JP5106858B2 - Projection objective having a high numerical aperture and a planar end face - Google Patents

Description

  The present invention relates to a projection objective that images a pattern arranged in its own object plane on its own image plane. This projection objective can be used in a microlithographic projection exposure apparatus. The present invention particularly relates to an exposure apparatus for a semiconductor structure that is designed for immersion treatment, that is, an image-side numerical aperture NA within an aperture range greater than 1.0.

  Especially in the case of optical reduction imaging of projection lithography, the image-side numerical aperture NA is limited by the refractive index of the surrounding medium in the image space. In immersion lithography, the theoretically possible numerical aperture NA is limited by the refractive index of the immersion medium. The immersion medium can be a liquid or a solid. The latter is also true for solid media.

However, for practical reasons, the numerical aperture should not be arbitrarily close to the refractive index of the last medium (ie, the medium closest to the image) because the propagation angle is very large relative to the optical axis. It is to become. It has proven practical that the numerical aperture does not substantially exceed about 95% of the refractive index of the last medium on the image side. This corresponds to a propagation angle of about 72 ° with respect to the optical axis. This corresponds to a numerical aperture of NA = 1.35 when water (n _{H2 O} = 1.43) is used as the immersion medium at 193 nm.

  When using a liquid having a refractive index higher than that of the last lens material or in the case of solid immersion, the material of the last lens element (ie the last optical element adjacent to the image of the projection objective) is the last It acts as a restriction on whether the design of the end surface (the exit surface of the projection objective lens) should be flat or very weakly curved. The planar design is advantageous, for example, for measuring the distance between the wafer and the objective lens, the hydrodynamic properties of the immersion medium between the wafer to be exposed and the last objective lens surface, and cleaning these. is there. Especially in the case of solid immersion, the last end face should be a planar design, which must likewise expose a planar wafer.

In DUV (operating wavelength of 248 nm or 193 nm), the material typically used for the last lens is fused silica (synthetic quartz glass, SiO ₂ ) or n _CaF2 = 1 with a refractive index of n _SiO2 = 1.56. CaF ₂ having a refractive index of .50. The synthetic quartz glass material is also simply referred to as “quartz” in the following. Since the radiation load on the last lens element is high, the synthetic quartz glass is damaged for a long time by this radiation load. Therefore, at 193 nm, calcium fluoride is preferable for the last lens. As a result, a numerical aperture of about 1.425 (95% of n = 1.5) can be achieved. If the disadvantage of radiation damage is acceptable, quartz glass further allows a 1.48 numerical aperture (corresponding to about 95% of the refractive index of quartz at 193 nm). This relationship is the same at 248 nm.

One object of the present invention is to provide a high numerical aperture of the projection objective lens capable to avoid the drawbacks of the prior design using immersion medium or fused silica and lens material such as CaF _2, such as water. It is yet another object of the present invention to provide a projection objective suitable for immersion lithography with an image side numerical aperture of at least NA = 1.35, having a reasonable size and material consumption.

BEST MODE FOR CARRYING OUT THE INVENTION

  As a method for achieving the above and other objects, the present invention is suitable for a microlithographic projection exposure apparatus that, according to one aspect, images a pattern disposed in its object plane onto its image plane. In a projection objective: consisting of a plurality of optical elements that are transparent to radiation at the operating wavelength of the projection objective; at least one optical element having a refractive index n ≧ 1.6 at the operating wavelength A projection objective is provided which is a high refractive index optical element made of a refractive index material.

  One embodiment preferably has an image-side numerical aperture greater than or equal to NA = 1.35 and at least the last lens element is a high refractive index material (refractive index n> 1.6, especially n> 1.8). It is comprised by the light-resistant lithography objective lens comprised by these.

In the following, various aspects of the present invention will be described in more detail using an exemplary embodiment for 193 nm. In these examples, the material used for the last lens element or part of the lens element is sapphire (Al ₂ O ₃ ), while the remaining lenses are made of fused silica. However, these examples can also be transferred to other high index lens materials and other wavelengths. For example, at 248 nm, germanium oxide (GeO ₂ ) can be used as the material of the last lens or part of the lens. In contrast to sapphire, this material has the advantage of not having birefringence. However, the material is no longer transparent at 193 nm.

  In the case of liquid immersion, NA> 1.35 can be achieved using an immersion liquid having a higher refractive index than water. In some applications, cyclohexane (refractive index n = 1.556) was used.

