WO2004057378A1

WO2004057378A1 - Coated optical element for corrective action obtained by producing layer thickness variations or by refraction factor variations in said coating

Info

Publication number: WO2004057378A1
Application number: PCT/EP2003/014543
Authority: WO
Inventors: Gerd Reisinger; Alexandra Pazidis; Aksel GÖHNERMEIER; Alexander Dinger; Thomas Petasch; Thure Böhm; Rainer BÖRRET
Original assignee: Carl Zeiss Smt Ag
Priority date: 2002-12-19
Filing date: 2003-12-18
Publication date: 2004-07-08
Also published as: AU2003290093A1

Abstract

The inventive optical element (10, 10') comprises a body (12) and a coating (8, 18) applied thereto and is used for modifying reflectivity. Corrective structures (23) for correcting representation errors, for example by a local material removal or by a local modification of a refraction index are formed in the coating. When said coating (18) comprises an outward directed upper layer (186) and one or several interlayers (181 to 185) which are disposed between the upper layer (186) and the body (12) the corrective structures preferably are not arranged in the upper layer (186) but in one of the interlayers. Said optical element (10, 10') is embodied in such a way that it is mechanically stable and better resistant to contamination than the optical elements in which the material removal for a corrective action is carried out directly on the element body

Description

COATED OPTICAL ELEMENT WITH CORRECTION BY PRODUCING A LAYER THICKNESS VARIATION OR REFRIGERATION VARIATION IN THE COATING

The invention relates to coated lenses and other optical elements with an optical correction effect. The invention relates in particular to those optical elements which are intended for use in microlithographic projection objectives. In addition, the invention relates to a method for manufacturing and a method for surface processing of such an optical element.

Microlithographic projection exposure systems, such as those used in the manufacture of highly integrated electrical circuits, have an illumination device which is used to generate a projection light beam. The projection light beam is directed onto a reticle, which contains the structures to be imaged by the projection illumination system and is arranged in an object plane of a projection objective. The projection lens reduces the structures of the reticle onto a light-sensitive layer that is located in an image plane of the projection lens and e.g. can be applied to a wafer.

Due to the small size of the structures to be imaged, high demands are placed on the imaging properties of the projection objective. aberrations can therefore only be tolerated to a very limited extent.

In general, aberrations that occur are assigned to the following two categories. First, there are such aberrations that result from the design of the projection lens, i.e. in particular the specification of the dimensions, materials and distances of the optical elements contained in the projection lens. These design errors are to be disregarded in the following.

On the other hand, there are imaging errors that can be traced back to manufacturing or material defects and can generally only be meaningfully corrected on the finished lens. Manufacturing errors include, for example, so-called pass errors, which are understood to mean deviations from the area fidelity in optical surfaces. Material defects, on the other hand, generally do not affect the properties of the optically effective surfaces, ie those penetrated by projection light, but instead lead to inhomogeneous refractive index profiles within the optical element. In the following, the possible causes of such manufacturing or material-related imaging errors are generally referred to as disturbances, which are locally limited but can also extend over a larger area of the optical element in question. In order to compensate for such interferences and in this way to reduce the imaging errors caused by the interferences, it is known to apply correction structures to suitable optical surfaces of the projection objective by way of a generally material-removing post-processing. Such post-processing methods are described in detail, for example, in an article by C. Hofmann et al. with the title "Nanometer Aspheres: How to Manufacture and For What?", Feinwerktechnik und Meßtechnechnik 99 (1991), 10, pp. 437 to 440.

US 6 268 903 B1 describes in detail how one can draw conclusions from imaging errors, which can generally be detected by measurement technology and which are caused by such disturbances, to the correction structures required for the compensation. In the method described there, the optical element, the surface of which is reworked for interference compensation, is preferably a plane-parallel plate which is arranged between the reticle and the projection lens of the projection exposure system.

