Optical diffraction element suppressing at least one target wavelength by destructive interference

Abstract

An optical diffraction element for suppressing at least one target wavelength by destructive interference. The optical diffraction element has at least three diffraction structure levels. The diffraction structure levels (N1, N2, N3, N4) can be assigned to at least two diffraction structure groups. The first of the diffraction structure groups is for suppressing a first target wavelength λ1. The second of the diffraction structure groups is for suppressing a second target wavelength λ2. For the two target wavelengths λ1 and λ2, the following holds: (λ1 - λ2) 2 / (λ1 + λ2) 2 < 20%. The topography of the diffraction structure levels can be described as a superposition of two binary diffraction structure groups. The boundary regions between adjacent surface sections of each of the binary diffraction structure groups have a linear path, and superimpose on each other at most along the sections of the linear path. As a result, it is an optical diffraction element with an extended use possibility especially for stray light suppression.

Description

[0001] This patent application claims the priority of German patent applications DE 10 2018 220 629.5 and DE 10 2019 210450.9, the contents of which are incorporated herein by reference. Technical Field

[0002] The invention relates to an optical diffraction element which suppresses at least one target wavelength by destructive interference. Furthermore, the invention relates to an extreme ultraviolet (EUV) collector of a projection exposure apparatus comprising such an optical diffraction element, an illumination system comprising such an EUV collector, an optical system comprising such an illumination system, a projection exposure apparatus comprising such an optical system, and a method for producing a structured element by means of such a projection exposure apparatus, and a structured element produced in this way. Background Art

[0003] An EUV collector comprising an optical diffraction element in the form of a grating is known from WO 2017 / 207401 A1 and from WO 2014 / 114405 A2. An embodiment of a grating for suppressing infrared (IR) wavelengths in EUV projection exposure equipment is known from the following publication: "Multilayer EUV optics with integrated IR-suppression gratings, T. Feigl et al., 2016 EUVL Workshop, Berkeley, June 13-16, 2016". EP 1 540 423 B1 describes a grating-based spectral filter for suppressing radiation outside the frequency band used in EUV lithography systems. US 2014 / 0131586 A1 describes a phase grating for a mask inspection system. DE 10 2009 044 462 A1 describes an optical filter element comprising a grating structure for diffracting infrared radiation in an EUV illumination system. The technical articles “Multilevel blazed gratings in resonance domain: an alternative to the classical fabrication approach”, M. Oliva et al., OPTICS EXPRESS, vol. 15, 2011, pp. 1473-1475, and “Highly efficient three-level blazed grating in the resonance domain”, M. Oliva et al., OPTICS LETTERS, vol. 35, 2010, pp. 2774-2776, describe different variants of blazed gratings. The technical article “Diffractive elements designed to suppress unwanted zeroth order due to surface depth error, V. Kettunen et al., Journal of Modern Optics, Vol. 51, No. 14, 2004, pp. 2111-2123” discloses diffractive elements for suppressing unwanted zeroth order diffraction due to profile depth error.

[0004] DE 195 16 741 A1 discloses a diffractive optically effective structural arrangement. DE 100 54 503 A1 discloses a light diffractive binary grating structure. WO 2007 / 031 992 A1 discloses a diffraction grating with a spatially continuously changing duty cycle.

[0005] The grating can be used to suppress stray light whose wavelength deviates from the wavelength of the light used. The stray light can then be diffracted by the grating towards a light trap (beam dump), whereas the light used takes a different path. Summary of the invention

[0006] The object of the present invention is to develop an optical diffractive element of the type mentioned above in such a way that its possibilities of use are expanded, in particular for stray light suppression.

[0007] This object is achieved by means of an optical diffraction element according to a first aspect of the present invention, wherein the optical diffraction element

[0008] - comprising a periodic grating structure profile having three diffractive structure levels, the periodic grating structure profile comprising a diffractive structure,

[0009] - predefined different structural depths relative to a reference plane,

[0010] - wherein the diffraction structure is arranged so that a first target wavelength λ in the infrared wavelength range 1 The wavelength range near the first target wavelength (the first target wavelength is diffracted by the grating structure profile) has a radiation component having at least 1 at least three different phases destructively interfering with each other in the zero and / or + / - first order diffraction,

[0011] - wherein the diffractive structure level predefines a topography of a grating period of the grating structure profile that is regularly repeated along a periodic running direction,

[0012] - wherein the diffractive structure level comprises:

[0013] - neutral diffraction structure level, which corresponds to a reference height of zero,

[0014] --Positive diffraction structure level, which is set to be λ higher than the neutral diffraction structure level 1 / 4+ / -20% of the optical path length, and

[0015] - a negative diffraction structure level, which is set to be λ lower than the neutral diffraction structure level 1 / 4+ / -20% of the optical path length.

[0016] The target wavelength λ can be selected 1 The wavelength range to be suppressed is close to the wavelength range to be suppressed so as to cover multiple wavelengths to be suppressed, such as different wavelengths of the pre-pulse and the main pulse of the EUV plasma light source.

[0017] In the case of the optical diffraction element according to the first aspect, firstly the positive diffraction structure level and secondly the negative diffraction structure level are implemented with a relative position at λ relative to the neutral diffraction structure level. 1 / 4 optical path length difference. 1 This tolerance may also be less than + / - 20% compared to + / - 4, and may be, for example, + / - 10%, + / - 5%, + / - 3%, + / - 2% or even + / - 1%.

[0018] In the case of the optical diffraction element according to the first aspect, the grating period of the grating structure profile can be subdivided into four periodic sections of the diffraction structure levels. Two of the four periodic sections can be implemented as neutral diffraction structure sections with neutral diffraction structure levels. One of the four periodic sections can be implemented as a positive diffraction structure section with a positive diffraction structure level. One of the four periodic sections can be implemented as a negative diffraction structure section with a negative diffraction structure level. In the case of this embodiment of the optical diffraction element, the two neutral diffraction structure levels can be arranged in the grating period in a manner separated from each other by positive diffraction structure levels or by negative diffraction structure levels. The separation of the two neutral diffraction structure levels from each other realizes a sequence of the diffraction structure levels, wherein in the direction of the periodic travel, there are an equal number of descending edges or side walls (the structure depth increases, the edge "towards the valley value") and rising edges or side walls (the structure depth decreases again, the edge "towards the peak value"), each with a comparable structure height difference. Firstly the falling edge and secondly the rising edge then respectively compensate one another with regard to possible phase errors, whereby the entire phase error which may originate from undesired edge structuring and / or undesired edge positions is reduced or completely avoided.

[0019] Optionally, the two neutral diffraction structure levels may also be directly arranged in sequence as neutral diffraction structure levels of twice the length in the grating period.

[0020] The four periodic segments into which the grating period of the grating structure profile can be subdivided can have equal lengths along the direction of travel of the period, wherein equal lengths are considered to exist if the lengths differ from each other by less than + / - 20%. Such an optical diffraction element produces a particularly good destructive interference suppression effect for the target wavelength. The lengths of the four periodic segments can deviate from each other by less than 20%, for example less than 15%, less than 10%, less than 5%, less than 2% or even less than 1%. The lengths of the four periodic segments can also be completely identical.

[0021] The four periodic segments into which the grating period of the grating structure profile can be subdivided can have the following sequence: positive diffraction structure level, neutral diffraction structure level, negative diffraction structure level, neutral diffraction structure level. Such a sequence of periodic segments has been found to be particularly suitable. A corresponding sequence can be achieved by cyclically exchanging the sequence indicated above, thus obtaining the following sequence, for example: neutral diffraction structure level, positive diffraction structure level, neutral diffraction structure level, negative diffraction structure level.

[0022] The following sequence of four periodic sections is also possible: negative diffraction structure level, neutral diffraction structure level, positive diffraction structure level, neutral diffraction structure level. Cyclic interleaving is also possible in this variant.

[0023] The following can be used as further variants of the sequence of the four periodic segments: neutral diffraction structure level, neutral diffraction structure level; positive diffraction structure level, negative diffraction structure level. In this case, two neutral diffraction structure levels are therefore directly adjacent to each other, being in particular a common neutral diffraction structure level of twice the length. For example, a cyclic exchange is also possible in the case of this variant.

[0024] In the case of the optical diffraction element according to the first aspect, the arrangement of the diffraction structure can be such that a target wavelength range including target wavelengths in the infrared wavelength range (which are diffracted by the grating structure profile) has radiation components having at least three different phases that destructively interfere with each other at least in the zero and / or + / - first order diffraction of the first target wavelength, wherein the target wavelength range except the first target wavelength λ 1 In addition, a second target wavelength λ 2, wherein the arrangement of the diffraction structure makes a wavelength range near the second target wavelength in the infrared wavelength range (which is diffracted by the grating structure profile) also have a radiation component, which has at least three different phases that destructively interfere with each other in at least zero and / or + / - first order diffraction of the first target wavelength, wherein the target wavelength range includes a target wavelength different from the first target wavelength in addition to the first target wavelength, wherein the arrangement of the diffraction structure makes a wavelength range near the second target wavelength in the infrared wavelength range (which is diffracted by the grating structure profile) have a radiation component, which has at least three different phases that destructively interfere with each other in at least zero and / or + / - first order diffraction of the second target wavelength, wherein for the two target wavelengths λ 1 and λ 2 The following holds true: 1 -λ 2 ) 2 / (λ 1 +λ 2 ) 2 <20%. The advantages of such a diffractive optical element correspond to those already explained above.

[0025] For the upper limit of the difference between the two target wavelengths, it can be established that: 1 -λ 2 ) 2 / (λ 1 +λ 2 ) 2 <10%, <5%, <2%, <1%, <0.5%, <0.2%, <0.1% or even <0.05%. For example, the upper limit value may be 0.037%. The upper limit value may also be significantly smaller, such as 0.0002%. The two target wavelengths suppressed by at least two diffractive structure groups of the optical diffraction element may be completely identical. The deviation (λ) characterizing the difference between the two target wavelengths 1 -λ 2 ) 2 / (λ 1 +λ 2 ) 2 It may be greater than 0.0001%, greater than 0.001%, greater than 0.01%, greater than 0.1%, greater than 0.2%, greater than 0.5%, greater than 0.7% and may be even greater.

[0026] The target wavelength may be in the IR wavelength range, for example, carbon dioxide (CO 2) laser. Alternatively or in addition, a wavelength in the near infrared (NIR) wavelength range, in the visible wavelength range, in the ultraviolet (UV) wavelength range or in the deep ultraviolet (DUV) wavelength range may constitute a target wavelength to be suppressed. One of the two target wavelengths may be 10.2 μm and the other of the two target wavelengths may be 10.6 μm. The target wavelengths may be adapted to the wavelengths of the pre-pulse and the main pulse of the EUV plasma light source.

[0027] The design of at least two diffractive structure groups for suppressing two different target wavelengths results in the suppression of wavelengths within a predefined wavelength bandwidth, which may also be referred to as the suppression design bandwidth. The wavelengths within this suppression design bandwidth (i.e., those that can be effectively suppressed by the optical diffraction element) may correspond to the target wavelengths, and / or may be between the target wavelengths, and / or may be outside the wavelength range between the target wavelengths. In order to suppress a wavelength of 10.2 μm, for example, the first target wavelength for which the first diffractive structure group is designed may be 10.25 μm, and the second target wavelength for which the second diffractive structure group is designed may be 10.55 μm. The target wavelengths are selected depending on the requirements of the optical diffraction element for suppressing a plurality of different wavelengths or wavelength bandwidths as required. In this case, in addition to the target wavelengths, the positions of further minima of destructive interference may also be taken into account, or it may be considered which wavelengths are deliberately not to be suppressed.

[0028] What has been discussed above in connection with the optical diffraction element may be used here in order to select the target wavelength λ 1 and λ 2 And established.

[0029] The aforementioned object is achieved by means of an optical diffraction element for suppressing at least one target wavelength by destructive interference according to a second aspect of the present invention, wherein the optical diffraction element

[0030] - comprises at least three diffractive structure levels with predefined different structure depths relative to a reference plane,

[0031] - wherein the three diffractive structure levels are assignable to at least two diffractive structure groups,

[0032] - wherein a first group of the diffractive structure groups is implemented to suppress a first target wavelength λ in the zero-order diffraction 1 ,and

[0033] - wherein the second group of the diffractive structure groups is implemented to suppress the second target wavelength λ in the zero-order diffraction 2 ,

[0034] - where for the two target wavelengths λ 1 and λ2 The following holds true:

[0035] - wherein the morphology of the diffractive structure level can be described as a superposition of two binary diffractive structure groups,

[0036] - wherein each of the binary diffractive structure groups has:

[0037] a first surface section having a first structural depth;

[0038] - second surface sections having a second structure depth, which alternate with the first surface sections along a running direction,

[0039] - wherein the boundary region between adjacent surface segments of each of the binary diffractive structure groups has a linear course, wherein

[0040] a first boundary region of the first of the two binary diffractive structure groups, and

[0041] -- A second boundary region of the second of the two binary diffraction structure groups

[0042] --At most the segments along their linear paths overlap each other.

[0043] The use of an optical diffraction element comprising at least three diffraction structure levels (which in turn can be assigned to at least two diffraction structure groups for suppressing corresponding target wavelengths that are not far from each other) surprisingly produces improvements in the suppression of target wavelengths that clearly exceed the suppression effect of individual diffraction structure groups. Compared with the optical diffraction elements of the prior art, this results in a design freedom that can be used to increase the flexibility of the use possibilities of the optical diffraction element. The different diffraction structure groups can occupy the same optically used area of ​​the optical diffraction element, i.e. they do not have to be arranged on mutually spaced sections on the aforementioned optically used area. The optical diffraction element can be designed in particular so that the two diffraction structure groups are designed specifically for suppressing the same target wavelength or stray light wavelength. Alternatively or in addition, the optical diffraction element can be designed specifically for suppressing multiple target wavelengths by means of an appropriate design of the diffraction structure groups. In the case of such an optical diffraction element comprising multiple diffraction structure groups, it is known that the diffraction effect is improved compared to an optical diffraction element comprising only one diffraction structure group. By using an optical diffractive element comprising a plurality of diffractive structure groups, the same suppression effect can thus be achieved with looser manufacturing tolerances compared to the prior art.

[0044] The diffraction structure group is an arrangement of at least two diffraction structure levels arranged and produced to suppress only one target wavelength. An example of a diffraction structure group is an optical grating. The assignment rule of the at least three diffraction structure levels to the at least two diffraction structure groups is such that at least one diffraction structure level is assigned to a plurality of diffraction structure groups.

[0045] The optical diffractive element according to the first aspect discussed initially may also comprise at least one or at least two groups of diffractive structures of this type.

[0046] The advantages with respect to the maximum difference between the two target wavelengths correspond to those already explained above. Those already discussed above in connection with the optical diffraction element according to the first aspect may here be used for selecting the target wavelength λ 1 and λ 2 And established.

[0047] For the second target wavelength λ 2 The latter is also true for the reduction or suppression of destructive interference due to appropriate design of the diffraction structure of the optical diffraction element.

[0048] The optical diffraction element may include exactly three diffraction structure levels and may include exactly two diffraction structure groups. Alternatively, the optical diffraction element may also include more than three diffraction structure levels (e.g., four, five, six or even more diffraction structure levels) and correspondingly also include more than two diffraction structure groups.

[0049] A binary structure is a structure comprising positive structures ("peaks") and negative structures ("valleys"), wherein the total area of ​​the positive structures corresponds to the total area of ​​the negative structures within a predefined tolerance. The difference between the total area of ​​the first positive structure and the second negative structure may be less than 20%, less than 10%, less than 5%, less than 2% and also less than 1%. The total areas may also be completely identical.

[0050] Since the boundary region of the first binary structure and the second binary structure at most overlaps with each other along the linear path of the boundary region, it is possible to produce the optical diffraction element by means of a relatively simple to produce photolithographic mask structure. This provides the possibility of accurately producing the optical diffraction element, wherein firstly narrow tolerances are met for the area of ​​the diffraction structure levels and also for their structure depth. In particular, it is possible to produce diffraction structure groups with a desired large and desired precise sidewall steepness of the boundary region.

[0051] The optical diffraction element can be manufactured so that a rising boundary region (ie, a rising level side wall) is assigned a falling boundary region with the same structural depth (ie, the same structural height difference).

[0052] Furthermore, the optical diffractive element according to the second aspect may have the features which have been discussed above with reference to the optical diffractive element according to the preceding claims.

[0053] In the case of the optical diffraction element, the first boundary region of the first of the two binary diffraction structure groups and the second boundary region of the second of the two binary diffraction structure groups can run completely separated from each other. Such a completely separated path of the boundary regions further simplifies the photolithographic production of the optical diffraction element, in particular.

