WO2004111690A1 - Projection lens and method for selection of optical materials in such a lens - Google Patents

Projection lens and method for selection of optical materials in such a lens

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Publication number
WO2004111690A1
WO2004111690A1 PCT/EP2003/006402 EP0306402W WO2004111690A1 WO 2004111690 A1 WO2004111690 A1 WO 2004111690A1 EP 0306402 W EP0306402 W EP 0306402W WO 2004111690 A1 WO2004111690 A1 WO 2004111690A1
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WO
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Patent type
Prior art keywords
optical
projection
crystal
birefringence
lens
Prior art date
Application number
PCT/EP2003/006402
Other languages
German (de)
French (fr)
Inventor
Michael Gerhard
Birgit Enkisch
Toralf Gruner
Original Assignee
Carl Zeiss Smt Ag
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date

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Classifications

    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B17/00Systems with reflecting surfaces, with or without refracting elements
    • G02B17/08Catadioptric systems
    • G02B17/0892Catadioptric systems specially adapted for the UV
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B13/00Optical objectives specially designed for the purposes specified below
    • G02B13/14Optical objectives specially designed for the purposes specified below for use with infra-red or ultra-violet radiation
    • G02B13/143Optical objectives specially designed for the purposes specified below for use with infra-red or ultra-violet radiation for use with ultra-violet radiation
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B17/00Systems with reflecting surfaces, with or without refracting elements
    • G02B17/08Catadioptric systems
    • GPHYSICS
    • G03PHOTOGRAPHY; CINEMATOGRAPHY; ELECTROGRAPHY; HOLOGRAPHY
    • G03FPHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70Exposure apparatus for microlithography
    • G03F7/70216Systems for imaging mask onto workpiece
    • G03F7/70225Catadioptric systems, i.e. documents describing optical design aspect details
    • GPHYSICS
    • G03PHOTOGRAPHY; CINEMATOGRAPHY; ELECTROGRAPHY; HOLOGRAPHY
    • G03FPHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70Exposure apparatus for microlithography
    • G03F7/708Construction of apparatus, e.g. environment, hygiene aspects or materials
    • G03F7/7095Materials, e.g. materials for housing, stage or other support having particular properties, e.g. weight, strength, conductivity, thermal expansion coefficient
    • G03F7/70958Optical materials and coatings, e.g. with particular transmittance, reflectance
    • GPHYSICS
    • G03PHOTOGRAPHY; CINEMATOGRAPHY; ELECTROGRAPHY; HOLOGRAPHY
    • G03FPHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70Exposure apparatus for microlithography
    • G03F7/708Construction of apparatus, e.g. environment, hygiene aspects or materials
    • G03F7/7095Materials, e.g. materials for housing, stage or other support having particular properties, e.g. weight, strength, conductivity, thermal expansion coefficient
    • G03F7/70958Optical materials and coatings, e.g. with particular transmittance, reflectance
    • G03F7/70966Birefringence

Abstract

The invention relates to a projection lens (10) for a microlithographic projection illumination unit, comprising several groups of serial optical elements, at least one first optical element made from a pure earth alkali metal fluoride crystal and at least one second optical element made from a mixed earth alkali metal fluoride crystal, comprising at least two different earth alkali metals, are arranged in at least one group. All optical elements made from a mixed earth alkali metal fluoride crystal and preferably none of the optical elements made from a pure earth alkali metal fluoride crystal fulfil the condition mi = GPLi * DB (θi) ≥ S. The parameter mi is a lag factor associated with each optical element Li, GPLi the geometrical path length of an aperture beam (28) incident on the optical element Li with a maximum aperture angle, θi is the aperture angle between the aperture beam (28) and the optical axis (26) of the optical element Li, DB(θi) is a measure of the birefringence of the optical element Li, independent of the material and the crystal orientation of the optical element Li and S is a unitary threshold value for all optical elements Li. The projection lens has a low birefringence and is more economical to produce than with all optical elements made from expensive mixed crystals.

Description

Projection lens, as well as method of selecting optical materials in such a lens

The invention relates to a projection lens for a microlithographic projection exposure apparatus, having a plurality of groups of successive optical elements, wherein a first optical element is disposed in at least one group at least consisting of an alkaline earth metal fluoride mixed crystal in which at least two different alkaline earth metals are included. The invention further relates to a method of selecting optical materials for such a lens.

