DE102020209590A1 - Apparatus and method for polishing an optical element - Google Patents

Abstract

The invention relates to a device for polishing an optical element (1), with a mount (2) to accommodate the optical element (1), the mount (2) having an edge region (8) which has a surface (4 ) of the optical element (1) protrudes. A seal (5) arranged between the optical element (1) and the mount (2) is also provided, the mount (2) and the seal (5) being arranged around a polishing medium that can be applied to the surface (4) to be polished (9) to be bordered. A secondary fuse (10) is also provided which, together with the seal (5) and the socket (2), forms a channel (11) which is filled with a liquid (21).

Description

The invention relates to a device for polishing an optical element according to the preamble of claim 1.

The invention also relates to a method for polishing an optical element according to the preamble of claim 9.

The invention also relates to a projection exposure system for semiconductor lithography according to the preamble of claim 15.

In a known way, optical elements influence the properties of light waves interacting with them. In order to avoid undesirable structures in the resulting wavefronts, the surface of the optical elements must be precisely processed. For example, planar mirrors, concave mirrors, curved mirrors, convex lenses, concave lenses, convex-concave lenses, plano-convex lenses and plano-concave lenses may be mentioned as optical elements. Glass and silicon, among others, are known as materials for optical elements, in particular mirrors.

Lithography systems, in particular projection exposure systems, have a large number of optical elements. Particularly when using the optical elements with a microlithographic DUV (Deep Ultra Violet) projection exposure system and especially when using a microlithographic EUV projection exposure system, a particularly precise surface processing is necessary, since this is modulated by the optical elements, for example EUV mirrors On the one hand, light has a very small wavelength and thus the resulting wave fronts are disturbed by even the slightest processing errors on the optical element. On the other hand, the structures shown on the projection surface are very small and therefore also susceptible to the slightest processing errors on the optical element. The accuracy requirements for the optical element can therefore amount to fractions of nanometers.

Surface treatment by polishing is known from the general prior art.

In known computer-controlled polishing processes, CCP, a polishing medium, which can contain colloids, is applied to a surface of the optical element to be polished. Subsequently, a polishing tool is used in a polishing process in a computer-aided calculated manner to precisely remove the surface in certain areas to be polished. The duration of such a polishing process depends on the size of the surface to be polished, the material on which the surface to be polished is based and the precision requirements of the surface to be polished. Polishing times of hours to several days are not uncommon. An abrupt termination of the polishing process is disadvantageous and should be avoided in favor of a defined stopping of the polishing process, possibly lasting up to hours.

The polishing media used tend to dry on surfaces that have not been polished during the polishing process and can only be reversed with unacceptably great effort, provided they come into contact with these non-polished surfaces of the optical element. This can lead to the uselessness of the product. Furthermore, when the optical element is placed in a vacuum, less outgassing of contaminated surfaces is to be expected if these are polished. Therefore, surfaces to be polished should float permanently in a wet polishing bath until the end of the polishing process. Immediately after the end of the polishing process, the optical element must be removed from a polishing device and cleaned directly.

Compared to grinding media, common polishing media are more difficult to remove from unpolished surfaces.

To cover the entire surface of the optical element to be polished while at the same time minimizing contact between the polishing medium and surface areas of the optical element that are not to be polished, the prior art provides a mount with an associated seal that is suitable for the optical element. Here, the optical element is arranged in the mount in such a way that an edge region of the mount protrudes beyond the surface to be polished. The mount is sealed against the optical element by means of a seal, so that the mount, seal and surface of the optical element to be polished form an enclosure for receiving the polishing medium, the polishing medium located in the enclosure, especially if the polishing medium is flowable, the surface to be polished completely covered, since the edge area of the socket protrudes beyond the surface to be polished. If the surface to be polished is a mirror surface, the mirror surface floats in the polishing medium while the lengthy computer-controlled polishing process takes place on the surface to be polished. So surfaces outside the mirror must not be contaminated with the polishing medium.

However, it can also be provided that areas to be polished and areas not to be polished lie on one and the same surface. In particular, it can be desired that edge areas of a surface of a mirror are not polished while an inner area of the surface is to be polished.

A disadvantage of the solution known from the prior art is that if the sealing effect of the seal used fails, the polishing medium comes into contact with surface areas of the optical element that are not to be polished. The likelihood of seal failure increases the longer the polishing process takes. This is particularly the case when using a simple seal, which cannot provide a reliable and stable seal with polishing times of several days, sometimes up to weeks. Interrupting the polishing process to replace a failed seal is only possible with great effort.

The requirements for the longevity of the seal increase with the increase in the polishing time for new types of mirror.