  An immersion medium with n> 1.6 is currently considered realistic.

  High refractive index immersion media can also be advantageous for small thicknesses because they generally also exhibit higher absorptance.

  The foregoing and other features are shown not only in the claims but also in the detailed description and drawings, wherein individual features may be used as embodiments of the invention, either alone or in subcombination, and others. As well as individually advantageous and patentable embodiments.

  In the following description of the preferred embodiment of the present invention, the term “optical axis” shall refer to a straight line or a series of straight lines passing through the center of curvature of the associated optical element. The optical axis can be bent by a refracting mirror (deflecting mirror). In the case of these examples presented herein, the relevant object is a mask (reticle) having either an integrated circuit pattern or some other pattern, for example a lattice pattern. In the example shown herein, the image of the object is projected onto a wafer that serves as a substrate covered by a photoresist layer, but other components such as liquid crystal display components or optical grating substrates. Different types of substrates are possible.

  Where tables are used to disclose the design details shown in the figures, the tables are indicated by the same numbers as the respective figures.

  FIG. 1 shows a first embodiment of a catadioptric projection objective 100 according to the present invention designed for an ultraviolet operating wavelength of about 193 nm. While this lens projects an image of a pattern on a reticle (or mask) placed in the object plane OP into the image plane IP at a reduced magnification, eg 4: 1, exactly two intermediate real images IMI1 and Designed to create IMI2. The first refractive objective lens portion ROP1 is designed to form a pattern in the object plane on the first intermediate image IMI1, and the second reflective (pure reflective) objective lens portion COP2 is the first reflective objective lens portion COP2. The first intermediate image IMI1 is formed on the second intermediate image IMI2 at a magnification close to 1: 1, and the third refractive objective lens portion ROP3 reduces the second intermediate image IMI2 on the image plane IP. Image at a rate. The second objective lens portion COP2 includes a first concave mirror CM1 having a concave mirror surface facing the object side, and a second concave mirror CM2 having a concave mirror surface facing the image side. The mirror surfaces are either continuous or non-intermittent, i.e. have no holes or holes. The mirror surfaces facing each other form an inter-mirror space surrounded by a curved surface formed by the concave mirror. The intermediate images IMI1 and IMI2 are both geometrically arranged inside the intermirror space, and at least the paraxial intermediate image is located sufficiently away from the mirror surface at the approximate center of the space.

  Each mirror surface of the concave mirror extends beyond the edge of the physical mirror surface and forms a “curvature surface” or “curvature surface” that is a mathematical surface that includes the mirror surface. The first and second concave mirrors are part of a rotationally symmetric curvature surface having a common rotational symmetry axis.

  The system 100 is rotationally symmetric and has a single linear optical axis AX that is common to all refractive and reflective optical elements. There is no refracting mirror. The concave mirror has a small diameter that allows these mirrors to be close together and can be quite close to an intermediate image located between the mirrors. Each of the concave mirrors is configured as an off-axis portion of an axisymmetric surface and is illuminated. The light beam passes through the edge of the concave mirror facing the optical axis without causing vignetting.

  Catadioptric projection objectives having this general structure are described, for example, in US Provisional Application Nos. 60 / 536,248 filed Jan. 14, 2004 and 60 / 587,504 filed Jul. 14, 2004. The application and the subsequent extension application filed on Oct. 13, 2004. The contents of these applications are incorporated in part of the specification of the present application. One unique feature of this type of catadioptric projection objective is that the pupil plane (in the axial position where the chief ray intersects the optical axis) is between the object plane and the first intermediate image, and Formed between the first and second intermediate images and between the second intermediate image and the image plane, all concave mirrors are optically far away from the pupil plane, in particular the principal ray height of the imaging process. Is disposed at a position exceeding the peripheral ray height of the imaging process. Furthermore, it is preferable that at least the first intermediate image is geometrically arranged 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 arranged in the inter-mirror space between the concave mirrors.

  The illustrative embodiments described below share these basic features that allow immersion lithography with numerical aperture NA> 1 by an optical system that can be constructed with relatively small amounts of optical material. ing.

