WO2009033639A2

WO2009033639A2 - Method for cleaning vacuum chambers for extreme uv lithography devices

Info

Publication number: WO2009033639A2
Application number: PCT/EP2008/007384
Authority: WO
Inventors: Dieter Kraus; Dirk Heinrich Ehm
Original assignee: Carl Zeiss Smt Ag
Priority date: 2007-09-14
Filing date: 2008-09-10
Publication date: 2009-03-19
Also published as: WO2009033639A3; DE102008041628A1

Abstract

In order to be able to clean and, if appropriate, also passivate a vacuum chamber (30) efficiently from contamination, it comprises a radiation source (31), which can in particular generate high-energy radiation (32). The irradiation is carried out with gradually increasing energy. In order to protect a multilayer mirror (35) against contamination during the irradiation, a protection element (37) is provided, which is mounted in a displaceable manner on a rail (39) and can be displaced out of a basic position (P2) into a protection position (P1) in front of the multilayer mirror (35).

Description

Method for cleaning vacuum chambers and vacuum chambers

Field of the invention

The present invention relates to a method for cleaning vacuum chambers, in particular of EUV lithography devices, wherein a place inside the vacuum chamber is exposed to radiation, and to a method for cleaning vacuum chambers with a reflective optical element, in particular of EUV lithography devices, wherein a place inside the vacuum chamber is exposed to radiation. Furthermore, the invention relates to a vacuum chamber, in particular for use in an EUV lithography device, in which a radiation source and a reflective optical element are arranged. Moreover, the invention relates to an EUV device with such a vacuum chamber.

Background and prior art

In EUV lithography devices, reflective optical elements for the extreme ultraviolet (EUV) or soft x-ray wavelength range (e.g. wavelengths between approx. 5 nm and 20 nm) such as for example photomasks or multilayer mirrors are used for the lithography of semiconductor components. Since EUV lithography devices as a rule comprise a plurality of reflective optical elements, the latter must exhibit a reflectivity as high as possible in order to ensure a sufficiently high total reflectivity. The reflectivity and the lifetime of the reflective optical elements can be reduced by contamination of the optically used reflective face of the reflective optical elements, which arises due to the shortwave radiation together with residual gases in the operating atmosphere. Since a plurality of reflective optical elements are usually arranged behind one another in an EUV lithography device, even fairly small contaminations on each individual reflective optical element have a fairly substantial effect on the total reflectivity.

The contamination in the gas phase should always lie below specific threshold values in vacuum chambers for Eϋv lithography, because otherwise the contamination from the gas phase interacts with the incident radiation in the EUV to soft x-ray wavelength range during the irradiation process and is deposited on the optically used faces of the reflective optical elements.

The occurrence of contamination is particularly problematic when a vacuum chamber of an EUV lithography device is commissioned for the first time by irradiation with EUV radiation. The assembly of EUV lithography devices often takes up to several weeks, during which a sufficient freedom from contamination cannot be guaranteed or can only be so at very great expense. It is true that the contamination can be kept as low as possible by heating and plasmatization of all the installed parts. However, during commissioning by direct irradiation of the surfaces with EUV radiation as well as by scattered light, a marked increase in contamination in the residual gas, caused in particular by induced desorption of contaminants, is brought about inside vacuum chambers of the EUV lithography device. This contamination, for its part, causes a contamination of the surfaces of the reflective optical elements, and this has a negative effect on their reflectivity. This problem of spreading contamination can also occur during the recommissioning of EUV lithography devices following maintenance work.

Summary of the invention

It is an object of the present invention to provide a possible way of cleaning vacuum chambers, wherein subsequent contamination during irradiation with EUV radiation in the vacuum chamber is avoided as far as possible.

This object is achieved by a method for cleaning vacuum chambers, in particular as part of EUV lithography devices, wherein a place inside the vacuum chamber is exposed to radiation, the energy of the radiation gradually being increased.

It has turned out that especially carbon-containing contamination such as for example polymers and long-chain hydrocarbons can be removed particularly effectively by being irradiated one after the other with energies at different levels. In the first range of lower energy, an amount of energy is supplied to the molecules, which is such that they transfer at least partially into the gas phase and can be pumped away. In a range of medium energy, bonds inside the molecules that have not yet transferred into the gas phase are broken, so that smaller molecular fragments are formed, which for their part transfer into the gas phase and can be pumped away. In a range of high energy, the still remaining molecules and molecular fragments are split into individual atoms or groups of atoms, which either also transfer into the gas phase, or in the case of carbon are deposited as a graphite- or diamond-like layer on the adjacent surfaces and thus effectively passivate them.

