DE10229614A1 - Catadioptric reduction lens - Google Patents

Abstract

A catadioptric projection lens for imaging a pattern arranged in the object plane of the projection lens into the image plane of the projection lens has a catadioptric lens part with a concave mirror (17) and a first deflection mirror (16) and at least a second deflection mirror (19) between the object plane and the image plane. In the light path between the deflecting mirrors, the preferred polarization direction of the light is rotated by approx. 90 ° using a polarization rotating device (26). As a result, polarization-dependent differences in reflectivity and phase effects of the deflecting mirrors can be at least partially compensated for. As a result, imaging with largely the same contrast is possible for all structural directions.

Description

The invention relates to a catadioptric projection lens for imaging one in an object plane of the projection lens arranged pattern in an image plane of the projection lens.

Such projection lenses are in projection exposure systems for the production of semiconductor components and other finely structured components used, in particular in wafer scanners and wafer steppers. They are used to create patterns of Photo masks or graticules, also referred to below as masks or reticle can be referred to one with a photosensitive Layer coated object with the highest resolution on a scaling down scale project.

It is always for generation finer structures necessary, on the one hand the numerical on the image side To increase the aperture (NA) of the projection lens and, on the other hand, always shorter wave prolong to be used, preferably ultraviolet light with wavelengths of less than approx. 260 nm.

In this wavelength range there are only little enough transparent materials to manufacture the optical Components available especially synthetic quartz glass and fluoride crystals such as calcium fluoride. Because the Abbé constants of the available Materials are relatively close together, it is difficult to get in refractive systems with sufficient correction of color errors (chromatic Aberration). Therefore, for high-resolution projection lenses are predominant Catadioptric system uses refractive and reflective ones Components, in particular lenses and seals, are combined.

When using imaging mirror surfaces it is necessary to use beam deflection devices if one Obscuration-free and vignetting-free imaging can be achieved should. They are both systems of geometric beam splitting using one or more, fully reflecting deflecting mirrors known as also systems with physical beam splitters, especially those with polarization-selective mirror surfaces. In addition to the function necessary existing. mirror surfaces can Plane mirrors for folding the beam path can be provided, for example To meet installation space requirements and to align the object and image plane parallel to each other.

When using a physical beam splitter axial (on-axis) systems can be implemented. Will prevail here polarization-selective effective mirror surfaces are used, which depend on reflecting the preferred polarization direction of the incident radiation or act as a transmitter. Such systems need in the light path between a first and a second use of the beam splitter area Device for rotating the preferred polarization direction of the light by a total of 90 °. Usually double quarter wave plates inserted between beam splitter and concave mirror. Disadvantageous such systems is that suitable transparent materials for the beam splitter block in the required large Volumes are only available to a limited extent are and that the production of sufficiently effective beam splitter layers for the given angular load can cause considerable difficulties.

Disadvantages of systems with a beam splitter block can Systems with geometric beam splitting can be avoided. This Systems have the principle disadvantage that it is off-axis (off-axis) systems, i.e. are systems with an off-axis object field.

Systems of this type have a first Deflecting mirror, the opposite the optical axis is tilted and serves either that of to redirect the radiation coming from the object plane to the concave mirror or to follow the radiation reflected by the concave mirror To divert lens parts. Usually there is a second deflecting mirror provided that serves as a folding mirror around the object plane and image plane to parallelize. To ensure a high reflectivity of these mirrors, they are common with reflective layers, mostly dielectric multiple layers or a combination of metallic and dielectric layers. Through dielectric layers that operate at a high angle of incidence the passing light can be influenced depending on the polarization become.

It has been observed that at different catadioptric systems under certain imaging conditions Structural directions with different contrast contained in the pattern to be displayed be mapped. These contrast differences for different structure directions are also called H-V differences (horizontal-vertical differences) or referred to as variations of the critical dimensions (CD variations) and make themselves in the photoresist as under different line widths for the different Structural directions noticeable.

