WO2003092256A2

WO2003092256A2 - Projection method and projection system comprising an optical filtering process

Info

Publication number: WO2003092256A2
Application number: PCT/EP2003/004012
Authority: WO
Inventors: Christian Wagner; Martin Brunotte; Volker Gräschus; Paul Gräupner
Original assignee: Carl Zeiss Smt Ag
Priority date: 2002-04-24
Filing date: 2003-04-17
Publication date: 2003-11-06
Also published as: WO2003092256A3; AU2003224088A8; DE10218989A1; AU2003224088A1

Abstract

According to the invention, an imaging system is used during the imaging of a pattern arranged in an object plane of an optical imaging system into the image plane of said imaging system, wherein a plurality of optical elements and at least one pupil plane are located between the object plane and the image plane, said pupil planes being Fourier-transformed into field planes of the imaging system. An angle-selective, optical filtering process is carried out in the region of the field planes by means of an optical filter element, the angle-dependent filter function of said filter element being calculated as a function of a desired fixed filter function for the region of the pupil.

Description

Projection method and projection system with optical filtering

The invention relates to a method for imaging a pattern arranged in an object plane of an optical imaging system into the image plane of the imaging system and to an imaging system for carrying out the method. The imaging process includes optical filtering of the light passing through the imaging system. Preferred areas of application of the invention are projection objectives for microlithography.

Projection lenses for microlithography are used in projection exposure systems for the production of

Semiconductor components and other finely structured components used. These imaging systems serve to pattern samples of photomasks or graticules, which are arranged in the object plane of the imaging system and are generally referred to as masks or reticles, on an object arranged in the image plane of the imaging system and coated with a light-sensitive layer with the highest resolution in a reducing size Map scale.

Since the resolution of optical imaging systems is proportional to the wavelength λ of the light used and inversely proportional to the image-side numerical aperture (NA) of the optical imaging system, efforts are being made to produce ever finer structures, on the one hand to increase the image-side numerical aperture of the projection objectives and on the other hand to use shorter and shorter wavelengths to use. Ultraviolet light with wavelengths of less than approximately 260 nm is preferably used, for example with 248 nm, 193 nm or 157 nm wavelength. In addition to the resolving power, the depth of focus (DOF) that can be achieved in the image plays an important role for a true-to-original image. The depth of field is also proportional to the wavelength used, but inversely proportional to the square of the numerical aperture. Therefore, increasing the numerical aperture without suitable measures to ensure a sufficient depth of field only makes sense to a limited extent.

It is known to use pupil filters to improve the resolution and the depth of field of microlithographic projection objectives.

A pupil filter is a space filter which is arranged in the region of a pupil plane of an optical imaging system.

The use of pupil filters is sometimes called optical

Called filtering or apodization. While the object plane and the image plane represent conjugate field planes of the imaging system, the pupil plane is one to the object plane and to the other

Image plane Fourier-transformed plane. This means in particular that a certain angle of incidence of light in the image plane of the

Projection lens corresponds to a certain radial coordinate in the pupil plane. With the help of a spatially resolving filtering in

The area of the pupil can thus influence the angular spectrum of the

Figure contributing rays are taken.

For systems with a large numerical aperture, the mapping of certain structures is becoming increasingly difficult. The depth of field can become so small that a process suitable for production is no longer possible. It has been shown, for example, that isolated contact holes with a larger process window can be imaged if the pupil is darkened in the middle. This blocks undiffracted light, while more diffracted light passes through the imaging system largely uninhibited and can effectively increase the contrast. An explanation of how Pupil filters and examples of projection objectives with such filters are given, for example, in EP 0 485 062 A1 (corresponding to US 5,316,896) or US 5,144,362 and in the documents cited therein.

In order to achieve optimal use of pupil filtering, it is expedient to adapt the mode of operation of the pupil filter, which is determined by the filter function of a pupil filter, to the type of reticle structures to be imaged. Accordingly, pupil filters are optimized for certain reticle structures (e.g. contact holes, lattice structures with one or more directions of periodicity). Since reticles of different structures are to be imaged with a projection lens, it is desirable to be able to use pupil filters with different effects. For this purpose, US Pat. No. 5,610,684 discloses a projection objective which has an exchange device for exchanging pupil filters, which can optionally be introduced into the region of the pupil plane of the projection objective. The

Exchange device comprises displacement devices for displacing lenses close to the pupil in order to provide sufficient space for the exchange process. EP 0 638 847 B1 (corresponding to US Pat. No. 5,448,336) shows a projection objective with a pupil filter exchange device, the operation of which does not require the movement of lenses close to the pupil. The technical implementation of such exchange devices is very complex in the case of high-performance projection lenses, since there are narrow tolerances for the material, fit and thickness of the optical components used and high demands are placed on the positioning accuracy and possibly gas tightness.

