TW201802499A - Mirror for the EUV wavelength range - Google Patents

Abstract

The invention relates to a mirror (S1, S2) for the EUV wavelength range and a projection lens (4) and illumination system (3) for microlithography comprising such a mirror (S1, S2). Furthermore, the invention relates to a projection exposure apparatus (1) for microlithography comprising such a projection lens (4) and/or such an illumination system (3). A mirror (S1, S2) for the EUV wavelength range according to the invention comprises a substrate and a layer arrangement, wherein the layer arrangement (X) comprises a reflective layer system (RL) having at least one layer subsystem (P') and a protective layer system (SPL) protecting the substrate, wherein the protective layer system (SPL) comprises a periodical sequence of at least two periods (PSPL), consisting of in each case two individual layers (AZ, R), characterized in that the first individual layer (AZ) of the period (PSPL) simultaneously protects the substrate by absorbing the EUV radiation and compensates for layer stresses in the layer arrangement (X), and the respective second individual layer (R) reduces the surface roughness of the protective layer system (SPL) by smoothing the surface roughness of the first individual layer (AZ).

Description

EUV wavelength range of mirrors

The present invention relates to a mirror of the extreme ultraviolet (EUV) wavelength range, and a projection lens and illumination system comprising such a mirror for lithography. Furthermore, the invention relates to a projection exposure apparatus comprising such a projection lens and/or such illumination system for lithography.

Projection exposure apparatus for lithography of the EUV wavelength range relies on the fact that the mirrors for exposing or imaging the reticle to the image plane have high reflectivity. This is because, first of all, the product of the reflectance values of the individual mirrors determines the total transmission of the projection exposure apparatus, and secondly, the optical power of the EUV source is limited. Furthermore, such mirrors must also have this desired optical imaging quality and ensure the desired optical imaging quality even after continuous illumination with high intensity EUV radiation for many years.

In order to achieve high reflectivity of the mirrors, the mirrors of the EUV wavelength range typically comprise a layer arrangement applied to the substrate and comprising a reflective layer system. In this case, the reflective layer system typically includes at least one layer subsystem comprising a periodic sequence of at least two cycles of individual layers. In this case, the periods include two individual layers composed of different materials for the high refractive index layer and the low refractive index layer, adjusted according to the thickness thereof to obtain high reflectance. In this case, in the EUV wavelength range, the so-called high refractive index and low refractive index are relative terms of the respective partner layers in the cycle of the layer subsystem. Layer subsystems generally only have layers that act optically with high refractive index It will only function in the EUV wavelength range when it is combined with the optically lower refractive index layer as the main component of the period of the layer subsystem.

Furthermore, in order to obtain high reflectivity of the mirrors, it is necessary to avoid loss due to stray light, which results in surface roughness of the mirrors for the EUV wavelength range, in particular for spatial wavelengths in the range of 10 nm to 1.5 μm. The strict requirements of the surface roughness.

In order to achieve this desired optical imaging quality, the layer stress of the layer configuration must be exceptionally low so that the substrate does not unacceptably warp due to the layer stresses in the layer configuration. For this purpose, the layer stresses generated, for example, in the reflective layer system must be compensated for by the layer stresses of other portions of the layer configuration. In this case, the layer stress is subdivided into tensile stress and compressive stress; whether the resultant forces acting perpendicular to the surface of the substrate have a positive sign (tensile stress) or a negative sign (compressive stress) set.

In order to ensure the desired optical imaging quality under continuous illumination with high intensity EUV radiation for many years, it is necessary to prevent excessive EUV radiation from being transmitted to the substrate so that the substrate is not exposed to high doses for a long period of time. EUV radiation. Substrates for EUV mirrors composed of materials such as Zerodur® from Schott AG or ULE® from Corning, tend to have a fractional order of compaction under high doses of EUV radiation. By virtue of the substantially uneven illumination of the mirrors, such compaction results in non-uniform variations in the shape of the surface, with the result that the optical imaging properties of the mirrors change undesirably during the operation.

DE 10 2009 054 653 A1 discloses, for example, a mirror comprising a substrate and a layer of EUV wavelength range. The layer configuration described above includes a reflective layer system and a protective layer system, wherein the protective layer system, together with the low surface roughness value, reduces overall transmission of EUV radiation across the layer configuration. By virtue of the intermediate layer configuration bonded between the substrate and the layer configuration, it is particularly possible to create tensile stresses for compensating for layer stresses in the layer configuration.

In this case, different protective layer subsystems are usually used, and therefore also used to protect the substrate from EUV radiation by absorption, for compensating for layer stress, and Different materials that smooth the surface roughness.

It is an object of the present invention to provide a mirror having an EUV wavelength range that simplifies the protective layer system compared to the prior art, whereas prior art mirrors with low surface roughness values reduce the transmission of EUV radiation across the layer configuration. And creating a layer stress for compensating for layer stress in the layer configuration.