The present invention is based on the object of creating a device for polishing which solves the disadvantages of the prior art, in particular to at least largely prevent contact between a polishing medium and surface areas of the optical element that are not to be polished, even during long polishing processes.

According to the invention, this object is achieved by a device with the features mentioned in claim 1.

The device according to the invention for polishing an optical element has a mount in order to receive the optical element, the mount having an edge region which protrudes beyond a surface of the optical element to be polished. A seal is arranged between the optical element and the mount, the mount and the seal being arranged to enclose a polishing medium that can be applied to the surface to be polished. According to the invention, a secondary seal is provided which, together with the seal and the socket, forms a channel which is filled with a liquid.

The present invention is also based on the object of creating a method for polishing which solves the disadvantages of the prior art, in particular at least largely preventing contact between a polishing medium and surface areas of the optical element that are not to be polished, even in long-lasting polishing processes.

According to the invention, this object is achieved by a method with the features mentioned in claim 9.

The present invention is also based on the object of creating a projection exposure system that solves the disadvantages of the prior art and, in particular, has optical elements that are manufactured in such a way that contact between a polishing medium and surface areas of the optical element that are not to be polished is also possible long-lasting polishing processes is at least largely prevented.

According to the invention, this object is achieved by a projection exposure system having the features mentioned in claim 15.

In the device according to the invention, a seal, together with a secondary seal and the socket, thus forms a channel which is filled with a liquid. The secondary seal significantly reduces the likelihood of contamination of surface areas that are not to be polished, since two seals instead of just one must fail so that the polishing medium can come into contact with surface areas of the optical element that are not to be polished. Because the channel is filled with a liquid according to the invention, if the seal fails with the secondary seal intact, it is difficult for the polishing medium to penetrate the channel already filled according to the invention. Furthermore, the penetrating polishing medium is diluted by the liquid in the channel. In an advantageous development of the device according to the invention, it can also be provided that the liquid has a greater density than the polishing medium, whereby mixing of the liquid and the polishing medium can be prevented and the polishing medium can penetrate through a layering with the polishing medium layered over the liquid can be prevented in the channel even with a defective seal.

If the polishing medium penetrates the channel due to a failure of the seal, it is diluted in the liquid and dries much more slowly on surface areas that are not to be polished.

In the event of failure of the secondary seal, the dilution of the polishing medium achieved by the liquid may be favored by a large volume of the liquid and thus of the channel in relation to the volume of the polishing medium used. The device according to the invention therefore considerably reduces the risk of contamination and the service life of the seal and the secondary seal formed sealing system compared with the previously known simple seal significantly increased.

Of course, provision can also be made to expand the device according to the invention in such a way that a tertiary seal, together with the secondary seal and the socket, forms a further channel. This series connection of seals to reduce the probability of failure of an overall sealing system is in principle only limited by geometric restrictions.

In an advantageous development of the invention, a device can be provided to exchange the liquid continuously or at intervals.

By means of the device for exchanging the liquid, any polishing medium which has penetrated the channel can be transported away from the channel or exchanged with the liquid, for example drained or sucked off. As a result of the rinsing carried out, the polishing medium can get into the wastewater together with the liquid. This reduces the risk of the polishing medium drying on to a surface area that is not to be polished. Edge areas of surfaces of the optical element that are not to be polished are not contaminated. Furthermore, a thinning effect is achieved with a smaller volume of the channel required.

The device for exchanging the liquid can also work continuously or at intervals. Continuous replacement has the advantage that the advantageous effects of dilution and removal of the polishing medium act permanently in the event of failure of the seal and / or the secondary seal. A device that works at intervals can be matched to the polishing process in its work intervals.

It can be advantageous to operate the device for exchanging the liquid in such a way that interval durations and pause durations are freely adjustable.

It can be advantageous if the device is a pump for exchanging the liquid. However, devices based on gravity, for example, can also be used.

Particularly advantageous in this context can be an embodiment in which the pressure gradient caused by the device for exchanging the liquid can be adjusted in such a way that contamination of the liquid with polishing medium in the event of failure of the seal is minimized as much as possible, but at the same time as little liquid as possible enters the enclosure space surrounding the polishing medium so as not to change the composition of the polishing medium. This may make it possible under certain circumstances to continue the polishing process despite the failure of the seal. This can be achieved, for example, by applying a pressure in the liquid that is increased by a certain pressure difference compared to the gravity pressure of the polishing medium in the area of the seal.

In addition to the device, a sensor can advantageously be provided which compares a volume flow flowing into the channel with a volume flow flowing out of the channel. If a difference between the outflowing and inflowing volume flow is detected, a negative value of the difference can, for example, indicate a loss of fluid due to failure of the secondary seal, while a positive value of the difference indicates an influx of polishing medium into the fluid due to failure of the seal, can suggest. A simple embodiment of such a difference determination provides a liquid reservoir for the exchange of the liquid. The fill level of the reservoir then shows a difference that has been accumulated over an observation period.

