WO2010034367A1

WO2010034367A1 - Dielectric mirror and method for the production thereof, and a projection illumination system for microlithography having such a mirror

Info

Publication number: WO2010034367A1
Application number: PCT/EP2009/004814
Authority: WO
Inventors: Alexandra Pazidis
Original assignee: Carl Zeiss Smt Ag
Priority date: 2008-09-29
Filing date: 2009-07-03
Publication date: 2010-04-01
Also published as: DE102008042439A1

Abstract

The invention relates to a reflecting dielectric mirror comprising at least one mixed layer stack (B) of an alternating sequence of fluoridic and oxidic layers between an oxidic layer stack (C) and a fluoridic layer stack (A). The invention further relates to a method for producing such a reflecting dielectric mirror, and to a projection illumination system having at least one such reflecting dielectric mirror.

Description

description

Dielectric mirror and method for its production, as well as a projection exposure apparatus for microlithography with such a mirror.

The invention relates to a reflective dielectric mirror. Furthermore, the invention relates to a method for producing such a reflective dielectric mirror. Moreover, the invention relates to a projection exposure apparatus for microlithography with at least one such reflective dielectric mirror.

Reflective dielectric mirrors are used inter alia in projection exposure systems for the microlithographic production of semiconductor components at wavelengths between 157 nm and 365 nm and in particular at angles of incidence between 0 ° and 85 °. Such mirrors are known for example from the European patent EP 1 749 222 B1 and consist of a substrate, a first layer stack on the substrate with oxidic layers and a second layer stack with fluoridic layers located on the first layer stack.

Both layer stacks consist here of alternating high- and low-refractive dielectric layers and thus ensure, given appropriately selected layer thicknesses, a high reflectivity of the respective layer stack at a predetermined wavelength. The fluoridic layers close the oxidic layers outwards in the light direction and thus ensure the laser resistance of the mirror. On the other hand, the oxide layers provide an increased reflectivity compared to a quartz substrate made entirely of fluoridic layers.

A disadvantage of these layers, however, is that the transition of the compressive to tensile stresses between the two layer stacks occurs abruptly and this can lead to cracking in the layers at the transition of the two layer stacks. In particular, a process stability in the production of such mirrors with a high yield of mirrors with good quality can not be guaranteed.

Another disadvantage of these layers is that within the two layer stacks no arbitrary refractive index differences between the high and low refractive dielectric layers can be introduced due to the available material. In the As a rule, this refractive index difference is only 0.3 for both the fluoride layer and the oxide layer stack over almost the entire wavelength range, see, for example, the refractive index difference between Al ₂ O ₃ and SiO ₂ or between MgF ₂ and GdF ₃ in FIG. 5 from EP 1 749 222 Bl.

As a result, the achievable with such a mirror reflectivity is limited. However, the reflectivity of a mirror is of crucial importance for the use of such mirrors within microlithography projection exposure apparatuses, since such projection exposure apparatuses consist of a multiplicity of mirrors and lenses whose reflectivities and transmissions as product determine the total transmission of the projection exposure apparatus and this total transmission for a given light source power decides on the throughput of wafers and thus on the economic success.

The object of the invention is therefore to increase the reflectivity of laser-stable dielectric mirrors of the aforementioned type, in particular for use within projection exposure apparatuses for microlithography, and thereby to reduce the risk of cracking in the layers of the dielectric mirror.

According to the invention, this object is achieved by a reflective dielectric mirror having at least one oxidic layer stack and at least one fluoridic layer stack, wherein at least one mixed layer stack consisting of an alternating sequence of fluoridic and oxidic layers is located between the oxidic layer stack and the fluoridic layer stack, since the achievable ones Refractive index differences within the mixed layer stack of fluoridic and oxidic layers are greater than in a pure oxidic or fluoridic layer stack.

Within the mixed layer stack, for example, it is possible to set a refractive index difference of almost 0.5 in the above-mentioned wavelength range between Al ₂ O ₃ and MgF ₂ . Even refractive index differences of greater than 0.35, in particular greater than 0.4 lead to a significant increase in reflectivity over the prior art.

Furthermore, a dielectric mirror according to the invention with a mixed layer stack of alternating fluoridic and oxidic layers between an oxidic layer stack and a fluoridic layer stack ensures a spatial separation of the layers Tensile stresses of the fluoridic layer stack of the compressive stresses of the oxide layer stack and thus prevents cracking in such a layer system with such different stress ratios within the layer system. In this case, the mixed layer stack should have at least more than 4 layers, in particular more than 6 layers, for adapting the layer stresses of the fluoridic layer stack to the oxidic layer stack. Fewer layers lead to a spatial proximity of the compressive stresses to the tensile stresses and significantly more layers lead to high costs, if no more layers are desired due to the layer design.

In a dielectric mirror according to the invention, in which at least one layer thickness of a layer changes in the direction along the mirror surface by more than 10% relative to the maximum layer thickness of the layer, the optimum angle of incidence ranges can be changed with high reflectivity over the mirror surface, so that the mirror in its reflectivity behavior can be optimally adapted to the requirements of its destination within an optical system.

Likewise, in a dielectric mirror according to the invention, in which at least one layer stack in the direction of the surface normal of the mirror at least two different periods of two successive layers of a high and a low refractive index material, the phase splitting of the light between the s and p polarization at the reflection can be optimally adapted to the requirements of its destination within an optical system. The s-polarization direction is in this case that direction of oscillation of the incident light perpendicular to the plane of incidence and the p-polarization direction corresponding to that direction of oscillation of the incident light parallel to the plane of incidence, which spans between the direction of incidence and the surface normal of the mirror at the point of impact of the light on the mirror.

