Projection lens, projection exposure apparatus, and projection exposure method

Abstract

A refractive projection lens (PO) for imaging a pattern arranged on an object plane (OS) of a projection lens onto an image plane (IS) of the projection lens using electromagnetic radiation with an operating wavelength in the ultraviolet region longer than 280 nm, includes a plurality of lens elements arranged along an optical axis (AX) between the object plane (OS) and the image plane (IS) and implemented such that a pattern arranged on the object plane can be imaged onto the image plane using the lens elements, a diaphragm plane (BE) suitable for mounting an aperture diaphragm (AS) is located between the object plane and the image plane, and a chief ray of imaging intersects the optical axis (AX) at the diaphragm plane. The projection lens is designed as a wide field lens with an object field radius of at least 52 mm and has a structure with an imaging scale of 1:1 that is mirror symmetrical with respect to the diaphragm plane (BE).

Description

[Technical field]

[0001] The following disclosure is based on German patent application No. 102022201002.7, filed January 31, 2022, which is incorporated herein by reference.

[0002] The present invention relates to a refractive projection lens for imaging a pattern arranged in the object plane of the projection lens onto an image plane of the projection lens using electromagnetic radiation with an operating wavelength in the ultraviolet range longer than 280 nm, a projection exposure apparatus equipped with the projection lens, and a projection exposure method which can be carried out using the projection lens. [Background technology]

[0003] Microlithographic projection exposure methods are currently mainly used for the production of semiconductor components and other finely structured components, for example masks for photolithography. In this case, a mask (reticle) or other pattern generating device is used which carries or forms the pattern of the structures to be imaged, for example the wiring pattern of a layer of a semiconductor component. The pattern is positioned in the projection exposure apparatus between the illumination system and the projection lens in the region of the object plane of the projection lens and is illuminated by illumination radiation provided by the illumination system. The radiation modified by the pattern passes through the projection lens as projection radiation, which images the pattern onto a substrate to be exposed. The surface of the substrate is arranged in the image plane of the projection lens, which is optically conjugate with the object plane. The substrate is covered overall with a radiation-sensitive layer (resist, photoresist).

[0004] Typically, the requirements for semiconductor component manufacturing are different for the exposure of critical and non-critical structures. Currently, critical structures, i.e. fine structures, are mainly manufactured using refractive or catadioptric immersion systems working in the deep ultraviolet range (DUV), specifically at an operating wavelength of about 193 nm. Currently, the finest structures are exposed using EUV systems. These are projection exposure apparatuses built using only reflective components working in the extreme ultraviolet range (EUV) at an operating wavelength between about 5 nm and 20 nm, for example about 13.4 mm.

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

[0006] To manufacture intermediate critical or non-critical layers with typical structure dimensions of significantly more than 150 nm, work is conventionally carried out using projection exposure apparatus built for operating wavelengths above 280 nm, in which region refractive optical (refractive) projection lenses are usually used, whose manufacture is easily controllable due to their rotational symmetry about the optical axis.

[0007] For these applications, projection exposure apparatus with an operating wavelength of 365.5 nm±2 nm (so-called i-line systems) are particularly often used. These use the i-line of a mercury lamp, the inherent overall bandwidth of which is limited by means of filters or in any other way to a narrower usable bandwidth Δλ, for example about 4 nm or 5 nm. During projection, in order to ensure aberration-free imaging with the required resolution even with broadband projection light, ultraviolet light of a relatively wide wavelength range is used, so that the projection lens necessarily provides a relatively strong correction of chromatic aberrations.

[0008] It has also been proposed in the past to design the projection lens in such a way that it is corrected in a very broadband manner for all three mercury lines (for example in WO 2007 / 1331161). If all Hg lines are used, more light is available, which results in shorter exposure times compared to conventional i-line systems, and therefore an increased throughput (number of components exposed per unit time). Summary of the Invention

[0009] It is an object of the invention to provide a projection lens, a projection exposure apparatus and a projection exposure method which function with UV radiation with an operating wavelength longer than 280 nm and which allow high throughput rates.

[0010] To achieve this goal, the invention provides a refractive projection lens having the features of claim 1. Also provided is a projection exposure apparatus having the features of claim 15 and a projection exposure method having the features of claim 18. Advantageous developments are specified in the dependent claims. All claim language is incorporated by reference into the content of this description.

[0011] According to a representation of the invention as claimed, a refractive projection lens is provided, which is embodied to image a pattern arranged in an object plane of the projection lens, on an image plane of the projection lens, using electromagnetic radiation with an operating wavelength in the ultraviolet range longer than 280 nm. All optical elements with refractive power are lens elements, i.e. refractive optical elements. The lenses are arranged along an optical axis between the object plane and the image plane, and are embodied in such a way that the whole results in this imaging. A diaphragm surface suitable for mounting an aperture diaphragm is located between the object plane and the image plane, and the chief ray of the imaging intersects the optical axis at said diaphragm surface.

[0012] According to the claimed invention, the projection lens is designed as a wide field lens with an object field height of at least 52 mm, has a mirror-symmetric structure with respect to the aperture plane and an imaging scale of 1:1, which corresponds to an imaging scale of |β|=1.

[0013] In this application, the phrase "wide field lens" refers to a projection lens designed such that due to the size of the usable objective field, at least the full width of a full 6 inch reticle (current standard size) can be exposed in a single exposure step. The usable size of the objective field is quantified in this case by the object field height OBH. This corresponds to the radius of the object field, i.e. the radius of the smallest circle that encloses the object field points for which the optical correction meets the specifications, i.e. is good enough. This circle must be large enough to enclose the effective object field that is actually used for imaging.