Various proposals have been made to avoid such directional contrast differences. The EP 964 282 A2 deals with the problem that a preferred polarization direction is introduced in catadioptric projection systems with deflecting mirrors when light passes through, which results from the fact that the multiply coated deflecting mirrors have different reflectances for s- and p-polarized light. As a result, light which is still unpolarized in the reticle plane is partially polarized in the image plane, which should lead to a directional dependence of the imaging properties. This effect is counteracted by creating a reserve of polarization in the lighting system by generating partially polarized light with a predetermined degree of residual polarization which is compensated by the projection optics in such a way that unpolarized light emerges at its output.

From the EP 0 602 923 B1 (corresponding US-A 5,715,084 ), a catadioptric projection lens with polarization beam splitter operated with linearly polarized light is known, in which a device for changing the polarization state of the light passing through is provided between the beam splitter cube and the image plane in order to convert the incident, linearly polarized light into circularly polarized light (as equivalent to unpolarized light). This is to ensure an image contrast that is independent of the structure direction. A corresponding proposal is also in the EP 0 608 572 (corresponding US-A 5,537,260 ) made.

The invention is based on the object to provide a catadioptical projection lens which for different Structural directions of a pattern are essentially an illustration without structure direction dependent Contrast differences allowed.

This task is carried out according to a Aspect of the invention through a catadioptical projection lens solved with the features of claim 1. Advantageous further training are specified in the dependent claims. The wording of all Expectations is made the content of the description by reference.

A catadioptric projection lens according to one Aspect of the invention has between the object plane and the image plane a catadioptric lens part with a concave mirror and a first deflecting mirror and at least one second deflecting mirror. The deflecting mirrors are preferably about parallel tilt axes compared to the optical Axis of the projection lens tilted and arranged so that Object plane and image plane are aligned in parallel. Between the the first deflecting mirror and the second deflecting mirror is a polarization rotating device for rotating a polarization preferred direction of passing through Light arranged. Their effect is designed so that polarization-dependent reflectivity and Differences in phase effects of the deflecting mirrors at least partially be compensated. With the help of the polarization rotating device Deflecting mirrors are operated so that overall with high overall reflectivity a vanishing or only very small amplitude and phase curve splitting of the perpendicular to each other vibrating field components of the electrical Field vector is present. The polarization rotating device is to be designed that a polarization-splitting effect of the first deflection mirror caused, for example, by dielectric multilayer reflective coatings, with the corresponding effect of the second deflecting mirror so far compensated for that after the second reflection a possibly still existing splitting of the polarization directions below one harmless Threshold lies.

With usual, highly reflective Multi-layer coatings are known to be the light component of the incident Light with higher Reflectance reflected, in which the electric field vector is perpendicular swings to the plane of incidence (s-polarization). The reflectance for p-polarized light, where the electric field vector vibrates parallel to the plane of incidence, is against the entire angle of incidence is smaller and reaches its minimum at the layer-specific Brewster angle. Accordingly result large splits in amplitude particularly in the area around the Brewster angle. Moreover there are phase differences between the different polarization directions. For example, falls circularly polarized light on such a conventional, aslant Deflecting mirror, the p component is after the reflection stronger weakened than the s component. Now takes place in the light path between the first and second deflecting mirror a rotation of the preferred polarization directions e.g. by about 90 ° instead the second deflecting mirror is irradiated with light, in which the (in Reference to the second deflection mirror) s-polarized component, which corresponds to the p-polarized component after the first reflection, has a lower amplitude than the p component. With conventional Coating, the second deflecting mirror will reflect the p-component again less than the s component, so that as a result a more or less equalization of the differences in the reflected amplitudes for s and p polarization is. There is also a compensation effect for the phase difference built up first deflection mirror. The polarization rotator is therefore preferred for rotating the preferred polarization direction by approx. 90 ° between the deflecting mirrors.

The targeted rotation of the polarization use allows between the first and second deflecting mirror conventional, relatively simply constructed and producible, highly reflective Reflective coatings for the deflecting mirror.

For projection lenses that are between the first deflecting mirror and the second deflecting mirror one from If the light has a double pass region, the polarization rotating device can Delay device arranged in the double continuous area with the effect of a quarter-wave plate and thus a conversion from linearly polarized light to circularly polarized Enable light and vice versa. The polarization rotating device can, for example, by a λ / 4 plate be formed between a geometric beam splitter and the concave mirror is attached and both in the light path between first deflecting mirror and concave mirror, as well as in the light path between Concave mirror and second deflecting mirror is irradiated.