In a dielectric mirror according to the invention, at a wavelength of 193 nm and incidence angles between 33 ° and 52 °, a maximum difference of the reflectivity of s-polarized light to the reflectivity of p-polarized light of less than 4%, in particular less than 2 %, the reflectivity splitting between s- and p-polarized light can be limited to avoid insufficient imaging performance of an optical system. This is particularly advantageous if, on the one hand, the installation space of an optical system is limited and, on the other hand, because of the design of the system, a very long optical distance between the elements of the system is required that the use of several such mirrors in succession becomes necessary in the optical system.

Furthermore, it is at the same boundary conditions within an optical system advantageous if the dielectric mirror at the wavelength of 193 nm and incidence angles between 33 ° and 52 °, a reflectivity for p-polarized light and unpolarized light of greater than 96%, in particular each greater than 97.5%, since then a total high transmission when using multiple such mirrors can be ensured within the optical path.

A dielectric mirror according to the invention which, at a wavelength of 193 nm and an angle of incidence of 75 °, has a difference in the reflectivity of s-polarized light to the reflectivity of p-polarized light of less than 14%, in particular less than 11% serve as part of a kaleidoscope for light mixing with low Rflektivitätsaufspaltung between s- and p-polarized light.

Since the costs of a mirror increase with the number of layers, depending on the layer design, and an optimum between reflectivity and phase splitting can be achieved for given angles of incidence range above a certain minimum number of layers, a balance must be made here. Such a balance can be made in a dielectric mirror according to the invention having a mixed layer stack with more than 10 layers. Although fewer layers lead to lower costs, they do not leave enough room for optimizing the layer design with regard to the optical requirements of the mirror.

If the dielectric mirror according to the invention has at least one further oxidic layer stack, then this oxidic layer stack can be used to adapt the layer stack to an adjacent surface, such as the surface of an oxidic substrate of the mirror. Likewise, for example, another additional fluoridic Schich stack can be used to adapt to a CaF ₂ substrate.

The object of the invention is further achieved by an inventive method for producing reflective dielectric mirror by depositing a sequence of dielectric layers, wherein at least between an oxide layer stack consisting of oxidic layers and a fluoridic layer stack consisting of fluoridic layers, a mixed layer stack consisting of alternating oxide and fluoridic layers with more than 4 layers, in particular more than 6 layers to adapt the voltages of the fluoridic layer stack to the voltage of the oxide layer stack is deposited. The advantageous effect of the more than 4, in particular more than 6 layers has already been explained above.

Advantageously, the methods according to the invention are carried out such that the magnitude of the compressive stresses is selectively adjusted or controlled by controlled ion bombardment of the material intended for the oxidic layers, in particular the mixed layer stack during vacuum vapor deposition. This makes it possible to adapt the course of the stress within the mixed layer stack to a desired course.

Furthermore, the object of the invention is achieved by a dielectric mirror according to the invention, which is produced by a method according to the invention.

In addition, the object of the invention is achieved by an inventive projection exposure apparatus for microlithography with at least one dielectric mirror according to the invention.

Due to the increased reflectivity of the dielectric mirror, it is possible to increase the throughput of wafers with a constant light source power of the projection exposure apparatus. In particular, projection exposure systems with multi-mirror arrays (MMA) for structuring intensity distributions in the system pupils within the illumination system of the projection exposure apparatus depend on a plurality of such inventive dielectric mirrors due to the limited space available. Therefore, it is precisely in these projection exposure apparatuses that each individual one of the dielectric mirrors is optimally designed with regard to the total transmission, the homogeneity and the illumination angle distribution in the illumination field of the illumination system of the projection exposure apparatus. Projection exposure systems with multi-mirror arrays (multi-mirror arrays, MMA) are the subject of the applications DE 10 2008 008 019.5 and US 61/015 918. These applications are to be fully inclusive including the description, the drawings, the claims and the abstract part of the present application ,

In a projection exposure apparatus according to the invention with at least one dielectric mirror according to the invention, in which the layer thickness of at least one Layer in the direction along the mirror surface by more than 10% based on the maximum layer thickness of the layer changes, z. B. in the deflection mirror of the so-called REMA objective of the illumination system of the projection exposure system, the course of the layer system along the mirror surface are designed so that the differences in intensity and the illumination angle distribution within the field to be exposed of the illumination system are minimized. For a description of the functionality of a REMA objective, reference is made to the description of FIGS. 9 to 11 of this application and to the applications referred to.

The projection exposure apparatus according to the invention with at least one dielectric mirror according to the invention, in which at least one layer stack has at least two different periods of two successive layers of a high and a low refractive index material in the direction of the surface normal, offers several advantages. On the one hand, the range of angles of incidence at which the mirror has an acceptable reflectivity can be increased. On the other hand, the reflectivity splitting between the reflectivity for s-polarized light and the reflectivity for p-polarized light can be reduced. Further, the phase splitting between the s-polarized light phase and the p-polarized light phase can be reduced. Too high reflectivity splitting or too high phase splitting can lead to unwanted image error contributions of the mirror within the optical design. Therefore, these characteristics of a mirror typically need to be considered in the design of an optical design, such as the design of a mirror. of a REMA lens as part of a total optimization considered or changed.

The projection exposure apparatus according to the invention with at least one dielectric mirror and at least one multi-mirror array (MMA) consisting of more than 1000 and less than 40,000 mirrors with a surface area of 2 cm ² to 80 cm ² can control the intensity distribution in the system pupil of the illumination system the projection exposure system by appropriate control of the individual mirrors of the multi-mirror array (multi-mirror array, MMA) change flexibly. This allows the operator of the projection exposure system to realize rapid changes of so-called lighting settings.