An advantageous development of the device according to the invention can provide a sensor in order to detect contamination of the liquid, in particular the presence of the polishing medium in the liquid.

If the sensor detects contamination of the liquid with polishing medium, this can indicate a failure of the seal. In this context, an advantageous embodiment can provide for a measurement of the conductivity of the liquid. If it is known that liquid contaminated with polishing medium has a different conductivity than non-contaminated liquid, a change in the conductivity of the liquid during the course of the polishing process can indicate contamination of the liquid with polishing medium and thus failure of the seal. Other embodiments can for example provide sensors for measuring light absorption, sensors for measuring light scattering, sensors for measuring density, sensors for microwave absorption and chromatographic sensors.

A sensor for measuring light absorption and / or light scattering appears to be advantageous, particularly when using colloid-containing polishing media in which colloids act as scattering centers. With a simple structure, including, for example, a light source that emits light that is transmitted through the medium, and a light sensor, for example a photodiode, the Detects the light emitted by the light source and transmitted through the medium and its intensity, an increase in a colloid concentration in the liquid can be detected under certain circumstances due to the resulting reduced light transmission. Such a structure can be advantageous in that no physical contact has to take place between parts of the measuring unit and the liquid for the measurement. This is particularly advantageous with regard to any harmful substances that may be used.

Of course, combinations of the named sensor types can also be provided to increase the measurement reliability.

In a particularly advantageous embodiment it can be provided that the liquid is ultrapure water.

Ultrapure water is understood to mean water with the least possible impurities, preferably the conductivity value should not be higher than 1 µS / cm at 25 ° C and the content of oxidizable material should not be higher than 1 mg / L, particularly preferably the conductivity value should not be higher than 0, 1 µS / cm at 25 ° C and the content of oxidizable matter not higher than 0.5 mg / L. In this context, ultrapure water is a polar solvent that is virtually free of contamination. The polishing medium can advantageously be absorbed by ultrapure water. The high degree of purity of the ultrapure water results in a correspondingly lower risk of contamination from the liquid on a surface that is not to be polished.

In an advantageous development, it can also be provided that the seal and / or the secondary seal are designed as seals that are suitable for clean rooms.

The advantage of seals suitable for clean rooms or, alternatively, EUV-approved seals or low-contamination, low-outgassing and low-abrasion seals, is that such seals release the smallest possible quantities of particles or gases into the environment. Such a configuration of the seals reduces the risk of contamination on the optical element and the risk of contamination which can be transported further through contact with the polishing medium and / or the liquid, for example on the entire surface to be polished. When the optical element is placed in a high vacuum, impurities, in particular through organic compounds such as oxidizable material, lead to outgassing processes which, among other things, impair the vacuum. In this context, it is particularly advantageous if the seals are silicone-free.

Furthermore, it can be provided that the seal and / or the secondary seal are designed as a full seal or as a hose seal.

A full seal is a type of seal in which a seal consists of sealing material over its entire cross-section. The advantage of such a full seal is that if the seal material is slightly damaged, the likelihood of seal failure is low, since a possible deformation of the seal by pressing the seal against the optical element, for example, has enough contact surface between the optical element and the seal despite the slight damage to the seal comes about to prevent seal failure.

A hose seal is a type of seal in which a seal does not consist of sealing material over its entire cross-section, but the inner area of the cross-section along the seal, the so-called core area of the seal, with air, gas, gas mixtures or a tensioning liquid to tension the seal is filled. This type of seal has the advantage that the seal can be in the unfilled state when it is attached between the mount and the optical element, and can thus take up less volume, which simplifies attachment. The seal can then be filled with air, gas, gas mixtures or a liquid and then assumes the geometry in which it can develop its sealing effect.

It can also be provided that the seal and / or the secondary seal is designed in such a way that a Pressure is generated which presses the seal or the secondary seal against the optical element. For this purpose, the seal or the secondary seal can preferably be designed as a sealing cord made of a solid material, which is displaced by the pressure or pressed against the optical element.

In the device according to the invention, a specific hose seal can also be used, in which the core area of the hose seal forms the channel filled with the liquid. With a sufficiently stable design of the outer area of the hose seal cross-section, two sections of the outer area of the hose seal cross-section thus fulfill the function of the seal and the secondary seal. The design should be sufficiently stable to ensure that in the event of a hose seal failure and the resulting loss of pressure, no change in volume of the hose seal occurs.

It can advantageously be provided that the holder is made of metal, glass, plastic, ceramic, glass ceramic, crystalline materials or composites.

