JP2008191693A - Refractive projection objective lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an entirely small-sized refractive projection objective lens to be produced with a tolerable material use amount, having a preferable compensation state in terms of the chromatic aberration, in particular, the horizontal chromatic aberration. <P>SOLUTION: A purely refractive projection objective lens is designed as a single waist type system having 5 lens groups including a first lens group with a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, a fourth lens group having a positive refractive power, and a fifth lens group having a positive refractive power. The contracted part to have a beam flux contracted most narrowly is disposed in the region of the waist part. The waist distance AT is formed between an object plane and the contracted part X. A condition AT/L ≤ 0.4 is satisfied in the distance ratio AT/L between the waist distance AT and the object image distance L of the projection objective lens. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a refractive projection objective that projects a pattern arranged on the object plane of the projection objective onto the image plane of the projection objective.

  Projection objectives for photolithography have been used for the manufacture of semiconductor structural elements and other microstructured elements for decades. These lenses serve the purpose of reducing and projecting a photomask or reticle pattern, also referred to below as a mask or reticle, onto an object covered by a photosensitive layer with very high resolution.

  The three developments being carried out in parallel contribute to the manufacture of even finer structures, mainly of the order of about 100 nm or less. First, an attempt is made to make the numerical aperture (NA) on the image side of the projection objective larger than the usual value so that NA = 0.8 or more. Secondly, ultraviolet light with even shorter wavelengths, preferably less than 260 nm, for example less than 248 nm, 193 nm or 157 nm, is used. Finally, the resolution is increased using still other measures such as phase shift masks and / or oblique illumination.

In addition, there already exist ways to increase the achievable resolution by introducing a high refractive index immersion medium into the space between the last optical element of the projection objective and the substrate. This technique is referred to herein as immersion lithography. A projection objective suitable for this purpose is shown as an immersion objective or immersion system. By introducing the immersion medium, an effective wavelength of λ _eff = λ ₀ / n is obtained, where λ ₀ is the vacuum operating wavelength and n is the refractive index of the immersion medium. This gives a resolution of R = k ₁ (λ _eff / NA ₀ ) and a DOF = ± k ₂ (λ _eff / NA ₀ ² ) depth of focus (DOF), where NA ₀ = sin θ _0. Is the “dry system” numerical aperture and θ ₀ is the aperture half-angle of the objective lens. The empirical constants k ₁ and k ₂ depend on the process.

  The theoretical advantage of immersion lithography is that the effective operating wavelength is reduced and resolution is thereby improved. This can be achieved in conjunction with a vacuum wavelength that does not change, so established techniques such as light generation, optical material selection, coating techniques, etc., can be employed largely without change for the appropriate wavelength. However, a strategy is needed to obtain a projection objective with a very high numerical aperture in the region of NA = 1 or higher. Furthermore, a suitable immersion medium must be available.

  Ultrapure water with n1≈1.43 has been found to be a suitable immersion medium for 193 nm.

M.M. M. Switkes and M. Switkes. Rothschild's paper entitled “Immersion Lithography at 157 nm”, J. Vac. Sci. Technol. Volume 19 (6), November / December 2001, p. 1 and later immersion liquids based on perfluoropolyether (PFPE) which have sufficient transparency for an operating wavelength of 157 nm and are compatible with some photoresist materials currently used in microlithography It is shown. One immersion liquid tested has a refractive index of n ₁ = 1.37 at 157 nm. In said publication, furthermore, immersion interference lithography operating with a calcium fluoride element and a silicon mirror intended to allow projection of structures below 60 nm with a numerical aperture of NA = 0.86. An optical system that does not include a special lens is described. This optical system is not suitable for use in continuous production of semiconductors and the like.

  U.S. Pat. No. 4,480,910 and U.S. Pat. No. 5,610,683 (corresponding to EP 0 605 103) provide an immersion liquid projection objective and substrate provided for immersion lithography. A projection exposure apparatus having an apparatus introduced between the two is described. No design is specified for the projection optics.

  Several projection objectives suitable for immersion lithography have recently become known. A purely refractive projection objective known from the applicant's international patent applications 03 / 077036A1 and 03 / 077037A1 (corresponding to US patent application 2003/0174408) comprises an object side barrel and an image side It is designed as a so-called single-waist system or a two-cylinder system having a body part and a waist part located between the body parts, that is, a contraction part of the beam diameter. In this case, an image-side numerical aperture up to NA = 1.1 was achieved.

  Attempts to achieve even higher numerical apertures are difficult because the maximum lens diameter increases dramatically as the numerical aperture increases, which complicates the production of the projection objective and makes it more expensive. become. In addition, chromatic aberration, here in particular lateral chromatic aberration, takes on alarming values. Lateral chromatic aberration (CHV), also called chromatic magnification aberration, has the effect that partial images are imaged at different sizes at different wavelengths. As a result, lateral chromatic aberration does not occur on the optical axis, but is observed with increasing intensity in the direction of the edge of the image field (field dependence).

