical element is removed from the beam path and with the compensation coating. If the optical surface of the optical element this layer is removed before it is re-occupied.

In a fourth step, the optical element with the compensation coating reattached to the original location within the lens.

Calcium fluoride is preferably used as the material for the lenses in projection objectives used because calcium fluoride when used together with quartz in a Working wavelengths of 193 nm are particularly suitable for color correction, respectively provides sufficient transmission at a working wavelength of 157 nm. But these also apply to the fluoride crystals strontium fluoride or barium fluoride statements made since they are crystals of the same cubic crystal type is.

The disruptive influence of intrinsic birefringence is particularly noticeable 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 have greater than 0.7, in particular greater than 0.8.

The intrinsic birefringence increases significantly as the working wavelength decreases. The intrinsic birefringence is more than double at a wavelength of 193 nm as large, at a wavelength of 157 nm more than five times as large as at one Wavelength of 248 nm. The invention can therefore be particularly advantageous use if the light rays have wavelengths smaller than 200 nm, especially smaller 160 nm.

The lens can be a purely refractive projection lens, that from a variety of rotationally symmetrical arranged around the optical axis There are lenses, or around a projection lens of the catadioptric lens type.

Such projection lenses can advantageously be used in microlithography Use projection exposure systems that start from the light source Lighting system, a mask positioning system, a structure-bearing mask Projection lens, an object positioning system and a light sensitive Include substrate.

With this microlithography projection exposure system can be microstructured Manufacture semiconductor devices.

The invention also provides a suitable method for making lenses. According to the method, lenses or lens parts made of fluoride crystal, whose lens axes point in a main crystal direction, are arranged rotated about the lens axes in such a way that the distribution ΔOPL (α _R , θ _R ) has significantly reduced values compared 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 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 exploits the inventive finding that by rotating the fluoride crystal lenses around the optical axis, the maximum values of the distribution ΔOPL (α _R , θ _R ) of the optical path differences can be significantly reduced. Using suitable simulation methods, a bundle of rays emanating from an object point is propagated through a projection objective and, based on the known optical properties of the fluoride crystal lenses, the distribution ΔOPL (α _R , θ _R ) in the image plane is determined. In an optimization step, the angles of rotation between the fluoride crystal lenses are changed until the birefringence has tolerable values. The optimization step can also take into account other boundary conditions, such as the compensation of non-rotationally symmetrical lens errors by turning the lens. By means of this optimization step, the maximum value of the distribution ΔOPL (α _R , θ _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, the fluoride crystal lenses become groups with lenses, the lenses of one group for an outermost aperture beam, with the lenses being oriented in the same way, 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. Thus, first the (100) lenses can be rotated in such a way that the optical path differences caused by the (100) lenses are reduced, and then the (111) lenses can be rotated in such a way that the optical ones caused by the (111) lenses Path differences can be reduced. The distribution of the fluoride crystal lenses on lenses with (100) orientation and (111) orientation must be such that the resulting (100) - distribution ΔOPL ₁₀₀ (α _R , θ _R ) and the resulting (111) -Distribute ΔOPL ₁₁₁ (α _R , θ _R ) largely. The same applies to the parallel use of (100) lenses and (110) lenses.

The invention also relates to a manufacturing method for a lens, in which in a first Step several sheets of fluoride crystal are optically seamlessly joined to a blank, and in a second step the lens from the blank by known manufacturing methods is worked out. The plates are used as before for lenses or lens parts described, arranged rotated relative to each other around the surface normal.

Plates whose surface normals are in the same main crystal direction or in one equivalent main crystal direction, advantageously have the same axial Thickness.

If (100) panels are joined seamlessly with (111) panels, the ratio of the Sum of the thicknesses of the (111) plates to the sum of the thicknesses of the (100) plates = 1.5 ± 0.2.

If (100) panels are joined seamlessly with (110) panels, the ratio of the Sum of the thicknesses of the (110) plates to the sum of the thicknesses of the (100) plates = 4.0 ± 0.4.

The invention is explained in more detail with reference to the drawings.

Fig. 1 shows a section through a fluoride crystal block perpendicular to the {100} - crystal planes together with an objective lens of a projection in a schematic representation;

Fig. 2A-C each show a plane-parallel (100) - (111) - and (110) lens, in a schematic three-dimensional representation;

Fig. 3 shows a coordinate system for defining the opening angle and the azimuth angle;

FIGS. 4A-F show the birefringence distribution for (100) lenses in different images and the birefringence distribution for two mutually twisted by 45 ° (100) lenses;

FIGS. 5A-F show the birefringence distribution for (111) lenses in different images and the birefringence distribution for two mutually twisted by 60 ° (111) lenses;

Figs. 6A-G show the birefringence distribution for (111) lenses in different images and the birefringence distribution for two mutually rotated by 90 ° (110) lenses, respectively for four mutually shifted by 45 ° twisted (110) lenses;

Fig. 7 shows the lens section of a refractive projection lens;

Fig. 8 shows the lens section of a catadioptric projection objective; and

Fig. 9 shows a microlithography projection exposure system in a schematic representation.

Fig. 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 are located. The fluoride crystal block 3 serves as a blank or starting material for the (100) lens 1. In this example, the (100) lens 1 is a biconvex lens with the lens axis EA, which is also the axis of symmetry of the lens. 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.

In FIG. 2A, a three-dimensional representation illustrates how the intrinic 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. In addition to the <100> crystal direction, the <101> -, <1 1 0> -, <10 1 > - and <110> crystal directions 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 1 0> -, <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 ° within the lens. For 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 °.

In FIG. 2B, a three-dimensional representation illustrates 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. In addition to 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 results 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 ° there are minimal values of the intrinsic birefringence. The intrinsic birefringence disappears for an opening angle of 0 °.

In FIG. 2C, a three-dimensional representation illustrates how the intrinsic birefringence is related to the crystal directions when the lens axis EA points in the <110> crystal direction. A circular, plane-parallel plate 209 made of calcium fluoride is shown. The lens axis EA points in the <110> crystal direction. In addition to the <110> crystal direction, the <01 1 > -, the <10 1 > -, the <101> - and the <011> crystal directions are 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 > -, <10 1 > -, <101> - and <011> -crystal direction, i.e. for light rays with an opening angle of 0 °, or with an opening angle of 60 ° and the four azimuth angles, which are defined by the projection of the <01 1 > -, <10 1 > -, <101> - and <011> crystal directions in 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 θ and azimuth angle α is shown in FIG. 3. For the (100) lens of FIG. 2, the z-axis points in the <100> crystal direction, the x-axis in the direction which results from projection of the <110> crystal direction in the {100} crystal plane. The z axis is the lens axis and the x axis is the reference direction.

