KR101200654B1 - Projection objective having a high aperture and a planar end surface - Google Patents

Abstract

A projection objective for imaging a pattern provided on the object plane of a projection objective lens suitable for use in a microlithographic projection exposure apparatus is transparent to radiation at the operating wavelength of the projection objective lens. Have At least one optical element is a high refractive index optical element made of a high refractive index material having a refractive index of n ≧ 1.6 at an operating wavelength.

Microlithography projection exposure apparatus, projection objectives, high refractive index materials, final optical elements, refractive index, high refractive index

Description

Projection objective having a high aperture and a planar end surface

The present invention relates to a projection objective for imaging an image provided on an object plane of a projection objective onto an image plane of a projection objective. Projection objectives can be used for microlithographic projection exposure apparatus. The present invention relates in particular to a semiconductor structural exposure apparatus designed for liquid immersion operation, that is to say an exposure apparatus in an aperture ratio range where the image-side numerical aperture NA is greater than 1.0.

When reducing the optical imaging, especially in projection lithography, the image-side numerical aperture NA is limited by the index of refraction of the surrounding medium in image space. The immersion medium can be liquid or solid. The latter is also called solid immersion.

However, for practical reasons the aperture ratio should not arbitrarily approach the index of refraction of the final medium (ie the medium closest to the image), since the propagation angle increases relatively relative to the optical axis. It has been demonstrated that the aperture ratio does not substantially exceed 95% of the refractive index of the image-side final medium. This corresponds to a propagation angle of approximately 72 ° relative to the optical axis. For 193 nm, this corresponds to a numerical aperture of NA = 1.35 when water is used as the immersion medium (n H _{2 O} = 1.43).

For liquids of refractive index greater than the refractive index of the material of the final lens or for solid immersion, if the design of the final end face (the exit face of the projection objective) is flat or very slightly bent, the final lens element (ie The material of the final optical element adjacent to the image acts as a constraint. For example, the flat design facilitates the measurement of the distance between the wafer and the objective lens, the hydrodynamic properties of the immersion medium between the wafer and the final objective surface to be exposed, and their cleaning. The final end face should be of flat design, especially in the case of solid immersion, as well for the exposure of flat wafers.

In the case of far ultraviolet rays (DUV, operating wavelength of 248 nm or 193 nm), the materials commonly used for the final lens are fused silica (synthetic quartz glass, SiO ₂ ) or n _{CaF 2} = 1.50 with a refractive index of n _{SiO 2} = 1.56. CaF ₂ with a refractive index of. In the following, the synthetic quartz glass material is also simply referred to as "quartz". Because of the large radiation load in the final lens elements, 193 nm calcium fluoride is particularly preferred for the final lens because synthetic quartz glass is damaged in the long term by the radial load. This results in a numerical aperture of approximately 1.425 (95% of n = 1.5) that can be achieved. Taking the disadvantage of radiation damage, quartz glass still allows a numerical aperture of 1.48 (corresponding to approximately 95% of the refractive index of quartz at 193 nm). The relationship is similar at 248 nm.

One object of the present invention is to provide a high aperture projection objective that avoids the disadvantages of conventional designs with immersion media such as water or the disadvantages of conventional designs with lens materials such as fused silica and CaF ₂ . It is a further object of the present invention to provide a projection objective suitable for immersion lithography at an image-side numerical aperture of at least NA = 1.35 with suitable size and material consumption.

As a solution to this and other objects, according to one embodiment the present invention provides a projection objective suitable for a microlithographic projection exposure apparatus for imaging a pattern provided on the object plane of the projection objective onto the image plane of the projection objective. Such a projection objective has a plurality of optical elements that are transparent to radiation at an operating wavelength of the projection objective lens, wherein at least one optical element has a high refractive index of n ≧ 1.6 at the operating wavelength. It is a high refractive index optical element formed of a refractive index material.