Chromatic aberrations are generally reduced by using at least two optical materials that are dispersed differently within the projection objective. However, in the deep ultraviolet (DUV) wavelength region at operating wavelengths below 200 nm, only a few transparent optical materials with sufficiently low absorption are available. In applications at 193 nm, synthetic quartz glass (fused quartz) (SiO ₂ ) is mainly used as the main material, and calcium fluoride (CaF ₂ ) or barium fluoride (BaF ₂ ) is used as the second type of material. The fluoride crystal material is used. Usually, at 157 nm, calcium fluoride is used as the main material and barium fluoride is used as the second material. However, the fluoride crystal material is available only to a limited extent, and is expensive and difficult to process. It is therefore desirable to have an optical design that requires only one type of material, especially synthetic quartz glass. In any case, chromatic aberration must be minimized so that the contrast loss caused by chromatic aberration is maintained within an acceptable range using an appropriate narrow band radiation source. Here, since lateral chromatic aberration causes contrast loss as a function of the field, correction of lateral chromatic aberration is particularly important.
M.M. M. Switkes and M. Switkes. Rothschild's paper entitled “Immersion Lithography at 157 nm”, J. Vac. Sci. Technol. Volume 19 (6), November / December 2001, p. 1 or later U.S. Pat. No. 4,480,910 US Pat. No. 5,610,683 European Patent 0 605 103 International Patent Application No. 03 / 077036A1 International Patent Application No. 03 / 077037A1 US Patent Application 2003/0174408

  The object of the present invention is a refraction that is particularly suitable for immersion lithography due to its small size as a whole, can be manufactured with acceptable material usage, and has a good correction for chromatic aberration, especially lateral chromatic aberration. It is to provide a projection objective lens.

  This object is achieved by a projection objective having the features of claim 1. Advantageous embodiments are described in the dependent claims. The wording of all claims is included herein by reference.

BEST MODE FOR CARRYING OUT THE INVENTION

According to one aspect of the present invention, there is provided a refractive projection objective that projects a pattern placed on the object plane of the projection objective onto the image plane of the projection objective:
A first lens group (LG1) having negative refractive power following the object plane;
A second lens group (LG2) having a positive refractive power following the first lens group;
A third lens group (LG3) having negative refractive power following the second lens group;
A fourth lens group (LG4) having positive refractive power following the third lens group;
A fifth lens group (LG5) having a positive refractive power, following the fourth lens group;
A system aperture (5) arranged in the transition region from the fourth lens group to the fifth lens group,
A waist portion (X) that is disposed between the object side barrel (6) and the image side barrel (8), and is disposed between the object side barrel and the image side barrel and contracts the beam most narrowly (X). 7) with a single waist-shaped system,
A waist distance AT is formed between the object plane and the contraction, and the condition AT / L ≦ 0.4 holds for the distance ratio AT / L between the waist distance AT and the object image distance L of the projection objective. And
The fifth lens group (LG5) has the last optical element formed as a plano-convex lens (29), and this plano-convex lens (29) substantially has a curved entrance surface (either spherical or spherical). And a flat emission surface.

  The distribution of refractive power over the individual lens groups gives a projection objective having two barrels and a waist between the barrels, resulting in good correction of field curvature (Pezval correction). Is brought about. In this case, the object-side body is substantially shorter than the known two-body system with respect to the total length (object image distance) L. The distance ratio AT / L can in particular be less than 0.38 or less than 0.36 or less than 0.34. Therefore, it is preferable that the waist portion be disposed very far in the front region near the object of the projection objective lens.

  Lateral chromatic aberration is a function of the peripheral beam height, main beam height and refractive power at each lens. Here, the peripheral beam height is the vertical distance of the peripheral beam from the optical axis, and the peripheral beam leads from the center of the object field to the aperture edge of the system aperture that determines the numerical aperture used. While the main beam height is the vertical distance of the main beam from the optical axis, within the meaning of this application, the main beam is from the outer edge of the object field that is parallel or acute to the optical axis. A beam that travels and intersects the optical axis in the region of the system aperture.

  In a two-cylinder system (single waist system), the main beam height is maximized in the object side barrel. The peripheral beam height also has a considerable value here. The height of the main beam must be kept small in the object-side body by appropriately selecting the refractive power. A good compromise of the requirements that must be met at the same time can be achieved if the waist is located far away in the front region near the object plane of the system. As an alternative or addition, it is particularly advantageous to correct lateral chromatic aberrations to set a suitable ratio of the system body diameter. In one development, the object-side barrel has a first diameter D1, the image-side barrel has a second diameter D3, and D3 / D1> 1. 5 holds. It is particularly advantageous if the barrel diameter ratio exceeds 1.6 or exceeds 1.7. A small barrel diameter at the object side barrel corresponds to a small peripheral beam height at the object side barrel and also a small main beam height, which is the main contributor to lateral chromatic aberration.