However, in order to decouple the temporal and spatial fluctuations of the light source used, the projection exposure apparatus according to the invention requires at least one homogenization optics or conditioning optics in the light direction before Multiple mirror arrangement (multi-mirror array, MMA), the homogenization optics or conditioning optics by design, the divergence of passing through them illuminating beam only by less than four times may increase because otherwise the same resolution for decoupling the required resolution in the system pupil of the illumination system of the projection exposure can not be guaranteed. However, a high resolution of the system pupil is necessary for imaging a wide variety of mask structures. A telescope optics in the light direction in front of the multi-mirror array (MMA) with a focal length of greater than 2 m, in particular greater than 5 m, ensures a superposition of light of the homogenizing optics or conditioning optics on the entire surface of the multi-mirror arrangement (Multi -Mirror array, MMA) and thus ultimately for optimal light mixing in the system pupil of the lighting system. Here, the low divergence angle after the homogenization optics or conditioning optics must be adapted to the entire extent or the entire diameter of the multi-mirror array (MMA) by a large focal length of the telescope optics. Dielectric mirrors according to the invention within the homogenizing optics or conditioning optics and / or the telescope optics are advantageous in limiting the installation space of the respective lens groups by folding the optical stretches.

Embodiments of the invention will be explained in more detail with reference to the drawing. In this show

Figure 1 is a schematic representation of a reflective dielectric mirror having at least one mixed layer stack of a sequence of alternating fluoridic and oxidic layers;

Figure 2 is a schematic representation of a reflective dielectric mirror having at least one mixed layer stack between a fluoridic and an oxide stack of layers;

FIG. 3 shows a reflection curve for a mirror according to the invention at 193.4 nm and an average angle of incidence of 75 °;

FIG. 4 shows a reflection curve for a mirror from the prior art

193.4 nm and a mean incidence angle of 75 °; FIG. 5 a reflection course for a further mirror according to the invention

193.4 nm and a mean incidence angle of 75 °;

FIG. 6 shows a reflection course for a mirror according to the invention at 193.4 nm and an average angle of incidence of 45 °;

FIG. 7 shows a reflection curve for a mirror from the prior art

193.4 nm and a mean angle of incidence of 45 °;

FIG. 8 a reflection course for a further mirror according to the invention

193.4 nm and a mean angle of incidence of 45 °;

9 shows a schematic representation of a projection exposure apparatus for the

Microlithography with a rod-light mixture in the illumination system;

Figure 10 is a schematic representation of a projection exposure system for microlithography with a honeycomb condenser light mixture in the lighting system;

FIG. 11 shows a schematic illustration of a pupil-forming unit of a

Lighting system;

Figure 12 is a schematic representation of an embodiment of a pupil shaping unit of a lighting system;

FIG. 13 shows a schematic illustration of a further embodiment of a pupil shaping unit of a lighting system;

FIG. 14 shows a schematic representation of a further embodiment of a pupil shaping unit of a lighting system;

FIG. 15 shows a schematic illustration of a further embodiment of a pupil shaping unit of a lighting system. FIG. 1 shows a reflective layer system according to the invention which comprises a first fluoridic layer stack A of 3-40 alternating high and low refractive fluoridic layers and a second mixed layer stack B of 2-50 alternating high and low refractive and alternating oxidic and fluoridic layers. In this case, the layer stack B of the layer system can be applied directly to a substrate S or to further unspecified layers, since the optically relevant reflection properties of the layer system with a larger number of layers are defined by the outer layer stacks A and B alone due to the Bragg reflection , In particular when using a substrate S made of CaF ₂ , it makes sense for reasons of tension to start with the mixed layer stack B of oxide and fluoridic layers on the substrate S. In the case of a substrate S made of quartz glass, on the other hand, in order to reduce the layer tension of the required layers, it makes sense to start with a layer stack C of the layer system consisting of alternating high and low refractive index oxidic layers directly on the substrate. Both possibilities mentioned, as well as the possibility of further unspecified layers between the layer stacks A, B and C and the substrate S are indicated in FIG. The invention is not limited to substrates made of quartz glass or CaF ₂ , for example, ceramic materials could be used for the substrate. In this case, however, the layer system immediately following the substrate should be adapted to the physical or chemical properties of the substrate. The number of layers is generally dependent on the wavelength of the radiation to be reflected and the conditions of production of the vapor deposition.

FIG. 2 shows a reflective layer system according to the invention which comprises a first fluoridic layer stack A of 3-40 alternating high- and low-index fluoridic layers, a second mixed layer stack B of 2-50 alternating high- and low-index layers, and alternating oxide and fluoridic layers third oxide layer stack C of 10-80 alternating high and low refractive index oxidic layers. In this case, the layer stack C of the layer system can be applied directly to a substrate S or to further unspecified layers, since the optically relevant reflection properties of the layer system with a larger number of layers due to the Bragg reflection alone by the outer layer stack A, B and C. To be defined. In particular, in the case of a substrate made of CaF _2, a further additional layer stack B can be started directly on the substrate due to stress reasons, followed by the layer system A, B and C according to the invention. As oxidic materials are preferably high-refractive alumina (Al ₂ O ₃ ) and low-refractive silica (SiO ₂ ). Suitable fluoridic materials are, for example, high-index lanthanum fluoride (LaF ₃ ) or gadolinium fluoride (GdF ₃ ) and low-index magnesium fluoride (MgF ₂ ) or aluminum fluoride (AlF ₃ ). The transition between the layer stacks A, B and C is preferably formed in narrow-band mirrors with high reflectivity by a respective high-refractive oxide or high-refraction fluoridic layer. A low refractive transition layer, on the other hand, is useful for a desired phase matching of the mirror. A preferred low-index end layer of the layer system according to the invention has a double optical layer thickness compared to the other fluoridic layers and increases the laser stability. Other fluoridic materials are also suitable for the fluoridic layers.

