Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B13/00—Optical objectives specially designed for the purposes specified below
  • G02B13/18—Optical objectives specially designed for the purposes specified below with lenses having one or more non-spherical faces, e.g. for reducing geometrical aberration
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B17/00—Systems with reflecting surfaces, with or without refracting elements
  • G02B17/08—Catadioptric systems
  • G02B17/0892—Catadioptric systems specially adapted for the UV
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B13/00—Measuring arrangements characterised by the use of fluids
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B17/00—Measuring arrangements characterised by the use of infrasonic, sonic or ultrasonic vibrations
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B17/00—Systems with reflecting surfaces, with or without refracting elements
  • G02B17/08—Catadioptric systems
  • G02B17/082—Catadioptric systems using three curved mirrors
  • G02B17/0828—Catadioptric systems using three curved mirrors off-axis or unobscured systems in which all of the mirrors share a common axis of rotational symmetry
• • 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
  • G03F7/70225—Optical aspects of catadioptric systems, i.e. comprising reflective and 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
• • 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
  • G03F7/7035—Proximity or contact printers
• • 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
• • 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
  • G03F7/70966—Birefringence

Definitions

• the present invention relates to a projection objective for imaging a pattern provided in an object plane of the projection objective onto an image plane of the projection objective.
• the projection objective may be used for microlithography projection exposure machines.
• the invention relates, in particular, to exposure machines for semiconductor structures which are designed for immersion operation, that is to say in an aperture range where the image side numerical aperture NA is greater than 1.0.
• the image side numerical aperture NA is limited by the refractive index of the surrounding medium in image space.
• the theoretically possible numerical aperture NA is limited by the refractive index of the immersion medium.
• the immersion medium can be a liquid or a solid. Solid immersion is also spoken of in the latter case.
• the material of the last lens element i.e. the last optical element of the projection objective adjacent to the image
• the design of the last end surface is to be planar or only weakly curved.
• the planar design is advantageous, for example, for measuring the distance between wafer and objective, for hydrodynamic behaviour of the immersion medium between the wafer to be exposed and the last objective surface, and for their cleaning.
• the last end surface must be of planar design for solid immersion, in particular, in order to expose the wafer, which is likewise planar.
• this invention provides a projection objective for imaging a pattern provided in an object plane of the projection objective onto an image plane of the projection objective suitable for microlithography projection exposure machines comprising: a plurality of optical elements transparent for radiation at an operating wavelength of the" projection objective; wherein at least one optical element is a high-index optical element made from a high-index material with a refractive index n > 1.6 at the operating wavelength.
• the object-side (mask-side) numerical aperture is then NA 0 bj > 0.33, preferably NA 0 bj ⁇ 0.36.
• a material used for the last lens element or a part thereof is sapphire (AI 2 O 3 ), while the remaining lenses are made from fused silica.
• the examples can be transferred to other high-index lens materials and other wavelengths.
• Germanium dioxide (Ge0 2 ) As material for the last lens or a part thereof.
• this material has the advantage that it is not birefringent.
• the material is no longer transparent at 193 nm.
• the thickness of the high-index liquid that is to say the immersion liquid, can preferably be between 0.1 and 10 mm. Smaller thicknesses within this range may be advantageous since the high-index immersion media generally also exhibit a higher absorption.
• Fig. 1 is a longitudinally sectioned view of a first embodiment of a catadioptric projection objective according to the invention
• Fig. 2 is a longitudinally sectioned view of a second embodiment of a catadioptric projection objective according to the invention
• Fig. 3 is a longitudinally sectioned view of a third embodiment of a catadioptric projection objective according to the invention.
• Fig. 4 is a longitudinally sectioned view of a fourth embodiment of a catadioptric projection objective according to the invention
• Fig. 5 is a longitudinally sectioned view of a fifth embodiment of a catadioptric projection objective according to the invention
• optical axis shall refer to a straight line or sequence of straight-line segments passing through the centers of curvature of the optical elements involved.
• the optical axis can be folded by folding mirrors (deflecting mirrors).
• the object involved is either a mask (reticle) bearing the pattern of an integrated circuit or some other pattern, for example, a grating pattern.