The delay device is preferably tion at a position where the divergence of the rays passing through is minimal, since the effect of conventional delay elements is strongly dependent on the angle. An arrangement in the vicinity of a pupil of the projection objective is particularly favorable. Since an exact compensation of the mentioned amplitude and phase effects is generally not necessary, tolerances around the exact delay effect in the range of ± 10 to 20% can be tolerated in many cases.

It is also possible that the polarization rotator a λ / 2 delay element which is in an area which is only traversed by light once arranged between the first deflecting mirror and the second deflecting mirror is. In systems with a geometric beam splitter, in which the first Deflecting mirror for deflecting object light towards the concave mirror and the second deflecting mirror for deflecting from the concave mirror incoming light towards the image plane can be a λ / 2 plate or an element of similar effect close behind the first deflecting mirror or arranged in front of the second deflecting mirror in an area be where the beam is do not overlap.

Polarization rotating devices with the (approximate) effect of a λ / 2 plate or the like can also be useful in projection lenses in which the object light first hits the concave mirror without deflection and the light reflected by it is deflected with the aid of two successive deflection mirrors between which the polarization rotating device is to be arranged. Such systems are for example in the US 6,157,498 or the EP 0 964 282 shown.

Catadioptric projection lenses in which the polarization rotating device has at least one delay element, which consists of a calcium fluoride crystal or a barium fluoride crystal or another cubic crystal material with intrinsic birefringence, are particularly advantageous, the optical axis of the delay element being approximately in the direction of a <110> Crystal axis or an equivalent main crystal axis is aligned. From the Internet publication "Preliminary determination of an intrinsic birefringence in CaF ₂ " by John H. Burnett, Eric L. Shirley and Zachary H. Levine, NIST Gaithersburg, MD 20899, USA (published on May 7, 2001) is known that calcium fluoride single crystals have intrinsic birefringence, i.e. birefringence that is not stress-induced.The presented measurements show that when the beam propagates in the direction of the <110> crystal axis or equivalent directions, a birefringence of (6.5 ± 0.4) nm / cm at a Wavelength of λ = 156.1 nm occurs. The value drops to higher wavelengths and is, for example, 193.09 nm (3.6 ± 0.2) nm / cm. Measurements by the applicant even show values of approximately 11 nm / cm for λ = 157 nm The birefringence in the other crystal directions, on the other hand, is small. Also in the case of barium fluoride single crystals, a corresponding residual birefringence with a maximum in the <110> direction of the crystal is found, which is approx. 25 nm / cm and is therefore about twice as high as with calcium fluoride single crystals.

The intrinsic birefringence of this Materials that pass parallel to crystal directions when the beam passes of the type <110> is maximum, can targeted as a mechanism of action for delay elements be used. Because of the relatively low values birefringence (compared to magnesium fluoride, for example) can such delay elements be several millimeters or centimeters thick, which makes manufacturing and, where appropriate, version of such elements is facilitated. Typical thicknesses can are more than approx. 5mm, in particular between approx. 10mm and about 50mm. It is also advantageous that because of the relatively small Birefringence slight variations in thickness of the elements only slight Influence on the delay effect to have. The high tolerance to thickness variations can e.g. to be used at least one area of a such delay element as a functional surface train. For example, at least one of the end faces can be spherical or aspherical or be curved as a free-form surface, so the delay element too can contribute to the correction of an optical system.

One or both interfaces can also be one significant curvature have so that the delay element one, preferably meniscus-shaped, Can form lens. Thus the delay element can also be positive or have negative refractive power. The integration of here in The primary effect of deceleration with a lens effect can for material-saving or constructively favorable designs can be used. Such lenses can also in purely dioptric optical systems, especially in microlithography projection lenses or lighting systems.

The intrinsic birefringence of the materials mentioned has its maximum value in <110> crystal directions. For rays that run through the material at an angle to <110> directions, the amount of intrinsic birefringence shows a parabolically decreasing course with increasing angle, while the axes of the intrinsic birefringence approximately maintain the direction. This fact can be used to even out the delay effect over the entire irradiated area. For this purpose, in the case of a delay element with two optical surfaces, the shape of the optical surfaces and the installation position of the delay element can be adapted to one another such that the light path of rays within the delay element The greater the angle between the beam and the optical axis or a <110> direction of the delay element, the greater the size between the optical surfaces. This means that beams with a larger angle to the <110> direction have a longer light path, so that the retarding effect that results from the product between intrinsic birefringence and light path becomes approximately uniform over the entire effective area.