In many embodiments, the optical thickness of a layer of the layer system is in each case a quarter of the wavelength of the useful light. However, a strict periodic sequence of layer thicknesses may deviate from the overall optimization of a layer system. For this purpose, the term "depth grading multilayer" has come to be used in English-speaking countries, as well as a strict alternating sequence of only two specific materials for the high- and low-refractive layers in stacks A, B and C with respect to the achievement deviated from high reflectivities.

Furthermore, for the use of a dielectric mirror within a projection exposure apparatus, it may be important for the light to experience different reflections with different reflectivity values at different angles of incidence and with different bandwidths of angles of incidence around a mean angle of incidence at different locations on the surface of the mirror. As a rule, this is necessary so that a field to be homogeneously illuminated is achieved with deliberately structured illumination angle distributions in the mask plane of a projection exposure apparatus, as will be explained in more detail below with reference to FIGS. 9 to 11. Because of these requirements for a dielectric mirror, it is possible to deviate from a uniform thickness of one, several or all layers of the layer system according to the invention over the entire surface, so that these layers have different thicknesses at different locations on the surface.

Usually, the mirrors according to the invention are produced in a vacuum chamber by vapor deposition in the PVD process, wherein for the oxidic materials Electron beam gun is used and the fluorides are preferably evaporated from a boat.

The layer properties can be influenced by adjusting the coating temperature and coating rate, but also by preheating the substrate. Primarily, however, in conjunction with these measures, a controlled, large-area ion bombardment, preferably with argon ions, is exploited to generate compressive stress conditions in the oxidic layers, especially within the mixed layer stack B. Thus, in addition to the spatial separation of the tensile stresses of the fluoridic layer stack A of the compressive stresses of the oxide layer stack C through the intervening layer stack B, the voltage profile within the layer stacks B and C can be influenced by the ion bombardment. For this, only a suitable adjustment of the ion source parameters in relation to the adjustment of the coating temperature and coating rate is required.

In the following FIGS. 3 to 8, the reflectivity profiles of different layer systems are discussed for different angles of incidence. In all these coating systems, AL ₂ O _{3 was used} for the highly oxidizing oxide, SiO ₂ for the low refractive index oxide, LaF ₃ for the high refractive index fluoride and MgF ₂ for the low refractive index fluoride.

FIG. 3 shows the reflectivity profile in percent of a layer system according to the invention with a mixed layer stack B of alternating oxidic and fluoridic layers and a fluoridic layer stack A with respect to the angle of incidence in degrees at the wavelength of 193.4 nm. Due to the large refractive index differences within the layer stack B it is possible to increase the reflectivity of the layer system according to the invention over the prior art and to achieve a high reflectivity of 96% at an angle of incidence of 75 ° for unpolarized light Ra. Further, the difference of the reflectivity Rs-Rp of s and p polarized light at this incident angle is hardly more than 7%, so that even for p-polarized light at this incident angle, a reflectance Rp of almost 92% is obtained. The layer system of the mirror according to the invention to Figure 3 consists of a total of 59 layers each having an optical thickness of a layer of the layer system which is optimized to a quarter of the wavelength of the useful light of 193.4 nm at an incidence angle of 75 °. The first 40 layers on the substrate form the mixed layer stack B of alternating oxide and fluoridic layers starting with a high refractive index oxide on the substrate. This is followed by the fluoridic layer stack A consisting of 18 Layers starting with a high refractive index fluoride on the mixed layer stack. A single high-index fluoride layer completes the layer system. However, this final high-index fluoride layer of the inventive mirror of FIG. 3, unlike the above, has the same optical thickness as any other layer of the layer system.

For comparison, FIG. 4 shows the reflectivity profile in percent of a layer system of the prior art with an oxide layer stack C and an outer fluoride layer stack A with respect to the angle of incidence in degrees at the wavelength of 193.4 nm. The optical thickness of a layer of the layer system corresponds to that 3 and 5. The first 40 layers on the substrate form the oxide layer stack C starting with a high refractive index oxide directly on the substrate. This is followed by the fluoridic layer stack A consisting of 18 layers starting with a high-index fluoride on the oxide layer stack. A single high-index fluoride layer completes the layer system. This final high-index fluoride layer in turn has the same optical thickness as any other layer of the layer system. The layer system according to FIG. 4 has a reflectivity of slightly more than 92% for unpolarized light Ra and of slightly more than 85% for p-polarized light Rp for an incident angle of 75 °. Furthermore, for the angle of incidence of 75 °, a difference of the reflectivity Rs-Rp from s- to p-polarized light of more than 14% results.

FIG. 5 shows the reflectivity profile as a percentage of a further layer system according to the invention with a mixed layer stack B of alternating oxidic and fluoridic layers between a fluoridic layer stack A and an oxide layer stack C with respect to the angle of incidence in degrees at the wavelength of 193.4 nm. Due to the large refractive index differences Within the layer stack B, it is possible to increase the reflectivity of the layer system of the invention over the prior art and to achieve a high reflectivity of 95% at an incident angle of 75 ° for unpolarized light Ra. It is also possible to increase the reflectivity for p-polarized light Rp to over 89% for the angle of incidence of 75 °. This makes it possible to limit the difference of the reflectivity Rs - Rp for s-polarized and p-polarized light to less than 11% for the angle of incidence of 75 °. The layer system of the mirror according to the invention to Figure 5 consists of a total of 59 layers each having an optical thickness of a layer of the layer system which is optimized to a quarter of the wavelength of the useful light of 193.4 nm at an incidence angle of 75 °. The first 20 layers on the substrate form the oxidic layer stack C starting with a high refractive index oxide directly on the substrate. Thereafter, the mixed layer stack B is followed by another 20 layers of alternating oxide and fluoridic layers starting with a high refractive index oxide on the oxide stack. This is followed by the fluoridic layer stack A consisting of 18 layers starting with a high-index fluoride on the mixed layer stack. A single high-index fluoride layer completes the layer system. This final high-index fluoride layer of the mirror according to the invention of FIG. 5 again has the same optical thickness as any other layer of the layer system.