Through a suitable choice of the material of the mount, the hardness properties of the mount can be selected in such a way that no damage occurs to the optical element in the event of an undesired contact between the mount and the optical element.

It is an advantage if the socket is suitable for clean rooms. Likewise, it is also conceivable that the mount is made of a different material with such hardness properties that no damage occurs to the optical element in the event of possible contact between the mount and the optical element.

In an advantageous embodiment it can be provided that the holder has at least one groove in order to at least partially accommodate the seal and / or the secondary seal.

Such an embodiment results in an advantageous guidance of the seal or the secondary seal, whereby these can be positioned exactly and are secured against slipping. Such an embodiment is particularly advantageous when placing the optical element in the mount if there is a relative movement between the optical element and the mount.

If the groove or the grooves are designed in such a way that the seal or the secondary seal is only partially received by the respective groove, this can have the advantageous effect that the seal or the secondary seal have sufficient contact area with the optical element. In particular, when the seal or secondary seal is compressed or jammed between the optical element and the mount, the contact surface can be enlarged through deformation of the seal or the secondary seal and thus the sealing effect can be increased. If the seal is completely received in the uncompressed state in the groove, such an improvement in the sealing effect is not to be expected.

In this context, an advantageous development of the device according to the invention is also conceivable in which the grooves accommodate the seal or the secondary seal in such a sealing manner that by introducing a gas or a liquid under a certain pressure into a groove channel formed by the groove and the seal is driven, the seal is driven out of the groove channel and pressed against the optical element. In this context, a further development can be particularly advantageous in which the seal resumes its starting position in the groove after the pressure prevailing in the groove channel has been adjusted to the atmospheric pressure. As a result, the assembly effort for the sealing system can be significantly reduced.

Also conceivable is a mount which has two parts which each enclose the optical element on one side and, after being joined together, enclose the optical element on its entire side. In this case, the at least one groove can accommodate the seal and / or the secondary seal after they have been joined.

An advantageous embodiment of the device can provide that a support surface is provided for supporting the optical element, which has a drain.

If the secondary seal fails, escaping liquid can flow out of the area of the optical element through the drain. This is particularly advantageous if the seal has already failed and liquid contaminated with the polishing medium escapes. The duration of the contaminated liquid in the area of the optical element and thus the risk of contamination of areas of the surface of the optical element that are not to be polished are minimized by the process. As a result of the drain, the possibly contaminated liquid can also be collected safely and in a defined manner, which is advantageous in particular with regard to ingredients of the polishing medium that may be hazardous to health.

An advantageous method for polishing an optical element is given by the features of claim 9.

The method for polishing according to the invention provides that the optical element is received in a mount in such a way that an edge region of the mount protrudes beyond a surface of the optical element to be polished, after which the mount is provided with a seal in such a way that the mount and the seal enclose the polishing medium that can be applied to the surface to be polished. Furthermore, the method according to the invention provides that the socket is provided with a secondary seal in such a way that a channel is formed between the seal and the secondary seal, after which the channel is filled with a liquid.

Features that have been described in connection with the device according to the invention can of course also be advantageously implemented for the method according to the invention - and vice versa. Furthermore, advantages that have already been mentioned in connection with the device according to the invention can also be understood in relation to the method according to the invention - and vice versa.

In an advantageous embodiment of the method, it can be provided that a leak test of the channel is carried out before the polishing medium is applied to the surface to be polished.

A leak test of the channel, which is carried out before the application of the polishing medium, can determine whether a seal failure is present or is to be feared even before the potential occurrence of contamination caused by the polishing medium. If this is the case, the sealing system can be repaired before the polishing process begins, or before the polishing medium is applied to the surface of the optical element. Without the aforementioned leak test, a seal failure may only be noticed during the polishing process, which makes repairing the sealing system more difficult and leads to an interruption of the polishing process.

In a particularly advantageous embodiment it can be provided that the leak test is carried out by introducing a gas, a test liquid or the liquid into the channel.

As an embodiment, it is particularly possible to introduce the gas, the test liquid or the liquid into the channel and then to inspect the area of the channel for escaping gas, escaping test liquid or escaping liquid. The use of a leakage sensor to detect a liquid leak, for example based on a conductivity measurement, can be particularly advantageous in this context. For example, a circuit attached to the optical element, preferably in the direction of flow of the exiting liquid, can be closed by escaping water, whereby a signal can be output which can indicate the presence of a leak. A test liquid can preferably be used which is particularly easy to detect with the leakage sensor, for example due to a particularly high conductivity. When filling the channel with a gas for leak testing, in a preferred embodiment, the gas can be introduced into the channel with a specific overpressure or a specific negative pressure compared to the surrounding atmosphere, after which the gas supply is shut off by means of a valve tap and the pressure curve of the gas pressure in the channel by means of a pressure measuring device can be tracked. If a drop in pressure can be observed over time, this can indicate a seal failure. The use of gas for leak testing also has the advantage that chemically particularly inert gases such as noble gases are available which do not lead to any contamination of the surface that is not to be polished, even if the seal fails.