The invention is based on the object of an imaging method with optical filtering and a corresponding optical imaging system to create, which allow the use of optical filters with different effects in a simple manner.

To achieve this object, the invention proposes a method with the features of claim 1 and an optical imaging system with the features of claim 9. Advantageous further developments are specified in the dependent claims. The wording of all claims is incorporated by reference into the content of the description.

The method according to the invention for imaging a pattern attached in the object plane of an optical imaging system into the image plane of the imaging system uses an imaging system in which, between the object plane and the image plane, a plurality of optical elements arranged along an optical axis and at least one to a field plane of the imaging system Fourier- transformed pupil plane are arranged. In the imaging, optical filtering of the light passing through the imaging system is carried out. The process includes the following steps:

Specification of a desired, location-dependent pupil filter function F _p for the area of the pupil plane as a function of pupil location coordinates; Calculation of an angle-dependent filter function F _f corresponding to the pupil filter function for the area of a field plane of the Fourier transformed to the pupil plane

Imaging system as a function of incidence angles in the field level; Angle-selective filtering according to the angle-dependent filter function in the area of the field level. According to the invention, it is therefore provided that the intervention in the beam path required for the optical filtering, which corresponds to pupil filtering as a result, is not carried out in the area of a pupil of the imaging system, but in an associated area near the field, i.e. in a field plane transformed to the Fourier pupil or in close to this field level. Here, for example, the knowledge is used that the angular spectrum of the rays running to the image plane on a surface of the projection objective lying close to the image plane can be directly transmitted in pupil coordinates. For example, a certain angle of incidence or angle of incidence in the image plane corresponds to a certain radial coordinate in the pupil plane. Therefore, an angle-selective filtering in an area close to the field can have the same effect as a location-selective filtering in the area of the pupil. Areas in the vicinity of the field are in particular those areas in which the marginal jet height is lower and significantly smaller than the main jet height. The edge jet height can be, for example, a maximum of 10% or a maximum of 20% of the main jet height. The marginal ray height is the ray height of marginal rays that run from the field center to the aperture edge; the main beam height is the beam height of main beams that run at the field edge and intersect the optical axis in the area of the aperture. The areas near the field are in particular the area of the image plane, the area of the object plane and, in the case of a system with at least one real intermediate image, the area of the intermediate image plane.

The angle-selective filtering according to the invention has the effect that the radiation impinging on an optical filter element differs from the radiation traveling away from the filter element in a defined manner as a function of the angle of incidence of the radiation, the difference being describable with the aid of the filter function. An angle-selective filter element can be designed as a transmission filter be to act on the radiation passing through the filter element. It is also possible to design angle-selective filter elements as reflection filters, which, for example, reflect light that strikes at large angles of incidence more strongly than light that strikes at small angles of incidence. Preferred embodiments of angle-selective filter elements are transmission filters with a dependence on the incidence angle of the incident radiation

Transmission function trained.

In a further development, a radially symmetrical pupil filter function F _p = f (r _p ) is specified, where r _{p is} a radial coordinate in the pupil plane with respect to an axis that normally coincides with the optical axis of the imaging system. The calculation of the associated, angle-dependent filter function F _f = f (α) for an area close to the field is carried out using the equation r _p = sin (α) / NA, where α is the angle of incidence of a light beam in the area of the field plane close to the filter and NA the numerical Is the aperture of the imaging system in the area of this field level. This field level can be the image level or the object level, in systems with a real intermediate image also an intermediate image level. In this way it is possible, for example, to influence the pupil transmission in a radially symmetrical manner if the transmission in the region of a last objective surface near the wafer or an object near the object on the objective or reticle is influenced as a function of the angle of incidence α.

