WO2018010960A1

WO2018010960A1 - Projection optical unit for euv projection lithography

Info

Publication number: WO2018010960A1
Application number: PCT/EP2017/065936
Authority: WO
Inventors: Markus Schwab; Hartmut Enkisch; Thomas Schicketanz
Original assignee: Carl Zeiss SMT GmbH
Current assignee: Carl Zeiss SMT GmbH
Priority date: 2016-07-11
Filing date: 2017-06-28
Publication date: 2018-01-18
Anticipated expiration: 2019-01-11
Also published as: US20190121107A1; TWI746594B; TW201812466A; CN109478020A; US10545323B2; JP2019527380A; DE102016212578A1; CN109478020B; JP7071327B2

Abstract

A projection optical unit (7) for EUV projection lithography has a plurality of mirrors (M1 to M10) for imaging an object field (4) into an image field (8) with illumination light (3). At least one of the mirrors (M1, M9, M10) is embodied as an NI mirror and at least one of the mirrors (M2 to M8) is embodied as a GI mirror. A mirror dimension Dx of the at least one NI mirror in a plane of extent (xz) perpendicular to a plane of incidence (yz) satisfies the following relationship: 4 LLWx/IWPV_max < Dx. A mirror dimension Dy of the at least one GI mirror in the plane of incidence (yz) satisfies the following relationship: 4 LLWy/(IWPV_maxcos(a)) < Dy. Here, LLWx and LLWy denote the étendue of the projection optical unit (7) in the plane of extent (xz) and in the plane of incidence (yz) and IWPV_max denotes the maximum difference between a maximum angle of incidence and a minimum angle of incidence of the illumination light (3) on the reflection surface of the NI mirror (M1, M9, M10) and on the reflection surface of the GI mirror (M2 to M8). a denotes the angle of incidence of a chief ray (16) of the central field point on the reflection surface of the GI mirror (M2 to M8). This results in a projection optical unit which is optimizable, in particular for very short EUV illumination light wavelengths.

Description

Projection optical unit for EUV projection lithography

The content of the German Patent Application DE 10 2016 212 578.8 is incorporated by reference herein.

The invention relates to a projection optical unit for EUV projection lithography. Further, the invention relates to an optical system comprising such a projection optical unit, a projection exposure apparatus comprising such an optical system, a method for producing a microstructured or nanostmctured component using such a projection exposure apparatus and a microstructured or nanostmctured component produced by this method.

Projection optical units of the type set forth at the outset are known from DE 10 2015 209 827 Al, from DE 10 2012 212 753 Al, from US

2010/0149509 Al and from US 4,964,706.

It is an object of the present invention to develop a projection optical unit of the type set forth at the outset in such a way that this results in a projection optical unit which is optimizable, in particular for very short EUV il- lumination light wavelengths.

According to the invention, this object is achieved by a projection optical unit having the features specified in claim 1. What was recognized according to the invention is that, on account of basic theoretical optical considerations, it is not possible to realize an optical design of a projection optical unit which permits reflection coatings for optimization even in the case of very short EUV illumination light wavelengths for as long as certain dimensional relationships are not satisfied for at least individual mirrors of the projection optical unit. In particular, a relationship was identified between a mirror minimum dimension and an angle of incidence bandwidth of the illumination light on the mirror.

The dimensional relationship specified for NI mirrors provides a lower bound for an NI mirror dimension perpendicular to the plane of incidence of the illumination light reflected by this mirror. Only if use is made of an NI mirror satisfying this relationship is it possible to find designs which permit a reflection coating of this mirror with a reflection efficiency required for the operation at very short EUV wavelengths. For the at least one NI mirror, a reflectivity which is greater than 60% and, in particular, at least 65% emerges for an EUV used wavelength of 6.7 nm. The specified dimensional relationship may apply to at least one of the NI mirrors of the projection optical unit. The specified dimensional relationship may also apply to a plurality of NI mirrors and, in particular, to all NI mirrors of the projection optical unit.

The maximum difference between a maximum angle of incidence and a minimum angle of incidence of the illumination light on a mirror is determined as follows: For each location on the mirror, the maximum angle of incidence and the minimum angle of incidence of the illumination light is determined at this mirror location. This is carried out for all locations on the mirror. Now, for each location on the mirror, the difference between the maximum angle of incidence and the minimum angle of incidence of the illumination light at this mirror location is formed, i.e. the difference be- tween the respective local maximum angle of incidence and the respective local minimum angle of incidence. The maximum difference between the respective local maximum angle of incidence and the minimum angle of incidence, which is found in this manner, is the maximum angle of inci- dence difference IWPVmax. Thus, this value is the maximum of all angle of incidence differences which occur locally on the respective mirror.

