Cleaning module, EUV lithography device and method for the cleaning thereof

In order to clean optical components (35) inside an EUV lithography device in a gentle manner, a cleaning module for an EUV lithography device includes a supply line for molecular hydrogen and a heating filament for producing atomic hydrogen and hydrogen ions for cleaning purposes. The cleaning module also has an element, (33) arranged to apply an electric and/or magnetic field, downstream of the heating filament (29) in the direction of flow of the hydrogen (31, 32). The element can be designed as a deflection unit, as a filter unit and/or as an acceleration unit for the ion beam (32).

This is a Continuation of International Application PCT/EP2009/051330, with an international filing date of Feb. 5, 2009, which was published under PCT Article 21(2) in German, and the complete disclosure of which, including amendments, is incorporated into this application by reference.

FIELD OF AND BACKGROUND OF THE INVENTION

The present invention relates to a cleaning module for the cleaning of components of an EUV lithography device comprising a heating unit, and to a cleaning module for an EUV lithography device with a supply line for molecular hydrogen and a heating filament for producing atomic hydrogen for cleaning purposes, as well as to an EUV lithography device or a projection system or an illumination system for an EUV lithography device with such a cleaning module. Moreover, the present invention relates to methods for the cleaning of a component inside an EUV lithography device.

In extreme-ultraviolet 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 and multilayer mirrors, are used for the lithography of semiconductor components. Since EUV lithography devices usually comprise a plurality of reflective optical elements, these elements must possess as high a reflectivity as possible in order to ensure a sufficiently high total reflectivity. The reflectivity and the service life of the reflective optical elements can be reduced by contamination of the optically used reflective area of the reflective optical elements, said contamination arising on account of 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 levels of contamination on each individual reflective optical element have a quite considerable effect on the total reflectivity.

In particular, the optical elements of an EUV lithography device can be cleaned in situ with the aid of, for example, atomic hydrogen, which reacts with, in particular, carbon-containing contamination to form volatile compounds. In order to obtain the atomic hydrogen, molecular hydrogen is often conveyed onto a heating filament. Metals or metal alloys with a particularly high melting point are used for the heating filament. So-called cleaning heads comprising a hydrogen supply line and an incandescent filament are arranged in the vicinity of mirror surfaces in order to clean them free from contamination. The volatile compounds, which are formed in the reaction of the atomic hydrogen with the, in particular, carbon-containing contamination, are pumped away with the normal vacuum system.

It has been a problem with the previous approach that, on the one hand, the cleaning heads are supposed to be arranged relatively close to the mirrors in order to achieve a high cleaning efficiency. On the other hand, reflective optical elements optimized precisely for the EUV or soft x-ray wavelength region are often sensitive to heat. Excessive heating of the mirrors during the cleaning leads to a deterioration in their optical properties. Hitherto, therefore, mirror cooling has been provided during the cleaning or the cleaning has been carried out as pulsed cleaning with cooling phases. Furthermore, with the production of atomic hydrogen via thermionic electrons from, for example, an incandescent or heating filament, the problem arises that the filament material can contaminate the surface to be cleaned.

SUMMARY OF THE INVENTION

It is an object of the present invention to improve the known cleaning heads such that a more gentle cleaning of the optical elements is enabled.

This object is achieved by a cleaning module for the cleaning of components of an EUV lithography device which comprises a heating unit, past which molecular gas can flow in order to convert it at least partially into ions, and which comprises at least one electromagnetic deflection unit in order to change the direction of motion of ions.

This object is also achieved by a cleaning module for an EUV lithography device with a supply line for molecular gas and a heating filament for the production of atomic gas for cleaning purposes, as well as an element applying an electric and/or magnetic field and arranged downstream of the heating filament in the flow direction of the atomic gas (e.g. hydrogen).

