WO2023144099A1 - Lentille de projection, appareil d'exposition par projection et procédé d'exposition par projection - Google Patents

Lentille de projection, appareil d'exposition par projection et procédé d'exposition par projection Download PDF

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Publication number
WO2023144099A1
WO2023144099A1 PCT/EP2023/051582 EP2023051582W WO2023144099A1 WO 2023144099 A1 WO2023144099 A1 WO 2023144099A1 EP 2023051582 W EP2023051582 W EP 2023051582W WO 2023144099 A1 WO2023144099 A1 WO 2023144099A1
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WIPO (PCT)
Prior art keywords
lens
lens element
projection
projection lens
flint
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PCT/EP2023/051582
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English (en)
Inventor
Alexander Epple
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Carl Zeiss Smt Gmbh
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Publication of WO2023144099A1 publication Critical patent/WO2023144099A1/fr

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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70216—Mask projection systems
    • G03F7/70241—Optical aspects of refractive lens systems, i.e. comprising only refractive elements
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70216—Mask projection systems
    • G03F7/70316—Details of optical elements, e.g. of Bragg reflectors, extreme ultraviolet [EUV] multilayer or bilayer mirrors or diffractive optical elements
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/708—Construction of apparatus, e.g. environment aspects, hygiene aspects or materials
    • G03F7/7095—Materials, e.g. materials for housing, stage or other support having particular properties, e.g. weight, strength, conductivity, thermal expansion coefficient
    • G03F7/70958—Optical materials or coatings, e.g. with particular transmittance, reflectance or anti-reflection properties

Definitions

  • the invention relates to a dioptric projection lens for imaging a pattern arranged in an object plane of the projection lens into an image plane of the projection lens by means of electromagnetic radiation at an operating wavelength in the ultraviolet range of longer than 280 nm, a projection exposure apparatus equipped with the projection lens and a projection exposure method that can be carried out with the aid of the projection lens.
  • Microlithographic projection exposure methods are predominantly used nowadays for producing semiconductor components and other finely structured components, for example masks for photolithography.
  • masks reticles
  • pattern generating devices which carry or form the pattern of a structure to be imaged, for example a line pattern of a layer of a semiconductor component.
  • the pattern is positioned in the region of the object plane of the projection lens between an illumination system and a projection lens in a projection exposure apparatus and illuminated by illumination radiation provided by the illumination system.
  • the radiation modified by the pattern travels through the projection lens as projection radiation, said projection lens imaging the pattern onto the substrate to be exposed.
  • the surface of the substrate is arranged in the image plane of the projection lens, which image plane is optically conjugate to the object plane.
  • the substrate is generally coated with a radiation-sensitive layer (resist, photoresist).
  • critical structures that is to say fine structures
  • DUV deep ultraviolet range
  • EUV extreme ultraviolet range
  • Projection exposure apparatuses for operating wavelengths at 365.5 nm ⁇ 2 nm are used particularly frequently for these applications. They use the i-line of a mercury vapour lamp, with the natural full bandwidth thereof being restricted with the aid of a filter, or in any other way, to a narrower used bandwidth AX, for example of approx. 4 nm.
  • ultraviolet light of a relatively broad wavelength band is used such that the projection lens must bring about a relatively strong correction of chromatic aberrations in order to ensure low-aberration imaging at the sought-after resolution, even with a broadband projection light.
  • the longitudinal chromatic aberration (CHL) in particular, must be corrected in order to attain a sufficient imaging quality.
  • Transparent materials used in the typical i-line projection lenses include, in particular, synthetic fused silica (SiOz) and the specialist glasses made commercially available under the designations FK5, LF5 and LLF1 by SCHOTT, Mainz, Germany.
  • the synthetic fused silica and the FK5 glass are typical representatives of glasses with relatively low dispersion (crown glasses), while the glasses LF5 and LLF1 are typical representatives of glasses with relatively high dispersion (flint glasses).
  • Other manufacturers provide different names for their types of glasses.
  • lens elements made of a crown glass are referred to as “crown lens elements” and lens elements made of a flint glass are also referred to as “flint lens elements” within this application.
  • the longitudinal chromatic aberration can be corrected by the use of a combination of at least one crown lens element of positive refractive power and at least one flint lens element of negative refractive power.
  • This lens element pair should be arranged in a region of the optical imaging system in which the marginal ray of the imaging has a ray height (marginal ray height) that is as large as possible. As a rule, this is the case in a stop region in the vicinity of the system stop.