  FIG. 1 shows, as a first illustrative embodiment, a lithographic objective lens for 193 nm having a sapphire lens and cyclohexane as an immersion medium with an image side numerical aperture of NA = 1.45. This sapphire lens is the last optical element LOE closest to the image plane. The image side working distance is 1 mm. This catadioptric design has two concave mirrors, mainly for color correction and Petzval correction, and intermediate images upstream and downstream of the pair of mirrors, respectively. However, these intermediate images are not fully corrected, mainly geometrically limiting the design and extending in a direction towards the mirror and in a direction away from the mirror after being reflected on the mirror. It serves to separate the beam path of the book. The image field (on the wafer) is rectangular. The outer diameter (wafer side) of the field is 15.5 mm, and the inner diameter is 4.65 mm. As a result, a 26 × 3.8 mm rectangular field is obtained.

  An aperture stop (aperture stop AS, system aperture) is arranged in the first refractive objective part ROP1 in the first exemplary embodiment. This is because, on the one hand, in order to form a smaller variable aperture stop, and on the other hand, the objective lens part (object plane (mask) that follows the object plane against the radiation load, which is largely unnecessary and interferes when the aperture stop is stopped. It is advantageous to protect (when viewed from the plane). The rear stop plane in the image side objective lens portion ROP3, that is, the position where the aperture stop can be arranged, is arranged in the convergent beam path in the region between the lens LMD with the maximum diameter and the image plane IP.

  In the front-side refractive objective lens portion ROP1 on the object side, a waist portion (a contraction portion of the beam and the lens diameter) that mainly serves to correct the image field curvature (Petzval sum) is formed. The aperture stop AS is disposed at the waist.

The use of CaF ₂ for the last lens is not preferred because it requires a numerical aperture of 1.425 or less (up to 95% of the refractive index of CaF ₂₎ as much as possible. At 193 nm, in this example sapphire (Al ₂ O ₃ ) is used as the high refractive index material in the last lens element LOE. In all the embodiments shown in the figures, optical elements made of sapphire are shaded gray for clarity.

  The birefringence that occurs when sapphire is used splits the last lens (last optical element LOE) into two lens elements LOE1 and LOE2 and rotates these two lens elements around each other about the optical axis. To compensate roughly. In this case, the dividing interface SI (the contact surface of the two lens elements LOE1 and LOE2) is preferably curved so that both lens elements have the same refractive power. As an alternative, for compensation, for example at a position close to the intermediate image or a position close to the object plane, it is made of sapphire arranged at a position in the objective lens that acts similarly from an optical point of view. A second element can be used. In the case of this example, the last sapphire lens LOE is divided into two lens elements LOE1 and LOE2 that perform substantially the same function. The front radius of these sapphire lenses LOE (i.e., the light incident side radius) is such that the aperture beam toward the center of the image field, i.e., the beam traveling in the image direction around the converging beam bundle is substantially refracted without being refracted. It is designed to pass through the interface, i.e. to impinge substantially perpendicular to the interface (the lens radius is substantially concentric with the intersection of the image plane and the optical axis). The radius of the split interface SI between the two lens elements of the split sapphire lens is flatter (the radius is less than 1.3 times the distance from the image plane on which the wafer can be placed).

  Compensation of the birefringence effect due to the relative rotation of elements made of birefringent materials corresponds to, for example, German patent 101 23 725 A1 (for example US 2004/0190151 A1), which is the applicant's patent application ) Or International Patent No. 03/077007 A2. A catadioptric projection objective with a final lens element closest to the image plane, designed as a split final lens made of birefringent material (calcium fluoride) is known from US Pat. No. 6,717,722B. It is.

  The design details of FIG. 1 are summarized in Table 1. The leftmost column lists the number of refractive, reflective or other designated surfaces, the second column lists the radius r [mm] of the surface, and the third column lists The distance d [mm] between one surface and the next surface, ie the parameter indicated as the “thickness” of the optical element, is listed, and the fourth column lists the materials used to manufacture the optical element. The fifth column lists the refractive index of the material used for its manufacture. The sixth column lists the effective optically usable radius [mm] of the optical element. In these tables, a radius value r = 0 is given for a plane having an infinite radius.

For this particular embodiment, the fifteen surfaces are aspheric. Table 1A lists the relevant data for these aspheric surfaces, from which the surface shape sagittal as a function of height h can be calculated using the following equation:

  Here, the reciprocal of the radius (1 / r) is the curvature at the surface vertex of the surface in question, and h is the distance from the optical axis to a point on the surface. Therefore, the sagittal p (h) represents the distance measured along the optical axis along the z direction from the surface vertex of the surface in question to the surface point. Constants K, C1, C2, etc. are listed in Table 1A.

