Imaging optical unit and projection exposure apparatus for projection lithography, having such imaging optical unit

An imaging optical unit for imaging an object field in an image field is disclosed. The imaging optical unit has an obscured pupil. This pupil has a center, through which a chief ray of a central field point passes. The imaging optical unit furthermore has a plurality of imaging optical components. A gravity center of a contiguous pupil obscuration region of the imaging optical unit lies decentrally in the pupil of the imaging optical unit.

The invention relates to an imaging optical unit with a plurality of optical components, in particular mirrors, which image an object field in an object plane in an image field in an image plane. The invention furthermore relates to an optical system with such an imaging optical unit, a projection exposure apparatus with such an optical system, a method for producing a microstructured or nanostructured component using such a projection exposure apparatus and a microstructured or nanostructured component produced via this method.

It is an object of the present invention to develop an imaging optical unit of the type mentioned at the outset in such a way that a well corrected imageable field results with, at the same time, a high imaging light throughput.

According to the invention, this object is achieved by an imaging optical unit for imaging an object field in an image field,wherein the imaging optical unit has an obscured pupil,wherein the pupil has a center, through which a chief ray of a central field point passes,with a plurality of imaging optical components,
wherein a gravity center or centroid of a contiguous pupil obscuration region of the imaging optical unit lies decentrally in the pupil of the imaging optical unit.

A pupil of the imaging optical unit is that region in an imaging beam path of the imaging optical unit in which individual imaging rays, which emanate from the object field points, intersect and are respectively associated with the same illumination angle relative to chief rays which emanate from these object field points. An intensity distribution of imaging light in a pupil plane, in which the pupil is arranged, correspondingly predetermines that range of illumination angles which reach the image field. There is always an imaging optical unit with an obscured pupil if there is a pupil obscuration region of impossible or forbidden illumination or imaging angles for each field point within a peripheral pupil of the imaging optical unit which is predetermined by the numerical aperture. Thus, in the case of an imaging optical unit with obscured pupil, there are imaging beam paths which, as a result of obscuration between components of the imaging optical unit or as a result of a region on at least one of the optical components of the imaging optical unit which do not contribute to the imaging beam path, are impossible. The invention departs from the previous demand that, in the case of obscured systems, a pupil obscuration region is always arranged in such a way that the gravity center thereof lies centrally in the pupil of the imaging optical unit. Departing from this demand leads to new degrees of freedom in the design, which can be used to bring about improved aberration correction. In particular, it was identified that imaging optical units with pupil obscurations can be realized, in which the pupil obscuration for illumination angles used in practice does not reduce the throughput.

A mirror symmetry of the pupil obscuration region, in which the pupil obscuration region is mirror symmetrical with respect to a plane of symmetry of the imaging optical unit, provides the option of a corresponding mirror symmetrical design of the imaging optical unit. The plane of symmetry can be a meridional plane of the imaging optical unit.

An embodiment of the pupil obscuration region, in which the center of the pupil lies outside of the pupil obscuration region, renders it possible for chief rays, i.e. rays which extend through the center of the pupil, to contribute to the imaging. This can be used, in particular, if specific orders of diffraction of the imaging light extend along the chief rays.

A diameter relationship, in which the pupil has a pupil diameter in a pupil plane of the imaging optical unit, wherein a completely usable pupil region about the center of the pupil has a diameter which is at least 10% of the pupil diameter, enables the use of a correspondingly large central pupil region without obscuration. The completely usable pupil region about the center of the pupil can be at least 20%, can be at least 30%, can be at least 40%, can be at least 50%, or can even be a greater percentage, of the pupil diameter. To the extent that the pupil and the completely usable pupil region are circular, the respective diameter corresponds to the diameter of the circle. In the case of other shapes of the pupil and/or of the completely usable pupil region about the center, a typical diameter is specified as diameter, which for example is the result of averaging the various diameters.

A pupil obscuration region, in which the pupil obscuration regionhas a radial pupil obscuration region extent in a radial dimension along a gravity center axis, on which the center of the pupil and the gravity center of the pupil obscuration region lie,has a tangential pupil obscuration region extent in a tangential dimension perpendicular to the gravity center axis,wherein the radial pupil obscuration region extent differs from the tangential pupil obscuration region extent by more than 10%,
can be finely adapted to guiding the imaging radiation through the imaging optical unit. The tangential pupil obscuration region extent can be greater than the radial one. In particular, the radial pupil obscuration region extent can differ from the tangential one by more than 20%, by more than 30%, by more than 40%, by more than 50% or else by an even larger percentage. The tangential pupil obscuration region extent can be a multiple of the radial pupil obscuration region extent.

An embodiment of the imaging optical unit as catoptric lens allows a high throughput even in the case of used wavelengths for which no sufficiently transmissive optical materials are available.