  According to one development form, the waist portion has a waist diameter D2 at the contraction portion, and D3 / D2 ≧ 3 holds for a diameter ratio D3 / D2 between the diameter of the image side barrel portion and the waist diameter. Therefore, the waist part is very thin compared with the second barrel part on the image side, and has an appropriate peripheral beam height. This in particular achieves an effective correction of field curvature.

  The main contribution to lateral chromatic aberration originates in the object side barrel, but is kept small by the small diameter of the object side barrel. Lateral chromatic aberration can also be corrected by skillful dispersion of refractive power at the waist. In particular, it has been found that the output lens or the lens group of the third lens group has a very strong correction action. The output lens or lens group should have a negative refractive power that is substantially stronger than at least one input negative lens of the third lens group. In particular, in the third lens group, the negative refractive power on the front side of the size VBK is disposed upstream of the contraction portion, and the negative refractive power on the rear side of the size HBK is disposed downstream of the contraction portion. It can be advantageous if HBK / VBK ≧ 3 holds for the ratio of the magnitudes of the refractive powers.

  The third lens group includes a rear negative lens and at least one front negative lens arranged upstream of the rear negative lens, and has a negative refractive power of the rear negative lens. It is particularly advantageous if the size is at least 20% greater than the negative refractive power of the at least one front negative lens of the third lens group. Therefore, the rear (final) negative lens of the third lens group should be far out of the lenses of this lens group and have a high negative refractive power. In some embodiments, the negative power of the negative lens behind the third lens group is at least 20% greater than the total power of the projection objective. The negative refracting power in the region of the waist portion can exert a particularly strong correction action on lateral chromatic aberration when these conditions are observed.

  Monochromatic aberration correction can be optimized by using an aspheric surface under the boundary condition of minimal material usage.

  In one embodiment, the first lens group includes at least one aspheric surface, and preferably at least two aspheric surfaces are provided in the first lens group. Distortion can be effectively corrected using an aspherical configuration in a region located near the field and where the main beam height is substantially greater than the peripheral beam height. Furthermore, a telecentric beam path on the object side can be achieved at least approximately. The first lens group preferably includes two lenses each having one aspheric surface. Distributing the aspherical surface to a large number of lenses can prevent large surface deformations, thus simplifying manufacturing.

  In the second lens group, it is preferable to dispose at least one aspherical surface that can be used to effectively correct the tangential shell and the coma in particular. It is advantageous to place an aspherical surface on the surface having the maximum main beam height of the second lens group. In some embodiments, this corrective action is supported by placing at least one aspheric surface upstream of the aspheric surface and at least one aspheric surface downstream of the aspheric surface.

  It has been found that coma correction can be enhanced if at least one concave surface is configured as an aspheric surface in the third and / or fourth lens group, respectively.

  At least one aspheric surface is preferably also provided in the fourth lens group and the fifth lens group. The aspheric surfaces in the fourth lens group and the fifth lens group mainly contribute to correction of aspherical aberrations and exhibit substantial contribution to coma correction.

  Therefore, it is particularly advantageous if at least one aspheric surface is arranged in each lens group.

  In one development, at least one meniscus lens that is concave toward the object plane is arranged in the fourth lens group. This lens is preferably designed as a negative meniscus lens. The lens can be placed in a region of very high peripheral beam height, just upstream of the system aperture. In particular, such a meniscus lens having a negative refractive power can substantially contribute to the correction of spherical aberration due to the effect of strong overcorrection. Thus, most of the spherical aberration subject to correction of the lens downstream of the system aperture, i.e. the lens of the fifth lens group, can be canceled out.

  For this correction action, it is advantageous to have incident light with a large incident angle on the concave surface side of the meniscus lens. It is preferred that the maximum incident angle in the entire system occurs at this concave surface. In a preferred embodiment, the large incident angle is supported on the one hand by at least the concave shape of the surface on which the weakly divergent beam is incident. At least one lens having a strong positive refractive power, in particular a biconvex lens, is preferably provided immediately upstream of the meniscus lens. With this lens, the angle of incidence at the subsequent concave surface can be further increased. Thus, in a preferred embodiment, at least one doublet having at least one preferably biconvex positive lens and one immediately downstream negative meniscus lens that is concave with respect to the object plane comprises a fourth In the lens group.

  The system aperture can be a planar system aperture, in which case the edge is kept independent of the aperture set in a plane perpendicular to the optical axis. In systems with aperture errors, it is advantageous if the system aperture has an aperture edge that determines the aperture and whose axial position relative to the optical axis of the projection objective can vary as a function of aperture. This makes it possible to optimally adjust the effective aperture position as a function of the aperture with respect to the beam path. The system aperture can be designed as a spherical aperture that can move the aperture edge along the spherical surface when adjusting the aperture, for example. Furthermore, it is also possible to design the system opening as a conical opening in which the opening edge can be moved on the side of the cone during aperture adjustment. This can be achieved, for example, by a planar opening that is axially displaceable.