The element applying an electric and/or magnetic field, respectively the electromagnetic deflection unit, makes it possible to spatially deflect the produced atomic gas, preferably produced atomic hydrogen, insofar as it is in ionized form, or the ionized gas. The heating filament for the production of atomic gas, preferably atomic hydrogen, or the heating unit for the ionization of molecular gas, can thus be positioned such that there is no free line of sight (i.e. no unimpeded travel) between the heating filament or the heating unit on the one hand and a component to be cleaned or an area to be cleaned on the other. On the contrary, the hydrogen atoms present as ions or other ions are deflected by electric and/or magnetic fields to the site to be cleaned. The area to be cleaned is therefore no longer directly exposed to the thermal radiation of the heating filament or the heating unit or to contamination with material of the heating filament or the heating unit, this being a considerable advantage especially in the case of mirrors for the EUV or soft x-ray wavelength region. This is because such mirrors are often provided with heat-sensitive multilayer systems, which endow them with their optical capabilities. The temperature sensitivity of the multilayer coating of a mirror for the EUV or soft wavelength range limits the cleaning time and therefore the cleaning efficiency per cleaning cycle. The required cleaning time is thus increased and this reduces the production time. The cleaning efficiency with conventional cleaning modules is also reduced by the fact that the surface to be cleaned may be contaminated by material emerging from the filament or the heating unit during heating. As a result of the enabled gentle and at the same time target-orientated cleaning, the required cleaning time can be reduced, additional contamination can be avoided and the production time can thus be lengthened.

Furthermore, this object is achieved by an EUV lithography device or a projection system or an illumination system for an EUV lithography device with at least one such cleaning module.

In addition, this object is achieved by a method for the cleaning of a component inside EUV lithography devices including: ionizing a molecular gas, deflecting ions into another direction and exposing the components to be cleaned to the prepared gas.

Moreover, this object is achieved by a method for the cleaning of a component inside EUV lithography devices including: producing atomic cleaning gas on a heating filament and deflecting the atomic cleaning gas with an electric and/or magnetic field onto the component to be cleaned.

By the fact that the part of the atomic cleaning gas, preferably the atomic hydrogen, which is present in an ionized state, respectively that the ion share of a cleaning gas is deflected with an electric and/or magnetic field onto the component to be cleaned, it is possible to position the heating filament and the component to be cleaned with respect to one another in such a way that the component to be cleaned is not directly exposed to the thermal radiation of the heating filament, which leads to a longer service life of the component on account of the lower heat input.

It should be pointed out that, apart from ionized hydrogen, any charged particles, in particular other ionized cleaning gases, are suitable for the comparatively gentle and the target-orientated cleaning described here, especially ions of atoms or molecules, which react with the contamination to be removed to form volatile compounds, or of noble gases, which can clean the surface predominantly through a sputtering effect.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

An EUV lithography device10is represented schematically inFIG. 1. Main components are a beam shaping system11, an illumination system14, a photomask17and a projection system20. The EUV lithography device10is operated under vacuum conditions or in special atmospheres with a low partial pressure of a gas or a combination of gases, in order that the EUV radiation is absorbed or scattered as little as possible in its interior. In the present example, a pressure of approx. 10−4mbar or less is complied with for this purpose, also with a special atmosphere.

A plasma source or also a synchrotron can for example be used as radiation source12. The emerging radiation in the wavelength range from approx. 5 nm to 20 nm is first bundled in collimator13b. Moreover, the desired operating wavelength can be filtered out with the aid of a monochromator13aby varying the angle of incidence. In the stated wavelength range, collimator13band monochromator13aare usually constituted as reflective optical elements. Collimators are often reflective optical elements constituted 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 as broad a wavelength range as possible should 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 system11with regard to wavelength and spatial distribution is then introduced into illumination system14. In the example represented inFIG. 1, illumination system14comprises two mirrors15,16that are constituted as multilayer mirrors in the present example. Mirrors15,16guide the beam onto photomask17, which comprises the structure, which is to be imaged onto wafer21. Photomask17is also a reflective optical element for the EUV and soft wavelength region, said element being replaced depending on the production process. With the aid of projection system20, the beam reflected by photomask17is projected onto wafer21and the structure of the photomask is thus imaged onto said wafer. In the example shown, projection system20comprises two mirrors18,19, which in the present example are also constituted as multilayer mirrors. It should be pointed out that both projection system20as well as illumination system14can each also comprise only one or also three, four, five or more mirrors.

Beam shaping system11as well as illumination system14as well as projection system20are constituted as vacuum chambers22,23,24, since multilayer mirrors15,16,18,19, in particular, can only be operated in a vacuum or a special atmosphere. Otherwise, too much contamination would be deposited on their reflective surface, which would lead to excessive deterioration of their reflectivity. Photomask17is therefore also located in a vacuum or a special atmosphere. For this purpose, it can be located in its own vacuum chamber or can be integrated into another vacuum chamber23,24.

