DE102009044462A1 - Optical element for filtering electromagnetic radiations for illuminating system of projection exposure system, has multilayer structure, which is designed for reflection of electromagnetic radiations in extreme ultraviolet wavelength range - Google Patents

Abstract

The optical element has a multilayer structure, which is designed for the reflection of electromagnetic radiations in the extreme ultraviolet wavelength range. The optical element has a lattice structure (13), which is designed for deflecting electromagnetic radiations in the visible to infrared wavelength range. An independent claim is also included for a projection exposure system with a field facet mirror.

Description

The The present invention relates to an optical element for Filtering electromagnetic radiation that is a multilayer structure which is responsible for the reflection of electromagnetic Radiation designed in the extreme ultraviolet wavelength range is, and which has a lattice structure, which for the Diffraction of electromagnetic radiation in the visible to infrared Wavelength range is designed. The present invention also relates to an optical element for filtering electromagnetic Radiation for a projection exposure machine used in a scan mode along a scan direction with a wavelength operated in the extreme ultraviolet wavelength range wherein it has a lattice structure and wherein the optical Element receives light from a light source on the object side and a Area in an image-side plane illuminates that of a local Coordinate system is spanned, with the y direction of the local Coordinate system parallel to the scan direction and the x-direction perpendicular to the scanning direction. Furthermore, the invention relates on lighting systems and projection exposure systems, the at a wavelength in the extreme ultraviolet wavelength range operated, with such optical elements.

Around in the production of semiconductor devices with lithographic Methods to be able to produce ever finer structures worked with increasingly short-wave light. Do you work in the extreme ultraviolet (EUV) wavelength range, such as in particular at wavelengths between about 5 nm and 20 nm no longer work with lenticular elements in transmission, but become illumination and projection lenses from mirror elements with reflective coatings adapted to the respective operating wavelength built on the basis of multilayer systems.

at Lighting systems for wavelengths smaller 100 nm is the problem that often the light source Such illumination systems emits radiation, the wavelengths which is outside the wavelength band for which in the illumination system or the projection exposure apparatus, in which the lighting system is used is designed. These electromagnetic radiation that is used outside of Wavelength band lies, can be an undesirable Exposure of the light-sensitive object in the wafer plane of the projection exposure apparatus to lead. Besides, it can be the optical components so far as to heat that by deformation of the optical components Imaging errors arise and / or reflectivity, for example of multi-level mirrors, which are very common at wavelengths be used in the range of 5 to 20 nm, impaired becomes. To make matters worse, that multi-level mirror not only certain EUV wavelengths for which they have been optimized reflect with higher reflectivity, but often also wavelengths from about 130 nm and more. Therefore, will with electromagnetic radiation from the deep ultraviolet (DUV) wavelength range (especially about 130 nm to 330 nm) or from the ultraviolet (UV) region, the visible (VIS) and the infrared (IR) range throughout the lighting system or guided through the entire projection exposure system.

To the Filtering out or mitigating these unwanted Radiation spectral filters are used. Preference is given to Spectral filter as early as possible in the beam path used to affect the imaging properties and a high heat load as much as possible avoid. Often, the first optical component becomes a collector mirror formed, which also assumes spectral filter functions.

From the US 2006/0245057 A1 For example, a spectral filter for EUV lithography is known, in which a multilayer system for reflecting a narrow EUV wavelength band on its surface is provided with a filter layer. This filter layer has one or more materials that absorb more wavelengths in the DUV range than in the EUV range.

Grid-based spectral filters are also often used for EUV lithography. From the EP 1 540 423 B1 For example, such a spectral filter is known, which has a lattice constant which is chosen so large that electromagnetic radiation is diffracted in the DUV wavelength range. For an illumination system with such a spectral filter, the 0th diffraction order is used and the higher diffraction orders are taken out by means of a diaphragm. As a result, the intensity in the DUV range can be reduced by approximately 20% relative to the operating wavelength in the EUV range at which the illumination system or the projection exposure apparatus is operated. This grid structure can also be mounted on curved surfaces, as they occur in collector mirrors or other EUV mirror elements. Preferably, the grid grooves are parallel to the beam of the incident beam.

From the US 6,707,602 B2 Also, a reflective spectral filter for the EUV wavelength range is known. It is a combination of lattice structure and multilayer structure. The multilayer structure reflects a desired working wavelength in the EUV range and undesirably longer wavelength light, approximately from 60 nm. The lattice period or lattice period length is tuned to the longer wavelength band to be out of the beam lengang is bent out. In the implementation, the multilayer structure may be continuously deposited over the lattice structure, or a multilayer structure deposited in the grooves and on the ridges of the lattice.

The WO 2005/119365 A2 describes a reflective spectral filter for the EUV region, which has a multilayer structure that is cut obliquely, so that a sawtooth or blazed grating is formed. The multi-layer structure has significantly more than 1000 absorber-spacer pairs, which makes its production very time-consuming and cost-intensive. The working wavelength at which EUV lithography is to be performed is conventionally reflected by Bragg reflection at the interfaces of the multilayer structure, while the EUV radiation in adjacent waves is absorbed by the multilayer structure. Wavelengths in the UV, VIS and IR ranges, on the other hand, are reflected specularly on the slants and thus deflected out of the beam path.

One category of projection exposure equipment commonly used in EUV lithography is the US 7,091,505 B2 described. This is a projection exposure apparatus which is operated in a scanning mode along a scanning direction with a wavelength in the EUV range. The projection exposure system from the US 7,091,505 B2 has a collector mirror with a plurality of mirror shells. In order to secure them, support spokes are necessary, which are arranged such that when they are projected in the plane to be illuminated on the image side, they are inclined with respect to the scanning direction in the image plane in order not to impair the illumination homogeneity too much.

