Projection lens, projection exposure apparatus, and projection exposure method

Abstract

A refractive projection lens (PO) for imaging a pattern disposed on an object plane (OS) of a projection lens onto an image plane (IS) of the projection lens using electromagnetic radiation from the ultraviolet region longer than 280 nm includes a plurality of lens elements arranged between the object plane (OS) and the image plane (IS) along an optical axis (AX) and implemented such that a pattern disposed on the object plane can be imaged onto the image plane using the lens elements, a diaphragm position (BP) suitable for mounting an aperture diaphragm (AS) is positioned between the object plane and the image plane, a chief ray of imaging intersects with the optical axis at said diaphragm position, and the lens elements include at least one flint lens element made of a first material having a relatively low Abbe number and at least one crown lens element made of a second material having a higher Abbe number with respect to the first material. A crown lens element having a positive refractive power, at least one flint lens element having a negative refractive power, and two or less flint lens elements (L16) having a negative refractive power are arranged in an aperture region (BB) surrounding an aperture position (BP), and a condition |CRH / MRH|<1 is applied to the ray height ratio CRH / MRH between the chief ray height CRH of the image and the marginal ray height MRH.

Description

[Technical Field]

[0001] The following disclosures are incorporated by reference in this application based on German Patent Application No. 102022201001.9, filed on 31 January 2022.

[0002] The present invention relates to a refractive projection lens for imaging a pattern placed on the objective surface of a projection lens onto the image plane of the projection lens using electromagnetic radiation with an operating wavelength in the ultraviolet region longer than 280 nm, a projection exposure apparatus equipped with a projection lens, and a projection exposure method that can be performed using a projection lens. [Background technology]

[0003] Microlithography projection exposure is currently primarily used for the manufacture of semiconductor components and other microstructure components, such as photolithography masks. In this case, a mask (reticle) or other pattern-generating device is used to support or form the pattern of the structure to be imaged, such as the wiring pattern of a layer of a semiconductor component. The pattern is positioned in the region of the objective plane of the projection lens between the illumination system and the projection lens in the projection exposure apparatus and is illuminated by illumination radiation supplied by the illumination system. The radiation modified by the pattern travels through the projection lens as projection radiation, and the projection lens images the pattern onto the substrate to be exposed. The surface of the substrate is positioned in the image plane of the projection lens, and the image plane is optically conjugate to the objective plane. The substrate is entirely coated with a radiation-sensitive layer (resist, photoresist).

[0004] Typically, the requirements for semiconductor component manufacturing differ depending on whether the exposure is for critical or non-critical structures. Currently, critical structures, or microstructures, are primarily manufactured using refractive or reflective immersion systems operating in the deep ultraviolet (DUV) region, specifically at an operating wavelength of approximately 193 nm. Currently, the finest structures are exposed using EUV systems. These are projection lithography systems that construct structures using only reflective components operating in the extreme ultraviolet (EUV) region at operating wavelengths between approximately 5 nm and 20 nm, for example, about 13.4 nm.

[0005] Non-critical structures, i.e., coarser structures, can be exposed using simpler, and therefore more cost-effective, systems.

[0006] To fabricate intermediate critical or non-critical layers with typical structural dimensions significantly exceeding 150 nm, projection lithography equipment designed for operating wavelengths in the ultraviolet region of approximately 280 nm to 400 nm is conventionally used. In this wavelength range, refractive projection lenses are typically used, as their fabrication is easily controllable due to rotational symmetry around the optical axis.

[0007] For these applications, projection lithography systems (so-called i-line systems) with an operating wavelength of 365.5 nm ± 2 nm are particularly commonly used. These use the i-line of a mercury lamp, and their intrinsic total bandwidth is limited to a narrower usable bandwidth Δλ, e.g., about 4 nm, using filters or any other method. During projection, ultraviolet light with a relatively wide wavelength range is used so that the projection lens inevitably provides relatively strong correction for chromatic aberration, ensuring low-aberration imaging with the desired resolution even when using broadband projection light. Specifically, longitudinal chromatic aberration (CHL) needs to be corrected to obtain sufficient image quality.

[0008] For broadband refractive projection lenses, different lens element materials with sufficiently different dispersion characteristics are used for color correction (i.e., correction of chromatic aberration), and these lens element materials need to be dispersed within regions of the projection lens that have different ray height ratios. Typical transparent materials used in i-ray projection lenses include synthetic fused silica (SiO2) and special glasses marketed by Schott AG in Mainz, Germany, under the names FK5, LF5, and LLF1. Among these optical glasses, synthetic fused silica and FK5 glass are typical examples of relatively low-dispersion glasses (crown glasses), while LF5 and LLF1 glass are typical examples of relatively high-dispersion glasses (flint glasses). Other manufacturers offer different names for each type of glass.

[0009] Therefore, within this application, lens elements made of crown glass are referred to as "crown lens elements," and lens elements made of flint glass are referred to as "flint lens elements."

[0010] As already mentioned, in these systems, at least the lowest-order longitudinal chromatic aberration, known as the "first-order spectrum," must be completely corrected. A specialized paper, for example, Volker Witt, “Wie funktionieren Achromat und Apochromat”, Sterne und Weltraum 10 / 2005, pp. 72-75 (http: / / rohr.aiax.de / SUW_2005_10_S072.pdf), discloses how the lowest-order longitudinal chromatic aberration can be corrected in an optical imaging system using crown and flint lens elements. From this paper, it is clear that the use of at least a divergent flint lens element and a converging crown lens element is essential to correct the longitudinal chromatic aberration of the imaging system.

[0011] Applying this teaching to projection lenses, it can be inferred that longitudinal chromatic aberration can be corrected using a combination of at least one crown lens element with positive refractive power and at least one flint lens element with negative refractive power. This lens element pair needs to be positioned in a region of the optical imaging system where the peripheral rays of the image have the largest possible ray height (peripheral ray height). Typically, this corresponds to the aperture region near the system aperture.

[0012] It is virtually impossible to track the number of different designs of refractive i-ray projection lenses. U.S. Patents 6,806,942 and 5,930,049 provide examples.

[0013] A common feature of many of the i-ray projection lens embodiments described in these patent documents is that neither the type of glass nor the dispersion of the glass is specified, and only the principal refractive index of the glass is revealed from the design sheet. In some cases, a great many different glasses with different refractive indices are used. The system was analyzed according to the refractive index of the materials used, and it was assumed that glasses with high refractive indices were flint-type glass, while glasses with lower refractive indices were crown-type glass. Assuming that this distinction between crown-type and flint-type glass is valid, it appears to have been established that the vast majority of crown-type lens elements have a positive refractive index, and at least one flint-type lens element has a greater negative refractive power, are used systematically near the system aperture for the purpose of correcting longitudinal chromatic aberration.