A projection lens of this type is from an article by John H. Burnett et al. entitled "Hidden in Piain Sight: Calcium Fluoride's intrinsic birefringence," photon ics Spectra 12/2001, page 88 et seq, are known..

Microlithographic Proj ektionsbelichtungsanlagen as those used in the manufacture of highly integrated electrical circuits, a lighting installations have direction which serves to generate a projection light beam. The projection light beam is directed to a reticle that includes the imaged by the projection exposure system structures and arranged in an object plane of a projection lens. The Projektionsob- objectively forms the structures of the reticle onto a light-sensitive surface ¬, which is located in an image plane of the projection objective and z. B. can be applied to a wafer.

As a rule, successive generations of products such projection exposure systems use projective onslicht with ever-shorter wavelengths. Since the resolution of projection objectives is inversely proportional to the wavelength of the projection light, can be defined in this way, structures with even smaller dimensions lithographically. In the currently that are available in the development of projection exposure apparatuses generations of projection light is used whose wavelength is 193 nm or even 157 nm, and thus far lies in the ultraviolet region of the electromagnetic radiation.

However, the use of projection light having such a short wavelength involves the problem is that conventional, used for the production of lenses, deviating prisms, and other similar optical elements of materials such as glass or quartz crystals in these WEI lenlängen have insufficient transparency. As a replacement for the conventional optical materials because of certain alkaline earth metal fluoride crystals, especially calcium fluoride (CaF2), barium fluoride (BaF 2) and strontium fluoride (SrF 2), have been proposed, among which in particular calcium fluoride (CaF2) takes special attention. These crystals have in the relevant wavelength range, although high transparency, the production and processing of such crystals is associated with great difficulties, and therefore expensive. In addition, it has been found that these crystals are intrinsically birefringent spite of its cubic crystal structure at least at short wavelengths. Intrinsic birefringence occurs, in contrast to commonly encountered stress-induced birefringence, even with perfect crisis stable growth and without any mechanical tension and leads, unless appropriate measures are taken to intolerable imaging errors.

One approach to reduce the intrinsic birefringence is in the above aforementioned article by John H. Burkina nice et al. described. In this approach, the fact is exploited that the intrinsic birefringence of the crystals is different in sign for the same crystal orientation depending on the alkaline earth metal. Mixed crystals containing a plurality of different alkaline earth metals, are in their properties between those of the above-mentioned pure crystals, by which such crystals are understood here as opposed to the mixed crystals containing only a single alkaline earth metal. With an appropriate choice of mixing ratio, a virtually vanishing intrinsic birefringence can thus be achieved. Particularly promising mixed crystals are containing calcium and barium, and can be described by the stoichiometric formula CAI y Ba y F 2nd Light is delayed in a certain polarization state, the maximum calcium fluoride in times with respect to the perpendicular polarization state, namely, not delayed in barium fluoride and vice versa. Characterized the assignable to the different alkaline earth metal ions birefringent effects are compensated when the determined by the parameter y stoichiometric blend ratio is suitably selected in the mixed crystal.

However, the preparation of such solid solutions in the required purity and size is more difficult and therefore more expensive than crystalline even at the fluoride containing pure is the case. Furthermore, the properties of the solid solutions are similar, depending on the barium content more or less those of barium, meaning they are relatively soft, so intractable and have a high water solubility.

under the sole point of minimal intrinsic birefringence such projection lenses are ideal in which all lenses contained therein and other optical elements that need to be transparent to the projection light, are made of such solid solutions. However, the costs for such a projection lens are extremely high. The object of the invention is therefore to provide a projection lens of the type mentioned, which has only very small, caused by intrinsic birefringence of the materials used aberrations and yet is relatively inexpensive.