Cleaning modules25,26,27are provided in the example shown inFIG. 1for the cleaning especially of the reflective optical elements. The cleaning modules can be provided either inside vacuum chambers, as in the case of illumination system23and projection system20, such that cleaning modules26,27are arranged in each case on the inside of vacuum chambers23,24. They can also be provided outside a vacuum chamber, as in the case of beam shaping system11in the present example, wherein cleaning module25is arranged on the outside of vacuum chamber22. In this case, a connection is provided between the cleaning module and vacuum chamber22, through which the atomic hydrogen required for the cleaning can pass. If individual or a plurality of optical elements, for example mirrors15,16,18,19or monochromators13aor collimators13b, are enclosed separately in a housing having its own vacuum system, the cleaning modules can also be arranged inside such a housing. A cleaning module can also be provided for photomask17.

In the present example, cleaning modules25,26,27are used for the cleaning of mirror surfaces. They are however also suitable for the cleaning of any other components inside EUV lithography device10.

According to a first embodiment, hydrogen supply lines are provided inside cleaning modules25,26,27in order to conduct molecular hydrogen onto a heating filament. In further variants, supply lines for gases other than hydrogen can be provided for cleaning purposes. A tungsten filament is preferably used as the heating filament, which can be heated up to 2000° C. in order to achieve a high splitting rate in atomic hydrogen. The produced atomic hydrogen is present partially in ionized form. This is used to deflect the ionized atomic hydrogen in a targeted manner through electric or magnetic or electromagnetic fields and to guide the ionized hydrogen onto the area to be cleaned in each case. Cleaning modules25,26,27can therefore now be arranged in EUV lithography device10in such a way that the components to be cleaned, such as for example mirrors15,16,18,19or monochromator13aand collimator13b, are no longer exposed directly to the thermal radiation of the tungsten filament. As a result of the controllability of the hydrogen beam, it is now also possible to provide a cleaning module for different optical elements to be cleaned. Depending on the requirements on the cleaning efficiency and depending on the geometric configurations inside an EUV lithography device or its projection system or illumination system, one or more separate cleaning modules can also be provided for each object to be cleaned or each area to be cleaned.

A first preferred embodiment of a cleaning module is represented schematically inFIGS. 2a, b. A heating filament29is arranged in a housing30. Molecular hydrogen is supplied to this heating filament29via hydrogen supply line28, said molecular hydrogen being split into atomic hydrogen by the heating effect of heating filament29. A hydrogen partial flow31thus arises, which is composed partially of non-split molecular hydrogen and non-ionized atomic hydrogen and which further comprises a partial flow32essentially consisting of hydrogen ions. The two partial flows31,32emerge from housing30in such a way that they flow towards a deflection element33. In the present example, deflection element33is constituted plate-shaped. It is positively charged, so that it has a deflecting influence on partial flow32with hydrogen ions. This is because the hydrogen ions are positively charged and repelled by deflection element33. Ion beam32is thus guided onto the surface of component35to be cleaned. As a result of the basic structure, it is possible to achieve an effect such that the direction of ion beam32is decoupled from the direction of the thermal beam, which coincides with the beam direction of non-ionized hydrogen31. Heating of the surface of component35to be cleaned is thus avoided, which in the case of a mirror surface would lead to a deformation or shift of the optical mirror surface, so that the imaging characteristic would be adversely affected.

Deflection element33can be made for example of metal, blackened or dark metal surfaces being particularly preferable. Anodized aluminum is used with very particular preference. This serves to absorb heat from hydrogen ion beam32. In order to enhance this effect still further, a cooling device34in thermal contact with deflection element33is additionally provided in the example represented inFIG. 2a. Cooling device34serves as a heat reservoir, into which heat from hydrogen ion beam32can flow away. The heat input into component35is thus further reduced. In addition, deflection plate33is connected to a charge reservoir, e.g. in the form of a voltage source, in order to be able to maintain deflection element33continuously at a positive potential. Hydrogen ion beam32can be controlled by varying the potential.

The example represented inFIG. 2bdiffers from the example represented inFIG. 2ain that an ionization device36is additionally provided between heating filament29and deflection element33. Ionization device36serves to increase the proportion of ionized hydrogen. The ionization preferably takes place by collision ionization or electric field ionization. The collision ionization can in particular also be ionization with high-energy photons, for example from the ultraviolet or the x-ray wavelength region. Depending on the desired cleaning efficiency, it may be necessary to have more or less ionized hydrogen in hydrogen ion beam32with which component35is cleaned. This can be adjusted by ionization device36.