A mirror dimension according to Claim 2 satisfies the dimensional rela- tionship. The mirror dimension may be at least 335 mm. The mirror dimension may be greater than 350 mm and may also be greater than 400 mm.

Corresponding considerations, which were made above for the dimensional relationship for the at least one NI mirror, also apply to a projection optical unit comprising at least one GI mirror according to Claim 3.

What was surprisingly recognized here is that the GI mirror dimension, which is important when entering a dimensional minimum size, is not the same mirror dimension perpendicular to the plane of incidence, like in the dimensional relationship discussed above for the NI mirror, but the mirror dimension in the plane of incidence. This discovery emerges from closely considering the light guiding conditions, taking into account the etendue and also the field dimensions of the projection optical unit. For the at least one GI mirror, a reflectivity which is greater than 75%, greater than 80% and, in particular, at least 81 % emerges for an EUV used wavelength of 6.7 nm. The GI mirror dimensional relationship may apply to at least one of the GI mirrors, may apply to a plurality of GI mirrors and, in particular, may apply to all GI mirrors of the projection optical unit. A mirror dimension according to Claim 4 satisfies the GI mirror dimensional relationship. The mirror dimension of the GI mirror in the plane of incidence may be at least 150 mm, may be at least 200 mm and may be at least 250 mm and also at least 270 mm. The projection optical unit may be constructed as a combination of NI mirrors and GI mirrors.

A projection optical unit according to Claim 5 unifies the advantages which were discussed above in conjunction with satisfying the NI mirror dimensional relationship and the GI mirror dimensional relationship.

Maximum angle of incidence bandwidths, i.e. the maximum differences between a maximum angle of incidence and a minimum angle of incidence of the illumination light, with lower bounds according to Claims 6 and 8 and with upper bounds according to Claims 7 and 9, were found to be very suitable for realizing a projection optical unit, the mirrors of which may be coated very efficiently, even for very short EUV illumination light wavelengths.

An object-side telecentricity according to Claim 10 leads to an advantageously small angle of incidence bandwidth of the illumination light when impinging the object field, i.e. during the operation of a projection exposure apparatus, the projection optical unit being a constituent thereof, at an object with, in particular, reflecting embodiment, i.e., for example, at a reticle.

An image field aspect ratio according to Claim 1 1 was found to be particularly suitable for realizing a projection optical unit, in which the mirrors may be coated in a reflection-optimized manner, even for very short EUV illumination light wavelengths. The x/y aspect ratio may be greater than 15, may be greater than 20, may be 21.67, may be greater than 30, may be greater than 50, may be greater than 80, may be 86.67 and may also be greater than 100. A reduced field dimension in an object displacement di- rection or scanning direction y may lead to a reduction in an angle of incidence bandwidth, in particular on a GI mirror of the projection optical unit.

The advantages of an optical system according to Claim 12, a projection exposure apparatus according to Claim 13, a production method according to Claim 14 and a microstructured or nanostructured component according to Claim 15 correspond to those which have already been explained above with reference to the projection optical unit according to the invention. The EUV light source of the projection exposure apparatus can be embodied in such a way that a used wavelength emerges which is at most 13.5 nm, which is less than 13.5 nm, which is less than 10 nm, which is less than 8 nm, which is less than 7 nm and which is e.g. 6.7 nm or 6.9 nm. A used wavelength of less than 6.7 nm and, in particular, in the region of 6 nm is also possible.

In particular, a semiconductor component, for example a memory chip, may be produced using the projection exposure apparatus.

Exemplary embodiments of the invention are explained in more detail be- low on the basis of the drawing. Therein:

Figure 1 schematically shows a projection exposure apparatus for EUV microlithography;

Figure 2 shows, in a meridional section, an embodiment of an imaging optical unit which can be used as a projection lens in the projection exposure apparatus according to Figure 1 , wherein an imaging beam path for chief rays and for an upper coma ray and a lower co- ma ray of a plurality of selected field points is depicted;

Figure 3 shows a perspective view of the imaging optical unit according to Figure 2;

Figures 4A to 4D show, in a plan view, edge contours of reflection surfaces respectively impinged by imaging light on the mirrors of the imaging optical unit according to Figure 2, an edge contour of an imaging light overall beam in a stop plane, and an edge contour of an object field of the imaging optical unit, from which the imaging light rays emanate, wherein, at the same time, an angle of incidence bandwidth of the imaging light on these components or in the arrangement planes thereof is plotted in the edge contours and scaled by way of a value scale depicted in each case next to the edge contour on the right, shown for an image field size of 26 mm x 1.2 mm;