Embodiments are particularly advantageous in which the angle-selective filtering takes place in the area of a field plane of the imaging system in such a way that a transmittance is smaller for small incidence angles than for large incidence angles. In particular, the transmittance can increase substantially continuously from small angles of incidence to large angles of incidence. There small incidence angles in the area close to the field correspond to rays that run near the optical axis in the area of the pupil, this angle dependency corresponds in effect to a pupil filter that has a lower transmission in the area of the optical axis than in the outer peripheral areas of the pupil. This corresponds to a pupil apodization with a darkening of the central region near the axis, as is advantageous, for example, to increase the depth of field when imaging contact holes. With a corresponding reflective filter element, the degree of reflection could increase from small to large incidence angles.

The angle-selective filtering can be carried out in any area sufficiently close to a field level. In an imaging system in which one or more real intermediate images are created between the object plane and the image plane, the angle-selective filtering can be carried out, for example, in or near an intermediate image plane. It is also possible to carry out the filtering in the area of the object level. For this purpose, for example, a corresponding coating can be provided on an entry plate or a first lens element. When using so-called hard pellicles, a corresponding filter layer can also be attached to the pellicle. It is expedient if the angle-selective filtering is carried out in the area of the image plane, so that the radiation changed by filtering no longer has to pass through any optical components of the imaging system. In this case, the angle spectrum desired for the location of the image (image plane) can be set with great accuracy. It is particularly expedient if the angle-selective filter is attached to a last optical element of the imaging system closest to the image plane or is formed by this last optical element. For example, the angle-selective filter can comprise an interference filter layer, which is on one of the image planes facing, last optical surface of the imaging system is attached.

In order to enable a simple change between filter elements with different filter functions, advantageous further developments provide for the angle-selective filter to be interchangeably coupled to the optical imaging system. For example, an angle-selective coating, which effects the pupil apodization, can be attached to the image-side exit surface of an exchangeable end element. It can be an exchangeable, plane-parallel end plate. In any case, it is advantageous if the effective filter layer of the filter is applied to a flat or only slightly curved surface in order to ensure a uniform, angle-selective effect over the entire filter surface.

It is possible that the angle-selective filter element has its own socket, which can be detachably connected to socket elements for the optical elements of the imaging system, for example with the aid of screws. It is also possible for the angle-selective filter element, as the last optical element of the imaging system, to be connected to the penultimate optical element so that it can be replaced and replaced. The connection can be made, for example, by starting. This type of attachment, which is particularly favorable for replacing optical elements, is described, for example, in EP 1 063 551, the disclosure content of which is made the content of this description by reference. The invention enables interchangeable and / or interchangeable filter elements to be arranged on the outside of the projection lens or in the vicinity thereof in such a way that it can be replaced without interfering with the interior of the imaging system. The invention can be used particularly advantageously in the case of dioptric, catadioptric or catoptical projection objectives for microlithography. An angle-selective filtering in the immediate vicinity of the wafer level (image level) is preferred. Alternatively or additionally, the filtering can also be carried out in the area of another field level, for example the object level or an intermediate image level which may be present. The invention is also suitable for other imaging systems, for example microscopes.

The above and other features go beyond the

Claims also from the description and the drawings, wherein the individual features can be implemented individually or in groups in the form of sub-combinations in one embodiment of the invention and in other areas and can represent advantageous and protectable versions.

1 is a schematic illustration of a microlithography projection exposure system designed as a wafer stepper with a projection objective, which is equipped with an embodiment of an angle-selective filter element according to the invention;

FIG. 2 is a schematic illustration of the end region of the projection objective according to FIG. 1 near the wafer with explanations of the filter function of preferred, angle-selective filter elements;

3 is a diagram illustrating the transmittance and reflectance of an embodiment of a filter layer according to the invention as a function of the angle of incidence for a wavelength of 157 nm. 1 schematically shows a microlithography projection exposure system in the form of a wafer stepper 1, which is provided for the production of highly integrated semiconductor components. The projection exposure system comprises an excimer laser 2 as the light source, which emits light with a working wavelength λ, which in the example is 157 nm and in other embodiments can also be below or above, for example 193 nm or 248 nm. A downstream lighting system 4 generates a large, sharply delimited and homogeneously illuminated image field which is adapted to the telecentricity requirements of the downstream projection lens 5. The projection lens 5 is a preferred embodiment of an optical imaging system according to the invention. 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. A device 6 for holding and manipulating a mask 7 is arranged behind the lighting system so that the mask (reticle) lies in the object plane 8 of the projection objective and can be moved in this plane for scanner operation in a departure direction 9 (y direction) with the aid of a scanner drive is.