One embodiment preferably has a radiation-proof lithographic objective having an image-side numerical aperture of NA = 1.35 or more and at least the final optical element is made of a high refractive index (n> 1.6 refractive index, in particular n> 1.8) material. It consists of a lens. For a typical (absolute) 4: 1 (| β | = 0.25) reduction ratio in lithography, the object-side (mask-side) numerical aperture is NA _obj ≧ 0.33, preferably NA _obj ≧ 0.36.

Hereinafter, various features of the present invention will be described in more detail with reference to exemplary embodiments for 193 nm. In embodiments, the material used for the final lens element or part thereof is sapphire (Al ₂ O ₃ ) and the other lenses are made of fused silica. However, embodiments may be modified for other high refractive index lens materials and other wavelengths. It is also possible to use germanium dioxide (GeO ₂ ) as a material for some of the final lens or part, for example for 248 nm. In contrast to sapphire, this material has the advantage that it is not anisotropic. However, this material is not transparent at 193 nm.

For liquid immersion, NA> 1.35 can be achieved by using immersion liquid with a refractive index greater than water. Cyclohexane (refractive index of n = 1.556) was used in some applications.

Immersion media with n> 1.6 are now considered realistic.

If immersion liquid is used, the thickness of the high refractive index liquid, that is, the thickness of the immersion liquid is 0.1 mm to 10 mm. Smaller thicknesses in this range are more desirable because high refractive index immersion media typically exhibit greater absorption.

These and other features are not only shown in the claims, but also in the description and drawings, and the individual features may be used alone or in subcombinations as one embodiment in the present and other areas, respectively. Advantageous and patentable embodiments will be presented.

1 is a longitudinal cross-sectional view of a catadioptric projection objective lens according to a first embodiment of the present invention.

2 is a longitudinal cross-sectional view of a reflective refractive projection objective lens according to the first embodiment of the present invention.

3 is a longitudinal cross-sectional view of a reflective refractive projection objective lens according to the first embodiment of the present invention.

4 is a longitudinal cross-sectional view of a reflective refractive projection objective lens according to the first embodiment of the present invention.

5 is a longitudinal cross-sectional view of a reflective refractive projection objective lens according to the first embodiment of the present invention.

In the following description of the preferred embodiments of the present invention, "optical axis" means one straight line or a series of straight pieces passing through the center of curvature of the included optical elements. The optical axis may be folded by folding mirrors (deflecting mirrors). In the following embodiments, the object included may be a mask (reticle) with an integrated circuit pattern or some other pattern such as, for example, a grating pattern. In the following embodiments, an image of the object is projected onto a wafer that acts as a substrate coated with a photoresist layer, where the substrate is another type of substrate, such as a component of a liquid crystal display, or another such as a substrate for diffraction gratings. It can also be a tangible substrate.

Tables to be described below are provided to disclose the details of the design shown in the drawings, the number of the table corresponds to the number of each drawing (for example, Table 1 is Figure 1, Table 2 is Figure 2).

1 shows a reflective refractive projection objective lens 100 according to a first embodiment of the present invention designed for a 193 nm UV operating wavelength. It is designed to project an image of a pattern on a reticle (or mask) placed in an object plane (OP) onto an image plane (IP) at a reduced scale, for example 4: 1, with exactly two intermediate images. Generate the fields IMI1 and IMI2. The first refractive objective part ROP1 is designed to image the pattern in the object plane into the first intermediate image IMI1, and the second reflective (pure reflective) objective part COP2 (catadioptric objective) Part 2) forms the first intermediate image IMI1 into the second intermediate image IMI2 at an enlargement ratio close to 1: 1, and the third refractive objective portion ROP3 has a strong reduction ratio of the second intermediate image IMI2. The image is formed on the image plane IP. The second objective lens portion COP2 includes a first concave mirror CM1 having a concave mirror face toward the object side and a second concave mirror CM2 having a concave mirror face toward the image side. . Both mirror surfaces are continuous or unbroken, ie they have no holes or holes. The mutually opposite mirror surfaces define an intermirror space, which is a space surrounded by curved surfaces defined by concave mirrors. Both intermediate images IMI1 and IMI2 are geometrically located in the intermirror space, at least the paraxial intermediate images being sufficiently spaced apart from the mirror surfaces and located almost in the center of the intermirror space.