The present invention is achieved by a mirror comprising a substrate and a layer of EUV wavelength range configured, wherein the layer configuration comprises a reflective layer system having at least one layer subsystem; and a protective layer system protecting the substrate, Wherein the protective layer system comprises a periodic sequence of at least two cycles, which in each case consists of two individual layers, characterized in that the respective first individual layer of the cycle simultaneously protects the EUV radiation by absorbing the EUV radiation The substrate compensates for layer stress in the layer configuration, and the respective second individual layers reduce the surface roughness of the protective layer system by smoothing the surface roughness of the first individual layer.

It has been recognized in accordance with the present invention that if each of the individual layers inherently incorporates more than one function, the construction of the protective layer system protecting the substrate can be simplified and the thickness of the protective layer system can be reduced. In this regard, the first individual layer is designed to first protect the substrate by absorbing the EUV radiation, as otherwise the substrate is compacted as mentioned above and thus at high doses of EUV radiation during the operation Undesirable changes in optical imaging properties occur. Second, the first individual layer simultaneously compensates for layer stress in the layer configuration because otherwise the substrate will unacceptably warp due to the layer stress. In this case, the reflective layer system and the roughness reducing layers typically have compressive stresses that must be compensated for by the tensile stresses generated in the protective layer system. This first individual layer therefore has two functions.

Furthermore, the second individual layer is designed to reduce the surface of the protective layer system Roughness. First, this is achieved by the fact that the absorption and layer stress compensation effects are not generated by thick layers, but rather by the fact that the second plurality of thinner first individual layers are interrupted by the second individual layers.

Thus, depending on their total thickness, the first individual layers do have individual desired effects with respect to absorption and separate layer stresses, but crystal growth in the first individual layers is interrupted. Thus, the surface roughness at the surfaces of the first individual layers is reduced relative to the single layer thick layer. Second, the second individual layers are designed such that the surface roughness is exceptionally reduced. In this case, the resulting surface roughness of the second individual layer depends on both the material and the type of deposition method of the individual layer. As a result, it is possible to generate a very smooth surface without high stray light loss.

These stringent requirements for the surface roughness of the protection system are necessary in order to avoid such losses due to stray light to obtain a high reflectivity of the mirror. The foregoing requirements are particularly applicable to such transitions of the individual layers of the reflective layer system since the EUV radiation is reflected there. However, in order for the reflective layer system to meet such requirements for the surface roughness, the underlying protective layer system must already have a sufficiently low surface roughness.

In an advantageous embodiment, the ratio of the thickness of the first individual layer to the thickness of the second individual layer is constant over all periods. The generation of such a protective layer system is simplified by virtue of the convenient scalability of such thicknesses of such individual layers of such a protective layer system, such as the parameters, and the process control facilitated thereby. This is because only regular repeating structures can determine the thickness of the cycle by means of X-ray optics.

In a particularly advantageous embodiment, the ratio of the thickness of the first individual layer to the thickness of the second individual layer decreases as the distance from the substrate increases. As a result, the first individual layers produced by the equal layer stress have a higher thickness in the lower plies than in the higher interlayers relative to the smoother second individual layers. Therefore, the layer stress is generated mainly in the lower region, and the effect of the individual layers of the roughness reduction is mainly manifested in the higher portion. The roughening of the lower layer portion is thus compensated again in this higher portion. As a result, by virtue of the lower total thickness of the protective layer system, the overall thickness of the first individual layer may be achieved The ratio of the thickness of the second individual layer to the same layer stress generation and roughness reduction effect for a layer stack having a constant period.

In an advantageous embodiment, the material of the first individual layer (AZ) has an absorption index k of more than 0.03 at a wavelength of 13.5 nm. In this case, the absorption index (k value) is the imaginary refractive index ñ=n-i. The imaginary part of k.

In an advantageous embodiment, the transmission of EUV radiation across the layer to the substrate level is less than 0.1%. It has been recognized in accordance with the present invention that protecting the substrate from excessively high doses of EUV radiation requires that the layer configuration be designed on the substrate of the mirror such that only a portion of the EUV radiation reaches the substrate. In a manner suitable for the reflective layer system, it may comprise many cycles of individual layers and thus also absorb a portion of the EUV radiation, in which case the protective layer system protecting the substrate is designed such that it is traversed through the layer anyway The EUV radiation transmission of the substrate is less than 0.1%.

In an advantageous embodiment, the mirror of the EUV wavelength range is characterized in that the protective layer under EUV radiation experiences an irreversible change in volume of less than 1%.

In this case, an irreversible change in volume under EUV radiation is understood to mean a long-term irreversible change in volume caused by high doses of EUV radiation due to structural changes in the material under consideration, rather than a reversible change in volume due to thermal expansion. In this case, it has been recognized in accordance with the invention that consideration must also be taken that the protective layer system must remain stable even under the high dose of EUV radiation accumulated during the life of the lithographic apparatus. Otherwise the problem of irreversible volume change is simply a transition from the substrate to the protective layer system.