An embodiment of the imaging optical unit according to the invention with a penultimate mirror and a last mirror in the imaging beam path upstream of the image field,wherein a chief ray of a central field point impinges on the last mirror of the imaging optical unit at an angle of incidence,wherein, in the imaging beam path upstream of the penultimate mirror, the chief ray passes through a passage opening in the last mirror and extends along a passage chief ray section,wherein the chief ray extends along an image field chief ray section between the last mirror and the image field,wherein the two chief ray sections extend in a common plane and include a chief ray angle between one another,
wherein the angle of incidence is greater than the chief ray angle, enables a mirror arrangement, in particular, in which a center of the last mirror upstream of the image field can be used, which can contribute to a reduction of aberrations.

An additional obscuration component which generates an additional pupil obscuration region, wherein the two pupil obscuration regions complement one another to form an overall pupil obscuration region which is arranged in a centrally symmetric fashion with respect to the center (Z) of the pupil, can be used when imaging relationships are demanded which require a centrally symmetric pupil obscuration.

According to a further aspect of the invention, the object specified at the outset is achieved by a catoptric imaging optical unit for imaging an object field in an image field,wherein the imaging optical unit has an obscured pupil,wherein the pupil has a center, through which a chief ray of a central field point passes,with a last mirror in the imaging beam path between the object field and the image field, wherein the last mirror has a passage opening for the passage of imaging light, wherein an edge region of a reflection surface of the last mirror, which edge region surrounds the passage opening, is used contiguously for reflecting the imaging light,with a penultimate mirror in the imaging beam path, with a reflection surface which is used in a completely contiguous or closed fashion, i.e. without an opening,wherein the passage opening is arranged in such a way that this generates a pupil obscuration region, which does not lie centrally in the pupil of the imaging optical unit.

The advantages of a decentrally arranged pupil obscuration region are particularly pronounced in the case of a catoptric imaging optical unit with a penultimate mirror used in a completely contiguous closed fashion. Here, it is not mandatory for the pupil obscuration region to have a gravity center which lies decentrally in the pupil of the imaging optical unit.

In accordance with a further aspect of the invention, the object stated at the outset is achieved by an imaging optical unit for imaging an object field in an image field,wherein the imaging optical unit has an obscured pupil,
wherein an overall pupil obscuration region of the imaging optical unit or portions thereof has an aspect ratio which deviates from 1 with respect to mutually perpendicular coordinates of a pupil coordinate system.

An obscuration with an aspect ratio which deviates from 1 can be finely adapted to the illumination angles required within an illumination pupil and to the necessity of an arrangement of non-obscured pupil regions in order to pass illumination light which is diffracted there on structures of an object to be imaged. An aspect ratio between a smaller obscuration dimension and a larger obscuration dimension can be of the order of 0.9, can be of the order of 0.8, can be of the order of 0.7, can be of the order of 0.6, can be of the order of 0.5, can be of the order of 0.4, can be of the order of 0.3 or can be even less than that.

The pupil obscuration region of this last-mentioned aspect can consist of contiguous portions or of a plurality of portions. The contiguous pupil obscuration region or at least one of the portions can be shaped like an ellipse, a rectangle or a trapezoid. In the case of an angular shape of the pupil obscuration region or of a portion thereof, at least individual corners, or all corners, of the pupil obscuration region or of the portions thereof can be embodied in a rounded-off fashion.

The features of the imaging optical units of the aspects explained above can be used together in any combination thereof.

The advantages of an optical system with an imaging optical unit according to the invention and an illumination optical unit for guiding the illumination light to the imaging optical unit, of a projection exposure apparatus for projection lithography with an optical system according to the invention and a light source for the illumination and imaging light, of a method for producing a structured component, comprising the following method steps:providing a reticle and a wafer,projecting a structure on the reticle onto a light-sensitive layer of the wafer with the aid of the projection exposure apparatus according to the invention,generating a microstructure or nanostructure on the wafer,
and of a microstructured or nanostructured component produced according to this method, correspond to those that were already discussed in the context of the imaging optical unit according to the invention.

A projection exposure apparatus1for microlithography has a light source2for illumination light or imaging light3. The light source2is an EUV light source which generates light in a wavelength region of, for example, between 5 nm and 30 nm, in particular between 5 nm and 15 nm. The light source2can, in particular, be a light source with a wavelength of 13.5 nm or a light source with a wavelength of 6.9 nm. Other EUV wavelengths are also possible. In general, use can even be made of any wavelength for the illumination light3guided in the projection exposure apparatus1, for example visible wavelengths or else other wavelengths which can find use in microlithography and for which suitable laser light sources and/or LED light sources are available (e.g. 365 nm, 248 nm, 193 nm, 157 nm, 129 nm, 109 nm). A beam path of the illumination light3is illustrated very schematically inFIG. 1.