Each mirror surface of the concave mirror defines a "curvature surface" or "surface of curvature", a mathematical surface that extends outside the edge of the physical mirror surface and includes the mirror surface. The first concave mirror and the second concave mirror are portions of the rotationally symmetric curvature surfaces having a common axis of rotation symmetry.

System 100 is rotationally symmetric and has one linear optical axis AX that is common to all refractive and reflective optical elements. There is no folding mirror. Concave mirrors have a small diameter that allows them to be located closer to each other and somewhat closer to intermediate images in between. The concave mirrors are constructed and illuminated as off-axis portions of the axial symmetric faces. The light beam passes through the edges of the concave mirrors facing the optical axis without vinetting.

Reflective refractive projection objectives having this general configuration are described, for example, in US Patent Application No. 60 / 536,248, filed Jan. 14, 2004, US Patent Application No. 60 / 587,504, filed July 14, 2004, and October 2004. It is disclosed in a subsequent extended application filed on the 13th. The contents of these applications are incorporated herein by reference. One feature of this type of refraction projection objective is that pupil surfaces (at an axial position where the chief ray intersects the optical axis) between the object plane and the first intermediate image, between the first intermediate image and the first intermediate image. The chief ray height of the imaging process, which is formed between the second intermediate image and between the second intermediate image and the image plane, and that all concave mirrors are arranged optically spaced from the pupil plane, exceeds the ambient ray height of the imaging process. Is placed in the position. Moreover, it is preferred that at least the first intermediate image is geometrically located in the intermirror space between the first concave mirror and the second concave mirror. Preferably, both the first intermediate image and the second intermediate image are geometrically located within the mirror space between the concave mirrors.

The exemplary embodiments described below share these basic features that enable immersion lithography at numerical aperture NA> 1 with an optical system that can be built with a relatively small amount of optical material.

FIG. 1 shows a 193 nm lithographic objective lens having an image-side numerical aperture NA = 1.45 as a first embodiment and having a cyclohexane and sapphire lens as an immersion medium. The sapphire lens is the last optical element (LOE) closest to the image plane. The working side of the image side is 1 mm. The refraction design has two concave mirrors, primarily for chromatic aberration correction and Petzval correction, and an intermediate image positioned before and after the pair of mirrors, respectively. However, the intermediate images are not fully corrected, but mainly serve as geometric limitations of the design and also separate the beam path to the mirror and the beam path away from the mirror after reflection. The image field (on the wafer) is rectangular. The outer field radius (on the wafer side) is 15.5 mm and the inner field radius is 4.65 mm. The result is a rectangular field of 26 X 3.8 mm.

An aperture diaphragm (aperture stop AS, system aperture) is disposed in the first refractive objective lens portion ROP1 in the first embodiment. On the one hand this is desirable to form a smaller variable aperture aperture, and on the other hand the roughly the objective lens portions after the unwanted interference radiation load (as seen from the object plane (mask plane)) when tightening the aperture stop. It is desirable to protect. The rear aperture plane at the image side objective lens portion ROP3, i.e. where the aperture stop can be placed, is between the lens of maximum diameter (LMD) and the image plane IP at the converging beam path. Located in the area.

A waist (contraction of the beam and lens diameter) is formed on the object side in front of the refractive partial objective ROP1, which serves to correct image field curvature (Petzbal sum). The aperture stop AS is arranged at the node.

The use of CaF ₂ for the final lens is not preferred because it requires a numerical aperture that is not greater than 1.425 (approximately 95% of the refractive index of CaF ₂ ) as possible. In this example at 193 nm, sapphire (Al ₂ O ₃ ) was used as the high refractive index material in the last lens element (LOE). In all embodiments in the drawings, optical elements made of sapphire are divided by shade for convenience.