FIG. 6 shows the reflectivity profile as a percentage of another layer system according to the invention with a mixed layer stack B of alternating oxidic and fluoridic layers and a fluoridic layer stack A with respect to the angle of incidence in degrees at the wavelength of 193.4 nm. The reflectivity of the layer system according to the invention is as shown in FIG for unpolarized light Ra and for an angle of incidence of 45 ° more than 99.7% and for p-polarized light Rp more than 99.5%. Thus, for this layer system, the difference in reflectivity Rs-Rp from s- to p-polarized light at an angle of incidence of 45 ° is less than 0.5%. Over the incident angle range of 33 ° to 52 °, the layer system according to FIG. 6 shows only a maximum difference of the reflectivity Rs-Rp between s- and p-polarized light of less than 2%. The layer system of the mirror according to the invention to FIG. 6 comprises a total of 59 layers each having an optical thickness of one layer of the layer system which corresponds to one quarter of the wavelength of the useful light of 193.4 nm at an angle of incidence of 45 °. The first 40 layers on the substrate form the mixed layer stack B of alternating oxide and fluoridic layers starting with a high refractive index oxide on the substrate. This is followed by the fluoridic layer stack A consisting of 18 layers starting with a high-index fluoride on the mixed layer stack. A single high-index fluoride layer completes the layer system. This final high-index fluoride layer of the mirror according to the invention of FIG. 6 again has the same optical thickness as any other layer of the layer system.

For comparison, FIG. 7 shows the reflectivity profile in percent of a layer system of the prior art with an oxide layer stack C and an outer fluoridic layer stack A with respect to the angle of incidence in degrees at the wavelength of 193.4 nm. The layer system of the prior art according to FIG for ranges of incidence range of 33 ° to 52 °, reflectivities of less than 96% for p-polarized light Rp, which results in a difference of the reflectivity Rs - Rp for s- and p-polarized light for the specified range of greater than 4%. Even for the limited angle of incidence range of 35 ° to 50 °, this difference Rs - Rp still results in an amount of more than 2%. The optical thickness of a layer of the layer system corresponds to that of the exemplary embodiments according to the invention to FIGS. 6 and 8. The first 40 layers on the substrate form the oxide layer stack C starting with a high-index oxide directly on the substrate. This is followed by the fluoridic layer stack A consisting of 18 layers starting with a high-index fluoride on the oxide layer stack. A single high-index fluoride layer completes the layer system. This final high-index fluoride layer in turn has the same optical thickness as any other layer of the layer system.

FIG. 8 shows the reflectivity profile as a percentage of a further layer system according to the invention with a mixed layer stack B of alternating oxidic and fluoridic layers between a fluoridic layer stack A and an oxide layer stack C with respect to the angle of incidence in degrees at the wavelength of 193.4 nm according to Figure 8, a reflectivity for p-polarized light Rp of over 96% for the incident angle range of 33 ° to 52 °, resulting in a difference in reflectivity Rs - Rp of s- and p-polarized light of less than 4%, in particular is this difference Rs - Rp for the incident angle range between 35 ° and 50 ° less than 1%. The layer system of the mirror according to the invention to Figure 8 consists of a total of 59 layers, each having an optical thickness of a layer of the layer system which corresponds to a quarter of the wavelength of the useful light of 193.4 nm at an angle of incidence of 45 °. The first 20 layers on the substrate form the oxide layer stack C starting with a high refractive index oxide directly on the substrate. This is followed by the mixed layer stack B with a further 20 layers of alternating oxidic and fluoridic layers starting with a high refractive index oxide on the oxide Schichstapel C. Subsequently, the fluoridic layer stack A consisting of 18 layers starting with a high refractive index fluoride on the mixed layer stack follows. A single high-index fluoride layer completes the layer system. This final high-index fluoride layer of the mirror according to the invention of FIG. 8 again has the same optical thickness as any other layer of the layer system.

All of the dielectric mirrors according to the invention of FIGS. 3, 5, 6 and 8 have a comparison with a comparable prior art mirror, cf. FIGS. 4 and 7 and FIGS Discussion of Figure 4 and 7, a higher reflectivity for p-polarized light Rp and thus also for unpolarized light Ra in the entire range of incidence angle shown. Therefore, it is possible by means of a mirror according to the invention over the prior art, on the one hand, to increase the reflectivity overall for an incident angle range and, on the other hand, to reduce the difference in reflectivity Rs-Rp from s-polarized light to the reflectivity of p-polarized light. Furthermore, it is possible by means of a mirror according to the invention to reduce the phase difference after the reflection between s-polarized light and p-polarized light.

Various forms of embodiment of projection exposure apparatuses according to the invention for microlithography with dielectric mirrors according to the invention are discussed with reference to the following FIGS. 9 to 15. In this case, the dielectric mirrors according to the invention at different places of use within the projection exposure systems satisfy different requirements. In particular, in projection exposure apparatuses according to the invention with a multi-mirror array (MMA), the use of at least one dielectric mirror according to the invention is necessary, in order to limit the installation space of the installation, as will be explained in more detail below.