  • the invention provides a dioptric 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 provided. Advantageous developments are specified in the dependent claims. The wording of all the claims is incorporated by reference in the content of the description.
  • a dioptric projection lens which is embodied to image a pattern arranged in the object plane of the projection lens into the image plane of the projection lens with the aid of electromagnetic radiation at an operating wavelength in the ultraviolet range of longer than 280 nm.
  • All optical elements equipped with refractive power are lens elements, that is to say refractive optical elements.
  • the projection lens contains exclusively lenses and does not include diffractive optical elements (DOEs) with optical power.
  • DOEs diffractive optical elements
  • a stop position suitable for attaching an aperture stop is located between the object plane and the image plane, a chief ray of the imaging intersecting the optical axis at said stop position.
  • the lens elements comprise at least one flint lens element made of a first material with a relatively low Abbe number and at least one crown lens element made of a second material with a higher Abbe number relative to the first material. At least one crown lens element with positive refractive power and at least one flint lens element with negative refractive power but no more than two flint lens elements with negative refractive power are arranged in a stop region around the stop position.
  • the stop region is distinguished in that the condition
  • flint material has a number of disadvantageous properties.
  • flint glasses typically exhibit a reduced transmission of the used light, which is tantamount to increased absorption.
  • a flint lens element of negative refractive power in the region of large marginal ray heights can contribute particularly effectively to the colour correction, in particular to the correction of the longitudinal chromatic aberration CHL, since, to a first approximation, the longitudinal chromatic aberration CHL of a lens element is proportional to the square of the marginal ray height at the location of the lens element (and proportional to the refractive power and inversely proportional to the Abbe number of the lens element). Nevertheless, the invention teaches only the reduced application of these correction means.
  • the projection lens having an imaging scale of more than 4:1 , that is to say (IPI > 0.25).
  • the imaging scale can be 2:1 (
  • 0.50) or less, optionally also 1 :1 (
  • 1).
  • the reduction of such lenses is not as significant as in the case of conventional i-line projection lenses, which are frequently designed for a 4:1 or 5:1 reduction.
  • This approach is based, inter alia, on the following considerations:
  • the throughput of the systems can be increased in comparison with projection lenses with a greater reduction (with
  • 0.25 or less).
  • the geometric etendue LLW can be defined as the product of the (dimensionless) object-side numerical aperture NAo and the object field size parameterized by the object field height OBH (in millimetres), that is to say
  • the object field height OBH corresponds to the object field radius, that is to say the radius of the minimal circle enclosing those object field points for which the optical correction satisfies the specification, that is to say is sufficiently good.
  • This circle needs to be so large that the effective object field is enclosed.
  • the image-side numerical aperture NA is less than 0.4, with preferably the condition 0.1 ⁇ NA ⁇ 0.4 applying.
  • the geometric etendue LLW is at least 7 mm, with the condition 10 mm ⁇ LLW ⁇ 18 mm preferably applying.
  • Some embodiments are distinguished in that they comprise only a single negative lens element made of flint material, that is to say only a single flint lens element with negative refractive power. Therefore, only the minimum required quantity of this correction means is used.
  • this negative lens element made of flint material is the only flint lens element in the projection lens, and so the latter comprises only exactly one flint lens element As a result, the use of flint material is reduced to a minimum.
  • the only flint lens element is a biconcave lens element.
  • a biconcave lens element large refractive powers (or curved surfaces) can be realized with angles of incidence that are not too large.
  • the single flint lens element with negative refractive power is arranged in the stop region, in particular in a region for which the condition
  • a flint lens element of negative refractive power in the region of large marginal ray heights can contribute particularly effectively to the colour correction, in particular to the correction of the longitudinal chromatic aberration CHL, since the longitudinal chromatic aberration CHL of a lens element is proportional to the square of the marginal ray height at the location of the lens element (and proportional to the refractive power and inversely proportional to the Abbe number of the lens element).
  • chromatic aberrations in particular longitudinal chromatic aberrations
  • lens elements made of flint material are negative lens elements.
  • no positive lens element made of flint material is provided.
  • only exactly two flint lens elements are provided.
  • the chromatic variation of the field curvature remains as limiting chromatic aberration. It may therefore be advantageous to use at least one positive lens element made of flint material, especially in view of correcting the chromatic variation of the field curvature.
  • the projection lens to comprise at least one lens element with positive refractive power (converging lens) made of a first material, that is to say at least one positive flint lens element.
  • a positive lens element made of flint material is arranged in a region in which the ray height ratio
  • the projection lens is embodied as a one-waist system.