[0014] Furthermore, it is possible to identify a tendency for many of the analyzed projection lenses to contain a number of additional lens elements (i.e., presumably flint lens elements) with high refractive indices. For example, of the 31 lens elements in the projection lens of U.S. Patent No. 5,930,049, only 8 lens elements consisted of a lower refractive index material with a refractive index of 1.488 (possibly fused silica with n365=1.47455), while the remaining 23 lens elements were manufactured from a higher refractive index material with n=1.613 (possibly LF5 with n365=1.619262). [Overview of the initiative]

[0015] The object of the present invention is to provide a projection lens, a projection exposure apparatus, and a projection exposure method that function with UV radiation in the ultraviolet region with operating wavelengths longer than 280 nm, specifically with mercury i-line UV radiation, enabling a high throughput rate.

[0016] To solve this problem, the present invention provides a refractive projection lens having the features of claim 1. Furthermore, a projection exposure apparatus having the features of claim 11 and a projection exposure method having the features of claim 14 are also provided. Advantageous developments are specified in the dependent claims. The expression of all claims is incorporated herein by reference.

[0017] According to the claimed expression of the present invention, a refractive projection lens is provided, which is constructed to image a pattern placed on the objective plane of a projection lens onto the image plane of the projection lens using electromagnetic radiation in the ultraviolet region with an operating wavelength longer than 280 nm. All optical elements with refractive power are lens elements, i.e., refractive optical elements. In other words, the projection lens comprises only lenses and does not include diffractive optical elements (DOEs) with optical power. The lens is positioned between the objective plane and the image plane along the optical axis and is constructed so as to produce this image. A suitable aperture position for mounting an aperture diaphragm is located between the objective plane and the image plane, at which the principal ray of the image intersects the optical axis. The lens element comprises at least one flint lens element made of a first material having a relatively low Abbe number and at least one crown lens element made of a second material having a higher Abbe number than the first material. At least one crown lens element having a positive refractive power and at least one flint lens having a negative refractive power, but two or fewer flint lenses having a negative refractive power, are arranged in the aperture region surrounding the aperture position.

[0018] The aperture region is distinguished by the condition |CRH / MRH|<1 being applied to the ratio of the principal ray height CRH to the peripheral ray height MRH in the image formation region. Therefore, the aperture region is the region where the peripheral ray height is greater than the principal ray height.

[0019] Therefore, two or fewer negative lens elements made of the first material are arranged in the aperture region in addition to at least one positive lens element made of the second material, and at least one negative lens made of the first material must be present in the aperture region.

[0020] This invention is based particularly on the following considerations: In order to correct chromatic aberration in a general-purpose imaging optical system, such as a projection lens, specifically to correct its longitudinal chromatic aberration, the individual lens elements of the lens need to be manufactured from flint material. However, flint material has several undesirable properties. For example, flint glass typically exhibits reduced transmittance of the light used, which is equivalent to an increase in absorptivity. This can lead to undesirable side effects such as lens heating and / or material compression. Also, all current flint materials that are transparent in the wavelength range around 365 nm contain a considerable amount of lead and further heavy metals, and therefore the use of these glasses is permitted only by special authorization. Equivalent lead-free alternative glasses are not currently practically available. Therefore, it is considered advantageous to develop a general-purpose projection lens that reduces the use of flint lens elements compared to the prior art.

[0021] For the first approximate reason, the longitudinal chromatic aberration of a lens element is proportional to the square of the peripheral ray height at the position of the lens element (and proportional to the refractive power of the lens element and inversely proportional to the Abbe number). Therefore, a flint lens element with negative refractive power in the region of high peripheral ray height can contribute particularly effectively to color correction, specifically to the correction of longitudinal chromatic aberration (CHL). Nevertheless, the present invention teaches only the reduction of the use of these correction means.

[0022] By restricting the use of flint lens elements, it is possible to improve the overall transmittance compared to conventional systems that use many flint lens elements, and as a result, a higher throughput can be achieved. In addition, the tendency of lens heating can be reduced.

[0023] According to one development, the projection lens having an imaging scale exceeding 4:1, that is, (|β|>0.25), helps to obtain the above-mentioned desired advantages. By way of example, the imaging scale may be 2:1 (|β|=0.50) or less, optionally 1:1 (|β|=1). Such reduction of the lens is not as great as in the case of conventional i-line projection lenses, which are often designed for 4:1 or 5:1 reduction. This approach is based in particular on the following considerations. That is, the throughput of the system can be improved compared to a projection lens with greater reduction (for example, |β|=0.25 or less). In the case of a constant geometric étendue LLW, there is a reduction in the image-side numerical aperture NA and the Rayleigh unit, thus increasing the depth of field range. As a result, the system becomes less susceptible to longitudinal aberrations such as defocus, astigmatism or field curvature. In some cases, this opens up the possibility of significantly reducing or even completely omitting correction for chromatic variation of the Petzval sum. This in turn directly affects the number of flint lens elements that are absolutely necessary in the lens, and can keep this number relatively low.

[0024] The geometric étendue LLW is the (dimensionless) object-side numerical aperture NA O multiplied by the object field size parameterized by the object field height OBH (in millimeters), that is, LLW=|OBH*NA O | can be defined as.

[0025] The object field height OBH corresponds to the object field radius, that is, the radius of the smallest circle surrounding object field points for which optical correction satisfies the specification, i.e., is sufficiently good. This circle needs to be large enough to enclose the effective object field.

[0026] In many embodiments, for an imaging scale of β=-0.5, the image-side numerical aperture NA is less than 0.4, and preferably the condition 0.1<NA<0.4 applies.

[0027] In many embodiments, the geometric etendue LLW is at least 7 mm, and preferably the condition 10 mm<LLW<18 mm applies.

[0028] Some embodiments are distinguished in that they include only a single negative lens element made of flint material, that is, only a single flint lens element having negative refractive power. Therefore, this correction means uses only the minimum necessary number of elements.

[0029] In some embodiments, this negative lens element made of flint material is the only flint lens element in the projection lens, and thus the projection lens may in some cases include exactly one flint lens element only. As a result, the use of flint material is reduced to a minimum.

[0030] Preferably, the only flint lens element is a biconcave lens element. In the case of a biconcave lens element, large refractive power (or curved surface) can be achieved with a not-so-large incident angle.