A Object of the present invention is the already known optical elements for filtering electromagnetic radiation, in particular for use in EUV lithography, to further develop.

In In a first aspect, this object is achieved by a optical element for filtering electromagnetic radiation, the has a multilayer structure that is responsible for the reflection of electromagnetic radiation in the extreme ultraviolet wavelength range is designed, which has a lattice structure for the bending of electromagnetic radiation in the visible to infrared Wavelength range is designed, and has the means which for the change of the relative intensity and / or propagation direction of electromagnetic radiation in ultraviolet to visible wavelength range are.

It has proved to be advantageous, the grid structure is not as previously known primarily for the diffraction of electromagnetic radiation in the ultraviolet wavelength range but for the bending of electromagnetic Radiation in the visible to infrared wavelength range. This has the advantage that the production of such spectral filters This significantly simplifies, especially if they are large and curved surfaces, such as for example the case is when they are used as a collector mirror. Because of the larger for the diffraction in the VIS to IR range geometric dimensions can be appropriate lattice structures make it easier. This also allows spectral filters with diameters of 50 cm and much more with comparatively little effort produce. The targeted filtering out of the VIS and IR content allows one efficient reduction of heat load. In which one besides filtering out the very long-wave area and slightly Functionally separates longer-wavelength light, the optical elements can be in their capacity as a spectral filter much better to each adjust the light source used and its emission spectrum.

In preferred embodiments is the lattice structure for the bending of electromagnetic radiation in the infrared wavelength range and are the means for changing the relative Intensity and / or propagation direction of electromagnetic Radiation in the ultraviolet wavelength range designed. These are particularly suitable when using radiation sources, where emissions in the visible wavelength range lower are, and / or when using photoresist for the lithographic process in the visible wavelength range has a lower sensitivity. Since in these embodiments the optical element for filtering out more specific ones Wavelength bands is designed, lets it Construct and make easier.

advantageously, is the grid structure formed as a binary grid, So with constant height difference between grid grooves and grid crests, each designed plateau-shaped are. Because of the comparatively large lattice constant can the lattice structure without problems simultaneously with the application of the highly reflective multi-layer structure are applied in the only by means of a diaphragm, which dimensioned according to the lattice constant is to shade the later furrows of the grid.

In a preferred embodiment, the additional means for filtering out the electromagnetic radiation in the ultraviolet wavelength range are formed as a layer comprising a material which absorbs electromagnetic radiation more in the ultraviolet wavelength range stronger as ultraviolet wavelength radiation reflected from the multilayer structure. While the electromagnetic radiation in the visible to infrared wavelength range is bent out of the beam path, the electromagnetic radiation in the UV wavelength range is absorbed by this absorbing layer, so that the relative intensity of the radiation in this wavelength range compared to the intensity of the radiation in the wavelength band the EUV lithography is performed is reduced.

The Absorbent layers can be used both on the spectral filter serving optical element, that is on the multilayer system or be applied to the lattice structure as the uppermost layer as well as on EU optical path subsequent optical surfaces.

Prefers is the material of one of the group silicon nitride, silicon carbide, amorphous carbon, diamond-like carbon, silica, Magnesium fluoride, calcium fluoride, lithium fluoride, sodium fluoride, Lead fluoride, cesium iodide, zinc sulphide, titanium dioxide, zirconium oxide, Barium titanate, tellurium, selenium, germanium and combinations thereof. Because each of these materials in a slightly different waveband absorbed particularly well, may be due to the choice of materials and in particular the combination of different absorbent materials the same optical surface or on different optical surfaces the spectral filter properties particularly good at the respective light source and its emission spectrum be matched.

In In another preferred embodiment, the additional ones are Means of mitigating the EUV share of radiation as an additional lattice structure on the optical element are formed. To disturbing electromagnetic radiation both in the VIS / IR range as well as in the UV range from the beam path, thus becomes a multiple lattice structure with a lattice constant, which is adapted to the long-wave range, and a second one Lattice constants adapted to the shorter wavelength range is proposed.

Prefers is the extra grid structure as binary Lattice formed, that is as a grid, in which the furrow depth is essentially constant. Very particularly preferred are both the primary lattice structure for bending the long-wave Light as well as the additional grid structure as binary Grid formed. This self-similar double lattice structure is characterized by the fact that they are particularly easy to manufacture can be where in the places where lattice furrows provided are appropriate apertures are provided. The finer grid structure for bending the UV wavelength range can also applied by subsequent microstructuring be, for. B. by removal by means of ions or electron beams. self-similar Grid structures can be not only as a double, but also as triple, quadruple, quintuple, etc. lattice structures form, with the extinction of other wavelengths be achieved by appropriate selected grid parameters can.

Furthermore let the self-similar lattice structures especially good with the previously described additional absorbent Layers on both the double lattice structure itself and on combine subsequent optical surfaces.

When particularly advantageous has been found, the additional Form grid structure as a blazed grid, that is instead of furrows and ridges, areas below provide a certain wedge angle or blaze angle. The blazed grid may have a sawtooth profile. The angle can be so dimensioned be that wavelengths in the UV range reflecting at this Surfaces are reflected, and thereby directed out of the beam path become. The inclined surfaces can be immediate into the multilayer system with lattice structure, both in furrows and on crests of primary Lattice structure, allowing also the reflection of the EUV radiation the individual layers of the multi-layer system remains unaffected. As already low processing depths for the production of blazed Lattice structures sufficient by etching or mechanical Processing of the basic structure of a grid system formed as a grid can be produced, such double lattice structures can be much easier and less effort to produce than conventional known blazed grids, which are all wavelengths, which longwave than the EUV range are to be reflected. The double lattice structure with blazed lattice can also with absorbing layers are combined.