  • This comprises a first lens element group with positive refractive power close to the object plane; a second lens element group with negative refractive power following the first lens element group, for producing a waist around a region of minimal ray heights between the object plane and the image plane; a third lens element group with positive refractive power following the second lens element group, between the second lens element group and a stop position; and a fourth lens element group with positive refractive power, between the stop position and the image plane.
  • a refractive power sequence P-N-P-P is realizable, where "P" represents a lens element group with positive refractive power overall and "N” represents a lens element group with negative refractive power overall.
  • the projection lens can be embodied so that no further lens element groups are present apart from the aforementioned four lens element groups. Then, the first lens element group immediately follows the object plane.
  • a front negative group with at least one lens element with negative refractive power is arranged between the object plane and the first lens element group.
  • a refractive power sequence N-P-N-P-P is realizable. If a projection lens is designed as a one-waist system, an important contribution can be made to the Petzval correction in the case of an overall compact building mass.
  • a class of projection lenses with particularly practical properties is characterized in that a projection lens is embodied as a one-waist system with 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 2:1 (
  • 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 with negative refractive power.
  • the projection exposure apparatus and hence also the projection lens are designed for radiation at the i-line of a mercury vapour lamp (central operating wavelength of approx.365.5 nm, optionally with a restricted bandwidth of a few nm).
  • a mercury vapour lamp central operating wavelength of approx.365.5 nm, optionally with a restricted bandwidth of a few nm.
  • An i-line system operates with a mercury vapour lamp as a light source and only uses i-line radiation for imaging purposes.
  • Suitable coatings for lenses and good photoresists, inter alia, are well established for these powerful light sources, and so it is possible in this respect to build on earlier developments.
  • other light sources and/or other UV operating wavelengths can also be used.
  • two or three lines of a mercury vapour lamp g-, h- and i-line at approx. 436 nm, approx.
  • a frequency tripled Nd:YAG laser at approximately 355 nm could be used.
  • LED sources which emit wavelengths between 360 and 400 nm.
  • the emission range may also be slightly tuned.
  • Fig. 1 shows a schematic illustration of a projection exposure apparatus according to one exemplary embodiment
  • Fig. 2 shows a schematic meridional lens element sectional view of a projection lens according to a first exemplary embodiment
  • Fig. 3 to Fig. 8 show schematic meridional lens element sectional views of a projection lens according to a second, third, fourth, fifth, sixth and seventh exemplary embodiment.
  • FIG. 1 shows an example of a microlithographic projection exposure apparatus WST, which is utilizable in the production of semiconductor components and other finely structured components and which operates with light or electromagnetic radiation from the ultraviolet (UV) range in order to obtain resolutions down to fractions of micrometres.
  • a mercury vapour lamp serves as primary radiation source or as light source LS. Said lamp emits a broad spectrum with emission lines of relatively high intensity I in wavelength ranges with centroid wavelengths at approx. 436 nm (visible light, blue, g-line), approx. 405 nm (visible light, purple, h-line) and approx. 365.5 nm (near ultraviolet, UV-A, i-line). This part of the spectrum is illustrated in the schematic l(X) diagram.
  • the projection exposure apparatus is an i-line system which only uses the light from the i-line, that is to say UV light around a central operating wavelength of approx. 365.5 nm.
  • the natural full bandwidth of the i-line is restricted with the aid of a filter, or in any other way, to a narrower used bandwidth AX, for example of approx. 5 nm.
  • an illumination system ILL disposed downstream of the light source LS generates a large, sharply delimited and substantially homogeneously illuminated illumination field, which is adapted to the requirements of telecentricity of the projection lens PO arranged downstream thereof in the light path.
  • the illumination system ILL has devices for setting different illumination modes (illumination settings) and, for example, it can be switched between conventional on-axis illumination with different degrees of coherence a and off-axis illumination.
  • Those optical components which receive the light from the light source LS and form illumination radiation from the light, which illumination radiation is directed to the reticle M, are part of the illumination system ILL of the projection exposure apparatus.
  • a device RS for holding and manipulating the mask M (reticle) in such a way that the pattern arranged at the reticle lies in the object plane OS of the projection lens PO, which coincides with the exit plane ES of the illumination system and which is also referred to here as reticle plane OS.
  • the projection lens PO that is to say an imaging system, which images an image of the pattern arranged at the mask M with a defined imaging scale, for example with a reducing scale 1 :2 (
  • 0.50), onto a substrate W coated with a photoresist layer, the light-sensitive substrate surface SS of which lies in the region of the image plane IS of the projection lens PO.