  The projection system according to the invention can be used in a wide range of suitable working distances. In this case, the working distance on the object side or the working distance in the object space is the (minimum) axial distance between the object plane and the entrance surface of the objective lens, while the working distance on the image side or the working distance in the image space. The distance is the (minimum) axial distance between the exit surface of the objective lens and the image plane. The working distance in the image space that is filled with gas when used as a drying system is filled with an immersion medium in operation when used as an immersion system.

  In the case of immersion systems, special criteria must be taken into account when fixing the working distance in image space. On the other hand, a large working distance increases the radiation loss due to the generally lower immersion liquid transmission (compared to gas) and tends to cause aberrations, especially spherical aberration, due to the surface in contact with the image plane. When considered for use as an immersion system, the working distance on the image side should be large enough to allow laminar flow of the immersion liquid. Furthermore, there should be room for instruments and sensors where appropriate. In a preferred embodiment for immersion lithography, the image side working distance is in the range of about 1 mm to about 15 mm, in particular in the range of about 1.5 mm to about 5 mm.

  One means of keeping the peripheral beam height small in the first barrel is to select the smallest possible numerical aperture on the object side. As a result, the peripheral beam height at the object side body portion does not take an excessive value. A small object-side numerical aperture can be controlled by selecting an appropriate magnification β along with a large image-side numerical aperture. The preferred embodiment is designed as a reduction objective. The magnitude of the magnification | β | is preferably in the range of 1/6 to 1/3, in particular 1 / 5.5 to 1/3, so that in particular reductions of 5: 1 and 4: 1 are possible. Within the range of .5.

In some embodiments, all the lenses of the projection objective are composed of the same material. The materials used can be, for example, synthetic quartz glass for an operating wavelength of 193 nm and calcium fluoride for an operating wavelength of 157 nm. By using only one type of material, manufacturing becomes easier and the objective lens design can be easily adapted to other wavelengths. It is also possible to combine many types of materials to help correct chromatic aberration, for example. Other UV transparent materials such as BaF ₂ , NaF, LiF, SrF or MgF ₂ can also be used.

The present invention has an image-side numerical aperture NA ≧ 1.0 when using a suitable immersion medium, and in some embodiments, NA> 1.1, especially NA = 1.2 or Enables the design of a projection objective that can have NA = 1.3 or higher. This projection objective can be adapted to an immersion liquid having a refractive index of n ₁ > 1.3 at the operating wavelength. As a result, the effective operating wavelength can be reduced by about 30% or more compared to a system that does not use immersion liquid.

  Due to the structural features of the preferred embodiment, the projection objective can be used as an immersion objective. However, according to the present invention, the projection objective is not limited to this application. Due to the optical structure, the projection objective can also be used for non-contact near-field projection lithography. Here, sufficient light energy can be coupled to the substrate to be exposed through the gas filled gap if a sufficiently small image-side working distance is maintained over time on average. This distance should be less than 4 times the operating wavelength used, in particular less than the operating wavelength. It is particularly advantageous if the working distance is less than one half of the operating wavelength, for example less than one third, one fourth or one fifth of the operating wavelength. Using such a short working distance allows projection in the optical near field, in which case the evanescent field that is in the immediate vicinity of the last optical surface of the projection system is used for the projection.

  If it is desired to use the projection objective for non-contact near field lithography rather than immersion lithography, this can be easily done with some modifications. If the immersion medium to which the optical design is adapted has essentially the same refractive index as the last optical element of the objective lens, the solid body can be configured to be thicker to achieve a small image-side working distance. Like that. For example, working distances in the range of 20-50 nm can be achieved in this way. Where appropriate, subsequent optical corrections may be advantageous, which may be performed using an appropriate manipulator, for example to adjust the air spacing of the lens elements in one or more lens elements.

  Accordingly, the present invention also includes a non-contact projection exposure method in which an evanescent field of exposure light located in the immediate vicinity of the exit surface is used in the lithography process. Here, assuming a sufficiently small (finite) working distance, the light component used for lithography is output from the exit surface of the objective lens, regardless of the geometrical conditions of total reflection at the last optical surface of the projection objective lens. In addition to being coupled, it can be coupled to an input coupling surface that is directly adjacent at a distance.

  Embodiments for non-contact near-field projection lithography preferably have a general working distance in the sub-operational wavelength range, for example in the range of about 3 nm to about 200 nm, especially about 5 nm to about 100 nm. This working distance is such that, on average, an input coupling efficiency of at least 10% is achieved over time, other characteristics of the projection system (projection objective characteristics near the exit surface, substrate characteristics near the input coupling surface) ).

  Thus, within the frame of the present invention, a method of manufacturing a semiconductor structural element or the like is possible, in which case a finite working distance is provided between the exposure light exit surface provided on the projection objective lens and the exposure light provided on the substrate. The working distance is set to a value smaller than the maximum range of the optical near field of light emitted from the exit surface at least temporarily within the exposure time interval.