This concept will be explained later of embodiments explains where the polarization rotator is close to the concave mirror arranged lens or lens group made of <110> -oriented fluoride crystal has the overall meniscus shape is and has negative refractive power. One placed near the pupil A lens or lens group of this type can largely cover the entire pupil have constant or little varying delay effect.

The integration described here a delay element with a lens element by manufacturing a (with refractive power) Lens element made of a <110> -oriented single crystal intrinsic birefringence (e.g. calcium fluoride or barium fluoride single crystal) not only with catadioptric projection lenses with geometric Beam splitting can be used with advantage. A suitably sized Lens or lens group with the retarding effect of a λ / 4 plate can also in systems with polarization-selective beam splitter as (functionally necessary) Retarder between beam splitter and concave mirror and / or at another Location of a projection lens, e.g. between Object plane and beam splitter and / or between beam splitter and Image plane.

The above and other features go except from the claims also from the description and the drawings, the individual Characteristics for each yourself or in groups of two in the form of sub-combinations embodiments of the invention and in other fields be realized and advantageous also for yourself protectable versions can represent.

1 is a schematic representation of a microlithography projection exposure system designed as a wafer stepper, which comprises a catadioptric projection objective with geometric beam splitting according to an embodiment of the invention;

2 is a schematic diagram showing the dependence of the reflectivity R of a mirror on the angle of incidence I of the incident radiation for s- and p-polarized light;

3 is a schematic detailed view of the catadioptric lens part of the in 1 projection lens shown;

4 is a schematic representation of an embodiment of a catadioptric projection objective with geometric beam splitting and a negative meniscus lens, which serves as a λ / 4 retarder; and

5 is a schematic representation of the catadioptric lens part of a projection lens with a physical beam splitter.

In 1 is a schematic of a microlithography projection exposure system in the form of a wafer stepper 1 shown, which is provided for the production of highly integrated semiconductor components. The projection exposure system comprises an excimer laser as the light source 2 , which emits ultraviolet light with a working wavelength of 157 nm, which in other embodiments can also be above this, for example 193 nm or 248 nm, or below. A downstream lighting system 4 creates a large, sharply delimited and homogeneously illuminated image field that meets the telecentricity requirements of the downstream projection lens 5 is adjusted. The lighting system has devices for selecting the lighting mode and can be switched, for example, between conventional lighting with a variable degree of coherence, ring field lighting and dipole or quadrupole lighting. There is a facility behind the lighting system 6 for holding and manipulating a mask 7 arranged so that the mask is in the object plane 8th of the projection lens and in this plane for scanner operation in a direction of departure 9 (y direction) is movable by means of a scan drive.

Behind the mask plane 8th follows the projection lens 5 , which acts as a reduction lens and an image of a pattern arranged on the mask on a reduced scale, for example on a scale of 1: 4 or 1: 5, onto a wafer covered with a photoresist layer or photoresist layer 10 maps that in the image plane 11 of the reduction lens is arranged. Other reduction scales are possible, for example larger reductions up to 1:20 or 1: 200. The wafer 10 is through an establishment 12 held, which includes a scanner drive to keep the wafer in sync with the reticle 7 to move parallel to this. All systems are controlled by a control unit 13 controlled.

The projection lens 5 works with geometric beam splitting and has between its object level (mask level 8th ) and its image level (wafer level 11 ) a catadioptric lens part 15 with a first deflecting mirror 16 and a concave mirror 17 , with the flat deflecting mirror 16 like this with respect to the optical axis 18 of the projection lens is tilted that the radiation coming from the object plane through the deflecting mirror 16 towards the concave mirror 17 is redirected. In addition to this mirror, which is necessary for the function of the projection lens 16 is a second, flat deflecting mirror 19 provided, which is tilted relative to the optical axis in such a way that that of the concave mirror 17 reflected radiation through the deflecting mirror 19 towards the image plane 11 to the lenses of the subsequent dioptric lens part 20 is redirected. The plane mirror surfaces standing perpendicular to each other 16 . 19 are on a beam deflection device designed as a mirror prism 21 provided and have parallel tilt axes perpendicular to the optical axis 18 ,

In the example shown, the catadioptric lens part is designed so that in the area of the second deflecting mirror 19 an intermediate image is created, which preferably does not coincide with the mirror plane, but either behind it or in the direction of the concave mirror 17 can lie in front of it. Embodiments without an intermediate image are also possible. It is also possible to use the mirror 16 . 19 to be trained as physically separate mirrors.