  • the substrate to be exposed which is a semiconductor wafer W in the exemplary case, is held by a device WS that is also referred to as "wafer stage".
  • the illumination field produced by the illumination system ILL defines the effective object field OF used during the projection exposure.
  • the latter is rectangular, it has a height A* measured parallel to the y-direction and it has a width B* ⁇ A* measured perpendicular thereto (in the x-direction).
  • the aspect ratio AR B*/A* is approximately 104/132.
  • the effective object field lies centred to the optical axis (on-axis field). With a system with this field size, a typical 6” reticle can be brought to imaging in a single exposure step.
  • scanning systems are often also used; their object fields are smaller than 104 x 132 mm 2 , for example only 104 x 28 mm 2 .
  • the effective image field in the image surface IS which is optically conjugate to the effective object field, has the same form and the same aspect ratio between the height B and width A as the effective object field, but, in the case of projection lenses with a reducing action (with
  • ⁇ 1), the absolute field dimension is reduced by the imaging scale P of the projection lens, that is to say A
  • A* and B
  • the image field has the size of the effective object field.
  • the projection exposure apparatus can be designed as a wafer stepper for a step-and-repeat process. It is possible to dispense with devices for carrying out scanning operations for the exposure of a die.
  • a projection exposure apparatus may also be designed as a wafer scanner for a step-and-scan process. Then devices for carrying out scanning operations for the exposure of a die should be provided.
  • the circle which is centred around the optical axis OA which encloses an effective object field OF and which touches the corners thereof specifies the size of the object field within which the optical correction at all field points must meet the specification. This then also applies to all field points in the effective object field. The correction of aberrations becomes more complicated the larger this object field has to be.
  • the size of the circle is parameterized by the object field radius OBH or half the object field diameter OBH, which simultaneously corresponds to the maximum field height of an object field point.
  • Chromatic aberrations are imaging aberrations of optical systems that arise due to the fact that the refractive index n of transparent optical materials varies as a function of the wavelength A. This dependence dn/dX is referred to as a dispersion of the optical material. In general, the refractive index of optical materials is greater for shorter wavelengths than for longer wavelengths.
  • Chromatic aberrations can be subdivided into various categories.
  • a first category of chromatic aberrations takes account of the fact that a dedicated image is produced for each wavelength in the paraxial region (on the optical axis) and that these images may vary in respect of their position along the optical axis, their form and/or their size.
  • the chromatic aberrations of the first category include the longitudinal chromatic aberrations CHL (axial chromatic aberration, axial colour, AX) and the chromatic magnification aberrations or the chromatic difference of magnification CHV (lateral colour LAT).
  • the longitudinal chromatic aberration is the longitudinal aberration of the paraxial focal position as a function of wavelength. If the refractive index for shorter wavelengths is greater than for longer wavelengths, the shorter wavelengths are refracted more strongly at each optical surface such that, for example in the case of a simple positive lens element, the rays of the relatively shorter wavelength are brought together at a focal position that lies closer to the lens element than the focus of the relatively longer wavelength.
  • the paraxial distance along the optical axis of the lens element between the two focal points is the longitudinal chromatic aberration. If the rays with a shorter wavelength are focused closer to the imaging system than the rays of longer wavelength, the longitudinal chromatic aberration is usually referred to as "under-corrected" or "negative".
  • a chromatic magnification aberration or a chromatic difference of magnification is present.
  • the chromatic difference of magnification can be quantified by the lateral distance between the paraxial image heights of the different wavelengths.
  • the dispersion that is to say the chromatic variation of the refractive index, of the utilized optics materials may also cause variations of monochromatic aberrations, which may be combined in a second category of chromatic aberrations.
  • these include the chromatic variation of the spherical aberration, the chromatic variation of the field curvature, etc.
  • the imaging with light from a broadband radiation source is considered, the latter emitting light with different wavelengths around a central wavelength A, wherein the radiation distribution is characterizable by a spectral bandwidth AA (full width at half maximum).
  • a spectral bandwidth AA full width at half maximum.
  • chromatic aberrations can be characterized with the aid of the focal positions for the different wavelengths along the optical axis for three wavelengths within the spectral bandwidth.
  • the three wavelength components have the wavelengths Ai , A2 and A3, where A1 ⁇ A2 ⁇ A3.
  • the size of the longitudinal chromatic aberration CHL then corresponds to the maximum length of the focal range along the optical axis into which the different wavelengths are focused. Typically, one of the wavelengths is focused closer to the imaging system than the other wavelengths. The distance between the closest focal position of the wavelengths and the focal position of the wavelengths furthest away corresponds to the size of the longitudinal chromatic aberration of the imaging system for the broadband light source.