• the image of the object is projected onto a wafer serving as a substrate that is coated with a layer of photoresist, although other types of substrate, such as components of liquid-crystal displays or substrates for optical gratings, are also feasible.
• Fig. 1 shows a first embodiment of a catadioptric projection objective 100 according to the invention designed for ca. 193 nm UV working wavelength. It is designed to project an image of a pattern on a reticle (or mask) arranged in the object plane OP into the image plane IP on a reduced scale, for example, 4:1 , while creating exactly two real intermediate images IMI1 and IMI2.
• a first refractive objective part ROP1 is designed for imaging the pattern in the object plane into the first intermediate image IMI1
• a second, catoptric (purely reflective) objective part COP2 images the first intermediate image IMI1 into the second intermediate image IMI2 at a magnification close to 1 :1
• a third, refractive objective part ROP3 images the second intermediate image IMI2 onto the image plane IP with a strong reduction ratio.
• the second objective part COP2 comprises a first concave mirror CM1 having the concave mirror surface facing the object side, and a second concave mirror CM2 having the concave mirror surface facing the image side.
• the mirror surfaces are both continuous or unbroken, i.e. they do not have a hole or bore.
• the mirror surfaces facing each other define an intermirror space, enclosed by the curved surfaces defined by the concave mirrors.
• the intermediate images IMI1 , IMI2 are both situated geometrically inside the intermirror space, at least the paraxial interme- diate images being almost in the middle thereof well apart from the mirror surfaces.
• Each mirror surface of a concave mirror defines a "curvature surface” or “surface of curvature” which is a mathematical surface extending beyond the edges of the physical mirror surface and containing the mirror surface.
• the first and second concave mirrors are parts of rotationally symmetric curvature surfaces having a common axis of rotational symmetry.
• the system 100 is rotational symmetric and has one straight optical axis AX common to all refractive and reflective optical components. There are no folding mirrors.
• the concave mirrors have small diameters allowing to bring them close together and rather close to the intermediate images lying in between.
• the concave mirrors are both constructed and illuminated as off-axis sections of axial symmetric surfaces. The light beam passes by the edges of the concave mirrors facing the optical axis without vignetting.
• Catadioptric projection objectives having this general construction are disclosed e.g. in the US provisional applications with serial numbers 60/536,248 filed on January 14, 2004, 60/587,504 filed on July 14, 2004 and a subsequent extended application filed on October 13, 2004. The contents of these applications is incorporated into this application by reference. It is one characterizing feature of this type of catadioptric projection objectives that pupil surfaces (at axial positions where the chief ray intersects the optical axis) are formed between the object plane and the first intermediate image, between the first and the second intermediate image and between the second intermediate image and the image plane and that all concave mirrors are arranged optically remote from a pupil surface, particularly at positions where the chief ray height of the imaging process exceeds a marginal ray height of the imaging process.
• At least the first intermediate image is located geometrically within the intermirror space between the first concave mirror and the second concave mirror.
• both the first intermediate image and the second intermediate image are located geometrically within the intermirror space between the concave mirrors.
• the sapphire lens is the last optical element LOE closest to the image plane.
• the image-side working distance is 1 mm.
• the catadioptric design has two concave mirrors, chiefly for chromatic correction and Petzval correction, and an intermediate image respectively upstream and downstream of the pair of mirrors.
• the intermediate images are, however, not fully corrected and serve primarily for the geometrical limitation of the design and for separating two beam paths running toward a mirror and runing from a mirror after reflection therupon.
• the image field (on the wafer) is rectangular.
• the external field radius (on the wafer side) is 15.5 mm, the inner one 4.65 mm. The result of this is a rectangular field of 26 x 3.8 mm.
• the aperture diaphragm (aperture stop AS, system aperture) is arranged in the first refractive objective part ROP1 in the first exemplary embodiment. This is advantageous in order, on the one hand, to fashion a smaller variable aperture diaphragm, and on the other hand largely to protect the subsequent objective parts (seen from the object plane (mask plane)) against useless and interfering radiation loads when stopping down the aperture diaphragm.