However, lenses are also suitable as carriers for correction structures. For this purpose, the lens bodies are first inserted into a frame, built into the projection lens or another optical system, and adjusted there. The shape of the correction structures on the lens body is now determined on the basis of measurements of the imaging properties of the projection objective. The lens body is then removed again in order to produce the correction structure on the selected lens surface. Finally, the surfaces of the lens body penetrated by projection light are provided with an anti-reflective coating. Such coatings, known per se, generally have n layers with different refractive indices, n being between 1 and about 12, typically between 2 and 10. The larger the angular range with which projection light strikes the coating, the greater the number n of layers in general.

However, it has been shown that the previously generated correction structures can be damaged by the coating. In addition, coatings which are applied to lens bodies provided with correction structures are generally mechanically relatively unstable and their action can easily be impaired by contamination. This applies in particular to coatings with a particularly large number of layers, such as those e.g. on high-angle lenses in high-aperture projection lenses. In order to remedy this problem, lenses are selected as carriers of the correction structures which are less stressed at an angle and can therefore be provided with thinner coatings.

Another disadvantage is that it is difficult or even impossible to corrective structures by ablative methods. to generate on a very small area or with steep gradients.

It is already known from US Pat. No. 5,757,017 and EP 0 824 721 B1 to apply a correction layer to a reflecting optical element, namely a mirror, in order to compensate for phase shifts in UV radiation which reflect due to deviations in the shape of the Surfaces occur. Instead of applying a correction layer, provision can also be made to achieve the desired accuracy by local deposition of layer elements or by removing a layer part. WO 02/077 692 AI also deals with the generation of correction effects in a coating.

The object of the invention is to provide an overall improved coated optical element with an optical correction effect.

In particular, it is an object of the invention to provide an optical element with a mechanically stable and resistant to contamination coating, the reflectivity of which is as uniform as possible.

The object of the invention is also to specify a method for producing such an optical element. In particular, a method for processing the surface of an optical element is to be specified by that a surface correction that has been carried out is retained as far as possible without change.

With regard to the optical element, this object is achieved by an optical element with an element body and a coating applied to the element body, the coating containing at least one correction structure by means of which the optical path length for light passing through is changed locally.

The invention is based on the knowledge that the mechanical instability and susceptibility to contamination of thick coatings which are applied to lenses with correction structures are a consequence of the production process. As already mentioned at the outset, the lens bodies must first be inserted into a holder before the correction structures are applied by removing material, since they can only be installed and adjusted in the optical system for the purpose of measurement. However, the lens bodies inserted into the frame only allow a relatively slight heating during the subsequent coating. The comparatively cold applied coating shows the undesirable properties mentioned, such as mechanical instability and susceptibility to contamination.

However, if the coating itself carries the correction structures, the lens body must be inserted into one

Lens holder only after applying several layers required. The further away the layer containing correction structures is from the element body, the more layers can be applied to the underlying layer or the element body at a higher temperature. These layers applied at a higher temperature are mechanically stable and resistant to contamination.

For the production of such an optical element, it is proposed that in a first step the coating is applied to the at least one surface and that in a second step the structure or composition of the coating is changed such that the fit of the optical element Element for image field optimization is changed.

As an alternative to this, in the second step the coating can be locally irradiated with high-energy radiation of such a high intensity that the refractive index of the coating at the irradiated point is corrected for image field optimization.

The change in the coating can e.g. in the first-mentioned embodiment of the invention by a removal process, such as a reactive ion etching process or an ion beam ablation process.

To process the coating in a targeted manner, it can also be subjected to a doping process, wherein due to the material introduced, eg atoms, the refractive index of the coating is changed so that image errors can be corrected.

For targeted processing of the coating and thus for targeted aspherization, masks, screens or similar parts can be used to cover the areas not to be processed. It is also possible to use local light beams or particle beams that are guided over the surface. The refractive index of the layer and also its thickness can be changed by means of high-intensity light. For example, by local light rays change the density of the material and thus locally the refractive index. This can e.g. done by applied masks or selectively by a guided light beam, the thickness of the

Layer itself is not changed, but only locally changes the refractive index due to the high radiation intensity.

The method according to the invention can also be used to carry out small-area structures, steep gradients and similar aspherizations that are not possible with the previously known methods.