  Similarly, the specifications of the following embodiments are in Tables 2 and 2A for FIG. 2, Tables 3 and 3A for FIG. 3, Tables 4 and 4A for FIG. 4, and Tables 5 and 5A for FIG. It is shown.

In the reference projection objective 200 according to FIG. 2, the last optical element LOE on the image side has the overall shape of a plano-convex lens. This lens is further divided into two optical elements LOE1 and LOE2 that are in contact with each other along the planar dividing interface SI. Specifically, a quartz glass lens LOE1 having an entrance surface with a positive radius of curvature and a planar rear side surface is brought into close contact with one (or two) parallel plane plates LOE2 made of sapphire. The NA value obtained in this way is at most the height possible in quartz glass, but the advantage is that the propagation angle of the light beam is reduced in the last objective lens part where the aperture is maximized by a high refractive index medium. is there. This is advantageous in view of reflection losses and scattered light effects at the interface and the protective layer that can be provided on the last end face, which constitutes a very large propagation angle problem. As a result, the maximum angle occurs only on the contact surface between the quartz lens LOE1 and the first high-refractive-index parallel flat plate LOE2. This close contact surface (contact interface where adjacent optical elements are bonded together by close contact) can be designed with a coating that is protected against contamination and damage and is also sensitive to environmental effects. When the parallel plane high refractive index element LOE2 is formed by using two parallel plane plates, ideally, two parallel plane plates made of sapphire are rotated with respect to each other around the optical axis. The birefringence effect can be substantially compensated for S and P polarizations in the x and y directions, which are mainly required to image the semiconductor structure.

  However, due to the lower refractive index, the quartz lens LOE1 is very much here because the condensing effect is lower, even though the image-side numerical aperture of the limited full length projection objective is not really large. The effect is that a large lens diameter is required. In the second exemplary embodiment (FIG. 2), the numerical aperture is NA = 1.35, but the lens diameter is larger than in the first exemplary embodiment. In this case, the lens diameter has already exceeded 143 mm and is therefore substantially 212 times the numerical aperture, while in the exemplary embodiment of FIG. 1, only 200 times the numerical aperture is achieved. In particular, in the illustrative embodiment of FIG. 2, a maximum half lens diameter of 143 mm exceeds even a mirror radius of about 136 mm.

Still another embodiment of the design example with NA = 1.45 (projection objective 300) to minimize the diameter of the largest lens element of the projection objective and at the same time minimize the effect of birefringence The last lens element LOE is formed of a thin sapphire lens LOE1 having a positive refractive power, a spherically curved entrance surface and a flat exit surface, which is brought into close contact with the thin quartz glass plate LOE2. Illustrative reference embodiment 3 of FIG. Thereby, the parallel flat quartz glass plate used as the exit surface of this objective lens can be replaced when damage occurs due to radiation load. Therefore, the quartz plate that is brought into close contact also acts as a replaceable protector against contamination and / or scratching or destruction of the sapphire lens LOE1. Embodiment 3 is adapted to cyclohexane as an immersion liquid having a refractive index (n = 1.556) similar to that of fused quartz (n = 1.560) used for the plate in contact with the immersion liquid. ing.

  In these cases, NA is limited by the refractive index of quartz glass. However, as a result, compared to a design with a last lens made of pure quartz glass, the beam angle is smaller upstream of the last lens, and hence the overall objective lens diameter is also smaller. At the same time, the sensitivity of the last lens element (disturbance sensitivity to manufacturing tolerances) is also lower. For this reason, in Embodiment 3, the maximum lens diameter of 135 mm is about 186 times the numerical aperture.

  Of course, the present invention can also be used with low numerical aperture objectives to substantially reduce the diameter of previous projection objectives. This has a beneficial effect on the price of the projection objective, since the amount of material can be substantially reduced.

In an illustrative fourth reference embodiment (FIG. 4), NA = at a working distance of 1 mm using a single last lens made of sapphire and water (n _H2O = 1.43) as immersion medium. A 193 nm lithography objective 400 that achieves 1.35 is shown. The top surface (incident surface) of this single-piece (single component, non-divided) sapphire lens LOE is an aspheric surface, and the aperture stop AS is the third side of the image-side refractive objective lens portion ROP3. Of the biconvex lens LMD having the maximum diameter in the objective lens portion ROP3 of the objective lens portion ROP3. The maximum lens diameter is limited to less than 190 times the numerical aperture.