[0014] The projection lens can preferably be used as a stepper lens, i.e. a lens for projecting a 104 x 132 mm 3D image in a single exposure without scanning. 2 (corresponding to a half diagonal of 84 mm) onto the wafer. For this, the projection lens must be corrected in such a way that the optical aberrations are corrected within the object field having an object field radius of 84 mm.

[0015] According to one development, the projection lens has an objective field radius of 84 mm or more. Due to the 1:1 imaging scale, it is possible to expose 16 "dies" simultaneously in a step-and-repeat process. This results in a high throughput of the process. However, the correction of aberrations becomes more difficult as a result of the enlargement of the objective field radius.

[0016] Scanner systems replace steppers. In this case, only a part of the object field is imaged by the projection lens at a time. A scanning movement is therefore necessary, in which adjacent sections of the reticle are successively transferred to the substrate to perform a single exposure step. To transfer the entire pattern of a 6-inch reticle in a single exposure step using scanning, the effective object field must have a width of 104 mm. This is possible with an object field radius of at least 52 mm, which greatly simplifies the correction of aberrations. An object field radius of 55 mm would lead to a slit height of approximately 35 mm or less (measured in the scan direction). However, the slit height should preferably be 56 mm, which requires an object field radius of 59 mm. Sufficient light intensity, especially at the wafer, is obtained using such slit dimensions.

[0017] First, the term "stepper system" only defines the size of the object field that is imaged. Also, the imaging scale β of the system then determines the size of the exposed image field. In this case, typical dimensions are 26×33 mm. 2 is given by the size of a single "die" in mm. If the (reduced) imaging scale is 4:1, then a stepper using a 6 inch reticle can fully expose exactly one single "die" in one exposure. Because of the 1:1 imaging scale, 16 "dies" can consequently be exposed simultaneously in a single exposure step.

[0018] As a result, the throughput can be improved as compared with conventional systems.

[0019] The key design issues are characterized primarily by three dimensions: (i) the field size, i.e., the field radius within which the aberrations must be corrected; (ii) the corresponding numerical aperture, which for a 1:1 system is the same on the object and image sides; and (iii) the level of aberrations that can be obtained.

[0020] The first two points are often combined into what is called the geometrical etendue LLW, which is the product of the (dimensionless) objective numerical aperture NAO and the objective field size parameterized by the objective field height OBH (in millimeters), i.e. LLW=|OBH*NAO| It can be defined as:

[0021] If the field size to be corrected is changed, for example increased from a scanner field to a stepper field, the numerical aperture must be adjusted accordingly (i.e. reduced) in order to achieve the same number of correction measures.

[0022] The projection lens is preferably designed to have a numerical aperture (NA) (object side and image side) of less than 0.3, in particular NA=0.25 or less. For example, the numerical aperture can be between 0.1 and 0.2, in particular 0.18. Due to this extremely small NA, the Rayleigh unit RU=λ / NA, which defines the scale of the depth of field, is 2 is very large, so that residual secondary spectrum is largely negligible, thus simplifying the correction of aberrations.

[0023] Within the scope of the invention, axially very compact projection lenses are realizable. According to one development, the projection lens has a installation length TT ("total track length") measured between the object plane and the image plane, an object field radius OBH and an object side numerical aperture NAO, where the condition (OBH*NAO) / TT>0.01 applies.

[0024] The installation length is preferably of the order of one meter, for example in the range between 800mm and 1200mm, in particular 1000mm.

[0025] Compared to the prior art, projection lenses of the type presented here can achieve extremely high geometrical etendue values. According to one development, the projection lens has a geometrical etendue LLW=OBH*NAO of at least 10 mm, with the geometrical etendue preferably being 15 mm or greater. Etendue can be considered as a measure of the performance of an imaging system. The higher the etendue, the more the system can image, e.g. a wider field of view (if OBH is larger) or finer structures (if a larger NA is used).

[0026] Common to all exemplary embodiments is their purely refractive design. Thus, only lens elements are required. This in particular simplifies manufacturing. For example, the use of mirrors as known in catadioptric Offner systems (see for example US Pat. No. 3,748,015, US Pat. No. 4,293,188 or US Patent Publication No. 2004 / 0001191) is deliberately omitted, which would simplify the correction of aberrations, such as field curvature or longitudinal chromatic aberration.

[0027] The projection lens according to the invention claimed has mirror symmetry with respect to the resulting diaphragm plane, which is located midway between the object field (reticle) and the image field (wafer). This means that all lens elements in the first lens section upstream of the diaphragm (between the object plane and the diaphragm plane) have counterparts of identical design arranged in mirror symmetry in the second lens section downstream of the diaphragm.

[0028] This symmetrical structure is particularly advantageous when correcting aberrations: due to the symmetry of the structure, transverse chromatic aberration is inherently corrected, as are distortion aberrations and coma aberrations and their chromatic variations, and therefore no separate correction means are required for this purpose.

[0029] Preferably, only the UV radiation of the Hg i-line is used. This is a substantial difference to conventional systems that are very broadband corrected for all three mercury lines. If all Hg lines were used, more light would be available for imaging, but correction of aberrations over a relatively large objective field radius would be difficult.