For example, a magnesium fluoride, aluminum oxide or zirconium oxide layer can be used as a coating on a silicon oxide basis as the lens material or can be integrated into the coating. Then this loading Layering can be irradiated with high-intensity i-line light (light of 365 nm wavelength), with aging of the coating and compaction occurring. This changes the layer thickness and / or the refractive index and consequently the optical path length.

Of course, it is a prerequisite that in the event of ablation to change the yoke, the thickness of the coating is thicker than the maximum layer thickness to be removed in order to achieve the desired image field optimization.

So by first one or more layers, e.g. by vapor deposition of an anti-reflective coating, and only then, in a second step, the coating, e.g. in the case of several layers, if the outermost layer is reworked to correct the yoke in order to optimize the image field, the previously known method is reversed. This avoids subsequent processing steps, as was the case with the known methods and which can lead to changes in the yoke.

The yoke is now corrected on the previously applied coating, for example vapor deposition, and no longer - as was previously the case - on the surface of the optical element itself. In a particularly preferred embodiment of the invention, the coating has an outwardly facing end layer and one or more intermediate layers arranged between the end layer and the element body, at least one of the intermediate layers containing the preferably non-rotationally symmetrical correction structure.

An optical element according to this configuration can be produced in the following steps:

a) providing the element body;

b) generating at least one selected intermediate layer which has a correction structure by means of which the optical path length for light passing through is changed locally;

c) application of the final layer.

Compared to optical elements in which the final layer contains a correction structure in the form of fluctuations in thickness or refractive index, such an optical element has the advantage of a more uniform reflectivity. In general, there are intermediate layers within the coating, in which such fluctuations have a significantly less effect on the reflectivity than is the case with the outermost layer. In addition, not only lenses and other refractive optical elements, but also reflective optical elements come into consideration as optical elements. The coating then does not serve to reduce the reflectivity, but rather to increase it. Even with such reflective coatings, there is the problem that the outermost layer is detuned by applying correction structures. If an intermediate layer is instead provided with a correction structure, the influence of this correction structure on the reflectivity is considerably less.

Since there is generally an intermediate layer in which fluctuations in thickness or refractive index have the least effect on the reflectivity of the entire coating, it is preferred if at least one, if possible even all, of the other layers of the coating which do not contain a correction structure, the layer thickness is constant or at least distributed rotationally symmetrically. This also applies in particular to the finishing layer, since there fluctuations in thickness have a particularly unfavorable effect on the reflective properties of the coating.

In principle, it is possible to provide several correction layers with locally varying layer thicknesses within the coating. This can be expedient, for example, if the layer thicknesses required to correct imaging errors caused by production. Fluctuations are too large to be realized within a single intermediate layer. In general, however, it is preferred if exactly one intermediate layer contains a correction structure.

When determining the intermediate layer that is most suitable for the application of a correction structure, it must be taken into account that the intermediate layers are generally of different thicknesses, which limits the maximum thickness fluctuations from the outset. In addition, fluctuations in thickness do not have the same effects on the reflective properties of the layer system in all intermediate layers. In order to determine the most suitable intermediate layer for applying the correction structures, the following steps can be carried out, for example:

a) Computer-aided determination of an optimal coating;

b) successively reducing the layer thicknesses of the intermediate layers by a predetermined amount and determining the respective effect on the reflection properties of the coating by simulation;

c) Determination of the intermediate layers in which a reduction in the layer thickness has the least effect on the reflection properties. Once the possible intermediate layers have been determined, it must also be taken into account that the more intermediate layers can be applied at a higher temperature, the closer the intermediate layer containing a correction structure is to the final layer. This increases the mechanical stability and resistance to contamination of the entire coating.