  By utilizing a high refractive index material for at least the last lens element, a numerical aperture of even greater than NA = 1.45 is possible.

A fifth illustrative reference embodiment 500 (FIG. 5) is designed for solid immersion (contact projection lithography) using planoconvex sapphire lenses LOE (n _sapphire = 1.92) for NA = 1.6. Has been. Therefore, in principle, even numerical apertures up to NA> 1.8 are possible. In this example, the field outer diameter on the wafer side is 15.53 mm and the inner diameter is 5.5 mm. In other words, the size of the rectangular field in this case is 26 × 3 mm.

  A high numerical aperture beam with a numerical aperture of NA> 0.52 undergoes total reflection during the transition from sapphire to air at the planar exit surface, so that solid immersion provides a working distance below the operating wavelength, Wafers must be exposed efficiently using evanescent waves. This can be done in vacuum by always placing the wafer to be exposed, for example at 100 nm (≈λ / 2) at a position close to the last lens surface.

  However, the power transmitted through the evanescent field is based on the exponential decay with distance, so that small changes in distance cause large variations in uniformity so that the wafer is projected to the last end face of the projection objective ( It is advantageous to make direct physical contact with the exit surface. For exposure, the wafer is brought into close contact with the last planar lens surface (contact surface CS) and exposed to obtain physical contact between the exit surface of the projection objective and the input coupling surface associated with the substrate. be able to. In this case, scanning step mode or stitching exposure, i.e. areas larger than the image field are exposed in separate steps, and the reticle mask is adjusted accordingly instead of the conventionally customary wafer. Are preferably aligned. This is also advantageous because the reticle can be adjusted with less accuracy than wafer adjustment for reduced imaging. Thereby, in a subsequent exposure step, adjacent exposure areas (target sections) or a series of levels of the semiconductor structure are superimposed by lateral and axial movement and rotation of the reticle mask, thereby causing the semiconductor The structure is exposed on a wafer that can be incompletely attached with a registration accuracy of over a few nanometers. To that end, for example, the alignment mark of the reticle is matched to the alignment mark already exposed on the wafer.

  Dissociation of the wafer from the last side is preferably done in a vacuum. If it is required, a thin layer (film / thin film) is placed between the wafer and the last planar lens surface, which can be exchanged after each exposure step, for example. This thin film is, for example, kept fixed on the wafer, can aid in dissociation, and in particular serves as a protector for the last planar lens surface. The lens surface can optionally be additionally protected by a thin protective layer.

  In the case of solid immersion, high intensity standing waves can be generated in the edge region of the last lens surface during exposure due to the illustration of imaging disturbances. Therefore, in order to repeatedly expose a structure on a wafer, if the wafer is unexpectedly placed within a certain range of a few micrometers due to close contact, it can be adjusted using a reticle. It is even more advantageous to compensate for something to prevent the systematic structure from being burned into the last lens.

  All the exemplary embodiments described above are such that in a catadioptric projection objective having exactly two concave mirrors and exactly two intermediate images, all optical elements are one non-refracting straight line. A projection objective that is aligned along a typical optical axis. Certain basic types of projection objectives selected for the description of the preferred variants of the invention have several fundamental variants and technical effects and advantages associated with the different variants of the invention. It is intended to help in illustrating. However, a lens or lens element made of a high refractive index material (for example, n ≧ 1.6, or even n ≧ 1.8) is used as described above, particularly in a projection objective lens for operating wavelengths in the far ultraviolet region (DUV). This is not limited to this type of projection objective. The invention can also be incorporated in purely refractive projection objectives. In these types, the last optical element closest to the image plane is often a plane that can be designed, for example, according to the general rules described above with respect to the last optical element LOE in each of the first to fifth embodiments. It is a convex lens. Examples include, for example, Applicant's US patent application Ser. Nos. 10 / 931,051 (see also WO 03/075049 A), 10 / 931,062 (see also US 2004/0004757 A1). No. 10 / 379,809 (see also US 2003/01744408) or International Patent No. 03/077036 A. The disclosures of these documents are incorporated herein by reference.