Behind the mask plane 8 follows the projection lens 5, which acts as a reduction lens and images an image of the mask on a reduced scale, for example on a scale of 1: 4 or 1: 5, onto a wafer 10 covered with a photoresist layer, which is in the image plane 11 of the reduction lens 5 is arranged. Other embodiments that are designed for coarser initial structures, for example for maskless lithography, can have larger reductions, for example between 1:20 and 1:200. The wafer 10 is held by a device 12, which comprises a scanner drive, in order to move the wafer in parallel with the reticle 7. All systems are controlled by a control unit 13.

The projection lens 5 is a catadioptric projection lens with geometric beam splitting. Between its object plane (mask plane 8) and its image plane (wafer plane 11), it has a catadioptric first objective part 15 with a concave mirror 16, a geometrical beam splitter 17 and behind this a dioptric second objective part 18. The beam splitter 17, designed as a mirror prism, has a flat first mirror surface 19 for deflecting the radiation coming from the object plane to the concave mirror 16 and a second mirror surface 20 for deflecting the radiation reflected by the concave mirror in the direction of the purely refractive second objective part 18. The catadioptric objective part is designed such that it is at a distance behind the second deflecting mirror 20 in the region an intermediate image plane 21 is a freely accessible real intermediate image, which is imaged into the image plane 11 by the subsequent lenses of the dioptric lens part. The optical axis 24 of the projection objective is folded on the mirror surfaces 19, 16 and 20.

The last optical element of the projection lens 5 closest to the image plane 11 is formed by a plane-parallel end plate 30, which is interchangeably attached to the lower end of the projection lens, protects the projection lens against contamination from the photoresist applied to the wafer and at the same time also seals the lens , The end plate 30, which is explained in more detail below, is designed as an angle-selective transmission filter element and has a plane-parallel substrate 31 made of a material which is transparent to the ultraviolet light used, for example quartz glass or calcium fluoride. A multilayer interference filter layer 32 is applied to the flat surface facing the wafer. This filter layer is in one Distance of a few millimeters (working distance) in the immediate vicinity of the image plane. The opposite entrance surface can have an anti-reflective coating.

The object plane 8, the intermediate image plane 21 and the image plane 11 are field planes of the imaging system 5 which are optically conjugated to one another. Between these lie plane pupil surfaces which are Fourier-transformed to the reticle plane 8 and the image plane 11. A first, flat pupil surface 3 lies in the region of the imaging concave mirror 16. The pupil plane 22 following the intermediate image plane 21 is freely accessible. The adjustable system diaphragm (not shown) of the projection lens is located in this area.

The exposure system 1 is designed to achieve resolutions of 0.1 μm or below and high throughput rates and has an image-side numerical aperture (NA) between approximately 0.65 and approximately 0.85 or higher. The high numerical apertures mean that radiation runs from a large incidence angle range to the image plane 11 in the vicinity of the image plane 11. The angle of incidence α here is the angle between the direction of incidence 25 of a light beam and the optical axis 24 (FIG. 2). For a system with NA = 0.8, the incidence angles run from 0 ° to approx. 53 °. The angular spectrum of the rays running to the image plane 11 in the vicinity of the image plane 11 can be directly transmitted in pupil coordinates, ie in spatial coordinates in the area of the nearest pupil surface 22. In natural units the pupil is a circle with radius 1. The translation between the angle of incidence α in the immediate vicinity of the image plane 11 and the pupil radius r _p essentially follows the equation

r _p = sin (α / NA), (1) where NA is the numerical aperture of the lens on the image side.

For such high aperture systems, the mapping of isolated contact holes is becoming increasingly difficult. E.g. If pure chrome masks are used, the depth of field or depth of field (DOF) can become so small that a process suitable for production is no longer possible. If suitable phase-shifting masks (PSM) are used, depth of field and contrast may be increased, but in addition to the desired contact holes, so-called sidelobes are also visible due to the depiction of secondary maxima. It has been shown that contrast and depth of field can be increased without annoying sidelobes if it is possible to mask 22 spatial frequencies in the area of the pupil, which are below a certain threshold (limit radius), in the area of the pupil, i.e. if you darken the pupil in the middle. An estimate of this effect for a system with NA = 0.85, a working wavelength of 193nm, contact hole diameter of 100nm and a degree of coherence of the lighting system of approx. 0.4 shows that with a radius of the central obscuration of approx. 0.7 (in units from NA) the depth of field when using chrome masks without filter is approx. 120nm and with filter approx. 480nm. With phase shift masks, no process can be implemented under these boundary conditions due to the sidelobes without a filter, while depths of focus of around 480nm can also be achieved with filters. The filtering thus causes a decisive enlargement of the process window.