This object is achieved in that a second optical element is in said at least one group arranged at least consisting of an alkaline earth metal fluoride-crystal, and that within the at least one group of all the optical elements of an alkaline earth metal fluoride solid solution and preferably none of the optical elements of an alkaline earth metal fluoride crystal clean the condition

Di 1 = 1 * DB GPL (G 1) ≥ S

meet, equal to the number of optical elements in the at least one group of associated delay parameter, GPL 1 than the geometric path length of one optical with Ki 1 as an each optical element L 1, i = 1 ... N with N to maximum opening angle of the element L 1 auftref- fenden aperture ray, Q 1 as the opening angle between the aperture ray and the optical axis of the optical element L 1, DB (B 1) as a measure of the birefringence of the optical element L 1, of the material and crystal orientation of the element L is independently 1 optical, and S as a standard for all of the optical elements 1 L threshold. The invention is based on the realization that the influence of the intrinsic birefringence not all optical elements within the projection objective has an effect equal to an unfavorable effect on the imaging properties. At the. most are caused by the intrinsic birefringence delays certain polarization states and hence the imaging errors in those optical elements, which on the one hand the intrinsic birefringence magnitude is very large and on the other hand, the distance traveled by the respective optical element path is particularly long.

According to the invention it is now proposed to use a single, simple to calculate, and called the delay parameter mi scalar quantity, which summarizes the adverse effects of intrinsic birefringence of the individual optical elements of the projection lens. With the above defined delay parameter nii is a reference value available that allows an estimation in which optical elements, the use of expensive worth mixed crystals and can be in which optical elements without the use of solid solutions.

Although it is possible in principle, predict by means of numerical simulations, the effects of birefringence for gege- bene materials and crystal orientations for different polarization states relatively accurately. These calculations are quite complicated but would have to be carried out for all conceivable material variants and also not lead to simple, associated with the individual optical elements sizes, permitting direct comparison of the effects of intrinsic birefringence.

In determining the delay parameter is first assumed that all the optical elements of tall alkaline earth fluoride pure crystals consist, whose orientation is selected low each other with respect to a mutual compensation effect. A known per se in each of crystal dependence of the birefringence of the azimuth angle is then so far weakened by mutual compensation effects that it is negligible. In addition, at a favorable orientation of the crystal lattice of a dependence of the birefringence on the opening angle θ, which seriously eligible orientations of the crystal lattice is the same for all and by the equation

DB (θ ±) α = k * sin 2 (θi) * (7 * cos 2 (G 1) - 1)

is given, where a ^ is a waste of the crystal orientation hanging parameters.

For smaller opening angle θi, in particular for θi ≤ 40 °, the size DB (θi) can be approximately determined by the equation: DB (θi) = α k * 9/7 * sin 2 (2, 17 * θi),

wherein ök is dependent on the crystal orientation Direction parameter.

In both cases it is assumed, moreover, that can be also found sol che favorable crystal orientations when there crystals only a part of the optical elements of alkaline earth metal fluoride-pure material for a replacement.

Since the delay parameter will only allow an estimation of the influence of the intrinsic birefringence, it does not depend on exact numerical values ​​when determining the size DB (θi). Therefore, the value iru used to determine the delay parameter for DB (θi) and at most 10%, preferably at most 5%, deviate from those constructed by the above formulas values.

Since the costs arising from the use of alkaline earth metal fluoride mixed crystals fees do not have to be the same for all the optical elements inside the projection lens, it may be expedient to make the choice of materials for the optical elements separated for individual groups of optical elements. Adjacent groups of optical element can thereby be, for example by polarization-selective beam splitter layers, delay platelets or diaphragm planes separated from each other. In most cases, but it will be the best to make no division into individual groups. At least one group then covers the entire projection lens.

Preferably consisting of at least a second optical element made of an alkaline earth metal fluoride crystal of the formula XF 2 with X = Ca, Ba or Sr. It is particularly preferred in this case calcium fluoride (CaF 2) as a material for the at least one first optical element.

The at least one first optical element is preferential, of an alkaline earth fluoride solid solution of the formula Xi.y X 'y F 2, wherein X, X' are the same Ca, Ba or Sr and the mixing ratio y of the alkaline earth metals X, X 'is determined.