Figures 5A to 5D show, in illustrations similar to Figure 4, the edge contours and the angle of incidence bandwidths present there, shown for an embodiment of the imaging optical unit with an image field size of 26 mm x 0.3 mm; and

Figure 6 schematically shows a plan view of a reflection surface of a GI mirror (mirror for grazing incidence) of a further embodiment of an imaging optical unit, which is usable as a projection lens in the projection exposure apparatus according to Figure 1 , for elucidating a definition of a mirror dimension Dy. A microlithographic projection exposure apparatus 1 has a light source 2 for illumination light or imaging light 3. The light source 2 is an EUV light source, which produces light in a wavelength range of e.g. between 5 nm and 30 nm, in particular between 5 nm and 15 nm. In particular, the light source 2 may be a light source with a wavelength of 13.5 nm or a light source with a wavelength of 6.7 nm or 6.9 nm. Other EUV wavelengths are also possible. In general, even arbitrary wavelengths are possible for the illumination light 3 guided in the projection exposure apparatus 1 , for example visible wavelengths or else other wavelengths which may find use in microlithography (for example, DUV, deep ultraviolet) and for which suit- able 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 light 3 is depicted very schematically in Figure 1.

An illumination optical unit 6 serves to guide the illumination light 3 from the light source 2 to an object field 4 in an object plane 5. Using a projection optical unit or imaging optical unit 7, the object field 4 is imaged into an image field 8 in an image plane 9 with a predetermined reduction scale. The projection optical unit 7 has exactly one object field 4. The projection optical unit 7 has exactly one image field 8.

In order to facilitate the description of the projection exposure apparatus 1 and the various embodiments of the projection optical unit 7, a Cartesian xyz-coordinate system is indicated in the drawing, from which system the respective positional relationship of the components illustrated in the fig- ures is evident. In Figure 1 , the x-direction runs perpendicular to the plane of the drawing into the latter. The y-direction runs toward the left, and the z-direction runs upward. The object field 4 and the image field 8 are rectangular. Alternatively, it is also possible for the object field 4 and the image field 8 to have a bent or curved embodiment, that is to say, in particular, a partial ring shape. The object field 4 and the image field 8 have an x/y-aspect ratio of greater than 1. Therefore, the object field 4 has a longer object field dimension in the x- direction and a shorter object field dimension in the y-direction. These object field dimensions extend along the field coordinates x and y.

The projection optical unit 7 is anamorphic, i.e. it has a different reduction scale in the x-direction (reduction scale in the xz-plane) than in the y- direction (reduction scale in the yz-plane). In the x-direction, the projection optical unit 7 has a reduction scale βχ of 4.8. In the y-direction, the projection optical unit 7 has a reduction scale y of -9.6.

Other absolute reduction scales for the reduction in the x-direction and for the reduction in the y-direction are also possible, e.g. 4x, 5x, 6x, 8x, or else reduction scales which are greater than 8x. An embodiment of the projection optical unit 7 with the same reduction scales as these in, firstly, the xz- plane and, secondly, in the yz-plane is also possible. What is imaged by the projection optical unit 7 is a section of a reflection mask 10, also referred to as reticle, coinciding with the object field 4. The reticle 10 is carried by a reticle holder 10a. The reticle holder 10a is displaced by a reticle displacement drive 10b. The imaging by way of the projection optical unit 7 is implemented on the surface of a substrate 1 1 in the form of a wafer, which is carried by a substrate holder 12. The substrate holder 12 is displaced by a wafer or substrate displacement drive 12a.

Figure 1 schematically illustrates, between the reticle 10 and the projection optical unit 7, a ray beam 13 of the illumination light 3 that enters into said projection optical unit and, between the projection optical unit 7 and the substrate 1 1, a ray beam 14 of the illumination light 3 that emerges from the projection optical unit 7. An image field-side numerical aperture (NA) of the projection optical unit 7 is not reproduced to scale in Figure 1.

The projection exposure apparatus 1 is of the scanner type. Both the reticle 10 and the substrate 1 1 are scanned in the y-direction during the operation of the projection exposure apparatus 1. A stepper type of the projection exposure apparatus 1, in which a stepwise displacement of the reticle 10 and of the substrate 1 1 in the y-direction is effected between individual exposures of the substrate 1 1, is also possible. These displacements are effected synchronously to one another by an appropriate actuation of the displacement drives 10b and 12a.