An illumination optical unit6serves for guiding the illumination light3from the light source2to an object field4in an object plane5. Using a projection optical unit or imaging optical unit7, the object field4is imaged in an image field8in an image plane9with a predetermined reduction scale. In the x-direction, the image field8has an extent of 26 mm and the image field extends 2 mm in the y-direction. The object field4and the image field8are rectangular. One of the exemplary embodiments illustrated inFIGS. 2 and 5can be used as the projection optical unit7. The projection optical unit7according toFIG. 2reduces by a factor of 4. Other reduction scales are also possible, for example 5×, 8×, or even reduction scales which are greater than 8×. In the embodiments according toFIGS. 2 and 5of the projection optical unit7, the image plane9is arranged parallel to the object plane5. A section of a reflection mask10which is also referred to as a reticle and coincides with the object field4is imaged in this case. The reticle10is held by a reticle holder10a. The reticle holder10ais displaced by a reticle displacement drive10b.

The imaging by the projection optical unit7takes place onto the surface of a substrate11in the form of a wafer, which is held by a substrate holder12. The substrate holder12is displaced by a wafer or substrate displacement drive12a.

InFIG. 1, a beam13of the illumination light3entering the projection optical unit7is schematically illustrated between the reticle10and the projection optical unit and a beam14of the illumination light3leaving the projection optical unit7is illustrated schematically between the projection optical unit7and the substrate11. An image field-side numerical aperture (NA) of the projection optical unit7is not reproduced to scale inFIG. 1.

In order to simplify the description of the projection exposure apparatus1and of the various embodiments of the projection optical unit7, a Cartesian xyz-coordinate system is specified in the drawing, from which the respective positional relations of the components illustrated in the figures emerge. InFIG. 1, the x-direction extends perpendicular to the plane of the drawing and into the latter. The y-direction extends to the right and the z-direction extends downward.

The projection exposure apparatus1is a scanner-type one. Both the reticle10and the substrate11are scanned in the y-direction during operation of the projection exposure apparatus1. A stepper-type projection exposure apparatus1, in which there is a step-wise displacement of the reticle10and of the substrate11in the y-direction between the individual exposures of the substrate11, is also possible. These displacements occur in a synchronized fashion with respect to one another as a result of an appropriate actuation of the displacement drives10band12a.

FIG. 2shows the optical design of a first embodiment of the projection optical unit7. Illustrated inFIG. 2is the beam path of in each case three individual rays15, which emanate from two object field points which, inFIG. 2, are spaced apart from one another in the y-direction. Chief rays16are illustrated, i.e. individual rays15which pass through the center of a pupil in a pupil plane of the projection optical unit7, and, in each case, an upper and a lower coma ray of these two object field points.

The object plane5lies parallel to the image plane9.

The projection optical unit7according toFIG. 2has a total of six mirrors, which, in the sequence of the beam path of the individual rays15, are numbered in sequence by M1to M6proceeding from the object field4. The imaging optical unit7can also have a different number of mirrors, for example four mirrors or eight mirrors. The calculated reflection surfaces of mirrors M1to M6are illustrated inFIG. 2. As can be seen from the illustration according toFIG. 2, only a portion of these calculated reflection surfaces is used. Only this actually used region of the reflection surfaces is in actual fact present in the real mirrors M1to M6. These used reflection surfaces are held by mirror bodies in a known fashion.

Apart from mirror M6, all mirrors M1to M5of the projection optical unit7have a contiguously used reflection surface, without a passage opening for the imaging light3. The penultimate mirror M5in the imaging beam path between the object field4and the image field8in particular has a completely contiguous or closed used reflection surface, i.e. one without an opening.

The mirrors M1to M6carry multiple reflection layers for optimizing their reflection for the incident EUV illumination light3. The multiple reflection layers are designed for a work wavelength of 13.5 nm. The optimization of the reflection can be improved the closer the angle of incidence of the individual rays15on the mirror surface is to perpendicular incidence. Overall, the projection optical unit7has small angles of reflection for all individual rays15.

All six mirrors M1to M6of the projection optical unit7are embodied as free-form surfaces which cannot be described by a rotational symmetric function. Other embodiments of the projection optical unit7, in which at least one or even none of the mirrors M1to M6has such a free-form reflection surface, are also possible.

Such a free-form surface can be generated from a rotationally symmetric reference surface. Such free-form surfaces for reflection surfaces of the mirrors of projection optical units of projection exposure apparatuses for microlithography are known from US 2007-0058269 A1.