The present invention is further to specify a method with which can select materials, which leads to a projection objective of a microlithographic projection exposure apparatus, comprising a plurality of groups of successive optical elements, wherein at least a group of a first optical element selected from an alkaline earth metal fluoride mixed crystal is, in the two different alkaline earth metals are contained at least, and is intended to contain a second optical element, at least consisting of an alkaline earth metal fluoride crystal purity. The inventive method comprises folic constricting steps of: a) determining a threshold value S;

b) determining a delay parameter mi for each optical member Li, i = 1 ... N with N equal to the number τa the group consisting of a fluoride crystal optical elements in the at least one group, wherein the delay parameter.± is given by

πii - GPLi * DB (G 1)

with GPL 1 as the geometrical path of an incident at the maximum opening angle to the optical element L1 aperture ray, θi than the opening angle between the aperture ray and the optical axis of the optical member Li, DB (θi) as a measure of the birefringence of the optical member Li that is independent of the material and crystal orientation of the optical member Li;

c) selecting an alkaline earth metal fluoride pure crystal for all optical elements L 1, the delay parameter is ITII smaller than the threshold S, and preferably selecting an alkaline earth fluoride solid solution as a material for optical elements L j, the delay parameter Irij greater or equal to the threshold S.

The threshold value S is set from the viewpoint that the aberrations occurring due to intrinsic birefringence are still tolerable in delay parameters m ± that are smaller than this threshold value. On the other hand, the threshold S should be as large as the products resulting from the use of mixed crystals additional costs are minimized in this way. It has been found that in practice threshold S is between 10 mm and 15 mm result in a particularly good balance between picture quality on the one hand and cost on the other.

Preferably, steps b) and c) are repeated at least once, wherein changes in the geometric path length resulting GPLi to be taken into account in each case for determining the delay parameter in the choice of the material after step c), if necessary.

This iterative process allows for the fact that in must be assumed that a certain design of the entire projection lens first when determining the delay parameter. These include the radii of curvature of the lenses used, coefficients describing aspherical surfaces, the lens thickness and

Air spaces. The influence of the choice of material after step c) to these design parameters is indeed low, but not at all costs negligible. For example has. B. a CAI y Ba y F 2 mixed crystal a different refractive index than a pure CaF2 crystal. Through the iterative optimization process, it is possible such an impact on the design parameters of the projection lens through the material dialing into account and finally to find a consistent solution, in which small changes of the design parameters is no longer a change in the delay parameter Hi 1 to lead.

The invention will be explained in the following using an exemplary embodiment with reference to the drawings. in which:

Figure 1 is a simplified illustration of a catadioptric projection objective according to the invention egg ner mikrolithographisehen projection exposure system in a meridional;

2 shows a graph in which the intrinsic birefringence is plotted as a function of wavelength for calcium fluoride and barium fluoride;

3 shows an enlarged detail of the projection objective of Figure 1 in which two lenses and this one, by kicking aperture ray are shown;

Figure 4 is a flow chart illustrating the selection process of invention material proper.

1 shows a projection objective of a microlithographic projection exposure apparatus is shown in simplified form in a meridional and records total sawn by 10. The projection lens 10 serves to structures contained in a reticle 12 reduced to a photosensitive surface map which is applied on a substrate fourteenth The reticle 12 is in an object plane and the photosensitive surface arranged in an image plane of the projection lens 10 degrees.

In Figure 1, indicated by dashed lines projection light 13, which is generated from an unillustrated lighting device of the projection exposure apparatus and in the illustrated embodiment, has a wavelength λ = 157 nm arrives after passing through the reticle 12 via a plane-parallel plate 15 and a lens Ll in a beam splitter cube 16. There, the projection light beam is reflected 17 and thrown through a lens L2, a quarter wave plate 18 and two further lenses L3 and L4 on a spherical mirror 20 to a splitter layer contained therein polarization selective beam. After re the lenses L4 and L3, the four telwellenlängenplättchen 18 and the lens L2 flexion of the spherical mirror 20 passes through the projection light beam again and falls on the polarization dependent beam splitter layer 17. There, the projection light beam is, however, not reflected but transmitted because the polarization of the product was jektionslichtbündels rotated by the two-time passage through the quarter-wave plate 18 by 90 °.

Of the beam splitter cube 16, the projection light beam passes via a plane mirror 22 in a dioptric part of the projection lens 10, in which lenses L5 to L18 and another plane-parallel plate 24 are arranged along a direction indicated by 26 optical axis.