The birefringence that occurs when sapphire is used is largely compensated by separating the final lens (final optical element, LOE) into two lens elements LOE1, LOE2 and rotating the two lens elements about the optical axis. In this case, the separation interface (SI) (contact surface of the two lens elements LOE1, LOE2) is preferably a curved surface such that all of the lens elements have similar refractive power. Alternatively, it is also possible to use a second element made of sapphire for compensation, which can be located in the same position in the optical term in the objective lens, for example near intermediate images or in the vicinity of the object plane. can do. In the present embodiment, the final sapphire lens LOE is separated into two substantially identical lens elements LOE1 and LOE2. The front radius of the sapphire lens (LOE) (i.e. the radius of the light incident side) is such that the aperture beam, i.e. the beam incident toward the image at the periphery of the converging light bundle, passes through the interface without being substantially refracted towards the center of the image field. In other words, it is designed to be incident substantially perpendicular to its interface (the lens radius is substantially concentric with the intersection of the image plane and the optical axis). The radius of the splittin interface (SI) between the two lens elements of the divided sapphire lens is flatter (more than 1.3 times the distance from the image plane where the wafer is to be placed).

Compensation of the birefringence effect by relative rotation of elements made of birefringent material is for example published in detail in DE 101 23 725 A1 (corresponding to US 2004/0190151 A1) or WO 03/077007 A2 by the applicant of the present application. Reflective refraction projection objectives in which the final lens element closest to the image plane is designed with a split final lens made of birefringent material (calcium fluoride) can be found from US 6,717,722 B.

The detailed description of the design shown in FIG. 1 is summarized in Table 1. The leftmost column represents the number of facets designed for refraction, reflection, or leg, the second column represents the radius r of the face [mm], and the third column is a variable called the "thickness" of the optical element. And the distance d between the next face (mm), the fourth column represents the material used to make the optical element, and the fifth column represents the refractive index of the material used to make the optical element. The sixth column represents the optically available and transparent half diameter of the optical component [mm]. In the table, a radius value of r = 0 means a flat face with an infinite radius.

In this particular embodiment, the fifteen faces are aspherical. Table 1A shows the data related to the aspherical surfaces from which the sagitta of the face shapes as a function of height h can be calculated using the following equation:

p (h) = [((1 / r) h ² ) / (1 + SQRT (1- (1 + k) (1 / r) ² h ² ))] + C1h ⁴ + C2h ⁶ + …

Where the value of the inverse of the radius (1 / r) is the curvature of the face at that face vertex in question, and h is the distance of the point on the face from the optical axis. The sagitta p (h) thus represents the distance of the point measured along the z direction, ie along the optical axis, from the surface vertex in question. Constants K, C1, C2 and the like are shown in Table 1a.

Likewise, the detailed description of the embodiments described below is shown in Tables 2, 2a, 3, 3a, 4, 4a and 5, 5a in a similar manner.

According to the projection objective lens 200 shown in FIG. 2, the final optical element LOE on the image side has a flat convex shape as a whole. The lens is divided into two optical elements LOE1 and LOE2, which are in contact with the dividing interface SI. Specifically, a quartz glass lens (LOE1) with an incidence plane of positive curvature radius and a flat back surface is placed on one (or two) plane-parallel plate (LOE2) made of sapphire. It is ringing. This results in a numerical aperture that is not larger than possible in quartz glass, but has the advantage of reducing the propagation angle of the light beam in the portion of the final objective with the largest aperture due to the high refractive index medium. This can be an advantage when considering scattered light effects and reflection losses in the protective film that can be provided on the interface and the final end face, such scattered light effects and reflection losses are problematic for very large propagation angles. Generate. The largest angle then occurs only at the ringing surface between the quartz lens LOE1 and the first high refractive index plane-parallel plate LOE2. This ringing surface (contact surface where adjacent optical elements are attached to each other by ringing) is protected from contamination and damage and may also be designed to have a coating that is sensitive to environmental influences. If two planar-parallel plates were used to form a planar-parallel high refractive index element (LOE2), the two planar-parallel plates made of sapphire were rotated relative to each other about the optical axis, essentially ideally in the x direction and The birefringence effect on S polarization and P polarization in the y direction can be compensated, which is mainly required for the imaging of the semiconductor structure.