Figures 2 and 3 show the optical design of a first embodiment of the projection optical unit 7. Figure 2 depicts the beam path of in each case three individual rays 15 emanating from a plurality of object field points which are spaced apart from one another in the y-direction in Figure 2. What is depicted are chief rays 16, i.e. individual rays 15 which pass through the centre of a pupil in a pupil plane of the projection optical unit 7, and in each case an upper coma ray and lower coma ray of these two object field points. Proceeding from the object field 4, the chief ray 16 of a central ob- ject field point includes an angle CRAO of 5.0° with a normal of the object plane 5.

The projection optical unit 7 has an image-side numerical aperture NA of 0.45. This numerical aperture has exactly the same size in the xz-plane of incidence on the image field 8 as in the yz-plane of incidence on the image field 8 (NAx = NAy = NA).

The projection optical unit 7 has a total of ten mirrors, which, proceeding from the object field 4, are numbered Ml to Ml 0 in the sequence of the beam path of the individual rays 15. The projection optical unit 7 is a purely catoptric optical unit. The imaging optical unit 7 can also have a different number of mirrors, for example four mirrors, six mirrors or eight mirrors. An odd number of mirrors is also possible in the projection optical unit 7.

Figures 2 and 3 depict the calculated reflection surfaces of the mirrors Ml to M10, the edge contours of which are also shown in a plan view in Figures 4 and 5. Use is made of a portion of the reflection surfaces which, in fact, are calculated over a larger region. Only this region of the reflection surfaces used in fact for reflecting the imaging light 3 is in fact present in the real mirrors Ml to M10 and, in particular, depicted in Figure 3. These used reflection surfaces are carried in a known manner by mirror bodies (not shown).

In the projection optical unit 7, the mirrors Ml, M9 and Ml 0 are embodied as mirrors for normal incidence, i.e. as mirrors on which the imaging light 3 is incident with an angle of incidence which is less than 45°. Thus, the projection optical unit 7 has a total of three mirrors Ml, M9 and Ml 0 for normal incidence. Below, these mirrors are also referred to as NI mirrors. The maximum angle of incidence, which is incident on the respective NI mirror, may be less than 40°, may be less than 35°, may be less than 30°, may be less than 25°, may be less than 20°, may be less than 15° and may also be less than 10°.

The mirrors M2 to M8 are mirrors for grazing incidence of the illumination light 3, that is to say mirrors onto which the illumination light 3 impinges with angles of incidence that are greater than 45°. A typical angle of inci- dence of the individual rays 15 of the imaging light 3 on the mirrors M2 to M8 for grazing incidence lies in the region of 80°. Overall, the projection optical unit 7 according to Figure 2 has exactly seven mirrors M2 to M8 for grazing incidence. Below, these mirrors are also referred to as GI mirrors. The minimum angle of incidence, which is incident on the respective GI mirror, may be greater than 50°, may be greater than 55°, may be greater than 60°, may be greater than 65°, may be greater than 70°, may be greater than 75° and may also be greater than 80°.

A different number distribution in relation to NI mirrors and GI mirrors is also possible in embodiments of the projection optical unit not depicted here. Configurations in which the projection optical unit only has NI mirrors and also those in which the projection optical unit only has GI mirrors are possible. In between these limit cases, all conceivable number distributions of NI and GI mirrors are possible for a given overall mirror number. Thus, in the case of a projection optical unit with N mirrors, the NI mirrors may number between 0 and N and, correspondingly, the GI mirrors may number between N and 0. The mirrors M2 to M8 of the projection optical unit 7 reflect the imaging light 3 in such a way that the angles of reflection of the individual rays 15 add up at the respective mirrors M2 to M8. The mirrors Ml to M10 carry a coating optimizing the reflectivity of the mirrors Ml to Ml 0 for the imaging light 3. For the GI mirrors in particular, this may be a lanthanum coating, a boron coating or a boron coating with an uppermost layer of lanthanum. Other coating materials may also be used, in particular lanthanum nitride and/or B₄C. In the mirrors M2 to M8 for grazing incidence, use can be made of a coating with e.g. one ply of boron or lanthanum. The highly reflecting layers, in particular of the mirrors Ml, M9 and Ml 0 for normal incidence, can be configured as multi-ply layers, wherein successive layers can be manufactured from different materials. Alternating material layers can also be used. A typical multi-ply layer can have fifty bilayers, respectively made of a layer of boron and a layer of lanthanum. Layers containing lanthanum nitride and/or boron, in particular B₄C, may also be used.

Information in respect of the reflection at a GI mirror (mirror for grazing incidence) can be found in WO 2012/126867 A. Further information in respect of the reflectivity of NI mirrors (normal incidence mirrors) can be found in DE 101 55 71 1 A.