Furthermore, one of the objects of the invention is achieved by means of a mirror of the EUV wavelength range, characterized in that the protective layer system is provided to prevent the position outside the illumination zone from being measured as compared to being measured in the same direction. An irreversible change in the surface of the substrate under EUV radiation of 0.1 nm measured in the normal direction of the substrate surface of the substrate surface, and simultaneously applying a layer stress for compensating the layer stress in the layer configuration .

In this case, it has been recognized in accordance with the present invention that in addition to protecting the substrate, Care must also be taken to ensure that the protective layer system is simultaneously suitable for compensating for such layer stresses in the layer configuration, since otherwise the substrate may unacceptably warp due to the layer stress. Therefore, in the design of the protective layer system, the layer stress generated from it must be taken into consideration. Furthermore, in the case of the protective layer system, by means of this material selection, care must be taken to ensure that these do not change in the case of high doses of EUV radiation, since this inevitably requires the layer stress and hence the change in surface shape. .

In an advantageous embodiment, the periods of the protective layer system have a thickness of from 5 nm to 100 nm in order to compensate for the roughness of the sub-layers produced by the tensile stresses occurring and to generate tensile stress as a whole.

In an advantageous embodiment, the protective layer system has a thickness of 50 nm to 1000 nm in order to be able to generate the substrate protection, the necessary layer stress, and also the scalability.

In an advantageous embodiment, the protective layer for compensating for the layer stress in the layer configuration exerts a tensile stress of +10 MPa to +2000 MPa, which is suitable to be compensated in the range from -1000 MPa to several -10 MPa. The layer stress of the conventional EUV reflective layer system.

In an advantageous embodiment, the material of the first individual layer (AZ) is composed of copper, chromium or nichrome, wherein the ratio of chromium:nickel in this case is 30:70 and 70:30. between. In this case, it has been recognized in accordance with the present invention that copper, chromium or nichrome is a material that simultaneously absorbs sufficient EUV radiation to protect the substrate from high doses of EUV radiation and has the effect of layer stress.

In an advantageous embodiment, the second individual layer is comprised of materials selected or constructed from the group of materials: boron carbide (B ₄ C), carbon (C), tantalum nitride (Si) Nitrile), Si carbide, Si boride, Mo nitride, Mo carbide, Mo boride, Ru nitride, Carbonization Ru carbide and Ru boride.

In an advantageous embodiment, the EUV wavelength range of the mirror It is characterized in that the protective layer system has a surface roughness of less than 0.6 nm rms, in particular less than 0.1 nm rms, in the spatial wavelength range from 10 nm to 1.5 μm. Such layers as mentioned above can result in low stray light losses.

In an advantageous embodiment, the mirrors of the EUV wavelength range are characterized in that the individual layers of the protective layer system are applied using a vacuum coating process. With these methods, layers of sufficient precision and reproducibility for EUV lithography can be generated.

A further object of the invention is achieved by means of a mirror of the EUV wavelength range, wherein the reflective layer system comprises at least one layer subsystem consisting of a periodic sequence of at least two cycles of individual layers, wherein the cycles comprise two Layers of individual layers consisting of different materials for the high refractive index layer and the low refractive index layer.

In this case, as mentioned above, in the EUV wavelength range, the so-called high refractive index and low refractive index are relative terms for the respective partner layers in the period of the layer subsystem. The layer subsystem is generally only in the EUV wavelength range when a layer with an optically high refractive index is combined with an optically lower refractive index layer relative thereto as the main component of the period of the layer subsystem. kick in.

In an advantageous embodiment, the EUV wavelength range of mirrors is further characterized in that the reflective layer system comprises a capping layer system that terminates the layer configuration of the mirror. As a result, the mirror can be protected from environmental influences.

Furthermore, one of the objects of the invention is achieved by means of a projection lens for lithography comprising a mirror according to the invention.

Furthermore, one of the objects of the invention is achieved by means of an illumination system for lithography comprising a mirror according to the invention.

Furthermore, one of the objects of the invention is achieved by a projection exposure apparatus for lithography comprising a projection lens according to the invention and/or an illumination system according to the invention.

Further features and advantages of the present invention are set forth in the following description of exemplary embodiments of the present invention, as well as It is revealed in the surrounding area. These individual features may be implemented individually in each case by themselves or in any variation of the invention in any desired combination.