Mathematically, the free-form surface can be described by the following equation as the sum of a conical base area and a free-form surface polynomial (Equation 1) or as a sum of a biconical base area and a free-form surface polynomial (Equation 2):

j=(m+n)2+m+3⁢n2+1
Z is the sagittal height of the free-form surface at the point x, y, wherein x2+y2=r2.

In the case of a conical base area, c is a constant which corresponds to the apex curvature of a corresponding aspheric lens element. k corresponds to a conical constant of a corresponding aspheric lens element. In the case of a biconical base area, cx, cyare the apex curvatures in meridional and sagittal directions, kx, kyare the associated conical constants. Cjare the coefficients of the monomials VT′. The values of c, k and Cjare typically determined on the basis of the desired optical properties of the mirror within the projection optical unit7. The order of the monomial, m+n, can be varied arbitrarily. A higher-order monomial can lead to a design of the projection optical unit with improved aberration correction, but is more complicated to calculate. m+n can assume values between 3 and more than 20.

Free-form surfaces can also be described mathematically by Zernike polynomials. In this case, a polynomial in the form of a Zernike polynomial is added to the conical (Equation 3) or biconical (Equation 4) base area:

Here, r=√{square root over (x2+y2)}/HNorm specifies the radial coordinate and φ=arctan(y/x) specifies the azimuth coordinate if the ray penetration point on the surface is given by the coordinates x and y and HNorm is the normalization height of the Zernike polynomials specified in the data.

Alternatively, the free-form surfaces can also be described with the aid of two-dimensional spline surfaces. Examples of this are Bézier curves or non-uniform rational basis splines (NURBS). By way of example, two-dimensional spline surfaces can be described by a network of points in an xy-plane and associated z-values or by these points and gradients associated therewith. Depending on the respective type of the spline surface, the complete surface is obtained by interpolating between the node points using e.g. polynomials or functions which have specific properties in respect of their continuity and differentiability. Examples of this are analytic functions.

The optical design data of the reflection surfaces of the mirrors M1to M6of the projection optical unit7can be gathered from the following tables. In each case, these optical design data proceed from the image plane9, i.e. describe the respective projection optical unit in the reverse direction of travel to the imaging light3between the image plane9and the object plane5. The first of these tables respectively specifies a thickness in mm for the optical surfaces of the optical components, which thickness corresponds to the z-distance of neighboring elements in the beam path, proceeding from the image plane6. The second table specifies (in mm) the apex radii RD=1/c or RDY=1/cyand RDX=1/cx, the conical constants k or kxand kyand the coefficients ZFRifor the respectively used Zernike polynomials in the above Equation (4) for mirrors M1to M6.

After the second table, the third table still specifies the absolute value along which the respective mirror, proceeding from a mirror reference design, was decentered in the y-direction (DCY) and tilted (TLA). This corresponds to a parallel displacement and tilting in the case of the free-form surface design method. The displacement in this case is in the y-direction in mm, and the tilt is about the x-axis. Here, the tilt angle is specified in degrees. Decentration is carried out first, followed by tilting.

In the first table, the column “half diameter” specifies the half diameter of the respective back surface of the mirror.

The projection optical unit7has an image-side numerical aperture of 0.45. The object field4has an x-extent of two-times 13 mm and a y-extent of 2 mm. The projection optical unit7is optimized for an operating wavelength of the illumination light3of 13.5 nm.

One of the pupil planes of the projection optical unit7according toFIG. 2lies in the imaging beam path in the region of a reflection on the mirror M2. A further pupil plane of the projection optical unit7according toFIG. 2lies in the imaging beam path between the mirrors M5and M6.

In the projection optical unit7the mirrors M1, M3and M5have an only slightly different geometric distance from the image plane9. This distance difference is less than 5% of the design length of the projection optical unit7, i.e. the distance between the object plane5and the image plane9.

The chief rays16of the object field points propagate substantially parallel to one another between the object field4and the mirror M1. Thus, the projection optical unit7according toFIG. 2is substantially telecentric on the object side.

The projection optical unit7is a pure mirror optical unit, i.e. a catoptric imaging optical unit.

An intermediate image ZB of the projection optical unit7is arranged in an intermediate image plane in the imaging beam path in the region of a reflection at the mirror M4. The mirror M4is configured as a field mirror adjacent to the intermediate image ZB.

The mirror M4is arranged downstream of an imaging light passage opening17in the mirror M6. Hence, the imaging light3passes through the passage opening17in the mirror M6just before and just after the reflection at the mirror M4. The passage opening17in the mirror M6provides a pupil obscuration region18of the imaging optical unit7according toFIG. 2. Hence it is possible to specify a region of forbidden illumination angles in the pupil planes of the imaging optical unit7, i.e. of illumination angles which belong to the imaging beam paths which, on account of the passage opening17, do not contribute to imaging. This region of forbidden illumination angles is the pupil obscuration region18. As a result of the pupil obscuration region18, which predetermines the forbidden illumination angles, the projection optical unit7has an obscured pupil. More details in respect of the pupil obscuration region18will still be explained below in the context ofFIG. 8f.