An overall reflectivity or system transmission of the projection optical unit 7, emerging as a product of the reflectivities of all mirrors Ml to Ml 0 of the projection optical unit 7, is approximately = 2.0%.

The mirror M10, that is to say the last mirror upstream of the image field 8 in the imaging beam path, has a passage opening 17 for the passage of the imaging light 3 which is reflected from the antepenultimate mirror M8 toward the penultimate mirror M9. The mirror M10 is used in a reflective manner around the passage opening 17. None of the other mirrors Ml to M9 have passage openings and said mirrors are used in a reflective manner in a continuous region without gaps.

The mirrors Ml to M10 are embodied as free-form surfaces which cannot be described by a rotationally symmetric function. Other embodiments of the projection optical unit 7, in which at least one of the mirrors Ml to M10 is embodied as a rotationally symmetric asphere, are also possible. It is also possible for all mirrors Ml to M10 to be embodied as such aspheres.

A free-form surface can be described by the following free-form surface equation (equation 1):

2 . 2

c_xx + C V

\ + ^\ - (\ + k_x)(c_xxf - (\ + k_y )(c_yy)

+ C₃x² + C₄xy + C₅y²

+ C₆x³ + ... + C₉y³

+ C₁₀x⁴ + ... + C₁₂x²y² + ... + C₁₄y⁴

+ C₁₅x⁵ + ... + C₂₀y⁵

+ C₂₁x⁶ + ... + C₂₄x³y³ + ... + C₂₇y⁶

(1)

The following applies to the parameters of this equation (1): Z is the sag of the free-form surface at the point x, y, where x² + y² = r². Here, r is the distance from the reference axis of the free-form equation (x = 0; y = 0). In the free-form surface equation (1), Ci, C₂, C₃... denote the coefficients of the free-form surface series expansion in powers of x and y.

In the case of a conical base area, c_x, c_y is a constant corresponding to the vertex curvature of a corresponding asphere. Thus, c_x = 1/ _X and c_y = 1/R_y applies. Here, k_x and k_y each correspond to a conical constant of a corresponding asphere. Thus, equation (1) describes a biconical free-form surface.

An alternative possible free-form surface can be generated from a rotation- ally symmetric reference surface. Such free-form surfaces for reflection surfaces of the mirrors of projection optical units of microlithographic projection exposure apparatuses are known from

US 2007 0 058 269 Al . Alternatively, free-form surfaces can also be described with the aid of two- dimensional spline surfaces. Examples for this are Bezier curves or nonuniform rational basis splines (NURBS). By way of example, two- dimensional spline surfaces can be described by a grid 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 interpolation between the grid points using for example polynomials or functions which have specific properties in respect of the continuity and the differentiability thereof. Examples for this are analytical functions. Figures 4 and 5 show edge contours of the reflection surfaces in each case impinged upon by the imaging light 3 on the mirrors Ml to M10 of the projection optical unit 7, i.e. the so-called footprints of the mirrors Ml to M10. These edge contours are in each case depicted in an x/y-diagram, which corresponds to the local x- and y-coordinates of the respective mirror Ml to M10. The illustrations are true to scale in millimetres. Moreover, the form of the passage opening 17 is depicted in the illustration relating to the mirror M10.

Moreover, Figures 4 and 5 also reproduce the edge contour of an aperture stop AS and the edge contour of the respectively used image field 8. In the embodiment according to Figure 4, the image field has an x/y-extent of 26 mm/1.2 mm (larger image field). In the embodiment according to Figure 5, the image field 8 has an x/y-extent of 26 mm/0.3 mm (smaller image field).

With reference to the scale depicted next to and to the right of the edge contours in each case, Figures 4 (4A to 4D) and 5 (5A to 5D) moreover still depict an angle of incidence bandwidth IWPV. Thus, what emerges from Figures 4 and 5 for the large image field and for the small image field is what difference IWPV between a maximum angle of incidence and a minimum angle of incidence of the illumination light 3, which impinges upon this location, is present at which location on the mirrors Ml to M10, when passing through the aperture stop AS and on the object field 8. A maximum difference IWPVmax can be determined at exactly one point on the mirror surface considered in each case from the differences IWPV on the reflection surface of one of the mirrors Ml to M10 in each case, on the aperture stop AS and on the object field 8. In the case of the projection optical unit 7, IWPVmax = 4° applies to the extent that the NI mirrors are con- sidered and IWPV_max = 1.8° applies to the extent that the GI mirrors are considered. An angle of incidence bandwidth of the illumination light 3 onto the image field 8 is practically constant over the entire image field 8, both in the embodiment according to Figure 4 and in the embodiment according to Figure 5, and emerges from the image-side numerical aperture.