An advantageous embodiment of the method can provide that the liquid flows into and out of the channel continuously or at intervals.

Likewise, in an advantageous embodiment of the method, it can be provided that contamination of the liquid, in particular the presence of the polishing medium in the liquid, is detected.

It is advantageous if the polishing process of the surface of the optical element to be polished is stopped in a defined manner if contamination is detected.

Since the polishing process - in order to avoid problems - can only be stopped at certain points in the process, it is advantageous if the process can proceed in the intended manner until such a point is reached, even after a failure of the seal has been detected. The development thus provides that after the detection of contamination, the polishing process is continued up to a defined stopping point provided for this purpose, while the interaction of the secondary seal and liquid prevents contamination of the optical element until the stopping point is reached. A particular advantage of the method results from the fact that reaching the stopping point in a defined manner can take several hours of process time. During such a period of time, if the seal fails without the method according to the invention, severe contamination of the optical element would result.

The optical element can in particular be an optical element of a lithography system, in particular a projection exposure system for semiconductor lithography, in particular an EUV projection exposure system. The optical element can be both an optical element of projection optics and an optical element of the lighting system, including an optical element of the radiation source, in particular also the collector.

The invention also relates to a lithography system, in particular a projection exposure system for semiconductor lithography, with an illumination system with a radiation source as well an optical system which has at least one optical element, at least one of the optical elements being at least partially processed using a method according to the invention and / or at least one of the optical elements being produced using a device according to the invention.

The optical element of the lithography system can in particular be an optical element, as already mentioned above.

The invention is particularly suitable for use with a microlithographic DUV (Deep Ultra Violet) projection exposure system and very particularly for use with a microlithographic EUV projection exposure system. A possible use of the invention also relates to immersion lithography.

Features that have been described in connection with the device according to the invention and the method according to the invention can of course also be advantageously implemented for the lithography system according to the invention, in particular the projection exposure system according to the invention for semiconductor lithography - and vice versa. Furthermore, advantages that have already been mentioned in connection with the device according to the invention and the method according to the invention can also be understood in relation to the lithography system, in particular the projection exposure system for semiconductor lithography - and vice versa.

In addition, it should be pointed out that terms such as “comprising”, “having” or “with” do not exclude any other features or steps. Furthermore, terms such as “a” or “that” which refer to a single number of steps or features do not exclude a plurality of features or steps - and vice versa.

Exemplary embodiments of the invention are described in more detail below with reference to the drawing.

The figures each show preferred exemplary embodiments in which individual features of the present invention are shown in combination with one another. Features of an exemplary embodiment can also be implemented separately from the other features of the same exemplary embodiment and can accordingly be easily combined with features of other exemplary embodiments by a person skilled in the art to form further meaningful combinations and subcombinations.

In the figures, functionally identical elements are provided with the same reference symbols.

• 1 eine EUV-Projektionsbelichtungsanlage;
• 2 eine DUV-Projektionsbelichtungsanlage;
• 3 eine immersionslithographische Projektionsbelichtungsanlage;
• 4 eine prinzipmäßige Draufsicht auf ein in einer Fassung angeordnetes optisches Element;
• 5 einen Querschnitt durch eine erfindungsgemäße Vorrichtung;
• 6 eine prinzipmäßige Darstellung einer Einrichtung zum Flüssigkeitsaustausch und eines Messsensors;
• 7 einen schematischen Querschnitt einer möglichen Ausführungsform der erfindungsgemäßen Vorrichtung mit einer bikonvexen Linse;
• 8 einen schematischen Querschnitt einer möglichen Ausführungsform der erfindungsgemäßen Vorrichtung mit einer bikonkaven Linse; und
• 9 einen schematischen Querschnitt einer möglichen Ausführungsform der erfindungsgemäßen Vorrichtung mit einer plankonvexen Linse.

They show schematically:

• 1 an EUV projection exposure system;
• 2 a DUV projection exposure system;
• 3 an immersion lithographic projection exposure system;
• 4th a principle plan view of an optical element arranged in a mount;
• 5 a cross section through a device according to the invention;
• 6th a basic representation of a device for fluid exchange and a measuring sensor;
• 7th a schematic cross section of a possible embodiment of the device according to the invention with a biconvex lens;
• 8th a schematic cross section of a possible embodiment of the device according to the invention with a biconcave lens; and
• 9 a schematic cross section of a possible embodiment of the device according to the invention with a plano-convex lens.

