Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B13/00—Optical objectives specially designed for the purposes specified below
  • G02B13/24—Optical objectives specially designed for the purposes specified below for reproducing or copying at short object distances
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B13/00—Optical objectives specially designed for the purposes specified below
  • G02B13/14—Optical objectives specially designed for the purposes specified below for use with infrared or ultraviolet radiation
  • G02B13/143—Optical objectives specially designed for the purposes specified below for use with infrared or ultraviolet radiation for use with ultraviolet radiation
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B9/00—Optical objectives characterised both by the number of the components and their arrangements according to their sign, i.e. + or -
  • G02B9/60—Optical objectives characterised both by the number of the components and their arrangements according to their sign, i.e. + or - having five components only
• • 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
  • G03F7/20—Exposure; Apparatus therefor
• • 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
  • G03F7/70341—Details of immersion lithography aspects, e.g. exposure media or control of immersion liquid supply

Definitions

• the invention relates to a projection lens for imaging a pattern arranged in the object plane of the projection lens into the image plane of the projection lens with ultraviolet light of a predetermined working wavelength.
• Photolithographic projection lenses have been used for the manufacture of semiconductor devices and other finely structured components for several decades. They serve to project patterns of photomasks or graticules, which are also referred to below as masks or reticles, onto an object coated with a light-sensitive layer with the highest resolution on a reduced scale.
• phase-shifting masks require obscuration-free systems, ie systems without shadowing in the image field. Systems without shadowing in the image field are in the Microlithography generally to be preferred, even if systems with obscuration with otherwise excellent optical properties are available (for example DE 196 39 586 corresponding to US 6,169,627 B1).
• NA 0.85
• limits are placed on the angular capacity, especially of the near-image lenses.
• the object of the invention is to create a projection objective which has a very high numerical aperture on the image side, an image field which is sufficiently large for practical use in wafer steppers or wafer scanners, and a good correction state.
• a projection lens for imaging a pattern arranged in the object plane of the projection lens into the image plane of the projection lens with ultraviolet light of a predetermined working wavelength has a multiplicity of optical elements which are arranged along an optical axis and one which is arranged at a distance in front of the image plane System cover with a cover diameter.
• the closest optical group with refractive power to the image plane is a plano-convex group with an essentially spherical entrance surface and an im substantially flat exit surface.
• the exit surface is the last optical surface of the system and should be arranged in the vicinity of a substrate to be exposed, but without touching it. If necessary, an optical contact can be imparted via an immersion medium, for example a liquid.
• the plano-convex group has a diameter that is at least 50% of the diaphragm diameter.
• the diameter of the plano-convex group can preferably even be more than 60% or more than 70% of the diaphragm diameter.
• the system aperture in the sense of this application is the area near the image plane in which the main beam of the image intersects the optical axis.
• a diaphragm for limiting and possibly adjusting the aperture used can be arranged in the area of the system diaphragm.
• the plano-convex group is formed by a single, one-piece plano-convex lens. It is also possible to design the plano-convex group in the form of a divided plano-convex lens, the parts of which are preferably pressed against one another. The division can take place along a flat or curved division surface. A division in particular makes it possible to produce the part of the plano-convex group close to the image field, in which particularly high radiation energy densities occur, from a particularly radiation-resistant material, for example as calcium fluoride, while less radiation-exposed areas can be made from another material, for example synthetic quartz glass. A plane-parallel end plate can optionally be provided as the next element of the plano-convex group.
• the plano-convex group is preferably blown onto the preceding optical element.
• the radii to the air gap should be curved this way be that there is no total reflection.
• the angular load preferably remains smaller than sin u ' from 0.85 to 0.95.
• the system diaphragm it is particularly advantageous if only lenses with a positive refractive power are arranged between the system diaphragm and the image plane, if appropriate plus one or more plane-parallel, transparent plates.
• at least one biconvex positive lens can be arranged between the system diaphragm and the plano-convex group. At least two, in particular exactly two, biconvex positive lenses are more favorable.
• a plano-convex meniscus is preceded by two positive lenses, which provide the essential part of the system power. Because they sit close to the system panel and can work in large diameters, a very small relative field load can also be achieved here.