  • the focal position of the central wavelength A along the optical axis can be considered to be the image plane within the focal range.
  • the variation of the paraxial focus position with the wavelength is normally expanded in a power series.
  • the linear portion is referred to as "primary spectrum” and the quadratic portion is referred to as “secondary spectrum”, moreover, it is also possible to define a "tertiary spectrum” by way of the cubic portion.
  • the primary spectrum can be corrected by combining converging and diverging lens elements that consist of different optical materials with different dispersion. More specifically, it is possible to correct the longitudinal chromatic aberration in such a way that the paraxial focal planes for two different wavelengths, for example the minimum Ai and the maximum A 3 wavelength of the spectral range, coincide on the optical axis.
  • Such optical imaging systems are also referred to as “achromatized” or as an "achromat" in this application.
  • a longitudinal chromatic aberration remainder remains for other wavelengths that are not captured by the correction.
  • This longitudinal chromatic aberration remainder is usually the "secondary spectrum”.
  • the secondary spectrum may possibly be corrected to such an extent that the focal positions of all three wavelengths Ai , A 2 and A 3 of the considered wavelength range lie at the same axial position; only the "tertiary spectrum" remains in turn.
  • an optical system where the secondary spectrum is also corrected is also referred to as "apochromatically corrected” or as an "apochromat".
  • the longitudinal chromatic aberration for two spaced apart wavelengths becomes very small (possibly down to a value of zero) in the case of an achromatic imaging system.
  • the longitudinal chromatic aberration for three spectrally spaced apart wavelengths becomes very small (possibly down to a value of zero) in the case of an apochromatic optical imaging system.
  • the Abbe number v facilitates a characterization of the dispersion properties of a material in a wavelength range of interest.
  • low Abbe numbers represent materials with a relatively strong dispersion and high Abbe numbers represent materials with a relatively weak dispersion. Therefore, the Abbe number is sometimes also referred to as "reciprocal relative dispersion".
  • the Abbe number v Hg should be related to the range of the ultraviolet spectral range.
  • the Abbe numbers for the glasses utilized are listed in Table 10.
  • Lens element materials for operating wavelengths at emission lines of a mercury vapour lamp can be divided into three different groups, depending on their refractive index and their Abbe number.
  • a first group includes those materials whose Abbe number is found in the range from 40 to 70.
  • the materials in the first group have typical refractive indices in the range from 1 .46 to 1.56 at the mercury i-line.
  • the materials of the first group include, inter alia, synthetic fused silica (SiO 2 ) and various borosilicate glasses, such as BK7 glass or the glasses K5, K7 or FK5.
  • a second group comprises materials with Abbe numbers of greater than 70.
  • Some materials in the second group for example crystalline calcium fluoride (fluorspar or CaF 2 ), have a refractive index of less than 1 .46.
  • a third group comprises materials with Abbe numbers of less than 40. These materials have refractive indices of more than approximately 1.56.
  • the materials of the third group include, inter alia, typical flint glasses such as LLF-6 glass, LLF-1 glass or LF-5 glass.
  • an optical system should have lens elements made of at least two materials with different dispersions or different Abbe numbers.
  • first optical elements made of a first material with a relatively low Abbe number and second optical elements made of a second material with a higher Abbe number relative to the first material should be combined.
  • materials of the second group are used as relative crown materials.
  • materials of the third group are used as relative flint materials.
  • Materials of the first group can act as relative crown material in combination with a material from the third group and as relative flint material in combination with a material of the second group.
  • synthetic fused silica S1O2 acts as a relative crown material.
  • synthetic fused silica is combined with a material of the second group, for example CaF2, the fused silica acts as a relative flint material.
  • first materials with a relatively low Abbe number are also referred to as “relative flint materials” and second materials with a relatively higher Abbe number are also referred to as “relative crown materials”.
  • lens elements made of a relative crown material are also referred to as “crowns lens elements” for short and lenses made out of a relative flint material are also referred to as “flint lens elements” for short in a more specific exemplary embodiment in this application.
  • materials from the first and the third material group are used.
  • the term "optical axis" denotes a straight line through the centres of curvature of the curved lens element surfaces.
  • the object is a mask (reticle) with the pattern of an integrated circuit; it may also relate to a different pattern, for example of a grating.
  • the image is projected onto a wafer provided with a photoresist layer, said wafer acting as a substrate.