For this reason, it is particularly preferred if only the outermost intermediate layer adjacent to the final layer contains a correction structure. If further intermediate layers with a constant layer thickness are applied to the element body underneath, this can be provided with a frame after the application of all layers with the exception of the final layer. Only at this stage of manufacture is the optical element installed and measured in the optical system. This allows all the intermediate layers, including the intermediate layer containing the correction structure, to be applied to the element body at high temperature, which has a favorable effect on the mechanical stability and resistance to contamination of the coating. Only the final layer is applied at a lower temperature, which does not significantly affect the stability and resistance to contamination of the entire coating. If only the second outermost intermediate layer contains a correction structure, the intermediate layer arranged above it must be applied at a lower temperature. Often, however, this second outermost intermediate layer has the property of being comparatively insensitive to fluctuations in the thickness or refractive index, so that fluctuations have only a relatively minor effect on the reflective properties of the layer system.

In the case of short-wave projection light and high-aperture projection objectives, the layer thicknesses of the coating can be designed, for example, such that the average layer thickness of the intermediate layer containing the correction structure is between 2 nm and 100 n, preferably between 10 nm and 50 nm.

The layer thickness fluctuations of the correction layer are then preferably between 0.1 nm and 50 nm and more preferably between 0.5 nm and 30 nm.

A locally varying layer thickness in an intermediate layer is preferably produced, as already mentioned above, by first applying the layer with a constant thickness and then removing material locally from the relevant intermediate layer. For this, for example, the known methods for material removal already mentioned above come into consideration. As an alternative to this, however, it is also possible to produce a locally varying layer thickness by applying the relevant intermediate layer directly with a locally varying layer thickness. So instead of first applying a layer with a constant layer thickness and then partially removing it again, the desired layer thickness distribution is immediately generated in this way. However, it must be taken into account that the need for correction must then have been determined beforehand. The optical element is therefore in this

Insert the case in a frame before the correction layer is applied and measure it. Consequently, in this production variant not all layers above the intermediate layer containing a correction structure, but also this intermediate layer must be applied even at a comparatively low temperature.

It is particularly preferred if the element body is introduced into a coating system with an outlet opening for dispensing a coating vapor. During the application of the intermediate layer containing a correction structure, a relative movement is generated between the element body and the outlet opening. In this way, the coating steam can be spatially directed over the surface to be coated. A locally higher layer thickness can be produced, for example, by the corresponding area being moved past the outlet opening several times. However, it is particularly preferred if the layer thickness of the intermediate layer containing the correction structure is varied by controlling the speed of the relative movement. The faster the outlet opening moves relative to the surface to be coated, the less the layer thickness with a constant steam flow.

Further features and advantages of the invention result from the following description of an exemplary embodiment with reference to the drawings. In it show:

FIG. 1 shows a basic illustration of a projection exposure system for microlithography, which can be used for the exposure of structures on wafers coated with photosensitive materials;

FIG. 2 shows a section through a lens provided with a coating;

Figure 3 is a plan view of a diaphragm shown in principle for targeted aspherization of the surface;

FIG. 4 shows a meridional section through a lens provided with a coating according to another exemplary embodiment; FIG. 5 shows an enlarged detail from the lens shown in FIG. 4;

Figure 6 shows a longitudinal section through a coating system in a schematic and not to scale.

FIG. 1 shows a projection exposure system 1 for microlithography. This serves to define structures by exposing a substrate coated with a photosensitive material. This generally consists predominantly of silicon and is referred to as wafer 2. The projection exposure system 1 can be used e.g. for the production of semiconductor components such as computer chips.

The projection exposure system 1 essentially consists of an illumination device 3, one

Device 4 for receiving and exact positioning of a mask provided with a lattice-like structure, a so-called reticle 5, by which the later structures on the wafer 2 are determined, a device 6 for holding, moving and exact positioning of the wafer 2 and an imaging device , namely a projection lens 7.

During the projection, the structures introduced into the reticle 5 are imaged on the wafer 2, in particular with a reduction in the structures a third or less of the original size. The requirements to be imposed on the projection exposure system 1, in particular on the projection objective 7, are in the range of a few nanometers.

After exposure has taken place, the wafer 2 is moved on, so that a large number of individual fields are each exposed on the same wafer 2 with the structure specified by the reticle 5. When the entire surface of the wafer 2 is exposed, it is removed from the projection exposure apparatus 1 and subjected to a number of chemical treatment steps, including a material removal which is generally carried out by etching. If necessary, several of these exposure and treatment steps are carried out in succession until a large number of computer chips have arisen on the wafer 2. Due to the gradual feed movement of the wafer 2 in the projection exposure system 1, this is often also referred to as a "stepper".