However, because of the lower refractive index, the quartz lens (LOE1) here-because of its lower collecting effect-requires a very large lens diameter even for the image-side numerical aperture of a limited full-length projection objective that is not really large. Has the effect. In the second embodiment (Fig. 2), the numerical aperture is NA = 1.35, but the lens diameter is larger than in the first embodiment. The lens diameter here is already at least 143 mm and thus substantially 212 times the numerical aperture, whereas in the first embodiment in FIG. 1 only 200 times the numerical aperture. In particular, in the embodiment of FIG. 2 the maximum half lens diameter at 143 mm is even larger than the mirror half diameter at approximately 136 mm.

In order to minimize the diameter of the largest lens element of the projection objective, and at the same time to minimize the birefringence effect, in another embodiment of the design example with NA = 1.45 (projection objective 300) the final lens element (LOE) is the incident surface. This sphere has a sapphire lens (LOE1) having a spherical curved surface and having a flat positive refractive power, which is ringed on the quartz glass plate (LOE2) (third embodiment of FIG. 3). The planar-parallel quartz glass plate, which provides the exit face of the objective lens, can be replaced when damage due to radial load occurs. The ringed quartz plate thus also acts as a replaceable protective material of the sapphire lens LOE1 against contamination and / or scratches or breakage. The third embodiment was adapted to cyclohexane as an immersion fluid, which has a refractive index (n = 1.556) similar to that of fused silica (n = 1.560) used for plates in contact with the immersion fluid.

In these cases, the numerical aperture NA is limited by the refractive index of the quartz glass. However, compared with designs with a final lens made of pure quartz glass, the result before the final lens is a smaller beam angle and therefore also the overall diameter of the objective lens is smaller and the sensitivity of the final lens element (interference sensitivity to manufacturing tolerances). It is also lower. In the third embodiment, the maximum lens diameter at 135 mm is now approximately 186 times the numerical aperture.

Of course, the present invention can also be used for small numerical aperture objectives to substantially reduce the diameter of conventional projection objectives. This has a favorable effect on the cost of the projection objective because the amount of material can be substantially reduced.

The fourth embodiment (Fig. 4) has a monolithic final lens made of sapphire and a lithographic objective lens for 193 nm, with water (n _H2O = 1.43) as an immersion medium for NA = 1.35 with an operating distance of 1 mm. 400 is shown. The upper side (incident side) of the integrated (one part, undivided) sapphire lens (LOE) is an aspherical surface, and the aperture stop AS is the third objective in the biconvex lens LMD having the largest diameter. In the region of converging radiation between the maximum beam diameter of the lens portion ROP3 and the image plane IP, it is located behind the image side refractive objective lens portion ROP3. The maximum lens diameter is limited to less than 190 times the numerical aperture.

A numerical aperture greater than NA = 1.45 is also possible using at least a high refractive index material for the final lens element.

The fifth embodiment 500 (FIG. 5) was designed for solid immersion (contact projection lithography) with a planar sapphire lens (LOE) (n _sapphire = 1.92) for NA = 1.6. Thus even a numerical aperture of NA> 1.8 is possible in principle. For example the outer field radius on the wafer side is at 15.53 mm and the inner field radius is at 5.5 mm, in other words here the size of the rectangular field is 26 × 3 mm.

Since a high aperture beam with a numerical aperture of NA> 0.52 is totally reflected at the exit surface during the movement from sapphire to air, an operating distance smaller than the wavelength must be realized in order to effectively use an evanescent wave for wafer exposure. This can be done in vacuo by bringing the wafer to be exposed constantly, such as at 100 nm (≒ λ / 2), near the final lens plane.