The effect of the method proposed here, therefore, is that the greatest possible quantity of contamination, especially in the form of polymers and long-chain hydrocarbons, is removed and any residues not pumped away are converted by the supply of high energy in such a way that they act in a passivating manner and do not cause subsequent outgassing. If EUV radiation is irradiated into a vacuum chamber cleaned in this way, the probability of a contamination of the residual gas atmosphere and moreover any re-contamination of surfaces inside the vacuum chamber such as the surface of reflective optical elements due to interaction of EUV radiation with surfaces inside the vacuum chamber is reduced to a minimum.

Furthermore, a particular advantage consists in the fact that, compared to irradiation of constantly high energy, any passivating carbon layer that may be formed is so thin that the reflectivity would only be slightly impaired even in the event of deposition on the reflective surface of a reflective optical element, which would be compensated for by the passivation effect. In the case of irradiation with constantly high energy, the whole of the contamination present would be converted into a passivating layer which would be correspondingly thicker. Both electromagnetic radiation and beams or atmospheres of charged particles can be used as radiation.

Furthermore, the object is achieved by a method for cleaning vacuum chambers with a reflective optical element, in particular of EUV lithography devices, whereby a place inside the vacuum chamber is subjected to high-energy radiation, the reflective optical elements being covered during the irradiation.

In this variant of the cleaning method, internal surfaces of the vacuum chamber are immediately irradiated with radiation in the energy range that leads to splitting up of the contamination into individual atoms, which especially in the case of carbon are deposited as a passivating protection layer on the surfaces inside the vacuum chamber, whilst remaining elements go into the gas phase and are pumped away. In order to protect reflective optical elements present in the vacuum chamber, the latter are covered by a protection element. It is assumed that a vacuum is to be applied to the vacuum chamber for a high-energy irradiation especially with charged particle beams, so that the conditions inside the vacuum chamber can be modelled as a molecular or atomic flow and a geometric shading of reflective optical elements is already sufficient in its protective function.

During the cleaning, in particularly preferred embodiments, the energy of the radiation is gradually increased and one or more reflective optical elements present in the vacuum chamber are covered during the irradiation. This is particularly advantageous in the case of vacuum chambers comprising very sensitive reflective optical elements, with which even a thin passivation layer would excessively impair their reflectivity.

This object is also achieved by a method for protecting a reflective optical element inside a vacuum chamber, in particular as part of an EUV lithography device, the reflective optical element being covered in the case of increased contamination.

This method is particularly advantageous if, for example, contaminations increased due to operational malfunctions are detected inside the vacuum chamber. In order to prevent contamination of the reflective optical element thus caused, the latter is covered.

Moreover, the object is achieved by a vacuum chamber, especially for use in an EUV lithography device, in which a radiation source and a reflective optical element are arranged, the vacuum chamber comprising a protection element, which is movable between the radiation source and the reflective optical element.

The proposed vacuum chamber permits the cleaning of the interior of the vacuum chamber free from contamination by irradiation of the contamination, in order to transfer it into the gas phase and pump it away or to convert it into coating material for a surface passivation, without the reflectivity of reflective optical elements inside the vacuum chamber being impaired. This is because, if need be, the provided protection element can be moved between the radiation source and the reflective optical element.

In preferred embodiments, the radiation source is constituted in such a way that the energy of the radiation can be gradually increased, in order in the first place to desorb contaminating molecules, to split them into fragments at higher energies and into atoms at high energies, in order to pump away the greatest possible part of the contamination.

Moreover, the object is achieved by an EUV lithography device, which comprises a vacuum chamber as just described.

Advantageous embodiments can be found in the dependent claims.