[0031] Preferably, the single flint lens element having negative refractive power is arranged in a stop region, specifically in a region where the condition |CRH / MRH|<0.5 or even |CRH / MRH|<0.2 applies to the ray height ratio. Since the longitudinal chromatic aberration CHL of a lens element is proportional to the square of the marginal ray height at the position of the lens element (and proportional to the refractive power of the lens element, and inversely proportional to the Abbe number), a flint lens element with negative refractive power in a region with large marginal ray height can particularly effectively contribute to color correction, specifically correction of longitudinal chromatic aberration CHL. As a result, a large contribution to the correction of chromatic aberration, specifically longitudinal chromatic aberration, can be achieved.

[0032] There are embodiments in which all lens elements made of flint material are negative lens elements. There are also embodiments in which no positive lens elements made of flint material are provided. Furthermore, there are embodiments in which exactly two flint lens elements are provided.

[0033] After correcting the lowest-order longitudinal chromatic aberration ("first-order spectrum") by using at least one flint lens element with negative refractive power in the aperture region, the chromatic change due to field curvature remains as a limiting chromatic aberration. Therefore, it may be advantageous to use at least one positive lens element made of flint material, especially considering the correction of the chromatic change due to field curvature.

[0034] Flattening the field of view is a critical requirement for the optical quality of projection lenses with a wide field of view. The requirement for this is that the Petzval sum of the projection lens should be as small as possible, specifically zero. In optical systems where the majority are made of a specific material (e.g., crown glass such as FK5 or synthetic fused silica) and a small number of lens elements are made of a second material (in this case, flint glass, e.g., LF5), the inventors have found that it is possible to derive the requirement that the Petzval sum must be corrected as much as possible within each material group. This cannot be satisfied if only negative dispersion lenses made of flint glass are used. Therefore, some embodiments provide a projection lens that includes at least one lens element (converging lens) with positive refractive power made of the first material, i.e., at least one positive flint lens element. What this makes possible is that the chromaticity change of the Petzval sum is sufficiently small or zero.

[0035] The use of a positive lens element made of flint material is an obstacle to correcting longitudinal chromatic aberration (CHL) using a negative lens element made of flint material. Therefore, the positive lens element should be used at a point in the beam path where the peripheral ray height is small, so as to contribute little to the correction of longitudinal chromatic aberration. This is in the optical vicinity of the field plane, i.e., in the vicinity of the objective plane, the image plane, or, if an intermediate image is generated between the objective plane and the image plane, in the optical vicinity of the intermediate image plane. Preferably, the positive lens element made of flint material is placed in a region where the ray height ratio |CRH / MRH| is greater than 0.5, or greater than 0.7, or greater than 1, or greater than 2.

[0036] According to one development, the projection lens is implemented as a single constriction system. This includes a first group of lens elements having a positive refractive power close to the objective plane, a second group of lens elements having a negative refractive power following the first group to create a constriction surrounding the region of minimum ray height between the objective plane and the image plane, a third group of lens elements having a positive refractive power following the second group, between the second group of lens elements and the aperture position, and a fourth group of lens elements having a positive refractive power between the aperture position and the image plane. Thus, the refractive power sequence PNPP is achievable, where "P" represents a group of lens elements having a positive refractive power as a whole, and "N" represents a group of lens elements having a negative refractive power as a whole. The projection lens can be implemented such that there are no further groups of lens elements other than the four groups of lens elements described above. In that case, the first group of lens elements follows immediately after the objective plane.

[0037] To obtain a higher numerical aperture, it may be advantageous to place a front negative group having at least one lens element with negative refractive power between the objective plane and the first lens element group. Thus, the refractive power sequence NPNPP is feasible. When the projection lens is designed as a single constriction system, it can make a significant contribution to Petzval correction in the case of a compact overall construction.

[0038] A particularly practically useful class of projection lenses is implemented as a single constricted system in which the projection lens has a refractive power sequence N-P-N-P-P, wherein the image-side numerical aperture NA is in the range of 0.2 < NA < 0.4, the imaging scale is on the order of 2:1 (|β|=0.50) or less, the geometric etendue LLW is in the range of 10 mm < LLW < 18 mm, and the projection lens includes only a single flint lens having negative refractive power.

[0039] Preferably, the projection exposure apparatus, and thus also the projection lens, is designed for radiation of the i-line of a mercury lamp (having a central operating wavelength of about 365.5 nm, optionally with a limited bandwidth of several nanometers). i-line systems function using a mercury lamp as a light source, and use only i-line for imaging. Suitable coatings for lenses and good photoresists are sufficiently well established especially for these powerful light sources, and therefore prior developments can be relied on in this regard. However, other light sources and / or UV operating wavelengths can also be used. By way of example, if the projection lens is corrected for a corresponding broadband type, two or three lines of a mercury lamp (g-line, h-line and i-line at about 436 nm, about 405 nm and about 365 nm, respectively) can be used simultaneously. Alternatively, for example, a frequency-tripled Nd:YAG laser of about 355 nm can be used. There are also various LED light sources that emit wavelengths between 360 nm and 400 nm. Optionally, the emission range may be slightly adjusted.

[0040] Further advantages and aspects of the present invention will become apparent from the claims and the following description of exemplary embodiments of the invention given with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] [Figure 1] It is a schematic diagram of a projection exposure apparatus according to an exemplary embodiment. [Figure 2] It is a schematic meridional sectional view of lens elements of a projection lens according to a first exemplary embodiment. [Figure 3]This figure shows a schematic cross-sectional view of the meridional lens element of a projection lens according to a second exemplary embodiment. [Figure 4] This figure shows a schematic cross-sectional view of the meridional lens element of a projection lens according to a third exemplary embodiment. [Figure 5] This figure shows a schematic cross-sectional view of the meridional lens element of a projection lens according to the fourth exemplary embodiment. [Figure 6] This figure shows a schematic cross-sectional view of the meridional lens element of a projection lens according to the fifth exemplary embodiment. [Figure 7] This figure shows a schematic cross-sectional view of the meridional lens element of a projection lens according to the sixth exemplary embodiment. [Figure 8] This figure shows a schematic cross-sectional view of the meridional lens element of a projection lens according to the seventh exemplary embodiment. [Modes for carrying out the invention]

[0042] Figure 1 shows an example of a microlithography projection exposure system (WST) that can be used in the fabrication of semiconductor components and other microstructure components, and which operates with ultraviolet (UV) light or electromagnetic radiation to obtain a resolution of up to a few micrometers. A mercury lamp functions as the primary radiation source or light source (LS). The lamp emits a broad spectrum with relatively high intensity I emission lines in the wavelength range having center wavelengths of approximately 436 nm (visible light, blue, g-line), approximately 405 nm (visible light, violet, h-line), and approximately 365.5 nm (near ultraviolet, UV-A, i-line). This portion of the spectrum is shown in the I(λ) schematic diagram.