  In yet another aspect, the projection objective according to the invention can also be used as a drying system for conventional projection lithography. For this purpose, the image-side working distance can be clearly larger than when used as an immersion system or a near-field projection system. Thus, in some situations it is not possible to use up the full potential of a very high image-side numerical aperture, so the system aperture is set to a smaller aperture, eg the numerical aperture used is NA = The size can be set to about 0.9 or NA = 0.8 or less.

  These and other features will be apparent not only from the claims but also from the detailed description and the drawings, and individual features may be singularly or a partial combination of features. Can be implemented in embodiments of the present invention and in other fields, and can constitute advantageous designs that can be patent protected based on their own value.

  In the following description of the preferred embodiment, the term “optical axis” refers to a straight line passing through the center of curvature of the optical element. The direction and distance are the image side or image direction when going to the image plane or the direction of the substrate to be exposed arranged on the image plane, and the object side or object direction when going to the object with respect to the optical axis. Is described as In the example, the object is a mask (reticle) with an integrated circuit pattern, but may also be associated with other patterns, such as a grating. In the example, the image is formed on a wafer that serves as a substrate and is provided with a photoresist layer, but may be other substrates, such as elements for liquid crystal displays or substrates for optical gratings. The identified focal length is the focal length for air.

  A general design of an embodiment of a purely refractive reduction objective 1 of the present invention is shown using FIG. Assuming a substantially homogeneous immersion liquid, the lens has a pattern such as a reticle arranged in the object plane 2 on the image plane 3 with a reduction ratio, for example, 5: 1 (magnification β = 0.2). It is used for the purpose of projection. This lens is a rotationally symmetric single waist or two-cylinder system with five consecutive lens groups arranged along an optical axis 4 perpendicular to the object plane and the image plane. The first lens group LG1 immediately after the object plane 2 has a negative refractive power. The second lens group LG2 immediately after the first lens group has a positive refractive power. The third lens group LG3 immediately after the second lens group has a negative refractive power. The fourth lens group immediately after the third lens group has a positive refractive power. The fifth lens group LG5 immediately after the fourth lens group has a positive refractive power. The image plane is arranged immediately after the fifth lens group so that the projection objective does not have any other lens or lens group apart from the first to fifth lens groups. By distributing the refractive power in this way, the first barrel 6 on the object side, the second barrel 8 on the image side, and the contraction X having the minimum beam bundle diameter are located between the barrels. A two-cylinder system with a waist part 7 arranged on the top is obtained. In the transition region from the fourth lens group to the fifth lens group, the system aperture 5 is located in a region of relatively large beam diameter.

Projection that can be performed using the projection objective can be characterized by the generation of its main beam and peripheral beam. As the main beam A, a beam is shown which travels from the outer edge of the object plane parallel or acute with the optical axis and intersects the optical axis 4 in the region of the system aperture 5. The peripheral beam B exits from the center of the object field, i.e. the axial field point, to the aperture edge of the aperture stop, which is generally located at or near the system aperture 5. The beam C that leaves the outer edge point and reaches the opposite edge of the aperture stop is shown here as a coma beam. The vertical distance of these beams from the optical axis gives the corresponding beam heights h _A , h _B and h _C.

The first lens region LB1 starts from the object plane 2 and ends at a plane where the peripheral beam B and the coma beam C intersect so as to satisfy the condition | h _B / h _C | <1 in the first lens region LB1. And The main beam light is larger than the peripheral beam height in the lens region LB1. The lens surface arranged here is shown as a near field. The second lens region LB2 extends from the object plane 2 to a region where the main beam height and the peripheral beam height are substantially equal in size. In this case, in particular, | h _B / h _A | < 1.2 holds. In a general variant of the projection system according to the invention, the length of the second lens region LB2 is greater than one quarter and less than one half of the distance L between the object plane 2 and the image plane 3. It is small. This object image distance is also indicated as the total length of the projection objective.

  In a general embodiment of the projection objective according to the invention, the first lens group LG1 comprises at least two negative lenses, the second lens group LG2 comprises at least three positive lenses and a third lens. The group LG3 has at least two negative lenses, the fourth lens group LG4 has at least two positive lenses, and the fifth lens group LG5 has at least three positive lenses.

  The first lens group LG1 following the object plane 2 serves to substantially widen the light beam and send it to the first object-side body 6. The lens group includes a thin biconcave negative lens 11 having an aspherical entrance surface and a spherical exit surface, and an aspheric entrance surface and a spherical exit surface disposed thereafter. Furthermore, it has another biconcave negative lens 12. The aspheric surface arranged in the near field of the entrance surfaces of the lenses 11 and 12 closest to the object effectively contributes to good correction of distortion and astigmatism. In particular, these aspheric surfaces ensure a substantially telecentric beam path on the object side. In the case of the system of this example, it is possible to provide two aspheric surfaces on a single lens, but in other embodiments it is avoided for manufacturing reasons.