A special feature of the lens construction is that in an area between which the beam deflection device is traversed twice by light 21 and the concave mirror 17 in an inclined side arm 25 of the lens a delay element 26 is arranged in the form of a λ / 4 plate. This serves as a polarization rotating device in the light path between the first and the second deflecting mirror 16 respectively. 19 causes a rotation of the preferred polarization direction of the light by 90 °. By tilting the side arm, a sufficient working distance across the entire width of the lens can be ensured on the mask side, among other things. Correspondingly, the angle of attack of the deflecting mirrors with their planes perpendicular to each other can 16 . 19 opposite the optical axis 18 deviate by several degrees from 45 °.

The mirror surfaces of the deflecting mirror 16 . 19 are used to achieve high levels of reflection with highly reflective layers 23 . 24 busy. These preferably comprise one or more layers of dielectric material, the calculation indices and layer thicknesses of which are selected such that a reflection amplification occurs in the angle of incidence range used.

These layers introduce a polarization-dependent phase difference between the mutually perpendicular field components of the electric field vector of the reflected light (s-polarization or p-polarization). This results from the fact that the layers for s and p polarization, depending on the angle of incidence of the beams, represent a different optical path depending on the angle of incidence. Common multilayers also have different reflectivities for s and p polarization. A typical course of the reflectance R for multiple layers as a function of the incidence angle I is shown schematically in 2 shown. Afterwards it is the case that the degrees of reflection for s and p polarization with perpendicular incidence (incidence angle 0 °) are the same. As the incidence angle increases, the degree of reflection for s polarization increases monotonously, while the degree of reflection for p polarization initially decreases up to the Brewster angle I _B , in order to increase again as the incidence angle increases. In general, the reflectance for s-polarization over the entire angular range is greater than for p-polarization in the case of conventional reflection layers, with particularly large differences in reflectivity resulting in the region of the Brewster angle of approximately 45 °.

This can be done with conventional Projection lenses with the geometric beam splitting shown as an example cause that the p component of the electric field is weakened more when passing through the lens than the s component, so that for example in the case of the entry-side, unpolarized or circularly polarized light that strikes the image plane Light a stronger s component having. This allows dependent on structural direction resolution differences arise.

These problems are avoided in the embodiment shown by the polarization of the light by means of the polarization rotating device 26 between the deflecting mirrors 16 . 19 is rotated by a total of approx. 90 °. For explanation shows 3 an example in which the first deflecting mirror 16 hitting entrance light 27 is circularly polarized, the amplitudes of s and p polarization symbolized by the arrow lengths being substantially the same. After reflection on the tilted mirror 16 the component of the electric field vibrating parallel to the plane of incidence is weakened more than the s component. This light passes through the delay element designed as a λ / 4 plate 26 , which delays the phases of the field components by a quarter wavelength against each other. After reflection on the concave mirror 17 , in which the state of polarization remains largely unchanged, the reflected light again passes through the λ / 4 plate, which has thus been passed through twice 26 , with a further phase delay of λ / 4 taking place. The double passage through the plate 26 thus leads overall to a λ / 2 delay, which corresponds to a rotation of the polarization preferred directions by 90 °. This ensures that in relation to the second deflecting mirror 19 s-polarized light has the (weaker) amplitude of the portion polarized behind the first deflecting mirror, while the p-component now has the larger amplitude. This p component is now based on the 3 explained reflectivity differences weakened more than the (weaker) s component, so that there is an adjustment of the amplitudes for s and p polarization. The multiple layers are favorable 23 and 24 designed so that behind the second deflecting mirror 16 there are essentially equal amplitudes of s and p polarization. With this light, imaging is possible without differences in contrast depending on the structure direction.