• the last lens group arranged between the system diaphragm and the image plane has a maximum of four optical elements with refractive power, ideally only three lenses, which are preferably positive lenses in each case.
• Lenses with a negative refractive power can be provided as long as their refractive power is low compared to the total refractive power of the lens group arranged between the system aperture and the image plane.
• Plane-parallel plates can also be provided.
• a refractive power distribution that is favorable for a high numerical aperture on the image side is characterized in that the last lens group arranged between the system aperture and the image plane advantageously has a focal length that is less than 20% or 17%, in particular less than 15%, of the overall length of the projection lens is.
• the axial distance between the object plane and the optically conjugate image plane is referred to as the overall length.
• the distance between the system diaphragm and the image plane is preferably less than 25%, in particular less than 22% of the overall length and / or less than approximately 95%, 90% or 86% of the diaphragm diameter. Overall, a very close-to-image position of the system cover is favorable.
• the aperture can be real or equivalent to the conjugate location of the real aperture in the presence of an intermediate image.
• Projection lenses according to the invention can be catadioptric or dioptric and should depict without obscuration. Purely refractive, ie dioptric projection lenses are preferred, in which all optical components with refractive power consist of transparent material.
• One example is a one-waist system with a stomach close to the object, a stomach close to the image and an intermediate waist, in the area of which the beam diameter is preferably less than approximately 50% of the maximum beam diameter in the area of one of the bellies.
• the systems can be set up so that all transparent optical elements are made of the same material.
• synthetic quartz glass is used for all lenses.
• the synthetic quartz glass can be replaced by a crystal material, eg calcium fluoride.
• high-aperture projection objectives in particular also purely refractive projection objectives, are possible, in which the numerical aperture NA> 0.85 on the image side.
• the projection objectives are also suitable for immersion lithography, in which the space between the exit surface of the objective and the substrate is filled with an immersion fluid with a suitable refractive index and sufficient transmission for the wavelength used.
• Suitable immersion liquids can, for example, mainly contain the elements H, F, C or S. Deionized water can also be used.
• the invention makes it possible to use lenses with a very large image field diameter that is sufficient for practical lithography, which in preferred embodiments is larger than approx. 10 mm, in particular larger than approx. 20 mm and / or more than 1 %, in particular more than 1.5% of the overall length of the projection lens and / or more than 1%, in particular more than 5% of the largest lens diameter.
• Preferred projection objectives are distinguished by a number of favorable constructive and optical features which, alone or in combination with one another, are conducive to the suitability of the objective for high-resolution microlithography, in particular in the optical near field and for immersion lithography.
• At least one aspherical surface is preferably arranged in the area of the system cover.
• several surfaces with aspheres come closely behind the diaphragm.
• at least one double-aspherical lens which is preferably a biconvex lens, can be provided between the system aperture and the image plane.
• the last optical surface before the system diaphragm and the first optical surface after the system diaphragm are aspherical.
• opposite aspherical surfaces with curvature pointing away from the diaphragm can be provided here.
• the high number of aspherical surfaces in the area of the system diaphragm is favorable for the correction of the spherical aberration and has a favorable effect on the setting of the isoplanasia.
• At least one meniscus lens with a concave surface on the object is preferably provided in the area immediately in front of the system diaphragm.
• at least two such menisci, which follow one another can be favorable, which can have positive or negative refractive power.
• a group of two menisci of this type is preferred, in which a meniscus with a negative refractive power and a meniscus with a positive one Refractive power follows.
• the negative refractive power is preferably so great that a slight cross-sectional narrowing (auxiliary waist) can occur in the beam.
• a meniscus group with a positive meniscus and a negative meniscus behind it, in which the centers of curvature of all optical surfaces are on the object or reticle side, can also be advantageous for other projection lenses, in particular directly in front of a diaphragm in the area, regardless of the other features of the invention
• the aperture can be a physical aperture for changing the bundle cross-section or a conjugated aperture.
• At least one meniscus lens with a negative refractive power and a concave surface directed toward the image is arranged between the waist and the system diaphragm.
• at least two consecutive meniscus lenses of this type, whose centers of curvature lie on the image side are often particularly favorable.
• the refractive power of the first meniscus on the object side is at least 30% stronger than that of the subsequent meniscus on the image side of the meniscus group.