From the Internet publication cited it is known that measurements with beam propagation in the <110> crystal direction has a birefringence value of (6.5 ± 0.4) nm / cm at a Wavelength of λ = 156.1 nm for calcium fluoride. With this reading the birefringence distribution Δn (θ, α) of a calcium Fluoride lens can be derived theoretically depending on the crystal orientation. To the formalisms known from crystal optics for calculating the Index ellipsoids are used depending on the beam direction. The theoretical Basics are, for example, in the "Lexicon of optics", spectrum academic publisher Heidelberg Berlin, 1999 under the keyword "crystal optics".

More recent measurements by the applicant have shown that when the beam propagates in the <110> crystal direction, the intrinsic birefringence is 11 nm / cm in calcium fluoride crystal at a wavelength of λ = 156.1 nm. The statements made below for the standardization quantity Δn _max = 6.5 nm / cm can be converted without difficulty to the standardization quantity Δn _max = 11 nm / cm.

In Fig. 4A, the amount of intrinsic birefringence as a function of the opening angle θ for the azimuth angle α = 0 ° shown for a (100) lens. The value for the intrinsic birefringence of 6.5 nm / cm at the opening angle θ = 45 ° corresponds to the measured value. The curve shape was determined according to the formulas known from crystal optics.

FIG. 4B shows the amount of intrinsic birefringence as a function of the azimuth angle α for the aperture angle θ = 45 ° for a (100) lens. The fourfold azimuthal symmetry is obvious.

In Fig. 4C, the birefringence distribution .DELTA.n (θ, α) is shown for individual beam directions (θ, α) -Winkelraum for a (100) lens. Each line represents the magnitude and direction for a beam direction defined by the opening angle θ and the azimuth angle α. 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 (θ, α) 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 maximum at the azimuth angles 0 °, 90 °, 180 ° and 270 °.

Fig. 4D now shows the birefringence distribution .DELTA.n (θ, α), which arises when two adjacent plane-parallel (100) lenses of the same thickness are arranged rotated by 45 °. The resulting birefringence distribution Δn (θ, α) is independent of the azimuth angle α. The longer main axes of the cutting ellipses are tangential. 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 plane-parallel (100) lenses. Rotationally symmetrical birefringence distributions are obtained by arranging n plane-parallel (100) lenses of the same thickness in such a way that the following applies to the angle of rotation β between two lenses:


where n is the number of plane-parallel (100) lenses and m is an integer. The maximum value of the birefringence for the aperture angle θ = 30 ° can be reduced by 30% in comparison 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.

FIG. 4E shows the amount of the intrinsic birefringence as a function of the opening angle θ for the azimuth angle α = 0 ° for the two adjacent plane-parallel (100) lenses of the same thickness in FIG. 4D. The maximum value for the intrinsic birefringence at the opening angle θ = 41 ° is 4.2 nm / cm and is thus reduced by 35% to the maximum value of 6.5 nm / cm in FIG. 4A.

FIG. 4F shows the amount of the intrinsic birefringence as a function of the azimuth angle α for the aperture angle θ = 41 ° for the two adjacent plane-parallel (100) lenses of the same thickness in FIG. 4D. The intrinsic birefringence is independent of the azimuth angle α.

In Fig. 5A the amount of intrinsic birefringence as a function of the opening angle θ for the azimuth angle α = 0 ° shown for a (111) lens. The value for the intrinsic birefringence of 6.5 nm / cm at the opening angle θ = 35 ° corresponds to the measured value. The curve shape was determined according to the formulas known from crystal optics.

FIG. 5B shows the amount of intrinsic birefringence as a function of the azimuth angle α for the aperture angle θ = 35 ° for a (111) lens. The threefold azimuthal symmetry is obvious.

FIG. 5C shows the birefringence distribution Δn (θ, α) for individual beam directions in the (θ, α) 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 maximal at the azimuth angles 0 °, 120 ° and 240 °. In contrast to a (100) lens, the birefringence orientation rotates by 90 ° when a beam passes through a lens at an azimuth angle of 180 ° instead of an azimuth angle of 0 °. Thus, for example, the birefringence can be compensated for by two identically oriented (111) lenses if the beam angles of a bundle of rays exchange their sign between the two lenses.

Fig. 5D now shows the birefringence distribution .DELTA.n (θ, α), which arises when two adjacent plane-parallel (111) lenses of the same thickness are arranged rotated by 60 °. The resulting birefringence distribution Δn (θ, α) is independent of the azimuth angle α. In contrast to FIG. 4C, however, the longer main axes of the cutting ellipses run radially. 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 (111) lenses. Likewise rotationally symmetrical birefringence distributions are obtained if n plane-parallel (111) lenses of the same thickness are arranged in such a way that the following applies to the angles of rotation between two lenses:


where k is the number of plane-parallel (111) lenses and 1 is an integer. In comparison to an equally oriented arrangement of the lenses, the value of the birefringence for the aperture angle θ = 30 ° can be reduced by 68%. 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.

FIG. 5E shows the amount of intrinsic birefringence as a function of the opening angle θ for the azimuth angle α = 0 ° for the two adjacent plane-parallel (111) lenses of the same thickness in FIG. 5D. The maximum value for the intrinsic birefringence at the opening angle θ = 41 ° is 2.8 nm / cm and is thus reduced by 57% to the maximum value of 6.5 nm / cm in FIG. 5A.

FIG. 5F shows the amount of intrinsic birefringence as a function of the azimuth angle α for the aperture angle θ = 41 ° for the two adjacent plane-parallel (111) lenses of the same thickness in FIG. 5D. The intrinsic birefringence is independent of the azimuth angle α.