Below, details are explained with reference to using the projection optical unit 7 with the larger image field 8. The use of the smaller image field 8 then emerges by a correspondingly reduced illumination of the object field 4.

The two following tables summarize the parameters "maximum angle of incidence", "extent of the reflection surface in the x-direction", "extent of the reflection surface in the y-direction" and "maximum mirror diameter" for the mirrors Ml to M10 of the projection optical unit 7 with the larger image field 8.

Ml M2 M3 M4 M5

Maximum

11.6 81.2 78.0 82.9 78.7 angle of incidence [°]

Extent of the reflection surface Dx in the 434.3 410.6 411.6 443.6 528.3 x-direction [mm]

Extent of the reflection surface Dy in the 169.7 360.7 302.5 307.4 616.6 y-direction [mm]

Maximum

434.3 425.7 412.0 445.3 623.2 mirror diameter [mm]

M6 M7 M8 M9 M10

Maximum

82.4 78.0 77.4 18.0 9.7 angle of incidence [°]

Extent of the reflection surface Dx in the 572.8 529.7 396.7 401.4 693.1 x-direction [mm]

Extent of the reflection surface Dy in the 274.7 285.5 298.2 174.5 663.2 y-direction [mm]

Maximum

573.6 530.5 397.9 401.4 693.2 mirror diameter [mm] The image-side numerical aperture -predetermining mirror M10 has the largest maximum mirror diameter, with a diameter of 693.2 mm. None of the other mirrors Ml to M9 has a maximum diameter which is greater than 625 mm. Six of the ten mirrors, namely the mirrors Ml to M4, M8 and M9, have a maximum mirror diameter which is less than 450 mm.

The largest angle of incidence on the NI mirrors is present on the mirror M9 and is 18.0°. The largest angle of incidence on the GI mirrors is present on the mirror M4 and is 82.9°.

The mirror dimensions Dx of the NI mirrors Ml, M9 and M10, i.e. the extent of the reflection surface thereof in the x-direction, satisfy the following relationship: 4 LLWx/IWPVmax < Dx (2)

Here:

LLWx: Etendue of the projection optical unit 7 in the xz-plane, i.e. the plane of extent corresponding to the mirror dimension Dx.

The following holds true: LLWx = NAx^■ Xbf/2. Thus, the etendue LLWx is the product of the numerical aperture NAx in the plane of extent xz and half of the extent of the image field Xbf in the x-direction. The following applies to the projection optical unit 7: LLWx = 5.85 mm.

IWPVmax is the maximum angle of incidence bandwidth on the respective NI mirror Ml , M9 and M10. This maximum angle of incidence bandwidth IWPVmax is present on the mirror M9 and is 4°, i.e. 0.698 rad, there. For the relationship (2) this yields:

335 mm < Dx.

Thus, the extents Dx for the NI mirrors must all be greater than 335 mm, which is satisfied for the projection optical unit 7.

For the GI mirrors M2 to M8, the following relationship applies in respect of the mirror dimension Dy in the plane of incidence yz:

4 LLWy/(IWPVmax cos(a)) < Dy (3)

Here:

LLWy: Etendue of the projection optical unit 7 in the plane of incidence yz. a is the folding angle of the respective GI mirror. This folding angle a corresponds to the angle of incidence of a chief ray of a central field point on the GI mirror.

The following applies to the projection optical unit 7 with the y-extent ybf of the image field 8 of 1.2 mm: LLWy = NAy^■ ybf/2 = 0.27 mm.

IWPVmax is the largest angle of incidence bandwidth on one of the GI mir- rors M2 to M8. This greatest angle of incidence bandwidth is present on the GI mirror M4 and is 1.8° = 0.0314 rad. In the case of a folding angle a of 75° and a maximum angle of incidence bandwidth IWPVmax of 0.0314 rad, the following emerges by insertion into relationship (3) above: 133 mm < Dy.

Thus, all GI mirrors must have a Dy extent which is greater than 133 mm, which is satisfied for the GI mirrors of the projection optical unit 7. If an angle of incidence bandwidth of IWPVmax 1.0° is assumed with otherwise unchanged parameters, this yields a lower limit for the Dy extent of 240 mm.

Satisfying the relationship also applies for the use of an image field with a small y-extent ybf = 0.3 mm. In this case, the GI mirrors have a maximum angle of incidence bandwidth of approximately 1° = 0.0174 rad (cf. GI mirror M4 in Figure 5). Etendue LLWy then is 0.0675 mm. With a = 83°, inserting these values into Equation (3) above leads to a lower bound for the extent Dy of 127 mm, which is likewise satisfied in the case of the GI mir- rors of the projection optical unit.