To th light losses as low as possible to HAL by absorption, all or more of the optical elements which must be transparent to the projection light, either from CaF 2, or of a CAI y Ba y F2 mixed crystal made. For simplicity, it is assumed in the following that it is in these optical elements exclusively to the lenses Ll to L18. However, it should be understood that in addition, for example, the plane parallel plates 15 and 24 or the beam splitter cube may be made of a fluoride crystal 16 and are then taken into account in the manner described below with material selection. Similarly, another present to the conditions can be adapted

Pre-selection of made of fluoride crystal optical elements are made.

2 shows with reference to a graph of the intrinsic birefringence An of BaF 2 and CaF 2 in dependence on the wavelength λ of projection light. In it can be seen that CaF2 has for larger wavelengths λ a practically vanishing birefringence An. Short wavelength λ, the intrinsic birefringence significantly increased with approximately 1 / λ. 2 BaF 2, however, also at longer wavelengths λ a non-negligible intrinsic birefringence which increases to short wavelengths λ out also with approximately 1 / λ. 2 At smaller wavelengths λ lower, however, the two materials with respect to the sign of birefringence An divorce. This means that with the same crystal orientation, the maximum retarded in both materials states of polarization orthogonally to one another.

In Caχ-y Bay y F 2 mixed crystals, the material properties and thus the intrinsic birefringence between those of CaF2 and BaF2 are. While at greater wavelengths λ such a mixed crystal a higher intrinsic see birefringence as CaF 2, the mixing ratio of calcium and barium determining stoichiometric parameter y can be found for a specific shorter wavelength λ a, at which the intrinsic birefringence An as between that is of CaF 2 and BaF 2, that it disappears (An = 0).

The intrinsic birefringence of made of CaF2 lenses, however, is not negligible. Is described by targeted, also referred to as "clocking" twisting of the crystal lattice of the made of CaF 2 lenses, as examples game, in WO 02/093209, can be indeed an at least partial compensation of the induced intrinsic birefringence delays within groups of achieve two existing lenses made of CaF. However, full compensation for the delays is generally not possible because the geometric path lengths differ even in exactly opposite acting birefringence within the lens and thus the caused by these delays. Thus, there remains generally also the "clocking" one can not be compensated residual birefringence that degrades imaging properties.

Made from solid solutions lenses are therefore, if only the imaging properties are considered to prefer consisting of CaF2 lenses in principle. However, consisting of mixed crystals lenses have the disadvantage of a much higher price, since the production of highly pure solid solutions and their processing are very expensive. In addition, consisting of mixed crystals lenses to moisture may be exposed because the mixed crystals have a significantly higher solubility in water than CaF second

Therefore, the projection lens 10 has not only from solid solutions, but also from CaF2-made lenses. In order to achieve the best possible compromise between cost and good imaging properties, it is however necessary stuffs to ermit- by a selection those lenses in which aberration due to intrinsic birefringence can be tolerated best.

In principle can be personalized with simulation method, the optical characteristics including aberrations also very complicated optical systems very precisely ER auxiliaries. However, the computational cost is usually too high to determine the imaging characteristics for all conceivable material variants in this way.

The choice of material for the lenses made of fluoride crystal is therefore performed assigned using a simple to be determined, each lens Li scale- ren size, defined by the equation

In GPL 1 = 1 * DB (θi) (1)

is defined and is hereinafter referred to as a delay parameter m ±. The delay parameter τa.± illustrates a proximity measure for the mapping error caused by domestic trinsische birefringence. If the delay parameter IUI is above an arbitrarily chosen in principle threshold S, the respective lens Li is made of the mixed crystal. If the delay parameter IUI below the selected threshold value S, then the respective lens Li is preferably made of CaF 2, unless it appear expedient use of the more expensive solid solution in the individual case other reasons.

Thus the delay parameter ITII an easy-to-determining, but meaningful size, have come in spite of the necessary approximations those factors expressed that are relevant to the extent of the aberrations caused by intrinsic birefringence. These factors are the geometric path length GPLi an impinging under maximum opening angle θi on the optical element Li aperture ray and the size DB (θi) as a measure of the birefringence of the optical element ± L. These two factors, plus the underlying approximations are more likely to be described below ausführli-.