1‧‧‧Projection exposure device

2‧‧·beamforming system

3‧‧‧Lighting system

4‧‧‧Projection lens; projection system

5‧‧‧EUV light source

6‧‧‧beam path

7‧‧ ‧collimator

8‧‧‧monochrome mirror

9, 10‧‧‧ first and second mirrors

11‧‧‧Photomask

12‧‧‧ wafer

13, 14‧‧‧ third and fourth mirrors

(AZ, R) ‧ ‧ individual layers

(d ₁ , d ₂ , d ₃ ) ‧ ‧ constant thickness

(P', P", P''') ‧ ‧ layer subsystem

(S1, S2) ‧‧‧Mirror

AZ‧‧‧ first individual layer

B‧‧‧Block layer

C‧‧‧ Coverage System

d _P , d _AZN , d _AZ , d _RN , d _R , d _SPL ‧‧‧ thickness

H, (H', H", H''') ‧ ‧ high refractive index individual layer

k‧‧‧Absorption index

L, (L', L", L''') ‧ ‧ low refractive index individual layer

M‧‧‧Terminal layer

Number of N ₂ , N ₃ ‧‧‧

P _SPL , (P ₁ , P ₂ , P ₃ ) ‧ ‧ cycles

R‧‧‧Second individual layer

RL‧‧·reflective layer system

S‧‧‧Substrate

SPL‧‧‧ protective layer system

X‧‧‧ layer configuration

Exemplary embodiments of the present invention are explained in more detail below with reference to the drawings. In the drawings: Figures 1A to 1B show schematic illustrations of a first mirror in accordance with the present invention; Figures 2A to 2B show schematic illustrations of a second mirror in accordance with the present invention; A schematic illustration of a projection lens according to the present invention of a lithographic projection exposure apparatus.

1A and 1B show schematic illustrations of a mirror (S1) according to the invention comprising an EUV wavelength range of a substrate (S) and a layer (X). In this case, the layer configuration (X) comprises a reflective layer system (RL); and a protective layer system (SPL) which protects the substrate. In this case, the protective layer system (SPL) is illustrated in detail in FIG. 1A, and FIG. 1B shows the reflective layer system (RL) in detail. The protective layer system (SPL) is especially used to protect the substrate from excessively high doses of EUV radiation, since for example the mirror substrate (S) manufactured by Zerodur® or ULE® exhibits a few percent by volume under high doses of EUV radiation. The magnitude of the irreversible compaction. The protective layer system (SPL) comprises a periodic sequence of at least two periods (P _SPL ), which in each case comprises two individual layers (AZ, R), see FIG. 1A. In this case, the first individual layer (AZ) is designed in such a way as to first protect the substrate (S) by absorbing the EUV radiation. For example, the first individual layer has an absorption index of more than 0.03 at 13.5 nm. Secondly, the first individual layer (AZ) simultaneously compensates for the layer stress in the layer configuration (X), since otherwise the substrate (S) would unacceptably warp due to the layer stress. For example, a protective layer system (SPL) for compensating for layer stress in the layer configuration (X) applies a tensile stress of +10 MPa to +2000 MPa. This first individual layer (AZ) therefore has two functions. The first individual layer (AZ) is formed from, for example, a copper, chromium or chromium nickel alloy having a chromium:nickel ratio between 30:70 and 70:30.

Further, the second individual layer (R) is designed to reduce the surface roughness of the protective layer system (SPL) by smoothing the surface roughness of the first individual layer (AZ). The individual layers (AZ) of all absorptions of the protective layer system which are indicated in the protective layer system (SPL) and which generate layer stresses in their cumulative total thickness have the respective requirements for absorption and/or layer stress effect. However, the crystal growth of the first individual layer (AZ) is interrupted due to interruption by the second individual layers (R). The second individual layer is composed, for example, of a material selected or composed of a group of such materials: boron carbide (B ₄ C), carbon (C), tantalum nitride (Si nitride), tantalum carbide (Si carbide) ), Si boride, Mo nitride, Mo carbide, Mo boride, Ru nitride, Ru carbide, and Boronization Ru boride. Therefore, it is possible to generate a very smooth surface without high stray light loss; for example, the protective layer system has a surface roughness of less than 0.6 nm rms in a spatial wavelength range of 10 nm to 1.5 μm. In particular, the surface roughness can also be less than 0.1 nm rms.

According to the invention, by virtue of the fact that the individual layer (AZ) essentially combines more than one function, the construction of the protective layer system protecting the substrate is simplified, and the thickness d _{P of} the protective layer system is thus reduced. For example, the protective layer system (SPL) has a thickness (d _P ) of 50 nm to 1000 nm. Alternatively, in order to protect against the protective effects of EUV radiation and to create layer stresses, different protective layer subsystems must be provided.

In this case, in FIG. 1A, for example, the individual thickness of the first layer (AZ) and the second individual layer (R) is a constant _{(d AZ1 = d AZ2 = ...} = d AZN = d _AZ , and d _R1 =d _R2 =...=d _RN =d _R ). The first individual layer thickness ratio (AZ) of the second individual d _AZN layer (R) of the thickness d _R for all cycles and therefore (P _SPL) is also constant.