[0043] The projection exposure system is an i-line system that uses only light from the i-line, i.e., UV light centered around a central operating wavelength of approximately 365.5 nm. The intrinsic total bandwidth of the i-line is limited to a narrower usable bandwidth Δλ, for example, approximately 5 nm, using filters or any other method.

[0044] At the exit surface ES, the illumination system ILL, positioned downstream of the light source LS, produces a wide, well-defined, substantially uniformly illuminated field of view, which is adapted to the telecentric requirements of the projection lens PO positioned downstream in the optical path. The illumination system ILL has a device for setting different illumination modes (illumination settings), and is switchable, for example, between conventional on-axis illumination with different coherence degrees σ and off-axis illumination.

[0045] These optical components, which receive light from the light source LS and form illumination radiation directed towards the reticle M, are part of the illumination system ILL of the projection exposure apparatus.

[0046] Downstream of the illumination system, a device RS is positioned to hold and manipulate the mask M (reticle) such that the pattern placed on the reticle is positioned on the objective surface OS of the projection lens PO, which coincides with the emission surface ES of the illumination system and is also referred to herein as the reticle surface OS.

[0047] Downstream from the reticle surface OS, there is an imaging system that projects an image of the pattern placed on the mask M onto a substrate W covered with a photoresist layer, where the photosensitive substrate surface SS is located in the region of the image plane IS of the projection lens PO, at a defined imaging scale, for example, a reduction scale of 1:2 (|β|=0.50).

[0048] In this example, the substrate to be exposed, which is a semiconductor wafer W, is held by a device WS also called a "wafer stage".

[0049] The illumination field generated by the illumination system ILL defines the effective objective field OF used during projection exposure. In this illustrated example, the effective objective field is rectangular, has a height A* measured parallel to the y-direction, and has a width B* < A* measured perpendicular thereto (in the x-direction). The aspect ratio AR=B* / A* is approximately 104 / 132. The effective objective field is located at the center of the optical axis (on-axis field). In a system having this field size, a typical 6-inch reticle can be imaged in a single exposure step.

[0050] However, scanning systems are also often used, whose objective field is 104×132 mm 2 and is smaller, for example only 104×28 mm 2 .

[0051] The effective image field on the image plane IS, which is optically conjugate with the effective objective field, has the same shape and the same aspect ratio of height B to width B as the effective objective field, but in the case of a projection lens having a reduction effect (due to |β|<1), the absolute field dimension is reduced by the imaging scale β of the projection lens, that is, A=|β|A* and B=|β|B*. In the case of a 1:1 system (imaging scale |β|=1), the image field has the same size as the effective objective field.

[0052] When the field size of the image field is 26×33 mm, a complete "die" can be exposed in a single exposure step without scanning. The term "die" refers to a single unpackaged piece of a semiconductor wafer in semiconductor and microsystem technology. Accordingly, the projection exposure apparatus can be designed as a wafer stepper for step-and-repeat processes. A device for performing a scanning operation for die exposure can be omitted. The projection exposure apparatus can also be designed as a wafer scanner for step-and-scan processes. In that case, it is necessary to provide a device for performing a scanning operation for die exposure.

[0053] In this rotationally symmetric system, a circle centered on the optical axis OA, enclosing the effective objective field of view OF and tangent to the angles of the effective objective field of view, defines the size of the objective field of view within which optical corrections at all field points must meet specifications. This also applies to all field points within the effective objective field of view. The more complex the aberration correction, the larger this objective field of view needs to be. In this case, the size of the circle is parameterized by the objective field radius OBH or half the objective field diameter OBH, where OBH also corresponds to the maximum field height of the objective field points.

[0054] To better understand the important aspects of the exemplary embodiments described below, we will first briefly explain chromatic aberration and its correction in optical refraction (refracting) optics in order to clarify the terms and their meanings used in this application.

[0055] Chromatic aberration is an imaging aberration in an optical system that arises from the fact that the refractive index n of a transparent optical material changes as a function of wavelength λ. This dependency, dn / dλ, is called the dispersion of the optical material. Generally, the refractive index of an optical material is greater at shorter wavelengths than at longer wavelengths.

[0056] Chromatic aberration can be subdivided into various categories. The first category of chromatic aberration considers that a dedicated image is generated for each wavelength in the paraxial region (on the optical axis), and that these images can vary in terms of their respective position along the optical axis, their respective form, and / or size. The first category of chromatic aberration includes longitudinal chromatic aberration (CHL, axial color, AX) and lateral chromatic aberration or lateral color difference (CHV, lateral color, LAT).

[0057] Longitudinal chromatic aberration is the longitudinal aberration of the paraxial focal position as a function of wavelength. When the refractive index of shorter wavelengths is greater than that of longer wavelengths, shorter wavelengths are refracted more strongly at each optical plane, for example, in the case of a simple positive lens element, so that relatively shorter wavelength rays are focused at focal positions closer to the lens element than at the focal points of relatively longer wavelengths. The paraxial distance along the optical axis of the lens element between these two focal points is the longitudinal chromatic aberration. When shorter wavelength rays are focused closer to the imaging system than longer wavelength rays, the longitudinal chromatic aberration is usually called "undercorrected" or "negative."

[0058] When an imaging system forms images of different sizes for different wavelengths, or when images at off-axis points form chromatic fringing, chromatic aberration or chromatic difference (CHV) exists. Chromatic difference can be quantified by the lateral distance between paraxial image heights at different wavelengths.

[0059] The dispersion of the optical materials used, i.e., the change in the chromaticity of the refractive index, can also cause variations in monochromatic aberration, which can be incorporated into a second category of chromatic aberration. Examples of these include the change in the chromaticity of spherical aberration and the change in the chromaticity of field curvature.

[0060] For further characterization of possible aberrations, imaging by light from a broadband source can be considered. A broadband source emits light of different wavelengths centered around a central wavelength λ, and the radiation distribution is characterized by the spectral bandwidth Δλ (full width at half maximum). Typically, the degree of chromatic aberration increases with increasing spectral bandwidth Δλ. Chromatic aberration can be characterized using the focal positions of three different wavelengths along the optical axis within the spectral bandwidth. These three wavelength components have wavelengths λ1, λ2, and λ3, with λ1 < λ2 < λ3.

[0061] In this case, the magnitude of the longitudinal chromatic aberration (CHL) corresponds to the maximum length of the focusing range along the optical axis where different wavelengths are in focus. Typically, one wavelength is focused closer to the imaging system than the other. The distance between the focal position of the nearest wavelength and the focal position of the farthest wavelength corresponds to the magnitude of the longitudinal chromatic aberration of the imaging system of a broadband light source. The focal position of the central wavelength λ along the optical axis can be considered as the image plane within the focusing range.