FIG. 9 schematically shows an example of a projection exposure apparatus according to the invention for microlithography. The light source 1 generates an illumination beam 12 that is adapted in a beam expansion optics 14. Subsequently, the adjusted illumination beam 12 impinges on a diffractive optical element 3a (DOE). The diffractive optical element 3a is in a field plane of the illumination optics and generates, depending on the embossed or comprehensive diffractive structures, an illumination angle distribution. The illumination beam 12 is then, with the impressed by the diffractive optical element illumination angle distribution, transferred by the optical module 2 in a subsequent pupil plane. This pupil plane (not shown in more detail) is located near the refractive optical element 3b. The optical module 2 comprises for further structuring of the illumination beam 12, a zoom system, schematically represented by the movable lens 22, and an axicon, shown schematically by the two elements 21. By a suitable design of the diffractive optical element 3 a and by a suitable choice of Position of Axikonelemente 21 and the zoom 22, it is possible, at the output of the optical module 2, in a pupil plane in the vicinity of the refractive optical element 3 b, any represent desired intensity distribution, ie to generate. This intensity distribution of the illumination beam 12 in the pupil plane is impressed by the refractive optical element 3 b, a field angle distribution to obtain a desired field shape in a field plane, such as a rectangular field shape with an aspect ratio of 10: 1. This field angle distribution of the illumination beam 12 in the pupil plane is converted by the subsequent field lens optics 4 into an illumination field 5e at the entrance of a rod 5. The illuminated field 5e at the input of the rod 5 is located in a field plane of the illumination optics and has an illumination angle distribution with a maximum illumination angle whose sine usually, but not necessarily, the numerical aperture of the previous field lens optics 4 corresponds. In contrast to the field in the case of the diffractive element 3a, the field 5e has the full optical conductivity of the illumination optics. By multiple total reflections on the rod walls of the rod 5 arise at the rod exit in the exit pupils of the field points of the field 5a secondary light sources with the field shape of the field 5e at the rod entry as a shape of each individual secondary light source. As a result of this kaleidoscope effect of the rod 5, the field 5a is homogenized with respect to the intensity distribution over the field, since the light of many secondary light sources is superimposed, as it were, in this field 5a. As an alternative to the total reflections within a bar 5, the reflection on mirror walls of dielectric mirrors according to the invention can also take place in order to produce the kaleidoscope effect for light mixing. In this case, the mirrors should be arranged opposite each other and, in particular at angles of incidence of around 75 °, have good reflectivity properties, in particular with regard to the difference between s- and p-polarized light, as shown in the exemplary embodiments of FIGS. 3 and 5.

A field stop 51 delimits the field 5a in its lateral extent and ensures a sharp light-dark transition of the field. A subsequent, so-called REMA objective 6 images the field 5a into the reticle plane 7. The light-dark edges of the field stop 51 are sharply transferred to the object or field plane 7. From this function of the sharp edge formation of the field stop 51 into the reticle or field plane 7, also referred to as "masking" of the reticle (in English "reticle masking"), the name REMA (REticleMAsking) of this lens group results. The REMA objective 6 consists, for example, of a condenser group 61, a pupil area in the vicinity of a pupil plane 62, a pupil lens group 63, a deflection mirror 64 according to the invention and a terminating field lens group 65. The deflection mirror 64 according to the invention is located in a transition area between a field plane and a pupil plane and has a slope of 45 ° with respect to the optical axis, so that one half of the mirror points in the direction of a pupil plane and the other half in the direction of a field plane. Therefore, this mirror must have not only for incident angle ranges of +/- 25 ° around a mean angle of incidence of 45 ° around high reflectivities, but locally change its reflectivity properties over the mirror surface. In addition, there are certain requirements due to the polarization-optical design of the lighting system. In order to meet all these requirements, the dielectric deflection mirror 64 according to the invention has at least one layer whose layer thickness changes in the direction along the mirror surface by more than 10% relative to the maximum layer thickness of the layer. Furthermore, the dielectric deflection mirror 64 according to the invention has at least one layer stack A, B or C which has at least two different periods of two successive layers of a high and a low refractive index material in the direction of the surface normal.

The object field plane 7 represents the separation plane between illumination optics and projection optics, e.g. A projection lens 8, a projection exposure system. The lighting optical system has the task of illuminating a sharp-edged field homogeneously and thereby to structure the illumination angle distribution or exit pupil of an object field point according to the specifications.

Reticles or masks are introduced into the object field plane 7 for chip production. These masks are illuminated by means of the illumination beam 12 prepared by the illumination optics. The projection objective 8 images the illuminated mask into a further field plane, the image field plane 10. There is a substrate 9, which carries on its upper side a photosensitive layer. The mask structures are transmitted through the projection lens 8 into corresponding exposed areas of the photosensitive layer.

After the exposure process step, the exposed substrate 9 is subjected to subsequent process steps, e.g. the etching. As a rule, the substrate 9 subsequently receives a new photosensitive layer and is subjected to a new exposure process step. These process steps are repeated until the finished microchip or the finished microstructured component is obtained.

FIG. 10 schematically shows a further example of a projection exposure apparatus according to the invention for microlithography. The elements in Figure 10, which correspond to those in Figure 9, are denoted by the same reference numerals. The projection exposure apparatus in FIG. 10 differs from the projection exposure apparatus in FIG. 9 only in the illumination optics. The illumination optics in FIG. 10 differs from the illumination optics in FIG. 9 in that the rod 5 or the mirror kaleidoscope 5 is lacking for generating secondary light sources. Furthermore, the illumination optical system in FIG. 10 differs in that a field-defining element 3c (FDE) not only provides for the generation of the necessary field angles in the pupil plane, but also, due to its construction as a two-stage honeycomb condenser, for the Generation of secondary light sources ensures. Thus, the field-generating element 3 c in Figure 3 includes both the functionality of the refractive optical element (ROE) 3b of Figure 9, and the functionality of the rod 5 and Kaleidoskops 5 of Figure 9. The field-generating element 3 c, designed as a two-stage honeycomb condenser, On the one hand introduces the necessary field angles in the pupil plane and on the other hand generates the secondary light sources in the pupil plane. As a result, a corresponding field shape with a desired homogenized intensity distribution over the field is generated in the subsequent field levels of the illumination optics by the superimposition of light of the secondary light sources.