  The second lens group LG2 is composed of three lenses 13, 14, and 15. The lens group begins with a thick positive meniscus lens 13 having an aspheric object-side concave surface and a spherical exit surface. The positive lens 14 immediately after the lens has an aspherical entrance surface and a spherical exit surface having a slightly convex curvature. The positive meniscus lens 15 following the lens has a spherical incident surface and an aspherical exit surface that is concave on both sides. The aspherical entrance surface of the lens 14 is arranged in the region of the maximum main beam height of the second lens group, and is particularly effective for correcting the tangential shell and the coma. The aspherical surfaces of the lens 13 arranged upstream of the lens and the lens 15 arranged downstream of the lens help this correction.

  The third lens group LG3 includes four negative lenses 16, 17, 18, and 19. The incident-side thick double-sided meniscus lens 16 having an image-side concave surface has a weak negative refractive power. The subsequent meniscus lens 17 having a weakly curved spherical entrance surface and a concave aspherical exit surface on the image side is arranged in the optical path upstream of the contraction X where the beam bundle has the smallest diameter in the waist region. . The lenses 16 and 17 provide the front negative refractive power VBK. A negative meniscus lens 18 that is spherical on both sides and has a concave surface on the object side is disposed downstream of the contraction portion X following the lens. The last negative lens 19 in the third lens group has a strongly curved spherical entrance surface that is concave on the object side, and a weakly curved aspherical exit surface. These two rear negative lenses 18, 19 jointly provide a strong rear negative refractive power HBK. It has been found that the concave aspherical exit surface of the lens 17 effectively contributes to the correction of coma.

  The fourth lens group LG4 is composed of six lenses. On the incident side, the lens group is concave with respect to the object plane, and the first two lenses are composed of three positive meniscus lenses 20, 21, 22 having both spherical surfaces, and the positive lens having the maximum diameter. The meniscus lens 22 has an aspherical incident surface that is concave with respect to the object plane. Following these three positive meniscus lenses, a biconvex bispherical positive lens 23 having a weakly curved lens surface is arranged. In the region of a large beam diameter just upstream of the system aperture 5, an incident-side biconvex lens 24 having a strong positive refractive power, and a negative meniscus disposed immediately upstream of the system aperture and having an aspheric concave surface on the object side Doublets 24, 25 having a lens 25 are arranged. The aspheric surfaces facing each other form a concave shape with respect to the object plane and surround an air lens having a positive lens shape. This doublet has a strong overcorrection effect on spherical aberration.

  The fifth lens group LG5 located downstream of the system aperture 5 substantially serves to provide a high numerical aperture. For this purpose, it is exclusively a condensing lens, specifically three direct successive positives each having a spherical entrance surface and an aspheric exit surface which is concave with respect to the image plane. Meniscus lenses 26, 27, and 28 and a final non-hemispherical plano-convex lens 29 having a spherical incident surface and a flat output surface are disposed. These positive lenses exhibit a strong spherical spherical undercorrection effect and an overcorrection effect with respect to coma.

  In this design, spherical aberration and coma correction are largely borne by the balance between the doublets 24, 25 immediately upstream of the system aperture and the lenses 26, 27, 28, 29 of the fifth lens.

  The system has an object side working distance of 32 mm, an object back focal length of about 36.6 mm, and an image side working distance of about 2 mm that can be filled by immersion liquid 10. The system is designed such that deionized water (refractive index n≈1.435) or other suitable transparent liquid with an equivalent refractive index can be used as an immersion liquid at 1.93 nm.

  The design specifications are summarized in tabular form in Table 1 in a well-known manner. Here, the first column clearly indicates the refractive surface number or other distinction, the second column shows the surface radius r (in mm), and the fourth column The distance d (in mm) from the subsequent surface, shown as the thickness of the surface, is shown, and the fifth column shows the material of the optical element. In the sixth column, the refractive index of the material is shown, and in half the effective free radius or free diameter of the lens (in mm) is shown in the seventh column. Aspheric surfaces are indicated by “AS” in the third column.

In the case of the present embodiment, 13 surfaces, specifically, the surfaces 1, 3, 5, 7, 10, 14, 18, 23, 28, 29, 33, 35, and 37 are aspherical surfaces. Table 2 shows the corresponding aspheric data, which is calculated using the following equation:

  Here, the reciprocal of the radius (1 / r) represents the curvature of the surface, and h represents the distance from the optical axis to the surface point (that is, the beam height). Therefore, p (h) represents the distance in the z direction, that is, the direction of the optical axis from the so-called arrow, that is, the surface vertex to the surface point. Constants K, C1, C2,... Are reproduced in Table 2.

The optical system 1 that can be reproduced using these data is designed for an operating wavelength of about 193 nm where the synthetic quartz glass used for all lenses has a refractive index n = 1.5603. The image-side numerical aperture NA is 1.3. The object side and image side telecentric systems are matched to the refractive index of the immersion liquid, n ₁ = 1.435. This objective lens has a total length L (distance between the image plane and the object plane) of about 1078 mm. A photoconductive LLW (product of numerical aperture and image size) of about 29 mm is achieved at an image size of 22.4 mm. The focal length Fg of the system as a whole is about 211 mm.