[0030] Preferred exemplary embodiments are provided or designed for use with an optical wavelength of about 365.5 nm and / or a bandwidth of a few nm (5 nm or less), so that correction of the first order spectrum (longitudinal chromatic aberration) is sufficient.

[0031] In the case of refractive projection lenses with broadband capabilities, different lens element materials are used that have sufficiently different dispersion characteristics for color correction (i.e. for correction of chromatic aberrations), and the lens element materials are dispersed in the projection lens into areas of different beam height ratios. Transparent materials used in typical i-line projection lenses include, in particular, synthetic fused silica (SiO2) and special glasses marketed by Schott, Mainz, Germany, under the names FK5, LF5 and LLF1. Among these optical glasses, synthetic fused silica and FK5 glass are representative of relatively low dispersion glasses (crown glasses), while LF5 and LLF1 glasses are representative of relatively high dispersion glasses (flint glasses). Other manufacturers use different names for each type of glass.

[0032] Thus, within this application, lens elements made from crown glass will be referred to as "crown lens elements" and lens elements made from flint glass will be referred to as "flint lens elements."

[0033] Longitudinal chromatic aberration can be corrected, for example, by 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 must be located in a region of the optical imaging system where the marginal rays of the image have as large a ray height (marginal ray height) as possible. Typically, this corresponds to the aperture region near the system aperture.

[0034] As a result of the symmetry of the structure, the exemplary embodiment is characterized in that the lens elements on both sides of the diaphragm surface include at least one flint lens element made of a first material with a relatively low Abbe number and a number of crown lens elements made of a second material with a higher Abbe number relative to the first material. At least one flint lens element is necessary to correct chromatic aberrations and must be used in this design. If a material with anomalous partial dispersion is not used as the flint material, a secondary spectrum is automatically set in the vertical direction. By way of example, this is the case for available materials such as LF5 or LLF1 or equivalent glasses.

[0035] The inventors have recognized that flint materials have some disadvantageous properties. As an example, flint glass typically exhibits a reduced transmission of the light used, which is equivalent to an increased absorption. This can result in undesirable side effects such as lens heating and / or material compression. In addition, all current flint materials transparent in the wavelength range above 280 m (e.g., about 365 nm) have a significant proportion of lead and further heavy metals, and therefore the use of these glasses is permitted only by special authorization. Comparable lead-free alternative glasses are not currently practically available. It would therefore be advantageous to develop a projection lens that uses fewer flint lens elements compared to the prior art.

[0036] The use of flint lens elements is reduced in some exemplary embodiments, preferably with no more than two flint lens elements positioned on each side of the aperture plane, and in some embodiments, the use of flint lens elements can be reduced to the extent that only a single flint lens element is used in each of the lens sections, specifically a flint lens element having negative refractive power.

[0037] Some exemplary embodiments are characterized in that at least one crown lens element with positive refractive power, at least one flint lens with negative refractive power and not more than two flint lenses with negative refractive power are arranged on each side of the diaphragm surface in a diaphragm area surrounding the diaphragm surface, with the condition that the ray height ratio CRH / MRH of the chief ray height CRH of the image and the marginal ray height MRH is |CRH / MRH|<1. Preferably, only a single flint lens element with negative refractive power is provided in the diaphragm area on each side of the diaphragm surface.

[0038] Further details regarding options for correcting aberrations, specifically chromatic longitudinal aberration (CHL), are described in relation to example embodiments.

[0039] Further advantages and aspects of the present invention will become apparent from the appended claims and the following description of exemplary embodiments of the invention which proceeds with reference to the drawings. [Brief description of the drawings]

[0040] [Figure 1] FIG. 1 shows a schematic diagram of a projection exposure apparatus according to an exemplary embodiment; [Diagram 2] FIG. 2 shows a schematic meridional lens element cross-section of a projection lens according to a first exemplary embodiment. [Diagram 3] FIG. 2 shows a schematic meridional lens element cross-section of a projection lens according to a second exemplary embodiment. [Figure 4] FIG. 13 shows a schematic meridional lens element cross-section of a projection lens according to a third exemplary embodiment. [Diagram 5] FIG. 13 shows a schematic meridional lens element cross-section of a projection lens according to a fourth exemplary embodiment. [Figure 6] FIG. 13 shows a schematic meridional lens element cross-section of a projection lens according to a fifth exemplary embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] Figure 1 shows an example of a microlithography projection exposure apparatus WST that can be used in the manufacture of semiconductor components and other microstructured components and that works with light or electromagnetic radiation in the ultraviolet (UV) range to obtain a resolution down to a few parts per micrometer. A mercury lamp serves as the main radiation source or light source LS. The lamp emits a broad spectrum with emission lines of relatively high intensity I in wavelength ranges with central wavelengths of about 436 nm (visible light, blue, g-line), about 405 nm (visible light, violet, h-line) and about 365.5 nm (near ultraviolet, UV-A, i-line). This part of the spectrum is shown in the I(λ) schematic diagram.

[0042] Projection exposure tools are i-line systems that use only light from the i-line, i.e. UV light centered at a central operating wavelength of about 365.5 nm. The full intrinsic bandwidth of the i-line is limited by filters or any other method to a narrower usable bandwidth Δλ, for example about 5 nm.

[0043] At the exit surface ES, an illumination system ILL arranged downstream of the light source LS produces a wide, well-defined and substantially uniformly illuminated illumination field which is adapted to the telecentricity requirements of a projection lens PO arranged downstream in the optical path. The illumination system ILL has a device for setting different illumination modes (illumination settings) and is, for example, switchable between conventional on-axis illumination with different coherence degrees σ and off-axis illumination.