  • substrates are also possible, for example elements for liquid crystal displays or substrates for optical gratings.
  • a chief ray CR refers to a ray which starts from an edge point of the object field and intersects the optical axis in the region of a pupil plane, that is to say in the region of a stop position suitable for attaching an aperture stop (AS).
  • a marginal ray MR within the meaning of the present application leads from the centre of the object field to the edge of the aperture stop. The perpendicular distance of these rays from the optical axis yields the corresponding ray height.
  • stop region denotes a region around the stop position (that is to say, upstream and downstream of the stop position), in which a ray height ratio
  • crown lens elements in particular fused silica lens elements or lens elements made of FK5
  • flint lens elements in particular lens elements made of LF5 or LLF1
  • Aspherical surfaces are marked by short asphere dashes.
  • Tables 2 to 8 summarize the specification of the respective design in tabular form.
  • column “SURF” indicates the number of a refractive surface or surface distinguished in some other way
  • column “RADIUS” indicates the radius r of the surface (in mm)
  • column “THICKNESS” indicates the distance d - designated as thickness - between the surface and the subsequent surface (in mm)
  • column “MATERIAL” indicates the material of the optical components.
  • Columns “INDEX1”, “INDEX2” and “INDEX3” indicate the refractive index of the material at the wavelengths 365.5 nm (INDEX1), 364.5 nm (INDEX2) and 366.5 nm (INDEX3).
  • SEMIDIAM indicates the usable, free radii or the free optical semidiameters of the lens elements (in mm) or of the optical elements.
  • Some optical surfaces are aspherical.
  • the reciprocal (1/r) of the radius indicates the surface curvature and h indicates the distance between a surface point and the optical axis (i.e. , the beam height). Consequently, p(h) indicates the sagittal height, that is to say the distance between the surface point and the surface vertex in the z-direction (direction of the optical axis).
  • the coefficients K, C1 , C2, ... are represented in the tables with appended “A”.
  • Table 9 assembles important design parameters of the exemplary embodiments in an overview. in the following description of exemplary embodiments, the same reference signs are used in all figures for the same or corresponding features. Lens elements are numbered in their sequence from the object plane to the image plane, and so, for example, the lens element L1 is the first lens element immediately following the object plane. Not all lens elements have been provided with a reference sign for reasons of clarity.
  • Figure 2 shows a schematic meridional lens element sectional view of a first exemplary embodiment of a dioptric projection lens 200 with selected beams for elucidating the imaging beam path or the projection beam path of the projection radiation passing through the projection lens during operation.
  • the projection lens is provided as an imaging system with a reducing effect, for imaging a pattern of a mask arranged in its object plane OS onto its image plane IS aligned parallel to the object plane directly, i.e. , without producing an intermediate image, and with a reduced scale, specifically In the scale of -1 :2 (the imaging scale is -0.5).
  • the only pupil plane PUP of the imaging system lies where the chief ray CR of the optical imaging intersects the optical axis OA.
  • the aperture stop AS of the system is attached in the region of the pupil plane. Therefore, the position suitable for attaching the aperture stop is also referred to as stop position BP here.
  • a stop region BB extends around the stop position, the condition
  • the marginal ray height is higher than the chief ray height.
  • a first lens element group LG1 with positive refractive power and a total of four lens elements L1 to L4 immediately follows the object plane OS.
  • the first lens element group collects the rays coming from the field points of the object plane and, as a result, forms, at least approximately, a bulge in the projection beam path.
  • a second lens element group LG2 with negative refractive power immediately follows the first lens element group LG1.
  • This second lens element group comprises the two lens elements L5 and L6 and produces a waist around a local minimum of the marginal ray height between the object plane OS and the image plane IS in the projection beam path.
  • a third lens element group LG3 with positive refractive power and a total of two lens elements L7 to L8 immediately follows the second lens element group LG2.
  • the lens elements of the third lens element group are arranged between the second lens element group LG2 and the stop position suitable for ataching an aperture stop AS.
  • a fourth lens element group LG4 with positive refractive power overall is situated between the stop position and the image plane IS.
  • the fourth lens element group LG4 comprises six lens elements L9 to L14 with refractive power.
  • the projection lens is characterized by the refractive power sequence P-N-P-P, where "P” represents a lens element group with positive refractive power and "N” represents a lens element group with negative refractive power.
  • P represents a lens element group with positive refractive power
  • N represents a lens element group with negative refractive power.