FIG. 11 schematically shows a pupil-shaping unit according to the invention for an illumination optical system for a lithographic projection exposure apparatus, as shown for example in FIG. 9 or 10. Here, the pupil-shaping unit according to the invention from FIG. 11 serves as a substitute for the pupil-shaping unit 2 of the projection exposure apparatus according to FIGS. 9 or 10. However, the use of the pupil-shaping unit of FIG. 11 is not limited to these projection exposure apparatuses. The pupil-forming unit of FIG. 11 terminates in the pupil plane 44, which is located in FIG. 9 in the vicinity of the refractive optical element 3b and in FIG. 10 in the vicinity of the field-generating element 3c and is to be regarded as the first system pupil of the illumination system in the context of this application. Instead of a DOE 3a in FIG. 9 and in FIG. 10, a multi-mirror array (MMA) 38 provides an illumination angle distribution which superimposes on the pupil plane 44 an intensity distribution in this pupil plane. This intensity distribution of the pupil planes 44 corresponds to the intensity distribution in the exit pupil or the illumination angle distribution of an object field point, if an ideal Fourier optics is used as the basis for the transmission. An illumination beam 12 of a light source is deflected by a deflection mirror 30 according to the invention and separated by a honeycomb condenser 32 into individual partial illumination beams and subsequently passed through a telescope optics 34, or a relay optic 34, or a condenser 34 onto a lens array 36. Of the Dielectric array 30 according to the invention corresponds in its reflectivity behavior to the exemplary embodiments of FIGS. 6 and 8. The lens array 36 concentrates the partial illumination beam bundles on the individual mirrors of the multiple mirror arrangement 38. The individual mirrors of the multiple mirror arrangement 38 can be tilted differently, ie at least part of the mirrors The multi-mirror arrangement can be rotated about at least one axis for changing an angle of incidence of the associated partial illumination beam, so that different intensity distributions can be set in the pupil plane 44. The partial illumination beam bundles emanating from the mirrors of the multiple-mirror arrangement 38 are imaged by a subsequent diffusing screen 40 and a subsequent condenser optical system 42 into the pupil plane 44 or system pupil of the illumination system. 11, various embodiments of dielectric mirrors according to the invention can be used, as will be explained in more detail below with reference to FIGS. 12 to 15.

FIG. 12 schematically shows a pupil shaping unit according to the invention with at least one dielectric mirror according to the invention comprising a honeycomb condenser 32, a condenser or relay or telescope optics 34, a lens array 36 and a multi-mirror array 38 (MMA). Since the honeycomb sensor 32 must not substantially increase the divergence of the illumination beam in order to ensure a high resolution in the structuring of the intensity distribution in the system pupil of the illumination system, it is necessary for a condenser, or a telescope optics, to have a large size Focal length, these low divergence values translated into corresponding heights relative to the optical axis on the multi-mirror array 38. For space reasons, it is therefore appropriate to fold this telescope optics 34 with a large focal length, by prisms or mirrors accordingly. In particular, dielectric mirrors according to the invention are to be preferred for this folding task because of their high reflectivity and their laser stability, since the total transmission of the projection exposure apparatus depends on the reflectivity of these mirrors and the overall transmission has an effect on the throughput of wafers to be exposed. Due to the low divergences and bundle cross sections at the named locations, mirrors must be used which can withstand high laser pulse energy densities of up to 250 mJ / cm ² . The dielectric mirrors according to the invention within the telescope optics 34 have a good reflectivity and a low reflectivity or phase splitting between s and 2, in particular at angles of incidence between 33 ° and 52 ° p-polarized light, as shown in the exemplary embodiment of Figures 6 and 8.

FIG. 13 schematically shows an alternative pupil shaping unit according to the invention with at least one dielectric mirror according to the invention in which the honeycomb condenser 32 of FIG. 12 has been exchanged for a corresponding rod 32a, an optical fiber 32a, an optical fiber bundle 32a or a kaleidoscope 32a of dielectric mirrors according to the invention , In accordance with the mirrors of the kaleidoscope 5 according to the invention for high angles of incidence, these inventive mirrors of the kaleidoscope 32a have a good reflectivity and a low reflectivity or phase splitting between s- and p-polarized light, as in the exemplary embodiments of FIGS. 3 and 5 are shown. Furthermore, the illustrated deflecting prisms of the telescope optics 34 in FIG. 13 can be replaced by dielectric mirrors according to the invention, as already discussed above with reference to FIG.

FIG. 14 schematically shows a further embodiment according to the invention of a pupil shaping unit with at least one dielectric mirror according to the invention. In this embodiment, the relay optics, or the condenser optics, or the telescope optics 34 is divided into two separate relay optics 34a and 34b. In contrast to the previous embodiments, an optical system which is formed from "auxiliary lenses" of two mutually perpendicular thin optical plates serves as the light-mixing device 32b in Figure 14. The two thin plates perpendicular to one another provide the corresponding light mixture on the multiple-mirror arrangement 38. Alternatively, it is possible to replace the two plates by two opposing dielectric mirrors according to the invention, in order to produce a kaleidoscope or light mixing effect in one direction Angle of incidence good reflectivity and a low Reflektivitäts- or phase splitting between s- and p-polarized light, as shown in the embodiments of Figures 3 and 5. In the inventive Ausf In the embodiment shown in FIG. 14, an optional beam shaping unit 31a adjusts the size and the divergence of the illumination beam. It is indicated by the two cutting planes 31b perpendicular to the beam propagation direction that inventive dielectric mirrors of the pupil shaping unit or of the conditioning unit of the illumination optics can also be located in front of the housing wall of the illumination optics, indicated by 3 lb. For the sake of clarity, no deflecting elements are shown in FIG. 14, but the location of use of such elements in FIG. 14 can always be recognized where the drawn light beam changes its direction. At these points, the use of dielectric mirrors according to the invention is preferable, since due to the low divergences and bundle cross sections at the above locations, mirrors must be used which can withstand high laser pulse energy densities of up to 250 mJ / cm ² and at the same time have high reflectivity. The dielectric mirrors according to the invention have a good reflectivity and a low reflectivity or phase splitting between s- and p-polarized light, in particular at angles of incidence between 33 ° and 52 °, as shown in the exemplary embodiments of FIGS. 6 and 8.