[0044] Those optical components that receive light from the light source LS and form from it an illumination radiation that is directed towards the reticle M are part of the illumination system ILL of the projection exposure apparatus.

[0045] Downstream of the illumination system is arranged a device RS for holding and manipulating a mask M (reticle) so that a pattern arranged on the reticle is located at an object plane OS of the projection lens PO, which coincides with the exit plane ES of the illumination system and is also referred to in this specification as the reticle plane OS.

[0046] Following the downstream of the reticle plane OS, there is an imaging system that forms an image on the substrate W coated 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, with the image of the pattern arranged on the projection lens, i.e., the mask M, defined by the defined imaging scale β.

[0047] In this exemplary case, the substrate W to be exposed, which is a semiconductor wafer, is held by a device WS, also called a "wafer stage".

[0048] The illumination field generated by the illumination system ILL defines the effective object field OF used during projection exposure. In this exemplary case, the effective object field is rectangular, has a height A* measured parallel to the y direction, and has a width B* < A* measured perpendicular thereto (x direction). The aspect ratio AR = B* / A* is approximately 104 / 132. The effective object field is located at the center of the optical axis (on-axis field). In a system with this field size, a typical 6-inch reticle can be imaged in a single exposure step.

[0049] The effective image field optically conjugate to the effective object field within the image section IS has the same shape as the effective object field and the same aspect ratio of height B and width A. In the case of a 1:1 (imaging scale |β| = 1) figure, the image field has the size of the effective object field.

[0050] Briefly explain the field size. 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. Therefore, the projection exposure apparatus can be designed as a wafer stepper for a step-and-repeat process. The device for performing the scanning operation for die exposure can be omitted. The projection exposure apparatus can also be designed as a wafer scanner for a step-and-scan process. In that case, a device for performing the scanning operation for die exposure needs to be provided.

[0051] In this rotationally symmetric system, a circle centered on the optical axis OA, enclosing the effective object field OF and tangent to the corners of the effective object field, defines the size of the object field within which the optical corrections at all field points must meet the specifications. This also applies to all field points within the effective object field. The more complex the correction of aberrations, the larger this object field must be. In this case, the size of the circle is parameterized by the object field radius (or half the object field diameter) OBH, which at the same time corresponds to the maximum field height of the object field points.

[0052] An exemplary embodiment is a stepper system that uses 1:1 imaging, so that 16 dies can be exposed simultaneously.

[0053] In order to better understand important aspects of the exemplary embodiments described below, we first provide a brief description of chromatic aberration and its correction in dioptric (refractive) optical systems in order to clarify the terms and meanings used in this application.

[0054] Chromatic aberration is an imaging aberration in optical systems that arises due to the variation of the refractive index n of transparent optical materials as a function of wavelength λ. This dependence dn / dλ is called the dispersion of the optical material. In general, the refractive index of an optical material is larger for shorter wavelengths than for longer wavelengths.

[0055] Chromatic aberration can be subdivided into various categories. The first category of chromatic aberration considers that for each wavelength in the paraxial region (on the optical axis), a dedicated image is generated and that these images may vary in terms of their respective position along the optical axis, their respective shape and / or size. The first category of chromatic aberration includes longitudinal chromatic aberration CHL (axial chromatic aberration, axial color, AX) and lateral chromatic aberration or lateral chromatic aberration CHV (lateral chromatic aberration LAT).

[0056] Longitudinal chromatic aberration is the longitudinal aberration of the paraxial focal position as a function of wavelength. If the refractive index of shorter wavelengths is greater than that of longer wavelengths, then the shorter wavelengths will be refracted more strongly at each optical surface, such that, for example, in the case of a simple positive lens element, the relatively shorter wavelength rays will be focused at a focal position located closer to the lens element than the focal points of the relatively longer wavelengths. The paraxial distance along the optical axis of the lens element between these two focal points is the longitudinal chromatic aberration. If the shorter wavelength rays are focused closer to the imaging system than the longer wavelength rays, the longitudinal chromatic aberration is usually called "undercorrected" or "negative".

[0057] When an imaging system produces images of different sizes for different wavelengths, or when the image of an off-axis point produces color fringes, lateral chromatic aberration or lateral chromatic difference (CHV) exists. lateral chromatic difference can be quantified by the lateral distance between the paraxial image heights of different wavelengths.

[0058] Dispersion of the optical materials used, i.e., chromatic variation of the refractive index, can also give rise to variations in monochromatic aberrations, which can be subsumed under the second category of chromatic aberrations. For example, these include chromatic variation of spherical aberration, chromatic variation of field curvature, etc.

[0059] For further characterization of possible aberrations, imaging with light from a broadband source is considered, where the broadband source emits light of different wavelengths centered around a central wavelength λ, and the radiation distribution is characterized by a 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 different wavelengths along the optical axis for three wavelengths within the spectral bandwidth. The three wavelength components have wavelengths λ1, λ2 and λ3, where λ1<λ2<λ3.

[0060] In this case, the magnitude of the longitudinal chromatic aberration CHL corresponds to the maximum length of the focal range along the optical axis where the different wavelengths are focused. Typically, one of the wavelengths 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 furthest wavelength corresponds to the magnitude of the longitudinal chromatic aberration of the imaging system of the broadband light source. The focal position of the central wavelength λ along the optical axis can be considered as the image plane within the focal range.