This reflective layer system (RL) is illustrated in more detail in Figure 1B. The reflective layer system may comprise a plurality of layer subsystems (P', P", P'''), each layer subsystem comprising a period of at least two periods (P ₁ , P ₂ , P ₃ ) of individual layers Sequences. The periods (P ₁ , P ₂ , P ₃ ) comprise two individual layers consisting of individual layers for high refractive index (H', H", H''') and low refractive index individual layers ( L', L", L''') are composed of different materials and have a constant thickness (d ₁ , d ₂ , d ₃ in each layer subsystem (P', P", P'''). And different from the thickness of the periods of the adjacent layer subsystem. In this case the cycle, the substrate layer furthest from the subsystem P '''may have a number of N ₃ P _3, which is greater than the layer subsystem (P ") away from the second substrate ₂ of the number of cycles N P _2. Further, the substrate away from the second (S) layer subsystem (P ") may have such period (P ₂₎ sequence, such that the substrate layer furthest from the subsystem (P ''') The first high refractive index individual layer (H''') directly follows the last high refractive index individual layer (H" of the layer subsystem P" that is second from the substrate.

Therefore, in FIG. 1B, the equal (H") and low refractive index (L") individual layers in the periods (P ₂ ) in the layer subsystem (P") farthest from the substrate. The order of the relative heights (H', H''') and the low refractive index (L' in the other periods (P ₁ , P ₃ ) of the other layer subsystems (P', P''') , L") the order of the individual layers is reversed such that the first low refractive index layer (L" of the layer subsystem P" farthest from the substrate is also optically effectively following the layer closest to the substrate The last low refractive index layer (L') of the subsystem (P').

Furthermore, for example, the individual layers of the reflective layer system of the mirror according to the invention in FIGS. 1A and 1B can be separated by at least one barrier layer (B), wherein the barrier layer (B) comprises Materials selected or constructed from the group of such materials: boron carbide (B ₄ C), carbon (C), silicon nitride (Si nitride), silicon carbide (Si carbide), silicon boride (Si boride), Mo nitride, Mo carbide, Mo boride, Ru nitride, Ru carbide, and Ru boride. Such a barrier layer (B) inhibits the inter-diffusion between the two individual layers of the cycle, thereby increasing the optical contrast of the transition of the two individual layers. By virtue of the use of molybdenum and tantalum materials for the two individual layers of the cycle, a layer of barrier layer (B) above the tantalum layer as observed from the substrate is sufficient to provide sufficient contrast. The second barrier layer (B) above the molybdenum layer may be omitted in this case. In this regard, in order to separate the two individual layers of the period, at least one barrier layer (B) should be provided, wherein the at least one barrier layer (B) may be composed of various materials or compounds thereof, or It is also possible to present a layered construction of different materials or compounds.

The layer configuration (X) of the mirror (S1) according to the present invention is contained in FIGS. 1A and 1B by, for example, rhodium (Rh), platinum (Pt), ruthenium (Ru), palladium (Pd), gold (Au). At least one layer of a chemically inert material of cerium oxide (SiO ₂ ) is terminated as a capping system (C) of a terminating layer (M). The aforementioned termination layer (M) thus prevents chemical changes in the mirror surface due to environmental influences. The cover layer system (C) of FIGS. 1A and 1B includes, in addition to the termination layer (M), a high refractive index individual layer (H), a low refractive index individual layer (L), and a barrier layer (B). .

It should be taken into account that these reflective properties, the transport properties and the stress properties of all such individual layers must be taken into account in any overall optimization of the layer configuration (X).

Table 1 indicates the refractive indices n = n - i of the materials used for this layer configuration (X) for a wavelength of 13.5 nm. k.

Furthermore, the following brief notation corresponding to the sequence of layers in FIGS. 1A and 1B provides for the design of the layers associated with FIGS. 1A and 1B:

Substrate / (AZ R). N _SPL /(P ₁ ). N ₁ /(P ₂ ). N ₂ /(P ₃ ). N ₃ /cladding system C, where P ₁ =H'BL'B; P ₂ =H"BL"B; P ₃ =H'''BL'''B; C=HBLM.

Here, the letters AZ symbolically represent the thickness of the first individual layers of the protective layer system, R represents the thickness of the second individual layer of the protective layer system, H represents the thickness of the high refractive index layer, and L represents low The thickness of the refractive index layer, the letter B indicates the thickness of the barrier layer, and the letter M indicates the thickness of the chemically inert termination layer. In this case, the unit [nm] applies to the thickness of the individual layers indicated between the parentheses.

The exemplary embodiments associated with Figures 1A, 1B can thus be clearly stated as follows:

Exemplary Embodiment 1: Transmission of EUV radiation across the layer configuration to the substrate is less than 0.1%, and the protective layer experiences a volume irreversible change of less than 1% and a surface roughness of less than 0.5 nm rms under EUV illumination.