For the amount of aberration caused by intrinsic birefringence in CaF 2, the delay is relevant, to know the orthogonal polarization states in CaF 2 relatively to each other. This delay depends inter alia on the amount of the intrinsic birefringence in CaF2, which is a function of the opening angle φ θi and the azimuth angle. the angle θi is understood under the opening angle thereby, the forming a light beam to the optical axis 26; the orientation egg nes beam is φ by the azimuth angle described to a plane perpendicular to the optical axis reference direction.

In determining the influence of the birefringence is assumed that the crystal orientations of all existing CaF2 lenses are aligned "clocking" favorable or even optimally to each other. Thus, the dependence of the birefringence can be neglected by the azimuth angle. Furthermore, then it turns a dependence of birefringence θ of the opening angle a, the eligible orientations of the crystal lattice takes the same pattern for all, by the equation DB (θi) = "k * siir 2 / (Qθi \) * m (7 * * ~ co_ s ~ 2 '(θi) - 1): D

given is. Here, * k c denotes a depending on the crystal orientation parameter which characterizes the relative effectiveness of the optical elements with respect to the intrinsic birefringence. For crystal orientations in which the [100] crystal axis is aligned along the optical axis, "k = -1/2, for crystal orientations in which the [111] crystal axis is aligned along the optical axis, is OC R = +1/3, and crystal orientations in which the [UO] - crystal axis is aligned along the optical axis, is α = k +1/8.

can θi small opening angle, instead of the equation (1), the approximate equation

DB (θi) = α k * 9/7 * sin 2 (2.17 * θ ±) (2)

be used.

In addition, the delay depends in CaF 2 on the geometric path length that defines a projection light beam in the respective lens L1. The geometric path length is different, depending on what angle of incident projection light beam on a lens and how large the thickness of the lens in this area. This will be explained with reference to FIG. 3 There, the two lenses are shown L3 and L4, the geometric path lengths GPL 3 or GPL4 the example that occur for an outer aperture ray 28 in these lenses. As aperture ray 28, a beam is referred to herein, which occurs under maximum opening angle Qx a lens Li. The lens L4 is thicker than the lens L3, and further, the opening angle is θ 4, under which the aperture ray 28 strikes the lens L4, due to the scattering effect of the lens L3 is greater than the opening angle θ. 3 That is why the distance from the aperture ray 28 in the geometric path length lens L4 GPL 4 is greater than that in the lens L3 distance geometric path length GPL. 3

In determining the delay factor mi according The same chung (1) are not all of the possible opening angle range or the entire geometry of the lens Li into consideration, but considered a single geometric path length GPLi, namely that of an aperture ray 28 in the respective lens Li is covered. This loading rests on the concept that the intrinsic birefringence is growing in the commonly used crystal orientations with increasing opening angle, so lenses in which large opening angle occur also have particularly large aberrations due to intrinsic birefringence. Moreover, even in thick lens such as the lens L17, the geometric path of a central ray along the optical axis 26 is generally not significantly longer than the geometric path length of one aperture ray incident on the lens at a large opening angle and this is why by an angle.

The beam path of the aperture rays is relatively easy for a given optical system generally lationsprogramme using appropriate simulation to determine. thus the delay parameter may be a lens πu Li together with the by measurement or by one of the equations (2) or (3) determined magnitude of the birefringence in a simple manner according to the equation (1) can be determined. For an aperture ray that does not intersect the optical axis, is moreover considered herein as opening angle θi is an angle formed between the aperture ray and an axis which intersects the aperture ray and seen by parallel displacement of the optical axis.

The procedure for the selection of materials is explained in more detail below with reference to the flow chart shown in Figure 4. First, in step Sl, a threshold value S is set, indicating which degree of imaging errors is no longer tolerable. In making this determination is to take into account, among other things, that request are placed on the imaging properties of the projection lens 10 degrees. whose delay parameters mi is then determined in a step S2, in the manner described above for each fluoride lens Li. In a further step S3 is made fixed, for which the lenses Li πii delay parameter is less than or equal to the threshold S is. For these lenses, the influence of the intrinsic birefringence when using CaF2 is tolerable as a lens material. For all other lenses of the delay parameter is IrII greater than the threshold value S, so that are not to be expected tolerable aberration due to intrinsic birefringence and the lenses in question should be therefore made of a mixed crystal.