If groups are combined with (100) lenses and groups with (111) lenses within a projection lens, the optical path differences introduced by these lenses can be largely compensated for two mutually orthogonal linear polarization states. For this purpose, it is necessary to first achieve an almost rotationally symmetrical distribution of the optical path differences within these groups by rotating the lenses and then to combine the two distributions of the optical ones by combining a group with (100) lenses and a group with (111) lenses Compensate for path differences. For this purpose, use is made of the fact that the orientations of the longer main axes of the cutting ellipses for the birefringence distribution of a group with rotated (100) lenses are perpendicular to the orientations of the longer main axes of the cutting ellipses for the birefringence distribution of a group with rotated (111) lenses, as is the case here It can be seen in FIGS. 4D and 5D. It is crucial that on the one hand an almost rotationally symmetrical distribution of the optical path differences is generated by the individual groups and on the other hand that the sum of the contributions of the groups with (100) lenses is almost the same in amount as the sum of the contributions of the groups with ( 111) lenses.

In Fig. 6A, the amount of intrinsic birefringence as a function of the opening angle θ for the azimuth angle α = 0 ° shown for a (110) lens. The value for the intrinsic birefringence of 6.5 nm / cm at the opening angle θ = 0 ° corresponds to the measured value. The curve shape was determined according to the formulas known from crystal optics.

FIG. 6B shows the amount of intrinsic birefringence as a function of the azimuth angle α for the aperture angle θ = 35 ° for a (110) lens. The two-fold azimuthal symmetry is obvious.

FIG. 6C shows the birefringence distribution .DELTA.n (.theta., .Alpha . ) For individual beam directions in the (.theta., .Alpha.) Angular space for a (110) lens in the representation already introduced with FIG. 4C. Both the directions and the lengths of the lines show the two-fold distribution. The line with the maximum length and thus the maximum birefringence results for the opening angle θ = 0 °.

Fig. 6D now shows the birefringence distribution .DELTA.n (θ, α), which arises when two adjacent plane-parallel (110) lenses of the same thickness are arranged rotated by 90 °. The resulting birefringence distribution Δn (θ, α) now exhibits a fourfold azimuthal symmetry. Maximum birefringence values occur at the azimuth angles α = 45 °, 135 °, 225 ° and 315 °, the value of the birefringence for the aperture angle θ = 40 ° being 2.6 nm / cm.

FIG. 6E now shows the birefringence distribution .DELTA.n (.theta., .Alpha.) 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 (110) lenses is 45 °. The resulting birefringence distribution Δn (θ, α) is independent of the azimuth angle α. In contrast to FIG. 4C, however, the longer main axes of the cutting ellipses run radially, that is to say similarly to the distribution of FIG. 5C. 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 (110) lenses. Also rotationally symmetrical birefringence distributions are obtained if 4.n plane-parallel (110) lenses of the same thickness are arranged in such a way that the following applies to the angle of rotation β between two lenses:

where 4.n indicates the number of plane-parallel (100) lenses and m is an integer. 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.

FIG. 6F shows the amount of intrinsic birefringence as a function of the opening angle θ for the azimuth angle α = 0 ° for the four adjacent plane-parallel (110) lenses of the same thickness in FIG. 6E. The value for the intrinsic birefringence at the opening angle θ = 41 ° is 1.0 nm / cm and is thus reduced by 84% to the maximum value of 6.5 nm / cm in FIG. 5A.

FIG. 6G shows the amount of intrinsic birefringence as a function of the azimuth angle α for the aperture angle θ = 41 ° for the four adjacent plane-parallel (110) lenses of the same thickness in FIG. 6E. The intrinsic birefringence is independent of the azimuth angle α.

If groups are combined with (110) lenses and groups with (100) lenses within a projection lens, the optical path differences introduced by these lenses can be largely compensated for two mutually orthogonal linear polarization states. For this purpose, it is necessary to first achieve an almost rotationally symmetrical distribution of the optical path differences within these groups by rotating the lenses and then to combine the two distributions of the optical ones by combining a group with (110) lenses and a group with (100) lenses Compensate for path differences. For this purpose, use is made of the fact that the orientations of the longer main axes of the cutting ellipses for the birefringence distribution of a group with rotated (110) lenses are perpendicular to the orientations of the longer main axes of the cutting ellipses for the birefringence distribution of a group with rotated (100) lenses, as is the case here 4D and 6E can be seen from FIGS.. The decisive factor here is that on the one hand an almost rotationally symmetrical distribution of the optical path differences is generated by the individual groups and on the other hand the sum of the contributions of the groups with (110) lenses is almost the same in amount as the sum of the contributions of the groups with ( 100) lenses.

In Fig. 7 the lens section is a refractive projection objective 611 shown for the wavelength of 157 nm. The optical data for this lens are summarized in Table 1. The exemplary embodiment is taken from the applicant's patent application PCT / EP 00/13148 and corresponds there to FIG. 7 or table 6. For a more detailed description of the functioning of the objective, reference is made to the patent application PCT / EP 00/13148. 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 1.8 mλ based on the wavelength of 157 nm. Especially with these high-performance lenses, it is necessary to reduce interfering influences such as that of intrinsic birefringence as much as possible.

For the exemplary embodiment in FIG. 6, the opening angle θ 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 starts from the object point with the coordinates x = 0 mm and y = 0 mm and has an angle in the image plane with respect to the optical axis which corresponds to the numerical aperture on the image side. 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 A 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 (111) lenses, (100) lenses and (110) lenses, the azimuth angle αL of the outermost edge 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 angle θ for the lenses L608, L617, L618, L619, L627, L628, L629 and L630 larger than 25 °, for lenses L618, L627, L628, L629 and L630 are even larger than 30 °. Are particularly affected by high opening angles the lenses L627 to L630 closest to the image plane.

The design of the projection lens achieved 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 lens L628. The use of two thick plane lenses L629 and L630 immediately in front of the image plane.

The diameter of the aperture, which is located between the lenses L621 and L622, is 270 mm. The diameter of the lens L618 is 207 mm and the diameter of the Lenses L627 to L630 are all smaller than 190 mm. So the diameters of these lenses, which have high opening angles, less than 80% of the diaphragm diameter.

Table 2 shows that it is for single lenses with large opening angles it is favorable to orient this in the (100) direction since the birefringence values as a whole are lower. This is because with (100) lenses the influence of the <110> - Crystal directions can only be felt at larger angles, as with (111) lenses. For example, the lenses L608, L609 and L617 have optical path differences by more than 30% lower.