[0061] The variation of paraxial focal position with wavelength is usually expanded in a power series, where the linear part is called the "first order spectrum", the second order part is called the "second order spectrum", and one can further define the third order part as the "third order spectrum".

[0062] The primary spectrum can be corrected by combining converging and diverging lens elements made of different optical materials with different dispersions. Specifically, the 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 of the spectral region, coincide on the optical axis. Such an optical imaging system is also referred to as "achromatized" or "achromat" in this application.

[0063] Typically, there remains longitudinal chromatic aberration remnant for other wavelengths that are not captured by the correction. This longitudinal chromatic aberration remnant is usually referred to as the "secondary spectrum."

[0064] In some cases, it is also possible to correct the secondary spectrum by appropriate selection of optical materials, lens element dimensions, distances, refractive powers, etc. The secondary spectrum can in some cases be corrected to the extent that the focal positions of all three wavelengths λ1, λ2 and λ3 of the wavelength range under consideration are located at the same axial position, resulting in only the "third order spectrum". In this application, an optical system in which the secondary spectrum is also corrected is also referred to as "apochromatically corrected" or "apochromatic".

[0065] In other words, for an achromatic imaging system, the longitudinal chromatic aberration for two spectrally separated wavelengths is very small (possibly even zero). For an apochromatic optical imaging system, the longitudinal chromatic aberration for three spectrally separated wavelengths is very small (possibly even zero).

[0066] In refractive projection lenses intended to work with spectrally broadband light sources, different lens element materials with Abbe numbers that differ as much as possible are used to correct chromatic aberrations. The Abbe number v facilitates the characterization of the dispersion properties of a 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) where n1, n2, and n3 are the refractive indices of the material at wavelengths λ1, λ2, and λ3, with λ1<λ2<λ3. Generally, a low Abbe number represents a material with relatively strong dispersion, and a high Abbe number represents a material with relatively weak dispersion. Therefore, the Abbe number is sometimes called the "inverse relative dispersion."

[0067] In this case, the Abbe number v Hg must be related to the extent of the ultraviolet spectral region. For this purpose, the refractive indices n1, n2 and n3 of the mercury spectral lines at 365.0 (n1 i-line), 404.7 (n2 h-line) and 435.8 nm (n3 g-line) are used. The Abbe numbers of the glasses used are tabulated in Table 10.

[0068] Lens element materials for operating wavelengths in the emission lines of mercury lamps can be divided into three different groups according to their refractive index and their Abbe number. The first group includes materials whose Abbe number is in the range of 40-70. 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 a mercury lamp. Materials of the first group have typical refractive indices in the range of 1.46-1.56 at the mercury i line. Materials of the first group include, in particular, synthetic fused silica (SiO2) and various borosilicate glasses such as BK7 glass or K5, K7 or FK5 glass.

[0069] The second group includes materials that have an Abbe number greater than 70. Some materials in the second group, such as crystalline calcium fluoride (fluorspar or CaF2), have a refractive index less than 1.46.

[0070] The third group includes materials with an Abbe number less than 40. These materials have a refractive index greater than about 1.56. The third group of materials includes, in particular, typical flint glasses such as LLF-6, LLF-1 or LF-5 glasses.

[0071] In order to reduce chromatic aberration by refractive means, an optical system needs to have lens elements made of at least two materials with different dispersions or different Abbe numbers, thus combining a first optical element made of a first material with a relatively low Abbe number with a second optical element made of a second material with a higher Abbe number relative to the first material.

[0072] Typically, the second group of materials is used as a relative crown material. Typically, the third group of materials is used as a relative flint material. The first group of materials can function as a relative crown material in combination with the third group of materials and as a relative flint material in combination with the second group of materials. As an example, synthetic fused quartz (SiO2) functions as a relative crown material in combination with the third group of materials (e.g., LF5, LLF1, LLF6). In contrast, when synthetic fused quartz is combined with a second group B material, e.g., CaF2, it functions as a relative flint material.

[0073] Within the scope of this application, the first material having a relatively low Abbe number is also referred to as the "relative flint material" and the second material having a relatively higher Abbe number is also referred to as the "relative crown material". For ease of explanation, in more specific exemplary embodiments of this application, the lens element made of the relative crown material is also referred to as the "crown lens element" for short, and the lens made of the relative flint material is also referred to as the "flint lens element" for short. Typically, materials from the first and third material groups are used.

[0074] 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 curved lens element surface. In an embodiment, the object is a mask (reticle) with a pattern of an integrated circuit, which may for example be associated with different patterns of gratings. In an embodiment, the image is projected onto a wafer with a photoresist layer, said wafer serving as a substrate. Other substrates are also possible, for example substrates for elements for liquid crystal displays or optical gratings.

[0075] Some peculiarities can be revealed based on the profile and relationship of the imaging chief and marginal rays. In this case, the chief ray CR starts from the edge of the objective field and intersects with the optical axis in the area of ​​the pupil plane, i.e. in the area of ​​the aperture plane BE suitable for mounting the aperture stop AS. The marginal ray MR within the meaning of the present application runs from the center of the objective field to the edge of the aperture stop. The vertical distance of these rays from the optical axis results in the corresponding ray height. Insofar as the present application speaks of "marginal ray height" (MRH) or "chief ray height" (CRH), this refers respectively to the paraxial marginal ray height and the paraxial chief ray height.