Brief description of the Figures The present invention will be explained in greater detail by reference to an example of a preferred embodiment. In the Figures:

Figure 1 shows schematically an embodiment of an EUV lithography device with an illumination system and a projection system;

Figure 2a shows schematically a first embodiment of a vacuum chamber with a first variant of a protection element;

Figure 2b shows schematically a first embodiment of a vacuum chamber with a second variant of a protection element;

Figures 2c-e show schematically a first embodiment of a vacuum chamber with a third variant of a protection element;

Figure 3a shows schematically a second embodiment of a vacuum chamber with a first variant of a protection element;

Figure 3b shows schematically a second embodiment of a vacuum chamber with a second variant of a protection element;

Figures 4a, b show energy curves for the operation of radiation sources;

Figures 5-7 show flow diagrams in respect of the various embodiments of the method for cleaning vacuum chambers; and

Figure 8 shows a flow diagram in respect of an embodiment of the method for protecting a reflective optical element.

Detailed description of the invention

Figure 1 represents schematically an EUV lithography device 10. Essential components are beam shaping system 11 , illumination system 14, photomask 17 and projection system 20. EUV lithography device 10 is operated under vacuum conditions, in order that the EUV radiation is absorbed as little as possible in its interior. A plasma source or also a synchrotron can be used as radiation source 12. The emitted radiation in the wavelength range of approx. 5 nm to 20 nm is first bundled in collimator 13b. Moreover, the desired operating wavelength is filtered out by varying the angle of incidence with the aid of a monochromator 13a. In the stated wavelength range, collimator 13b and monochromator 13a are usually constituted as reflective optical elements. Collimators are often reflective optical elements formed saucer-shaped, in order to achieve a focusing or collimating effect. The reflection of the radiation takes place at the concave face, a multilayer system often not being used on the concave face for the reflection since a wavelength range as wide as possible is intended to be reflected. The filtering-out of a narrow wavelength band by reflection takes place at the monochromator, often with the aid of a grid structure or a multilayer system.

The operating beam prepared in beam shaping system 11 with regard to wavelength and spatial distribution is then introduced into illumination system 14. In the example shown in Figure 1 , illumination system 14 comprises two mirrors 15, 16, which in the present example are constituted as multilayer mirrors. Mirrors 15, 16 convey the beam onto photomask 17, which has the structure that is intended to be imaged on wafer 21. Photomask 17 is also a reflective optical element for the EUV and soft wavelength range, which is exchanged depending on the production process. With the aid of projection system 20, the beam reflected by photomask 17 is projected onto wafer 21 and the structure of the photomask is thus imaged onto it. In the example shown, projection system 20 comprises two mirrors 18, 19, which in the present example are also constituted as multilayer mirrors. It should be pointed out that both projection system 20 and illumination system 14 can also each comprise only one or also three, four, five or more mirrors.

Both beam shaping system 11 as well as illumination system 14 and projection system 20 are constituted as vacuum chambers, since multilayer mirrors 15, 16, 18, 19, in particular, can only be operated in a vacuum. Otherwise, excessive contamination would be deposited on their reflective face, which would lead to an excessive deterioration of their reflectivity.

Even with great care, the dragging-in of contamination during assembly of the individual vacuum chambers and installation and adjustment of the multilayer mirrors, during assembly of the vacuum chambers in the EUV lithography device and during maintenance work, when the vacuum chambers have to be opened, cannot be prevented or can be so only at very great expense. Especially during the initial commissioning following assembly of the. EUV lithography device through irradiation with an EUV radiation, but also during the commissioning after maintenance work, contamination dragged-in due to interaction with the EUV radiation can transfer into the residual gas phase and can be deposited from there on other surfaces inside the respective vacuum chamber. Contamination is particularly harmful which is deposited on the reflective face of reflective optical elements such as for example multilayer mirrors and which can thus significantly impair the imaging behaviour of the respective optical elements. In the presence of contamination on the reflective optical elements, it is no longer possible to guarantee that the structure defined by mask 17 will be imaged correctly on wafer 21 or on another object to be structured.

In order to be able to clean the vacuum chambers efficiently before commissioning, radiation sources 22, 23 are provided both on illumination system 14 and also on projection system 20 in the example shown in Figure 1. Radiation sources 22, 23 preferably provide directed radiation. In the case of electromagnetic radiation, which is provided for example by lamps, this can be guaranteed by suitable diaphragms at the radiation source. Halogen lamps are used with particular preference, which provide in particular ultraviolet (UV) radiation.