In a further preferred embodiment, the additional means for attenuating the intensity in the ultraviolet wavelength range are formed as scattering centers for electromagnetic radiation in the ultraviolet wavelength range on the surface of the optical element. For this purpose, after the production of the multi-layer structure with lattice structure, particle clusters can be deposited on the surface or the surface can be subsequently roughened. When using particle clusters, these preferably have a material which has a particularly low absorption in the EUV wavelength range, in particular in the working wavelength band. The lateral extent of the Scattering centers is preferably clear, preferably one to two orders of magnitude above the wavelengths to be scattered. The use of scattering centers can be combined with the aforementioned embodiments on the basis of absorbent layers or in particular with the additional grid structures.

In a further preferred embodiment, for Projection exposure equipment is suitable, which in a scanning mode along a scanning direction with a wavelength in the extreme ultraviolet wavelength range are operated, wherein the optical element receives light from a light source on the object side and illuminates an area in an image-side plane which is from spanned by a local coordinate system, the y-direction of the local coordinate system parallel to the scan direction and the x direction is perpendicular to the scan direction is the lattice structure oriented in such a way that, if they are to be illuminated in the image side Level is projected, which in the far field caused by the lattice structure Shadowing with respect to the y-direction of the local coordinate system are inclined in the image-side plane.

This Approach can be used both in conjunction with the previously described implement optical elements, which is a combination of multi-layer system with first lattice structure against visible and infrared light as well from other agents against UV light, as well as in any further optical elements having a grid structure.

this Approach is based on the knowledge that shadows in the Image plane, which are caused by grid grooves, the illumination a mask or a reticle and the image quality on a wafer least negatively affect if they are not parallel to the scanning direction. It is particularly advantageous when they are substantially perpendicular to the scan direction. The Matching the orientation of the lattice structure with the scanning direction in the image plane, lattices have a particularly advantageous effect, in comparison with the illuminated or projected structures are big as for example grid for suppression the visible and infrared wavelengths. at the embodiments with additional grid structure to reduce the UV content is preferably their lattice structure essentially coincident with the lattice structure for diffracting electromagnetic radiation in visible oriented to infrared wavelength range.

advantageously, the lattice structure has lattice grooves whose distance in the y-direction, that is variable in the scanning direction. This has the advantage that rays of one wavelength are not limited to one, two or one a few points complained about being deflected in the beam path, but on a variety of points, so the heat load spread over a larger area, to avoid thermal deformation as much as possible.

This Effect can be achieved in a further embodiment be that the grid structure has grid grooves, the one have a curved course. In particularly preferred embodiments The lattice grooves both have a curved course as well as a variable distance in the y-direction to the deflected Radiation components on a particularly large area to distribute.

In particularly preferred embodiments is the above-described optical element formed as a collector mirror. But it can also elsewhere in a lighting system or a Projection exposure system used for EUV lithography become.

In In another aspect, the object is achieved by a Illumination system for a projection exposure apparatus, those with a wavelength in the extreme ultraviolet wavelength range is operated, which is one of the above-described optical elements having.

In a preferred embodiment, the illumination system yet another optical element on his Surface has a layer comprising a material the electromagnetic radiation in the ultraviolet wavelength range absorbed more strongly than in the ultra-ultraviolet wavelength range. In the above-described optical element of the illumination system according to this embodiment may be to an optical element in the basic version with a EUV multilayer system with grating structure for diffraction of visible and infrared radiation, wherein the absorbing layer on the further optical element the function of the additional Means to suppress the ultraviolet wavelength range takes over. The absorbent layer on one or more other optical Elements can with all other optical elements described above be combined according to the present invention.

In a further aspect, the object is achieved by a projection exposure apparatus which is operated with a wavelength in the extreme ultraviolet wavelength range, or by a projection exposure apparatus which is operated in a scanning mode along a scanning direction with a wavelength in the extreme ultraviolet wavelength range, which one of the above optical elements according to the present invention having.

In preferred embodiments is between the optical Element and the image side illuminated plane a field facet mirror arranged, wherein the grid grooves substantially in the longitudinal direction the facets of the field facet mirror run. This is based on recognizing that in the presence of a field facet mirror in the beam path behind the optical element, which serves as a spectral filter whose grid structure is based on the arrangement of the field facets of the field facet mirror can be tuned to a homogeneous Illumination of the reticle or the mask and a homogeneous beam uniformity to get in the scanning direction. If one chooses the course of the Grid furrows excellent in the longitudinal direction of the Field facets on the field facet mirror, one achieves that shadowing in the Far field through the lattice structure substantially perpendicular to Scanning direction of the projection exposure device are and thus cancel.

In Another preferred embodiment has the projection exposure system at least one further optional optical element, wherein on the surface of which a layer is arranged, the a material containing electromagnetic radiation in the ultraviolet Wavelength range absorbed more strongly than in extremely ultraviolet wavelength range.

The The foregoing and other features are excluded from the claims also from the description and the drawings, the individual Characteristics in each case alone or in several form sub-combinations in one embodiment of the invention and be realized and advantageous in other fields as well represent protectable versions can.