The optical filtering described, which as a result corresponds to a central obscuration in the area of the pupil 22, is brought about in the embodiment shown by the end plate 30 attached close to the field, which is designed as an angle-selective filter element. An optical filter is referred to here as an angle-selective filter element, whose filter function is specifically optimized as a function of the angle of incidence of the radiation impinging on the filter. In the case of the transmissive transmission filter 30 shown, the transmittance T is set as a function of the angle of incidence α, ie T = f (). The angle-dependent filter function is calculated according to the specification of a desired pupil filter function F _p for the area of the pupil 22.

In the exemplary embodiment shown, it is desirable to influence the pupil transmission T _p radially symmetrically, ie T _p = f (r _p ), where r _{p is} the radial coordinate in the pupil plane 22. The explained central obscuration of the pupil corresponds to a course of the pupil transmission T _p , in which it is small near the optical axis (r _p = 0) and ideally increases continuously to the degree of transmission near the edge of the pupil, ie to larger radii r _p 1 (see Fig. 2 (a)). In order to achieve this effect, in the embodiment shown an angle-selective filtering is carried out in the immediate vicinity of the field plane 11 with the aid of the filter layer 32 of the filter element 30. The transmission T _f at this location close to the field is set specifically as a function of the angle of incidence α, ie T _f = f (α), the conversion being carried out using equation (1). It follows that the transmission profile shown schematically in FIG. 2 (a) in the area of the pupil 22 corresponds to the transmission profile T _f (α) shown schematically in FIG. 2 (b) in the area of the field plane 11. The transmission characteristic of a suitable, angle-selective filter element to be installed close to the field is generally such that the transmittance is smaller for small incidence angles (axis-parallel or almost axis-parallel radiation) than for large incidence angles (oblique radiation). The transmittance can be in the range of small incidence angles, for example between 0 ° and approx. 10 ° below 50%, in the range above about 20 °, however, above 50%. In particular, it can be the case that the transmittance increases from small to large incidence angles continuously, for example more or less linearly. For high incidence angles, for example greater than 30 ° or 40 °, the transmittance should increase to 80% or more in order to have sufficient light intensity overall for image formation. Since small incidence angles in the vicinity of the wafer correspond to axes near the axis, this angle selectivity corresponds to a pupil filter with a comparatively low transmission in the region of the optical axis.

The filter effect required for central pupil obscuration with low transmission for small and high transmission for large incidence angles differs significantly from the effect of conventional antireflection coatings, which are usually optimized in such a way that they cause a strong reflection reduction (and thus transmission increase) at least for small incidence angles , with the reflection-reducing effect normally decreasing at higher incidence angles, so that for higher incidence angles there is less transmission than at small incidence angles.

The filter element 30 has a plane-parallel, plate-shaped substrate 31, which consists of crystalline calcium fluoride and, in other embodiments, can also consist of a different crystalline fluoride material or synthetic quartz glass. On the surface of the plate 31, which in the installed state of the filter element 30 faces the nearest field level (image level 11), a multi-layer filter layer 32 is applied with several layers one above the other, each consisting of a dielectric material that is transparent to the ultraviolet light used. The layer materials are alternately high refractive index and low computational, whereby a high refractive index material im Compared to the refractive index of the other layer material has a higher refractive index. In the example, the refractive index of the substrate material (n = 1, 56 at 157 nm) lies between the refractive index of the high-index layer material (n = 1, 76) and that of the low-index layer material (n = 1, 51). Lanthanum fluoride (LaF ₃ ) is used as the high-index material and magnesium fluoride (MgF ₂ ) as the low-index material. The layer system is laser stable up to at least 2W / cm ^{2 with} respect to the radiation used, in the example has thirty-three layers and a total thickness of approx. 736nm. The layers are applied to the substrate 31 by physical vapor deposition (PVD) in vacuum. Any other suitable technique can also be used for the assignment.