Moreover, deflection element33is arranged in a mobile manner. In the present example, it can rotate about an axis as symbolized by the arrow. The effect of a rotation of deflection element33is that hydrogen ion beam32is moved up and down relative to the area of component35to be cleaned, as is indicated by the double arrow. This enables targeted scanning of the surface to be cleaned. Deflection element33particularly preferably has up to six degrees of freedom, in order for it to be able to move freely in space and for hydrogen ion beam32thus to be able to be positioned arbitrarily on areas to be cleaned.

In the example of embodiment represented inFIG. 3, there are arranged in the flow direction downstream of the heating filament (not represented inFIG. 3), which is located in housing30, plates37in order to be able to apply an electric field38, and in addition a magnet, which is not represented here, in order to apply a magnetic field39. Both fields38,39are essentially homogeneous fields, which are oriented normal to one another. This spatial arrangement is also called a Wien filter and serves to filter out hydrogen ions32of a specific energy range from hydrogen beam31. The energy range is preferably selected such that the hydrogen ions have an energy, which is so small that no sputtering effects occur. This is because sputtering could lead to a destruction of the surface that is being cleaned, this being undesirable especially when cleaning multilayer mirrors. Depending on the nature of the contamination to be removed and depending on the surface to be cleaned, however, it may also be advantageous to select the energy range so high that removal of the contamination can occur not only through a chemical reaction but also mechanically through sputtering.

Plates37also serve, moreover, to shield off the area or component to be cleaned against the thermal radiation, which is emitted from the heating filament to generate the atomic hydrogen.

The element shown inFIG. 3for applying an electric field38and a magnetic field39can be combined for example with deflection element33from the example of embodiment shown inFIGS. 2a, b, an arrangement of the deflection element in front of the Wien filter and also behind the Wien filter being possible. Further elements for applying electric and/or magnetic fields, e.g. electric lenses, can also be provided in order to form ion beam32and/or in order to scan the surface of a component to be cleaned in a more targeted manner with a beam32. A unit for filtering the ions according to their mass can additionally be used.

The execution of the cleaning of a component inside an EUV lithographic device according to a first embodiment will now be dealt with in somewhat greater detail with reference toFIGS. 4a, band5. Since there is only limited space available in the interior of an EVU lithographic device or a projection system or an illumination system for an EVU lithographic device, it often happens that different components41,40, as represented inFIG. 4a, partially shadow one another. In the situation represented inFIG. 4a, component41is arranged in the flow direction of the hydrogen upstream of component40, whose surface is intended to be cleaned. When use is made of conventional cleaning modules, wherein a heating filament is arranged in the vicinity of a component to be cleaned, so that the produced atomic hydrogen can directly strike the area to be cleaned, whole area42would be exposed to atomic hydrogen. However, since component41protrudes into the hydrogen cone, component41is partially exposed to atomic hydrogen, which may be undesirable, since reactions of atomic hydrogen with the material of component41may occur. Moreover, no hydrogen atoms arrive in the region of component40downstream of component41, so that this region cannot be adequately cleaned.

By using the cleaning module proposed here, it is possible to clean areas of component40in a targeted manner without component41essentially coming into contact with atomic hydrogen. For this purpose, atomic hydrogen is first generated on a heating filament (seeFIG. 5, step101), as also in the past. In the present example, the atomic hydrogen is then ionized (step103). This preferably takes place by collision ionization or electric field ionization. In the case of collision ionization, it may in particular also involve ionization with high-energy photons, for example from the ultraviolet or the x-ray wavelength region. The hydrogen beam with a high proportion of hydrogen ions is directed with of a cooled deflection element, for the purpose of cooling and deflecting the beam, in the direction of the area to be cleaned (step105), the deflection element being positively charged. Ions having a specific energy are then filtered out using an electromagnetic field (step107), in order to carry out chemical and/or mechanical cleaning of the area to be cleaned depending on the surface to be cleaned and depending on the contamination to be removed. The penetration of contaminating material of the heating filament can thus be additionally suppressed. With this specially prepared hydrogen ion beam, the area of a component to be cleaned inside an UV lithography device is scanned with ions having a specific energy (step109).