The illumination device 3 provides a projection beam 8, for example light or a similar electromagnetic radiation, required for imaging the reticle 5 on the wafer 2. A laser, for example, can be used as the source for this radiation. The radiation is shaped in the illumination device 3 via optical elements so that the projection beam 8 has the desired properties when it hits the reticle 5. Shafts, for example with regard to diameter, polarization and shape of the wavefront.

With the aid of the projection beam 8, an image of the reticle 5 is transferred from the projection objective 7 to the wafer 2 in a reduced size, as has already been explained above. The projection lens 7 consists of a large number of individual refractive and / or diffractive optical elements, such as e.g. Lenses, mirrors, prisms and end plates.

FIG. 2 shows a section through a lens 10 provided with a coating 9, which is installed together with other lenses in the projection objective 7 via a mount 11. The coating 9 can be applied to a surface 10a of the lens 10 before the lens 10 is installed in the mount or afterwards. The coating 9 can e.g. be formed as a vapor-deposited anti-reflective layer.

If the optical element is a mirror, the coating 9 can be designed as a highly reflective surface.

After the lens 10 has been inserted into the mount 11 and possibly also after it has been installed in the projection objective 7, the projection exposure system 1 is measured for image field accuracy. If it turns out that changes are required to optimize the image field the fit of one or more optical elements in the projection lens 7 can be corrected accordingly. It is also possible to correct the sum of all deformations of one or all of the lenses 10 on a lens surface 10a in whole or in part , This can be done, for example, by a local removal process on the surface 9a of the coating. For example, an ion beam ablation process can be used for this. Reactive ion etching is also possible.

When processing the surface 9a of the coating 9 in the removal process, it must of course be ensured that the thickness or thickness of the coating 9 is greater than the maximum removal. The maximum thickness to be removed is shown by dashed lines in FIG. 2 and is designated by reference number 9b. As can be seen, there is still sufficient thickness in this case for the coating 9 to be effective, e.g. as an anti-reflective coating.

In the above-described processing of one or both sides of the lens 10 via the previously applied coating 9, subsequent negative influences on the image field quality can be avoided in this way after a passport correction, since no further method steps are carried out on the lens 10. The coating process and also the correction process can also be used for standard lenses. As a material for the lenses 10 can, for example _. , Calcium fluoride or quartz glass can be used. The removal of the coating 9 can take place, for example, in a range from 1 nm to 10 nm.

FIG. 3 shows a mask 15 which is placed on the coating 9a to be processed. As can be seen, only two openings, namely an elliptical opening 13a and a circular opening 13b, are kept free. At these points there is a targeted removal or an order for local aspherization.

A change in the layer thickness and the refractive index can also be achieved by irradiation with high-intensity radiation of high intensity (e.g. i-line of a sodium vapor lamp at 365 nm). This results in a corresponding change in the optical path length and a corresponding image error correction of the projection lens.

A further, particularly preferred exemplary embodiment of the invention is explained below with reference to FIGS. 4 to 6.

Another lens suitable for installation in the projection objective 7 is shown in simplified form in FIG. 4 and is designated overall by 10 '. The lens 10 'has a plano-convex lens body 12 which is inserted into a lens frame 14. The lens frame 14 has fastening elements, not shown, with which the lens 10 'can be fastened and adjusted in the projection objective 7 or in another optical system.

The convexly curved surface 16 of the lens body 12 carries a layer system, designated overall by 18, which forms an anti-reflective coating. A similar layer system 19 is also applied to the opposite surface 17 of the lens body 12.

FIG. 5 shows an excerpt from the lens 10 ′, designated by 20 in FIG. 4, in the region of the convex surface 16 of the lens body 12 in an enlarged representation. This shows that the layer system 18 comprises a total of six layers 181 to 186 with different refractive indices. The five lower layers 181 to 185 are referred to below as intermediate layers and the outermost layer 186 as an end layer. Since such layer systems are known per se in the prior art, further details are not shown.