The The present invention is intended to be better understood with reference to a preferred Embodiment will be explained in more detail. Show this

1 schematically the basic structure of an embodiment of the optical element with spectral filter action;

2 a way of making the in 1 illustrated basic structure;

3 schematically a first variant of the embodiment of 1 as a component of a lighting system;

4 schematically a second variant of the embodiment of 1 ;

5 schematically a third variant of the embodiment of 1 ;

6 schematically a fourth variant of the embodiment of 1 ;

7 a schematic diagram of the operation of the fourth variant;

8th schematically a projection exposure system for EUV lithography;

9 schematically the local coordinate systems of the projection exposure system 8th ;

10 a first variant of the alignment of grating structures of a spectral-filtering optical element;

11 a second variant of the alignment of grating structures of a spectral-filtering optical element;

12 a third variant of the alignment of grating structures of a spectral-filtering optical element;

13 a fourth variant of the alignment of grating structures of a spectral-filtering optical element; and

14 a fifth variant of the alignment of grating structures of a spectral-filtering optical element.

In 1 is an example of an embodiment of the optical element 1 shown schematically, in which the optical element as a collector mirror 1 is designed for an EUV lithography device. The collector 1 has in the example shown here a diameter D of about 650 mm with a radius of curvature of about 350 mm. It is arranged around the light source, that of a plasma droplet 2 is formed by an infrared laser 3 is stimulated. In order to obtain wavelengths in the range of, for example, 13.5 nm in the EUV wavelength range, tin, for example, can be excited to a plasma by means of a carbon dioxide laser operating at a wavelength of 10.6 μm. Instead of a carbon dioxide laser, for example, solid state lasers can be used. In addition to the radiation in the EUV wavelength range, the plasma also emits long-wave radiation, for example in the UV wavelength range, in particular in the DUV wavelength range. About the infrared laser 3 In addition, infrared radiation is introduced into the system to a greater extent.

The collector 1 has on its inner surface a lattice structure 13 that in a multi-day system 12 is trained. The multi-layer system is on a substrate 9 applied, preferably from a Material with the lowest possible coefficient of thermal expansion is, for example, glass-ceramic or titanium-doped silica. In the multi-day system 12 These are essentially layers of a material which is somewhat more absorbent at the desired working wavelength, and also absorbers 10 called, and a little less absorbent material, also spacers 11 called. About these alternating layers 10 . 11 a crystal is simulated, with the absorber layers 10 correspond to the lattice planes at which Bragg reflection can take place. The thickness of a stack of absorber layer 10 and spacer layer 11 Can over the whole multi-day system 12 be constant or variable. There may also be additional layers between absorber 10 and spacers 11 be provided. The first layer on the substrate 9 can be an absorber layer 10 or a spacer layer 11 be. Also, the final vacuum towards the position can both an absorber layer 10 or a spacer layer 11 be. Both between substrate 9 and multi-day system 12 as well as on the multi-day system 12 towards the vacuum, one or more additional layers may be provided.

Im in 1 illustrated embodiment is in the multi-layer system 12 into a grid structure 13 educated. In the present example, this is a binary grid whose depth t, the height distance between the grid groove 15 and the grid comb 14 is a constant value. The grid structure 13 has a lattice constant G, which is a measure of the distance between two lattice grooves 15 or two grid combs 14 is, and as well as the depth t is chosen so that in particular the infrared component of the incident electromagnetic radiation, which is located for example in the wavelength range around 10.6 microns, at which the laser of the radiation source is operated, is bent away. As in 1 shown schematically, the infrared beam 6 on the beam path out on the aperture 5 steered while the UV rays 7 and the EUV rays 8th in the intermediate focus 4 cross and through the aperture 5 pass.

The multi-layer coating with a lattice structure on the surface of the collector mirror can be produced particularly simply in the case of a binary lattice structure. As in 2 is shown schematically, after a first number of stacks of absorber layers 10 and spacer layers 11 was applied over a blind holder 17 a panel 16 on the substrate 9 attached, as well as with spacers 18 is provided to both the lattice constant G and the depth T of the grid to be produced 13 in the multi-day structure 12 set. Thus, the production of the lattice structure 13 problem-free in the production of the multi-layer system 12 can be integrated, which can be carried out by conventional coating methods such as electron beam evaporation, chemical vapor deposition (CVD), sputtering, such as magnetron sputtering, and the like. This allows, even larger optical surfaces such. B. at a collector mirror or even in the beam path behind arranged mirrors, which can also reach diameters of up to 1 m or more, and in curved surfaces in the in 1 applied example presented grid structure.

The in 1 illustrated collector mirror has additional means, which are designed for the change of the relative intensity and / or propagation direction of electromagnetic radiation in the UV wavelength range. These means can be designed in various ways.

In the in 3 variant shown are absorbent layers 20 provided, the material which absorbs electromagnetic radiation in the UV wavelength range stronger than EUV wavelength range, in particular in the working wavelength band for which the multi-layer system 12 was optimized. In 3 is the collector 1 in conjunction with a lighting system that is part of a projection exposure apparatus for EUV lithography. On the already described collector 1 follow after the aperture 5 at the intermediate focus 4 a field facet mirror 16 with individual facets 18 and a pupil facet mirror 17 with individual facets 19 With. Before the rays strike the reticle to be scanned in the y direction with the structure to be projected onto a wafer, it is still deflected by a folding mirror. The folding mirror 22 has less visual function, but rather serves to optimize the space requirement of the lighting system.