  • the design as a one-waist system contributes to the Petzval correction
  • all lens elements consist of crown glass, specifically either synthetic fused silica (SiOz, abbreviated SILUV in Table 2), that is to say a material of the first group with an Abbe number of v Hg ⁇ 60, or the lens element material denoted FK5, that is to say a lens element material of the first group with an Abbe number of v Hg ⁇ 52.
  • SILUV synthetic fused silica
  • the (biconcave negative lens element L8) is a flint lens element; it consists of flint glass with the designation LF5, that is to say a lens material of the third group with a relatively low Abbe number of vn g ⁇ 31.
  • the only necessary flint lens element is the lens element L8 in the direct vicinity of the aperture stop. It is placed approximately at the position of maximum marginal ray height and, together with lens elements L7 to L11 , it is decisive in the correction of the longitudinal chromatic aberration.
  • the very moderate numerical aperture at the image field it is possible to dispense with the correction of the chromatic variation of the Petzval sum, and consequently the only flint lens element required is the lens element L8 in the direct vicinity of the aperture stop and approximately at the point of maximum marginal ray height.
  • the second exemplary embodiment ( Figure 3, projection lens 300) likewise is a one-waist system. However, a refractive power sequence N-P-N-P-P is realized here.
  • a front negative group NV with two lens elements biconvex positive lens element L1 and biconcave negative lens element L2 is arranged between the object plane OS and the first lens element group LG1 , which has positive refractive power overall.
  • Such a negative group in the direct vicinity of the object plane enables the formation of a subsequent bulge at an axially short length, and is consequently conducive to compact structural shape.
  • the second exemplary embodiment ( Figure 3) was supplemented with a further flint lens element.
  • the latter is an imageside convex negative meniscus lens element L19.
  • the individual refractive powers of the two flint lens elements are smaller than the refractive power of the individual flint lens element in Figure 3, which leads to a relaxation of the exemplary embodiment.
  • two diverging flint lens elements are used here on account of the symmetry of the design and the required accessibility to the stop.
  • the projection lens in Figure 5 has mirror symmetry with respect to the stop plane.
  • the stop plane is arranged halfway between the object field (reticle) and image field (wafer). This means that every lens element occurring in the first lens part upstream of the stop (between object plane and stop plane) has an identically designed corresponding part arranged in mirror symmetric fashion in the second lens part downstream of the stop.
  • the design is provided or designed for use with a light wavelength of 365 nm and the bandwidth of a few nm. Therefore, a longitudinal correction of the primary spectrum (longitudinal chromatic aberration) is sufficient. This is brought about by a diverging fling lens element in the vicinity of the aperture stop (i.e. , in the case of a large marginal ray height). If no material with anomalous partial dispersion is used as flint material, a secondary spectrum sets in automatically in the longitudinal direction. This is the case for the available materials such as LF5 or LLF1.
  • the transverse chromatic aberration is intrinsically corrected by way of the symmetry of the structure, just like the distortion and coma aberrations and the chromatic variations thereof. Hence, no separate correction means are required to this end.
  • Petzval sum PTZ is given by where i denotes the index of the surface in the optical system (the system is described by k surfaces), denotes the radius of the i-th surface and n/ denotes the refractive index upstream and downstream of the surface.
  • Petzval sum of a one-material system vanishes it follows that the j variation with the wavelength also vanishes.
  • a Petzval-corrected, dioptric one-material system thus exhibits no variation of the Petzval sum with the wavelength.
  • this approach is implemented in the following exemplary embodiments, by virtue of an additional flint lens element, specifically a flint lens element with a positive refractive power, being additionally introduced into the design.
  • this converging flint lens element is an obstacle to the correction of the longitudinal chromatic aberration.
  • the converging flint lens element should therefore preferably be used at a point in the design where the marginal ray height is as small as possible. This is the case in the vicinity of the reticle or the wafer in particular, that is to say in an optical field-near position.
  • the flint lens element with positive refractive power has been used in the vicinity of the wafer.
  • the additional flint lens element with positive refractive power may also be used in the vicinity of the reticle, for example as part of the front negative group NV, specifically as a first lens element L1 of the design.
  • This is depicted in the sixth exemplary embodiment ( Figure 7, projection lens 700). The remaining argument is identical to the description of Figure 5.
  • the seventh exemplary embodiment ( Figure 8, projection lens 800) can be considered to be a variant of the first exemplary embodiment.
  • a further flint lens element is used in the vicinity of the reticle in addition to the first exemplary embodiment. This substantially serves to correct the chromatic variation of the Petzval sum; however, this is not mandatory in the case of the present small numerical aperture of 0.18.