The layer thicknesses of the layers 181 to 186 to be measured perpendicular to the convex surface 16 are determined in such a way that the light incident on the coating 18 is reflected only to a very small extent. This applies not only to parallel light rays close to the axis, but also to those light rays that have greater incidence angle strike the lens 10 '. Such light rays are indicated at 21 in FIG. Large angles of incidence occur, for example, with lenses in high-aperture projection objectives of microlithographic projection exposure systems.

As can be seen in FIG. 5, the four lower intermediate layers 181 to 184 have different, but constant layer thicknesses within one layer. The same also applies to the end layer 186. Only the penultimate layer 185 below, ie the outermost intermediate layer, has a region 22 within which the layer thickness of the outermost intermediate layer 185 varies locally. The different layer thicknesses within the area 22 are generated by a location-dependent material removal of the thickness Δ from the intermediate layer 185, which otherwise has the layer thickness d ₀ . The thickness fluctuations within the area 22 represent a correction structure 23 with which imaging errors that are not rotationally symmetrical can also be compensated.

Since the layer thickness of the end layer 186 is constant over the entire extent of the end layer 186 and thus also in the vicinity of the area 22, a recess 28 is formed above the area 22 on an outside 26 of the coating 18, the waviness of which is the material removal in the outermost region Intermediate layer 185 corresponds. Light that is in the area of this recess 28 the lens 10 'strikes and the coating 18 passes through, due to the locally thinner correction layer 185, an imaging error-compensating phase change with respect to light which strikes the lens 10' away from the recess 28. The coating 18 prevents significant amounts of light from being reflected when entering the optically denser lens body 12 and from being lost to the optical system in which the lens 10 'is installed.

A possible method for producing the lens 10 'is described below.

First, the lens body 12 is manufactured and polished in a manner known per se. Then the five lower intermediate layers 181 to 185 are applied in succession, each with a constant layer thickness, the lens body 12 being heated to a temperature of approximately 200 ° C. Because of this comparatively high temperature, these five lower intermediate layers 181 to 185 are mechanically very stable and resistant to contamination.

In a further step, the lens body 12 with the five intermediate layers 181 to 185 applied thereon is inserted into the lens mount 14 and inserted and adjusted in the optical system, the lens 10 'of which is to be a component. The imaging errors of the optical system then become known in a manner known per se determined and a need for correction determined. This results in the shape and arrangement of the correction structure 23.

In a further step, in the area 22 of the outermost intermediate layer 185, so much material is removed in accordance with the specifications determined on the basis of the measurement of the lens 10 ′ that the correction structure 23 arises in the form of fluctuations in thickness. The material can be removed, for example, using methods known per se, such as ion beam etching.

After the material has been removed in the area 22 of the intermediate layer 185, the final layer 186 is finally applied to the outermost intermediate layer 185 in a further step. The lens body 12 with the intermediate layers 181 to 185 carried by it is only heated up to a temperature of below 60 ° C. since the lens body 12 is already accommodated in the lens frame 14. At a significantly higher temperature there would be a risk that the lens body 12 would permanently deform due to its greater thermal expansion than the lens frame 14.

As an alternative to the abovementioned removal of material, the different layer thicknesses of the outermost intermediate layer 185 can also be produced by a locally varying amount of material being applied to the intermediate layer during the coating process. layer 184 is applied. However, the need for correction is then to be determined beforehand, for which purpose the lens 10 ′ is to be inserted into the lens frame 14 and measured. In this case, therefore, not only the end layer 186 but also the correction layer 185 must be applied even at a comparatively low temperature.

FIG. 6 shows a highly simplified and not to scale sectional view of a coating system 30 with a vacuum chamber 32, in which an outlet 34 for a coating steam is arranged. The lens body 12 already encased in the lens frame 14 is arranged on an X-Y displacement table 26 on which the lens body 12 can be moved in the X and Y directions.