• At least one positive meniscus lens with a concave surface on the object side is arranged between the waist and the system diaphragm in the vicinity of the waist.
• several, for example two, successive lenses of this type can be provided instead of such a meniscus lens.
• Embodiments are particularly advantageous in which at least one meniscus lens with a concave surface on the object side and behind at least one between the waist and the system diaphragm in this order a meniscus lens with a concave surface on the image side is arranged.
• Two consecutive menisci of the respective curvatures are preferably provided.
• the meniscus lenses facing the waist preferably have positive refractive powers, the menisci facing the image plane preferably have negative refractive powers. In the area between these lenses or lens groups, there is therefore a change in the position of the center of curvature of menisci.
• a plurality of negative lenses are preferably arranged one after the other in the region of the waist, in preferred embodiments there are at least two, preferably three negative lenses. These bear the main burden of the Petzval correction.
• a lens group with a strong positive refractive power which represents the first belly of the beam guidance, preferably follows behind this input group.
• at least one meniscus lens with positive refractive power and concave surfaces on the image side can be favorable in the area of large beam heights in the vicinity of the object plane.
• the center of curvature of which lies on the image side, the exit side facing the image preferably has a relatively strong curvature, the radius of which can be, for example, less than 50% of the overall length of the projection objective.
• 1 is a lens section through an embodiment of a refractive projection objective which is designed for a 193 nm working wavelength.
• optical axis denotes a straight line through the centers of curvature of the spherical optical components or through the axes of symmetry of aspherical elements.
• Directions and distances are described as image-side, wafer-side or image-wise when they are in the direction of the If the image plane or the substrate to be exposed there is directed and as the object side, reticle side or object side, if they are directed towards the object in relation to the optical axis, the object is a mask (reticle) with the pattern of an integrated circuit in the examples
• the image is formed in the examples on a wafer serving as a substrate and serving with a photoresist layer, but other substrates are also possible, for example elements for liquid crystal displays or substrates for optical he grating
• the focal lengths given are focal lengths with respect to air.
• FIG. 1 shows a characteristic structure of a purely refractive reduction objective 1 according to the invention. It serves to insert a pattern of a reticle or the like into an object plane 2 image an image plane 3 conjugated to the object plane on a reduced scale without obscurations or shadowing in the image field, for example on a 5: 1 scale. It is a rotationally symmetrical one-waist system, the lenses of which are arranged along an optical axis 4 which is perpendicular to the object and image plane and form an abdomen 6 on the object side, an abdomen 8 on the image side and an intermediate waist 7. A small auxiliary waist 9 is formed within the second belly 8 close to the system cover 5.
• the system diaphragm 5 is in the near-image area of large beam diameters.
• the lenses can be divided into several successive lens groups with specific properties and functions.
• a first lens group LG1 following the object plane 2 at the input of the projection lens has negative refractive power overall and serves to expand the beam coming from the object field.
• a subsequent second lens group LG2 with an overall positive refractive power forms the first belly 6 and brings the beam together again in front of the subsequent waist 7.
• a third lens group LG3 with negative refractive power is followed by a lens group 4 consisting of positive meniscus lenses with positive refractive power, followed by a fifth lens group LG5 consisting of negative meniscus lenses with negative refractive power.
• the subsequent lens group LG6 with positive refractive power leads the radiation to the system aperture 5.
• the first lens group LG1 opens with three negative lenses 11, 12, 13 which, in this order, have a biconcave negative lens 11 with an aspherical entry side, a negative meniscus lens 12 with an image-side center of curvature and an aspherical entry side and a negative meniscus lens 13 with an object side
• Center of curvature and aspherical exit side includes.
• at least one aspherical surface should be provided on at least one of the first two lenses 11, 12 in order to limit the generation of aberrations in this area.
• an aspherical surface is provided on each of the three negative lenses.
• the second lens group LG2 with a small air gap behind the last lens 13 of the first lens group LG1, has a positive meniscus lens 14 with a center of curvature on the object side, a further positive meniscus lens 15 with an object side
• the only slightly curved entry side of the lens 15, the likewise only slightly curved exit side of the lens 17 and the exit side of the last meniscus lens 20 are aspherical.