[0062] The change in the paraxial focal position with respect to wavelength is usually expressed as a power series. In this case, the linear part is called the "first-order spectrum," the second-order part is called the "second-order spectrum," and a third-order part, the "third-order spectrum," can also be defined.

[0063] The primary spectrum can be corrected by combining a converging lens element and a diverging lens element made of different optical materials with different dispersions. Specifically, longitudinal chromatic aberration can be corrected so that the paraxial focal planes of two different wavelengths, for example, the minimum λ1 wavelength and the maximum λ3 wavelength in the spectral region, coincide on the optical axis. In this application, such an optical imaging system is also referred to as "achromatization" or "achromat."

[0064] Typically, residual longitudinal chromatic aberration at other wavelengths that are not captured by the correction remains. This residual longitudinal chromatic aberration is usually known as the "secondary spectrum."

[0065] In some cases, secondary spectra can be corrected by appropriate selection of optical materials, lens element dimensions, distance, and refractive power. Secondary spectra can, in some cases, be corrected to the extent that the focal positions of all three wavelengths λ1, λ2, and λ3 in the wavelength range under consideration are located in the same axial position, resulting in only a "tertiary spectrum" remaining. In this application, an optical system in which secondary spectra are also corrected is referred to as "apochromatic correction" or simply "apochromatic."

[0066] In other words, in an achromatic imaging system, the longitudinal chromatic aberration between two separated wavelengths becomes extremely small (sometimes zero). In an apochromatic optical imaging system, the longitudinal chromatic aberration between three spectrally separated wavelengths becomes extremely small (sometimes zero).

[0067] In refractive projection lenses intended to function with spectrally broadband light sources, different lens element materials with the largest possible difference in Abbe numbers are used to correct chromatic aberration. The Abbe number v facilitates the characterization of the dispersion properties of the material in the wavelength range of interest. As an example, the Abbe number of a material can be calculated using the following formula: v = (n2-1) / (n1-n3) Here, n1, n2, and n3 are the refractive indices of the material at wavelengths λ1, λ2, and λ3, respectively, and the condition λ1 < λ2 < λ3 applies. Generally, low Abbe numbers represent materials with relatively strong dispersion, while high Abbe numbers represent materials with relatively weak dispersion. Therefore, Abbe numbers are sometimes also called "inverse relative dispersion."

[0068] In this case, the Abbe number v Hg This needs to be related to the range of the ultraviolet spectral region. For this purpose, the refractive indices n1, n2, and n3 of the mercury spectral lines at 365.0 nm (i-line of n1), 404.7 nm (h-line of n2), and 435.8 nm (g-line of n3) are used. The Abbe numbers of the glasses used are listed in Table 10.

[0069] Lens element materials for the operating wavelengths in the emission lines of mercury lamps can be divided into three distinct groups according to their refractive index and Abbe number. The first group includes materials with Abbe numbers in the range of 40 to 70. Here, the Abbe number is calculated for wavelengths λ1=365.01 nm, λ2=404.65 nm, and λ3=435.84 nm, which correspond to the wavelengths of the i, h, and g emission lines of mercury lamps. Materials in the first group have a typical refractive index in the range of 1.46 to 1.56 in the mercury i line. Materials in the first group include, in particular, synthetic fused silica (SiO2) and various borosilicate glasses such as BK7 glass or K5, K7, or FK5 glass.

[0070] The second group includes materials with Abbe numbers greater than 70. Some materials in the second group, such as crystalline calcium fluoride (fluorite or CaF2), have a refractive index of less than 1.46.

[0071] The third group includes materials with an Abbe number of less than 40. These materials have a refractive index greater than approximately 1.56. Materials in the third group include typical flint glasses such as LLF-6 glass, LLF-1 glass, or LF-5 glass.

[0072] To reduce chromatic aberration by refractive means, the optical system must have lens elements made of at least two materials having different dispersions or different Abbe numbers. Therefore, a first optical element made of a first material having a relatively low Abbe number must be combined with a second optical element made of a second material having a higher Abbe number than the first material.

[0073] Typically, materials from the second group are used as relative crown materials. Typically, materials from the third group are used as relative flint materials. Materials from the first group can act as relative crown materials in combination with materials from the third group, and as relative flint materials in combination with materials from the second group. For example, when combined with materials from the third group (e.g., LF5, LLF1, LLF6), synthetic fused silica (SiO2) functions as a relative crown material. Conversely, when synthetic fused silica is combined with materials from the second group, such as CaF2, the fused silica functions as a relative flint material.

[0074] Within the scope of this application, a first material having a relatively low Abbe number is also referred to as a "relative flint material," and a second material having a relatively higher Abbe number is also referred to as a "relative crown material." For simplicity of explanation, in the more specific exemplary embodiments of this application, a lens element made of a relative crown material is also abbreviated as a "crown lens element," and a lens made of a relative flint material is also abbreviated as a "flint lens element." Typically, materials from the first and third material groups are used.

[0075] In the following description of preferred embodiments of the projection lens, the term “optical axis” refers to a straight line passing through the center of curvature of the surface of the curved lens element. In the embodiment, the object is a mask (reticle) having a pattern of an integrated circuit, and may be related to different patterns of a grating, for example. In the embodiment, the image is projected onto a wafer having a photoresist layer, and the wafer functions as a substrate. Other substrates, such as elements for liquid crystal displays or substrates for optical diffraction gratings, are also possible.

[0076] Based on the profiles and relationships of the principal and peripheral rays of the image, several specificities can be revealed. In this case, the principal ray CR intersects the optical axis starting from the edge of the objective field of view in the region of the pupil plane, i.e., the region of the aperture position suitable for mounting the aperture diaphragm (AS). Within the scope of this application, the peripheral ray MR extends from the center of the objective field of view to the edge of the aperture diaphragm. The perpendicular distance of these rays from the optical axis results in the corresponding ray height. To the extent that this application refers to “peripheral ray height” (MRH) or “principal ray height” (CRH), these refer to the paraxial peripheral ray height and paraxial principal ray height, respectively.

[0077] The term "aperture region" refers to the area surrounding the aperture position (i.e., upstream and downstream of the aperture position), where the ratio of the principal ray height (CRH) to the peripheral ray height (MRH) of the image (|CRH / MRH|) is less than 1. Therefore, a relatively large peripheral ray height occurs in the aperture region.

[0078] In the drawings, crown lens elements, specifically fused silica lens elements or FK5 lens elements, are represented by outlined lens elements, while flint lens elements, specifically LF5 or LLF1 lens elements, are represented by shaded lens elements. Aspherical elements are marked with a short aspherical dash.