The through the aperture 5 passing UV radiation 7 and EUV radiation 8th meets the individual facets 18 of the field facet mirror 16 , Every facet 18 is with an absorbent layer 20 equipped with the UV rays 7 absorbed more strongly than the UV rays 8th so on the facets 19 of the pupil facet mirror 17 also with absorbent layers 20 equipped, UV rays 7 occur in which the intensity has decreased significantly more than the also of the facet mirror 16 on the pupil facet mirror 17 steered EUV rays 8th , Due to the combined effect of the absorbent layers on the facets 18 of the field facet mirror 16 and on the facets 19 of the pupil facet mirror 17 will be in 3 example shown that on the reticle 23 the proportion of UV light is negligibly small while the EUV radiation 8th still striking with a sufficient intensity. When choosing the thickness of the absorbent layers 20 is advantageously taken to ensure that As little as possible EUV radiation, in particular at the operating wavelength at which the lithography process is performed, is absorbed.

The absorbent layers may be constructed of one or more layers of one or more materials. Different facets can use different materials of their absorbent layer 20 exhibit. Likewise, on different optical elements such. B. the field facet mirror 16 and the pupil facet mirror 17 different materials for the absorbent layers 20 be provided. Particularly preferred materials are silicon nitride, silicon carbide, amorphous carbon, diamond like carbon, silica, magnesium fluoride, calcium fluoride, lithium fluoride, sodium fluoride, lead fluoride, cesium iodide, zinc sulfide, titanium dioxide, zirconium oxide, barium titanate, tellurium, selenium, germanium, and combinations thereof.

In the present example, the field facet mirror was made with absorbing layers 20 made of silicon nitride and the pupil facet mirror with absorbing layers of silicon carbide. Silicon nitride tends to absorb in the DUV range, while silicon carbide tends to absorb in the longer wavelength UV range. At the same time, both materials have a very low absorption coefficient in the range of, for example, 13.5 nm, which in the present example is the operating wavelength for EUV lithography. This effectively prevents false light from the UV wavelength range from striking the REticle and possibly also the wafer and leading to incorrect exposures.

The absorbing layer 20 can also be already on the collector 1 be applied or applied exclusively on the collector. Likewise, an absorbent layer 20 also be provided on other optical elements, such as the folding mirror 22 or also on mirrors of the projection system arranged in the beam path behind the reticle. Preferably, particularly long-wave radiation such as VIS and especially IR radiation is removed from the beam path as early as possible in order to reduce the heat load in the system on the individual optical elements as efficiently as possible. Long-wave radiation is particularly preferably removed as completely as possible in the illumination system, since the thermal load, which can lead to poor imaging properties due to thermally induced deformations and reflectivity losses of the multilayer systems, merely leads to defocusing or drift of focus within the illumination system, which is easier to achieve compensate as wave field aberrations that could occur in the projection system.

Investigations have shown that, for example, an arrangement of a collector with a binary grid such as in 1 Silicon carbide shown and absorbing layers with thicknesses of about 5 nm to 15 nm, preferably 7 nm to 10 nm on both the grating structure of the collector and on the facets of a subsequent field facet mirror and a subsequent pupil facet mirror stray light in a wavelength range of about 100 nm to 400 nm from a ratio of stray light to EUV radiation of about 1 in the radiation emitted by a plasma source to a ratio of stray light to working wavelength band in EUV of less than 1% of the wafer to be exposed suppressed. By optimizing the thicknesses of the absorbent layers, a ratio of 0.5% on the wafer can be achieved.

Another variant of a means for filtering out the UV radiation in conjunction with in 1 The illustrated basic structure of the spectral filtering optical element is shown in FIG 4 shown. On the already explained lattice structure with lattice constant G1 and depth t1, an additional lattice structure with lattice constant G2 and depth t2 is arranged, wherein both lattices are similarly designed as binary lattices. Here, the G2 and t2 are designed so that they lead to destructive extinction in the 0th diffraction order, the back reflection for at least one further wavelength, which is significantly smaller than, for example, the infrared wavelength by 10.6 microns. While for the infrared radiation destructive interference takes place at the first lattice structure with lattice constant G1 and depth t1, the structure of the second lattice structure with lattice constant G2 and depth t2 is not resolved by it, while at this second lattice structure destructive interference for UV radiation 7 takes place. The EUV radiation 8th remains unaffected by lattice structures. It penetrates the multi-day system 12 in which reflection takes place at each interface, which constructively adds up.

This variant is particularly well suited if the light source emits less a continuous spectrum but distinct emission peaks. By tuning the lattice constants and the depth to the wavelength of these emission peaks, these interfering wavelengths can be deliberately suppressed. In particular, grating structures can be provided not only for the first and second wavelength but also for a third and fourth or further wavelength. At all these wavelengths destructive interference in the 0th diffraction order takes place at the grating structures, so that these wavelengths are bent away from the intermediate focus and, for example, over the diaphragm 5 can be removed from the system. This variant works well with absorbent layers as regards 3 explain how to combine.

Another variant of an optical element with spectral filter effect such. B. the collector 1 out 1 with means for spectral filtering of UV radiation is in 5 shown. On the surface of in 1 explained basic structure are scattering centers 24 applied. For the scattering centers 24 Preferably, a material is selected which has a low absorption coefficient for EUV radiation, in particular in the range of working wavelength. Im in 5 example shown are the scattering centers 24 made of silicon. The spacer layers 11 of the multi-day system 12 are also made of silicon, while the absorber layers 10 of molybdenum to achieve a working wavelength at about 13.5 nm. In order in particular to scatter the UV components of the incident radiation, the lateral formation of the scattering centers should be adapted to the wavelength to be scattered. Thus, for a high scattering, the lateral extent of the scattering centers should 24 are on the order of 100 to 1000 times the wavelength to be scattered, which is between about 100 nm and 500 nm for the UV to VIS range. The PV values or peak-to-valley values of the surface profiles resulting from the scattering centers are preferably in the range of 15 to 35% of the wavelength. Particularly preferred are PV values in the range of 25 to 125 nm. In addition to the good scattering effect must also be taken into account that scattering centers should not be so thick that too much EUV radiation 8th is absorbed. At the specified values for the in 5 As shown, one can assume an absorption of the EUV radiation by the silicon scattering centers in the range of about 10 to 20%.