[0054] A first group of the diffraction structures can be implemented as a first diffraction grating arranged on a grating surface. The aforementioned first diffraction grating can have a first grating period and a first structure depth, which is the optical path difference between first diffraction positive structures and first diffraction negative structures measured perpendicular to the surface section of the grating surface surrounding these first structures respectively. A second group of the diffraction structures can be implemented as a second diffraction grating arranged on a grating surface. Such a second diffraction grating can have a second grating period and a second structure depth, which is the optical path difference between second diffraction positive structures and second diffraction negative structures measured perpendicular to the surface section of the grating surface surrounding these second structures respectively. With such an embodiment, compared to gratings of the prior art, the use of a grating comprising at least two diffraction gratings having substantially mutually independent grating periods and substantially mutually independent structure depths, wherein the structure depth is small compared to the grating period in at least one of the diffraction gratings, results in a degree of design freedom that can be used to increase the flexibility of the use possibilities of the grating. The two diffraction gratings can occupy the same grating surface, in other words are not arranged on separate sections on the grating surface. The two diffraction gratings are therefore present in a superimposed manner on each other on the grating surface. The grating can be designed such that its stray light suppression is improved by virtue of two diffraction gratings designed for suppressing identical stray light wavelengths. Alternatively or additionally, the grating can be designed such that a plurality of stray light wavelengths can be suppressed. Furthermore, it has surprisingly been found that by virtue of the use of such a grating comprising a plurality of diffraction gratings, the diffraction effect, in particular the suppression effect due to destructive interference in the zero-order diffraction, is improved compared to a grating comprising only one diffraction grating. The same suppression effect can therefore be achieved with loose manufacturing tolerances by virtue of the use of a grating comprising a plurality of diffraction gratings.

[0055] The grating can be embodied as a reflection grating, but alternatively also as a transmission grating and, for example, as a phase grating.

[0056] The grating surface may be implemented as a plane or a curved surface, such as a convex or concave surface. The grating surface may be part of an optical surface of an optical element having some other optical function attached, for example, to a beam dump or a reflector. The first diffraction grating and / or the second diffraction grating may be implemented as a binary grating, wherein the surface area of ​​the positive structure is equal to the surface area of ​​the negative structure. In the simplest case, the structure depth may be the height difference between the corresponding diffractive positive structure and the associated diffractive negative structure.

[0057] The grating can additionally be provided with a highly reflective layer and, in particular, optional auxiliary layers for protecting the grating and / or the highly reflective layer. The highly reflective layer can be implemented as a multilayer. The highly reflective layer can be implemented for EUV light in the wavelength range between 5 nm and 30 nm in particular.

[0058] The optical diffraction element may be implemented as a multi-level diffraction grating having correspondingly arranged diffraction structure levels.

[0059] In this case, the structure depth can be one sixth of the target wavelength. With the multi-level gratings produced in this way, the structure depth can also be one quarter of the target wavelength.

[0060] Depending on the number of different diffraction structure levels m, depending on the target wavelength λ N The structural depth can be determined as follows: b = λ N / (2m).

[0061] The grating period may be in the millimeter range and may be, for example, 1 mm or 2 mm.

[0062] The diffractive structure levels may be implemented as planar surfaces.

[0063] The grating periods of different diffraction gratings may be in integer ratios to each other. The grating periods may have a defined phase shift with respect to each other.

[0064] The ratio of the grating periods can be 1:2. By using three diffraction gratings, the ratio of the grating periods can be 1:2:4 or 1:2:2.

[0065] The surface area ratio of the surface area of ​​the first diffraction positive structure to the surface area of ​​the first diffraction negative structure may be in the range of 0.9 to 1.1. The surface area ratio of the surface area of ​​the second diffraction positive structure to the surface area of ​​the second diffraction negative structure may be in the range of 0.9 to 1.1. Correspondingly, an accurate binary diffraction structure group is obtained.

[0066] A ratio between the first grating period and the first structure depth may be greater than 10. A ratio between the second grating period and the second structure depth may be greater than 10.

[0067] Correspondingly, different target wavelengths can be suppressed. In addition to the two target wavelengths λ 1and λ 2 In addition, further more significantly deviating target wavelengths can thus also be suppressed. For example, it is possible to suppress different target wavelengths in the infrared wavelength range and further target wavelengths in the ultraviolet wavelength range simultaneously.

[0068] A period ratio of the first grating period to the second grating period may be in a range between 0.9 and 1.1.

[0069] An optical diffraction element having such a period ratio can be easily manufactured. The grating periods of the first and second diffraction gratings can be completely equal, but can also be different.

[0070] The advantages of such an optical diffraction element combined with good reflection conditions in particular for EUV wavelengths enable good stray light suppression at higher wavelengths included in the case of the second diffraction grating.

[0071] The structure depth ratio of the structure depth of the first diffraction grating to the structure depth of the second diffraction grating can be in the range between 0.9 and 1.1. The structure depths of the first and second diffraction gratings can be different from each other, but can also be equal. In the range between 1.1 and 20, significantly larger structure depth ratios between the two diffraction gratings are also possible, for example a structure depth ratio in the vicinity of 10.

[0072] In the case of an optical diffraction element comprising two diffraction gratings arranged on a grating surface, the first grating period may run along a first periodic running direction of the first diffraction grating, and the second grating period may run along a second periodic running direction of the second diffraction grating, wherein the two periodic running directions may not run parallel to each other. Such an optical diffraction element in which the periodic running directions of the first and second diffraction gratings do not run parallel to each other has proven to be worth adopting. The minimum angle between the periodic running directions may be 90°, so that the two periodic running directions are perpendicular to each other. Smaller minimum angles (e.g. in the range of 60°, 55°, 45° or 30°) are also possible.

[0073] Alternatively, embodiments of the optical diffraction element are also possible in which the two periodic running directions of at least two diffractive structure groups run parallel to each other.

[0074] An optical diffraction element comprising two diffraction gratings arranged on a grating surface may comprise at least one additional diffraction grating arranged on the grating surface. The aforementioned additional diffraction grating may comprise an additional diffraction positive structure and an additional diffraction negative structure, wherein the surface area ratio of the surface area of ​​the additional diffraction positive structure to the surface area of ​​the additional diffraction negative structure is in the range between 0.9 and 1.1. The aforementioned additional diffraction grating has an additional grating period and an additional structural depth, which is the optical path difference between the additional diffraction positive structure and the additional diffraction negative structure measured perpendicular to the surface section of the grating surface surrounding these additional structures respectively. Such an optical diffraction element comprising at least one additional diffraction grating is further improved in terms of the available design freedom. At least two of the periodic travel directions of the at least three diffraction gratings may have mutually different directions. Alternatively, all periodic travel directions of the at least three diffraction gratings may also travel parallel to each other.

[0075] In the case of an optical diffraction element comprising a first diffraction grating, the second diffraction grating and the further diffraction grating are both arranged on the grating surface, and the ratio between the further grating period and the further structure depth may be greater than 10. The period ratio of the first grating period to the further grating period may be in the range between 0.9 and 1.1. The first grating period may run along a first period running direction of the first diffraction grating, and the further grating period may run along a further period running direction of the further diffraction grating, wherein the two period running directions do not run parallel to each other.

[0076] The advantages of such an optical diffraction element correspond to those explained above. The grating periods of the first diffraction grating and the further diffraction grating can be identical, but can also be different. Corresponding period ratios or identical grating periods in the range between 0.9 and 1.1 can also exist between the second diffraction grating and at least one further diffraction grating.

[0077] The structure depth ratio of the first diffraction grating with respect to the further diffraction grating may be in the range between 0.9 and 1.1; the structure depths of the first and further diffraction gratings may differ from one another, but may also be equal. A corresponding structure depth ratio in the range between 0.9 and 1.1 or an identical structure depth may also exist between the second diffraction grating and at least one further diffraction grating. Significantly larger structure depth ratios between the structure depth of the further diffraction grating and the first and / or second diffraction grating in the range between 1.1 and 20, for example around 10, are also possible.

[0078] The minimum angle between the periodic travel direction of the first diffraction grating and the further diffraction grating may be in the range between 20° and 25°. Some other minimum angles (e.g. in the range between 10° and 80°) are also possible. Corresponding travel direction angles may also exist between the periodic travel direction of the second diffraction grating and the periodic travel direction of at least one further diffraction grating.

[0079] The surface areas of the diffractive positive structures and diffractive negative structures of the various diffractive structure groups can contribute equally to the entire grating surface. Such an equal surface area contribution in particular produces a binary grating for different diffractive structure groups of the optical diffraction element. This ensures high stray light suppression in the region of the zero-order diffraction in the case of a suitable design of the optical diffraction element.

[0080] The features of the optical diffraction elements of the two aspects discussed above may also be combined with each other.

[0081] An optical diffraction element of at least one type in the two aspects discussed above can be manufactured by a mask etching method in which at least one mask structure is used. A plurality of mask structures that differ in the position of their mask regions and / or mask gaps can also be used. Then, the substrate can be etched by sequentially using these different masks or by shifting the same mask structure in at least two sequential etching steps. Three or more different mask structures can also be used in such a mask etching method for manufacturing an optical diffraction element.

[0082] The advantages of a collector or a collector mirror of an optical diffraction element which can be used in a projection exposure apparatus, in particular in an EUV projection exposure apparatus, and which has the properties described above, correspond to those which have been explained above with reference to the optical diffraction element. These advantages are evident in particular in the case of use in connection with an EUV light source in which the plasma is induced by a laser-induced discharge. The collector or the collector mirror can be an EUV collector / collector mirror for a wavelength range, in particular between 5 nm and 30 nm, and / or a deep ultraviolet (DUV) collector / collector mirror, i.e. a collector mirror for a wavelength range, in particular between 150 nm and 250 nm.

[0083] This applies in particular to EUV collector mirrors, wherein the collector mirror is implemented in such a way that it directs EUV radiation towards a focal region, and wherein the optical diffraction element is implemented in such a way that it directs radiation of at least one target wavelength away from the focal region. The radiation of at least one target wavelength is also called stray light.

[0084] The illumination system can comprise such a collector, in particular an EUV collector, and an illumination optical unit for illuminating an object field, in which the object to be imaged can be arranged. Light used by DUV or EUV can be used as illumination light. The advantages of such an illumination system correspond to those already explained above with reference to the collector according to the invention. The light used is precisely not suppressed by the optical diffraction element, i.e. has a wavelength different from the stray light to be suppressed.

[0085] The illumination system can be made by means of an optical diffraction element implemented as described above, so as to obtain a homogeneous distribution of the stray light in the region of the stray light removal location and, for example, in the region of a beam pile provided for this purpose. Alternatively or in addition, it is possible to ensure a predefined distribution function of the light used, in particular in a specified section of the illumination beam path of the illumination system, for example in the region of a pupil plane.

[0086] The optical system may comprise such an illumination system, and a projection optical unit for imaging the object field into an image field, wherein a substrate may be arranged in the image field and wherein a section of the object to be imaged can be imaged onto the substrate. A projection exposure device may comprise such an optical system and a light source, in particular an EUV light source. For the production of structured elements, a mask and a wafer may be provided. The structures on the mask can be projected onto the photosensitive layer of the wafer by means of such a projection exposure device. In this way, it is possible to produce microstructures and / or nanostructures on the wafer. The advantages of such an optical system, such a projection exposure device, such a production method and such a microstructured and / or nanostructured element correspond to those already explained above with reference to the collector according to the invention.

[0087] As long as an EUV light source is used, a pump light source may be included, which is used to produce a plasma that generates an EUV wavelength. The pump light source may be implemented to produce a pre-pulse having a pre-pulse light wavelength and to produce a main pulse having a main pulse light source. The pre-pulse light wavelength may be different from the main pulse wavelength. In the case of a pump light source of an EUV light source of the projection exposure apparatus, the corresponding difference between the wavelengths of the pre-pulse light and the main pulse light may have the wavelengths that have been described above with respect to the target wavelength λ. 1 and λ 2 An upper limit value and / or a lower limit value explained in association therewith.

[0088] In particular, semiconductor components, such as memory chips, can be produced using the projection exposure apparatus.

[0089] In particular during the production of the structured element, light of a wavelength range may be irradiated onto the collector such that light having a first wavelength λ 1 The light of the first wavelength λ is diffracted away from the focusing area of ​​the collector. 1The wavelength range may be within the infrared wavelength range. Such a wavelength range may include radiation components including at least three different phases that destructively interfere with each other in at least one diffraction order. Such at least one diffraction order may be a first wavelength λ 1 The zeroth order diffraction, the first wavelength λ 1 The positive first order of diffraction or the first wavelength λ 1 The wavelength range may also include a second wavelength λ 2 , and the method may further include a second wavelength λ away from the collector focal region 2 The second wavelength λ 2 Can be different from the first wavelength λ 2 The wavelength range may include radiation components including at least three additional different phases that destructively interfere with each other in at least one diffraction order, which may be a second wavelength λ 2 The zeroth order diffraction, the second wavelength λ 2 The positive first-order diffraction and the second wavelength λ 2 The negative first-order diffraction. BRIEF DESCRIPTION OF THE DRAWINGS

[0090] Exemplary embodiments of the present invention are explained in more detail below with reference to the accompanying drawings. In the accompanying drawings:

[0091] Figure 1 A schematic diagram of a projection exposure apparatus for EUV microlithography;

[0092] Figure 2 Details of a light source of a projection exposure apparatus are shown in the context of an EUV collector for directing EUV use light from a plasma source region to a field facet mirror of an illumination optics unit of the projection exposure apparatus, wherein the EUV collector is illustrated in a meridional section;

[0093] Figure 3 With Figure 2 Compared to a more abstract illustration, firstly the guidance of the EUV light used and secondly of the stray light components of different wavelengths in the case of reflection / diffraction at the EUV collector are shown;

[0094] Figure 4 A plan view of a section of a grating surface comprising two diffraction gratings as gratings of a group of diffraction structures with mutually perpendicular periodic running directions and equal grating periods, wherein a predefined Figure 4 The structure depths of three diffractive structure levels of a square diffractive structure in FIG. 1 are illustrated by means of different thin line types, wherein the grating constitutes an embodiment of an optical diffractive element which suppresses at least one target wavelength by destructive interference;

[0095] Figure 5 The graph shows the calculated ideal situation, the calculated more realistic situation and the reference grating not according to the invention. Figure 4 a wavelength-dependent reflectivity R of a grating of , wherein the two diffraction gratings of the grating are implemented to suppress two different wavelengths;

[0096] Figure 6 With Figure 5 A similar graph is shown based on Figure 4 in the case of gratings of , in which the two diffraction gratings have an equal structural depth, so that the gratings are implemented to suppress only one wavelength;

[0097] Figure 7 With Figure 4 Similar illustrations showing a further embodiment comprising two diffraction gratings as gratings of a group of diffraction structures having periodic progression directions at an angle of 45° with respect to each other, wherein the gratings constitute an embodiment of an optical diffraction element for suppressing at least one target wavelength by destructive interference;

[0098] Figure 8 With Figure 4 and Figure 7 A similar illustration shows another embodiment of a grating comprising three diffraction gratings as a diffraction structure group (two of which have periodic running directions perpendicular to each other, and wherein the third diffraction grating has a diagonal periodic running direction opposite thereto), wherein the grating constitutes an embodiment of an optical diffraction element that suppresses at least one target wavelength by destructive interference;

[0099] Fig. 9 With Figure 5 and Figure 6 A similar graph is shown based on Figure 8 Reflection relationship for the case of a grating of , wherein all three diffraction gratings are implemented to suppress the same wavelength;

[0100] Fig.10 With Fig. 9 A similar graph is shown in Figure 8 Reflection relationships in the case of gratings of the type shown, in which the three diffraction gratings have different structural depths, so that the gratings are embodied to suppress different wavelengths;

[0101] Fig.11 With Figure 8 Similar illustrations showing a further embodiment comprising three diffraction gratings as gratings of a group of diffractive structures having respective periodic travel directions presenting an angle different from zero in pairs, wherein the gratings constitute an embodiment of an optical diffraction element for suppressing at least one target wavelength by destructive interference;

[0102] Fig.12 and Fig.13 With Fig.11 Similar illustrations show that each includes three diffraction gratings as having corresponding Fig.11 A further embodiment of the grating of the diffraction structure group of the periodic travel direction of the embodiment of Fig.12 and Fig.13 The diffraction structures of the embodiments are offset relative to each other in the direction of the corresponding periodic movement and are in accordance with Fig.11 Embodiments of the invention are arranged in a manner related to further embodiments wherein the grating constitutes an optical diffraction element that suppresses at least one target wavelength by destructive interference;

[0103] Fig.14 A first group of diffractive structures belonging to a further embodiment of an optical diffractive element for suppressing at least one target wavelength by destructive interference is shown in a side view, which is implemented as a binary grating with a first grating period and a first structure depth;

[0104] Fig.15 With Fig.14 A similar illustration showing a further group of diffractive structures as part of the optical diffraction element, wherein the further group of diffractive structures is in turn implemented as a binary grating with a grating period and a structure depth, wherein possible overlay errors during the production of this group of diffractive structures are additionally indicated in a dashed line manner;