[0076] The term "stop region" BB refers to a region surrounding the stop surface BE (i.e., upstream and downstream of the stop surface) in which the ray height ratio |CRH / MRH| between the image chief ray height CRH and the marginal ray height MRH is less than 1. Thus, a relatively large marginal ray height occurs in the stop region.

[0077] In the figures of the drawings, crown lens elements, specifically fused silica lens elements or lens elements made of FK5, are represented by open lens elements, flint lens elements, specifically lens elements made of LF5 or LLF1, are represented by shaded lens elements, and aspheric surfaces are marked by short aspheric dashes.

[0078] The specifications of the projection lenses shown in the figures of the drawings are given in the tables compiled at the end of this specification, the numbering of the tables corresponding respectively to the numbering of the corresponding figures in the drawings.

[0079] Tables 2 to 6 summarize the specifications of the respective designs in tabular form. In this case, the column "Surface" indicates the number of the refractive surface or surfaces distinguished in some other way, the column "Radius" indicates the radius r (in mm) of the surface, the column "Thickness" indicates the distance d between that surface and the subsequent surface, i.e. 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 materials at wavelengths 365.5 nm (Refractive Index 1), 364.5 nm (Refractive Index 2) and 366.5 nm (Refractive Index 3). The column "Radius" indicates the usable free radius or free optical radius (in mm) of the lens element or of the optical element. The radius r=0 (column "Radius") corresponds to a plane. Some optical surfaces are aspheric. The tables marked with "A" indicate the corresponding aspheric data, the asphericity being calculated according to the following provisions:

[0080]

number

[0081] In this case, the reciprocal of the radius

number

[0082] Table 7 provides a clear summary of important design parameters of the exemplary embodiment, such as numerical aperture NA, objective field radius OBH and imaging scale.

[0083] In the following description of the exemplary embodiments, the same reference numbers are used for identical or corresponding features in all figures. The lens elements are numbered in order from the object plane to the image plane, so for example, lens element L1 is the first lens element immediately following the object plane. For clarity, reference numbers have not been applied to all lenses.

[0084] FIG. 2 shows a schematic meridional lens element cross-section of a first exemplary embodiment of a refractive projection lens 200 with selected beams to reveal the imaging or projection beam paths of projection radiation passing through the projection lens during operation.

[0085] The projection lens is configured as a 1:1 imaging system that images the pattern of a mask located in its object plane OS directly onto its image plane IS aligned parallel to the object plane, i.e. without generating an intermediate image and without any change in size, specifically a -1:1 scale (imaging scale is -1).

[0086] Between the object plane and the image plane lies only the pupil plane PUP of the imaging system, where the chief ray CR of the optical imaging intersects with the optical axis OA. The aperture stop AS of the system is attached in the region of the pupil plane. A position or surface suitable for attaching the aperture stop is therefore also referred to as the aperture plane BE in this document.

[0087] A stop area BB extends around the stop surface, and the condition |CRH / MRH|<1 applies to the ray height ratio between the chief ray height CRH and the marginal ray height MRH of the image formed in the stop area BB. The marginal ray height is therefore higher than the chief ray height. This optical design can be characterized as follows:

[0088] In the object-side first lens part OP1, the object surface OS is immediately followed by a front lens element group NV (the "negative group") having a negative refractive power provided by an object-side concave meniscus lens element L1.

[0089] This is immediately followed by a first lens element group LG1 having positive refractive power and a total of three lens elements L2-L4, which collects the light rays entering from the front negative group and as a result forms a bulge in the projection beam path.

[0090] The first lens element group LG1 is immediately followed by a second lens element group LG2 having negative refractive power, which comprises five lens elements L5-L9 and creates a waist surrounding a marginal ray height minimum in the projection beam path between the object surface OS and the aperture surface BE.

[0091] The second lens element group LG2 is immediately followed by a third lens element group LG3 having a positive refractive power and a total of three lens elements L10-L12, the lens elements of which are arranged between the second lens element group LG2 and a diaphragm surface suitable for mounting an aperture diaphragm AS.

[0092] Mirror symmetry with respect to the aperture plane results in a mirrored refractive power sequence on the other side of the aperture plane BE in the image-side second lens part OP2: each lens element Lx of the first lens part OP1 between the object plane OS and the aperture plane B has a mirrored identical corresponding part Lx' in the second lens part OP2 between the aperture plane and the image plane IS.

[0093] For example, three positive lens elements are arranged immediately next to the diaphragm surface on both sides. According to the conventional teaching, it is more advantageous to mount a flint negative lens element next to the diaphragm surface, because the marginal ray height is larger next to the diaphragm surface, so that the flint lens element has a better effect on longitudinal chromatic aberration. However, it is currently assumed that it is more advantageous to arrange at least two, and optionally three, positive lens elements immediately next to the diaphragm surface in order to obtain a good correction state in a wide objective field.

[0094] The projection lens is characterized by the refractive power sequence NPNPPNPN, where "P" represents the lens element groups having positive refractive power and "N" represents the lens element groups having negative refractive power. There is only a single pronounced waist on each side of the aperture surface in the region of the negative third lens element group LG3.

[0095] A first exemplary embodiment includes a stepper field with OBH=84 mm, with an image-side numerical aperture of NA=0.18, and an imaging scale of -1. The etendue is LLW=15.12.