Halogen lamps also have the advantage that their emission spectrum is shifted to higher energies by increasing their input voltage. This corresponds to a shift of the emission spectrum to shorter wavelengths. If use is additionally made of mirrors or grid structures, the generated UV radiation can be directed to arbitrary places inside respective vacuum chambers 14, 20, in order to clean the surface there free from contamination. It is also possible to provide a plurality of radiation sources with different emission spectra, which supplement one another in their effect or the energy ranges of their radiation. If need be, a radiation source can also be provided in beam shaping system 11 for cleaning purposes.

Apart from electromagnetic radiation, charged particle beams are also suitable for removal of contamination. Electron beams are particularly preferred, since electron beam sources can easily be obtained in a variety of designs. It is also possible with charged particle beams, by increasing the input voltage of the particle beam source, to increase the energy of the particle beam and thus to adjust the radiation energy with which the contamination is to be irradiated. If magnetic fields and/or electric fields are also applied, charged particle beams can also be readily directed to places inside respective vacuum chambers 14, 20, in order to clean places, which are difficult to access, or to passivate them by deposits of graphite- or diamond-like carbon layers. In the example shown in Figure 1 , radiation source 23 in projection system 20 is a particle beam source, at the output whereof a magnetic field is applied in order to direct the charged particle beam (indicated by the broken line) onto the side wall. Especially carbon-containing contamination such as for example polymers or long-chain hydrocarbons can be particularly effectively removed by being irradiated one after the other with energies at different levels. In a range of lower energy, an amount of energy is first supplied to the molecules such that they transfer at least partially into the gas phase and can be pumped away. In a range of medium energy, bonds inside the molecules that have still not transferred into the gas phase are broken, so that smaller molecular fragments are formed, which for their part transfer into the gas phase and can be pumped away. In a range of high energy, the still remaining molecules and molecular fragments are split up into individual atoms, which either also transfer into the gas phase or, in the case of carbon, are deposited as a graphite- or diamond-like layer especially on the immediately adjacent surfaces and thus effectively passivate the latter.

In order to protect reflective optical elements present in the vacuum chambers of an EUV lithography device 10 during the cleaning irradiation, protection elements 24, 25, 26, 27 are provided, which are shown in Figure 1 schematically in a position between radiation source 22, 23 and respective adjacent mirror 15, 16, 17, 18. In order not to disrupt the operation of EUV lithography device 10 after the cleaning, in particular not to project into the beam path of the EUV radiation, they are designed movable or removable.

Protection elements 24, 25, 26, 27 can also be used to protect respective mirrors 15, 16, 17, 18 against mechanical effects during transport, assembly or maintenance of EUV lithography device 10 or individual parts such as for example illumination system 14 or projection system 20. They can also be used for protection against impurities or contamination during assembly or maintenance work. Particularly preferably, they are used, if an increased contamination is detected during operation, in order to protect the mirrors against contamination. Any methods can be used, such as for example residual gas analysis, for the detection of contamination inside an EUV lithography device 10 or individual parts such as for example illumination system 14 or projection system 20. It is advantageous to provide one or more sensors for contamination and to couple the latter with the protection elements in such a way that, in the case of suddenly increased contamination, such as can occur for example during operational malfunctions, the protection elements can be arranged between the radiation source and the respective mirror. In the case of a plurality of sensors, which are located at different places inside EUV lithography device 10 or in different vacuum chambers such as illumination system 14 or projection system 20, the protection elements protecting the mirrors located in the vicinity of the sensor, which has detected an increased contamination, can be controlled selectively.

In order to be able make effective use of a charged particle beam, in particular an electron beam, a vacuum of approx. 10^"5 mbar or better should advantageously prevail in the respective vacuum chamber. A vacuum is also advantageous with the use of electromagnetic radiation, preferably UV radiation. The conditions inside the vacuum chamber during the cleaning irradiation can thus be modelled as a molecular or atomic flow and a geometric shading of reflective optical elements is therefore sufficient in its protective function. The reflective optical elements are protected not only against deposits of graphite- or diamond-like carbon layers, but also against molecules or molecular fragments that have transferred into the gas phase, which could strike the reflective face of a reflective optical element.

Figures 2a, b and 3a, b show schematically, by way of example, two embodiments of -vacuum chambers 30 with in each case two different variants of protection elements.