[0105] Fig.16 Display according to Fig.14 and Fig.15 An optical diffraction element that appears as a result of the superposition of the two diffraction structure groups;

[0106] Figures 17 to 19 With Figures 14 to 16 A similar illustration showing two groups of diffractive structures and the additional optical diffractive elements emerging therefrom as a result of the superposition;

[0107] Figure 20 to Figure 22 With Figures 14 to 16 A similar illustration showing two groups of diffractive structures and the additional optical diffractive elements emerging therefrom as a result of the superposition;

[0108] Fig.23 Display as a curve graph Fig.16 , Fig.19 or Fig. 22 The reflectivity of an optical diffractive element of the type shown, wherein the structure height of a respective first diffractive structure group is fixed at a value for suppressing a target wavelength, and the reflectivity is plotted as a function of the structure height of a further diffractive structure group;

[0109] Fig.24The reflectivity of the optical diffraction element is again shown in a graph, again wherein the structure depth of the first diffractive structure group is fixed, which is plotted as a function of the difference between the structure depths of the two diffractive structure groups and normalized to the structure depth of the first diffractive structure group;

[0110] Fig.25 With Fig.14 Similar illustrations show a diffractive structure group implemented as a binary grating with a grating period and a structure depth as part of a further embodiment of an optical diffractive element for suppressing at least one target wavelength by destructive interference, the aforementioned further embodiment arising from the superposition of three diffractive structure groups;

[0111] Fig.26 shows a further group of diffractive structures, which are again implemented as binary gratings for this variant embodiment of the optical diffractive element;

[0112] Fig. 27 shows a further group of diffractive structures, which are again implemented as binary gratings for this variant embodiment of the optical diffractive element;

[0113] Fig.28 Display optical diffraction element, which is formed based on Figure 25 to Figure 27 The superposition of the three diffraction structure groups;

[0114] Figure 29 to Figure 32 With Figure 25 to Figure 28 Similar illustrations show three groups of diffractive structures, which are again implemented in each case as binary gratings with a grating period and a structure depth, and further embodiments of optical diffraction elements which suppress at least one target wavelength by destructive interference, from which the aforementioned further embodiments emerge as a result of superposition;

[0115] Fig.33 With Fig. 9 and Fig.10 A similar graph is shown based on Figure 8 , Figures 11 to 13 , Fig.28 or Fig.32 The wavelength-dependent reflection relationship in the case of an optical diffraction element of any type, wherein the diffraction structure groups have different structure depths so that the grating is implemented to suppress different wavelengths, but they are different from those according to Fig.10 The variants are closer to each other than the others;

[0116] Fig.34 With Figure 4A similar illustration shows a section of a grating surface of a grating comprising three diffraction gratings as a diffraction structure group, wherein two of the gratings have parallel periodic running directions and the third grating has a periodic running direction perpendicular thereto, and wherein the diffraction structure group having the same periodic running direction is arranged according to Fig.16 , Fig.19 or Fig. 22 An embodiment of the present invention is superimposed in which Fig.34 The structure depth of the rectangular diffractive structure in FIG. 1 is illustrated by means of different thin line types as a further embodiment of an optical diffraction element which suppresses at least one target wavelength by destructive interference.

[0117] Fig.35 A further embodiment of a light diffraction element for suppressing at least one target wavelength by destructive interference is shown again in a schematic side view, which is implemented as a three-level grating, implemented to suppress only one target wavelength;

[0118] Fig.36 With Fig.35 Similar illustrations showing a further embodiment of a light diffraction element for suppressing at least one target wavelength by destructive interference, again made by means of three diffractive structure levels assignable to two diffractive structure groups, the depicted variables being depicted for a theoretical description of the calculation of the suppression efficiency of the at least one target wavelength;

[0119] Fig.37 With Fig.35 and Fig.36 A similar illustration shows another embodiment of an optical diffraction element for suppressing at least one target wavelength by destructive interference, which is implemented with four diffractive structure levels assignable to corresponding multiple diffractive structure groups;

[0120] Fig.38 and Fig.39 With Fig.37 Similar illustrations showing two further embodiments of an optical diffractive element for suppressing at least one target wavelength by destructive interference, again implemented with four diffractive structure levels;

[0121] Fig.40 Displays the graph including, for example, Figure 4 , Figure 7 , Fig.16 , Fig.19 , Fig. 22 , Fig.35 , Fig.36 wavelength-dependent reflectivity of an optical diffraction element of two diffraction structure groups of the type of an embodiment of the present invention, wherein the two diffraction structure groups are implemented with a structure depth for suppressing two DUV wavelengths;

[0122] Fig.41 With Fig.40 A similar illustration shows the wavelength-dependent reflectivity for an optical diffraction element comprising a total of five diffractive structure levels (to which four diffractive structure groups with different structure depths can be assigned), with two target wavelengths in the IR range above 10 μm and at a wavelength corresponding to Fig.40 Two target wavelengths within the DUV range of the target wavelength are suppressed;

[0123] Fig.42 Shown in the DUV range between 0.1μm and 0.4μm, Fig.41 Enlarged detail shown;

[0124] Fig.43 Again, the graph shows the wavelength-dependent reflectivity between 10.0 μm and 11.0 μm for various optical diffraction elements having different sidewall steepness tolerances of the diffraction structure group;

[0125] Fig.44 Display by Fig.16 An optical diffraction element and two photolithographic mask structures, which can be used in the manufacture of the optical diffraction element for predefining boundary areas between adjacent surface sections of a binary structure of the optical diffraction element, the aforementioned binary structures being superimposed on each other;

[0126] Fig.45 With Fig.44 Similar illustrations, showing the basis Fig.19 an optical diffraction element and two photolithography mask structures, which can be used in the production of the optical diffraction element for predefining boundary areas between surface segments of the group of diffraction structures;

[0127] Fig.46 A further embodiment of an optical diffraction element showing suppression of at least one target wavelength by destructive interference comprises a periodic grating structure profile comprising a diffractive structure having three diffractive structure levels arranged in such a way that the target wavelength is suppressed by destructive interference;

[0128] Fig.47 Display by Fig.46 an optical diffraction element, wherein the three diffraction structure levels have height or level differences with respect to one another which result in perfect destructive interference at the target wavelength with respect to the zeroth order of diffraction;

[0129] Fig.48 With Fig.47 Similar illustrations, showing the basis Fig.46A variant of an optical diffraction element, wherein, in order to illustrate the diffraction compensation effect occurring in the case of such a height error, firstly a positive diffraction structure level and a secondary negative diffraction structure level are implemented with a height difference value which is somewhat excessive relative to the neutral diffraction structure level;

[0130] Fig.49 With Fig.46 Similar illustration showing inclusion and basis Fig.46 Another embodiment of an optical diffraction element having three diffraction structure levels in a different sequence compared to the embodiment of;

[0131] Fig.50 A further embodiment of an optical diffraction element is shown, wherein substantially one grating period is exemplified and wherein the periodic grating structure profile of the optical diffraction element comprises a diffraction structure having four diffraction structure levels;

[0132] Fig.51 With Fig.50 A similar illustration shows another embodiment of an optical diffraction element including five diffraction structure levels within one grating period;

[0133] Fig.52 With Figure 5 A similar graph shows the effect of three diffractive structure levels that can be assigned to two diffractive structure groups. Fig.19 , Fig.36 , Fig.45 and Fig.46 the wavelength-dependent reflectivity R of an optical diffraction element in the form of a grating produced in a manner such that in each case there is a structure depth difference of λ / 4 between the diffraction structure levels, where λ is in each case the target wavelength to be suppressed;

[0134] Fig.53 With Fig.44 and Fig.45 A similar illustration shows Fig.19 , Fig.36 , Fig.45 and Fig.46 An optical diffraction element of the type shown, and further embodiments of two photolithographic mask structures, which can be used in the production of the optical diffraction element for again predefining surface sections of the diffraction structure groups or boundary regions between the diffraction structure levels;

[0135] Fig.54 With Fig.44 and Fig.45 A similar illustration shows Fig.19 , Fig.36 , Fig.45 and Fig.46An optical diffraction element of the type shown, and further embodiments of two photolithographic mask structures, which can be used in the production of the optical diffraction element for again predefining surface sections of the diffraction structure groups or boundary regions between the diffraction structure levels;

[0136] Fig.55 With Fig.44 and Fig.45 A similar illustration shows Fig.19 , Fig.36 , Fig.45 and Fig.46 Further embodiments of an optical diffraction element of the type shown, as well as further embodiments of two photolithographic mask structures, which can be used in the production of an optical diffraction element for again predefining surface sections of the diffraction structure groups or boundary regions between the diffraction structure levels; and

[0137] Fig.56 With Fig.44 and Fig.45 A similar illustration shows Fig.19 , Fig.36 , Fig.45 and Fig.46 Further embodiments of an optical diffraction element of the type shown, as well as further embodiments of two photolithography mask structures, can be used in the manufacture of an optical diffraction element for again predefining surface segments of the diffraction structure groups or boundary areas between the diffraction structure levels. DETAILED DESCRIPTION

[0138] The projection exposure device 1 for microlithography comprises a light source 2 for illumination light or imaging light 3, which will be explained in more detail below. The light source 2 is an EUV light source that generates light in a wavelength range of, for example, between 5 nm and 30 nm, in particular between 5 nm and 15 nm. The illumination light or imaging light 3 is also referred to below as EUV light.

[0139] In particular, the light source 2 can be a light source with a wavelength of 13.5 nm or a light source with a wavelength of 6.9 nm. Other EUV wavelengths or wavelengths in the DUV range between 150 nm and 250 nm, for example 193 nm, are also possible. The beam path of the illumination light 3 is Figure 1 The illustration is very schematic.

[0140] The illumination optical unit 6 is used to guide the illumination light 3 from the light source 2 to the object field 4 in the object plane 5. The illumination optical unit comprises: a field facet reflector FF, which Figure 16a and 6b, which are arranged downstream in the beam path of the illumination light 3 and are also illustrated very schematically; and a pupil facet mirror PF, which is arranged downstream in the beam path of the illumination light 3 and is also illustrated very schematically. A field forming mirror 6b for grazing incidence (GI mirror; grazing incidence mirror) is arranged in the beam path of the illumination light 3 between the pupil facet mirror PF arranged in the pupil plane 6a of the illumination optical unit and the object field 4. Such a GI mirror 6b is optional.

[0141] The pupil facets (not illustrated in greater detail) of the pupil facet mirror PF are part of a transmission optical unit which transmits, in particular images, the field facets (likewise not illustrated) of the field facet mirror FF in a manner superimposed on one another into the object field 4. Embodiments known from the prior art can be used for the field facet mirror FF on the one hand and the pupil facet mirror PF on the other hand. Such an illumination optical unit is known, for example, from DE 10 2009 045 096 A1.

[0142] Using a projection optical unit or imaging optical unit 7, the object field 4 is imaged with a predetermined reduction ratio into an image field 8 in an image plane 9. Projection optical units which may be used for this purpose are known, for example, from DE 10 2012 202 675 A1.

[0143] In order to facilitate the description of various embodiments of the projection exposure apparatus 1 and the projection optical unit 7, a Cartesian xyz coordinate system is indicated in the diagram, from which the respective positional relationships of the elements illustrated in the figures are apparent. Figure 1 The x direction runs perpendicular to the plane of the diagram. The y direction runs Figure 1 extends toward the left in the z direction Figure 1 The object plane 5 runs parallel to the xy plane.

[0144] The object field 4 and the image field 8 are rectangular. Alternatively, it is also possible for the object field 4 and the image field 8 to have a curved or curved embodiment, i.e. in particular a partially annular embodiment. The object field 4 and the image field 8 have an x / y aspect ratio greater than 1. Thus, the object field 4 has a longer object field dimension in the x direction and a shorter object field dimension in the y direction. These object field dimensions extend along the field coordinates x and y.

[0145] One of the exemplary embodiments known from the prior art can be used for the projection optical unit 7. In this case, what is imaged is a portion of a reflection mask 10 (also called reticle) which coincides with the object field 4. The reticle 10 is carried by a reticle holder 10a. The reticle holder 10a is displaced by a reticle displacement drive 10b.

[0146] Imaging by the projection optical unit 7 is effected on the surface of a substrate 11 in the form of a wafer carried by a substrate holder 12. The substrate holder 12 is displaced by a wafer or substrate displacement drive 12a.

[0147] Figure 1 The schematic diagram shows a light beam 13 of the illumination light 3 entering the projection optical unit 7 between the mask master 10 and the projection optical unit 7, and a light beam 14 of the illumination light 3 emerging from the projection optical unit 7 between the projection optical unit 7 and the substrate 11. Figure 1 In the figure, the numerical aperture (NA) on the image field side of the projection optical unit 7 is not reproduced to scale.

[0148] The projection exposure apparatus 1 is of the scanner type. Both the reticle 10 and the substrate 11 are scanned in the y-direction during operation of the projection exposure apparatus 1. A stepper type of projection exposure apparatus 1 is also possible, in which a stepwise shifting of the reticle 10 and the substrate 11 in the y-direction is effected between individual exposures of the substrate 11. These shiftings are synchronized with one another by appropriate actuation of the shift drives 10b and 12a.

[0149] Figure 2 Details of light source 2 are shown.

[0150] The light source 2 is a laser produced plasma (LPP) source. For the purpose of generating plasma, tin droplets 15 are generated as a continuous sequence of droplets by a tin droplet generator 16. The trajectory of the tin droplets 15 extends laterally to the main ray direction 17 of the light 3 used for EUV. Here, the tin droplets 15 fall freely between the tin droplet generator 16 and the tin capture device 18, wherein the aforementioned droplets pass through the plasma source region 19. The light 3 used for EUV is emitted through the plasma source region 19. When the tin droplets 15 arrive at the plasma source region 19, they are hit there by pump light 20 from a pump light source 21. The pump light source 21 can be, for example, a CO 2 Infrared laser source in the form of a laser. Some other IR laser sources are also possible, in particular solid-state lasers, such as Nd:YAG lasers. The pump light source 21 may comprise a light source unit for generating a light pre-pulse; and a light source unit for generating a main light pulse. The light pre-pulse on the one hand and the main light pulse on the other hand may have different light wavelengths.

[0151] Pump light 20 is transmitted into the plasma source region 19 through a reflector 22 (which may be a reflector that can be tilted in a controlled manner) and through a focusing lens member 23. The plasma emitting the EUV light 3 is generated by the impact of the pump light from the tin droplets 15 arriving at the plasma source region 19. The beam path of the EUV light 3 is Figure 2 Between the plasma source region 19 and the field facet reflector FF is illustrated to the extent that the EUV used light is reflected by a collector reflector 24 (which is also referred to as EUV collector 24 below). The EUV collector 24 comprises a central passage opening 25 for the pump light 20 focused toward the plasma source region 19 by the focusing lens member 23. The collector 24 is implemented as an elliptical reflector and transmits the EUV used light 3 emitted by the plasma source region 19 (which is arranged at one elliptical focus) to an intermediate focus 26 of the EUV used light 3 (which is arranged at another elliptical focus of the collector 24).

[0152] The field facet mirror FF is arranged downstream of the intermediate focus 26 in the beam path of the EUV light 3 in the far-field region of the EUV light 3 .

[0153] The EUV collector 24 and other elements of the light source 2, which may be the Sn droplet generator 16, the Sn capture device 18 and the focusing lens element 23, are arranged in a vacuum housing 27. The vacuum housing 27 has a passage opening 28 in the region of the intermediate focus 26. In the region of the pump light 20 incident on the vacuum housing 27, the vacuum housing comprises a pump light incident window 29 for the light pre-pulse and for the main light pulse.

[0154] Figure 3 The guidance of the light used for EUV, i.e. the illumination light 3, and of secondary stray light 30, in particular radiation of a longer wavelength, such as IR radiation having the wavelength of the light pre-pulse and / or the main light pulse, between the plasma source region 19 of the light source 2 and an intermediate focal plane 26a, in which the intermediate focus 26 is arranged, is shown in a very abstract manner. At the same time, Figure 3A variant of the lateral guidance of the pump light 20 into the plasma source region 19 is shown, i.e. a guidance without a channel opening of the type of the channel opening 25 in the EUV collector 24. Both the used light 3 and the stray light 30 are emitted from the plasma source region 19. Both the used light 3 and the stray light 30 are incident on surface sections 31, 32 of the entire impact surface 33 of the EUV collector 24. The surface sections 31, 32 are sections of a grating surface (also designated by 33 in this illustration) of the EUV collector 24, on which a grating for diffracting and stacking the stray light radiation 30 is arranged. An embodiment of this grating is described below. The grating surface can be arranged only at the locations of the surface sections 31, 32, on which the stray light 30 impinges, or it can also cover a larger section of the impact surface 33 and, in a further variant, cover the entire impact surface 33.