This is represented inFIG. 4bwith the aid of components41,40. With the method described here, it is possible to scan individual areas43to47in a targeted manner. The scanning direction is symbolized by the arrows and is arbitrary. Component41is now not exposed to hydrogen ions. By the application of additional magnetic fields, moreover, regions of the area can be reached which lie in the region shadowed by component41. Cleaning can be adapted to the actual cleaning requirement in each case with the aid of the prepared and deflectable hydrogen ion beam. Instead of cleaning large regions of the area without differentiation, the hydrogen beam is directed solely onto regions43to47of the area with contamination to be removed. Moreover, the hydrogen beam is prepared in terms of energy in such a way that the required cleaning performance is achieved. The cleaning performance is determined not only by the energy of the hydrogen ions, but also by the speed at which a region43to47of the area is scanned.

It should be pointed out that not only ionized hydrogen is suitable for the gentle and target-orientated cleaning described here, but any charged particles, in particular ions of atoms or molecules which react with the contamination to be removed to form volatile compounds. In further embodiments, therefore, other cleaning gas instead of hydrogen can be supplied and converted into atomic cleaning gas.

An example of a further embodiment of a cleaning module50is represented inFIG. 6, wherein arbitrary gases GG are prepared for the cleaning of surfaces. Gas GG is introduced via gas supply line51into housing60and brought into the vicinity of heating unit52. In the present example, heating unit52is constituted as a heating filament, from which thermionic electrons emerge which ionize gas GG at least partially to form positive ions G+and negative ions G−. In further embodiments, the heating unit can also be a plasma source or it can comprise heating elements, which are constituted in an arbitrarily different manner.

The selection of the kind of heating unit52depends on the gas to be ionized and the desired ionization rate. In the case of the embodiment as a heating filament, the heating filament material can also be selected with regard to the cleaning gas and the ionization rate. Preferred materials are for example tungsten, osmium, iridium and rhenium. To a certain extent, the ionization rate can be influenced by the voltage or current applied to the heating filament. It should be noted that, in the case of gases with smaller atomic radii, less energy has to be supplied than in the case of gases with a larger atomic radius in order to achieve ionization. This applies in particular to the use of noble gases.

Housing60has, for instance, the function of separating the atmospheres inside and outside of cleaning module50from one another. Pressure fluctuations outside cleaning module50can thus be compensated for inside cleaning module50in order to ensure a constant generation of ions. Such pressure fluctuations can occur, for example, when the interior of the EUV lithography device or one of its optical systems such as, for example, the illumination system or the projection system is being pumped off on account of a raised contamination risk. By way of support, a diaphragm can be arranged at outlet61in order to separate the volume inside housing60from the surroundings, and/or cleaning module50can comprise a pump with a suction power regulator. The diaphragm can also contribute towards ensuring that as few contaminants as possible exit from cleaning module50and contaminate component63to be cleaned. The free path length of the ions can also be adjusted via the pressure inside cleaning module50. The kinetic energy of the ions and the probability of their emergence from housing60can thus be influenced.

The ions formed at heating unit52move, e.g., towards electromagnetic deflection unit53, in which the ions are deflected into different directions by electric and/or magnetic fields depending on their polarity. For this purpose, deflection unit53can for example include deflection electrodes64, as represented schematically inFIG. 6.

For the sake of clarity, only positive ions G+are represented inFIG. 6. In order to shield off undesired ions or molecules, a partition wall62is provided inside housing60between heating unit52and outlet61, from which the particles of the cleaning gas prepared for the cleaning emerge.

As a result of the deflection of the ions, it is ensured that a line of sight between heating unit52and component63to be cleaned is avoided, in order to keep the thermal load on component63as low as possible. The ions are preferably deflected by an angle between 60° and 120°, particularly preferably between 80° and 100°, very particularly preferably by approx. 90°. As an additional measure, component63can also be exposed in a pulsed manner to the prepared cleaning gas, i.e. with interruptions in which component63can cool down again, and/or over such short time intervals that component63heats up only within a tolerable temperature range during the exposure to the cleaning gas. For this purpose, gas supply line51and/or one or more of electromagnetic units53,54,55,56can be operated in a pulsed manner.

The positive ions then pass through electromagnetic filter unit54, the magnetic fields and/or electric fields whereof are adjusted in such a way that only ions having a mass in a specific mass range pass through filter unit54. In order to increase the precision of the mass filtering, a pinhole65can be arranged between deflection unit53and filter unit54, as represented schematically inFIG. 6. The mode of functioning of filter unit54essentially corresponds to that of a mass spectrometer. Filter unit54is particularly advantageous when a gas mixture is made available as a cleaning gas and the cleaning is intended to be carried out preferably with one or another component of the gas mixture at different times. Moreover, filter unit54makes it possible to stop contaminating ions, for example of a material of heating unit52or of housing60or of partition wall62, so that they do not contaminate the surface of component63to be cleaned. Filter unit54can for example comprise a quadrupole magnet66.