With constant steam flow from the outlet 34, the

Layer thickness can be varied locally by changing the travel speeds in the X and Y directions with the help of a control program. This leads to different lengths of stay, which individual areas of the surface to be coated do

Be exposed to steam flow. The longer a surface unit is exposed to the steam flow, the greater the layer thickness there.

A further possibility for generating a correction structure consists in a fluctuation in the refractive index in the instead of a local layer thickness fluctuation Insert intermediate layer 185. For this purpose, the intermediate layer 185 can be exposed to locally high-energy electromagnetic radiation or particle radiation before the application of the closing layer 186. This leads to a local change in the material structure and thus the refractive index of the intermediate layer 185.

Claims

claims

1. Optical element with an element body (12) and with one applied to the element body (12)

Coating (9; 18),

characterized in that

the coating (9; 18) contains at least one correction structure (23) through which the optical path length for light passing through is changed locally.

2. Optical element according to claim 1, characterized in that the correction structure (23) is formed by a region of the coating in which the coating (9; 18) has predetermined fluctuations in the coating thickness.

3. Optical element according to claim 1 or 2, characterized in that the correction structure is formed by a region of the coating (9; 18) in which the coating has predetermined fluctuations in the refractive index.

4. Optical element according to one of the preceding claims, characterized in that the coating has an outwardly facing closure layer (186) and one or more between the closure layer (186) and has intermediate layers (181 to 185) arranged on the element body (12), and that at least one of the intermediate layers (185) contains the correction structure (23).

5. Optical element according to claim 4, characterized in that the correction structure (23) is not rotationally symmetrical.

6. Optical element according to claim 4 or 5, characterized in that in all layers (181 to

184) of the coating (18), which do not contain a correction structure (23), the layer thickness is distributed constantly or rotationally symmetrically.

7. Optical element according to one of claims 4 to 6, characterized in that only the outermost intermediate layer (185) adjacent to the end layer (186) contains a correction structure (23).

8. Optical element according to one of claims 4 to 6, characterized in that only the second extreme

Intermediate layer (184) contains a correction structure (23).

9. Optical element according to one of claims 4 to 8, characterized in that the average layer thickness of the intermediate layer (185), which contains the correction structure (23), is between 2 nm and 100 nm, preferably between 10 nm and 50 nm.

10. Optical element according to one of the preceding claims, characterized in that the intermediate layer (185), which contains the correction structure (23), has local fluctuations in layer thickness, preferably between 0.1 nm and 50 nm, more preferably between 0, 5 nm and 30 nm.

11. Optical element according to one of the preceding claims, characterized in that the coating (18) is an anti-reflective coating.

12. Optical element according to one of claims 1 to 10, characterized in that the coating is a reflective coating.

13. Optical element according to one of the preceding claims, characterized in that the optical element is a lens (10; 10 ') of a projection lens

(7) a microlithographic projection exposure system (1).

14. A method for processing the surfaces of an optical element (10; 10 '), at least one surface (10a; 16) of the optical element (10; 10') being provided with a coating (9; 18),

characterized in that

in a first step the coating (9; 18) on the at least one surface (10a; 16) is applied, and that in a second step the coating (9; 18) is changed in its structure or in its composition such that the fit of the optical element (10; 10 ') is changed to optimize the image field becomes.

15. The method according to claim 14, characterized in that to change the structure of the coating

(9; 18) is processed in a removal process in the second step, and that in the first step the coating (9; 18) is applied in a thickness which is greater than the maximum removal occurring in the subsequent processing.

16. Method for processing the surfaces of an optical element (10; 10 '), at least one surface (10a; 16) of the optical element (10; 10') being provided with a coating (9; 18),

characterized in that

in a first step the coating (9; 18) is applied to the at least one surface (10a; 16), and in a second step the coating (9; 18) is locally irradiated with high-energy radiation of such a high intensity that the Refractive index of the coating (9; 18) at the irradiated point is corrected for image field optimization.

17. The method according to any one of claims 14 to 16, characterized in that for processing the coating (9; 18) particle beams are guided over the surface (10a; 16) of the coating (9; 18) to be processed.