• the aperture stop AS is arranged at the waist.
• CaF 2 for the last lens is not to be preferred, since this requires a numerical aperture that is as far as possible not greater than 1.425 (-95% of the refractive index of CaF 2 ).
• sapphire Al 2 0 3
• optical elements made of sapphire are shaded gray for easier reference.
• the birefringence occurring when sapphire is used is largely compensated by splitting the last lens (last optical element LOE) into two lens elements LOE1 and LOE2 and rotating the two lens elements relative to one another around the optical axis.
• the separation interface SI contact surface of the two lens elements LOE1 and LOE1
• the compensation a second element made from sapphire which is located at a site in the objective which acts similarly in optical terms, for example in the vicinity of the intermediate images or in the vicinity of the object plane.
• the last sapphire lens LOE is split into two lens elements LOE1 and LOE2 which act virtually identically.
• the front radius of the sapphire lens LOE (i.e. the radius of the light entry side) is designed such that an aperture beam, i.e. a beam running towards the image at the parimeter of the convergent light bundle, toward the center of the image field passes through the interface virtually without being refracted, that is to say strikes the interface virtually perpendicularly (lens radius is virtually concentric with the point of intersection of the image plane with the optical axis).
• the radius of the splitting interface SI between the two lens elements of the split sapphire lens is flatter (radius > 1.3 times the distance from the image plane where a wafer can be placed).
• the specifications for the design of Fig. 1 are summarized in Table 1.
• the leftmost column lists the number of the refractive, reflective, or otherwise designated surface
• the second column lists the radius, r, of that surface [mm]
• the third column lists the distance, d [mm], between that surface and the next surface, a parameter that is referred to as the "thickness" of the optical element
• the fourth column lists the material employed for fabricating that optical element
• the fifth column lists the refractive index of the material employed for its fabrication.
• the sixth column lists the optically utilizable, clear, semi diameter [mm] of the optical component.
• Table 1A lists the associated data for those aspherical surfaces, from which the sagitta of their surface figures as a function of the height h may be computed employing the following equation:
• the last optical element LOE on the image side has the overall shape of a plano-convex lens.
• the lens is subdivided into two optical elements LOE1 and LOE2 which are contacted along a plane splitting interface SI.
• a quartz glass lens LOE1 with a positive radius of curvature of the entry surface and a rear planar surface is wrung onto one (or two) plane-parallel plates LOE2 made from sapphire. This yields values of NA no higher than possible in quartz glass, but there is the advantage that the angle of propagation of the light beams is reduced in the last objective part where the aperture is greatest owing to the high-index medium.
• the two plane-parallel plates made from sapphire can be rotated relative to one another around the optical axis virtually ideally to compensate the birefringence effect for the S- and P-polarisations in the x- and y-directions which are chiefly required for imaging the semiconductor structures.
• the quartz lens LOE1 has the effect here that - because of its lesser collecting effect - very large lens diameters are required even for image-side numerical apertures of a projection objective of limited overall length which are not really so large.
• the lens diameter is already over 143 mm and thus virtually 212 times the numerical aperture, while in the exemplary embodiment in Fig. 1 only 200 times the numerical aperture is reached.
• the maximum half lens diameter is even greater than the mirror semi- diameter at approximately 136 mm.
• the last lens element LOE comprises a thin sapphire lens LOE1 with positive refractive power, a spherically curved entry surface and a planar exit surface, which is wrung onto a thin quartz glass plate LOE2 (exemplary embodiment 3 in Fig. 3).
• the plane-parallel quartz glass plate providing the exit surface of the objective can then be interchanged upon the occurrence of damage owing to the radiation load.
• a wrung quartz plate therefore also acts as interchangeable protection of the sapphire lens LOE1 against contamination and/or scratches or destruction.
• the NA is limited by the refractive index of the quartz glass.
• the result upstream of the last lens is smaller beam angles and therefore also smaller diameters of the overall objective and lower sensitivities (interference susceptibilities to manufacturing tolerances) of the last lens element.
• the maximum lens diameter is now approximately 186 times the numerical aperture.