  The maximum diameter D1 of the first barrel on the object side is 232 mm, the diameter D2 at the contraction portion X of the minimum beam diameter in the waist region is 126 mm, and the maximum diameter of the second image side barrel. D3 is 400 mm.

  For various lens groups and the overall system, the value of the focal length f ′, the refractive power F ′, and the parameter F ′ / Fg (the refractive power normalized with respect to the overall refractive power Fg of the objective lens). The values of F ′ · LLW and axial length are shown in Table 3.

  The values of the various parameters are shown in Table 4 for the individual lenses of the system shown in the first column. Here, f ′ is a focal length, F ′ is a refractive power (reciprocal of the focal length), LLW is a geometric light induction value (etendue), and CHV is a lens with respect to lateral chromatic aberration. It is a value related to contribution (CHV contribution), and CHV / CHVm is the relative CHV contribution of individual lenses normalized to the maximum value CHVm.

The color magnification error CHV is a function of the peripheral beam height, the main beam height, and the refractive power of each lens i. The contribution CHV _i of each lens is proportional to the peripheral beam height h _B , the main beam height h _A, and the refractive power F ′,

Is indirectly proportional to the Abbe number vi.

  In order to make the explanation of the distribution of related values easier to understand, FIG. 2 shows the relative contribution of individual lenses to lateral chromatic aberration (CHV contribution normalized to the maximum value CHVm for lens 4). FIG. 3 shows the refractive power (F ′ / Fg) normalized with respect to the overall refractive power of the lens as a function of the lens number.

  Table 5 shows the sine value sin (i) of the incident angle i, the corresponding angle in degrees, and the sin (i) value for the image-side numerical aperture NA for the lens surface shown in the first column. The ratio is shown. The sin (i) value corresponds to the maximum value of the sine of the incident angle or reflection angle on each surface. Therefore, these values are always specified in the air.

A few salient features of the projection objective are described below. The objective lens starts with two aspherical negative lenses 11, 12 which serve the purpose of beam widening and distortion and telecentricity correction. Due to the relatively small image-side numerical aperture of NA ₀ = 0.26, the peripheral beam height in the input area of the projection objective is moderately maintained. Within the first body 6, the maximum peripheral beam height is achieved in the region of the positive meniscus lens 15, in which the maximum peripheral beam height achieved in the region of the system aperture 5. Only 24.3%. The maximum main beam height is achieved in the region of the spherical exit surface of the fourth lens 14 where the peripheral beam height has not yet reached its maximum value. The maximum main beam height is only 40.8% of the maximum peripheral beam height corresponding to the maximum aperture radius. Since the CHV contribution is proportional to the peripheral beam height and the main beam height, the maximum CHV contribution of the lens (lens 14) having the maximum main beam height is achieved (compare with FIG. 2).

  The contribution to the color magnification error CHV originating primarily at the first barrel is compensated by the subsequent lens group. For this purpose, it is particularly effective to concentrate a strong negative refractive power just upstream of the entrance to the object side barrel starting with the fourth lens group of positive refractive power. The strong correction action of the negative refractive power in the region of the output part of the third lens group is here that, on the one hand, the peripheral beam height already takes a substantial value again, and on the other hand the main beam height is also It can also be explained in part by having a very large value and a strong corrective action being exerted on the main beam.

  The three positive meniscus lenses 20, 21, 22 that are concave with respect to the object plane induce recombination of the beam bundle after maximum magnification downstream of the negative lens 19, so that a gentle beam with a very low incident angle is obtained. Induction is achieved (Table 5). With the downstream weak positive biconvex lens 23, spherical undercorrection is induced. The negative meniscus lens 25 immediately upstream of the system aperture contributes substantially to the correction of spherical aberration, particularly in the sense of strong overcorrection. As a result, most of the spherical shortage correction of the positive lenses 26 to 29 in the fifth lens group downstream of the system aperture 5 is canceled out. Furthermore, it is significant that the incident angle becomes very large on the concave incident surface of the meniscus lens 25. Such an incident angle is caused on the one hand by the strong curvature of the concave surface and on the other hand by the large positive refractive power of the biconvex lens immediately upstream of the meniscus lens. The maximum incident angle in the overall system occurs at the aspherical entrance surface of the negative meniscus lens 25. The maximum sine of the incident angle is about 99% of the image-side numerical aperture NA.

  The four consecutive positive lenses 26 to 29 of the fifth lens group LG5 generate an appropriate incident angle in combination with a high image-side numerical aperture, and also have a mode and a coma that perform a strong spherical shortage as a whole. This affects the mode of overcorrection. This compensates for the inverse contribution of each of the fourth lens groups upstream of the system aperture and provides an excellent correction state at the image plane 3 after the light beam has passed through the thin immersion layer 10. .