Using the two plane-parallel lenses L629 and L630 it is easy to show how through mutual rotation of the lenses the birefringence can be significantly reduced. Both lenses have the same opening angle for the outermost aperture beam of 35.3 ° and similar beam paths of 27.3 mm, respectively 26.0 mm on both lenses as (100) lenses are installed with the same orientation, an optical Path difference of 30.7 nm result. However, if you twist the two (100) lenses mutually by 45 °, the optical path difference is reduced to 20.9 nm, i.e. by 32%. If both lenses were installed as (111) lenses with the same orientation, then there is an optical path difference of 34.6 nm. If you twist the two (111) - However, lenses mutually 60 °, so the optical path difference is reduced 13.6 nm, i.e. by 61%.

Almost complete compensation of the optical path differences for two linear polarization states orthogonal to each other due to the intrinsic Birefringence caused by lenses L629 and L630 can be achieved when the lens L629 into the lenses L6291 and L6292 and the lens L630 into the Lenses L6301 and L6302 is split, the lens L6291 being a (100) lens of the Thickness 9.15 mm, the lens L6292 a (111) lens with a thickness of 13.11 mm, the lens L6301 a (100) lens with a thickness of 8.33 mm and the lens L6302 a (111) lens with a thickness Is 12.9 mm. The lenses L6291 and L6301 are mutually 45 °, the lenses L6292 and L6302 rotated by 60 °. The resulting maximum optical path difference is in this case 0.2 nm. Lenses L6291 and L6292, as well as lenses L6301 and L6302 can be joined optically seamless, for example by cracking. This principle is also applicable when the projection lens is only a crystal lens contains. This is then broken down into at least two lenses that are rotated towards each other to be ordered. It is possible to put them together by starting. Another Possibility is to first individual plates of the desired crystal orientation optically seamless to connect and in a further process step the lens from the to manufacture joined plates.

Another way to avoid the disruptive influence of intrinsic birefringence To reduce the lenses L629 and L630 is to put the lens L629 in the lenses L6293 and L6294 and the lens L630 split into the lenses L6303 and L6304 the lens L6293 then a (110) lens with a thickness of 11.13 mm, the lens L6294 a (110) lens with a thickness of 11.13 mm, lens L6303 a (110) lens with a thickness 10.62 mm and the lens L6304 is a (110) lens with a thickness of 10.62 mm. The L6293 lenses and L6294, as well as the lenses L6303 and L6304 are mutually at 90 ° rotated, the angle of rotation between the lens L6293 and L6303 is 45 °. The the resulting maximum optical path difference in this case is 4.2 nm. The lenses L6293 and L6294, just like the lenses L6303 and L6304, can be used as lens parts optically seamlessly, for example by wringing.

The optical path differences for two are almost completely compensated for linear polarization states orthogonal to each other, which are caused by the highly stressed Lenses L629 and L630 is produced when each lens is divided into three lens parts L6295, L6296 and L6297 or L6305, L6306 and L6307 is split, taking the lens L6295 then a (100) lens with a thickness of 4.45 mm, the lenses L6296 and L6297 (110) - Lenses 8.90 mm thick, lens L6305 a (100) lens 4.25 mm thick and the L6306 and L6307 (110) lenses are 8.49 mm thick. The lenses L6294 and L6304 are mutually 45 °, two of the lenses L6295, L6297, L6306 and L6307 rotated by 45 °. In this combination, the resulting maximum optical is reduced Path difference to less than 0.1 nm. The lenses L6295 to L6297, as well as the lenses L6305 to L6307 can be optically seamless as lens parts, for example by be added.

Another way to avoid the disruptive influence of intrinsic birefringence to reduce the lenses L629 and L630 is to use two (110) lenses with one (100) - Combine lens. The two (110) lenses are rotated 90 ° to each other to be installed while the angle of rotation between the (100) lens and the (110) lenses 45 ° + m.90 °, where m is an integer. For this purpose, the lens L629 in the Lenses L6298 and L6299 as well as the lens L630 in the lenses L6308 and L6309 split, the lens L6298 then a (110) lens with a thickness of 17.40 mm, the lens L6299 a (110) lens with a thickness of 4.87 mm, lens L6308 a (110) lens with a thickness 12.53 mm and the lens L6309 is a (100) lens with a thickness of 8.70 mm. The resulting one maximum optical path difference is 3.1 nm. The lenses L6298 and L6299, likewise like the lenses L6308 and L6309 can be optically seamless as lens parts, for example by wringing.

In FIG. 8, the lens section of a catadioptric projection objective 711 is shown for the wavelength of 157 nm. The optical data for this lens are summarized in Table 3. The exemplary embodiment is taken from the applicant's patent application PCT / EP 00/13148 and corresponds there to FIG. 9 or table 8. For a more detailed description of the functioning of the lens, reference is made to patent application PCT / EP 00/13148. All lenses of this lens are made of calcium fluoride crystal. The numerical aperture of the objective on the image side is 0.8.

For the exemplary embodiment in FIG. 8, the opening angles θ and beam paths RL _{L of} the upper outermost aperture beam 713 and the lower outermost aperture beam 715 were calculated for the individual lenses L801 to L817. The outermost aperture beams 713 and 715 proceed from the object point with the coordinates x = 0 mm and y = -82.15 mm and have angles in the image plane with respect to the optical axis which correspond to the numerical aperture on the image side. 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. In addition to the opening angles θ and the path lengths RL _L for the outermost aperture beam, Table 4 and Table 5 summarize the optical path differences for two mutually orthogonal linear polarization states for different lens orientations; namely for (111) lenses, (100) lenses and (110) lenses, the azimuth angle α _{L of} the outermost edge ray within the lenses for a (111) lens 0 ° and 60 °, for a (100) Lens is 0 ° and 45 ° and for a (110) lens is 0 °, 45 °, 90 ° and 135 °. Table 4

Table 5

Table 4 and Table 5 show that the opening angles θ 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


is. 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 193 mm. The diameters of the lenses L815 to L817 are all less than 162 mm. Thus the diameters of these lenses, which have high opening angles, less than 85% of the aperture diameter.

Table 4 and Table 5 show that it is for lenses with large opening angles it is favorable to orient this in the (100) direction since the birefringence values as a whole are lower. For example, the lenses L815 to L817 are optical Path differences are more than 20% lower.