The mirror M4satisfies the field mirror parameter relationship:
P(M4)<0.5.

The following applies:
P(M)=D(SA)/(D(SA)+D(CR)).

Here, D(SA) is the maximum diameter of a sub-aperture of an imaging beam, which emanates from an object field point, on a reflecting surface of the respective mirror M. D(CR) is a maximum spacing of chief rays which emanate from the object field4, wherein the spacing D(CR) is measured in a reference plane of the projection optical unit7on the reflecting surface of the mirror M. This maximum distance need not lie in the plane of the drawing ofFIG. 2, but can, in particular, also be present in the object field4in the x-direction perpendicular to the plane of the drawing. In the field planes of the projection optical unit7, D(SA)=0 applies and hence P=0. In the pupil planes of the projection optical unit7, D(CR)=0 applies and hence P=1.

The reflection relationships for selected object field points on the mirrors M4and M6of the projection optical unit7according toFIG. 2are explained in more detail below on the basis ofFIGS. 3 and 3a.

FIG. 3ashows a section (not to scale) of the object plane5with the rectangular object field4. In the x-direction, the object field4has an extent of 104 mm and, in the y-direction, it has an extent of 8 mm. A total of eight representative reference object field points19are highlighted.

FIG. 3shows a plan view of the mirror M6and, situated in or behind the rectangular passage opening17, the mirror M4.FIG. 3illustrates sub-apertures20, i.e. outer edges of the imaging beams emanating from the reference object field points19. Shown here are the sub-apertures2025,2050,2075and 20100, which respectively belong to 25%, to 50%, to 75% and to 100% of the numerical aperture of the projection optical unit7according toFIG. 2.

Since the mirror M4is a near-field mirror, the sub-apertures20xof respectively one of the reference object field points19overlap in a tightly delimited region, which approximately corresponds to an image of the respective reference object field point19. The sub-apertures20Xof different reference object field points19do not overlap on the mirror M4.

The outer edges of the sub-apertures20Xare separated on the comparatively pupil-near last mirror M6. The sub-apertures, which belong to a specific percentage of the numerical aperture of the projection optical unit7, i.e., for example, the sub-apertures2025, of the different reference object field points19overlap strongly there.

The passage opening17has such extents in the x- and y-directions that all sub-apertures20100of all object field points of the used object field4, i.e., in particular, of the reference object field points19, can pass without losses through the mirror M6for reflecting the imaging light3at the mirror M4. InFIG. 3, an x-extent of the passage opening17is denoted by2D and a y-extent of the passage opening17is denoted by2C. A radius of the mirror M6is denoted by A and a y-distance between a center of the passage opening17and a center of the mirror M6is denoted by B.

Since the mirror M6is near the pupil, the pupil obscuration region18, caused as a result of the obscuration by the passage opening17, approximately has the shape of the passage opening17in a pupil plane of the projection optical unit7. This is, once again, also indicated very schematically inFIG. 10, where the pupil obscuration region18is indicated as a round region in a used pupil21(seeFIG. 10) of the projection optical unit7according toFIG. 2. The pupil obscuration region18can in fact also have a different shape than a round shape. The actual shape of the pupil obscuration region18depends on which of the individual rays15cannot pass through the pupil21as a result of an obscuration, which is caused by the passage opening17or by another obscuring component such as, for example, a stop. A gravity center SP of the pupil obscuration region18, which, in respect of its x- and y-coordinates approximately coincides with the position of the center of the passage opening17on the mirror M6, does not lie centrally in the used pupil21of the projection optical unit7according toFIG. 2.

The pupil obscuration region18is mirror symmetrical in relation to the yz-plane of the pupil21, i.e. it is mirror symmetrical to a symmetry plane of the imaging optical unit7, which symmetry plane, in this embodiment, coincides with the meridional plane of the imaging optical unit7according toFIG. 2.

A center Z of the pupil21lies outside of the pupil obscuration region18. The pupil obscuration region18lies decentrally in the pupil21. In particular, the chief ray16of the central field point passes through the center Z of the pupil21.

The dimensions A to D of the mirror M6and of the passage opening17correspond to the dimensions A′, B′, C′ and D′ of the pupil21and of the pupil obscuration region18. Here, A′ is a radius of the pupil21. B′ is a y-offset of the pupil obscuration region18with respect to the center Z of the pupil21. An extent of the pupil obscuration region18is2C′ in the y-direction and2D′ in the x-direction. The extent2C′ can also be understood as a radial extent of the pupil obscuration region18along a gravity center axis y, on which the center Z of the pupil21and the gravity center SP of the pupil obscuration region18lie. The dimension2D′ can be understood as a tangential pupil obscuration region extent in a tangential dimension x perpendicular to the gravity center axis y.