[0155] Figure 4 A section of a grating surface 33 is shown that employs one embodiment of a grating 34. The grating 34 constitutes an optical diffraction element that suppresses at least one target wavelength by destructive interference.

[0156] The grating surface of the grating 34 can be implemented as a flat surface or a curved surface, for example, according to Figure 2 and Figure 3 The impact surface 33 in the case of the collector reflector 24 may be concave, or convex.

[0157] The grating 34 has two diffraction gratings 35, 36 arranged (as a diffraction structure group) on the grating surface 33. The diffraction grating 35 is also referred to as the first diffraction grating in the following text. The diffraction grating 36 is also referred to as the second diffraction grating in the following text.

[0158] In the case of the diffraction grating 35, the diffractive positive structure 37 and the diffractive negative structure 38 are Figure 4 The periodic travel direction 39 of the first diffraction grating 35 runs vertically. For this horizontal path of the diffraction structures 37 and 38, the periodic travel direction 39 is thus Figure 4 Vertical movement.

[0159] exist Figure 4 In the embodiment, the second diffraction grating 36 has diffraction positive structures 40 running vertically and diffraction negative structures 41 alternating therewith. The periodic running direction 42 of the second diffraction grating 36 runs vertically to the diffraction structures 40 and 41 again. Figure 4 Medium level.

[0160] The diffraction structures 37, 38 and 40, 41 of the two diffraction gratings 35, 36 of the grating 34 are realized by four diffraction structure types or diffraction structure levels, which have different structure depths and are arranged at Figure 4exemplified in FIG. 1 by different fine line types and by the numbers 1, 2, 3, 4 applied to the respective diffractive structures. Diffractive structure type "1" has a structure depth "0". Diffractive structure type "2" has a structure depth "dv". The surface section of the grating surface occupied by the respective diffractive structure type "2" is therefore perpendicular to Figure 4 The plane illustrated in FIG. 5 is located at a position deeper than the diffractive structure type “1” by a structure depth dv.

[0161] The respective structure depth can be assigned a depth value relative to a reference plane, wherein as a general rule the reference plane is chosen to be one from which no material has been removed (structure depth=0).

[0162] The respective areas of the diffractive structure types "1" to "4" are in each case square. Other boundary shapes of the diffractive structure types are also possible which result in complete coverage of the grating surface.

[0163] Diffractive structure type "3" has a structure depth dh, which is again perpendicular to Figure 4 The planes illustrated in are measured relative to diffractive structure type "1". Diffractive structure type "4" has a corresponding measured structure depth dv+dh.

[0164] In the case of grating 34, four diffractive structure types "1" to "4" are respectively arranged in a 2×2 array, wherein diffractive structure type "1" is arranged at the top left, diffractive structure type "2" is arranged at the top right, diffractive structure type "3" is arranged at the bottom left, and diffractive structure type "4" is arranged at the bottom right. These 2×2 arrays of such a group of the four diffractive structure types are in each case further arranged in accordance with Figure 4 In the embodiment of the present invention, the superstructure is arranged in the form of a 3×3 array. In general, the grating 34 on the grating surface 33 can of course be extended horizontally and vertically in any desired manner by attaching further corresponding 2×2 arrays of the four diffractive structure types "1" to "4".

[0165] The diffraction positive structure 37 and the diffraction negative structure 38 located at a deeper structure depth dh thus follow one another in the periodic running direction 39 of the first diffraction grating 35. In the case of the second diffraction grating 36, one of the diffraction positive structures 40 follows the diffraction negative structure 41 located at a deeper structure depth dv in the periodic running direction 42. Two diffraction gratings 35, 36 superimposed on one another and having corresponding structure depths dh and dv are thus realized in the grating 34.

[0166] Based on Figure 4In the case of the embodiment of , the structure depth is the height difference between the corresponding diffractive positive structure and the associated diffractive negative structure. More generally, the structure depth can be understood as the optical path difference between the diffractive positive structure and the associated diffractive negative structure.

[0167] On the diffractive positive structures 37, 40 and on the diffractive negative structures 38, 41, over the entire area, it is possible to apply a highly reflective coating on the grating 34 and, if necessary, also an auxiliary layer.

[0168] The auxiliary layer arranged below the highly reflective coating may be a layer which increases the service life of the grating 34. Alternatively or in addition, an auxiliary layer may also be applied on the highly reflective coating in order to protect the latter from damage.

[0169] The highly reflective coating may be a multilayer coating, such as is known for efficient reflection, in particular of radiation having EUV wavelengths.

[0170] The diffraction gratings 35, 36 of the grating 34 are each designed as binary gratings. In this case, the surface area of ​​the diffractive positive structure is equal to the surface area of ​​the diffractive negative structure.

[0171] The grating period of the diffraction grating 35 may be in the range of 0.5 mm to 5 mm, for example, 2 mm. The grating period of the diffraction grating 36 may be in the range of 0.5 mm to 5 mm, for example, 2 mm. Such a grating period is Figure 4 For the second diffraction grating 36 in FIG. 3 , it is marked by P. The structure sidewalls of the respective diffractive structures 37, 38, 40, 41 may have an extent in the range between 1 μm and 10 μm, for example in the region of 5 μm, perpendicular to the extension of the respective diffractive structure, i.e. measured in the respective periodic running direction 39 to 42. Such a sidewall extent or sidewall extension is indicated at F, where for Figure 4 The size of the second diffraction grating 36 in FIG.

[0172] Figure 5 The result of the calculation of the wavelength-dependent reflectivity of the grating 34 for the design parameters dv=2.65 μm and dh=2.55 μm is shown in a graph. The reflectivity of the grating 34 is plotted at 43, which is the result of the calculation with the additional assumption that the sidewall extension F is 0, i.e. the result in the case of a grating 34 with ideally steep sidewalls between the diffractive structures. In the case of the suppressed design wavelengths of 10.2 μm and 10.6 μm for the corresponding stray light wavelengths (which are referred to as target wavelengths), the result is that the wavelength of the grating 34 is 10.2 μm and 10.6 μm, which is 10.6 μm. -8 The reflectivity suppression of the grating 34 in the ideal case is better than the reflectivity curve 43. The two wavelengths correspond to the wavelengths of the pre-pulse and the main pulse of the pump light source 21.

[0173] For two target wavelengths 10.2μm (λ 1 ) and 10.6μm(λ 2 ) the following holds:

[0174] (λ 1 -λ 2 ) 2 / (λ 1 +λ 2 ) 2 =3.77·10 -4

[0175] For this normalized target wavelength ratio, it is thus true that:

[0176] (λ 1 -λ 2 ) 2 / (λ 1 +λ 2 ) 2 <10%

[0177] The normalized target wavelength ratio may also be less than 20%.

[0178] With regard to the manufacturing accuracy of the structure depths dv and dh and the sidewall steepness being first considered, the reflectivity curve R(λ) taking into account the specified tolerances is plotted on Figure 5 In the case of the target wavelengths of 10.2 μm and 10.6 μm, the result is that the -6 Better reflectivity suppression.

[0179] Reference reflectivity curve 45 is also provided for comparison purposes. Figure 5 , the aforementioned reference reflectivity curve represents the suppression result for an optical reference grating comprising only one diffraction grating, i.e. for example a diffraction grating 35 with a horizontal diffraction structure or a diffraction grating 36 with a vertical diffraction structure. The same tolerances for the structure depth and for the side wall steepness as in the case of the reflectivity curve 44 are taken into account here. It is clear that, despite the same tolerances, the reference reflectivity curve 45 exhibits a suppression result for 10 -4 Since the reference grating for which the reference reflectivity curve 45 is calculated contains only one diffraction grating, only one wavelength (ie 10.6 μm) is suppressed here as well.

[0180] The two diffraction gratings 35 , 36 have a ratio between grating period (2 mm) and structure depth (in the region of 2.6 μm) which is significantly greater than 10 and in fact greater than 500 and in the region of 1000.

[0181] Since the two diffraction gratings 35, 36 are implemented as binary gratings, the surface area ratio of the surface area of ​​the diffractive positive structures 37, 40 to the surface area of ​​the diffractive negative structures 38, 41 is 1. Depending on the embodiment of the grating 34, the aforementioned surface area ratio may also deviate from 1 and may be in the range between 0.9 and 1.1.

[0182] The two diffraction gratings 35, 36 have the same grating period p, so that the period ratio of the two grating periods is 1. Depending on the embodiment of the grating 34, this period ratio may be in the range between 0.9 and 1.1. The difference between the two grating periods may also be significantly larger, so that a period ratio of 1:2 or 1:5 is obtained, for example.

[0183] The grating 34 is configured to suppress at least one target wavelength λ by destructive interference. 1 , 2 The optical diffraction element comprises at least three diffraction structure levels corresponding to diffraction structure types 1 to 4. 1 To N 4 Predefine different structure depths d relative to the reference plane i The diffraction structure level N 1 To N 4 can be assigned to two diffraction gratings (ie two diffraction structure groups 35, 36), which in turn are used to suppress the two target wavelengths λ 1 , 2 The first group of the aforementioned diffraction structure groups (ie, the diffraction grating 35) is used to suppress the first target wavelength λ in the zero-order diffraction. 1 , and the second group of the diffraction structure groups (i.e., the diffraction grating 36) is used to suppress the second target wavelength λ in the zero-order diffraction 2 .

[0184] The diffractive structure level N 1 To N 4 The morphology of can be described as a superposition of two binary diffractive structure groups 35 and 36. Each of the two binary diffractive structure groups has a first surface segment (with a first structure depth) and a second surface segment (with a second structure depth) alternating with the first surface segment along the direction of travel of the respective diffractive structure group 35, 36. The boundary region between these adjacent surface segments of each of the binary diffractive structure groups has a linear path. Depending on the embodiment of the grating 34, the aforementioned linear path corresponds to Figure 4 The first boundary region of the first group of the two binary diffractive structure groups 35 (i.e. Figure 4 ), and the second boundary region of the second group of the two binary diffraction structure groups 36 (i.e. Figure 4The columns of the lines in the formula (in the formula), at most, the segments along their linear path overlap with each other, that is, according to Figure 4 In the example diagram, the region of the intersection between the column lines and the row lines is described.

[0185] The diffraction grating 35 has a first grating period (with a first structure depth), which is the optical path difference between the first diffraction positive structure 37 and the first diffraction negative structure 38, measured perpendicularly to the surface section of the grating surface 33 respectively surrounding these first structures. The second diffraction grating 36 has a second grating period and a second structure depth, which in turn is implemented as the optical path difference between the second diffraction positive structure 40 and the second diffraction negative structure 41, perpendicularly to the surface section of the grating surface 33 respectively surrounding these second structures. The two period running directions along which the two grating periods of these gratings 35, 36 run are perpendicular to each other, that is, they do not run parallel to each other.

[0186] Due to the grating 34 , the collector mirror of the EUV collector 24 is embodied such that it directs EUV radiation 3 through towards the focal region 26 , wherein the grating 34 is embodied as an optical diffraction element such that it directs radiation 30 of at least one target wavelength, ie stray light, away from the focal region 26 .

[0187] Figure 6 With Figure 5 A similar illustration shows the reflectivity relationship in a variant of the grating 34, in which the structure depths dv, dh are equal in magnitude and have an absolute value of 2.65 μm. Then, both diffraction gratings 35, 36 contribute to suppressing the stray light wavelength of 10.6 μm. Hereby, again a better suppression relationship occurs in the case of the ideal reflectivity curve 43, and in the case of the reflectivity curve 44 calculated using the design tolerances.

[0188] Figure 7 With Figure 4 Similar illustrations showing alternatives to Figure 4 The grating 34 is used as a variation of the grating of the optical diffraction element for suppressing at least one target wavelength by destructive interference. Figure 4 Elements and functions of those explained carry the same reference numerals and are not discussed again in detail.

[0189] in accordance with Figure 7 The grating 46 and Figure 4 The illustrated one is primarily different in that the periodic running direction 39 of the first diffraction grating 35 does not run vertically, but at an angle of 45° to the horizontal. Accordingly, the diffraction structure types "1" to "4" appear as rhombus-shaped areas.

[0190] Figure 8A further embodiment of a grating 47 is shown which can be used as an alternative or in addition to the gratings described above as an optical diffraction element for suppressing at least one target wavelength by destructive interference. Figures 1 to 7 , and with particular reference to Figures 4 to 7 Elements and functions of those explained carry the same reference numerals and are not discussed again in detail.

[0191] The grating 47 has a total of three diffraction gratings as a diffraction structure group, wherein two of the three diffraction gratings correspond to Figure 4 The diffraction gratings 35 and 36 of the embodiment. Figure 8 In FIG. 1 , the grating period of the diffraction grating 35 is illustrated at ph, and the grating period of the diffraction grating 36 is illustrated at pv.

[0192] The third diffraction grating 48 of the grating 47 has a diffraction positive structure 49 and a diffraction negative structure 50 running diagonally relative to the diffraction structures 37, 38 and 40, 41 of the first two diffraction gratings 35, 36. Compared with the diffraction positive structure 49, the diffraction negative structure 50 is Figure 8 , with the structural depth exemplified by dd.

[0193] The overall height profile over the entire illustrated section of the grating surface of the grating 47 can be understood as a juxtaposition of elementary sections in the form of a 2×4 array, which is predefined by the boundaries of the horizontally running diffraction structures 37, 38 of the diffraction grating 35 and the vertically running diffraction structures 40, 41 of the diffraction grating 36. The diffraction structure types or diffraction structure levels on this 2×4 array are Figure 8 The numbers are denoted by “000”, “001”, “010”, “011”, “100”, “101”, “110” and “111” in a 2×4 array at the upper left.

[0194] The following table indicates the structure depths of these diffractive structure types in units of grating period ph, pv, and their surface area ratios:

[0195] Diffraction structure type Structure Depth Surface area ratio 000 0 (ph+pv) / 4 001 dd (ph+pv) / 4 010 dv (ph+pv) / 4 011 dv+dd (ph+pv) / 4 100 dh (ph+pv) / 4 101 dh+dd (ph+pv) / 4 110 dh+dv (ph+pv) / 4 111 dh+dv+dd (ph+pv) / 4

[0196] Table 1

[0197] All diffractive structure types "000" to "111" have the same surface area ratio (ph+pv) / 4 to the total surface area of ​​the grating 47. This ensures that all three diffraction gratings 35, 36 and 48 of the grating 47 form a binary grating and that their diffractive positive structures 37, 40, 49 have a surface area ratio of 1 in each case relative to their diffractive negative structures 38, 41, 50.

[0198] The periodic running direction 51 of the third diffraction grating 48 runs along a grating period pd at an angle of about 23° relative to the periodic running direction 39 of the diffraction grating 35. This periodic running direction 51 is selected together with an offset of the arrangement of the diffraction structures 49, 50 of the third diffraction grating 48 such that the boundary between the diffraction structures 49, 50 of the third diffraction grating 48 runs along the diagonal of two structural blocks horizontally adjacent to each other (which are formed by the diffraction structures 37, 38 and secondarily 40, 41 intersecting each other). Offset variants of this arrangement of the diffraction structures 49, 50 along the periodic running direction 51 of the third diffraction grating 48 are possible, as in Figure 8 Indicated by a double-headed arrow 52.

[0199] The grating period pd of the third diffraction grating 48 is of the order of the grating periods ph, pv and is approximately 1.7 mm in the case of the grating 47 .

[0200] Fig. 9 With Figure 5 and Figure 6 A similar illustration shows data on the wavelength-dependent reflectivity R for the case where the structure depths dh, dv and dd are each equal in magnitude and have a value of 2.65 μm in the illustrated example.

[0201] The reflectivity for the ideal case of preferably steep sidewalls (sidewall extension of 0) for the diffraction gratings 35, 36 and 48 is exemplified in Fig. 9 53 of them. The reflectivity suppression ratio of the target wavelength of 10.6μm is 10 -10 Several orders of magnitude better.

[0202] 54 shows an example of a calculated result for the wavelength-dependent reflectivity, wherein realistic tolerances are again assumed for the structure depths of the diffractive structures 37, 38, 40, 41, 49, 50 and for the side wall extensions. The result for the grating 47 comprising the three diffraction gratings 35, 36, 48 is a reflectivity suppression which, although lower than in the ideal case, is still significantly lower than 10 -10 better.

[0203] As a reference value, Fig. 9 Firstly, also for a grating 34 comprising two diffraction gratings 35, 36 and for a conventional grating comprising only one diffraction grating, the following is described. Figure 6 Reflectivity curves 44 and 45.

[0204] Fig.10 Again, the wavelength dependence graph shows the reflectivity relationship for embodiments of gratings 47 having the following structural depths:

[0205] dh=2.55μm, dv=2.65μm and dd=0.26μm.

[0206] The structure depth dd of the diagonally running diffractive structures 49 , 50 is therefore approximately ten times smaller than the structure depth of the diffractive structures 37 , 38 , 40 , 41 of the diffraction gratings 35 , 36 of the grating 47 .