[0079] The specifications of the projection lenses shown in the drawings are given in a table summarized at the end of this specification, where the numbering in the table corresponds to the numbering of the corresponding figures in the drawings.

[0080] Tables 2 to 8 summarize the specifications of each design in tabular form. In this case, the column "Surface" indicates the number of a surface distinguished by a refractive surface or any other method, the column "Radius" indicates the radius r of the surface (in mm), the column "Thickness" indicates the distance d between the surface and the subsequent surface, that is, the distance expressed as thickness (in mm), and the column "Material" indicates the material of the optical component. The columns "Refractive index 1", "Refractive index 2" and "Refractive index 3" indicate the refractive indices of the material at wavelengths of 365.5 nm (refractive index 1), 364.5 nm (refractive index 2) and 366.5 nm (refractive index 3). The column "Radius" indicates the available free radius or free optical radius of the lens element or optical element (in mm). A radius r = 0 (in the column "Radius") corresponds to a plane. Some optical surfaces are aspheric. Tables marked with "A" indicate corresponding aspheric data, and the aspheric surface is calculated according to the following definition. p(h)=[((1 / r)h 2 ) / (1+SQRT(1-(1+K)(1 / r) 2 h 2 ))]+C1*h 4 +C2*h 6 +....

[0081] In this case, the reciprocal of radius (1 / r) represents the surface curvature, and h represents the distance between the surface point and the optical axis (that is, the ray height). Therefore, p(h) represents the sagittal height, that is, the distance between the surface point and the surface vertex in the z-direction (the direction of the optical axis). The coefficients K, C1, C2, ... are shown in the tables marked with "A".

[0082] Table 9 summarizes the key design parameters of the exemplary embodiments.

[0083] In the following description of the exemplary embodiments, the same reference signs are used for identical or corresponding features in all drawings. The lens elements are numbered in order from the object plane to the image plane, therefore, for example, lens element L1 is the first lens element immediately following the object plane. For clarity, reference signs are not marked on all lenses.

[0084] Figure 2 shows a schematic meridional lens element cross-section of a first exemplary embodiment of a refractive projection lens 200 having a selected beam, in order to reveal the imaging beam path or projection beam path of the projection radiation passing through the projection lens during operation.

[0085] The projection lens is provided as an imaging system with a reduction effect, which directly images the pattern of the mask placed on its objective plane OS onto its image plane IS, which is aligned parallel to the objective plane, without generating an intermediate image, at a reduced scale, specifically at a scale of -1:2 (imaging scale of -0.5).

[0086] Between the objective plane and the image plane, only the pupil plane PUP of the imaging system is located, where the principal ray CR of the optical image intersects the optical axis OA. The aperture diaphragm AS of the system is attached to the pupil plane region. Therefore, the position suitable for attaching the aperture diaphragm is also referred to as the diaphragm position BP in this specification.

[0087] An aperture region BB extends around the aperture position, and the condition |CRH / MRH|<1 is applied to the ratio of the principal ray height CRH to the peripheral ray height MRH in the image formed within the aperture region. Therefore, the peripheral ray height is higher than the principal ray height. This optical structure can be characterized as follows.

[0088] Immediately following the objective plane OS is a first lens element group LG1 having a positive refractive power and a total of four lens elements L1 to L4. The first lens element group collects light rays incident from the field of view point of the objective plane, thereby forming at least approximately a bulge in the projected beam path.

[0089] Immediately following the first lens element group LG1 is a second lens element group LG2 having negative refractive power. This second lens element group includes two lens elements L5 and L6, creating a constriction in the projection beam path that surrounds the local minimum of peripheral ray height between the objective plane OS and the augmentation plane IS.

[0090] Immediately following the second lens element group LG2 is a third lens element group LG3, which has a positive refractive power and a total of two lens elements L7-L8. The lens elements of the third lens element group are positioned between the second lens element group LG2 and an aperture position suitable for attaching the aperture diaphragm AS.

[0091] A fourth lens group LG4, which has a positive refractive power overall, is located between the aperture position and the image plane IS. The fourth lens element group LG4 includes six lens elements L9 to L14, each possessing refractive power.

[0092] Therefore, the projection lens is characterized by a refractive power sequence PNPP, where "P" represents a group of lens elements with positive refractive power and "N" represents a group of lens elements with negative refractive power. There is only a single obvious constriction in the region of the second negative lens element group LG2 between the object near-field bulge (in LG1) and the image near-field bulge (in LG3 and LG4). This design as a single constriction system contributes to Petzval correction.

[0093] With the sole exception (the biconcave negative lens element L8), all lens elements are made of crown glass, specifically synthetic fused silica (SiO2, abbreviated as SILUV in Table 2), i.e., Abbe number v Hg A first group of materials having approximately 60, or a lens element material referred to as FK5, i.e., Abbe number v Hg It consists of a first group of lens element materials having approximately 52.

[0094] In contrast, (the biconcave negative lens element L8) is a flint lens element, and is made of flint glass named LF5, i.e., v Hg It consists of a third group of lens materials having a relatively low Abbe number of approximately 31.

[0095] The first exemplary embodiment includes a stepper field with an image-side numerical aperture NA=0.18 and an OBH=84mm, with an imaging scale of -0.5×. The only required flint lens element is lens element L8, which is in direct proximity to the aperture diaphragm. The flint lens element is positioned at approximately the maximum ray height and, together with lens elements L7-L11, plays a crucial role in correcting longitudinal chromatic aberration. As a result of the extremely small numerical aperture in the image field, it is possible to omit correction of the chromaticity change of the Petzval sum, and therefore the only required flint lens element is lens element L8, which is in direct proximity to the aperture diaphragm and located at approximately the maximum peripheral ray height.

[0096] In the following illustrative embodiments, the same reference numerals are used for corresponding or similar features, but for clarity, these will not be mentioned again separately.

[0097] The second exemplary embodiment (Figure 3, projection lens 300) is similarly a single constriction system. However, in this case, the refractive force sequence NPNPP is realized. For this purpose, a front negative group NV having two lens elements (a biconcave positive lens element L1 and a biconcave negative lens element L2) is positioned between the objective plane OS and the first lens element group LG1, which has an overall positive refractive force. Such a negative group in direct proximity to the objective plane allows for the formation of a subsequent bulge over a short axial length, thus resulting in a compact structural shape.