• the present invention can also be used for objectives of low numerical aperture, in order to reduce substantially the diameter of previous projection objectives. This advantageously affects the price of the projection objective, since the amount of material can be reduced substantially.
• the top side (entrance side) of the monolithic (one part, not split) sapphire lens LOE is aspheric, and the aperture stop AS is situated in the rear part of the image side refractive objective part ROP3 in the region of convergent radiation between the region of largest beam diameter in the third objective part ROP3 at biconvex lens LMD with largest diameter and the image plane IP.
• the outer field radius on the wafer side is at 15.53 mm, and the inner one is at 5.5 mm, that is to say the size of the rectangular field here is 26 x 3 mm.
• the wafer can be wrung onto the last planar lens surface (contact surface CS) for this purpose in order to obtain a mechanical contact between the exit surface of the projection objective and the incoupling surface associated to the substrate.
• a step-and-scan mode or stitching methods of exposure is to be preferred in this case, that is to say larger regions than the image field are exposed in individual steps, the reticle mask being correspondingly adjusted for alignment instead of, as previously customary, the wafer.
• the reticle can be adjusted with less accuracy than an adjustment of the wafer.
• Mutually adjoining exposure regions (target areas) or sequential levels of the semiconductor structure from subsequent exposure steps are thereby brought into overlay by lateral and axial movement and rotation of the reticle mask in order thereby to expose the semiconductor structures onto the possibly also defectively wrung wafers with an overlay accuracy of better than a few nm.
• Alignment marks, for example, of the reticle are brought into agreement for this purpose with alignment marks already exposed on the wafer.
• the release of the wafer from the last surface is preferably performed in vacuo. If required, there is located between the wafer and last planar lens surface a thin layer (pellicle/membrane) which can be exchanged after each exposure step, for example.
• This membrane can, for exam- pie, also remain bonded on the wafer and assist in the separation and serves, in particular, as protection for the last planar lens surface. The latter can optionally be protected in addition by a thin protective layer.
• All exemplary embodiments discussed above are catadioptric projection objectives with exactly two concave mirrors and exactly two intermediate images, where all optical elements are aligned along one straight, unfolded optical axis.
• the uniform basic type of projection objective chosen to explain preferred variants of the invention is intended to help illustrate some basic variants and technical effects and advantages related to different variants of the invention.
• the demonstrated use of lenses or lens elements made of high refractive index material (e.g. n ⁇ 1.6 or even n > 1.8) in projection objectives particularly for operating wavelength in the deep ultraviolet range (DUV) is not restricted to this type of projection objectives.
• the invention can also be incorporated into purely refractive projection objectives.
• the last optical element closest to the image plane is often a plano-convex lens which can be designed, for example, according to the rules laid out above for the last optical elements LOE in each of the first to fifth embodiment.
• Examples are given e.g. in applicants US applications having serial numbers 10/931 ,051 (see also WO 03/075049 A), 10/931 ,062 (see also US 2004/0004757 A1 ), 10/379,809 (see US 2003/01744408) or in WO 03/077036 A. The disclosure of these documents is incorporated herein by reference.
• the invention can be implemented into catadioptric projection objectives having only one concave mirror, or catadioptric projection objectives having two concave mirrors in a arrangement different from that shown in the figures, or in embodiments having more than two concave mirrors. Also, use of the invention can be made independent of whether or not folding mirrors are present in the optical design. Examples of catadioptric systems are given e.g. in applicants US applications having serial numbers 60/511 ,673, 10/743,623, 60/530,622, 60/560,267 or in US 2002/0012100 A1. The disclosure of these documents is incorporated herein by reference. Other examples are shown in US 2003/0011755 A1 and related applications.

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• 2004
  • 2004-12-10 KR KR1020067011811A patent/KR101200654B1/ko active IP Right Grant
  • 2004-12-10 JP JP2006543484A patent/JP5106858B2/ja not_active Expired - Fee Related
  • 2004-12-10 WO PCT/EP2004/014062 patent/WO2005059617A2/en active Application Filing
  • 2004-12-10 EP EP04803712A patent/EP1697798A2/de not_active Withdrawn

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