[0207] Again, for the reflectivity of an ideal design of such a grating 47 with zero sidewall extension, the example is Fig.10 55 in. For about 10.2μm (λ 1 ) and about 10.59μm(λ 2 ) and an additional wavelength in the region of 1.05 μm, the reflectivity suppression of the grating is in each case within 10 -8 Or better yet, in the area.

[0208] For the two IR wavelengths λ suppressed by the grating 47 as target wavelengths 1 , 2 , the above and based on Figure 4 The explanation given in association with the grating 34 of φ1, then holds true for the normalized difference in the target wavelength.

[0209] The reflectivity curve with predefined tolerances for first the structure depth and secondly its sidewall extensions is then Fig.10 56 of them are calculated.

[0210] In the case of the grating 47, a diffraction grating 48 with a further grating period pd and a further structure depth dd is thus present, the aforementioned structure depth being the optical path difference between the diffractive positive structures 49 and the diffractive negative structures 50, measured perpendicularly to the surface section of the grating surface 33 surrounding the two structures 49, 50 respectively. The ratio pd / dd between the grating period pd of the diffraction grating 48 and the structure depth dd of the diffraction grating 48 is greater than 10. Alternatively or additionally, the period ratio ph / pd may be in the range between 0.9 and 1.1. Alternatively or additionally, the first grating period ph may run along the first period running direction 39 of the first diffraction grating 35, and the further grating period pd may run along the further period running direction 51 of the further diffraction grating 48, and the two period running directions 39, 51 run parallel to each other.

[0211] The surface areas of the diffractive positive structures 37 , 40 , 49 and the diffractive negative structures 38 , 41 , 50 of the various diffractive structure groups 35 , 46 , 48 contribute equally to the entire grating surface 33 .

[0212] Another embodiment of the grating 57 also includes three diffraction gratings 35, 36, 48, which is described below with reference to Fig.11 Corresponding to the above reference Figures 1 to 10, and with particular reference to Figure 8 Elements and functions of those explained carry the same reference numerals and are not discussed again in detail.

[0213] The grating 57 differs from the grating 47 mainly in the orientation of the three periodic travel directions 39, 42 and 51 of the three diffraction gratings 35, 36 and 48 stacked on top of each other. The periodic travel direction 39 of the first diffraction grating 35 is oriented relative to Fig.11 The vertical line in the second diffraction grating 36 runs at an angle of about 23. The periodic running direction 42 of the second diffraction grating 36 runs horizontally.

[0214] The periodic running direction 51 of the third diffraction grating 48 in turn runs at an angle of approximately 23° to the vertical, wherein the two periodic running directions 39 and 51 of firstly the first diffraction grating 35 and secondly the third diffraction grating 48 present an angle of approximately 46° to each other.

[0215] Fig.11 The rhombus-shaped basic sections of the grating 57 corresponding to the 2×4 array of the grating 47 are emphasized again with the diffractive structure types “000” to “111”. In the case of these diffractive structure types “000” to “111” of the grating 57, the assignment of the structure depth and the surface area ratio is the same as above in relation to Figure 8 As indicated in Table 1.

[0216] In the case of grating 57, the displacement of the structural boundary of the third diffraction grating 48 along the periodic travel direction 51 makes the structural boundaries between the diffraction structures 37 and 38 of the first diffraction grating 35, between the diffraction structures 40 and 41 of the second diffraction grating 36, and between the diffraction structures 49 and 50 of the third diffraction grating 48 intersect at Fig.11 At point P on the center of the basic segment illustrated in .

[0217] In the case of grating 57, the grating period ph is approximately 3.25 mm, the grating period pv is 2 mm, and the grating period pd is exactly the same magnitude as the grating period ph.

[0218] Fig.12 and Fig.13 A further embodiment of gratings 58, 59 is shown which differs from grating 57 only in the offset size of the arrangement of the structure boundaries between the diffractive structures 49, 50 along the periodic running direction 51. Fig.12 In the case of the grating 58 of FIG. 5A , the aforementioned offset makes it possible for the structural boundaries of the various diffraction gratings 35 , 36 , 48 not to intersect at points in the corresponding elementary segments. Fig.13 In the case of the grating 59, the offset makes the structure boundaries of the three diffraction gratings 35, 36, 48 and the basis Fig.11Compared with the embodiments, the intersection occurs at different positions within the corresponding basic segments, thereby resulting in different distributions of diffraction structure types "000" to "111".

[0219] exist Fig.12 and Fig.13 The assignment of the structural depth and surface area ratios of the indicated diffraction structure types "000" to "111" within the emphasized cells is again as described with respect to Figure 8 As indicated in Table 1.

[0220] As another embodiment of a grating 60 of an optical diffraction element that suppresses at least one target wavelength by destructive interference, reference is made below to Figures 14 to 16 Corresponding to the above reference Figures 1 to 13 Elements and functions of those explained are denoted by the same reference numerals and are not discussed again in detail.

[0221] The grating 60 is implemented as a single Fig.14 (diffraction grating 61) and Fig.15 The two diffraction gratings 61 and 62 shown in FIG. 6 are superimposed. The diffraction gratings 61 and 62 constitute a diffraction structure group for suppressing the corresponding target wavelength.

[0222] The diffraction grating 61 has a structure depth d 1 and the grating period p 1 The diffraction grating 62 has a structure depth d 2 and the grating period p 2 The two diffraction gratings 61, 62 are both implemented as binary gratings.

[0223] The grating 60 resulting from the superposition of the two diffraction gratings 61, 62 has a total of three diffraction structure levels or diffraction structure types with a structure depth of 0 (diffraction structure level N 1 ), structural depth d 2 (Diffraction structure level N 2 ), with a structural depth d 1 (Diffraction structure level N 3 ) and has a structural depth d 1 +d 2 (Diffraction structure level N 4 ).

[0224] Grating period p 1 and p 2 This is equivalent in the case of grating 60. The structural depth d 1 ,d 2This is different in the case of the grating 60. With respect to the common periodic running direction x of the diffraction gratings 61 and 62, the two diffraction gratings 61 and 62 are phase-shifted relative to each other by a quarter of the common period, i.e. relative to each other p 1 / 4=p 2 / 4.

[0225] exist Fig.15 and Fig.16 In FIG. 6 , the coverage error 63 along the periodic traveling direction x is illustrated by a dashed line. Such a coverage error 63 can be understood as the superimposed phase error of the two diffraction gratings 61 and 62 along the periodic traveling direction, and leads to various diffraction structure levels N 1 、N 2 、N 3 、N 4 The change in the extension of pixel x along the direction of periodic travel.

[0226] For the two structural depths d 1 and d 2 In an alternative embodiment of the grating 60, the two diffractive structure levels N are equivalent. 2 、N 3 Degenerate to a common structure level, the result is that such a grating comprising two diffraction gratings with equal structure depth has only three diffractive structure levels.

[0227] In the case of grating 60, the surface section of the diffractive structure group is formed by 61 P and 61 N The boundary region of the first group 61 of the two binary diffraction structure groups 61 and 62 of the grating 60 (ie, the level N of the diffraction structure group 61) is i The sidewalls between the two diffraction structure groups 61 and 62 and the boundary region of the second group 62 (i.e. Fig.15 The layer side wall N i / N j ) move completely apart from each other.

[0228] As another embodiment of a grating 60 of an optical diffraction element that suppresses at least one target wavelength by destructive interference, reference is made below to Figures 17 to 19 Corresponding to the above reference Figures 1 to 16 , and with particular reference to Figures 14 to 16 Elements and functions of those explained carry the same reference numerals and are not discussed again in detail.

[0229] Fig.19 The display is obtained as diffraction grating 65 ( Fig.17 ) and 66( Fig.18) in the form of a superimposed grating 64 of two diffraction structure groups. The grating 64 is an example of an optical diffraction element.

[0230] In the case of the diffraction gratings 65, 66, the following holds:

[0231] p 1 =p 2 and 1 =d 2 .

[0232] The phase shift of the two diffraction gratings 65, 66 relative to each other along the periodic travel direction x is p 1 / 4=p 2 / 4.

[0233] The extension ratio between the diffraction positive structures 67, 68 of the first diffraction gratings 65, 66 and their second associated diffraction negative structures 69, 70 is completely inverted with respect to one another, resulting in the diffraction positive structures 67 having the same extension along the periodic running direction x as the diffraction negative structures 70 of the diffraction grating 66, and the diffraction negative structures 69 of the diffraction grating 65 having the same extension along the periodic running direction x as the diffraction positive structures 68 of the diffraction grating 66. Therefore, the extension of the first diffraction positive structures 67, 68 and their second associated diffraction negative structures 69, 70 are not identical in the respective diffraction gratings 65, 66, so that in this sense the two diffraction gratings 65, 66 are not binary gratings. In the case of the diffraction gratings 65, 66, this extension ratio can deviate very significantly from 1:1 and be approximately 1:3. Different extension ratios in the range between 10:1 and 1:10 between the firstly diffractive positive structures 67 , 68 and the secondly diffractive negative structures 69 , 70 of the respective diffraction grating 65 , 66 are also possible.

[0234] Coverage error 63 again in Fig.18 and Fig.19 Unlike in the case of grating 60, the overlay error 63 in the case of grating 64 does not result in the three diffractive structure levels N along the periodic running direction x. 1 (Structure depth 0), N 2 (Structure depth d 1 =d 2 ) and N 3 (Structure depth d 1 +d 2 ) between the surface area ratios.

[0235] Therefore, the grating 64 constitutes an optical diffraction element, which comprises a periodic grating structure profile comprising a diffraction structure and has three diffraction structure levels (N 1 To N 3), which predefine different structural depths d relative to a reference plane i .

[0236] In the case of grating 64, the diffraction structure is arranged so that the first target wavelength λ in the infrared wavelength range 1 The wavelength range near the first target wavelength (which is diffracted by the grating structure profile) has a radiation component having at least 1 At least three different phases that destructively interfere with each other in the zero and / or + / - first order diffraction.

[0237] The diffractive structure level N 1 To N 3 The grating period of the grating structure profile that is regularly repeated along the periodic travel direction x is predefined. 1 To N 3 Includes: Neutral diffraction structure level N 2 , which has a reference height of 0; the positive diffraction structure level N 1 , which is set relative to the neutral diffraction structure level N 2 High λ 1 / 4 optical path length, wherein a tolerance of + / -20% is possible for the aforementioned optical path length; and a negative diffraction structure level N 3 , which is set relative to the neutral diffraction structure level N 2 Low λ 1 / 4+ / -20% of the optical path length.

[0238] The grating period of the grating structure profile of the grating 64 is subdivided into diffraction structure levels N 1 To N 3 Four periodic segments, wherein two of the four periodic segments (i.e., having a diffraction structure level N 2 The two segments of the periodic structure are implemented as neutral diffraction structure segments, and one of the four periodic segments (i.e., having a diffraction structure level N 1 The periodic segments of the four periodic segments are implemented as positive diffraction structure segments, and one of the four periodic segments (i.e., having a diffraction structure level N 3 The periodic segments) are implemented as negative diffraction structure segments.

[0239] These four periodic segments (sequences such as N 2 、N 1 、N 2 、N 3 ) each have the same length along the periodic travel direction x, but a tolerance range of + / - 20% is also possible here.

[0240] As another embodiment of a grating 60 of an optical diffraction element that suppresses at least one target wavelength by destructive interference, reference is made below to Figure 20 to Figure 22 Corresponding to the above reference Figures 1 to 19 , and with particular reference to Figures 14 to 19 Elements and functions of those explained carry the same reference numerals and are not discussed again in detail.

[0241] Fig. 22 The display is generated as two diffraction gratings 72 ( Fig. 20 ) and 73( Fig.21 ) of the superimposed grating 71.

[0242] The diffraction grating 72 has a structure depth d 1 and the grating period p 1 The diffraction grating 73 has a structure depth d 2 and the grating period p 2 .

[0243] p 2 =2p 1 . The following holds: d 1 ≠d 2 .

[0244] The diffraction gratings 72 , 73 are both embodied as binary gratings having an identical extension of the diffractive positive structure and the diffractive negative structure along the periodic progression direction x.

[0245] The grating 71 has four diffraction structure levels, namely N 1 (Structure depth 0), N 2 (Structure depth d 2 ), N 3 (Structure depth d 1 ) and N 4 (Structure depth d 1 +d 2 ).

[0246] Fig.21 and Fig. 22 Also illustrated in dashed form is an overlay error 63 due to the phase shift of the two diffraction gratings 72, 73 along the periodic travel direction x. Due to the size ratio of the two diffraction gratings 72, 73, the diffraction structure levels N and N are taken into account. 2 The overlay error 63 is indeed evident in terms of the relative extension of the grating 71, such that 2 During the period, it was seen that the diffraction structure level N 1 and N 2 The ratio of the extension does not change regardless of the size of the overlay error 63 .

[0247] Due to the size ratio of the two diffraction gratings 72, 73, a level change occurs, which is caused by the diffraction grating 73 for one diffraction structure type of the diffraction grating 72, in this case for its diffraction positive structure. The phase relationship between the two diffraction gratings 72, 73 along the periodic running direction x is such that the side walls F of the diffraction gratings 72, 73 are not superimposed at the same position along the periodic running direction x.

[0248] Fig.23 For the above reference Figures 14 to 22 Gratings of the type described for gratings 60, 64 or 71 show the dependence of the reflectivity R of the grating on the structural depth d of the corresponding second diffraction grating constituting the grating. 2 The correlation has a structural depth d 1 The corresponding first diffraction grating of is designed to suppress the target wavelength of 10.6 μm by destructive interference. For a structure depth d of 2.65 μm 2 , that is, at about one quarter of the target wavelength, the maximum suppression of the target wavelength is obtained (reflectivity is less than 10 -8 ).

[0249] The tolerances for the structure depth and / or the side wall steepness are taken into account in the associated reflectivity curve 74 .

[0250] The second structural depth d 2 The closer to the fixed first structure depth d of 2.65 μm 1 , the better the suppression of the target wavelength. 2 From 0 to approximately twice the structure depth d 1 In the range between Fig.23 In the range of about 0.2 μm to 5 μm, by having a structure depth d 1 The improvement in the suppression effect achieved by the first diffraction grating is already evident. 1 and d 2 It is obvious that starting from the two structural depths being at a certain distance from each other, with a structural depth d 1 and d 2 The suppression effects of the two diffraction gratings reinforce each other. 1 (for the first diffraction grating) and λ 2 The conditions for the separation between the two (for the second diffraction grating) so that the suppression effects reinforce each other, the following relationship is known:

[0251] |λ 2 -λ 1 | / λ 1 <0.5

[0252] Assuming that the two target wavelengths do not differ from each other to a large extent, this condition can be written as follows, regardless of whether it is the same as the first wavelength λ 1 or with the second wavelength λ 2 Correlated and without absolute value:

[0253] (λ 1 -λ 2 ) 2 / (λ 1 +λ 2 ) 2 <0.1

[0254] As long as this condition is true for the two target wavelengths λ to be suppressed by the two diffraction gratings (i.e., the two diffraction structure groups of the optical diffraction element) 1 , 2 is satisfied, then the suppression is 1 , 2 mutually reinforcing situations.

[0255] This is Fig.24 The reflectivity is plotted against the first structure depth (d 2 -d 1 ) / (d 1 ). Between values ​​of -0.5 and 0.5 for this normalized structure depth difference, the corresponding reflectivity curve 75 is already significantly lower than the asymptotic reflectivity value for larger structure depth differences.

[0256] As another embodiment of a grating 60 of an optical diffraction element that suppresses at least one target wavelength by destructive interference, reference is made below to Figure 25 to Figure 28 Corresponding to the above reference Figures 1 to 24 , and with particular reference to Figures 14 to 22 Elements and functions of those explained carry the same reference numerals and are not discussed again in detail.

[0257] Fig.28 The display is generated as three diffraction gratings 77 ( Fig.25 )、78( Fig.26 ) and 79( Fig. 27 ) of the superimposed grating 76. The structural depth d of the three diffraction gratings 77 to 79 is 1 d 2 d 3 The following holds true:

[0258] d 1 >d 2 >d 3 .

[0259] The three diffraction gratings 77 to 79 are in each case embodied as binary gratings.

[0260] The grating period p of the three diffraction gratings 77 to 79 is 1 、p 2 and p 3 The following holds true for the ratio:

[0261] p 1 :p 2 :p 3 =1:2:4.

[0262] The result is an optical diffraction element by virtue of which in principle three different target wavelengths can be suppressed by destructive interference and which comprises three diffraction structure groups employing the three diffraction gratings 77 to 79. Due to this period ratio, the grating 76 is insensitive to overlay errors, i.e. related to possible phase shifts of the diffraction structures of the three diffraction gratings 77 to 79 along the periodic running direction x.