[0096] This exemplary embodiment has a number of (2x12) lens elements with relatively low refractive power. The lens elements (L1, L2, L5-L8, L10-L12) are made of fused silica. Longitudinal chromatic aberration is corrected by a diverging flint lens element (L9 made of LF5 material).

[0097] The two flint lens elements L2 and L3 in the front part have positive refractive power and have a negative effect on the correction of longitudinal chromatic aberration, but this is negligible due to the significantly smaller marginal ray height of the lens elements relative to L9. That is, the contribution of the lens elements to the correction of longitudinal chromatic aberration is proportional to the square of the marginal ray height. The reason for using flint material in this respect can be seen more precisely in two properties: (i) flint lens elements have a higher refractive index, which helps to correct monochromatic aberrations such as spherical aberration and astigmatism; (ii) flint lens elements contribute to the overall flint refractive power of the system and, as a result, correct the chromatic change of the Petzval sum.

[0098] It is possible to prove that the chromaticity shift of the Petzval sum is zero whenever the sum of the individual refractive powers across the various materials is zero. Therefore, to correct the chromaticity shift of the Petzval sum, in addition to the at least one negative lens element of flint material required to correct the longitudinal chromatic aberration, at least one flint lens element with positive refractive power is also required.

[0099] This design has a pronounced waist structure. Thus, the negative refractive power of L1 allows the formation of a significant bulge of the positive lens elements L2, L3, L4. This is followed by a long waist with significant negative refractive power (L5, L7, L9) and individual weak positive lens elements (L6, L8). The beam is then gently collimated by lens elements L10, L11, L12 and directed through the central aperture stop. The collimation of the beam is a necessary condition for focusing of the image plane following the symmetry of the structure.

[0100] Aberration correction is further aided by the use of 2 x 4 aspheric surfaces, which are only on the quartz lens elements.

[0101] The entire design has a installation length TT (axial distance between the object and image planes) of 1000 mm, so the condition (OBH NAO) / TT>0.01 is observed. There are only small deviations from telecentricity on both the object and image sides.

[0102] In the following exemplary embodiments, the same reference numbers are used for corresponding or similar features, which will not be mentioned separately again for the sake of clarity. The second to fourth exemplary embodiments each include a stepper field with OBH=84 mm for an image-side numerical aperture NA=0.18, the imaging scale is −1 in each case, and the installation length is 1000 mm.

[0103] The second exemplary embodiment (projection lens 300 in FIG. 3) has a structure very similar to the first exemplary embodiment in the aperture region BB. One difference is the double aspheric surfaces arranged in each lens section, specifically as lens elements L1 and L1', respectively, designed as negative meniscus lens elements with their concave side facing the nearest field surface, closest to the field. This allows the number of lens elements per lens section to be reduced by one lens element, resulting in eleven flint lens elements. Similarly, the number of flint lens elements is reduced to two flint lens elements per lens section. As in the first exemplary embodiment, each lens section includes only a single flint lens element L8 or L8', designed as a biconcave lens element in the aperture region BB. Moreover, as in the first exemplary embodiment, an additional positive flint lens element L3 or L3' is arranged in the region closer to the field.

[0104] Compared to the second exemplary embodiment, the third exemplary embodiment (projection lens 400 in FIG. 4) is distinguished by the replacement of the positive lens element (L3) made of flint material in the second exemplary embodiment with a lens element made of fused silica. This exemplary embodiment therefore has only a single flint lens element per lens section, specifically L8 or L8'. As a result, the chromaticity shift of the Petzval sum cannot in principle be completely corrected. However, this appears to be relatively unimportant with respect to imaging performance due to the relatively small numerical aperture (NA=0.18) and the associated relatively large depth of field.

[0105] The projection lens 500 of FIG. 5 (fourth exemplary embodiment) is a further example of a minimal use of flint lens elements, by providing only one flint lens element per lens section. Proceeding from the previous exemplary embodiment, the number of used lens elements could also be further reduced. An essential contribution to this was achieved by the use of additional aspheric surfaces. In this case, all lens elements that do not consist of flint glass are designed as aspheric lens elements with a single aspheric lens element surface. Thus, the number of aspheric surfaces is increased from 2×4 (in the third exemplary embodiment) to 2×6, and as a result, the number of lens elements could be reduced to 2×8.

[0106] A fifth exemplary embodiment (projection lens 600 in FIG. 6) shows that the number of lens elements can be further reduced by the use of a near field double aspheric surface per lens section (lens element L1 or L1′), which reduces the number to seven lens elements per lens section in each case.

[0107] A symmetrical 1:1 lithography system for mercury i-line (365.5 nm) intended for use as a stepper is presented as an example, i.e. capable of imaging a full 6 inch reticle using a single exposure without scanning. However, the 104 x 132 mm 2 Smaller than, say, only 104 x 28 mm 2 A scanning system having an objective field of view of 100 nm can also be used.

[0108] [Table 1-1] [Table 1-2]

[0109] [Table 2]

[0110]

Table 3-1

Table 3-2

[0111]

Table 4

[0112]

Table 5-1

Table 5-2

[0113]

Table 6

[0114]

Table 7

[0115]

Table 8

[0116]

Table 9

[0117]

Table 10

[0118]

Table 11

Claims

1. A refractive projection lens (PO) for imaging a pattern disposed in an object plane (OS) of said projection lens (PO) onto an image plane (IS) of said projection lens using electromagnetic radiation having an operating wavelength in the ultraviolet region longer than 280 nm, said projection lens comprising: a plurality of lens elements arranged along an optical axis (AX) between the object plane (OS) and the image plane (IS), the lens elements being implemented so that a pattern (PAT) arranged on the object plane can be imaged on the image plane using the plurality of lens elements, a stop plane (BE) suitable for mounting an aperture stop (AS) is positioned between the object plane and the image plane, and a chief ray of the image intersects with the optical axis (AX) of the stop plane; A refractive projection lens, characterized in that the projection lens is designed as a wide-field lens with an objective field radius (OBH) of at least 52 mm and has a structure with an imaging scale of 1:1 that is mirror-symmetric with respect to the aperture plane (BE).