The invention furthermore relates to a projection exposure apparatus for microlithography which is distinguished by including a refractive projection objective according to the invention. The projection exposure apparatus preferably further comprises a device for introducing and holding an immersion medium, for example a liquid of appropriate refractive index, between the last optical surface of the projection objective and the substrate to be exposed. The present invention still further provides a method for manufacturing a semiconductor structural element and other fine structural elements, wherein an image of a pattern arranged in the object plane of the projection objective lens is projected in the region of the image plane, Including a method of being disposed between the projection objective and the substrate to be exposed and being transparent to the illuminating operating wavelength light.

1 is a lens cross section of a first example of a refractive projection objective designed for an operating wavelength of 193 nm. FIG. It is a diagram which shows the relative contribution of each lens with respect to lateral chromatic aberration. FIG. 4 is a diagram showing the normalized refractive power of individual lenses.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reduction objective lens 2 Object plane 3 Image plane 4 Optical axis 5 System opening 6 1st trunk | drum 7 Waist part 8 2nd trunk | drum 11, 12 Biconcave negative lens 13, 14, 15 Lens 16, 17, 18, 19 Negative lens 20, 21, 22 Positive meniscus lens LG1 1st lens group LG2 2nd lens group LG3 3rd lens group LG4 4th lens group LG5 5th lens group

Claims (17)

A refractive projection objective for projecting a pattern placed on the object plane of a projection objective onto the image plane of the projection objective:
A first lens group (LG1) having negative refractive power following the object plane;
A second lens group (LG2) having a positive refractive power following the first lens group;
A third lens group (LG3) having negative refractive power following the second lens group;
A fourth lens group (LG4) having positive refractive power following the third lens group;
A fifth lens group (LG5) having a positive refractive power, following the fourth lens group;
A system aperture (5) arranged in the transition region from the fourth lens group to the fifth lens group,
A waist portion (X) that is disposed between the object side barrel (6) and the image side barrel (8), and is disposed between the object side barrel and the image side barrel and contracts the beam most narrowly (X). 7) with a single waist-shaped system,
The waist distance AT exists between the object plane and the contraction, and the condition AT / L ≦ 0.4 holds for the distance ratio AT / L between the waist distance AT and the object image distance L of the projection objective lens. And
The fifth lens group (LG5) has the last optical element formed as a plano-convex lens (29), and this plano-convex lens (29) has a curved entrance surface (either spherical or spherical) A refractive projection objective having a substantially planar exit surface.   Refractive projection objective according to claim 1, wherein the plano-convex lens (29) is a non-hemispheric plano-convex lens.   The image plane is arranged immediately after the fifth lens group (LG5), and the refractive projection objective lenses are the first lens group (LG1), the second lens group (LG2), the third lens group (LG3), The refractive projection objective according to claim 1, which does not include any lens other than the fourth lens group (LG4) and the fifth lens group (LG5).   The refractive projection objective according to claim 1, having an image side numerical aperture of NA ≧ 1.0.   The projection objective uses an immersion medium placed between the last optical element of the projection objective and the image plane to create a pattern on the object plane of the projection objective on the image plane of the projection objective. The refractive projection objective according to claim 1, wherein the objective lens is an immersion immersion objective.   The refractive projection objective according to claim 1, wherein the image-side working distance is between about 1 mm and 15 mm.   The fourth lens group (LG4) has at least one meniscus lens, and the at least one meniscus lens is concave with respect to the object plane (2) and has a positive refractive power. The refractive projection objective according to claim 1, which is disposed in an object-side incident region of the fourth lens group (LG4).   The refractive projection objective according to claim 7, wherein the at least one meniscus lens is composed of at least two meniscus lenses.   Refractive projection objective according to claim 1, wherein the fourth lens group (LG4) comprises at least one meniscus lens (25) concave to the object plane (2).   Refractive projection objective according to claim 9, wherein the at least one meniscus lens is a negative meniscus lens (25).   Refractive projection objective according to claim 9, wherein the meniscus lens (25) is arranged immediately upstream of the system aperture (5) in the region of a large peripheral beam height.   The refractive projection objective according to claim 9, wherein the maximum angle of incident light of the projection objective occurs at the concave surface of the at least one meniscus lens.   Refractive projection objective according to claim 9, further comprising at least one lens (24) disposed immediately upstream of the meniscus lens (25) and having a positive refractive power.   Refractive projection objective according to claim 13, wherein the at least one lens (24) having a positive refractive power is a biconvex lens.   The fifth lens group (LG5) has at least one meniscus lens, and the at least one meniscus lens has a positive refractive power and a lens surface that is concave with respect to the image plane. A refractive projection objective according to claim 1.   The fifth lens group (LG5) has at least two meniscus lenses, and the at least two meniscus lenses have a positive refractive power and a concave lens surface with respect to the image plane. A refractive projection objective according to claim 1. The fifth lens group (LG5) has a group of three continuous meniscus lenses (26, 27, 28), each of which has a positive refractive power and is concave with respect to the image plane. The refractive projection objective according to claim 1, having a lens surface of:

Images