However, because of the principle of output transmission that decreases exponentially with distance, even if it is extinct, small changes in distance cause large fluctuations in uniformity, so that the wafer is placed directly on the final end face of the projection objective. It is desirable to have mechanical contact. In order to obtain a mechanical contact between the exit plane of the projection objective and the incoupling plane associated with the substrate, for this purpose, the wafer to be exposed can be ringed on the final flat lens plane (contact surface CS). . The step-and-step mode of exposure or the stitching method is preferred in this case, that is, areas larger than the image field can be exposed at each step, and in the past Unlike the mask, the reticle mask is adjusted to correspond for alignment. This can be an advantage because the reticle can be adjusted with lower accuracy than the adjustment of the wafer due to shrinkage imaging. Consecutive levels of semiconductor structure from mutually adjacent exposure areas (target areas) or subsequent exposure steps move the reticle mask laterally and axially to expose the semiconductor structures on the ringed wafer with overlapping accuracy better than several nm. As it rotates, it overlaps. For this purpose, for example, the alignment masks of the reticle will coincide with the alignment marks already exposed on the wafer.

Desorption of the wafer from the final surface is preferably performed in vacuo. If desired, a thin film (pellicle / membrane) can be placed between the wafer and the flat final lens surface, for example after each exposure step. The membrane may also serve as a particularly flat final lens surface protection member, for example remaining on the wafer to aid in separation. The latter can optionally be further protected by a thin protective film.

In the case of a solid liquid, a large intensity standing wave may occur during exposure in the edge region of the final lens surface due to the presence of imaging interference. Therefore, it may be desirable to repeatedly expose the structure on the wafer when the wafer is accidentally positioned incorrectly within the range of a few micrometers due to ringing, so that the reticle is prevented to prevent systemic structures from burning into the final lens. It can be compensated by the adjustment used.

All the embodiments described above are reflective refractive projection objectives with exactly two concave mirrors and exactly two intermediate images, with all the optical elements arranged along one straight unfolded optical axis. Certain basic types of projection objectives selected to illustrate preferred variants of the present invention are intended to illustrate the technical effects and advantages associated with the basic variants and other variations of the present invention. However, for projection objectives, in particular for projection objectives for operating wavelengths in the far-ultraviolet region, it is possible to use the lenses described above or lens elements made of a high refractive index (e.g., n ≥ 1.6 or n ≥ 1.8) material. It is not limited to these types of projection objectives. The invention can also be applied to purely refractive projection objectives. In that type, the final optical element closest to the image plane is sometimes a flat convex lens, for example a flat convex lens designed according to the rules described above for the final optical elements LOE in the first to fifth embodiments. to be. Examples are described, for example, in US Patent Application Nos. 10 / 931,051 (WO 03/075049 A), 10 / 931,062 (US 2004/0004757 A1), 10 / 379,809 (US 2003/01744408) or WO 03/077036 A of the applicant. Given. These are incorporated herein by reference.

Similarly, the present invention may be applied to a reflective refractive projection objective lens having only one concave mirror, or a reflection having two concave mirrors in a different arrangement than that shown in the drawing or described in the embodiment having two or more concave mirrors. It may also be applied to refractive projection objectives. In addition, the use of the present invention is possible regardless of the presence of a folding mirror in the optical design. Examples of reflective refraction systems are given, for example, in US Application Nos. 60 / 511,673, 10 / 743,623, 60 / 530,622, 60 / 560,267 or US 2002/0012100 A1. These are incorporated herein by reference. Other examples are published in US 2003/0011755 A1 and related applications.

Similarly, the present invention can be applied to a projection objective without an intermediate image or to a projection objective having an appropriate number of intermediate images as necessary.

According to the present invention, it is possible to implement a high aperture projection objective that avoids the disadvantages of conventional designs with immersion media such as water or the disadvantages of conventional designs with lens materials such as fused silica and CaF ₂ .