A complete, i.e. usable in an unobscured fashion, circular pupil region around the center Z of the pupil21has a radius B′-C′, which is at least 10% of the pupil radius A′.

The projection optical unit7according toFIG. 2can have a further obscuration stop or any other component which brings about an additional pupil obscuration, which leads to an overall pupil obscuration being created, which, overall, is arranged in a centrally symmetric fashion with respect to the center Z of the pupil21. An example for an additional pupil obscuration is supplied inFIGS. 23 and 26, which will still be described below.

In the following text, a further embodiment of the projection optical unit22is explained on the basis ofFIGS. 4 and 5, which projection optical unit can be used in the projection exposure apparatus1according toFIG. 1in place of the projection optical unit7. Components and functions which were already explained above in conjunction withFIGS. 1 to 3, 3aand in conjunction withFIG. 10, are, if need be, denoted by the same reference signs and will not be discussed again in detail.

The optical design data of the projection optical unit22can be gathered from the following tables, which, in their design, correspond to the tables in respect of the projection optical unit7according toFIG. 2. For specifying the free-form surfaces, use is made of the above Equation (2) (RDY=1/cy; RDX=1/cx.

The projection optical unit22has an image-side numerical aperture of 0.45. The object field4has an x-extent of two-times 13 mm and a y-extent of 2 mm. The projection optical unit22is optimized for an operating wavelength of the illumination light3of 13.5 nm.

In the projection optical unit22, the mirror M4is distanced far from the mirror M6. The distance between these two mirrors is approximately half the design length of the projection optical unit22, i.e. half the distance between the object plane5and the image plane9. In the projection optical unit22, mirrors M3and M6on the one hand and mirrors M1and M6on the other hand are arranged back-to-back.

An intermediate image ZB lies in the imaging beam path between the mirrors M4and M5, just after the passage through the passage opening17in the mirror M6. A distance between the intermediate image ZB and the passage opening17is approximately 10% of a distance between the mirrors M4and M5.

FIG. 5clarifies the relationships during the reflection of the imaging light3at the mirror M6and when the imaging light3passes through the passage opening17in the mirror M6. Since the intermediate image ZB is at a distance from the passage opening17in the projection optical unit22, the sub-apertures20are significantly larger when passing through the imaging light passage opening17than in the projection optical unit7according toFIGS. 2 and 3. Due to the shape of the sub-apertures20when passing through the passage opening17, the passage opening17in the mirror M6can have a trapezoidal design, wherein an x-extent of the passage opening17adjacent to the center of the mirror M6is smaller than at a distance therefrom.

The following applies to the size ratios of the dimensions A to D in the projection optical unit22: B/A equals 0.28. C/A equals 0.09. D/A equals 0.20.

In the following text, a further embodiment of a projection optical unit23is explained on the basis ofFIGS. 6 and 7, which projection optical unit can be used in the projection exposure apparatus1according toFIG. 1in place of the projection optical unit7. Components and functions which were already explained above in conjunction withFIGS. 1 to 3, 3a,4and5and in conjunction withFIG. 10, are, if need be, denoted by the same reference signs and will not be discussed again in detail.

The optical design data of the projection optical unit23can be gathered from the following tables, which, in their design, correspond to the tables in respect of the projection optical unit22according toFIG. 4. For specifying the free-form surfaces, use is made of the above Equation (2) (RDY=1/cy; RDX=1/cx.

The projection optical unit23has an image-side numerical aperture of 0.45. The object field4has an x-extent of two-times 13 mm and a y-extent of 2 mm. The projection optical unit23is optimized for an operating wavelength of the illumination light3of 13.5 nm.

In terms of its design, the projection optical unit23is similar to the projection optical unit22according toFIGS. 4 and 5. In contrast thereto, an intermediate image ZB is arranged between the mirrors M4and M5in the imaging beam path, level with the passage opening17in mirror M6. In contrast to the projection optical unit22, the mirror M1is closer to the image plane9than the mirror M6in the projection optical unit23. The mirrors M3and M6are once again arranged back-to-back. In turn in contrast to the projection optical unit22, the mirror M2is closer to the object plane5than the mirror M4in the projection optical unit23. Furthermore, the intermediate image ZB lies geometrically closer to the mirror M6in the projection optical unit23, and so the passage opening17in the mirror M6can have a correspondingly small design.

FIG. 7once again clarifies the relationships during the reflection at the mirror M6or when passing through this mirror M6.