In the present example, the ions emerging from filter unit54are again deflected inside a further deflection unit55and directed to an electromagnetic acceleration unit56. In the example represented schematically inFIG. 6, deflection unit55also comprises deflection electrodes68and a pinhole67is arranged between filter unit54and deflection unit55. In acceleration unit56, the previously selected ions are brought to the kinetic energy for the cleaning of the surface of component63preferably using electric fields which can be generated for example by acceleration electrodes (not shown). The kinetic energy can also be changed during the cleaning process. Depending on the contamination to be removed, it may be advantageous to work, for example, first with high-energy particles and to reduce the energy at the end of the cleaning process in order to proceed in a more gentle manner, in order that the surface lying beneath the contamination, for example, is not damaged. In addition, it is also possible, by regulating heating unit52, to reduce the ionization rate and/or to deflect and/or filter out other ions and/or to supply another cleaning gas. Moreover, the area to be cleaned can be scanned with the ion beam with the aid of deflection unit55.

A variant of the embodiment shown inFIG. 6is represented inFIG. 7. It differs from the embodiment shown inFIG. 6in that a radical generation unit58is arranged, in the ion flow direction, downstream of deflection units53,55, filter unit54and acceleration unit56. Depending on the surface to be cleaned or the contamination to be removed, it may be advantageous to work with radicals of the cleaning gas instead of with ions of the cleaning gas.

Moreover, it should be pointed out that each deflection unit, filter unit, acceleration unit and optionally radical generation unit can be provided either singly or multiply in the cleaning module, the arrangement of the electromagnetic units, such as deflection unit, filter unit and acceleration unit, being arbitrary. Moreover, each unit can include any device for generating electric, magnetic or electromagnetic fields, which the person skilled in the art can select for example according to the geometry of the module and the surroundings in which it is intended to be used, or according to the desired cleaning particles. The radical generation unit is preferably arranged following the electromagnetic units, as in the example represented inFIG. 7. This is because radicals can scarcely be influenced by the electromagnetic units.

The example of a radical generation unit58represented inFIG. 7comprises an electron source59. Electrons e−interact with positive ions G+in order to convert them into uncharged radicals G, which act on the contamination on component63to be cleaned. The radicals or the ions are preferably selected such that they react with the contamination to form volatile compounds. The energy of the radicals or ions can also be adjusted such that the removal of the contamination proceeds physically, e.g. by sputtering effects. It may also be desirable to carry out simultaneously chemical as well as physical cleaning. In the case of component63with a particularly sensitive surface, it may be advantageous initially to clean predominantly physically and gradually to increase the proportion of the chemical cleaning. This can be influenced by the kinetic energy, the particle density and/or the type of particles.

An example of a further embodiment of a cleaning method is shown in a flow diagram inFIG. 8. This method is preferably carried out with cleaning modules such as have been described in connection withFIGS. 6,7.

A gas is first ionized by a heating device (step201). Hydrogen, deuterium, tritium, noble gases, halogen gases, oxygen, nitrogen or a mixture of two or more of these gases are preferably used as the gas. Hydrogen, nitrogen and noble gases are particularly preferable. Gases, which act in a reducing manner, are particularly advantageous for a chemical cleaning effect. Noble gases are preferred for a physical cleaning effect.

The ions obtained at the heating device are filtered according to their mass (step203), in order to obtain only the ions desired for the cleaning, and are deflected (step205) in order that the surface to be cleaned is not exposed directly to the thermal radiation of the heating device. The ions are then accelerated to the kinetic energy desired for the given cleaning step (step207). The step also comprises, as the case may be, a negative acceleration in order to reduce the kinetic energy of the ions.

The ions thus obtained are converted by electron bombardment into radicals (step209), to which the surface to be cleaned is exposed (step211).

Step209can also be dispensed with in a variant of this embodiment and the surface to be cleaned is exposed to the selected ions brought to the desired energy.

The above description of exemplary, preferred embodiments has been given by way of example. From the disclosure given, those skilled in the art will not only understand the present invention and its attendant advantages, but will also find apparent various changes and modifications to the structures and methods disclosed. The applicant seeks, therefore, to cover all such changes and modifications as fall within the spirit and scope of the invention, as defined by the appended claims, and equivalents thereof.