[0263] The grating 76 has the following eight diffraction structure levels: N 1 (Structure depth 0), N 2 (Structure depth d 3 ), N 3 (Structure depth d 2 ), N 4 (Structure depth d 1 ), N 5 (Structure depth d 2 +d 3 ), N 6 (Structure depth d 3 +d 1 ), N 7 (Structure depth d 1 +d 2 ) and N 8 (Structure depth d 1 +d 2 +d 3 ). These diffraction structure levels can be assigned to the three diffraction structure groups of the three diffraction gratings 77 to 79.

[0264] As another embodiment of a grating 60 of an optical diffraction element that suppresses at least one target wavelength by destructive interference, reference is made below to Figure 29 to Figure 32 Corresponding to the above reference Figures 1 to 28 , and with particular reference to Figure 25 to Figure 28 Elements and functions of those explained carry the same reference numerals and are not discussed again in detail.

[0265] Fig.32 Display consists of three binary diffraction gratings 81 ( Fig.29)、82( Fig.30 ) and 83( Fig.31 The structure depth d of the three diffraction gratings 81 to 83 is 1 d 2 d 3 The following holds true: 1 >d 2 >d 3 The grating period p of the diffraction gratings 81 to 83 is 1 、p 2 and p 3 The following holds true:

[0266] p 1 :p 2 :p 3 =2:2:1.

[0267] The overlay error of the phase relationship along the periodic travel direction x between the diffraction structures of the three diffraction gratings 81 to 83 (similar to the above description of the phase relationship according to Figures 14 to 22 and Figure 25 to Figure 28 In accordance with the embodiments already explained), in relation to the ratio between the diffraction gratings 81 and 82, the latter only accounts for a portion since they have the same grating period.

[0268] The grating 80 also corresponds to eight different diffraction structure levels which can be assigned to the three diffraction structure groups of the three diffraction gratings 81 to 83 .

[0269] Fig.33 With Figure 5 and Fig.10 Similar illustrations, for example, show Fig.28 and Fig.32 The suppression effect of a grating of the type of embodiment (comprising three diffraction structure groups for suppressing three different target wavelengths).

[0270] The reflectivity curve 84 shows the reflectivity of the structure for the depth d 1 =2.65μm, d 2 =2.55μm and d 3 = 2.60 μm, i.e. for suppressing the target wavelengths 10.2 μm, 10.40 μm and 10.6 μm, assuming that the sidewall extension F along the periodic running direction x is 0, i.e. the ideal steep path of the diffraction structure of the associated diffraction grating. -11 Better inhibition.

[0271] The reflectivity curves taking into account the tolerance of structure depth and / or sidewall steepness are then plotted on Fig.33In the case of the reflectivity curve 85, the edge target wavelengths 10.2 μm and 10.6 μm are obtained compared with 10 -9 Better suppression is obtained for the central target wavelength 10.40μm than 10 -10 Better inhibition.

[0272] exist Fig.33 As a reference, reflectivity curves 44 and 45 are plotted for a grating comprising only two diffraction gratings and for a grating comprising only one diffraction grating (see also Figure 5 ).

[0273] Fig.34 A further embodiment of a grating 86 is shown as an optical diffraction element for suppressing at least one target wavelength by destructive interference. Figures 1 to 33 , and with particular reference to Figures 4 to 8 Elements and functions of those explained carry the same reference numerals and are not discussed again in detail.

[0274] The grating 86 is produced as a superposition of a total of three diffraction gratings 87, 88, 89. Two of these diffraction gratings (i.e., diffraction gratings 87 and 88) have a Fig.34 The third diffraction grating 89 has a periodic travel direction x that travels horizontally. Fig.34 The periodic travel direction y is vertical. Figure 4 and Figure 7 In a similar manner to that in the case of the grating 86, the diffraction structure types (ie the different diffraction structure levels) are emphasized by different thin lines. If the three diffraction gratings 87 to 89 have three different structure depths d 1 d 2 and 3 , the result is again eight different diffraction structure levels corresponding to eight different fine line types. If the three structure depths d of the diffraction gratings 87 to 89 are 1 d 2 and 3 If two or all three structure depths are equal, the result is a correspondingly smaller number of different diffractive structure levels.

[0275] In the case of the embodiment according to the grating 86, the suppression of the respective target wavelength is independent of the overlay error.

[0276] As far as the number of diffraction structure levels is concerned, refer to the above reference to Fig.28 Grating 76 and based on Fig.32 An explanation of an embodiment of 80.

[0277] Based on Fig.35An example of an optical diffraction element 91 including three diffraction structure levels is illustrated in FIG. 1 , and the basic properties of such a diffraction element will also be explained below. Figures 1 to 34 Elements and functions of those explained bear the same reference numerals and are not discussed in detail again. Fig.35 Through N 1 、N 2 and N 3 Calibration.

[0278] The target wavelength to be suppressed has λ N wavelength.

[0279] Diffraction structure level N 1 With a structure depth of 0. Diffractive structure level N 2 With λ N / 6 structure depth d. The deepest diffraction structure level N 3 With 2d(=λ N / 3) structural depth.

[0280] With structural depth d 1 ,d 2 ,…d n The superposition of a total of n diffraction gratings is suitable for suppressing a total of n target wavelengths λ 1 , 2 , …λ n In this case, the number of possible diffraction structure levels is 2 n Therefore, as explained above, given three structural depths d 1 ,d 2 ,d 3 , and obtain eight diffraction structure levels N 1 To N 8 Preferably, the various diffraction structure levels N i Arrange so that all diffraction structure levels N i They all occupy an equal surface area ratio of the total surface area of ​​the diffraction element 91.

[0281] The optical diffraction element 91 is designed as a variant of a so-called m-level grating, which in this case has three levels. Such an m-level grating contains m different diffraction structure levels, each of which occupies an equal surface area and has a relative density of d=λ in each case with respect to one another. N / (2m) structure height difference. The target wavelength λ is obtained again N Good suppression of wavelength sensitivity.

[0282] in accordance with Fig.35 The three-level grating is provided with three identically repeated diffraction structure levels N 1 、N2 、N 3 The sequence is based on the grating period p.

[0283] Fig.36 Another embodiment of an optical diffraction element 92 is shown that suppresses at least one target wavelength by destructive interference. The illustration shows that at the deepest diffraction structure level N n The diffraction structure level N in the vicinity i , that is, the diffraction structure level N n-2 、N n-1 、N n 、N n+1 、N n+2 .

[0284] The intensity of the reflected light in the zeroth order diffraction can be written as follows, in a simplified manner for an N-level periodic phase grating, starting from the Fraunhofer approximation for the diffraction far field:

[0285]

[0286] In this case, I(0) is the intensity of the zeroth order diffraction, ie the square of the absolute value of the field amplitude of the diffracted far field.

[0287] N is the number of phase grating levels. n is the phase term assigned to the corresponding grating level. Corresponding to the corresponding diffraction structure level N i The phase term L along the extension of the periodic travel direction x n , exemplified in Fig.36 In. n is a measure of the structural depth of the corresponding diffractive structure level (see Fig.36 ). Λ is the wavelength of the diffracted light.

[0288] For further embodiments of the optical diffraction element 93 that suppresses at least one target wavelength by destructive interference, see Fig.37 Corresponding to the above reference Figures 1 to 36 , and with particular reference to Fig.36 Elements and functions of those explained carry the same reference numerals and are not discussed again in detail.

[0289] Fig.37 Displays the equivalent structure depth (here denoted as h) with various grating levels. 0 ), and the diffraction structure level N 1 、N 2 、N 3 and N 4Another embodiment of a stepped grating of equal length along the periodic running direction (in this case designated by R). The periodic running direction R can also be the radius of a concentric diffractive structure, wherein the center of this diffractive structure can coincide with the center of the collector mirror 24.

[0290] Therefore, the diffractive element 93 has a total of four diffractive structure levels N 1 To N 4 , whose structural depths differ in each case by h 0 . In this h 0 =λ N / 4 holds, where λ N is the target wavelength to be suppressed.

[0291] In the periodic running direction R, a complete period p of the diffractive element includes firstly the four descending diffractive structure levels N 1 To N 4 , and then two successive rising diffraction structure levels N 5 、N 6 , where the diffraction structure level N 5 The structural depth corresponds to the diffraction structure level N 3 The structure depth, and the diffraction structure level N 6 The structural depth corresponds to the diffraction structure level N 2 The structural depth.

[0292] For further embodiments of optical diffraction elements 94, 95 that suppress at least one target wavelength by destructive interference, see below. Fig.38 and Fig.39 Corresponding to the above reference Figures 1 to 37 , and with particular reference to Figure 36 to Figure 37 Elements and functions of those explained carry the same reference numerals and are not discussed again in detail.

[0293] in accordance with Fig.38 The diffraction element 94 has diffraction structure levels N successively along the periodic travel direction R within one grating period p. 1 (with structure depth 0), N 2 (with a structural depth h 1 ), N 3 (with a structural depth h 1 +h 2 ) and N 4 (with a structural depth h 2 ). The following holds: h 1 <h 2 .

[0294] In accordance with Fig.39In the case of a diffractive element 95, within a period p and along the direction of travel R of the period, the following follow one another: a diffractive structure level N with a structure depth 0 1 , with a structural depth h 1 The diffraction structure level N 2 , with a structural depth h 2 The diffraction structure level N 3 , and with a structural depth h 1 +h 2 The diffraction structure level N 4 . Here, the following also holds: h 1 <h 2 .

[0295] From the above Fig.36 Starting from the equations described above, the intensity in the zeroth order diffraction can be specified as:

[0296]

[0297] In this case, λ 1 and λ 2 are the two target wavelengths to be suppressed by destructive interference by means of diffraction elements 94 and 95, respectively. The following holds: 1 =λ 1 / 4 and h 2 =λ 2 / 4.

[0298] For λ=λ 1 And for λ=λ 2 For , the following holds: I(0) = 0. Therefore, these two wavelengths are optimally suppressed.

[0299] exist Figure 35 to Figure 39 In the embodiment of the present invention, such a multi-level grating of the type of grating can be generalized to suppress a number n of target wavelengths by destructive interference. In order to suppress n wavelengths, 2n different diffraction structure levels N with the following heights are required. i :h 1 、h 2 ,…h n , 0, h 1 +h 2 、h 1 +h 3 ,…,h 1 +h n , where in addition, the different structural depths h 1 to h n The following relations are satisfied:

[0300] h 1 <h i <hi+1 <2h 1

[0301] By means of the optical diffraction element described above, as an alternative or in addition to the target wavelength being suppressed in the infrared wavelength range, for example wavelengths in other wavelength ranges can also be suppressed, for example in the DUV wavelength range.

[0302] Fig.40 Displayed as a curve, for example Fig.16 , Fig.19 and Fig. 22 The gratings of the type 60, 64 or 71 have two structural depths d 1 and d 2 The wavelength-dependent reflectivity R of a variant of the optical diffraction element. In this case, the structural depth present is as follows: d 1 =45nm and d 2 =52nm. The result is Fig.40 The reflectivity curve 96 is shown as a solid line in FIG. 1 . In addition, the dashed line shows the reflectivity curve 96 for a structure having only one diffraction grating (designed with a structure depth d 1 (Reflectivity curve 97) and d 2 (Reflectivity curve 98)) corresponds to the reflectivity curves 97 and 98 of the grating.

[0303] Reflectivity curve 96 shows the reflectivity for the two target wavelengths λ 1 ≈180nm and λ 2 ≈210nm suppression.

[0304] For these two target wavelengths λ 1 , 2 For the difference measure, the following holds:

[0305] (λ 1 -λ 2 ) 2 / (λ 1 +λ 2 ) 2 =0.006

[0306] Here, the suppression ratio at these two DUV wavelengths is 10 -5 better.

[0307] Fig.41 show Figures 14 to 22 or Figures 25 to 32 Reflectivity R of an exemplary embodiment of an optical diffractive element of the type shown, which in this case is produced with different structure depths d 1 to d 4 The following holds true here: d 1=45nm, d 2 =2nm, d 3 =2.55μm, and d 4 =2.65μm.

[0308] Fig.41 The wavelength-dependent reflectivity curve 97 shown in FIG. 9 corresponds to the structure depth d 3 and d 4 Displays two reflectance minima, where the ratio is 10 -6 Better suppression at λ 3 =10.2μm and at λ 4 =10.6μm.

[0309] In addition, corresponding to the two structural depths d 1 and d 2 , the grating with reflectivity curve 97 also suppresses the two DUV wavelengths λ 1 ≈ equal to 180nm and λ 2 ≈ equal to 210nm, where Fig.42 Magnified details in the DUV range show a ratio of 10 -6 Better suppression.

[0310] Fig.43 The graph illustrates how the requirements regarding the tolerance of the structure depth and / or the sidewall steepness are relaxed as the number of diffractive structure groups increases by using an optical diffractive element consisting of a plurality of diffractive structure groups. The illustration again shows the reflectivity as a function of the wavelength in the range between 10.0 and 11.0 μm. In this case, the target wavelength in the region of 10.6 μm is subject to a greater tolerance than 10. -4 Better suppression.

[0311] The reflectivity curve for an optical diffraction element comprising only one diffraction structure group (i.e. comprising only one diffraction grating) is exemplified in Fig.43 At 98 in FIG. 1 , the structural depth d is assumed to be 2.65 μm and is allowed to vary within a tolerance bandwidth of 0.5%.

[0312] 99 denotes the reflectivity curve for an optical diffraction element comprising two diffraction gratings as diffraction structure group, which in each case have an equivalent structure depth d of 2.65 μm. 1 =d 2 , and a ten-fold tolerance bandwidth of 5% is permitted. In the region of the target wavelength, in the case of the reflectivity curve 99 , a better suppression is obtained than in the case of the reflectivity curve 98 , despite the ten-fold higher tolerance bandwidth.

[0313] exist Fig.43, 100 indicates a reflectivity curve for an optical diffraction element comprising two diffraction gratings as a diffraction structure group, whose structure depths are different (d 1 =2.65μm, d 2 =2.55 μm), allowing in each case a tolerance bandwidth of 3.5%. A suppression of 90 % corresponding to the suppression of the reflectivity curve 99 is obtained at a target wavelength of 10.6 μm.

[0314] exist Fig.43 , 101 indicates a structure comprising three diffraction gratings (having an equivalent structure depth d of 2.65 μm). 1 =d 2 =d 3 and a tolerance bandwidth of 12% for the structure depth) in the form of three diffraction structure groups of optical diffraction elements.

[0315] This very high tolerance bandwidth results in a bandwidth corresponding to the requirement of “better than 10” due to the mutually reinforcing suppression effect of the three diffraction gratings in the region of the target wavelength. -4 Better inhibition” of very good inhibition.

[0316] Fig.44 Again, the diffraction structure level N is displayed. 1 To N 4 The grating 60, as has been described above, in particular with reference to Figures 14 to 16 In addition, Fig.44 Two photolithographic mask structures 105 , 106 that may be used during the photolithographic fabrication of the grating 60 are illustrated.

[0317] exist Fig.44 The photolithographic mask structure 105 illustrated as being closest to the grating 60 has a mask region 107 that is impermeable to the etching medium and an intervening mask gap 108 that is permeable to the etching medium. The periodicity of the mask structure 105 corresponds to the periodicity according to Fig.15 The periodicity of the diffraction grating 62. The mask structure 105 defines the first diffraction structure level N 4 With N 3 The layer side wall N 4 / N 3 , and the second diffraction structure level N 1 With N 2 N 1 / N 2 .

[0318] The arrangement offset in the periodic running direction x is a second lithographic mask structure 106 with mask regions 109 and mask gaps 110. The periodicity of this second lithographic mask structure 106 corresponds to Fig.14The second photolithography mask structure 106 defines the first diffraction structure level N 3 With N 1 The layer side wall N 3 / N 1 , and the second diffraction structure level N 2 With N 4 N 2 / N 4 location.

[0319] The diffraction structure level N of the grating 60 1 To N 4 The morphology can be described as (i.e., the diffraction structure groups 61, 62 (see also) which can be manufactured with the aid of the photolithography mask structures 105, 106 Fig.14 and Fig.15 Each of these binary structures 61, 62 has a first surface section (with a first structure depth), i.e., the positive structure 61 of the structure group 61, 62. P , 62 P , and having a second surface section (having a second structure depth), namely a negative structure 61 N , 62 N , which is parallel to the first surface section 61 along the periodic travel direction x P , 62 P Alternately. These adjacent surface segments first 61 P / 61 N And then 62 P / 62 N The boundary region between the binary structures 61 and 62 is the layer sidewall N described above. i / N j , both of which are perpendicular to the direction of periodic travel and perpendicular to Figures 14 to 16 and Fig.44 The linear path of the illustrated plane in FIG. These boundary regions N of the first binary structure 61 3 / N 1 、N 2 / N 4 and the boundary region N of the second binary structure 62 4 / N 3 、N 1 / N 2 They travel completely apart from each other, ie they do not overlap each other in their path perpendicular to the periodic travel direction x.