Since im in 5 example shown, the scattering centers 24 made of the same material as the Spacerlagen 11 , the application of the scattering centers 24 immediately after the production of the multi-layer system 12 be performed. By suitable screens, the size of the scattering centers 24 influence. In further modifications, scattering centers can also be produced by microlithographic processes or by mechanical processing of the surface. Here are the scattering centers 24 be designed as other surface roughness. The removal of the UV radiation from the beam path by means of scattering centers can be done well with the removal of UV light by diffraction by means of self-similar grating as in 4 combine described. While by means of the grating structures particularly strong emission peaks are bent out of the radiation, at the same time the scattering centers can be used 24 the remaining UV wavelengths of the continuous emission spectrum are scattered out of the beam path.

A particularly efficient variant in terms of filtering out harmful UV radiation 7 is in 6 shown. On the already described basic grid for diffracting infrared radiation 6 a blazed grid is superposed with blaze height d, blaze width b and blaze angle α. While the basic lattice has a depth of about 2.65 microns and the lattice constant is about 0.5 to 1 mm to obscure 10.6 microns of infrared radiation, the dimensions of the superimposed blazed lattice are chosen such that the UV Shares 7 the incident radiation is reflected specularly on the roof-like structure of the Blaze grating, so that they too are deflected out of the beam path. For the destructive interference of infrared rays 6 the blaze grid structure is without influence. Rather, the Blazegitter is in its dimensions by one or two orders of magnitude too small to the infrared radiation 6 to be dissolved. To get a specular reflection for the UV radiation 7 having wavelengths in the range of about 100 nm to 500 nm, the blazed grating has an extension in the range of 50 to 200 μm. Looking at an example of a blazed grating with a blaze height d of 400 nm and a blaze width b of 40 μm, a blaze angle of α = 10 mrad would result. If the blazed lattice structure were located about 1 m from the intermediate focus, this would result in a deflection from the intermediate focus of 20 mm for the UV components. Due to the specular reflection of the UV component 7 the radiation thus substantially completely removed from the beam path. This is comparatively better than with the use of absorber layers in which the proportion of UV radiation at each absorber layer is only slightly more suppressed. However, the absorber layers have a higher suppression factor, namely from 4 to 5, than the self-similar lattices, which lead to only a factor of 2 suppression. The disadvantage, however, is that the blazed lattice structure is somewhat more expensive to produce. It can be produced by etching or mechanical processing. Since the etching depth in the range of usually less than 0.5 microns, the production cost is manageable.

In 7 the function of the superposed bladder structure is shown schematically enlarged. In a multi-layered structure 12 , for example, molybdenum and silicon as absorber and spacer for reflection of EUV light 8th of about 13.5 nm, the stack of absorber and spacer has a thickness d of about 7 nm. As a rule, the UV radiation penetrates 8th in about 50 stacks in and is reflected at each molybdenum-silicon interface. Constructive interference of the individual reflections in the far field produces an EUV reflex with a reflectivity of more than 50%. Since the calculation index is almost identical to 1 for both silicon and molybdenum, a tapered surface with a wedge angle α is used as in 7 barely a change of direction of the reflected th UV ray 8th , At a wedge angle α of 1 mrad the direction change is only 60 mrad. The false light background with wavelengths of more than about 50 nm no longer dissolves the multilayer structure on the order of 7 nm, so that only a reflective reflection on the surface can take place to the vacuum. However, according to the geometric optics, the angle of incidence is equal to the angle of reflection. At a wedge angle α of 1 mrad thus results in a change in direction of the false light beam 7 by 2 mrad. It is therefore larger by a factor of 30 than in the EUV beam 8th , This results in that at a distance of 1 m the EUV beam 8th and the UV ray 7 already separated by 2 mm from each other.

In 8th is a principle view of a projection exposure system for the production of, for example, microelectronic components operated in a scanning mode along a scanning direction with a working wavelength in the EUV range and can have one or more optical elements with spectral filter function.

In the 8th The projection exposure apparatus shown comprises a light source 1 , as well as a collector 30 for illuminating a plane 103 with the help of the plane mirror 300 in the beam path between the collector 30 and the intermediate focus Z. The plane mirror 300 is used to fold the system to build space for mechanical and electronic components in the object plane 114 in which the wafer holder is arranged to provide. The collector 30 and / or the plane mirror can spectral filter function and be provided with a lattice structure, in particular the already explained structures for filtering different wavelength bands. Together with the aperture 302 in the vicinity of the intermediate focus Z of the radiation source can thus unwanted radiation with, for example, wavelengths substantially greater than the desired wavelength, in this case 13.5 nm, from entering the part of the rear of the aperture 302 lying lighting system are held.

The lighting system is followed by a field facet mirror 102 and a pupil facet mirror 104 , The subsequently arranged mirrors 106 . 108 and 110 essentially serve the field in the object plane 114 to shape. In the object plane 114 a structured mask, not shown, arranged by means of a projection lens 126 with in this example nice mirrors 128.1 -6 to the object to be exposed in the plane 124 is shown. The coordinate systems for all components of the illumination system of the projection exposure apparatus according to 8th except the collector 30 are in 9 shown. All optical elements have the same reference numerals as in 8th busy. Shown are the y-direction, which corresponds to the scan direction, as well as the z-direction, which roughly corresponds to the beam direction.