Substrate / (8nm chromium 2nm boron carbide). 25/RL

Exemplary Embodiment 2: The periods of the protective layer system have a thickness of 10 nm to 100 nm, and the protective layer system has a thickness of 50 nm to 1000 nm.

Substrate / (30nm copper 1nm carbon). 5/RL

Exemplary Concrete Example 3: This layer configuration applies a tensile stress of +10 MPa to +2000 MPa while preventing irreversible changes in the surface of the substrate under EUV radiation exceeding 0.1 nm in the normal direction.

Substrate / (40nm chromium nickel 2nm boron carbide). 4/RL

In this case, the reflective layer system RL can be constructed, for example, as follows:

RL = (0.4 boron carbide 2.921 矽 0.4 boron carbide 4.931 molybdenum). 8/

(0.4 boron carbide 4, 145 molybdenum 0.4 boron carbide 2.911 矽). 5/

(3.509 矽 0.4 boron carbide 3.216 molybdenum 0.4 boron carbide). 16/2.975矽0.4BoCar Carbide 2Molybdenum 1.5钌

Since the barrier layer of boron carbide in this example is always 0.4 nm thick, it can also be omitted to exemplify the basic configuration of the layer configuration, so that the layer design of the reflective layer system can be indicated in a shortened form as follows:

(2.921矽4.931 molybdenum). 8/(4.145 molybdenum 2.911矽). 5/

(3.509 矽 3.216 molybdenum). 16/2.975矽2Molybdenum 1.5钌

As is clear from the first exemplary embodiment according to FIGS. 1A and 1B, the order of the high refractive index layer and the low refractive index layer molybdenum in the second layer subsystem including five periods is relative to the other layers. The system is reversed such that the first high refractive index layer of the layer subsystem having a thickness of 3.509 nm furthest from the substrate directly follows a thickness of 2.911 nm and the last high refractive index layer of the second far layer subsystem of the substrate .

2A and 2B illustrate yet another embodiment of the present invention. In this case, the control 1A, a first specific exemplary embodiment illustrated in FIG. 1B embodiment, the thickness of the individual layers of the first (AZ) d ratio of the second individual layer, _AZ (R) d _R of a thickness See Figure 2A as the distance from the substrate (S) increases. In this case, the first individual layer (AZ) generated by the layer stresses has and is in the lower interlayer (closer to the substrate) relative to the smooth second individual layers (R) A higher thickness than a higher interlayer (farther from the substrate). Therefore, the layer stress that produces the compensation is mainly manifested in the lower region, and the effect of the individual layers of the roughness reduction is mainly manifested in the higher portion. The roughening of the lower layer portion is thus compensated again in this higher portion. As a result, by virtue of the same or even a small total thickness of the protective layer system (SPL), it is possible overall to achieve a ratio of the thickness of the first individual layer (AZ) to the thickness of the second individual layer (R) All cycles are the same layer stress compensation and roughness reduction effects in the case of a constant layer stack.

In this case, the reflective layer system (RL) comprises a plurality of layer subsystems (P', P", P'''), each layer subsystem comprising at least two cycles of individual layers (P ₁ , The periodic sequence of P ₂ , P ₃ ), see Fig. 2B. The periods (P ₁ , P ₂ , P ₃ ) comprise two individual layers for the high refractive index layer (H', H", H ''') and low refractive index layers (L', L", L''') are composed of different materials and have a constant thickness in each layer subsystem (P', P", P''') (d ₁ , d ₂ , d ₃ ), and differs from the thickness of the periods of adjacent layer subsystems. In this case, the layer farthest from the substrate subsystem (P ''') having a number of periods of N ₃ P _3, which is far greater than the distance of the second sub-layer of the substrate (P ") of the number N ₂ Period P ₂ . In this case, unlike in the exemplary embodiment with respect to Figures 1A, 1B, the layer subsystem (P" farthest from the substrate has a sequence of periods P ₂ , Corresponding to the sequence of periods P ₁ and P ₃ of the other layer subsystems P′ and P′′′, such that the first high refractive index layer (H′′ of the layer subsystem (P′′′) furthest from the substrate ') optically effectively follows the last low refractive index layer (L") of the layer subsystem (P") that is farthest from the substrate.

Moreover, for example, similar to the exemplary embodiment of FIGS. 1A and 1B, the individual layers of the reflective layer system of the mirror according to the present invention in FIGS. 2A and 2B may be at least one barrier layer ( B) Separated. Also similar to this first exemplary embodiment, the layer configuration (X) of the mirror (S2) according to the invention may be terminated by a cover layer system (C).

Furthermore, for the layer designs associated with Figures 2A and 2B, the following short marks are specified in accordance with the sequence of layers in Figures 2A and 2B:

Substrate / (AZ R...AZ R) / (P ₁ ). N ₁ /(P ₂ ). N ₂ /(P ₃ ). N ₃ /cladding system C, where P ₁ =BH'BL'; P ₂ =BL"BH"; P ₃ =H'''BL'''B; C=HBLM.