As an alternative to the double run delay element 26 with the effect of a λ / 4 plate, it is also possible to mount a delay element with a λ / 2 delay in a single light path between the first and second deflection mirrors, for example immediately behind the first deflection mirror in position 28 or immediately in front of the second deflecting mirror 29 , The element can be free-standing or combined with another optical element, for example by wringing onto a flat or only slightly curved surface, e.g. B a lens.

The λ / 4 plate or the mentioned λ / 2 plates can consist of birefringent crystal material, such as magnesium fluoride. Due to the strong birefringence, the lowest-order delay plates become very thin, which can cause manufacturing and setting difficulties. Plates with a higher delay order and a correspondingly larger thickness are possible, but have a much smaller angular tolerance, so that the delay effect varies greatly for different angles of incidence. In contrast, plates made of calcium fluoride or another crystal material, which has stress birefringence due to external forces or due to the manufacturing process, are more favorable (cf. e.g. US 6,191,880 or US 6,201,634 ).

In preferred embodiments are delay elements, which in particular the function of a λ / 4 plate or λ / 2 plate can have, made of a cubic crystal material with intrinsic birefringence manufactured, in particular from a calcium fluoride single crystal or a barium fluoride single crystal in which a crystal axis extends from Type <110> essentially in Direction of the optical axis of the delay element. These materials show intrinsic birefringence, the maximum amount parallel to <110> directions and at about 157nm wavelength in the order of magnitude of 11 nm / cm (for calcium fluoride) or approx. 25 nm / cm (for barium fluoride) lies. The corresponding delay elements can typical thicknesses of the order of several millimeters, especially of centimeters (e.g. approx. 36mm for a λ / 4 plate as calcium fluoride) have so that they are easy to manufacture, easy to handle, self-supporting and are easy to grasp if necessary.

If the angle of incidence is not very are great can to use a plane-parallel plate as a delay element. For oblique passage of light however, the geometric path in the material is longer. This compensates for the nearly parabolic weakening the intrinsic birefringence in the event of a deviation from the <110> direction up to one certain limit, so that even at angles of incidence up to the range from 15 ° only changes the delay effect up to approx. 10% of the setpoint.

Based on 4 Another embodiment of a catadioptric projection lens with a geometric beam splitter is explained, in which between the beam splitter 35 and the concave mirror 36 a polarization rotator 37 is arranged in the form of a λ / 4 retarder that has been pushed through twice. This is a lens made of <110> -oriented calcium fluoride crystal, which is arranged near the concave mirror and is overall meniscus-shaped and has negative refractive power. The negative lens located near the pupil 37 has a double function. On the one hand, it supports as an optical lens together with the concave mirror 36 the chromatic correction of the projection lens. At the same time, it acts as a λ / 4 delay element with a largely constant or only slightly varying delay effect over the entire pupil. It has been recognized that a largely constant distribution of the delay over the pupil can be achieved if the (axial) thickness d of the delay element is optimized as a function of the radial distance x from the optical axis so that the light path of rays within the Delay element between light entry and light exit becomes larger, the larger the angle α _in between the beam and the optical axis of the delay element or the <110> direction running parallel to it. The adjustment is ideally such that the increase in thickness largely or completely compensates for the parabolic drop in intrinsic birefringence in the event of a deviation from the <110> direction.

To determine the ideal curvature in the central area of the delay element, consider a bundle of rays 38 in the center of the delay element 37 , Make the condition for all rays that the optical path length in the material is λ / 4. This defines a surface that is in two-dimensional space through the equations
X = (λ / 4 * sin (α in )) / .DELTA.n (α in ) and
Z ≡ d (x) = (λ / 4 * cos (α in )) / .DELTA.n (α in )

Δn is the difference in refractive index between the medium surrounding the delay element (normally air) and the material of the delay element, α _in the angle between the optical axis or the <110> axis and the beam under consideration 38 and d (x) the thickness as a function of the radius x of the delay element. This calculation gives an approximately parabolic course of the thickness in the radial direction of the delay element, that of the negative meniscus lens 37 taking into account the curvatures of the entrance surface and the exit surface which are ideal for optical reasons.