In respect of the dimensional ratios of the dimensions A to D, the following applies in the projection optical unit23: B/A equals 0.34. C/D equals 0.045. D/A equals 0.15.

The dimensional ratios of the dimensions A to D specified above for the projection optical units7,22and23correspondingly apply also to the dimensional ratios A′ to D′ of the pupil obscuration region18.

FIGS. 8 to 19 and 23 to 26will be used below to explain the illumination and imaging relationships in the projection exposure apparatus1. In this case, it is unimportant which one of the projection optical units7,22or23is used. In the following text, the illumination and imaging relationships are explained in an exemplary fashion on the basis of the projection optical unit7.

FIG. 8shows an illumination setting, i.e. an illumination intensity distribution, in an illumination pupil24of the illumination optical unit6of the projection exposure apparatus1. The illumination setting is an x-dipole with two secondary illumination light sources25,26. The case is considered where a line structure with lines27(seeFIG. 9) is illuminated as reticle10, which lines extend parallel to the y-direction and have a distance61from one another. The y-line structure according toFIG. 9is, as a result of the x-dipole illumination setting according toFIG. 8, illuminated from two illumination directions according to the secondary illumination light sources25,26.

FIG. 10clarifies an intensity distribution of imaging light in the used pupil21of the projection optical unit7as a result of the illumination by purely the illumination light source25. The illustrated pupil obscuration region18is not a physical obscuration stop, which can for example lie on one of the three mirrors M1, M2or M3for defining the pupil obscuration region18. The pupil obscuration region18specified inFIG. 10and the subsequent figures constitutes a projection of the actual obscurations in the entry pupil21of the respective projection optical unit7,22and23.

The actual physical obscuration stop can be deformed with respect to the entry pupil21. Such a physical obscuration stop can, in the projection optical unit7according toFIG. 2, for example be applied to the mirror M2since this mirror lies in the region of a pupil plane of the projection optical unit7. Corresponding statements apply to the projection optical units22and23.

InFIGS. 8 to 19 and 23 to 26, the pupil obscuration region18is illustrated in a shaded manner in the form of a circular obscuration. The actual shape of the obscuration projected into the entry pupil21can deviate from a circular obscuration and can be elliptical, rectangular, rectangular with rounded-off corners, trapezoidal or trapezoidal with rounded-off corners.

A zero order of diffraction28of the illumination light3, in its position corresponding to the illumination light source25, passes through the pupil21as imaging light. As a result of the diffraction on the lines27, a first order of diffraction29passes through the pupil21at a point which coincidentally corresponds to the point of the second illumination light source26. Since the two orders of diffraction28,29do not overlap with the pupil obscuration region18, the pupil obscuration as a result of the passage opening17in the mirror M6plays no role for the imaging light3which passes through the projection optical unit7in the case of illumination according toFIG. 8. Hence, in the illumination setting according toFIG. 8, the imaging light passes through the projection optical unit7without there being losses in the reflection at the mirror M6as a result of the passage opening17.

In the following text, the illumination and imaging relationships in the projection exposure apparatus1when illuminating a further reticle10with a less tightly packed y-line structure are explained on the basis ofFIGS. 11 to 13, which correspond toFIGS. 8 to 10. Neighboring lines30of the reticle10according toFIG. 12have a distance62from one another, which is approximately twice the size of the line distance61of the reticle10according toFIG. 9. As a result of the larger line distance, there is a smaller diffraction angle during the diffraction of the illumination light3from the direction of the illumination light source25, the extent of which through the projection optical unit7being illustrated schematically inFIG. 13. As a result of the smaller diffraction angle, the first order of diffraction21now lies approximately centrally in the pupil21. A second order of diffraction31likewise lies within the used pupil21during the illumination of the y-line structure with the lines30according toFIG. 12and it lies at a point which coincidentally corresponds to the point of the illumination light source26in the illumination pupil24.

Since the diameter of the first order of diffraction29in the imaging light beam path according toFIG. 13is greater than a y-distance of the pupil obscuration region18from the center Z of the pupil21, the first order of diffraction29and the pupil obscuration region18overlap. However, since the overlap region is small compared to the overall extent of the first order of diffraction29, this still results in good imaging of the lines30. The decentral position of the pupil obscuration region18in the entry pupil21prevents the pupil obscuration region18from overlapping with the first order of diffraction29, which would undesirably result in this first order of diffraction29not contributing to imaging the object with the lines30, as a result of which, in turn, imaging of such an object structure would be badly afflicted.

FIGS. 14 to 19show imaging relationships using figures that correspond toFIGS. 8 to 13.

FIG. 14shows an illumination setting in the form of a y-dipole with secondary illumination light sources32,33, which are used to illuminate a reticle10with an x-line structure with lines34(seeFIG. 15).