[0098] The etendue of the system in the second exemplary embodiment is slightly increased compared to the first exemplary embodiment, but is mainly distributed in a significantly different manner. The objective field radius is reduced to the scanner field (OBH = 59 mm), but the image-side numerical aperture of the system is more than doubled, with NA = 0.38. Nevertheless, in this case, it is also possible to realize a well-corrected optical design with the minimum required number of flint lens elements. Of the 22 lens elements L1 to L22, only one lens element is a flint lens element, specifically a biconcave negative lens element L16 in the region of the highest peripheral ray height near the aperture diaphragm AS. In this case as well, along with the adjacent positive lens elements L15, L17, and L18, this negative lens element L16 employs correction for longitudinal chromatic aberration.

[0099] In the third exemplary embodiment (Figure 4, projection lens 400), the second exemplary embodiment (Figure 3) is complemented by an additional flint lens element, which is an image-side convex negative meniscus lens element L19. As a result, the correction of longitudinal chromatic aberration is distributed by the combination of two flint lens elements and a positive lens element consisting of a surrounding crown material. The individual refractive powers of the two flint lens elements are smaller than the refractive powers of the individual flint lens elements in Figure 3, which leads to the relaxation in this exemplary embodiment.

[0100] The fourth exemplary embodiment (Figure 5, projection lens 500) is also a symmetric 1:1 system (imaging scale β=-1) in which only one flint lens element is used for one system portion upstream and downstream of the aperture. In this case, it is also conceivable to use exactly one negative lens element made of flint material with a large refractive power precisely midway between the object plane and the image plane. However, this would make it impossible to access the aperture at the same position. Therefore, for the symmetry of the design and the necessary accessibility to the aperture, two divergent flint lens elements are used here.

[0101] The projection lens in Figure 5 has mirror symmetry with respect to the aperture plane. The aperture plane is located midway between the objective field of view (reticle) and the image field of view (wafer). This means that all lens elements in the first lens section upstream of the aperture (between the objective plane and the aperture plane) have corresponding parts of the same design arranged mirror-symmetrically in the second lens section downstream of the aperture.

[0102] This design is provided or designed for use with a 365 mm optical wavelength and a bandwidth of several nanometers. Therefore, the longitudinal correction of the primary spectrum (longitudinal chromatic aberration) is sufficient. This is achieved by the divergent flint lens element near the aperture diaphragm (i.e., when the peripheral ray height is large). If a material with anomalous partial dispersion is not used as the flint material, a secondary spectrum is automatically set in the longitudinal direction. This is the case for available materials such as LF5 or LLF1.

[0103] Due to its extremely small numerical aperture (NA) of 0.18, the Rayleigh unit RU = λ / NA defines the measure of field depth. 2 The chromatic aberration is extremely large, and therefore the residual secondary spectrum is negligible. Due to the structural symmetry, transverse chromatic aberration is essentially corrected, as are distortion and coma aberration and their chromatic variations. Therefore, no separate correction means are required for this.

[0104] Previously, only the major longitudinal chromatic aberration was corrected by the flint material used. However, as a result of the excess negative refractive power in the flint material, it is not possible to simultaneously correct the chromaticity change of the Petzval sum. The following explanation will help to understand possible correction methods.

[0105] For the design of projection lenses with a wide field of view, flattening of the field of view is a crucial requirement. The requirement related to this is that the Petzval sum of the lens is zero. The Petzval sum PTZ is given by the following formula:

number

[0106] Here, i represents the index of a surface in the optical system (the system is represented by the k surface), r i indicates the radius of the i-th face, n i , n i ' indicates the refractive index upstream and downstream of the surface.

[0107] If the system consists of a sequence of K lens elements in air (n=1), it can be simply written as follows.

number

[0108] If this is a single-material system, that is, if all lens elements are manufactured from the same material, then it is possible to derive the common refractive index n of all lens elements from the sum, and the following can be obtained.

number

[0109] In order to make the Petzval sum zero, the sum over the curvature difference of the lens elements must be zero, as shown here.

number

[0110] Here, we need to consider the change in the Petzval sum with respect to wavelength. A change in wavelength changes the refractive index of the material. Therefore, the following occurs for a lens element in air.

number

[0111] Therefore, the Petzval sum of the entire system changes as follows:

number

[0112] Here again, the following applies. If this is a system consisting of only one material, we can derive the refractive index before the sum, and obtain the following.

number

[0113] The Petzval sum of a single-material system becomes zero.

number

[0114] Given two material systems, A and B, the Petzval sum and its chromaticity change are as follows:

number

[0115] However, in that case, the requirement that the Petzval sum and its chromaticity change are simultaneously zero is equivalent to the sum of the radius differences of the lens elements within the individual materials being zero.

number

[0116] In an optical system consisting mainly of one material (crown glass, e.g., FK5) with a small number of lens elements made of a second material (flint glass, e.g., LF5), this means that the Petzval sum must be corrected within each material group. This is impossible if only flint divergent negative lens elements are used. To make the chromaticity change of the Petzval sum completely zero, the design must also include at least one flint converging lens element.

[0117] This technique is implemented in the following exemplary embodiments by adding an additional flint lens element, specifically a flint lens element with positive refractive power, to the design. However, this converging flint lens element hinders the correction of longitudinal chromatic aberration. Therefore, to minimize this adverse effect on the correction of longitudinal chromatic aberration, the converging flint lens element should preferably be used in the design at a point where the peripheral ray height is as small as possible. This specifically refers to the vicinity of the reticle or wafer, i.e., the optical field proximity position.

[0118] In the fifth exemplary embodiment (Figure 6, projection lens 600), a flint lens element having a positive refractive power is used near the wafer.

[0119] However, as a substantially equivalent alternative to the fifth exemplary embodiment, an additional flint lens element having a positive refractive power may be used in the vicinity of the reticle, for example, as part of the front negative group NV, specifically as the first lens element L1 of the design. This is shown in the sixth exemplary embodiment (Figure 7, projection lens 700). The remaining description is the same as that for Figure 5.

[0120] The seventh embodiment (Figure 8, projection lens 800) can be considered a variation of the first exemplary embodiment. In this case, in addition to the first exemplary embodiment, an additional flint lens element is used near the reticle. This substantially serves to correct the chromaticity change of the Petzval sum, although this is not essential for the small numerical aperture of 0.18.

[0121] The use of this first flint lens element further significantly simplifies the first group of lens elements downstream of the reticle. Compared to the first exemplary embodiment, the aspherical element and two lens elements can be omitted as a result of this flint lens element. This is because, despite the increase in individual refractive power, the flint lens element with a higher refractive index greatly simplifies aberration correction.

[0122] The exemplary embodiment demonstrates, as an example, the inventor's success in developing an i-line lens that reduces the use of flint lens elements. Although the i-line of a mercury lamp is "nothing more" than a single emission line, its bandwidth is large enough that, even after bandwidth limiting, for example, 5 nm, correction of longitudinal chromatic aberration in the imaging system is unavoidable with respect to at least the lowest-order, i.e., first-order spectrum correction.