• This second lens group LG2 represents the first belly 6 of the objective.
• a special feature is the positive meniscus lens 16 arranged at the largest diameter, the centers of curvature of which lie on the image side.
• the radius of the exit surface of this lens 16 has a value that is less than half the object image distance.
• This lens group is used primarily for Petzval correction, distortion telecentricity correction and image field correction outside of the main sections.
• the first negative lens 20 of the third group is preferably a strongly biconcave lens, so that the main waist 7 opens with strongly curved surfaces.
• the fourth lens group LG4 following the waist 7 consists of two positive meniscus lenses 23, 24 with concave surfaces on the image side, the exit side of the meniscus lens 23 on the input side being aspherical, the other surfaces being spherical. In other embodiments, only a single positive meniscus of corresponding curvature can be provided at this point.
• the subsequent fifth lens group LG5 also has two meniscus lenses 25, 26, but these each have negative refractive power and the concave surfaces are directed toward the image field 3. If necessary, only a negative meniscus can be provided at this point, the center of curvature of which lies on the wafer side. It has turned out to be favorable if the negative refractive power of the negative meniscus 25 on the object side is at least 30% stronger than that of the subsequent meniscus 26.
• Such a group with at least one negative meniscus is a central correction element for the function of the one-waist system, to elegantly correct off-axis image errors. In particular, this enables a compact design with relatively small lens diameters.
• the sixth lens group LG6 begins with a sequence of positive lenses 27, 28, 29, 30, it having turned out to be advantageous if at least two of these lenses are biconvex lenses, such as the lenses 27, 28 which follow one another immediately at the input of the sixth lens group each spherical lens surfaces.
• the biconvex lenses 27, 28 are followed by a weakly positive meniscus lens 29 with a concave surface on the image side.
• the sixth lens group LG6 immediately in front of the system diaphragm 5 there is a meniscus group with two meniscus lenses 30, 31, the centers of curvature of which are all on the reticle or object side.
• a corresponding meniscus lens with positive or negative refractive power could also be provided, in particular in the case of lenses with lower apertures.
• the group of two 30, 31 shown is preferred, the meniscus lens 30 on the input side preferably having positive refractive power and the subsequent meniscus lens 31 preferably having negative refractive power.
• their negative refractive power is so great that a slight constriction in the form of an auxiliary waist 9 occurs in the beam path. In this way it can be achieved that oblique spherical tangential to oblique spherical sagital can be balanced out favorably.
• the seventh lens group LG7 arranged between system aperture 5 and image plane 3 represents a further special feature of the invention Projection lenses. Particularly in this area, special measures are required to master the surface loading of the optical surfaces overall in such a way that low-aberration imaging can be achieved with sufficient transmission of the overall lens. For this purpose, it should be ensured between the aperture 5 and the wafer 3 that no apertures are formed in the component that reach an aperture close to 1 as a component against air. A significant contribution to achieving this goal is made here in that a plano-convex lens 34 with a spherical entrance surface and a flat exit surface is arranged as the last optical element directly in front of the image plane 3.
• the aim should therefore be the longest possible radius with a high opening of this, preferably spherical, entry surface. This long radius is desirable because it reduces the field load on the entry surface. The longer the radius, the smaller the relative field and thus the induced field aberrations.
• the entrance surface can also be aspherical.
• the near-image plano-convex group which is formed here by a single, one-piece lens element 34, has a refractive effect. This can be seen from the fact that the entrance surface is not arranged concentrically to the center of the image field because the radius differs from the lens thickness. Axially elongated lenses of this type are preferred, in which the center of curvature of the entrance surface lies within the lens. Plano-convex groups or plano-convex lenses of this type therefore differ significantly from hemispherical plano-convex lenses in which the radius corresponds essentially to their thickness and which are used, for example, in microscopy to improve the coupling of the light into the microscope objective and themselves may not have any refractive properties.
• the plano-convex meniscus 34 is preceded by two very large positive lenses 32, 33, which provide the essential contribution to the system power.
• the fact that they sit close behind the diaphragm in the area of large beam diameters also minimizes the relative field load here.
• the example thus shows a very simple and efficient design of a lithographic lens suitable for the highest apertures with regard to the area behind the system aperture.