  • this first flint lens element moreover still significantly simplifies the first lens element group LG1 downstream of the reticle; in comparison with the first exemplary embodiment, an asphere and two lens elements can be saved as a result of the flint lens element.
  • the flint lens element with its higher refractive index significantly simplifies the correction of the aberrations despite increased individual refractive powers.
  • the exemplary embodiments verify by way of example that the inventor has been successful in developing i-line lenses with a reduced use of flint lens elements.
  • the i-line of the mercury vapour lamp is "only" a single emission line, the bandwidth thereof, even after a bandwidth restriction to 5 nm for example, is nevertheless so large that the correction of the longitudinal chromatic aberration of the imaging system is unavoidable, at least in terms of the lowest order, that is to say the correction of the primary spectrum.
  • the imaging scale has been changed from previously 4x to 2x or less in all pictorially represented examples.
  • the image-side numerical aperture therefore reduces and the Rayleigh unit and hence the depth of field range increase.
  • the systems become less sensitive to longitudinal aberrations such as defocus, astigmatism or field curvature.
  • the inventor has recognized that, as a consequence thereof, it is possible to either significantly reduce or entirely dispense with the correction of the chromatic variation of the Petzval sum. This in turn directly affects the number of flint lens elements absolutely necessary within the projection lens. This number is kept as small as possible.

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Abstract

Une lentille de projection dioptrique (PO) servant à imager un motif disposé dans un plan d'objet (OS) de la lentille de projection dans un plan d'image (IS) de la lentille de projection au moyen d'un rayonnement électromagnétique compris dans la plage des rayons ultraviolets de plus de 280 nm comprend une multiplicité d'éléments de lentille qui sont agencés entre le plan d'objet (OS) et le plan d'image (IS) le long d'un axe optique (AX) et qui sont conçus de telle sorte qu'un motif disposé dans le plan d'objet peut être imagé dans le plan d'image au moyen des éléments de lentille, une position d'arrêt (BP) appropriée pour fixer une butée d'ouverture (AS) étant située entre le plan d'objet et le plan d'image, un rayon principal de l'imagerie croisant l'axe optique au niveau de ladite position d'arrêt, les éléments de lentille comprenant au moins un élément de lentille flint constitué d'un premier matériau ayant un nombre d'Abbe relativement faible et au moins un élément de lentille de couronne constitué d'un second matériau ayant un nombre d'Abbe plus élevé par rapport au premier matériau. Un élément de lentille de couronne ayant une réfringence positive et au moins un élément de lentille flint ayant une réfringence négative et pas plus de deux éléments de lentille flint (L16) ayant une réfringence négative sont disposés dans une région d'arrêt (BB) qui est située autour de la position d'arrêt (BP), et dans laquelle la condition | CRH/MRH | < 1 s'applique à un rapport de hauteur de rayon CRH/MRH entre une hauteur de rayon principal CRH et une hauteur de rayon marginal MRH de l'imagerie.
PCT/EP2023/051582 2022-01-31 2023-01-23 Lentille de projection, appareil d'exposition par projection et procédé d'exposition par projection WO2023144099A1 (fr)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5930049A (en) 1996-10-01 1999-07-27 Nikon Corporation Projection optical system and method of using such system for manufacturing devices
US6806942B2 (en) 2002-05-14 2004-10-19 Carl Zeiss Smt Ag Projection exposure system
US20090080086A1 (en) * 2006-05-05 2009-03-26 Carl Zeiss Smt Ag Symmetrical objective having four lens groups for microlithography
CN112415865A (zh) * 2020-12-01 2021-02-26 中国科学院光电技术研究所 一种应用于投影光刻机的单倍率大视场投影曝光物镜

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5930049A (en) 1996-10-01 1999-07-27 Nikon Corporation Projection optical system and method of using such system for manufacturing devices
US6806942B2 (en) 2002-05-14 2004-10-19 Carl Zeiss Smt Ag Projection exposure system
US20090080086A1 (en) * 2006-05-05 2009-03-26 Carl Zeiss Smt Ag Symmetrical objective having four lens groups for microlithography
CN112415865A (zh) * 2020-12-01 2021-02-26 中国科学院光电技术研究所 一种应用于投影光刻机的单倍率大视场投影曝光物镜

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
VOLKER WITT: "Wie funktionieren Achromat und Apochromat", STERNE UND WELTRAUM, pages 72 - 75, Retrieved from the Internet <URL:http://rohr.aiax.de/SUW_2005_10_S072.pdf>

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