The layer structure of a preferred layer system can be represented with the following notation.

S | 21.8H | 13.6L | 23.7H | 15.7L | 26.5H | 18.3L | 26.3H | 17.2L | 25.9H |

17.3L | 26.2H | 19.2L | 26.2H | 19.8L | 26.0H | 18.7L | 25.4H | 17.1 L |

24.9H | 19.2L | 25.5H | 21, 9L | 25.7H | 23.1 L | 25.7H | 23.5L | 25.9H | 23.5L | 26.0H | 22.8L | 26.3H | 19.9L | 17.8H with H = LaF ₃ and L = MgF ₂

In this notation, S denotes the substrate, a vertical line (|) an interface and the indication 21, 8H a layer made of a highly refractive material (H) with a layer thickness of 21, 8 nm. The letter (L) stands for a low refractive index material.

As alternative layer materials for GdF ₃ (high refractive index), AIF ₃ or Na3AIF ₆ (low refractive index) can be used for 157 nm, for 193 nm also Al ₂ 0 ₃ (high refractive index) or Si0 ₂ (low refractive index). The essential optical properties of the layer system shown are explained using the diagram in FIG. 3. The transmittance T (in%) and the reflectance R (in%) of the layer system are shown there as a function of the incidence angle α of the incident electromagnetic radiation. The solid line represents the transmittance T, the dashed line the reflectance R. It can be seen that the transmittance for radiation incident parallel to the axis (incidence angle α = 0 °) is below approx. 20% and with increasing incidence angle up to a value of approx 80% increases largely linearly at α = 50 °. The degree of reflection R essentially has the opposite course. It is approx. 80% at α = 0 ° and largely drops linearly to approx. 10% at α = 50 °. With this angle-dependent transmission of the coating, the pupil apodization can be influenced in a radially symmetrical manner in such a way that the pupil is darkened in the center and there is a high transmission of more than 80% in the edge region. As a result, pupil spatial frequencies below a certain radius limit value (corresponding to rays with a small angle of incidence in the area near the image plane 11) can be masked out to a greater or lesser extent, so that, for example, undeflected light can be blocked. The more diffracted light occurring at the edge of the pupil, on the other hand, can pass largely uninhibited through the optical system, since the transmission is high for the edge region of the pupil (correspondingly large incidence angles in the region near the wafer plane 11).

With the help of the invention, the optical filtering, which is advantageous for an expansion of the process window, can be carried out with a filter element 30, which can be easily replaced without interfering with the interior of the optical system, since it is the last optical element of the projection objective. It can optionally have a separate frame, which can be detachably connected to frames of the objective lenses, for example by means of screws. A frame-free attachment to the exit surface of a last lens or plate of the projection lens is also possible. An exchangeable filter element offers the possibility to easily adapt the filter function to the structure to be imaged. The filtering can optionally also be carried out directly on the substrate to be exposed. For this purpose, for example, a filter layer with a corresponding effect can be applied to the photoresist.

Claims

claims

1. A method for imaging a pattern attached in the object plane of an optical imaging system into the image plane of the imaging system with the aid of an imaging system in which between the object plane and the image plane a plurality of optical elements arranged along an optical axis and at least one to a field plane of the Fourier imaging system -transformed pupil plane is arranged, with an optical filtering of the by the

Imaging system running light is carried out, the procedure with the following steps:

Specification of a desired, location-dependent pupil filter function F _p for the area of the pupil plane as a function of pupil location coordinates;

Calculating an angle-dependent filter function F _f corresponding to the pupil filter function F _p for the area of a field plane of the imaging system transformed to the pupil plane Fourier as a function of incidence angles in the area of the field plane;

Angle-selective filtering according to the angle-dependent filter function F _f in the field level.

2. The method as claimed in claim 1, in which the angle-selective filtering is carried out in the region of the image plane of the imaging system.

3. The method according to claim 1 or 2 with the following steps: specification of a radially symmetrical pupil filter function F _p = f (r _p ), where r _{p is} a radial coordinate in the pupil plane;

Calculation of an associated angle-dependent filter function F _f = f () for an associated field-near area.