Using the exemplary embodiment in FIG. 8, the following is intended to show how the intrinsic birefringence can be largely compensated for by the parallel use of groups with (100) lenses rotated relative to one another and groups with lenses rotated relative to one another (111).

First, all calcium fluoride in (111) orientation without twisting of the (111) lenses. In this case there is a maximum optical Path difference for two mutually orthogonal linear polarization states of 136 nm. By turning the (111) lenses, the maximum optical path difference can be approx. 38 nm be reduced. For this purpose, the lenses L801 and L804 become one group and the lenses L802 and L803 combined into another group, the angle of rotation is 60 ° between the lenses. The lenses become a group of three L808, L809 and L810, and the lenses L815, L816 and L817 combined, the Angle of rotation between two of these lenses is 40 °. Lenses L811, L812, L813 and L814 are combined into a group of four with a mutual 30 ° rotation angle.

Are all calcium fluoride in (100) orientation without twisting each other (100) lenses installed, there is a maximum optical path difference for two mutually orthogonal linear polarization states of 90.6 nm. By rotating the (100) lenses, the maximum optical path difference can be reduced to approx. 40 nm. For this purpose, the lenses L801 and L804 become one group and the lenses L802 and L803 combined into another group, the angle of rotation between the lenses is 45 ° each. The lenses L808, L809 and L810, and the lenses L815, L816 and L817 combined, the angle of rotation between two of these lenses are 30 °. Lenses L811, L812, L813 and L814 become one Group of four combined with a mutual rotation angle of 22.5 °.

A maximum optical path difference for two mutually orthogonal linear Polarization states of 7 nm can be obtained by using groups with (100) lenses Groups combined with (111) lenses. For this purpose, the lenses L801 and L804 become one Group of (111) lenses combined, the angle of rotation between the lenses Is 60 °. Lenses L802 and L803 become a group of (100) lenses summarized, the angle of rotation between the lenses is 45 °. To a triple Group of (100) lenses, the lenses L808, L809 and L810 are combined, the angle of rotation between two of these lenses is 30 °. To a group of three of (111) lenses, lenses L815, L816 and L817 are combined, the Angle of rotation between two of these lenses is 40 °. Lenses L811, L812, L813 and L814 are combined into a group of four (100) lenses with one Angle of rotation of 22.5 °. The lens axes of the not grouped together Lenses L805 and L807 are oriented in the <111> crystal direction, while the lens axis the lens L806 is oriented in the <100> crystal direction. The groups can be mutual can be arranged rotated around the optical axis. Let these degrees of freedom of rotation use to compensate for non-rotationally symmetrical aberrations that for example, be generated by the frame of the lenses.

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 . Only the birefringence contributions of the two lenses L629 and L630, which consist of calcium fluoride and thus show intrinsic birefringence, should be considered. In this exemplary embodiment, the two lenses have a (111) orientation and are rotated by 60 ° with respect to one another. This results in an almost rotationally symmetrical distribution of the optical path differences ΔOPL. For an outermost aperture beam, the maximum optical path difference ΔOPL is between 13.6 nm and 14.6 nm, depending on the azimuth angle α _R. Now the compensation coating 613 described in Table 6 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 6 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. With the compensation coating, the resulting optical path difference is 1.1 nm and is therefore significantly reduced compared to the lens without a compensation coating. Table 6

An analogous procedure is also possible if instead of the last two lenses entire lens is considered. Instead of birefringence with just one optical one It is also possible to compensate for several elements with a compensation coating cover optical elements with compensation coatings.

The method can also be applied to birefringence in one Compensate overall system, taking the causes of this birefringence Stress birefringence, intrinsic birefringence and birefringence through the remaining layers can be.

After the final adjustment of a system, the distribution of the optical path differences ΔOPL determined for one or more tufts of rays in the image plane. By means of a The program to optimize layers will then be necessary Compensation layer calculated and for example on the closest to the image plane applied system area. It is convenient if that is closest to the image plane located optical element is interchangeable. So birefringence effects, that arise only with the operation of the lens.

To compensate for birefringence of crystals in UV, you can, as above described crystal elements with different orientations of the crystal axes arrange one after the other. If you have lenses with different in an optical system Arranging crystal directions one behind the other, one has the problem that lenses often have be irradiated at different angles, the compensation may then only is possible to a limited extent. This is the case for optics that contain only one crystal lens compensation is not possible at all.

One solution is to constructively split a lens into two that twists are to be blown against each other. In practice, this process suffers from tensions that deform the yoke and remember that the two halves laterally with an accuracy of Micrometers must be positioned.

It is suggested that blanks be blasted against each other in terms of orientation of the crystal axes to produce twisted individual plates, which then become one Lens can be milled and polished. All of the above about orientation also applies here. In addition to the classic wringing of optics manufacturing, everyone else is Joining techniques with intimate contact and the lowest possible tension input possible and encompassed by the invention. The wringing can in particular by layers, for. B. made of quartz glass. It is important that there is no refraction or Reflection occurs that would be distracting.

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 produced. The lens L816 has a convex aspherical front surface with an apex radius of 342.13 mm and a concave spherical rear surface with an apex radius of 449.26 mm. The axial thickness is 37.3 mm. The lens material is calcium fluoride. The lens diameter is 141 mm. The blank from which the lens is to be worked out requires at least a total thickness of 45 mm and a diameter of 150 mm. The blank can consist of two (100) plates with a thickness of 9.0 mm rotated against each other by 45 ° and two (111) plates with a thickness of 13.5 mm rotated against each other by 60 °, which are optically seamless. The (100) plates and the (111) plates should each be arranged adjacent to one another.

In a further embodiment, six are rotated relative to one another by 45 ° (100) plates with a thickness of 3.0 mm and six (111) rotated against each other by 60 ° Panels of thickness 4.5 optically joined seamlessly, two after every two (100) panels (111) plates follow.

In a further embodiment, four are rotated relative to one another by 45 ° (110) plates with a thickness of 9.0 mm and two (100) plates of the Thickness 4.5 optically seamlessly joined, with the two (100) plates on the four (110) plates consequences.

In a further embodiment, eight are rotated relative to one another by 45 ° (110) plates with a thickness of 4.5 mm and four (100) plates rotated against each other by 45 ° Thickness 2.25 optically joined seamlessly, whereby after four (110) plates two (100) plates each consequences.