• the plano-convex meniscus 34 picks up the convergent tufts coming from the positive lenses 32, 33 in air or another suitable gaseous medium within the projection lens with a low refractive power in order to pass them on to the light-sensitive layer of the substrate.
• Embodiments are therefore favorable in which there are only positive lenses between the aperture 5 and the wafer, it also being possible for one or more plane-parallel plates to be provided in addition.
• the lowest possible number of optical surfaces in this area is also advantageous, since each surface causes reflection losses even with good anti-reflective coating.
• the number of lenses should be four or fewer here, and again plane-parallel plates can optionally be provided.
• surfaces with aspheres should be provided in the area of the diaphragm, particularly close behind it. These can face each other in a lens, as is the case with the biconvex, double-aspherical positive lens 32. It is also advantageous if an aspherical surface is provided both directly in front of the diaphragm plane and immediately behind it. In the example, these are the exit surface of the negative meniscus 31 and the entry surface of the biconvex positive lens 32.
• the high number of aspheres in the area around the system aperture 5 serves in the example above all to correct the spherical aberration (Zemike coefficients Z9, Z16, Z25, Z26, Z36, Z49) and the setting of the isoplanasia, i.e. the correction of the aperture-related imaging scale.
• Table 1 summarizes the specification of the design in a known manner in tabular form.
• Column 1 gives the number of a refractive or otherwise distinguished surface
• column 2 the radius r of the surface (in mm)
• column 3 the distance d of the surface from the following surface (in mm), which is referred to as thickness
• column 4 the material of the optical components
• column 5 the refractive index or the refractive index of the material of the component, which follows the entry surface.
• Column 6 shows the usable free radii or half the free diameter of the lenses (in mm).
• p (h) [((1 / r) h 2 ) / (1 + SQRT (1 - (1-fK) (1 / r) 2 h 2 )] + C1 * h 4 + C2 * h 6 +. ...
• the numerical aperture on the image side is 1.1.
• the lens has an overall length (distance between image plane and Object level) of 1297mm. With an image size of 22mm, a light guide value (product of numerical aperture and image size) of 24.1 mm is achieved.
• the image-side working distance, ie the distance between the flat exit surface of the last optical element 34 and the image plane 3 is not listed separately. For example, it can be 20 to 50nm. This makes the projection lens suitable for near-field lithography.
• the immersion medium has essentially the same refractive index as the last optical element of the objective (which consists, for example, of glass or crystal), the solid is shortened to achieve a greater distance from the image plane and the resulting larger space is created by the immersion medium, e.g. deionized water filled. If the refractive index of the immersion medium deviates from that of the last optical component, both thicknesses are matched to one another as best as possible.
• a spherical post-correction is advantageous, which can be carried out, for example, with the aid of suitable manipulators on one or more lens elements, for example by adjusting the air gaps. It may also be favorable to easily modify the design shown here as an example.
• the example presented offers further development possibilities in the direction of a higher aperture and / or a smaller number of interfaces.
• some lenses that are adjacent in pairs can be combined to form a single lens in order to reduce the number of interfaces by two.
• the lenses 23 and 24, the lenses 18 and 19, the lenses 13 and 14, the lenses 26 and 27 and / or the lenses 11 and 12 can each be combined to form a lens.
• aspherical surfaces must be installed or modified.
• a combination of lenses is especially useful for shorter wavelengths, e.g. 157nm cheap, where anti-reflective coating and surface roughness of lens surfaces can be problematic.
• a further positive lens behind the diaphragm can be favorable at the highest apertures in order to introduce new aberrations with as few apertures as possible when the apertures are increased.
• the advantages of the invention can be used not only with purely refractive projection lenses, but also with catadioptric projection lenses, in particular those that work with geometric or physical (polarization-selective) beam splitting. Special features are in the structure and function in the area of the near-system screen and between this and the picture plane.
• the upstream lens parts which in the case of catadioptric projection lenses comprise at least one imaging mirror, should at least provide an overcorrection of the longitudinal color error in order to correct the corresponding undercorrection of the last lens group compensate.
• a Petzval overcorrection should preferably be provided in order to provide a lead for the Petzval undercorrection of the last lens group.

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