4. The method according to claim 3, wherein the calculation of the angle-dependent filter function is carried out using the equation r _p = sin (α / NA), where α is the angle of incidence of a light beam in the region of the field plane and NA is the numerical one

Aperture of the imaging system is in the area of the field level.

5. The method according to any one of the preceding claims, wherein the angle-selective filtering in the field level is carried out in such a way that a transmission filter

Transmittance is smaller for small incidence angles than for large incidence angles, or that in the case of a reflection filter, the reflectance for smaller incidence angles is smaller than for large incidence angles.

6. The method according to claim 5, wherein the angle-selective filtering is carried out in such a way that in the case of a transmission filter, a transmittance or in the case of a reflection filter, the degree of reflection increases substantially continuously in the region of the field plane from small incidence angles to large incidence angles.

7. The method according to any one of the preceding claims with the following steps: providing a first angle-selective filter with a first angle-dependent filter function;

Provision of at least one second angle-selective filter with a second angle-dependent filter function that differs from the first angle-dependent filter function; Exchange of the first angle-selective filter for the second angle-selective filter depending on the properties of a pattern to be imaged by the imaging system.

8. The method of claim 7, wherein the exchange of filter elements is carried out without intervention in the interior of the imaging system.

9. Optical imaging system for imaging a pattern arranged in the object plane of the imaging system in the image plane of the imaging system, a plurality of optical elements arranged along an optical axis and at least one pupil plane transformed to a field plane of the imaging system being arranged between the object plane and the image plane and wherein the imaging system has at least one angle-selective filter element which is arranged in the region of a field plane of the imaging system and which has an angle-dependent

Has filter function F _f , which corresponds to a desired pupil filter function F _p for the area of the pupil plane.

10. The imaging system as claimed in claim 9, in which the angle-selective filter element has an angle-dependent filter function F _f = f (α) which is radial-symmetrical about an axis, where α is an incidence angle of radiation impinging on the filter element.

11. Optical imaging system according to claim 9 or 10, in which the angle-dependent filter function of the angle-selective filter is set such that in the case of a transmission filter the transmittance of the filter is smaller for small incidence angles than for large incidence angles, or that for a reflection filter the reflectance for small incidence angles is smaller is considered for large incidence angles.

12. The optical imaging system as claimed in claim 11, in which the angle-dependent filter function of the angle-selective filter is set such that, in the case of a transmission filter, the transmittance or in the case of a reflection filter, the reflectance of small incidence angles is too great

Incidence angles are increasing substantially continuously.

13. Imaging system according to one of claims 9 to 12, wherein the angle-selective filter element is arranged in the vicinity of the image plane of the imaging system.

14. Imaging system according to one of claims 9 to 13, in which one of the image plane, the last, optical element of the imaging system is designed as an angle-selective filter element.

15. The imaging system as claimed in one of claims 9 to 14, in which the angle-selective filter element comprises an interference filter layer which is attached to a last optical surface of the imaging system facing the image plane.

16. The imaging system according to one of claims 9 to 15, wherein the angle-selective filter element is interchangeably coupled to the optical imaging system.

17. The imaging system as claimed in one of claims 9 to 16, in which the optical filter element can be replaced without intervention in the interior of the imaging system.

18. Imaging system according to one of claims 9 to 17, wherein the angle-selective filter element has a substantially plane-parallel, transparent plate, which at least a plate surface is coated with an angle-selective interference filter layer.

19. Imaging system according to one of claims 9 to 18, wherein the angle-selective filter element has a substantially flat optical surface on which an angle-selective interference filter layer is applied.

20. Imaging system according to one of claims 9 to 19, in which the angle-selective filter element as the last optical element of the imaging system is connected without interchangeability and interchangeably with the penultimate optical element of the imaging system.

21. Angle-selective filter element for ultraviolet light with a filter function F _f = f (α) dependent on the incidence angle α of the incident radiation, with a substrate in which a transmitting interference multilayer system with several superimposed layers of high-index or low-index material is applied to at least one surface. the multilayer system being designed such that a transmittance of the filter element is smaller for small incidence angles than for large incidence angles.

22. Angle-selective filter element for ultraviolet light with a filter function F _f = f (α) dependent on the incidence angle α of the incident radiation with a substrate in which a reflective interference

Multi-layer system with several superimposed layers of high-index or low-index material is applied, the multi-layer system being designed that the reflectance of the filter is smaller for small incidence angles than for large incidence angles.