The reticle is in the drawn as a scanning system projection exposure system in the direction shown 116 movable and is successively illuminated in sections to the respective structures of the reticle with the projection lens 126 according to, for example, to project a wafer. The exit pupil of the illumination system is largely homogeneously illuminated. The exit pupil coincides with the entrance pupil E of the subsequent projection objective 126 together. The entrance pupil is located at the point of intersection of the principal ray reflected by the reticle with the optical axis of the projection objective 126 ,

In particular, when used in projection exposure systems, which are operated in a scanning mode along a scanning direction, as just in connection with 8th . 9 explained, it is advantageous if the geometry of the grid structure is optimized so that it affects the illumination of the reticle and the projection of the reticle structure on the wafer as little as possible. If light from a light source is received by the optical element on the object side and a region in an image-side plane spanned by a local coordinate system, the y-direction of the local coordinate system is parallel to the scanning direction and the x-direction is perpendicular to the scanning direction have proven advantageous that the grating structure is oriented such that when it is projected in the plane to be illuminated on the image side, the shadowing caused in the far field by the grating structure with respect to the scanning direction in the image-side plane are inclined. Particularly preferably, they run as parallel as possible to the x-direction. This is especially true for the primary lattice structure, which serves to diffract visible as well as infrared light. Because these structures have macroscopic dimensions that can certainly lead to greater shadowing. Although microscopic structures such as the self-similar lattices or the superposed Blazegittern have a lower shading effect. Preferably, however, they are oriented according to the primary lattice structure.

In projection exposure systems such as in 8th representing a field facet mirror 16 the shading effect can be advantageously reduced by the lattice grooves of the lattice structure 13 of the optical element 1 if possible in the longitudinal direction of the field facets 18 on the field facet mirror 16 run like in 10 shown. This is where the facets run 18 of the field facet mirror substantially parallel to the scanning direction y. In this way it is achieved that shadows in the far field through the grating structure are perpendicular to the scanning direction of the projection exposure apparatus and thus cancel each other during the scanning of the reticle. As a result, the highest possible homogeneity of the reticle illumination is obtained.

A particularly good illumination homogeneity is achieved if the lattice structure is arranged substantially parallel to the x-direction and thus perpendicular to the scanning direction, as in FIG 11 shown. This in 11 illustrated optical element 1 with spectral effect has a lattice structure 13 with over the entire y-direction constant lattice constant. This optical element 1 leads to a spectral separation at the intermediate focus 4 , in which the UV and the EUV share 7 . 8th the incident radiation is essentially in the intermediate focus 4 and thus through the aperture 5 can pass through while the infrared portion 6 so far from the intermediate focus 4 he is distracted from the aperture 5 is stopped. The diffraction takes place in the y direction. With a lattice constant of 1 mm, the first diffraction order for infrared radiation of about 10 μm is 10 mm away from the intermediate focus. The high energy density in the first diffraction order leads to a locally very strong thermal load. In general, about 80% of the intensity of the infrared radiation is in the first diffraction orders and about 10% to 15% in the second diffraction orders further from the intermediate focus 4 removed and not shown. The higher diffraction orders have less energy and are even further away from the intermediate focus.

In 12 is another variant of the optical element 11 in which the lattice constant is a function of the direction y. While the lattice constant G (y) is particularly large in the central region, it becomes smaller and smaller towards the edges in the y direction. This has the positive effect of depending on where on the optical element 1 the infrared radiation 6 was bent, it is pictured in another location in the y-direction. This allows better distribution of the thermal load. The distribution over a larger area also allows easier integration of cooling devices to absorb the thermal load.

In the in 13 illustrated modifications of the 12 the grating period is again a function of the direction y, wherein also the grating structure is slightly curved, so the grating structure is also dependent on the x-direction. In this way, the previously line-like illumination is additionally smeared in the azimuthal direction, so to speak, which further reduces the local power density. However, since the structures are still mostly in the x-direction, the homogeneity of the reticle illumination is not significantly affected.

In 14 is a variant of the optical element 1 shown, which are suitable for light sources with a particularly high power density, in which the thermal load maximum on the area, for example, the aperture 5 must be distributed. The grid structure 13 is now rotationally symmetric about the center of the optical element 1 , This leads to the smearing of the first diffraction orders of the infrared radiation 6 in a circle. However, in this embodiment, the homogeneity of the reticle illumination is more impaired.

LIST OF REFERENCE NUMBERS

1

collector

2

plasma droplets

3

IR laser

4

intermediate focus

5

cover

6

IR beam

7

UV-beam

8th

EUV beam

9

substratum

10

absorber

11

spacer

12

Multilayer system

13

lattice structure

14

grid comb

15

grid furrow

16

Field facet mirror

17

Pupil facet mirror

18

facet

19

facet

20

absorbing layer

22

folding mirror

23

reticle

24

scattering center

30

collector

102

Field facet mirror

103

level

104

Pupil facet mirror

106

mirror

108

mirror

110

mirror

114

object level

124

level

126

projection lens

126.1-6

mirror

300

plane mirror

302

cover

D

Collector diameter

G, G1, G2

lattice constant

t, t1, t2

Grating grooves depth

y

scanning direction

b

Blaze width

d

Blaze height

a

Blaze angle

d

stack thickness

x

direction perpendicular to scan direction in scan plane

z

direction perpendicular to scan plane

e

entrance pupil

Z

intermediate focus

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• US 2006/0245057 A1 [0005]
• - EP 1540423 B1 [0006]
• - US 6707602 B2 [0007]
• WO 2005/119365 A2 [0008]
• US 7091505 B2 [0009, 0009]