On the basis of Figure 6, there still is a clarifying definition for the extent Dy of a reflection surface 20 of a mirror M, which has a sickle-shaped, symmetrically curved embodiment. Dy denotes an extent of the reflection surface in a meridional plane of the mirror M, i.e. at x = 0. This extent of the reflection surface Dy is less than a y-extent of the reflection surface Dy,ges, as seen over the entire mirror M. Dy should be inserted into the above relationship (3), and not Dy,ges. Corresponding tables for the mirror dimensions emerge for the projection optical unit 7 with the small image field with x/y-dimensions of 26 mm/0.3 mm:

Ml M2 M3 M4 M5

Maximum

11.4 80.9 77.5 82.8 78.5 angle of incidence [°]

Minimum angle of

9.7 76.5 75.5 76.0 77.1 incidence

Extent of the reflection surface Dx in the 434.9 411.4 412.1 442.8 527.2 x-direction [mm]

Extent of the reflection surface Dy in the 162.3 350.6 289.5 265.1 603.6 y-direction [mm]

Maximum

435.0 422.4 412.2 443.0 611.0 mirror diameter [mm]

M6 M7 M8 M9 M10

Maximum

82.1 77.8 77.1 17.9 9.6 angle of incidence [°]

Minimum angle of

74.3 73.7 73.6 0.0 4.6 incidence

Extent of the reflection surface Dx in the 572.8 529.7 392.8 400.8 692.9 x-direction [mm]

Extent of the reflection surface Dy in the 258.2 252.1 280.3 174.8 662.5 y-direction [mm]

Maximum

573.1 529.7 392.9 401.0 693.5 mirror diameter [mm] In the projection optical unit with the small image field (26 mm x 0.3 mm), the mirror dimensions Dy tend to be slightly smaller than in the projection optical unit with the large image field.

The optical design data of the reflection surfaces of the mirrors Ml to M10 of the projection optical unit 7 can be gathered from the following tables. These optical design data in each case proceed from the image plane 9, i.e. describe the respective projection optical unit in the reverse propagation direction of the imaging light 3 between the image plane 9 and the object plane 5.

The first of these tables provides an overview of the design data of the projection optical unit 7 and summarizes the numerical aperture NA, the cal- culated design wavelength for the imaging light, the dimensions of the image field in the x-direction and y-direction, image field curvature and stop locations. This curvature is defined as the inverse radius of curvature of the field. The image field 8 has an x-extent of two times 13 mm and a y-extent of 1.2 mm. The projection optical unit 7 is optimized for an operating wavelength of the illumination light 3 of 6.7 nm.

The second of these tables provides vertex point radii (Radius x = R_x, Ra- dius_y = R_y) and refractive power values (Power_x, Power_y) for the optical surfaces of the optical components. Negative values of radius mean curves which are concave toward the incident illumination light 3 in the section of the respective surface with the considered plane (xz, yz), which is spanned by a surface normal at the vertex point with the respective direc- tion of curvature (x, y). The two radii adius_x, Radius_y may explicitly have different signs.

The vertex points at each optical surface are defined as points of incidence of a guide ray which travels from an object field centre to the image field 8 along a plane of symmetry x = 0, i.e. the plane of the drawing of Figure 2 (meridional plane).

The refractive powers Power_x (P_x), Power_y (P_y) at the vertex points are defined as:

T> _ 2 cos AOI

1 x - p ²

y R_y cos AOI Here, AOI denotes an angle of incidence of the guide ray with respect to the surface normal.

The third table specifies, for the mirrors Ml to Ml 0, in millimetres, the conic constants k_x and k_y, the vertex point radius R_x (= Radius x) and the free-form surface coefficients C_n. Coefficients C_n not tabulated in the table each have a value of 0.

The fourth table still specifies the magnitude along which the respective mirror, proceeding from a reference surface, was decentred (DCY) in the y- direction, and displaced (DCZ) and tilted (TLA, TLB, TLC) in the z- direction. This corresponds to a parallel shift and a tilting in the case of the freeform surface design method. Here, a displacement is carried out in the y-direction and in the z-direction in mm, and tilting is carried out about the x-axis, about the y-axis and about the z-axis. In this case, the angle of rotation is specified in degrees. Decentring is carried out first, followed by tilting. The reference surface during decentring is in each case the first surface of the specified optical design data. Decentring in the y-direction and in the z-direction in the object plane 5 is also specified for the object field 4. In addition to the surfaces assigned to the individual mirrors, the fourth table also tabulates the image plane as the first surface, the object plane as the last surface and a stop surface (with the stop label "AS").