Vacuum chamber 30 shown in Figures 2a,b comprises an electron beam source 31 and a reflective optical element in the form of a multilayer mirror 35, which is fixed by means of a mirror holder 36 to vacuum chamber 30. In order to protect multilayer mirror 35 during the irradiation of a place inside vacuum chamber 30 with an electron beam 32, a cover 37 (Figure 2a) or 40 (Figure 2b) is provided. Cover 37 or 40 is mounted on a rail 39 by means of a holder 38 (Figure 2a) or 41 (Figure 2b) respectively. By being displaced on rail 39, cover 38 or 40 can be moved out of a basic position at P2 inside vacuum chamber 30 into a protection position at P1 between radiation source 31 and multilayer mirror 35.

Covers 37 and 40 are constituted essentially plate-shaped in order to produce a geometrical shading with a molecular or atomic flow. For this purpose, the area of covers 37 or 40 is selected greater than the area of the side of multilayer mirror 35 facing radiation source 31. Advantageously, the precise dimensioning of covers 37, 40 depends on the distance from multilayer mirror 35. The distance of a cover from a mirror is preferably calculated depending on how great is the probability of finding charged particles such as electrons, molecular fragments or radicals as well as desorbed contamination molecules to be in the region between cover and mirror. For example, the distance can be selected such that the probability of finding these particles to be in the region between cover and mirror does not amount to more than 5%. Depending on the sensitivity of the mirror to be protected and according to the reactivity of the particles to be expected, a higher or lower probability can be selected as a threshold value. The probability of finding these particles to be in the region between cover and mirror can be determined on the basis of the assumption of a molecular or atomic flow and depends, amongst other things, on the geometrical conditions inside the vacuum chamber during the irradiation, on the nature and energy of the beam and the nature or composition of the contamination to be removed.

In order to achieve a particularly efficient protection of multilayer mirror 35, an additional cover 37 or 40 can be provided at position P3, in order to avoid contamination or damage due to secondary radiation. This is from radiation energies which lead to an energy input of approx. 5 eV, in particular 10 eV and over into the contamination to be removed. In contrast to cover 37 from Figure 2a, cover 40 from Figure 2b is angled off. This lowers somewhat the probability of finding particles to be in the region between cover 40 and multilayer mirror 35. In particular, however, it increases the suitability of cover 40 as a mechanical protection for multilayer mirror 35. Overall, it is advantageous to use covers 37, 40 in position P1 and if appropriate also P3 as a mechanical protection, for example during the transport of a vacuum chamber with the reflective optical element already installed or during maintenance work inside the vacuum chamber, in order to avoid loose parts or maintenance personnel coming into contact in particular with the reflective face of reflective optical elements and damaging or even destroying the latter. If appropriate, in the case of use as a mechanical protection, a different distance from the reflective optical element may have to be selected from that during the cleaning irradiation. For example, the distance should be so narrow during transport that no small parts that could become detached could penetrate into the region between protection element and reflective element.

A further variant of a cover 48, which is installed fixed inside vacuum chamber 30, is represented schematically in Figures 2c-e from the side (Figure 2c) and from the front (Figures 2d,e) in two different positions. Cover 48 is constituted as a kind of iris diaphragm, which is brought into a protection position during irradiation by closing diaphragm element 50, for example via cover holder 49, as shown in Figure 2d. Otherwise, it is located in an open basic position, as shown in Figure 2e. In the example shown, a source 33 for UV radiation 34 is provided for cleaning purposes. Mercury, xenon or similar lamps or also lasers, for example, are suitable as a UV source. Any other radiation sources, such as for example electron beam sources, can however also be provided. Mercury, xenon or similar lamps are particularly well suited for irradiation with essentially constant energy, said lamps emitting particularly intensely at specific energies. Lasers or particle beams, in particular electron beams, with which the beam energy can be arbitrarily adjusted and successively increased, are particularly well suited for irradiation with gradually increasing energy. In the case of particle beams, especially electron beams, use is preferably made of beam-widening elements in order to be able to clean or passivate larger areas inside the vacuum chamber all at once. Moreover, it is possible to combine several different radiation sources with one another.