[0123] To improve the throughput of the system compared to the prior art, the imaging scale was changed from the previous 4× to 2× or less in all illustrated embodiments. Therefore, for a constant geometric etendue LLW, the image-side numerical aperture is reduced, increasing the Rayleigh units and thus the depth of the field of view. As a result, the system becomes less susceptible to longitudinal aberrations such as focus blur, astigmatism, or field curvature. The inventors have found that, as a result, it is possible to significantly reduce or completely eliminate the correction of chromaticity changes in the Petzval sum. This further directly affects the number of flint lens elements absolutely required in the projection lens, which can be kept as low as possible.

[0124] [Table 1]

[0125] [Table 2]

[0126] [Table 3]

[0127] [Table 4]

[0128] [Table 5]

[0129] Table 6

[0130] Table 7

[0131] Table 8

[0132] Table 9

[0133] Table 10

[0134] Table 11

[0135] Table 12

[0136] Table 13

[0137] Table 14

[0138] Table 15

[0139] Table 16

Claims

1. A refractive projection lens for imaging a pattern placed on the objective surface (OS) of a refractive projection lens (PO) onto the image plane (IS) of the projection lens using electromagnetic radiation with an operating wavelength in the ultraviolet region longer than 280 nm, The system includes a plurality of lens elements arranged between the objective plane (OS) and the image plane (IS) along the optical axis (AX), wherein the diffractive optical elements are not arranged between the objective plane (OS) and the image plane (IS) along the optical axis (AX), the lens elements are embodied in such a way that a pattern arranged on the objective plane can be imaged onto the image plane using the lens elements, an aperture position (BP) suitable for attaching an aperture diaphragm (AS) is located between the objective plane and the image plane, and the principal rays of the image intersect the optical axis at the aperture position. The lens element comprises at least one flint lens element and at least one crown lens element, wherein the flint lens element is made of a first material and the crown lens element is made of a second material, and the first material has an Abbe number less than 40, which is lower than the Abbe number of the second material. At least one crown lens element having a positive refractive power and a single flint lens element having a negative refractive power are arranged in an aperture region (BB) surrounding the aperture position (BP), and the single flint lens element is included in the at least one flint lens element. In the aperture region (BB), the ray height ratio CRH / MRH between the principal ray height CRH and the peripheral ray height MRH of the image is |CRH / MRH| < 1. The aforementioned projection lens, A first lens element group (LG1) having a positive refractive power and located close to the objective surface (OS), A second lens element group (LG2) having negative refractive power following the first lens element group (LG1) is provided to create a constriction (TL) surrounding the minimum peripheral ray height region between the objective plane (OS) and the image plane (INS), A third lens element group (LG3) having a positive refractive power following the second lens element group (LG2) and the aperture position (BP), wherein the single flint lens element is a lens element in direct proximity to the aperture diaphragm (AS), A refractive projection lens characterized by being implemented as a single constricted system, including a fourth lens element group (LG4) having positive refractive power between the aperture position (BP) and the image plane.

2. The projection lens according to claim 1, characterized in that the projection lens has an imaging scale |β| > 0.

25.

3. A refractive projection lens for imaging a pattern placed on the objective surface (OS) of a refractive projection lens (PO) onto the image plane (IS) of the projection lens using electromagnetic radiation with an operating wavelength in the ultraviolet region longer than 280 nm, The system includes a plurality of lens elements arranged between the objective plane (OS) and the image plane (IS) along the optical axis (AX), wherein the diffractive optical elements are not arranged between the objective plane (OS) and the image plane (IS) along the optical axis (AX), the lens elements are embodied in such a way that a pattern arranged on the objective plane can be imaged onto the image plane using the lens elements, an aperture position (BP) suitable for attaching an aperture diaphragm (AS) is located between the objective plane and the image plane, and the principal rays of the image intersect the optical axis at the aperture position. The lens element comprises at least one flint lens element and at least one crown lens element, wherein the flint lens element is made of a first material and the crown lens element is made of a second material, and the first material has an Abbe number lower than the Abbe number of the second material. At least one crown lens element having a positive refractive power and a single flint lens element having a negative refractive power are arranged in the aperture region (BB) surrounding the aperture position (BP). In the aperture region (BB), the ray height ratio CRH / MRH between the principal ray height CRH and the peripheral ray height MRH of the image is |CRH / MRH| < 1. The aforementioned projection lens, A first lens element group (LG1) having a positive refractive power and located close to the objective surface (OS), A second lens element group (LG2) having negative refractive power following the first lens element group (LG1) is provided to create a constriction (TL) surrounding the minimum peripheral ray height region between the objective plane (OS) and the image plane (INS), A third lens element group (LG3) having a positive refractive power following the second lens element group (LG2) and the aperture position (BP), It is implemented as a single constricted system, including a fourth lens element group (LG4) having positive refractive power between the aperture position (BP) and the image plane. The projection lens has an imaging scale |β| > 0.

25. A projection lens characterized in that the imaging scale is 1:2 (|β| = 0.50).

4. The projection lens according to claim 1 or 2, characterized in that the image-side numerical aperture (NA) is less than 0.

4.

5. The projection lens according to claim 4, wherein the condition 0.1 < NA < 0.4 applies.

6. The projection lens according to claim 1 or 2, characterized in that the single flint lens element having negative refractive power is arranged in a region where the ray height ratio is |CRH / MRH| < 0.5, and / or the single flint lens element is a biconcave lens element (L16).

7. The projection lens according to claim 1 or 2, characterized in that the projection lens (600, 700) includes at least one flint lens element (L21, L1) having a positive refractive power.

8. The projection lens according to claim 7, characterized in that the flint lens elements (L21, L1) having positive refractive power are arranged in the optical vicinity of the field of view in a region where the ray height ratio of the image satisfying the condition CRH / MRH > 0.

7.

9. The projection lens (200, 300, 400, 500, 600, 700, 800) according to claim 1, comprising a front negative group (VN) having a negative refractive power and at least one lens element (L2) positioned between the objective plane (OS) and the first lens group (LG1).

10. The projection lens according to claim 1 or 2, characterized in that it is implemented as a single constricted system having a refractive power sequence N-P-N-P-P, an image-side numerical aperture NA in the range of 0.2 < NA < 4, an imaging scale of the order of 1:2 (|β| = 0.50) or less, and a geometric etendue LLW in the range of 10 mm < LLW < 18 mm, and comprises only a single flint lens element having negative refractive power.

11. The projection lens according to claim 1 or 2, characterized in that the projection lens is designed for the emission of i-rays from a mercury lamp (LS).

Images