In this case, similar to the description of the first exemplary embodiment, the letters symbolically represent the thickness of the respective individual layers in the unit [nm]. These exemplary embodiments associated with Figures 2A, 2B can thus be clearly stated as follows:

Exemplary Embodiment 4: Transmission of EUV radiation across the layer configuration to the substrate is less than 0.1%, and the protective layer experiences a volume irreversible change of less than 1% and a surface roughness of less than 0.5 nm rms under EUV illumination.

Substrate / (10nm chromium 2nm boron carbide). 10/(8nm chromium 2nm boron carbide). 6 / (5nm chromium 2nm boron carbide). 6/RL

Exemplary Embodiment 5: The periods of the protective layer system have a thickness of 10 nm to 100 nm, and the protective layer system has a thickness of 50 nm to 1000 nm.

Substrate / (50nm copper 1nm boron carbide). 2 / (30nm copper 1nm boron carbide) X / (5nm copper 2nm boron carbide). 6/RL

Exemplary Embodiment 6: This layer configuration applies a tensile stress of +10 MPa to +2000 MPa while preventing irreversible changes in the surface of the substrate under EUV radiation exceeding 0.1 nm in the normal direction.

Substrate / (50nm chromium nickel 2nm boron carbide). 2 / (25nm chromium nickel 1nm boron carbide). 1 / (5nm chromium nickel 2nm boron carbide). 4/RL

In this case, the reflective layer system RL of the second exemplary embodiment can be clearly stated as:

RL = (4.737 矽 0.4 boron carbide 2.342 molybdenum 0.4 boron carbide). 28

/ (3.443 矽 0.4 boron carbide 2.153 molybdenum 0.4 boron carbide). 5

/ (3.523 矽 0.4 boron carbide 3.193 molybdenum 0.4 boron carbide). 15

/2.918矽0.4BoCB 2Molybdenum 1.5钌

Since the barrier layer of boron carbide in this example is again 0.4 nm thick again, it can also be omitted to clarify the aforementioned layer configuration, so that the layer design with respect to FIGS. 2A and 2B can be clearly explained as follows:

RL = (4.737 矽 2.342 molybdenum). 28/(3.443矽2.153 molybdenum). 5/

(3.523 矽 3.193 molybdenum). 15/2.918矽2 molybdenum 1.5钌

It goes without saying that the layer design explicitly stated above is to be understood by way of example only, and that the protective layer system (SPL) of the second exemplary embodiment may in particular also be derived, for example, from the first exemplary embodiment. Different reflective layer systems (RL) of the embodiments are combined.

Fig. 3 schematically shows a projection exposure apparatus (1) comprising a beam shaping system (2), an illumination system (3) and a projection lens (4) advancing from an EUV light source 5 of the beam shaping system (2) The beam path (6) is arranged in order. For example, a plasma source or synchrotron source can be used as the EUV source (5). The emerging radiation in the wavelength range between about 5 nm and about 20 nm is first focused in the collimator (7). By means of the downstream monochromator (8), the desired operating wavelength is filtered by varying the angle of incidence, as indicated by the double-headed arrow. Within the wavelength range, the collimator (7) and the monochromator (8) are typically designed as mirrors, wherein at least the monochromator (8) is on its optical surface There is no multi-layer system on top to reflect the wavelength range with the largest possible bandwidth.

The radiation processed with respect to the wavelength and the spatial distribution in the beam shaping system (2) are directed into the illumination system (3) with, for example, first and second mirrors (9, 10). The two mirrors (9, 10) direct the radiation onto the reticle (11) as a further reflective optical element having a reduced scale imaging onto the wafer (12) by means of the projection system (4) structure. For this purpose, for example, third and fourth mirrors (13, 14) are provided in the projection system (4). The mirrors (9, 10, 13, 14) used in the projection exposure apparatus may, for example, be in each case a mirror according to the invention from the first or second exemplary embodiment ( S1, S2) are formed here, see FIG. 1A, FIG. 1B and FIG. 2A, FIG. 2B.

The present invention may be embodied in other specific forms without departing from the spirit and scope of the invention. The aspects of the specific embodiments are to be considered as illustrative and not restrictive. Accordingly, the scope of the invention is indicated by the appended claims rather All changes that fall within the meaning and scope of the patent application are deemed to fall within the scope of the patent application.