In contrast with vacuum chambers 30 shown in Figures 2a, b, in the case of vacuum chambers 30 shown in Figures 3a, b protection element 42 (Figure 3a) or 44 (Figure 3b) is arranged in its basic position P2 outside vacuum chamber 30. Before cleaning irradiation is started, which is carried out with UV radiation 34 of a halogen lamp 33 in the example shown in Figures 3a, b, or if a mechanical protection of the multilayer mirror is desired, protection element 42 or 44 is inserted through openings 47 sealable vacuum-tight by means of seals 45 into the interior of vacuum chamber 30. There, protection element 42 or 44 assumes protection position P1 , in which at least a part of the protection element is located between radiation source 33 and multilayer mirror 35. As described in respect of the covers from Figures 2a, b, protection element 42 from Figure 3a is also constituted as a plate-shaped cover, whilst protection element 44 from Figure 3b is constituted as a half- cylinder which protects multilayer mirror 35 over an angular range of approx. 180°.

Generally, the shape of the protection elements is arbitrary and depends above all on the usable space and the dimensioning and shape of the reflective optical element to be protected as well as the geometrical conditions inside the vacuum chamber. The protection elements are preferably made from a material which is not only suitable for a vacuum, but is also inert with respect to the cleaning radiation employed as well as any molecular fragments and radicals arising during the cleaning. High-grade steel, for example, is particularly well suited.

In Figures 5 to 7, examples for the performance of the method proposed here for the cleaning of vacuum ciiamueis are represented in now diagrams. In the example shown in Figure 5, a reflective optical element or also a plurality thereof is first installed in a vacuum chamber and aligned (step 101 ). The vacuum chamber with the reflective optical element is then installed in an EUV lithography device (step 103). Before the cleaning irradiation is started, the reflective optical element is covered (step 105) and a vacuum necessary for the selected type of radiation is applied (step 107). One or more places inside the vacuum chamber are then irradiated with high-energy radiation (step 109) in order to convert the whole of the contamination as far as possible into a passivating coating material. The whole interior surface of the vacuum chamber or at least the places particularly critical with respect to the possible presence of contamination are preferably swept with the radiation. When the vacuum chamber is sufficiently cleaned, which can be checked for example with the aid of a residual gas analysis, the irradiation is ended and the cover is removed from the reflective optical element (step 111 ). The removal can take place under a vacuum as for example in the case of the variants shown in Figures 2a, b, 3a, b. If the cover is to be removed completely from the vacuum chamber, it is advantageous to work in an inert gas counterflow in order to avoid contamination during the removal of the cover.

In the embodiment of the cleaning method shown in Figure 6, the procedure is in principle the same as described in Figure 5. Solely during the irradiation is the procedure somewhat different, in that irradiation is not carried out with constantly high-energy radiation, but rather the energy of the cleaning radiation is gradually increased (step 110). Energy E can thus be allowed to increase linearly with time t (see Figure 4a) or essentially in steps (see Figure 4b). Letters A, B, C denote the time segments in which the radiation has an energy at which different interactions take place with the irradiated contamination. In zone A, the long-chain molecules of the contamination are at least partially desorbed by the surface. The desorbed molecules can be pumped away. The desorption usually takes place with an energy input into the contamination to be removed of up to approx. 5 eV. In zone B, the longer-chain molecules are split into shorter molecular chains, which can then be desorbed into the gas phase and pumped away. A fragmentation of molecules takes place predominantly in an energy input range of approx. 5 eV to approx. 100 eV. In zone C, i.e. as a rule with an energy input of approx. 100 eV and over, the still present longer-chain molecules and shorter molecular chains or molecular fragments are split into even smaller units down to individual atoms, which depending on their type recombine to form volatile compounds or, in the case of carbon, are deposited again from the gas phase as a passivating layer. The energy to be adjusted with a specific radiation source in order to achieve a desired effect A, B, C depends, beyond the effective cross-section, i.a. on the type of radiation, its intensity and me contamination to be removed and can be calculated in the usual way.

Since, even with the molecular fragments and longer-chain molecules, there is a probability greater than zero that some of them will be adsorbed again at a surface before they can be pumped away, the critical places, ideally the whole surface inside the vacuum chamber, are subjected, if possible more than once, to the irradiation with the cleaning radiation. A turbomolecular pump, for example, can be used for pumping away the particles in the gas phase. For this purpose, a vacuum of approx. 10^"5 mbar or better should be applied before the start of the cleaning irradiation.