If the resulting lens thickness is un is viewed favorably, it is also possible to distribute the delay over several delay lenses or combinations of delay lenses and delay plates, the total thickness of which can be determined, for example, according to the above equation (cf. 5 ).

In order to be able to optimally benefit from this aspect of the invention, the combined lens / delay element should be arranged in an area with the smallest possible angle of incidence. Ideally, the maximum angle of incidence in air should not be greater than approx. 39 °, otherwise a crystallographic four-wave ripple of the deceleration as a function of the crystal direction can be noticeable. It is also favorable if the curvature of the lens is made smaller the smaller the angle α _in . The sum of the lens thicknesses should approximately correspond to the corresponding thickness of a λ / 4 delay element consisting of the material. Small corrections to the overall thickness to adjust the retarding effect can be advantageous. For example, it may be more favorable if the retarding effect for marginal rays is set more precisely than for central rays. This can lead to a homogenization of the intensity distribution after double passage through the delay element.

The aspect of the invention also leaves corrective actions for the If the ideal total thickness determined is too large or too large is small. For example, the delay may be weakened if two approximately equally thick, <110> -cut lenses by 45 ° with respect to the <110> axis against each other twisted. If the total thickness is too small, one can, for example additional plane-parallel plate made of <110> -oriented material. Here it is particularly important to ensure that the inclination of the rays is not too big.

Based on 5 an embodiment of a catadioptric projection lens with a polarization-selective beam splitter 40 explained in the form of a beam splitter cube. In this embodiment, there is between the beam splitter 40 and the concave mirror 41 a polarization rotator 43 arranged with the effect of a λ / 4 radar. The polarization rotator consists of two negative meniscus lenses 44 . 45 , each consisting of <110> -oriented calcium fluoride crystal. The total axial thickness of the lenses in the central region near the axis corresponds to the corresponding thickness of a λ / 4 retardation plate (for example approx. 36 mm for calcium fluoride at a working wavelength of 157 nm) and increases parabolically in the radial direction in order to equalize the retarding effect over the entire lens cross section in the range of Pupil arranged lenses 44 . 45 to achieve.

The projection lens is designed for operation with circularly polarized input light and has between the object plane 46 and beam splitter 40 a λ / 4 plate 47 to convert the input light into light related to the beam splitter surface 48 is s-polarized. This light passes through the two lenses 44 . 45 and due to its retarding effect is converted into circularly polarized light which is emitted by the concave mirror 41 is reflected and by the delay device 43 running back. After passing through the delay lenses again 44 . 45 is the light in relation to the beam splitter layer 48 p-polarizes and passes through it with little loss in the direction of a deflecting mirror 49 that redirects the light towards the object plane. It is hereby explained by way of example that the λ / 4 redarder between the beam deflection device, which is necessary for such systems 40 and concave mirror can be formed by one or more lenses with a suitable retarding effect. The conventionally required λ / 4 plate between the beam splitter and the concave mirror can thus be omitted.

Claims (20)