The basic structure of a microlithography projection exposure system is described with reference to FIG. 9. 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 of the lens assembly 89 are shown in FIG. 6 and FIG. Given. 7 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 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 λ of the light used for the illumination and on the numerical aperture of the projection lens 85 on the image side, the maximum achievable resolution of the projection exposure system 81 with decreasing wavelength λ of the illumination device 83 and with increasing numerical aperture of the projection lens on the image side 85 rises. With those shown in FIG. 6 and FIG. 7, the embodiments shown resolutions can realize small nm 150th Therefore effects such as intrinsic 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. TABLE 1







TABLE 3

Claims (66)

1. lens ( 611 , 711 ), in particular a projection lens for a microlithography projection exposure system ( 81 ), with a plurality of lenses (L601-L630, L801-L817), with at least one lens ( 1 ) made of fluoride crystal, characterized that the at least one lens ( 1 ) is a (100) lens with a lens axis (EA) which is approximately perpendicular to the {100} crystal planes or to the equivalent crystal planes of the fluoride crystal. 2. Lens according to claim 1, wherein the (100) lens with a rotationally symmetrical lens is an axis of symmetry and the axis of symmetry with the lens axis of the (100) lens coincides. 3. Lens according to one of claims 1 to 2 with an optical axis (OA), wherein the The lens axis of the (100) lens coincides with the optical axis of the lens. 4. Objective according to one of claims 1 to 3, wherein within the objective light rays run from an object plane (O) to an image plane (O ') and at least one light beam ( 609 , 713 , 715 ) within the (100) lens has a beam angle with respect to the lens axis, which is greater than 25 °, in particular greater than 30 °. 5. Objective according to one of claims 1 to 4, wherein within the objective light rays run from an object plane to an image plane and all light rays within the (100) lens have beam angles with respect to the lens axis that are at most 45 °, in particular at most


amount, where NA denotes the numerical aperture on the image side and n _FK the refractive index of the fluoride crystal. 6. Lens according to one of claims 1 to 5 with an aperture plane, wherein the Aperture plane has an aperture diameter and the (100) lens one Has lens diameter and wherein the lens diameter is less than 85%, is in particular less than 80% of the diaphragm diameter. 7. Lens according to one of claims 1 to 6 with an image plane, wherein the (100) lens (L630, L817) is the lens closest to the image plane. 8. lens ( 611 , 711 ), in particular projection lens for a microlithography projection exposure system,
with at least two lenses or lens parts made of fluoride crystal,
wherein the lenses or the lens parts have lens axes which each point approximately in a main crystal direction,
where a bundle of rays with rays strikes an image point in an image plane,
which each have an azimuth angle α _R , an aperture angle θ _R and an optical path difference ΔOPL for two mutually orthogonal linear polarization states,
characterized,
that the lenses or the lens parts are arranged rotated relative to one another about the lens axes in such a way that the distribution of the optical path differences ΔOPL (α _R , θ _R ) of the bundle of rays as a function of the azimuth angle α _R and the opening angle θ _{R has} significantly reduced values compared to lenses or lens parts, the lens axes of which point in the same main crystal direction and which are not rotated relative to one another about the lens axes. 9. Lens according to claim 8, wherein the optical path differences ΔOPL as a function of the azimuth angle α _R for a predetermined aperture angle θ ₀ vary less than 30%, in particular less than 20%. 10. Lens according to one of claims 8 or 9, wherein the lenses or lens parts each have a birefringence distribution Δn (α _L , θ _L ), the birefringence values Δn of azimuth angles α _L with respect to a reference direction perpendicular to the lens axis and of opening angles θ _R with respect to Depend on the lens axis, the birefringence distribution Δn (α _L , θ _L ) having a k-fold azimuthal symmetry,
where angles of rotation γ are defined between the reference directions of the individual lenses or lens parts,
wherein a number of n lenses or n lens parts form a group within which the lens axes point in the same main crystal direction or an equivalent main crystal direction and within which the birefringence distributions Δn (α _L , θ _L ) have the same azimuthal course with respect to the reference directions, where for the angle of rotation γ between two lenses or lens parts of a group:


where m is an integer. 11. The lens of claim 10, wherein an outermost aperture beam (609, 713, 715) of the bundle of rays within the lenses or lens parts each has an opening angle θ _L and wherein the opening angle θ _L within the lenses or lens parts of the group by a maximum of 30%, in particular vary by a maximum of 20%. 12. Lens according to any one of claims 10 or 11, wherein an outermost aperture (609, 713, 715) of the light bundle within the lenses or lens portions each traverses a beam path RL _L and wherein the beam paths RL _L within the lens or lens parts of the group by a maximum of 30%, in particular vary by a maximum of 20%. 13. Objective according to one of claims 10 to 12, wherein the optical path differences ΔOPL for an outermost aperture beam ( 609 , 713 , 715 ) of the bundle of rays determined at a rotation angle γ = 0 ° for the individual lenses or lens parts of a group do not exceed 30%, in particular vary by a maximum of 20%. 14. Lens according to one of claims 10 to 13, wherein the group 2 to 4 lenses or Includes lens parts. 15. The lens of claim 14, wherein the lenses (L629, L630) or lens parts are arranged adjacent, in particular are blown against each other. 16. Lens according to one of claims 10 to 15, wherein the lens at least two Has groups with each other twisted lenses or lens parts. 17. Objective according to one of claims 8 to 16, wherein the lens axes point in the <111> crystal direction or main crystal directions equivalent thereto and the birefringence distribution Δn (α _L , θ _L ) of the lenses or lens parts has a 3-fold azimuthal symmetry. 18. Objective according to one of claims 8 to 16, wherein the lens axes point in the <100> crystal direction or main crystal directions equivalent thereto and the birefringence distribution Δn (α _L , θ _L ) of the lenses or lens parts has a 4-fold azimuthal symmetry. 19. Objective according to one of claims 8 to 16, wherein the lens axes point in the <110> crystal direction or main crystal directions equivalent thereto and the birefringence distribution Δn (α _L , θ _L ) of the lenses or lens parts has a 2-fold azimuthal symmetry. 20. Lens according to one of claims 8 to 19, wherein the lens axes of the lenses or Lens parts of a first group in the <100> crystal direction or in one of them have equivalent main crystal direction and the lens axes of the lenses or Lens parts of a second group in the <111> crystal direction or in one of them have equivalent main crystal direction. 21. Lens according to one of claims 8 to 19, wherein the lens axes of the lenses or Lens parts of a first group in the <100> crystal direction or in one of them have equivalent main crystal direction and the lens axes of the lenses or Lens parts of a second group in the <110> crystal direction or in one have equivalent main crystal direction. 22. Lens according to claim 20 or 21, wherein the distribution of the optical path differences ΔOPL (α _R , θ _R ) from a first distribution of the optical path differences ΔOPL ₁ (α _R , θ _R ), which through the lenses or lens parts of all the first Groups, and a second distribution of the optical path differences ΔOPL ₂ (α _R , θ _R ), which is caused by the lenses or lens parts of all second groups, and the amount of the maximum value of the first distribution of the optical path differences ΔOPL ₁ ( α _R , θ _R ) differs by a maximum of 30%, in particular by a maximum of 20% from the amount of the maximum value of the second distribution of the optical path differences ΔOPL ₂ (α _R , θ _R ). 23. Objective ( 611 ) according to one of claims 8 to 22, wherein the lenses or lens parts belong to a plurality of optical elements with optical surfaces, and wherein at least one optical surface is covered with a compensation coating ( 613 ), the compensation -Coating is designed such that the distribution of the optical path differences ΔOPL (α _R , θ _R ) of the beam as a function of the azimuth angle α _R and the aperture angle θ _{R has} significantly reduced values compared to a lens without a compensation coating. 24. Objective ( 611 ) according to claim 23, wherein the optical element with the compensation coating has an element axis, and wherein the compensation coating has an effective birefringence distribution whose effective double calculation values of azimuth angles α _F with respect to a reference direction perpendicular to the element axis and of Depend opening angles θ _F with respect to the element axis. 25. The lens of claim 24, wherein the effective birefringence distribution of the compensation coating for the aperture angle θ _F = 0 ° is approximately zero. 26. Objective according to one of claims 24 and 25, wherein the effective double calculation distribution primarily depends only on the aperture angle θ _F. 27. Lens according to one of claims 23 to 26, wherein the optical element with the Compensating coating is one of the fluoride crystal lenses, and being the Element axis is the lens axis of the fluoride crystal lens. 28. Lens according to one of claims 23 to 27, wherein a plurality of optical elements with Compensation coatings are occupied. 29. Lens according to one of claims 23 to 28, wherein all optical elements with Compensation coatings are occupied. 30. Lens according to one of claims 1 to 29, wherein the fluoride crystal is a calcium Fluoride crystal, a strontium fluoride crystal or a barium fluoride crystal. 31. lens ( 611 ), in particular projection lens for a microlithography projection exposure system,
with several optical elements, in particular lenses made of fluoride crystal, with optical surfaces,
wherein a bundle of rays strikes an image point in an image plane, each having an optical path difference ΔOPL for two mutually orthogonal linear polarization states, characterized in that at least one optical surface is coated with a compensation coating ( 613 ), the compensation Coating is designed such that the optical path differences AOPL of the bundle of rays have significantly reduced values compared to a lens without a compensation coating. 32. Objective according to claim 31, wherein the optical element with the compensation coating has an element axis, and wherein the compensation coating has an effective birefringence distribution, the effective birefringence values of azimuth angles α _F with respect to a reference direction perpendicular to the element axis and of opening angles θ _F depend on the element axis. 33. Lens according to claim 32, wherein the effective birefringence distribution of the compensation coating for the aperture angle θ _F = 0 ° is approximately zero. 34. Lens according to one of claims 32 and 33, wherein the effective birefringence distribution of the compensation coating depends primarily on the opening angle θ _F. 35. Lens according to one of claims 32 to 36, wherein the optical element with the Compensation coating is interchangeable. 36. Objective according to one of claims 31 to 35, wherein at least two optical elements are lenses or lens parts made of fluoride crystal, wherein the lenses or the lens parts have lens axes, the lenses or the lens parts being rotated relative to one another about the lens axes in such a way that the distribution of the optical path differences ΔOPL (α _R , θ _R ) of the bundle of rays as a function of the azimuth angle α _R and the aperture angle θ _{R has} significantly reduced values in comparison to lenses or lens parts whose lens axes point in the same main crystal direction and which do not conflict with each other Lens axes are arranged twisted. 37. Objective according to claim 36, wherein the optical path differences ΔOPL as a function of the azimuth angle α _R vary for a predetermined aperture angle θ ₀ less than 30%, in particular less than 20%. 38. Objective according to one of claims 36 or 37, wherein the lenses or lens parts each have a birefringence distribution Δn (α _L , θ _L ), the birefringence values Δn of azimuth angles α _L with respect to a reference direction perpendicular to the lens axis and of opening angles θ _R with respect to Depend on the lens axis,
the birefringence distribution Δn (α _L , θ _L ) having a k-fold azimuthal symmetry,
where angles of rotation γ are defined between the reference directions of the individual lenses or lens parts,
wherein a number of n lenses or n lens parts form a group within which the lens axes point in the same main crystal direction or an equivalent main crystal direction and within which the birefringence distributions Δn (α _L , θ _L ) have the same azimuthal course with respect to the reference directions, where for the angle of rotation γ between two lenses or lens parts of a group:


where m is an integer. 39. Lens according to one of claims 36 to 38, wherein the optical element with the Compensation coating is one of the fluoride crystal lenses, and being the Element axis is the lens axis of the fluoride crystal lens. 40. Lens according to one of claims 30 to 39, wherein a plurality of optical elements with Compensation coatings are occupied. 41. Lens according to one of claims 1 to 40, wherein the lens is an image-side has numerical aperture NA and the image-side numerical aperture NA is greater than 0.7, in particular greater than 0.8. 42. Lens according to one of claims 1 to 41, wherein the lens for wavelengths is designed smaller than 200 nm. 43. Lens according to one of claims 1 to 42, wherein the lens for wavelengths is designed smaller than 160 nm. 44. Lens according to one of claims 1 to 43, wherein the lens ( 611 ) is a refractive lens. 45. Lens according to one of claims 1 to 44, wherein the lens is a catadioptric Objective (711) with lenses and at least one mirror (Sp2). 46. Lens according to one of claims 1 to 45, wherein all lenses made of calcium fluoride are. 47. Microlithography projection exposure system ( 81 ), comprising
a lighting system ( 83 ),
a lens 85) according to any one of claims 1 to 46, which images a structure-bearing mask (89) on a light-sensitive substrate ( 815 ). 48. A method for producing semiconductor components with a microlithography projection exposure system ( 81 ) according to claim 47. 49. Method for producing lenses, in particular projection lenses for a microlithography projection exposure system,
with at least two lenses or lens parts made of fluoride crystal,
wherein the lenses or the lens parts have lens axes which each point approximately in a main crystal direction,
characterized,
that for a bundle of rays with rays, each having an azimuth angle α _R , an aperture angle θ _R and an optical path difference ΔOPL for two mutually orthogonal linear polarization states in an image plane, the distribution of the optical path differences ΔOPL (α _R , θ _R ) for lenses or Lens parts is determined
that the lenses or the lens parts are arranged rotated relative to one another about the lens axes such that the distribution of the optical path differences ΔOPL (α _R , θ _R ) of the bundle of rays has significantly reduced values compared to lenses or lens parts whose lens axes point in the same main crystal direction and which are not rotated against each other around the lens axes. 50. The method of claim 49, wherein the lens is a first group with lenses or Has lens parts and a second group with lenses or lens parts and the Lens axes of the lenses or lens parts of the first group in the <100> - Point crystal direction or in an equivalent main crystal direction and the Lens axes of the lenses or lens parts of the second group in the <111> - Point crystal direction or in an equivalent main crystal direction. 51. The method of claim 49, wherein the lens is a first group with lenses or Has lens parts and a second group with lenses or lens parts and the Lens axes of the lenses or lens parts of the first group in the <100> - Point crystal direction or in an equivalent main crystal direction and the Lens axes of the lenses or lens parts of the second group in the <110> - Point crystal direction or in an equivalent main crystal direction. 52. The method according to any one of claims 49 to 51,
a distribution of the optical path differences ΔOPL (α _R , θ _R ) for a bundle of rays with beams which each have an azimuth angle α _R , an aperture angle θ _R and an optical path difference ΔOPL for two mutually orthogonal linear polarization states in an image plane,
an effective birefringence distribution of a compensation coating for reducing the optical path differences ΔOPL (α _R , θ _R ) is determined from the distribution of the optical path differences ΔOPL (α _R , θ _R ),
the effective birefringence values of the compensation coating depending on azimuth angles α _F with respect to a reference direction perpendicular to an element axis of the optical element and with opening angles θ _F with respect to the element axis,
the structure of a compensation coating is determined from the birefringence distribution, and
wherein an optical element of the lens is coated with the compensation coating. 53. Method for compensating birefringence effects in objectives, in particular in projection objectives for a microlithography projection exposure system, the objective having a plurality of optical elements, in particular lenses made of fluoride crystal, with optical surfaces,
at least one optical element being interchangeable,
a beam bundle with rays striking an image point in an image plane, each having an azimuth angle α _R , an aperture angle θ _R and an optical path difference ΔOPL for two mutually orthogonal linear polarization states in an image plane,
a distribution of the optical path differences ΔOPL (α _R , θ _R ) is determined,
an effective birefringence distribution of a compensation coating is determined from the distribution of the optical path differences ΔOPL (α _R , θ _R ), the effective birefringence values of azimuth angles α _F with respect to a reference direction perpendicular to an element axis of the optical element and of opening angles θ _F with respect to the Depend on the element axis,
the structure of a compensation coating is determined from the effective birefringence distribution,
removing the interchangeable optical element from the lens,
wherein the interchangeable optical element is coated with the compensation coating and
wherein the interchangeable optical element with the compensation coating is reinstalled in the lens. 54. Lens manufacturing process, characterized in that several plates crystal material twisted with respect to the crystal orientation, preferably fluoride crystal and in particular calcium fluoride, optically seamless added, in particular blown on and then as a uniform blank machined and polished. 55. The lens manufacturing method according to claim 54, wherein the plates each have a birefringence distribution Δn (α _L , θ _L ), the birefringence values Δn of which depend on azimuth angles α _L with respect to a reference direction perpendicular to the lens axis and on opening angles θ _R with respect to the lens axis and which have a k has multiple azimuthal symmetry,
where for a number of N plates the surface normals point in the same main crystal direction or an equivalent main crystal direction and the birefringence distributions Δn (α _L , θ _L ) have the same azimuthal course with respect to the reference directions,
where the angle of rotation γ is defined between the reference directions of the individual plates, the following applies to the angle of rotation γ between two plates:


where m is an integer. 56. The lens manufacturing method according to claim 55, wherein two plates are joined seamlessly. 57. Lens manufacturing method according to one of claims 55 and 56, wherein the plates have approximately the same thickness. 58. Lens manufacturing method according to one of claims 54 to 57, wherein in the first plates the surface normals in the <111> crystal direction or in an equivalent Point the main crystal direction and the surface normals in the case of second plates <100> crystal direction or in a main crystal direction equivalent thereto. 59. The lens manufacturing method of claim 58, wherein the first plates are approximately one have the same first thickness and the second plates have an approximately the same second Have thickness and the ratio of the sum of the first thicknesses to the sum of second thickness is 1.5 ± 0.2. 60. Lens manufacturing method according to one of claims 54 to 57, wherein in the first plates the surface normal in the <110> crystal direction or in an equivalent Point the main crystal direction and the surface normals in the case of second plates <100> crystal direction or in a main crystal direction equivalent thereto. 61. The lens manufacturing method of claim 60, wherein the first plates are approximately one have the same first thickness and the second plates have an approximately the same second Have thickness and the ratio of the sum of the first thicknesses to the sum of second thickness is 4.0 ± 0.4. 62. Lens manufacturing method according to one of claims 60 and 61, wherein two first plates be seamlessly joined with a second plate. 63. Lens manufacturing method according to one of claims 60 and 61, wherein four first plates optically seamless with two second plates. 64. Lens, characterized by the production according to one of claims 54 to 63. 65. Objective, in particular a projection objective ( 611 , 711 ) for a microlithography projection exposure system ( 81 ), characterized in that it comprises a lens according to claim 64. 66. Lens according to at least one of claims 1 to 46, characterized in that it comprises a lens according to claim 64.