FIG. 16in turn shows the intensity of the imaging light in the pupil21of the projection optical unit7as a result of the illumination by purely the illumination light source33. This once again results in a zero order of diffraction35and a first order of diffraction36in the pupil21. The zero order of diffraction35lies at the point corresponding to the illumination light source33and the first order of diffraction36coincidentally lies at the point in the pupil21which corresponds to the point of the other illumination light source32. The first order of diffraction36and the pupil obscuration region18overlap one another. Once again, this overlap is small, and so in practice it does not adversely affect imaging the lines34.

FIGS. 17 to 19in turn show the relationships in the illumination of a reticle10with lines37, which are spaced apart at a greater distance and extend in the x-direction, using the y-dipole illumination setting according toFIG. 14. Then, the zero order of diffraction35, the first order of diffraction36, which lies approximately centrally in the pupil21, and a second order of diffraction38result in the pupil21of the projection optical unit7. Both the first order of diffraction36and the second order of diffraction38overlap with the pupil obscuration region18. Once again, this overlap is small in each case, and so in practice it does not adversely affect the imaging of the lines37.

The overlap geometries of the pupil obscuration region18with orders of diffraction36or38when imaging an x-line structure with a y-dipole can be avoided by virtue of the fact that the reticle10according toFIGS. 15 and 18with lines34and37is rotated by 90° about the local z-axis prior to the illumination, such that this results in a y-line structure in accordance withFIGS. 9 and 12. An x-dipole illumination setting according toFIG. 8is then selected in place of the y-dipole illumination setting according toFIG. 14. In particular, in the illumination geometry and line orientation geometry according toFIG. 8 to 13, the case can be avoided that one of the orders of diffraction coincidentally lies more or less precisely at the point of the pupil obscuration region18.

FIG. 20schematically shows part of the illumination beam path of the projection optical units7,22and23after the reflection at the mirror M4. The chief ray16of the central object field point is illustrated from the passage through the passage opening17up until incidence on the substrate12.

An angle of incidence of the chief ray16on the mirror M6is denoted by a′ inFIG. 20.

When passing through the passage opening17, the chief ray16extends to the mirror M5along a passage chief ray section16D. Between the last mirror M6and the image field8, i.e. the substrate12, the chief ray16extends along an image field chief ray section16B. The two chief ray sections16D and16B extend in a common plane, namely in the yz-meridional plane of the projection optical unit7,22,23and include a chief ray angle between one another, which is denoted by α inFIG. 20.

The following applies: α′>α.

FIGS. 21 to 26in turn show imaging relationships with figures which correspond toFIGS. 8 to 13, wherein, inFIGS. 21 to 26, use is also made, like inFIGS. 8 to 13, of the reticle10with the more tightly extending y-line structure (FIG. 22) and the less tightly extending y-line structure (FIG. 25).

The x-dipole setting with the secondary illumination light sources25,26and the orders of diffraction28,29and31correspond to that which was already explained above with reference toFIGS. 8 to 13.

During imaging which uses the illumination pupil24according toFIGS. 21 and 24, use is made of an additional obscuration element such that an overall pupil obscuration region39with portions39aand39bis generated, which complement one another to form an overall pupil obscuration region39arranged in a centrally symmetric fashion with respect to the center Z of the pupil21. The additional obscuration component, which generates the obscuration portion39b, can be created by an appropriate stop in a pupil of the imaging optical unit7,22or23.

The overall pupil obscuration region39according toFIGS. 23 and 26has an extent of E in the x-direction and an extent of F in the y-direction. This results in an aspect ratio E/F which is smaller than 1 and, in the illustrated embodiment, is approximately 0.33.

In place of the above-described pupil obscuration portions39a,39b, use can also be made of an elliptical, rectangular or trapezoidal pupil obscuration region, which can be arranged centered with respect to the center Z of the pupil21, or else decentered with respect thereto. To the extent that such a pupil obscuration region has an edge with a number of corners, it can have rounded-off corners.

In order to produce a microstructured or nanostructured component, the projection exposure apparatus1is used as follows: first of all, the reflection mask10or the reticle and the substrate or the wafer11are provided. Subsequently, a structure on the reticle10is projected onto a light-sensitive layer of the wafer11with the aid of the projection exposure apparatus1. By developing the light-sensitive layer, a microstructure or nanostructure is then produced on the wafer11and hence the microstructured component is produced.

Prior to the projection exposure, structures on the reticle10can be checked in terms of the structure in order, optionally, to bring about an illumination and imaging geometry in which orders of diffraction of the illumination light do not overlap, or do not overlap too strongly, with the pupil obscuration region18in order to avoid an adverse effect on the imaging power of the projection exposure apparatus1.