  Similarly, the present invention provides a catadioptric projection objective having only one concave mirror or a catadioptric projection objective having two concave mirrors in an arrangement different from that shown in the figure, or two. It can also be implemented in embodiments having a greater number of concave mirrors. Furthermore, the present invention can be used regardless of whether a refractive mirror is present in the optical design. Examples of catadioptric systems include, for example, Applicants' U.S. Patent Application Nos. 60 / 511,673, 10 / 743,623, 60 / 530,622, 60 / 560,267 or U.S. Pat. It is shown in 2002/0012100 A1. The disclosures of these documents are incorporated herein by reference. Other examples are shown in US 2003/0011755 A1 and related applications.

Similarly, the invention can be implemented in projection objectives that do not have intermediate images or have an appropriate number of intermediate images as required.

1 is a longitudinal sectional view of a first embodiment of a catadioptric projection objective according to the present invention. FIG. FIG. 6 is a longitudinal sectional view of a second embodiment of a catadioptric projection objective according to the present invention. FIG. 6 is a longitudinal sectional view of a third embodiment of a catadioptric projection objective according to the present invention. FIG. 6 is a longitudinal sectional view of a fourth embodiment of a catadioptric projection objective according to the present invention. 6 is a longitudinal sectional view of a fifth embodiment of a catadioptric projection objective according to the present invention. FIG.

Claims (13)

In a projection objective suitable for a microlithographic projection exposure apparatus, in which a pattern arranged in the object plane of the projection objective is imaged on the image plane of the projection objective:
It comprises a plurality of optical elements that are transparent to radiation at the operating wavelength of the projection objective, and at least one optical element is made of a high refractive index material having a refractive index n ≧ 1.6 at the operating wavelength. High refractive index optical element to be manufactured,
A last optical element closest to the image plane, and with respect to aberrations, the image side working distance between the last optical element and the image plane is adapted to be filled by an immersion medium having a refractive index greater than 1. Designed as an immersion objective,
The last optical element is constituted by at least two optical elements that are in optical contact with each other along the dividing interface, and the dividing surface is curved ,
The last of the at least one of the optical elements forming the optical element, the projection objective lens that consists by a high refractive index material having a refractive index n> 1.6.   The projection objective according to claim 1, wherein the high refractive index material has a refractive index n ≧ 1.8 at the operating wavelength.   The projection objective according to claim 1, wherein the high refractive index material is sapphire.   The projection objective according to claim 1, wherein the high refractive index material is germanium dioxide.   A first high-refractive-index optical element; and at least one second high-refractive-index optical element made of the same material as the first high-refractive-index optical element, Each of the second high refractive index optical elements is made of a high refractive index material exhibiting birefringence that defines the birefringence orientation of each optical element, and the first and second high refractive index optical elements are 5. Projection according to one of the preceding claims, arranged differently with respect to the orientation of the birefringence, so that the birefringence effect provided by the high refractive index optical element is at least partially compensated. Objective lens. The projection objective according to claim 1 , wherein the last optical element is shaped as a plano-convex lens, and the dividing surface is curved so that both optical elements in contact with the dividing surface become a lens portion having the same refractive power. lens.   Projection objective according to claim 1, adapted for an immersion liquid having a refractive index greater than 1.4 at the operating wavelength. 8. Projection objective according to claim 7 , designed for an operating wavelength of 193 nm, wherein the immersion liquid is cyclohexane. Projection objective according to one of claims 1-8 where the image side numerical aperture NA precedes exceeds 1.3. Pupil plane that is located closest to the image plane, claim the preceding are arranged in the region of the converging beam between the region and the image plane of the nearest local maximum beam diameter in the image plane 1-9 The projection objective lens according to 1 above. A microlithographic projection exposure method for imaging a pattern provided on a mask arranged in an object plane of a projection objective on a substrate arranged in an image plane of the projection objective, the preceding claim 11. A method in which the microlithographic projection objective according to any one of 1 to 10 is used, and an immersion liquid is introduced between the last lens of the microlithography projection objective and the substrate to be exposed. 12. The method according to claim 11 , wherein an immersion liquid having a refractive index greater than 1.4 at the operating wavelength of the projection objective is used. The method of claim 12 , wherein the immersion liquid has a refractive index greater than 1.5 at the operating wavelength.

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