1 shows an example of the basic structure of an EUV projection exposure system 400 for semiconductor lithography to which the invention can be applied. In particular, the invention can be used by installing an optical element polished by means of the device according to the invention or the method according to the invention. A lighting system 401 the projection exposure system 400 has next to a radiation source 402 a look 403 for illuminating an object field 404 in one object level 405 on. A is illuminated in the object field 404 arranged reticle 406 , that of a reticle holder shown schematically 407 is held. A projection optics shown only schematically 408 serves to map the object field 404 in an image field 409 in one image plane 410 . A structure is imaged on the reticle 406 onto a light-sensitive layer in the area of the image field 409 in the image plane 410 arranged wafers 411 , that of a wafer holder also shown in detail 412 is held.

The radiation source 402 can EUV radiation 413 , in particular in the range between 5 nanometers and 30 nanometers, in particular 13.5 nm, emit. For controlling the path of the EUV radiation 413 optically differently designed and mechanically adjustable optical elements are used. The optical elements of the in 1 illustrated EUV projection exposure system 400 as an adjustable mirror in suitable embodiments mentioned below only by way of example.

The one with the radiation source 402 generated EUV radiation 413 is by means of an in the radiation source 402 integrated collector so that the EUV radiation 413 in the area of an intermediate focus plane 414 passes through an intermediate focus before the EUV radiation 413 on a field facet mirror 415 meets. According to the field facet mirror 415 becomes the EUV radiation 413 from a pupil facet mirror 416 reflected. With the help of the pupil facet mirror 416 and an optical assembly 417 with mirrors 418 , 419 , 420 become field facets of the field facet mirror 415 in the object field 404 pictured.

In 2 is an exemplary DUV projection exposure system 100 shown. The projection exposure system 100 has a lighting system 103 , a reticle day 104 said device for receiving and exact positioning of a reticle 105 , through which the later structures on a wafer 102 be determined, a wafer holder 106 for holding, moving and exact positioning of the wafer 102 and an imaging device, namely a projection lens 107 , with several optical elements 108 that over sockets 109 in a lens housing 140 of the projection lens 107 are kept on.

The optical elements 108 can be used as individual refractive, diffractive and / or reflective optical elements 108 such as B. lenses, mirrors, prisms, end plates and the like can be formed.

The basic functional principle of the projection exposure system 100 that provides that in the reticle 105 introduced structures on the wafer 102 can be mapped.

The lighting system 103 provides one for imaging the reticle 105 on the wafer 102 required projection beam 111 in the form of electromagnetic radiation. A laser, a plasma source or the like can be used as the source for this radiation. The radiation is in the lighting system 103 Shaped via optical elements so that the projection beam 111 when hitting the reticle 105 has the desired properties in terms of diameter, polarization, shape of the wavefront and the like.

By means of the projection beam 111 becomes an image of the reticle 105 generated and from the projection lens 107 correspondingly reduced on the wafer 102 transfer. The reticle 105 and the wafer 102 are moved synchronously, so that areas of the reticle are practically continuous during a so-called scanning process 105 on corresponding areas of the wafer 102 can be mapped.

In 3 is a third projection exposure system 200 exemplified in training as an immersion lithographic DUV projection exposure system. On the further background of such a projection exposure system 200 is for example on the WO 2005/069055 A2 referenced, the content of which is incorporated into the present description by reference; The exact functionality is therefore not discussed in detail at this point.

Can be seen, comparable to the DUV projection exposure system 100 according to 2 , a reticle day 104 through which the later structures on the wafer 102 that is on the wafer holder 106 or wafer table is arranged to be determined. The projection exposure system 200 the 3 also has several optical elements for this purpose, in particular lenses 108 and mirror 201 , on.

The method according to the invention and the device according to the invention are not aimed at optical elements of projection exposure systems 100 , 200 , 400 limited, in particular not to optical elements of projection exposure systems 100 , 200 , 400 with the structure described. However, the invention is particularly suitable for optical elements of projection exposure systems, in particular for mirrors of EUV projection exposure systems.

The description of the invention takes place in the exemplary embodiments with reference to optical elements of projection exposure systems, but the disclosure is to be understood in such a way that the method according to the invention or the device according to the invention can be used for any optical elements.

The following figures represent the invention only by way of example and in a highly schematic manner.

4th shows a basic representation of an optical element 1 which of a version 2 is recorded in plan view. The version 2 here has a raised edge area 8th with an upper face 3 on the one surface to be polished 4th of the optical element 1 towers. Between the frame 2 and the optical element 1 is the poetry 5 arranged.

The version 2 in the present embodiment is preferably made of a material suitable for clean rooms, in particular a material Cleanroom-compatible metal, glass, plastic, ceramic, glass ceramic, crystalline material or composite material.