Claims (31)

A projection objective lens for forming a pattern provided on an object plane of a projection objective lens on an image plane of a projection objective lens, A plurality of optical elements transparent to radiation at the operating wavelength of the projection objective lens, At least one optical element is a high refractive index optical element made of a high refractive index material having a refractive index of n ≧ 1.6 at an operating wavelength, Having a final optical element closest to the image plane, the final optical element being at least partially made of a high refractive index material with a refractive index n> 1.6, A projection objective filled with an immersion medium having an index of refraction greater than 1 between the final optical element and the image plane. The method of claim 1, High refractive index materials are projection objective lenses having a refractive index of n ≧ 1.8 at an operating wavelength. The method according to claim 1 or 2, High refractive index material is sapphire projection objective lens. The method according to claim 1 or 2, The high refractive index material is germanium dioxide projection objective lens. The method according to claim 1 or 2, The object-side numerical aperture NA _Obj is a projection objective greater than 0.3. The method of claim 5, The object-side numerical aperture is the absolute reduction factor | β | with NA _Obj > 0.36. Projection objective with ≤ 0.25. The method according to claim 1 or 2, A projection objective lens having a first high refractive index optical element and at least one second high refractive index optical element. The method of claim 7, wherein The first high refractive index optical element and the second high refractive index optical element are each made of a high refractive index material exhibiting birefringence, and the first high refractive index optical element and the second high refractive index optical element are installed differently with respect to the birefringence direction so that the high refractive index optical element A projection objective in which the effect of birefringence caused by the elements is at least partially compensated for. The method according to claim 1 or 2, The final optical element is a projection objective lens, which is an integral planar lens made of a high refractive index material with a refractive index n> 1.6. The method according to claim 1 or 2, The final optical element is composed of at least two optical elements which are in contact with each other along the dividing interface, wherein at least one of the optical elements forming the final optical element is made of a high refractive index material having a refractive index n> 1.6. The method according to claim 1 or 2, The final optical element is a projection objective lens comprising an incidence plane convex lens element having an incidence side and a flat outgoing side of a curved surface, and an outgoing plane-parallel plate that is in optical contact with the convex lens element along a flat dividing plane. 12. The method of claim 11, The planar lens element is a projection objective lens made of a high refractive index material having a refractive index n> 1.6, and the exit-side plane-parallel plate is made of fused silica. 12. The method of claim 11, A projection objective lens consisting of fused silica and an exit-side plane-parallel plate made of a high refractive index material having a refractive index n> 1.6. The method of claim 10, The final optical element is shaped as a flat convex lens and the dividing surface is curved. The method according to claim 1 or 2, Projection objectives are projection objectives adapted to immersion fluids having refractive indices greater than 1.4 at an operating wavelength. 16. The method of claim 15, The projection objective is for a 193 nm operating wavelength and the immersion fluid is cyclohexane. The method according to claim 1 or 2, The image-side numerical aperture NA is a projection objective lens larger than 1.3. The method according to claim 1 or 2, The pupil plane located closest to the image plane is a projection objective positioned in the region of the local maximum beam diameter closest to the image plane and in the region of the beam that converges between the image plane. The method according to claim 1 or 2, A projection objective having an image plane and a lens furthest from it, a beam path converging from the lens to the image plane, and the pupil plane or system aperture located at a distance of at least 10 mm on the image side of the lens. As a microlithographic projection exposure method for imaging a pattern provided on a mask located on the object plane of the projection objective lens on a substrate provided on the image plane of the projection objective lens, a projection objective lens according to claim 1 or 2 is used. A microlithographic projection exposure method in which immersion fluid is introduced between the final lens of the projection objective and the substrate to be exposed. 21. The method of claim 20, Microlithographic projection exposure method in which an immersion fluid having a refractive index greater than 1.4 is used at the operating wavelength of the projection objective lens. 22. The method of claim 21, Immersion fluid microlithographic projection exposure method having a refractive index greater than 1.5 at the operating wavelength. 21. The method of claim 20, A microlithographic projection exposure method using the projection objective according to claim 1. 22. The method of claim 21, Microlithographic projection exposure method wherein cyclohexane is used as the immersion fluid. delete delete delete delete delete delete delete

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