18. The method according to claim 17, characterized in that the processing of the coating (9; 18) is carried out by means of a reactive ion etching process.

19. The method according to claim 17, characterized in that the processing of the coating (9; 18) is carried out by means of an ion beam ablation process (IBF process).

20. The method according to claim 16, characterized in that the coating (9; 18) is subjected to a doping process in the second step.

21. The method according to claim 16, characterized in that the coating (9; 18) is irradiated with i-line light of high intensity and compacted.

22. The method according to claim 21, characterized in that the coating (9; 18) is provided with a magnesium fluoride, aluminum oxide or zirconium oxide layer.

23. The method according to any one of claims 14 to 22, characterized in that with the coating

(9; 18) provided surface of the optical element (10; 10 ') for targeted processing with masks or screens (15) is covered.

24. The method according to any one of claims 14 to 23, characterized in that the optical element (10;

10 ') is a lens of a projection objective (7) of a microlithographic projection exposure system (1).

25. A method for producing an optical element (10 ') with a coating (18) applied to an element body (12), which has an outwardly facing end layer (186) and one or more between the end layer (186) and the element body (12 ) has arranged intermediate layers (185),

characterized by the following steps:

a) providing the element body (12);

b) generating at least one selected intermediate layer (185) which has a correction structure by means of which the optical path length for light passing through is changed locally;

c) applying the final layer (186).

26. The method according to claim 25, characterized in that the at least one selected intermediate layer

(185) has a locally varying layer thickness.

27. The method according to claim 26, characterized in that between the steps a) and b) further intermediate layers (181 to 184) with a constant or rotationally symmetrically distributed layer thickness are applied to the element body (12).

28. The method according to claim 26 or 27, characterized in that the locally varying layer thickness of the at least one selected intermediate layer (185) is produced by the at least one selected intermediate layer (185) initially applied with a constant layer thickness and then locally from the material at least one selected intermediate layer (185) is removed.

29. The method according to claim 28 when referring back to claim 27, characterized in that between the

Applying the at least one selected intermediate layer (185) and producing the locally varying layer thickness of the element body (12) is provided with a holder (14).

30. The method according to claim 29, characterized in that the optical element (10 ') between the verse hen is measured with the frame (14) and the generation of the locally varying layer thickness.

31. The method according to claim 27 and according to one of claims 28 to 30, characterized in that the temperature of the element body (12) when applying the further intermediate layers (181 to 184) and the at least one selected intermediate layer (185) is higher than the temperature of the element body (12) when each layer (186) arranged above the at least one selected intermediate layer (185) is applied.

32. The method according to any one of claims 25 to 27, characterized in that the at least one selected intermediate layer (185) is applied with a locally varying layer thickness.

33. The method according to claim 32, characterized in that the element body (12) is introduced into a coating system (30) with an outlet opening (34) for dispensing a coating vapor, and that during the application of the at least one selected intermediate layer (185) a relative movement between the element body (12) and the outlet opening (34) is generated.

34. The method according to claim 33, characterized in that the layer thickness of the at least one selected intermediate layer (185) is varied by controlling the speed of the relative movement.

35. The method according to any one of claims 25 to 34, characterized in that the final layer (186) is applied directly to the at least one selected intermediate layer (185).

36. The method according to any one of claims 25 to 34, characterized in that at least one further intermediate layer is applied to the at least one selected intermediate layer (185) before the application of the final layer (186).

37. The method according to any one of claims 25 to 36, characterized by the following steps:

a) computer-assisted determination of an optimal coating (18);

b) Successively reducing the layer thicknesses of the intermediate layers (181 to 185) by a predetermined one

Amount and determination of the respective effect on the reflection properties of the coating (18) by simulation;

c) determination of the intermediate layers in which a reduction in the layer thickness has the least effect on the reflection properties; d) Selection of the intermediate layer (185) determined in step c) that is closest to the final layer (186).

38. Projection objective for a microlithographic projection exposure system (1) with at least one optical element according to claim 13.

39. Microlithographic projection exposure system with at least one projection objective (7)

Claim 38.