5 shows a schematic cross section through an embodiment of the device according to the invention. In 5 is the optical element 1 designed as a frustoconical mirror, which has a mirror body 6th and a mirror body 7th having. The version 2 has an edge region designed as a hollow cylinder in the exemplary embodiment 8th on the surface to be polished 4th the optical element 1 towers. In the embodiment according to 5 is that between the optical element 1 and the frame 2 arranged seal 5 approximately toroidal, with the socket 2 and the seal 5 are suitably arranged to put an on the surface to be polished 4th Applicable polishing medium 9 to border.

According to the invention is a secondary seal 10 provided the one with the seal 5 and the frame 2 a channel 11 that trains with a liquid 21 is filled.

In the exemplary embodiment, the secondary fuse is 10 is approximately toroidal, but the exemplary embodiment is not to be understood as being restricted to this.

The seal 5 and the secondary seal 10 are preferably designed as cleanroom-compatible seals in the exemplary embodiment.

The embodiment according to 5 shows that the version 2 a groove 12th identifies to the seal 5 at least partially to accommodate, as well as a groove 12th to the secondary seal 10 at least partially. In the exemplary embodiment, the grooves extend 12th in the the optical element 1 facing surface of the socket 2 completely circumferential. The seal 5 and the secondary seal 10 are from the groove 12th each only partially recorded. By compressing the seal 5 or the secondary seal 10 between the frame 2 and the optical element 1 a deformation effect occurs, leading to an approximately elliptical cross-section of the seal 5 or the secondary seal 10 leads in the embodiment shown.

The seal 5 and the secondary seal 10 are designed as inflatable seals in the exemplary embodiments.

Furthermore shows 5 a support surface 13th for supporting the optical element 1 , the one, executed in the embodiment as a bore, drain 14th having.

6th shows in principle a structure of a further development of the device according to the invention, wherein a device, designed as a pump in the example shown, is used 15th to exchange the liquid 21 by means of hoses 16 with the channel 11 connected to the liquid 21 to be exchanged continuously or at intervals.

A device for pressure measurement, with which the polishing medium is applied before the polishing medium is applied, is not shown, but is optionally possible 9 on the surface to be polished 4th a leak test of the sewer 11 is carried out. In particular by the fact that a gas, a test liquid or the liquid 21 in the canal 11 is introduced.

Furthermore, in the embodiment according to 6th a sensor designed as an ammeter 17th shown to the liquid for contamination, in the exemplary embodiment on the presence of the polishing medium 9 which is the conductivity of the liquid 21 would increase to investigate.

In particular, the presence of the polishing medium increases 9 the conductivity of the liquid 21 , since this is preferably provided as ultrapure water in the exemplary embodiment.

Not shown, but preferably provided, is a control loop by means of which a polishing process of the surface to be polished is carried out 4th of the optical element 1 is stopped in a defined manner if contamination is detected.

7th shows schematically a cross section of a possible further embodiment of the device according to the invention. The optical element 1 is here as a biconvex lens 18th educated. The seal 5 and the secondary seal 10 are on areas of convex surfaces of the biconvex lens that are not to be polished 18th appropriate. The seal 5 and the secondary seal 10 form with the frame 2 the channel 11 for the liquid 21 .

8th shows schematically a cross section of a possible further embodiment of the device according to the invention. The optical element 1 is here as a biconcave lens 19th educated. the poetry 5 and the secondary seal 10 are on a lateral surface of the biconcave lens 18th appropriate. The seal 5 and the secondary seal 10 form with the frame 2 the channel 11 for the liquid 21 .

9 shows schematically a cross section of a possible embodiment of the device according to the invention. The optical element 1 is called a plano-convex lens 20th educated. The seal 5 and the secondary seal 10 are on a lateral surface of the plano-convex lens 18th appropriate. The seal 5 and the secondary seal 10 form with the frame 2 the channel 11 .

In the case of the optical element 1 it can in particular be an optical element of a lithography system, in particular a projection exposure system 100, 200, 400 for semiconductor lithography, in particular an EUV projection exposure system 400 Act. In the case of the optical element 1 in particular, it can be both an optical element 1 a projection optics 408 as well as an optical element 1 of the lighting system 401 , including an optical element of the radiation source 402 , in particular also act the collector.