Catadioptric projection objective for imaging a pattern arranged in an object plane of the projection objective into the image plane of the projection objective, with a catadioptric objective part between the object plane and the image plane ( 15 ) with a concave mirror ( 17 . 36 . 41 ) and a first deflecting mirror ( 16 ) and at least one second deflecting mirror ( 19 ) are arranged and a polarization rotating device () for compensating polarization-dependent reflectivity and / or phase differences of the deflection mirror between the first deflection mirror and the second deflection mirror ( 26 . 37 ) is arranged to rotate a polarization preferred direction of passing light. Projection objective according to Claim 1, in which the polarization rotation device ( 26 . 37 ) is designed to rotate the preferred polarization direction by approximately 90 ° between the deflecting mirrors. Projection objective according to claim 1 or 2, which between the first deflecting mirror ( 16 ) and the second deflecting mirror ( 19 ) has an area which is traversed twice by the light, the polarization rotating device ( 26 . 37 ) is a delay device arranged in the double-traversed area, which has at least approximately the effect of a λ / 4 plate. Projection objective according to one of the preceding claims, in which the polarization rotating device ( 26 . 37 ) is arranged in a region of low divergence of the radiation passing through, preferably in the vicinity of a pupil plane of the projection objective, in particular in the vicinity of the concave mirror ( 17 . 36 ). Projection objective according to one of the preceding claims, in which the polarization rotating device is a delay device which has at least approximately the effect of a λ / 2 plate and which is in a region through which the light passes only once ( 28 . 29 ) between the first deflecting mirror ( 16 ) and the second deflecting mirror ( 19 ) is arranged. Projection objective according to one of the preceding claims, in which the polarization rotating device ( 37 ) has at least one retardation element, which consists of a cubic crystal material with intrinsic birefringence, in particular a calcium fluoride crystal or a barium fluoride crystal, the optical axis of the retardation element being aligned approximately in the direction of a <110> crystal axis of the crystal. A projection lens according to claim 6, wherein the delay element a thickness of at least 5mm, in particular between approx. 10mm and about 50mm. Projection objective according to one of claims 6 or 7, characterized in that at least one delay element ( 37 ) is designed as a lens element with a positive or negative refractive power, preferably as a meniscus-shaped lens, in particular with a negative refractive power. Projection objective according to one of Claims 6 to 8, in which at least one delay element ( 37 ) has two optical surfaces, the shape of the optical surfaces and the installation position of the delay element being matched to one another such that the light path of rays ( 38 ) within the delay element between the optical surfaces, the greater the angle between a beam passing through and the optical axis of the delay element. Projection objective according to one of Claims 6 to 9, in which the polarization rotating device has at least one lens ( 37 ) made of a cubic crystal material with intrinsic birefringence, in which the thickness as a function of the radius has an approximately parabolic course with a radially increasing thickness. Projection objective according to one of Claims 6 to 10, in which the polarization rotating device has at least one lens consisting of a cubic crystal material with intrinsic birefringence, which is located in the vicinity of a pupil plane of the projection objective, in particular in the vicinity of the concave mirror ( 36 ) is arranged and preferably has negative refractive power. Catadioptric projection objective for imaging a pattern arranged in an object plane of the projection objective into the image plane of the projection objective, a catadioptric objective part with a concave mirror (between the object plane and the image plane). 41 ) and a polarization-selective beam splitter ( 40 ) with a beam splitter surface ( 48 ) is arranged, between the beam splitter surface ( 48 ) and the concave mirror ( 41 ) a polarization rotating device ( 43 ) is arranged with the effect of a λ / 4 plate, and wherein the polarization rotating device has at least one delay element designed as a lens ( 44 . 45 ), which consists of an intrinsic birefringence cubic crystal material, in particular calcium fluoride crystal or barium fluoride crystal, the optical axis of the delay element being oriented approximately in the direction of a <110> crystal axis of the crystal. Projection objective according to claim 12, characterized in that at least one delay element ( 44 . 45 ) is designed as a meniscus-shaped lens, in particular with a negative refractive power. Projection objective according to one of Claims 12 to 13, in which at least one delay element ( 44 . 45 ) has two optical surfaces, the shape of the optical surfaces and the installation position of the delay element being matched to one another in such a way that the light path of rays within the delay element between the optical surfaces is greater, the greater the angle between a beam passing through and the optical axis of the delay element. Projection objective according to one of claims 12 to 14, wherein the delay element ( 44 . 45 ) the total thickness as a function of the radius has an approximately parabolic course with a radially increasing thickness. Projection objective according to one of Claims 12 to 14, in which the polarization rotating device ( 43 ) in the vicinity of a pupil plane of the projection lens, in particular in the vicinity of the concave mirror ( 41 ), is arranged. Projection objective according to one of Claims 12 to 16, in which between the beam splitter surface ( 48 ) and the concave mirror ( 41 ) no λ / 4 plate is arranged. Optical system, in particular projection objective according to one of the preceding claims, which has at least one delay element ( 37 . 44 . 45 ), which has an intrinsic birefringence cubic crystal material, in particular made of calcium fluoride crystal or barium fluoride crystal, wherein the optical axis of the delay element is aligned approximately in the direction of a <110> crystal axis of the crystal. Optical system according to Claim 18, in which the delay element ( 37 . 44 . 45 ) is a meniscus lens, especially with a negative refractive power. Optical system according to claim 18 or 19, wherein the thickness of the delay element as Approximate function of the radius parabolic course with radially increasing thickness.