It should be pointed out that, in a modification of the two embodiments discussed with respect to Figures 5 and 6, step 103 can also be dispensed with and cleaning of the interior of the vacuum chamber can already be carried out before installation of the vacuum chamber in an EUV lithography device.

Compared to an irradiation with constantly high energy, any passivating carbon layer that may be formed is so thin in the case of irradiation with continuously increasing energy that, even in the event of deposition on the reflective surface of a reflective optical element, the reflectivity would be only slightly impaired. In the case of radiation with constantly high energy, a large part of the contamination present is converted into a passivating layer, which is correspondingly thicker. Both electromagnetic radiation and beams of charged particles can be used as radiation.

When use is made of an electron beam for the removal of long-chain hydrocarbons, which are common in vacuum chambers of EUV lithography devices, one would need energies from 1eV to 10OeV in zone A, energies of 10OeV to 100OeV in zone B and energies of greater than 100OeV in zone C. If it is intended to irradiate with a constant energy, an energy in the range of approx. 5OeV to 20OeV is preferred. With an average degree of contamination of a few nm contamination layer thickness, irradiation times of approx. 1 min to 5h are preferred in this energy range.

When use is made of UV radiation of an Hg or Xe lamp, on the other hand, one would need energies of 3eV to 10eV in zone A, energies of 10eV to 10OeV in zone B and energies of 10OeV to 100OeV in zone C. This corresponds to wavelengths of 380nm to 200nm (A), 200nm to 50nm (B) and 50nm to 1 nm (C). If it is intended to irradiate at a constant energy, the energy range from approx. 10OeV up to approx. 100OeV and the wavelength range from 50nm to 1 nm is preferred. With an average degree of contamination of a few nm contamination layer thickness, irradiation times of approx. 1 min to 5h are preferred in this energy range.

In the case of the embodiment of the cleaning method shown in Figure 7, the cleaning is carried out during an operational shutdown of the EUV lithographic device, if for example a raised contamination in the interior of the vacuum chamber has been established by means of a residual gas analysis or other detection methods (step 201). This may be due for example to a leakage or outgassing of the lubricant of a vacuum pump. After optional covering of the reflective optical element or elements present in the vacuum chamber (step 203), the interior face of the vacuum chamber is first irradiated in places with radiation of a specific starting energy (step 205) and the radiation is continuously increased up to the final energy (step 207), as described in connection with Figures 4a, b, 6. If, as preferred, a number of places or the whole interior surface of the vacuum chamber is swept, if possible repeatedly, with the cleaning beam, a sweeping procedure can be carried out with a constant energy and can then be repeated at a higher energy or there can be a dwell time at each sweeping place which is long enough for the whole desired energy range of the radiation to be used, before the beam is directed to the next sweeping place.

The described measures permit the cleaning of a vacuum chamber, in particular a vacuum chamber as part of an EUV lithography device, so that a very small and therefore harmless outgassing of the vacuum chamber takes place during commissioning, with optimum protection of reflective optical elements located in the vacuum chamber. Moreover, it is suitable for the cleaning of contamination during an operational shutdown, said cleaning being such as to treat the reflective optical elements with care.

Figure 8 shows an embodiment of the method for the protection of a reflective optical element inside a vacuum chamber. The vacuum chamber is preferably an EUV lithography device or a part of an EUV lithography device such as for example the projection or illumination system. In the embodiment represented, the degree of contamination inside the vacuum system is monitored as in Figure 7. If an increased contamination is detected inside the vacuum system, i.e. the vacuum chamber or the pump system connected thereto (step 201 ), the reflective optical element is covered as quickly as possible, preferably automatically (step 203), in order to protect it against contamination. Unexpected increases in contamination are often due to operational malfunctions. These can be removed by maintenance work (step 206). Optionally, the maintenance work can also include cleaning, such as described previously foi wλarπpie. When the normal operation can be resumed, the cover of the reflective optical element is removed again (step 208). Reference numbers

10 EUV lithography device

11 beam shaping system

12 EUV radiation source

13a monochromator

13b collimator

14 illumination system

15 first mirror

16 second mirror

17 mask

18 third mirror

19 fourth mirror

20 projection system

21 wafer

22 radiation source

23 radiation source

24 cover

25 cover

26 cover

27 cover

30 vacuum chamber

31 electron beam source

32 electron beam

33 UV lamp

34 UV beam

35 multilayer mirror

36 mirror holder

37 cover

38 uυver hoider

39 rail

40 cover

41 cover holder

42 protection element

43 holder

44 protection element 45 seal

46 seal

47 opening

48 cover 49 cover holder

50 diaphragm element

101-111 process steps

201-209 process steps

E energy t time

A, B, C zones

P1, P2, P3 positions

Claims

1. A method for cleaning vacuum chambers, especially as part of EUV lithography devices, from contamination by exposing a place inside the vacuum chamber to radiation,

5 characterised in that the energy of the radiation is gradually increased.