Since CaF 2, and the mixed crystals typically have a different refractive index, those lenses which are to be replaced by lenses of a mixed crystal according to the selection in step S3, after the replacement have different optical properties. This may make it necessary to make 10 modifications in terms of radii of curvature, lens distances and similar design parameters of the design of the projection objective. These modifications to the geometric path lengths of the aperture rays and thus the delay parameter Hi 1 may in turn change.

In order to improve the material selection further, it may therefore be expedient in an iterative process according to egg ner for the first time according to step S3 material selection made initially adjust, in a step S4, the projection lens to the taken preliminary selection. This results in generally modified geometric path lengths GPLi. Thereafter, steps S2 and S3 performed again, where u is. U. may result a change of the original material selection. Preferably, steps S2, S3 and S4 are repeated until the change delay parameters no longer ITII or a change at a predeterminable limit remains.

Claims

claims
1. projection objective for a microlithographic
Projection exposure apparatus, having a plurality of groups of successive optical elements, wherein a first optical element is disposed in at least one group at least consisting of an alkaline earth metal fluoride
Mixed crystal is, in the two different alkaline earth metals are contained at least
characterized,
that a second optical element is in said at least one group arranged at least consisting of an alkaline earth metal fluoride-crystal, and that within the at least one group of all the optical elements of an alkaline earth fluoride solid solution condition
meet, with mi than one each optical element Li, i = 1 ... N with N equal to the number of the group consisting of a fluoride crystal optical elements in the at least one group of associated delay parameter, GPLi than the geometric path length of a under maximum opening angle incident on the optical member Li aperture ray (28), θi than the opening angle between the aperture ray (28) and the optical axis (26) of the optical member Li, DB (θi) as a measure of the birefringence of the optical member Li, which by the material and the crystal orientation of the optical member Li is independent, and S as a unitary for all optical elements Li threshold.
2. Projection objective according to claim 1, characterized in that none of the optical elements of an alkaline earth metal fluoride-crystal satisfies the specified condition within the at least one group.
3. Projection objective according to claim 1 or 2, characterized in that
DB (G 1) = cx k * sin 2 (θi) * (7 * cos 2 (B 1) - I]
, where α k is a dependent Direction of the crystal orientation parameters.
4. Projection objective according to claim 1 or 2, characterized in that
DB (θi) = α k * 9/7 * sin 2 (2, IV * Qi)
, where k is a dependent oc Direction of the crystal orientation parameters.
5. Projection objective according to claim 3 or 4, characterized in that the value ITII used to determine the delay approximately parameters for DB (θi) by at most 10%, preferably at most 5%, of the by calculation resulting according to claims 3 or 4 values for DB (θ ±) deviates.
6. Projection objective according to one of the preceding
Claims, characterized in that the at least one group comprises the entire projection lens (10).
7. Projection objective according to one of claims 1 to 5, characterized in that in each case two adjacent groups are separated by a polarization-selective beam splitter layer (17).
8. Projection objective according to one of claims 1 to 5, characterized in that each two adjacent
Groups are separated by a delay plate (18).
9. Projection objective according to one of claims 1 to 5, characterized in that each two adjacent
Groups are separated by a diaphragm plane.
10. Projection objective according to one of the preceding claims, characterized in that the at least one second optical element consists of an alkaline earth metal fluoride crystal of the pure XF formula 2 where X is Ca, Ba or Sr.
11. Projection objective according to one of the preceding claims, characterized in that consisting of at least a first optical element made of an alkaline earth fluoride solid solution of the formula Xi_ y X τ y F 2, wherein X, X 1 are the same Ca, Ba or Sr, and y, the mixing ratio of the two alkaline earth metals X, X 'determined.
12. A method of selecting optical materials for a projection objective of a microlithographic
Projection exposure apparatus, the consecu- more groups derfolgender optical elements, wherein at least one group, a first optical element which consists of an alkaline earth fluoride solid solution, in which two different alkaline-earth metals are contained at least, and is intended to contain a second optical element, at least, the consists of an alkaline earth metal fluoride-crystal,
with the following steps:
a) determining (Sl) a threshold value S;
b) determining (S2) a delay parameter mi for each optical element L 1, i = 1 ... N with N equal to the number of the group consisting of a fluoride crystal optical elements in the at least one group, wherein the delay parameter mi is given by
(mi = GPL 1 * DB (G 1) with GPL 1 as the geometrical path of an incident at the maximum opening angle to the optical element L1 aperture ray (28), θi than the opening angle between the aperture ray (28) and the optical axis 26) of the optical element L 1, DB (θi) as a measure of the birefringence of the optical element L 1, that is independent of the material and crystal orientation of the optical element 1 L;
c) selecting an alkaline earth metal fluoride mixed crystal as a material for optical elements L 3, the delay parameter m is greater than or equal to the threshold S.
13. The method of claim 12, wherein steps b) and c) are repeated at least once, said to take into account in each case for determining the delay parameter Hi 1 of the material selection according to step c) if appropriate, resulting changes in the geometric path length GPL 1 (S4 ) become.
14. The method of claim 12 or 13 with the following additional step:
d) selecting (S3) an alkaline earth metal fluoride crystal purity for all optical elements L 1, whose encryption deceleration parameter Hi 1 is smaller than the threshold S.
PCT/EP2003/006402 2003-06-18 2003-06-18 Projection lens and method for selection of optical materials in such a lens WO2004111690A1 (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7239450B2 (en) 2004-11-22 2007-07-03 Carl Zeiss Smt Ag Method of determining lens materials for a projection exposure apparatus
WO2011146273A1 (en) * 2010-05-21 2011-11-24 Eastman Kodak Company Designing lenses using stress birefringence performance criterion