List of reference symbols

1

Optical element

2

Version

3

Face of the socket

4th

Surface to be polished

5

poetry

6th

Mirror body

7th

Mirror body

8th

Edge area of the frame

9

Polishing medium

10

Secondary seal

11

channel

12th

Groove

13th

Support surface

14th

sequence

15th

Exchange facility

16

hose

17th

sensor

18th

Biconvex lens

19th

Biconcave lens

20th

Plano-convex lens

21

liquid

100

Projection exposure system

102

Wafer

103

Lighting system

104

Reticle days

105

Reticle

106

Wafer holder

107

Projection lens

108

Optical element

109

Version

111

Projection beam

140

Lens housing

200

Projection exposure system

201

mirrors

400

Projection exposure system

401

Lighting system

402

Radiation source

403

optics

404

Object field

405

Object level

406

Reticle

407

Reticle holder

408

Projection optics

409

Field of view

410

Image plane

411

Wafer

412

Wafer holder

413

EUV radiation

414

Intermediate focus plane

415

Field facet mirror

416

Pupil facet mirror

417

Optical assembly

418

mirrors

419

mirrors

420

mirrors

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• WO 2005/069055 A2 [0084]

Claims (15)

Device for polishing an optical element (1, 18, 19, 20, 415, 416, 418, 419, 420, 108, 201), with a mount (2), around the optical element (1, 18, 19, 20, 415, 416, 418, 419, 420, 108, 201), the mount (2) having an edge region (8) which has a surface (4) to be polished of the optical element (1, 18, 19, 20, 415 , 416, 418, 419, 420, 108, 201), and with one between the optical element (1, 18, 19, 20, 415, 416, 418, 419, 420, 108, 201) and the mount (2 ) arranged seal (5), wherein the holder (2) and the seal (5) are arranged to enclose a polishing medium (9) which can be applied to the surface (4) to be polished, characterized in that a secondary seal (10) is provided, which with the seal (5) and the socket (2) forms a channel (11) which is filled with a liquid (21). Device according to Claim 1 , characterized in that a device (15) is provided to exchange the liquid (21) continuously or at intervals. Device according to one of the Claims 1 or 2 , characterized in that at least one sensor (17) is provided in order to detect contamination of the liquid (21), in particular the presence of the polishing medium (9) in the liquid (21). Device according to one of the Claims 1 until 3 , characterized in that the liquid (21) is ultrapure water. Device according to one of the Claims 1 until 4th , characterized in that the seal (5) and / or the secondary seal (10) are designed as cleanroom-compatible seals. Device according to one of the Claims 1 until 5 , characterized in that the socket (2) is made of metal, glass, plastic, ceramic, glass ceramic, crystalline materials or composites. Device according to one of the Claims 1 until 6th , characterized in that the holder (2) has at least one groove (12) to at least partially accommodate the seal (5) and / or the secondary seal (10). Device according to one of the Claims 1 until 7th , characterized in that a support surface (13) for supporting the optical element (1, 18, 19, 20, 415, 416, 418, 419, 420, 108, 201) is provided, which has a drain (14). Method for polishing an optical element (1, 18, 19, 20, 415, 416, 418, 419, 420, 108, 201), after which the optical element (1, 18, 19, 20, 415, 416, 418, 419 , 420, 108, 201) is received in a mount (2) in such a way that an edge region (8) of the mount is a surface (4) to be polished of the optical element (1, 18, 19, 20, 415, 416, 418, 419, 420, 108, 201), after which the mount (2) is provided with a seal (5) in such a way that the mount (2) and the seal (5) have a polishing medium (4) that can be applied to the surface to be polished (4). 9), characterized in that the socket (2) is provided with a secondary seal (10) in such a way that a channel (11) is formed between the seal (5) and the secondary seal (10), after which the channel (11) is filled with a liquid (21). Procedure according to Claim 9 , characterized in that a leak test of the channel (11) is carried out before the polishing medium (9) is applied to the surface (4) to be polished. Procedure according to Claim 10 , characterized in that the leak test is carried out by introducing a gas, a test liquid or the liquid (21) into the channel (11). Procedure according to Claim 9 , 10 or 11 , characterized in that the liquid (21) flows continuously or at intervals into and out of the channel (11). Method according to one of the Claims 9 until 12th , characterized in that contamination of the liquid (21), in particular the presence of the polishing medium (9) in the liquid (21), is detected. Procedure according to Claim 13 , characterized in that a polishing process of the surface to be polished (4) of the optical element (1, 18, 19, 20, 415, 416, 418, 419, 420, 108, 201) is stopped in a defined manner when a contamination is detected. Projection exposure system (100, 200, 400) for semiconductor lithography with an illumination system (103, 401) with a radiation source (402) and optics (107, 403, 408), which have at least one optical element (1, 18, 19, 20, 415, 416, 418, 419, 420, 108, 201), at least one of the optical elements (1, 18, 19, 20, 415, 416, 418, 419, 420, 108, 201) at least partially using a method after one of the Claims 9 until 14th is processed and / or at least one of the optical elements (1, 18, 19, 20, 415, 416, 418, 419, 420, 108, 201) using a device according to one of Claims 1 until 8th is made.

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