Claims (23)

An electromagnetic radiation filtering optical element having a multilayer structure designed for the reflection of electromagnetic radiation in the extreme ultraviolet wavelength range, having a lattice structure designed to diffract electromagnetic radiation in the visible to infrared wavelength range, and 20 . 24 ) for the change in the relative intensity and / or propagation direction of electromagnetic radiation ( 7 ) are designed in the ultraviolet to visible wavelength range. An optical element according to claim 1, characterized in that the grating structure is for diffracting electromagnetic radiation in the infrared wavelength range and the means ( 20 . 24 ) for changing the relative intensity and / or propagation direction of electromagnetic radiation ( 7 ) are designed in the ultraviolet wavelength range. Optical element according to claim 1 or 2, characterized in that the additional means as a layer ( 20 ) are formed, which comprises a material, the electromagnetic radiation ( 7 ) is more strongly absorbed in the ultraviolet wavelength range than radiation ( 8th ) in the extreme ultraviolet wavelength region reflected from the multilayer structure. Optical element according to claim 3, characterized in that the material of the layer ( 20 ) is one of silicon nitride, silicon carbide, amorphous carbon, diamond-like carbon, silica, magnesium fluoride, calcium fluoride, lithium fluoride, sodium fluoride, lead fluoride, cesium iodide, zinc sulfide, titanium dioxide, zirconium oxide, barium titanate, tellurium, selenium, germanium, and combinations thereof. Optical element according to claim 3 or 4, characterized in that the layer ( 20 ) on the surface of the lattice structure ( 13 ) is arranged. Optical element according to one of claims 1 to 5, characterized in that the additional means as additional lattice structure (G2, t2, b, d, α) are formed. Optical element according to Claim 6, characterized that the additional lattice structure as binary Grating (G2, t2) is formed. Optical element according to Claim 6, characterized that the additional grid structure as a blazed grid (b, d, α) is formed. Optical element according to one of claims 1 to 8, characterized in that the additional means as scattering centers ( 24 ) for electromagnetic radiation ( 7 ) in the ultraviolet wavelength range on the surface of the optical element ( 1 ) are formed. Optical element according to one of claims 1 to 9, characterized in that the lattice structure ( 13 ) is formed as a binary grid (G, t). An optical element according to any one of claims 1 to 10 for a projection exposure apparatus operated in a scanning mode along a scanning direction having a wavelength in the extreme ultraviolet wavelength range, wherein the optical element receives light from a light source on the object side and illuminates an area in an image side plane, which is spanned by a local coordinate system, wherein the y-direction of the local coordinate system is parallel to the scanning direction and the x-direction is perpendicular to the scanning direction, characterized in that the grating structure ( 13 ) is oriented in such a way that when it enters the plane ( 114 ) is projected in the far field by the grid structure caused shadowing with respect to the y-direction of the local coordinate system in the image-side plane ( 114 ) are inclined. Optical element according to Claim 11, characterized in that the additional lattice structure has substantially the same orientation as the lattice structure ( 13 ) for diffracting electromagnetic radiation ( 6 ) in the visible to infrared wavelength range. An electromagnetic radiation filtering optical element for a projection exposure apparatus operated in a scan mode along a scanning direction having a wavelength in the extreme ultraviolet wavelength region, having a lattice structure and wherein the optical element receives light from a light source on the object side and a region in an image-side plane spanned by a local coordinate system, wherein the y-direction of the local coordinate system is parallel to the scan direction and the x-direction is perpendicular to the scan direction, characterized in that the grid structure ( 13 ) is oriented in such a way that when it enters the plane ( 114 ), the shadows caused in the far field by the grid structure with respect to the y direction of the local coordinate system in the image-side plane ( 114 ) are inclined. Optical element according to one of claims 11 to 12, characterized in that the grid structure is arranged such that the Abschat tions are at least partially perpendicular to the y-direction. Optical element according to one of claims 11 to 14, characterized in that the grid structure grid grooves ( 15 ), whose distance in the y direction is variable. Optical element according to one of claims 11 to 15, characterized in that the grid structure grid grooves ( 15 ), which have a curved course. Optical element according to one of claims 1 to 16, characterized in that it is used as a collector mirror ( 1 . 30 ) is trained. Illumination system for a projection exposure apparatus, those with a wavelength in the extreme ultraviolet wavelength range is operated, with an optical element according to one of the claims 1 to 17. Illumination system according to claim 18 with a further optical element, characterized in that it has on its surface a layer ( 20 ) comprising a material containing electromagnetic radiation ( 7 ) is more strongly absorbed in the ultraviolet wavelength range than in the extreme ultraviolet wavelength range (US Pat. 8th ). Projection exposure machine with one wavelength operated in the extreme ultraviolet wavelength range is, with an optical element according to one of the claims 1 to 10 or 17. Projection exposure machine operating in a scan mode along a scanning direction with a wavelength in the extreme ultraviolet wavelength range is operated with An optical element according to any one of claims 11 to 17th A projection exposure apparatus according to claim 21, wherein a field facet mirror is arranged between the optical element and the plane to be illuminated on the image side, characterized in that the grid grooves ( 15 ) substantially in the longitudinal direction of the facets ( 18 ) of the field facet mirror ( 16 ). Projection exposure apparatus according to one of claims 20 to 22 with a further optical element, characterized in that it has on its surface a layer ( 20 ) comprising a material containing electromagnetic radiation ( 7 ) is more strongly absorbed in the ultraviolet wavelength range than in the extreme ultraviolet wavelength range (US Pat. 8th ).

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