FIG. 15 schematically shows a further embodiment according to the invention of a pupil shaping unit according to the invention with a dielectric mirror according to the invention. In this embodiment, an optical conditioning unit 32c serves to symmetrize the illumination beam at the output of the conditioning unit 32c without resorting to the polarization properties of the light for symmetrization. The functioning of the optical conditioning unit 32c is based on the fact that a part of the illumination beam is deflected by the dielectric mirrors 37a and 37b according to the invention, this part of the illumination beam passing through a so-called dove prism 35. Within the dove prism 35, the actual reflection or symmetrization of the partial exposure beam takes place, so that an exposure beam exists at the output of the optical conditioning unit 32c, which is formed from two partial exposure beam bundles which are symmetrized with respect to an axis along the propagation direction of the light.

In the exemplary embodiment according to FIG. 15 as well, as with the exemplary embodiments according to FIG. 13 or 14, particular preference is given to dielectric mirrors according to the invention because of their high reflectivity and their laser stability for beam deflection. The mirrors 37a and 37b of the conditioning unit 32c are explicitly drawn in FIG. 15, whereas the illustration of the deflection mirror within the telescope optics 34 has been omitted for the sake of clarity.

Claims

claims:

1. Dielectric mirror with at least one oxidic layer stack (C) consisting of oxidic layers and at least one fluoridic layer stack (A) consisting of fluoridic layers, characterized in that the mirror at least one mixed layer stack (B) consisting of a sequence of alternating fluoridic and oxidic Layers between the oxide layer stack (C) and the fluoridic layer stack (A).

2. Dielectric mirror according to claim 1, wherein the mixed layer stack (B) for adapting the layer stresses of the fluoridic layer stack (A) to the oxidic layer stack (C) is used and for this purpose more than 4 layers, in particular more than 6 layers.

3. Dielectric mirror according to one of the preceding claims, wherein at least one refractive index difference between two successive layers of the mixed layer stack (B) is greater than 0.35, in particular greater than 0.4.

4. Dielectric mirror according to one of the preceding claims, wherein at least one layer thickness of a layer changes in the direction along the mirror surface by more than 10% based on the maximum layer thickness of the layer.

5. Dielectric mirror according to one of the preceding claims, wherein at least one layer stack (A, B, C) in the direction of the surface normal of the mirror has at least two different periods of two successive layers of a high and a low refractive index material.

6. Dielectric mirror according to one of the preceding claims, wherein the mirror at a wavelength of 193 nm and incidence angles between 33 ° and 52 °, a maximum difference in the reflectivity of s-polarized light (Rs) to the reflectivity of p-polarized light (Rp ) of less than 4%, in particular less than 2%.

7. Dielectric mirror according to one of the preceding claims, wherein the mirror at a wavelength of 193 nm and incidence angles between 33 ° and 52 ° a Has reflectivity for s-polarized light (Rs) and / or p-polarized light (Rp) and / or unpolarized light (Ra) of greater than 96%, in particular greater than 97.5%.

8. Dielectric mirror according to one of claims 1 to 5, wherein the mirror at a wavelength of 193 nm and an incident angle of 75 °, a difference in the reflectivity of s-polarized light (Rs) to the reflectivity of p-polarized light (Rp) less than 14%, in particular less than 1 1%.

The dielectric mirror according to any one of the preceding claims, wherein the mixed layer stack (B) has more than 10 layers.

10. A method for producing reflective dielectric mirrors by depositing a sequence of dielectric layers, characterized in that at least between an oxide layer stack (C) consisting of oxidic layers and a fluoridic layer stack (A) consisting of fluoride layers, a mixed layer stack (B) of alternating oxidic and fluoridic layers with more than 4 layers, in particular more than 6 layers for adaptation of stresses of the fluoridic layer stack (A) to stresses of the oxide layer stack (C) is deposited.

11. The method according to claim 10, wherein the oxidic layers of the mixed layer stack (B) undergo controlled ion bombardment during vacuum evaporation, whereby in particular the stresses of the layers are adjusted.

12. Dielectric mirror produced by a method according to one of claims 10 to 11.

13. The projection exposure apparatus for microlithography with at least one dielectric mirror according to one of claims 1 to 9 or 12.

14. A projection exposure apparatus according to claim 13 having at least one multiple mirror arrangement (38) consisting of more than 1000 and less than 40,000 mirrors with a surface area of 2 cm ² to 80 cm ² .

15. A projection exposure apparatus according to claim 14 having at least one homogenizing optic or conditioning optic (32; 32a; 32b; 32c) in the light direction in front of the multiple mirror arrangement (38), wherein the homogenizing optic or conditioning optics (32; 32a; 32b; 32c) detects the divergence of a It is increased by less than four times the illuminating beam (12) passing through it and the at least one dielectric mirror is a component of the homogenizing optics or conditioning optics (32; 32a; 32b; 32c).

16. Projection exposure system according to claim 14 or 15 with a telescope optical system (34) in the light direction in front of the multiple mirror arrangement (38) with a focal length of greater than 2 m, in particular greater than 5 m, wherein the at least one dielectric mirror is part of the telescope optics (34) ,