2. 2. The projection lens of claim 1, wherein the objective field radius OBH is at least 84 mm.

3. 3. The projection lens according to claim 1, characterized in that the object-side and image-side numerical aperture is less than 0.3, said numerical aperture preferably being in the range of 0.1 to 0.

2.

4. 4. The projection lens according to claim 1, wherein the projection lens has an objective field radius OBH, an objective side numerical aperture NAO, and a geometric etendue LLW=OBH·NAO of at least 10 mm, the geometric etendue being 15 mm or more.

5. 5. The projection lens according to claim 1, characterized in that the projection lens has a installation length TT measured between the object plane (OS) and the image plane (IS), an object field radius OBH, and an object-side numerical aperture NAO, and in that the condition (OBH NAO) / TT>0.01 applies.

6. 6. The projection lens according to claim 1, characterized in that the lens elements comprise at least one flint lens element made of a first material having a relatively lower 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, preferably no more than two flint lens elements being arranged on each side of the aperture plane, in particular only a single flint lens element being arranged on each side of the aperture plane (BE).

7. Projection lens according to any one of the preceding claims, characterized in that the single flint lens element (L6, L8) has a negative refractive power.

8. 8. The projection lens according to claim 7, characterized in that the single flint lens element (L6, L8) having a negative refractive power is arranged in the aperture region (BB), in particular in a region where the ray height ratio |CRH / MRH|<0.5, and / or the single flint lens element is a biconcave lens element.

9. Projection lens according to any one of the preceding claims, characterized in that it comprises at least one flint lens element (L21, L1) with positive refractive power on each side of the diaphragm surface (BE).

10. 7. The projection lens according to claim 6, characterized in that the flint lens elements (L21, L1) having positive refractive power are arranged in the optical vicinity of a field surface in a region in which the ray height ratio of the image satisfies the condition CRH / MRH>0.

7.

11. Projection lens according to any one of the preceding claims, characterized in that at least two positive lens elements are arranged immediately adjacent to, on each side of, said diaphragm surface (BE).

12. 12. Projection lens according to any one of claims 1 to 11, characterized in that at least one of the lens elements on each side of the aperture plane (BE) is aspheric having at least one rotationally symmetric aspheric lens element surface.

13. 13. The projection lens according to claim 12, characterized in that at least one of the aspheric surfaces is configured as a double aspheric surface, the entrance surface and the exit surface are designed as rotationally symmetric aspheric lens surfaces, preferably the lens element closest to the object surface (OS) and the lens element closest to the image surface (IS) being double aspheric.

14. 14. The projection lens according to claim 1, characterized in that the projection lens is designed for UV radiation of the i-line of a mercury lamp (LS) and / or for UV radiation with a bandwidth of 5 nm or less.

15. 1. A projection exposure apparatus (WST) for exposing a radiation-sensitive substrate arranged in the area of ​​an image plane (IS) of a projection lens (PO) using at least one image of a pattern arranged in the area of ​​an object plane (OS) of said projection lens (PO), a light source (LS) emitting electromagnetic radiation with an operating wavelength in the ultraviolet region longer than 280 nm; an illumination system (ILL) for receiving light of the light source and for forming an illumination radiation that is directed towards the pattern; and a projection lens (PO) for imaging structures of said pattern onto a photosensitive substrate (W), said projection lens (PO) being embodied according to any one of claims 1 to 14.

16. 16. The projection exposure apparatus according to claim 15, characterized in that the projection exposure apparatus (WST) is designed as a wafer stepper for a step-and-repeat process.

17. 17. The projection exposure apparatus according to claim 15 or 16, characterized in that the light source is a mercury lamp (LS) emitting electromagnetic radiation in the i-line of a mercury lamp (LS) and / or the radiation has a bandwidth of less than or equal to 5 nm.

18. 1. A projection exposure method for exposing a radiation-sensitive substrate using at least one image of a pattern of a mask, comprising the steps of: - providing the pattern between an illumination system of a projection exposure apparatus and a projection lens such that the pattern is located in the area of ​​an object plane of the projection lens; holding the substrate such that a radiation sensitive surface of the substrate is located in a region of an image plane of the projection lens that is optically conjugate with the object plane; illuminating an illumination area of ​​the mask with illumination radiation provided by the illumination system at an operating wavelength in the ultraviolet range longer than 280 nm; and a step of projecting, using the projection lens, a portion of the pattern located in the illumination area onto an image field on the substrate, in which all rays of projection radiation contributing to image generation in the image field form a projection beam path, wherein a projection lens according to any one of claims 1 to 14 is used.

19. 16. Projection exposure method according to claim 15, characterized in that the substrate is exposed in a step-and-repeat process without scanning and / or that illumination radiation of the i-line of a mercury lamp and / or illumination radiation with a bandwidth of less than 5 nm is used.

Images