[0320] As viewed along the periodic travel direction x, the grating 60 has a further characteristic in that each ascending level sidewall (i.e., first N 3 / N 1 and its secondary N 4 / N 3 ) are respectively assigned to the descending level sidewalls of the same structural depth. In this case, the ascending level sidewall N 3 / N 1 Assigned to the descending level sidewall N 2 / N 4 The rising level side wall N 4 / N 3 Assigned to the descending level sidewall N 1 / N 2 First, the assigned level sidewall N 3 / N 1 and N 2 / N 4 In this case, the structure depth d 1 . The level side walls N are also assigned to each other 4 / N 3 and N 1 / N 2 With structural depth d 2 .

[0321] During the production of the grating 60, first one of the two mask structures 105, 106 (e.g. mask structure 105) is used and in the region of the mask gap 108, in a first etching step using an etching region provided by a corresponding source, a grating having a width of the mask gap 108 (with a predefined first etching depth d 2 ). Then, the mask structure 105 is removed and the mask structure 106 is used, and in a further etching step, a further etching step is performed with a depth of d 1 The substrate is etched until it corresponds to Fig.44 The diffraction structure level N of the bottom illustration 1 To N 4 Thus, the mask manufacturing of the grating 60 involves using a first mask structure for photolithographically etching the substrate first, and then a second mask structure that differs with respect to the position of the mask regions and mask gaps. This difference in the position of the mask regions / mask gaps can be achieved by replacing the first mask structure with another mask structure and / or by shifting the mask structure along the travel direction x.

[0322] The manufacturing method may also include more than two etching steps and may also use more than two different mask structures and / or more than two etching steps.

[0323] Fig.45 shows the relationship during the photolithographic fabrication of the grating 64 (see also Figures 17 to 19 ). Corresponds to the above reference Figures 1 to 44 , and with particular reference to Figures 14 to 19 and Fig.44Elements and functions of those explained carry the same reference numerals and are not discussed again in detail.

[0324] exist Fig.45 , two photolithographic mask structures 111 and 112 are illustrated for the grating 64, which also have periodically successive mask regions and mask gaps. In this case, the photolithographic mask structure 111 has a mask region 113 and a mask gap 114, and the photolithographic mask structure 112 has a mask region 115 and a mask gap 116.

[0325] During the lithographic fabrication of the grating 64, the lithographic mask structure 111 defines the layer sidewalls N 3 / N 2 and its secondary N 2 / N 3 , and the additional photolithographic mask structure 112 defines the level sidewalls first N 2 / N 1 and its secondary N 1 / N 2 Here, the grating 64 is also produced as two binary structures 65, 66 (see Fig.17 and Fig.18 ), the two binary structures are perpendicular to the periodic travel direction x and perpendicular to Figures 17 to 19 and Fig.45 The boundary area of ​​the illustrated plane (ie, the layer side wall N i / N j ) are completely separated from each other, i.e. they do not overlap each other.

[0326] Here, too, if viewed along the periodic running direction x, it is true that each rising level side wall (ie side wall N 2 / N 1 and N 3 / N 2 ) is again assigned to the descending level sidewall of the same structural depth, that is, the ascending level sidewall N 2 / N 1 Assign the descending level side wall N 1 / N 2 , and the rising level side wall N 3 / N 2 Assign the descending level side wall N 2 / N 3 .

[0327] The above especially refers to Figure 20 to Figure 22 , Figure 25 to Figure 28 and Figure 29 to Figure 32 The illustrated gratings 71, 76, 80 can also be described as the boundary regions between their surface segments (i.e., their level sidewalls N i / N j) corresponding superposition of binary structures that are not superimposed on each other, as has been explained above with reference to the gratings 60 and 64. In the case of the gratings 76 and 80, these can be described as their boundary regions (ie the level sidewalls N i 、N j ) is a superposition of three binary structures that are not superimposed on each other. For these gratings 71, 76, 80, as viewed along the periodic running direction x, it is also true that each rising level side wall is assigned a descending level side wall of the same structural depth.

[0328] In the case of the above-described optical diffractive elements with periodic progression directions of the diffractive structure groups that are not parallel to one another, this results in intersections of the level side walls (i.e. of the boundary regions between different surface sections of the diffractive structures). In this case, the aforementioned boundary regions also overlap one another only at points, i.e. at most along the sections of the linear path of the level side walls, i.e. where the level side walls intersect.

[0329] For further embodiments of the optical diffraction element 117 in the form of a grating that suppresses at least one target wavelength by destructive interference, reference is made below to Fig.46 Corresponding to the above reference Figures 1 to 45 Elements and functions of those explained are denoted by the same reference numerals and are not discussed again in detail.

[0330] The grating 117 is implemented as a grating structure profile that is periodic along the periodic running direction x and includes a diffractive structure having three diffractive structure levels N 1 、N 2 、N 3 .

[0331] Intermediate diffraction structure level N 2 A reference height of 0 (d=0) is predefined, which is therefore also referred to as the neutral diffraction structure level. 1 The third diffractive structure level N has a structure depth of d=+λ / 4 measured relative to this reference height and is therefore also referred to as a positive diffractive structure level. 3 A structure depth of d=−λ / 4 measured relative to this reference height is therefore also referred to as a negatively diffractive structure order.

[0332] Therefore, the three diffraction structure levels N 1 To N 3 Different structure depths are predefined relative to this reference plane d=0.

[0333] The grating period p of the grating structure profile of the grating 117 is subdivided into diffractive structure levels N 1 To N 3 There are a total of four periodic sections. Two of the four periodic sections are implemented as neutral diffraction structure level N2 One of the four periodic sections is implemented as a positive diffraction structure level N 1 , and the fourth segment of the four periodic segments is implemented as a negative diffraction structure level N 3 In the periodic travel direction x, along Fig.46 The sequence of the selected unit monomers (the aforementioned unit monomers are surrounded by dotted lines) is: N 2 、N 1 、N 2 、N 3 .

[0334] Along the periodic travel direction x, the four periodic segments within one grating period p have the same structural length x N .

[0335] Alternatively, the length of the periodic segment (ie, the corresponding diffraction structure level N) 1 To N 3 The x extensions of the diffractive structures may also differ from each other in pairs. Then, the following should be used as for the diffractive structure level N 1 To N 3 The length of the periodic segment x Ni The constraints are satisfied:

[0336] x N1 +x N3 =2x N2

[0337] The sum of the extensions of the orders deviating from the neutral diffractive structure order should therefore be equal (to a good approximation) to twice the extension of the neutral diffractive structure order.

[0338] The diffractive structure level N described 1 To N 3 The arrangement (i.e., the structure depth and length along the periodic travel direction x) is such that the first target wavelength λ in the infrared wavelength range 1 (which is diffracted by the grating structure profile) has a radiation component having a wavelength at the first target wavelength λ 1 The three different phases in the zero-order diffraction of , which interfere destructively with each other, are thus obtained, as has been described above, especially in accordance with Figures 1 to 45 As revealed by theoretical considerations, this suppression effect is quadratic compared to the suppression of a single binary grating (not shown), so that if the positive diffraction structure level N 1 Then set up instead of negative diffraction structure level N 3 The binary grating has 10 -2 The grating 117 has, for example, 10 -4 The inhibitory effect.

[0339] The target wavelength may be in the range between 10 μm and 11 μm.

[0340] The effect of structural depth error on diffraction efficiency is discussed below. Fig.47 and Fig.48 Here, it is assumed that light with a wavelength λ to be suppressed is Fig.47 and Fig.48 In the figure, normal incidence is assumed onto the grating 117 from above. This assumption "normal incidence" serves only as a model assumption for the following considerations. In practice, the angle of incidence of the light often deviates from normal incidence. As a result, the structural depth of the optical diffraction element described here is subsequently adapted to the corresponding angle of incidence. Methods for performing this design adaptation are known to those skilled in the art. In practice, the angle of incidence of the light varies with the wavelength to be suppressed, and the structural depth of the optical diffraction element therefore also varies above the EUV collector. In the case of an EUV collector 24 with a rotationally symmetrical design, the structural depth of the diffraction structure group can continuously vary from the center of the EUV collector 24 towards the edge of the EUV collector 24.

[0341] The equivalent phase P of the reflected light wave 0 area, in Fig.47 and Fig.48 As the diffraction structure level is first N 1 and its secondary N 3 In each case relative to the neutral diffraction structure level N 2 The optical path length is shifted by λ / 4, so it is obvious that Fig.47 For a total of four period sections of the grating period of the grating 117 illustrated in FIG. 1 , two regions of reflected light are obtained in each case, whose phase P 0 The reflection is offset by only half a wavelength (i.e. λ / 2) relative to the two further regions, which Fig.47 In the case of a structural depth of exactly λ / 4 in , this results in an exact suppression of the incident light, ie, in destructive interference of the reflected light.

[0342] Fig.47 Shows the positive diffraction structure level N 1 With a structure depth greater than λ / 4 and negative diffraction structure level N 3 The structural depth is related to the positive diffraction structure level N 1 The absolute value of the structural depth is the same (that is, the absolute term corresponds to the same greater than λ / 4). Therefore, the height error exists in accordance with Fig.47 in the case of the grating.

[0343] First, the positive diffraction structure level N 1 Reflection and then negative diffraction structure level N 3The equivalent phase P of the reflected light 0,d area, in Fig.48 Indicated by hollow circles.

[0344] As respectively subject to the level N 1 and N 3 The two phases P of the reflection 0,d The position of the reflected light in the direction of the beam is based on Fig.47 The corresponding phase position P in the case of perfect inhibition 0 As shown in the comparison, based on Fig.48 In the case of the situation, these two phases P 0,d The two phases P are located near the correct phase position in a manner of being shifted upward and downward by the same distance, respectively. As a result, the two shifted phases P 0,d The average value becomes again located according to Fig.47 At the exact phase position of 1 and N 2 Compared with the binary grating with only two diffraction structure levels and the corresponding height error, this average is obtained in the binary grating with three diffraction structure levels N. 1 To N 3 The case of the grating results in an improvement in suppression.

[0345] Fig.49 Display contains diffraction structure, also has three diffraction structure levels N 1 、N 2 and N 3 A further variant of the optical diffraction element for suppressing at least one target wavelength in the form of a grating 118. Figures 1 to 48 , and with particular reference to Figure 46 to Figure 48 Elements and functions of those explained carry the same reference numerals and are not discussed again in detail.

[0346] Fig.49 Again, a unit cell extending along the periodic direction x during one period p is illustrated using a dashed line. First, there is a neutral diffraction structure level N in this unit cell in the periodic direction x. 2 , has twice the length 2x compared to the other two diffractive structure levels N Therefore, within the illustrated unit cell, the sequence of the diffraction structure levels in the direction of periodic progression is: twice the length 2x N The neutral diffraction structure level N 2 , with a single length x N The positive diffraction structure level N 1 , with a single length x N The negative diffraction structure level N 3Therefore, in the case of grating 118, within the unit cell, the positive diffraction structure level N 1 Then there is the negative diffraction structure level N 3 , so that the layer sidewalls therebetween have a structural depth of λ / 2.

[0347] Fig.50 A further embodiment of an optical diffraction element for suppressing at least one target wavelength is shown, the optical diffraction element being made as a grating 120, again comprising a diffraction structure having four diffraction structure levels N 1 To N 4 . Corresponding to the above reference Figures 1 to 49 , and with particular reference to Figure 46 to Figure 49 Elements and functions of those explained carry the same reference numerals and are not discussed in detail again. Along the periodic progression direction, the grating 120 has the following sequence of diffractive structure levels: positive diffractive structure level N with a structure depth of +λ / 4 1 , neutral diffraction structure level N 2 , negative diffraction structure level N with structure depth -λ / 4 3 , with a structure depth of -λ / 2 and a double negative diffraction structure level N 4 , negative diffraction structure level N 3 , and the neutral diffraction structure level N 2 Therefore, the unit cell of the grating 120 includes a diffraction structure level sequence N 1 、N 2 、N 3 、N 4 、N 3 、N 2 Or a corresponding cyclic exchange.

[0348] Fig.51 A further embodiment of an optical diffraction element for suppressing at least one target wavelength is shown, the optical diffraction element being made as a grating 121, again comprising a diffraction structure having five diffraction structure levels N 1 To N 5 . Corresponding to the above reference Figures 1 to 50 , and with particular reference to Figures 46 to 50 Elements and functions of those explained carry the same reference numerals and are not discussed in detail again. Along the periodic running direction, the grating 121 has the following sequence of diffractive structure levels: positive diffractive structure level N with a structure depth of +λ / 4 1 , neutral diffraction structure level N 2 , negative diffraction structure level N with structure depth -λ / 4 3 , with a structure depth of -λ / 2 and a double negative diffraction structure level N 4 , triple negative diffraction structure level N with structure depth -3λ / 45 , with a structure depth of -λ / 2 and a double negative diffraction structure level N 4 , negative diffraction structure level N with structure depth -λ / 4 3 , and the neutral diffraction structure level N 2 Therefore, the unit cell of the grating 121 includes a diffraction structure level sequence N 1 、N 2 、N 3 、N 4 、N 5 、N 4 、N 3 、N 2 Or a corresponding cyclic exchange.

[0349] Additional diffractive structure levels N in the case of grating 120 4 , and N in the case of grating 121 4 、N 5 This results in an additional intensification of the diffraction effect, namely in a further intensification of the destructive interference at the target wavelength λ.

[0350] Fig.52 It shows that there are diffraction structure levels N 1 、N 2 and N 3 sequence of Fig.46 Reflectivity curve 125 of a grating of the type shown, the aforementioned diffractive structure levels having a structure depth d of in each case λ / 4 (d≈2.6 μm) and a periodic progression direction x (x N1 =x N2 =x N3 ) on the diffraction structure level N 1 To N 3 The equivalent structural length x N The result is that at a wavelength of λ = 10.4 μm, the 1·10 -6 The reflectivity curve 125 has a broad reflectivity minimum at 10.2 μm to 10.6 μm, and the reflectivity is less than 2·10 -6 Between 10.1μm and 10.7μm, the reflectivity is less than 3·10 -6 Between 10.0μm and 10.8μm, the reflectivity is less than 5·10 -6 This results in a very good suppression of interfering wavelengths in the indicated wavelength range.

[0351] Fig.53 by Fig.44 and Fig.45 The way of showing that when the period is p = 4x N The grating 64 (see also Figures 17 to 19) during lithography manufacturing.

[0352] Corresponding to the above reference Figures 1 to 52 , and with particular reference to Figures 14 to 19 , Fig.44 and Fig.45 Elements and functions of those explained carry the same reference numerals and are not discussed again in detail.

[0353] For grating 64, Fig.53 Further embodiments of lithographic mask structures 126, 127 are illustrated for use during lithographic fabrication of grating 64 and again having periodic successive mask regions and mask gaps. In this case, lithographic mask structure 126 has successive mask regions 128 and 129 with mask gaps 130 and 131 therebetween, and mask structure 127 has successive mask regions 132 and 133 with mask gaps 134 and 135 therebetween.

[0354] During the lithographic fabrication of the grating 64, the mask region 128 of the mask structure 126 defines the layer sidewalls N 3 / N 2 and its secondary N 1 / N 2 The further mask region 129 of the mask structure 126 defines the level side wall N for the next sequence of diffractive structure levels of the grating 64 that follows in the periodic progression direction x. 2 / N 1 and N 2 / N 3 The further photolithographic mask structure 127 defines the diffractive structure level N starting with the mask region 132 in the periodic running direction x. i The periodic level side wall N 2 / N 1 and N 2 / N 3 , and the mask region 133 of the mask structure 127 defines the diffractive structure level N i The next cycle of the layer sidewall N 3 / N 2 and N 1 / N 2 The grating 64 is generated as a superposition of two binary structures, the two binary structures being perpendicular to the periodic travel direction x (perpendicular to Fig.53 The boundary areas of the diagram plane in the figure are completely separated from each other, that is, they do not overlap with each other.

[0355] The mask structures 128, 129 and 132, 133 all have the same x extension, ie 2x N The mask gaps 131 and 134 have the same x extension, ie, both are xN The mask structures 130 and 135 also have the same x extension, namely 3x N .

[0356] Therefore, the mask structures 126, 127 alternately predefine different levels of sidewalls for respectively successive periods p of the grating 64. By means of a shift in the period length p, most of the mask structures 126 and 127 can be converted into one another.

[0357] Fig.54 An alternative embodiment of two mask structures 136, 137 is shown during the lithographic production of the grating 64. Figures 1 to 53 , and with particular reference to Figures 14 to 19 , Fig.44 and Fig.53 Elements and functions of those explained carry the same reference numerals and are not discussed again in detail.

[0358] The mask structure 136 has mask regions 138, 139 and mask gaps 140, 141 therebetween. The mask structure 137 has mask regions 142, 143 and mask gaps 144 and 145 therebetween. The x extension of the mask regions 138 and 143 is firstly 3x N , so x N The mask regions 139 and 142 have an x ​​extension of three times the magnitude. The mask gaps 140, 141, 144 and 145 all have a 2x N extension of.