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EP1006373A2 (en) * 1998-11-30 2000-06-07 Carl Zeiss Objective with crystal lenses and projection exposure apparatus for microlithography
JP2000356701A (en) * 1999-06-15 2000-12-26 Tsuguo Fukuda Optical member for vacuum ultraviolet region comprising colquiriite type fluoride mixed crystal and coating material for optical member
EP1063684A1 (en) * 1999-01-06 2000-12-27 Nikon Corporation Projection optical system, method for producing the same, and projection exposure apparatus using the same
WO2003006367A1 (en) * 2001-07-09 2003-01-23 The Government Of The United States Of America, As Represented By The Secretary Of Commerce Minimizing spatial-dispersion-induced birefringence
US20030104318A1 (en) * 2001-09-14 2003-06-05 Allan Douglas C. Photolithographic element blank calcium strontium fluoride UV transmitting mixed fluoride crystal with minimized spatial dispersion

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1006373A2 (en) * 1998-11-30 2000-06-07 Carl Zeiss Objective with crystal lenses and projection exposure apparatus for microlithography
EP1063684A1 (en) * 1999-01-06 2000-12-27 Nikon Corporation Projection optical system, method for producing the same, and projection exposure apparatus using the same
JP2000356701A (en) * 1999-06-15 2000-12-26 Tsuguo Fukuda Optical member for vacuum ultraviolet region comprising colquiriite type fluoride mixed crystal and coating material for optical member
WO2003006367A1 (en) * 2001-07-09 2003-01-23 The Government Of The United States Of America, As Represented By The Secretary Of Commerce Minimizing spatial-dispersion-induced birefringence
US20030104318A1 (en) * 2001-09-14 2003-06-05 Allan Douglas C. Photolithographic element blank calcium strontium fluoride UV transmitting mixed fluoride crystal with minimized spatial dispersion

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7239450B2 (en) 2004-11-22 2007-07-03 Carl Zeiss Smt Ag Method of determining lens materials for a projection exposure apparatus
WO2011146273A1 (en) * 2010-05-21 2011-11-24 Eastman Kodak Company Designing lenses using stress birefringence performance criterion
CN102906616A (en) * 2010-05-21 2013-01-30 伊斯曼柯达公司 Designing lenses using stress birefringence performance criterion

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