AZ‧‧‧ first individual layer

d _P , d _AZN , d _RN , d _SPL ‧‧‧ thickness

P _SPL ‧‧ cycle

R‧‧‧Second individual layer

RL‧‧·reflective layer system

S‧‧‧Substrate

S1‧‧‧ mirror

SPL‧‧‧ protective layer system

X‧‧‧ layer configuration

Claims (18)

An ultra-ultraviolet (EUV) wavelength range of mirrors (S1, S2) comprising: a substrate (S); and a layer configuration (X), wherein the layer configuration comprises a reflective layer system (RL) having at least one a layer subsystem (P'); and a protection layer system (SPL) that protects the substrate, wherein the protection layer system (SPL) comprises a periodic sequence of at least two periods (P _SPL ), each period being Two layers of individual layers (AZ, R), characterized in that the first individual layer (AZ) of the period (P _SPL ) simultaneously protects the substrate by absorbing the EUV radiation and compensates for the layer configuration (X) Layer stress, and the respective second individual layers (R) reduce the surface roughness of the protective layer system (SPL) by smoothing the surface roughness of the first individual layer (AZ); and the first individual layer ( The material of AZ) is composed of copper, chromium or nickel-chromium alloy, wherein the ratio of chromium: nickel is between 30:70 and 70:30. The mirrors (S1, S2) of the EUV wavelength range of claim 1 are characterized in that the transmission of EUV radiation to the extent of the layer is less than 0.1%. Mirrors (S1, S2) of the EUV wavelength range, as described in the aforementioned patent applications, are characterized in that the protective layer (SPL) under EUV radiation undergoes an irreversible change in volume of less than 1%. A mirror (S1, S2) of the EUV wavelength range according to any of the aforementioned patent claims, characterized in that the protective layer system (SPL) prevents the illumination zone from being measured in excess of, for example, in the same direction a substrate (S) on the surface of the substrate (S) at an external position is a position of the substrate (S) under EUV radiation measured at a position in the normal direction at a position in the normal direction Reversibly varying and simultaneously applying a layer of stress for compensating for layer stress in the layer configuration (X). A mirror (S1, S2) of the EUV wavelength range according to any of the aforementioned patent claims, characterized in that the thickness (d _AZ ) of the first individual layer (AZ) is the thickness of the second individual layer (R) The ratio of (d _R ) is constant for all periods (P _SPL ). A mirror (S1, S2) of the EUV wavelength range of any one of claims 1 to 4, characterized in that the thickness (d _AZ ) of the first individual layer (AZ) is for the second individual The ratio of the thickness (d _R ) of the layer (R) decreases as the distance from the substrate (S) increases. A mirror (S1, S2) of the EUV wavelength range of any of the aforementioned patent applications is characterized in that the material of the first individual layer (AZ) has an absorption index of more than 0.03 at 13.5 nm. A mirror (S1, S2) of the EUV wavelength range according to any of the aforementioned patent applications, characterized in that the periods (P _SPL ) of the protective layer system ( _SPL ) have a thickness of 10 nm to 100 nm (d _SPL) ). The mirrors (S1, S2) of the EUV wavelength range of any of the aforementioned patent applications are characterized in that the protective layer system (SPL) has a thickness (d _P ) of 50 nm to 1000 nm. A mirror (S1, S2) of the EUV wavelength range according to any of the aforementioned patent claims, characterized in that a protective layer system (SPL) for compensating for layer stress in the layer configuration (X) is applied +10 MPa to + A tensile stress of 2000 MPa. A mirror (S1, S2) of the EUV wavelength range according to any of the preceding claims, characterized in that the second individual layer (R) consists of a material selected or composed of a group of such materials: Boron carbide (B ₄ C), carbon (C), Si nitride, Si carbide, Si boride, Mo nitride, Mo carbide Mo boride, Ru nitride, Ru carbide and Ru boride. A mirror (S1, S2) of the EUV wavelength range according to any of the aforementioned patent applications, characterized in that the protective layer system (SPL) has a rms of less than 0.6 nm in a spatial wavelength range of 10 nm to 1.5 μm, in particular A surface roughness of less than 0.1 nm rms. Mirrors (S1, S2) of the EUV wavelength range of any of the aforementioned patent applications are characterized in that the individual layers (AZ, R) of the protective layer system (SPL) are applied using low pressure plasma. A mirror (S1, S2) of the EUV wavelength range according to any of the preceding patent claims, characterized in that the reflective layer system (RL) comprises at least one layer subsystem (P', P", P''') , which consists of a periodic sequence of at least two periods (P ₁ , P ₂ , P ₃ ) of the individual layers, wherein the periods (P ₁ , P ₂ , P ₃ ) comprise two individual layers, which are Different material compositions for a high refractive index layer (H''') and a low refractive index layer (L'''). A mirror (S1, S2) of the EUV wavelength range according to any of the preceding patent claims, characterized in that the reflective layer system (RL) further comprises a cover layer system (C) which terminates the layer of the mirror Configuration (X). A projection lens for lithography, comprising a mirror (S1, S2) according to any one of claims 1 to 15. An illumination system for lithography, comprising items 1 through 15 of the scope of the patent application One of the mirrors (S1, S2). A projection exposure apparatus for lithography, comprising a projection lens according to item 16 of the patent application and/or an illumination system according to item 17 of the patent application.