2. The method according to claim 2, characterised in that directed radiation is used.

3. The method according to claim 1 or 2, characterised in that the energy of the radiation is 10 increased in such a way that an energy input into the contamination in the energy range from below 1 eV to over 100 eV is guaranteed.

4. The method according to any one of claims 1 to 3, characterised in that UV radiation or an electron beam is used.

15

5. The method according to any one of claims 1 to 4, wherein a reflective optical element is located in the interior of the vacuum chamber, characterised in that the reflective optical element is covered during the irradiation.

20 6. The method according to any one of claims 1 to 5, characterised in that radiation of energy in the range from 1eV to over 1000 eV is used.

7. The method according to any one of claims 1 to 6, characterised in that irradiation times of 1 min to 5 h are selected.

25

8. A method for cleaning vacuum chambers with a reflective optical element, especially of EUV lithography devices, by exposing a place inside the vacuum chamber to high-energy radiation, characterised in that the reflective optical element is covered during the irradiation.

όϋ y. l he method according to claim 8, characterised in that radiation in the range from 50 eV to 100O eV is used.

10. A method for protecting a reflective optical element inside a vacuum chamber, especially as part of an EUV lithography device, characterised in that the reflective optical element is 35 covered in the case of increased contamination.

11. The method according to claim 10, wherein irradiation is carried out into the vacuum chamber by means of a radiation source, characterised in that a protection element is arranged between radiation source and reflective optical element in the case of increased contamination.

12. A vacuum chamber (14, 20, 30), especially for use in an EUV lithography device (10), wherein a radiation source (22, 23, 31 , 33) and a reflective optical element (15, 16, 18, 19, 35) are arranged, characterised in that the vacuum chamber (14, 20, 30) comprises a protection element (24, 25, 26, 27, 37, 40, 42, 44) which is movable between the radiation source (22, 23, 31 , 33) and the reflective optical element (15, 16, 18, 19, 35).

13. The vacuum chamber according to claim 12, characterised in that the radiation source (22, 23, 31 , 33) can be regulated with regard to differing energy (E) of the radiation.

14. The vacuum chamber according to claim 12 or 13, characterised in that an electron beam source (31 ) or a UV radiation source (33) is provided as a radiation source.

15. The vacuum chamber according to any one of claims 12 to 14, characterised in that the protection element (24, 25, 26, 27, 37, 40, 42, 44) is arranged in a basic position (P2) outside the vacuum chamber (14, 20, 30) and the vacuum chamber (14, 20, 30) comprises an opening (47) through which the protection element (24, 25, 26, 27, 37, 40, 42, 44) can be moved into the interior of the vacuum chamber (14, 20, 30).

16. The vacuum chamber according to any one of claims 12 to 14, characterised in that the protection element (24, 25, 26, 27, 37, 40, 42, 44) is arranged in a basic position inside the vacuum chamber (14, 20, 30).

17. The vacuum chamber according to any one of claims 12 to 16, characterised in that it comprises a rail system for moving the protection element (24, 25, 26, 27, 37, 40, 42, 44) out ot a basic position (P2) into a protection position (P1 ) between radiation source (22, 23, 31 , 33) and reflective optical element (15, 16, 18, 19, 35).

18. The vacuum chamber according to any one of claims 12 to 17, characterised in that the protection element (24, 25, 26, 27, 37, 40, 42, 44) is plate-shaped.

19. The vacuum chamber according to claim 18, characterised in that the area of the plate- shaped protection element (24, 25, 26, 27, 37, 40, 42, 44) is selected greater than the area of the side of the reflective optical element (15, 16, 18, 19, 35) facing the radiation source (22, 23, 31 , 33).

20. An EUV lithography device (10) with a vacuum chamber (14, 20) according to any one of claims 12 to 19.