[0359] During the lithographic production of the grating 64, the lithographic mask structure 136 defines the diffractive structure levels N of the grating 64 by means of the mask regions 138. 1 To N 3 The first period p of the level sidewall N 3 / N 2 and N 2 / N 3 , and the mask area 139 defines the diffraction structure level N 1 To N 3 The second period p of the layer sidewall first N 2 / N 1 and its secondary N 1 / N 2 The further photolithographic mask structure 137 defines the layer sidewalls N of the first period by means of the mask region 142. 2 / N 1 and N 1 / N 2 , and defines the diffraction structure level N by means of the mask area 143 1 To N 3 The layer sidewall N of the successive period p3 / N 2 and N 2 / N 3 .

[0360] Here, based on Fig.54 In the case of the embodiment of the invention, the mask structures 136 and 137 alternately predefine the diffraction structure level N. 1 To N 3 The mask structures 136 and 137 can also be formed by using a period length p=4x N The shifts are converted into each other.

[0361] For the relationship during the further embodiment of manufacturing the grating 146 by means of two mask structures 147, 148, reference will be made to Fig.55 Explain. Fig.53 and Fig.54 (each of which shows two grating periods of grating 64), Fig.55 A grating period p is shown in FIG. Within this grating period p, the grating 146 has the following diffraction structure levels N in the travel direction x: i Sequence: N 1 、N 2 、N 1 、N 2 、N 3 and N 2 The grating period p has 6x N Extension of all diffraction levels N 1 In each case, x N extension of.

[0362] The mask structure 147 has mask regions 149, 150 and mask gaps 151, 152 therebetween according to a period p, and the mask structure 148 has only one assigned mask region 153 and one mask gap 154 ​​according to a period p. The mask regions 149 and 150 have a 2x N The mask gaps 151 and 152 have x N The mask area 153 has a 3x N The mask gap 154 ​​also has a 3x N extension of.

[0363] Within the sequence of level sidewalls during a period p along the periodic progression direction x, the following assignment holds true with regard to the predefinition of the respective level sidewalls by the mask regions of the respective mask structure:

[0364] Layer side wall Predefined mask areas <![CDATA[N 2 / N 1 ]]> 153 <![CDATA[N 1 / N 2 ]]> 149 <![CDATA[N 2 / N 1 ]]> 150 <![CDATA[N 1 / N 2 ]]> 153 <![CDATA[N 2 / N 3 ]]> 150 <![CDATA[N 3 / N 2 ]]> 149 <![CDATA[N 2 / N 1 ]]> 153 etc. etc.

[0365] For the relationship during the further embodiment of manufacturing the grating 155 by means of two mask structures 156, 157, reference will be made to Fig.56 Explain. Fig.53 and Fig.54 (each of which shows two grating periods of grating 64), Fig.56 A grating period p is shown in FIG. Within this grating period p, the grating 155 has the following diffraction structure levels N: i Sequence: N 2 、N 1 、N 2 、N 3 、N 2 and N 3 . Thus, in the case of grating 155, with 6x N The extended period p also exists. i All have x along the direction x of the period N extension of.

[0366] For the fabrication of grating 155, again two photolithography mask structures 156 and 157 are illustrated in Fig.56 In this case, the mask structure 156 has mask regions 158 and 159 and mask gaps 160, 161 therebetween, and the mask structure 157 has only one mask region 162 and one mask gap 163 according to the period. The mask regions 158 and 159 both have an extension x N The mask gaps 160 and 161 also have a 2x N Firstly the mask area 162 and secondly the mask gap 163 have in each case 3x N extension of.

[0367] During the lithographic production of the grating 155, the following holds true for the assignment of mask areas to the level sidewalls:

[0368] Layer side wall Predefined mask areas <![CDATA[N 3 / N 2 ]]> 162 <![CDATA[N 2 / N 1 ]]> 158 <![CDATA[N 1 / N 2 ]]> 158 <![CDATA[N 2 / N 3 ]]> 162 <![CDATA[N 3 / N 2 ]]> 159 <![CDATA[N 2 / N 3 ]]> 159 <![CDATA[N 3 / N 2 ]]> 162 etc. etc.

[0369] The structure of the grating explained above may have the effect that stray light radiation having, for example, an infrared wavelength reflected by the EUV collector 24 destructively interferes in the zeroth order, where the stray light intensity is therefore suppressed. In this case, the optical diffraction element described above generally acts as a reflective element.

[0370] The body of the EUV collector 24 may be made of aluminum. Alternative materials for this body are copper, alloys containing the components copper and / or aluminum, or alloys of copper and aluminum oxide or silicon produced by powder metallurgy.

[0371] To produce microstructured or nanostructured elements, a projection exposure apparatus 1 is used as follows: First, a reflective mask 10 or reticle and a substrate or wafer 11 are provided. Thereafter, the structure on the reticle 10 is projected onto a photosensitive layer of the wafer 11 by means of the projection exposure apparatus 1. The microstructure or nanostructure on the wafer 11, and thus the microstructured element, is then produced by developing this photosensitive layer.

Claims

1. An optical diffraction element (64; 117; 118; 119; 120; 121) - comprising a periodic grating structure profile having three diffractive structure levels (N1 to N3; N1 to N4; N1 to N5), the periodic grating structure profile comprising a diffractive structure, - predefined different structural depths relative to a reference plane, - wherein the arrangement of the diffractive structure is such that a wavelength range around a first target wavelength λ1 in the infrared wavelength range has a radiation component, the first target wavelength being diffracted by the periodic grating structure profile, the radiation component having at least three different phases that destructively interfere with each other at least in the zero and / or + / - first order diffraction of the first target wavelength λ1, - wherein the diffractive structure levels (N1 to N3; N1 to N4; N1 to N5) predefine the morphology of the grating period (p) of the periodic grating structure profile that is regularly repeated along a periodic running direction (x), - wherein the diffractive structure levels (N1 to N3; N1 to N4; N1 to N5) comprise: - neutral diffraction structure level (N2), which corresponds to a reference height of zero, a positive diffractive structure level (N1) arranged at an optical path length λ1 / 4 + / - 20% higher than the neutral diffractive structure level (N2), and - Negative diffraction structure levels (N3; N3, N4; N3, N4, N5) which are arranged at an optical path length λ 1 / 4 + / - 20% lower than the neutral diffraction structure level (N2).

2. The optical diffraction element according to claim 1, characterized in that: The grating period of the grating structure profile is subdivided into four period segments of the diffraction structure level, wherein two of the four period segments are implemented as neutral diffraction structure segments having the neutral diffraction structure level (N2), one of the four period segments is implemented as a positive diffraction structure segment (N1) having the positive diffraction structure level, and one of the four period segments is implemented as a negative diffraction structure segment (N3) having the negative diffraction structure level.

3. The optical diffraction element according to claim 2, characterized in that: The four periodic segments have the same length (x) along the direction (x) of the periodic travel. N )+ / -20%.

4. The optical diffraction element according to claim 2, characterized in that The sequence of the following four periodic segments: positive diffraction structure level (N1), neutral diffraction structure level (N2), negative diffraction structure level (N3), neutral diffraction structure level (N2).

5. The optical diffraction element according to any one of claims 1 to 4, characterized in that: The diffraction structure is arranged so that the target wavelength range in the infrared wavelength range including the first target wavelength λ1 has a radiation component, the first target wavelength is diffracted by the periodic grating structure profile, and the radiation component has at least three different phases that destructively interfere with each other in at least zero and / or + / - first order diffraction of the first target wavelength λ1, wherein the target wavelength range includes a second target wavelength λ2 different from the first target wavelength λ1 in addition to the first target wavelength λ1, wherein the diffraction structure is arranged so that the wavelength range near the second target wavelength λ2 in the infrared wavelength range also has a radiation component, the second target wavelength is diffracted by the periodic grating structure profile, and the radiation component has at least three different phases that destructively interfere with each other in at least zero and / or + / - first order diffraction of the second target wavelength λ2, wherein the following is true for the two target wavelengths λ1 and λ2: (λ1-λ2) 2 / (λ1+λ2) 2 <20%.

6. A method for suppressing at least one target wavelength (λ) by destructive interference N ) of an optical diffraction element (34; 46; 47; 57; 58; 59; 60; 64; 71; 76; 80; 86; 91; 92; 93; 94; 95; 117; 118; 119; 120; 121), - contains at least three diffractive structure levels (N i ), the three diffraction structure levels predefine different structure depths (d i ), - wherein the three diffraction structure levels (N i ) can be assigned to at least two diffractive structure groups (35, 36; 61, 62; 65, 66; 72, 73; 77, 78, 79; 81, 82, 83; 87, 88, 89; N1, N2; N2, N3; N3, N1; N n 、N n +1), - wherein the first group (35; 61; 65; 72; 77; 81; 87; N n 、N n +1) is implemented to suppress the first target wavelength λ1 in the zero-order diffraction, and - wherein the second group (36; 62; 66; 73; 78; 82; 88; N n +1, N n +2) is implemented to suppress the second target wavelength λ2 in the zero-order diffraction, - wherein the following holds for the two target wavelengths λ1 and λ2: (λ1-λ2) 2 / (λ1+λ2) 2 <20%, - wherein the diffraction structure level (N i ) can be described as the superposition of two binary diffraction structure groups (35, 36; 61, 62; 65, 66; 72, 73; 77, 78, 79; 81, 82, 83; 87, 88, 89), - wherein each of the binary diffractive structure groups has: A first surface section having a first structural depth (61 P ; 62 P ); A second surface section having a second structural depth (61 N ; 62 N ), which is connected to the first surface section (61 along a running direction (x) P ; 62 P )alternately, - wherein the binary diffraction structure group (35, 36; 61, 62; 65, 66; 72, 73; 77, 78, 79; 81, 82, 83; 87, 88, 89; N1, N2; N2, N3; N3, N1; N n 、N n +1) of each of the adjacent surface segments (61 P , 61 N ; 62 P , 62 N ) have a linear path between the boundary regions (N3 / N1, N2 / N4, N4 / N3, N1 / N2), where -- The two binary diffraction structure groups (35, 36; 61, 62; 65, 66; 72, 73; 77, 78, 79; 81, 82, 83; 87, 88, 89; N1, N2; N2, N3; N3, N1; N n 、N n +1) of the first group of first boundary regions (N3 / N1, N2 / N4) and -- The two binary diffraction structure groups (35, 36; 61, 62; 65, 66; 72, 73; 77, 78, 79; 81, 82, 83; 87, 88, 89; N1, N2; N2, N3; N3, N1; N n 、N n +1) of the second group of the second boundary region (N4 / N3, N1 / N2) --At most the segments along their linear paths overlap each other.

7. The optical diffraction element according to claim 6, characterized in that: The two binary diffraction structure groups (61, 62; 65, 66; 72, 73; 77, 78, 79; 81, 82, 83; 87, 88, 89; N1, N2; N2, N3; N3, N1; N n 、N n +1) and the first boundary region (N3 / N1, N2 / N4) of the first group and the two binary diffraction structure groups (61, 62; 65, 66; 72, 73; 77, 78, 79; 81, 82, 83; 87, 88, 89; N1, N2; N2, N3; N3, N1; N n 、N n +1), the second boundary areas (N4 / N3, N1 / N2) of the second group are completely separated from each other.

8. The optical diffraction element according to claim 6 or 7, characterized in that: A first group of the diffraction structure groups (35; 61; 65; 72; 77; 81; 87) is implemented as a first diffraction grating arranged on a grating surface (33), wherein the first diffraction grating -- having a first grating period (ph; p1), - has a first structure depth (dh; d1), which is the optical path difference between the first diffractive positive structure (37) and the first diffractive negative structure (38), measured perpendicular to the surface section of the grating surface (33) surrounding these first structures (37, 38), - wherein the second group (36; 62; 66; 73; 78; 82; 88) of the diffraction structure groups is implemented as a second diffraction grating arranged on the grating surface (33), wherein the second diffraction grating -- having a second grating period (pv; p2), --having a second structure depth (dv; d2), which is the optical path difference between the second diffractive positive structure (40) and the second diffractive negative structure (41), measured perpendicular to the surface section of the grating surface (33) surrounding these second structures (40, 41) respectively.

9. The optical diffraction element according to claim 8, characterized in that: - the first grating period (ph) runs along a first period running direction (39) of the first diffraction grating (35), the second grating period (pv) runs along a second period running direction (42) of the second diffraction grating (36), - wherein the two periodic travel directions (39, 42) do not travel parallel to each other.

10. The optical diffraction element according to claim 8, characterized in that At least one further diffraction grating (48) is arranged on the grating surface (33), the further diffraction grating - having a further diffractive positive structure (49) and a further diffractive negative structure (50), wherein the surface area ratio of the surface area of ​​the further diffractive positive structure (49) to the surface area of ​​the further diffractive negative structure (50) is in the range of 0.9 to 1.1, - having another grating period (pd), - having a further structure depth (dd), which is the optical path difference between the further diffractive positive structure (49) and the further diffractive negative structure (50), measured perpendicularly to a surface section of the grating surface (33) surrounding the further structures (49, 50) respectively.

11. The optical diffraction element according to claim 10, characterized in that: - a ratio (pd / dd) between the further grating period (pd) and the further structure depth (dd) is greater than 10, and / or - a period ratio (ph / pd) of the first grating period (ph) to the further grating period (pd) is in the range of 0.9 to 1.1, and / or -in the first grating period (ph) runs along a first period running direction (39) of the first diffraction grating (35), the further grating period (pd) runs along a further period running direction (51) of the further diffraction grating (48), - wherein the two periodic travel directions (39, 51) do not travel parallel to each other.

12. The optical diffraction element according to claim 6 or 7, characterized in that: The surface areas of the diffractive positive structures (37, 40, 49) and the diffractive negative structures (38, 41, 50) of the various diffractive structure groups (35, 36, 48) contribute equally to the entire grating surface (33).

13. A collector (24) for use in a projection exposure device comprising an optical diffraction element (34; 46; 47; 57; 58; 59; 60; 64; 71; 76; 80; 86; 91; 92; 93; 94; 95; 117; 118; 119; 120; 121) as claimed in any one of claims 1 to 12.

14. The collector according to claim 13, characterized in that The projection exposure equipment is EUV projection exposure equipment, and the collector is an EUV collector.

15. The collector according to claim 13, characterized in that The collector mirror is embodied in such a way that it directs the radiation (3) towards a focal region (26), wherein the optical diffraction element is embodied in such a way that it directs the radiation (30) of the at least one target wavelength away from the focal region (26).

16. The collector according to claim 14, characterized in that The collector mirror is embodied in such a way that it directs the radiation (3) towards a focal region (26), wherein the optical diffraction element is embodied in such a way that it directs the radiation (30) of the at least one target wavelength away from the focal region (26).

17. An illumination system comprising a collector (24) as claimed in any one of claims 13 to 16 and comprising an illumination optical unit (6) for illuminating an object field (4) in which an object (10) to be imaged can be arranged.

18. An optical system comprising an illumination system as claimed in claim 17 and comprising a projection optical unit (7) for imaging the object field (4) into an image field (8), in which a substrate (11) can be arranged and onto which a section of the object (10) to be imaged can be imaged.

19. A projection exposure apparatus (1) comprising an optical system as claimed in claim 18 and comprising a light source (2).

20. The projection exposure apparatus (1) according to claim 19, characterized in that The light source (2) is implemented as an EUV light source and comprises a pump light source for producing a plasma that generates an EUV wavelength, wherein the pump light source is implemented to produce a pre-pulse having a pre-pulse light wavelength and a main pulse having a main pulse light wavelength, wherein the pre-pulse light wavelength is different from the main pulse light wavelength.

21. A method for producing a structured element, comprising the following method steps: - providing a mask master (10) and a wafer (11), - projecting the structure on the reticle (10) onto the photosensitive layer of the wafer (11) by means of a projection exposure apparatus as claimed in claim 19 or 20, - Producing microstructures and / or nanostructures on the wafer (11).

22. A structured element manufactured according to the method of claim 21.

23. A method for manufacturing an optical diffraction element as claimed in any one of claims 1 to 12, comprising the following steps: - providing a substrate, - providing at least one mask structure (105, 106; 111, 112; 126, 127; 136, 137; 147, 148; 156, 157) having mask areas (113, 115; 128, 129, 132, 133; 138, 139, 142, 143; 149, 150, 153; 158, 159, 162) impermeable to an etching medium and having an intervening mask gap (114, 116; 130, 131, 134, 135; 140, 141, 144, 145; 151, 152, 154; 160, 161, 163) disposed between the substrate and a source for the etching medium, - performing a first etching of the substrate by means of the etching medium, - replacing the mask structure (111; 126; 136; 147; 156) with another mask structure (112; 127; 137; 148; 157) and / or shifting the mask structure (105; 126) along the travel direction (x), - performing a second etching of the substrate by means of the etching medium.

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