The fifth table specifies the transmission data of the mirrors M 10 to Ml, namely the reflectivity thereof for the angle of incidence of an illumination light ray incident centrally on the respective mirror. The overall transmission is specified as a proportional factor remaining from an incident inten- sity after reflection at all mirrors in the projection optical unit.

The sixth table specifies an edge of the stop AS as a polygonal chain in local coordinates xyz. This stop is arranged in the imaging light beam path between the mirrors M9 and M10. As described above, the stop is decen- tred and tilted. The aperture stop edge serves to define an outer limit of a pupil of the projection optical unit 7. In addition to the aperture stop AS, the projection optical unit 7 may also have further aperture stops which are not described here. In addition to the aperture stop AS, the projection optical unit 7 may have at least one obscuration stop for defining an obscured region situated in the interior of the pupil-imaging optical unit 7. Two obscuration stops are provided in the projection optical unit 7. One of these obscuration stops lies on the mirror M9 and the other one lies on the mirror M10. Such an obscuration stop may, alternatively or additionally, lie in the arrangement plane of the aperture stop AS such that the aperture stop AS defines both an outer boundary of the pupil with a first edge contour and an inner boundary of the pupil with a second edge contour.

An edge of a stop surface of the stop AS (cf, also, the table) emerges from intersection points on the stop surface of all rays of the illumination light 3 which, on the image side, propagate at selected field points in the direction of the stop surface with a complete image-side telecentric aperture. To predetermine the edge of the stop surface of the stop AS, use is made of the intersection points on the stop surface of all rays of the illumination light 3 which, on the image side, propagate from the field centre point in the direction of the stop surface with a complete image-side telecentric aperture. In principle, there may also be a different selection of the employed image- side field points when defining the stop. The "field centre point" and "overall field" selections, specified above, are the possible extreme situations in this case.

When the stop is embodied as an aperture stop, the edge is an inner edge. In the case of an embodiment as an obscuration stop, the edge is an outer edge.

The stop AS can lie in a plane or else have a three-dimensional embodiment. The extent of the stop AS can be smaller in the scanning direction (y) than in the cross scanning direction (x). The non-illuminated obscuration region in the system pupil can be round, elliptical, square or rectangular. Moreover, this surface in the system pupil which cannot be illuminated can be decentred in the x-direction and/or in the y-direction in relation to a centre of the system pupil. Exemplary embodiment Fig. 2/3

NA 0.45

Wavelength 6.7 nm

beta_x 4.8 beta_y -9.6 Field_dimension_x 26.0 mm

Field_dimension_y 1.2 mm

Field_curvature 0.0 1/mm

Stop AS

Table 1

Surface Radius_x[mm]Power_x[1/mm] Radius_y[mm]Power_y[1/mm] Operating mode

M10 -961.6144466 0.0020668 -778.1556786 0.0025864 REFL

M9 -3549.5601410 0.0005634 479.6400618 -0.0041698 REFL

M8 -620.8460283 0.0008058 71 13.1614570 -0.001 1240 REFL

M7 -756.3513402 0.0006395 -5014.9275129 0.0016491 REFL

M6 -1417.7690170 0.0002887 19382.9071 106 -0.0005041 REFL

M5 -5516.9441039 0.0000734 -3790.9287721 0.0026038 REFL

M4 -80255.931716 0.0000051 -3861.9193175 0.0025093 REFL

M3 2865.0062520 -0.0001599- ^■13352.6807188 0.0006538 REFL

M2 3837.7582418 -0.0001010 4704.6489122 -0.0021935 REFL

M1 -3810.8666433 0.0005161 -1340.8257677 0.0015167 REFL

TablIte 2

Coefficient M10 M9 M8

KY 0.00000000 0.00000000 0.00000000

KX 0.00000000 0.00000000 0.00000000

RX -961.61444660 -3549.56014100 -620.84602830

C7 4.122838e-08 -2.43451201 e-07 1.21077589e-06

C9 1.73793078e-08 8.2540602e-07 2.39494778e-07

C10 -6.02821066e-12 4.80631486e-10 3.71758146e-10

C12 -4.01766351 e-1 1 -3.46236258e-10 -1.1 1440751 e-09

C14 -9.03062505e-12 1.17817415e-09 7.77249821 e-10

C16 3.08588436e-14 1.12613826e-12 1.63296635e-12

C18 8.65663335e-14 1.41409841 e-12 3.57926329e-12

C20 2.17991987e-14 2.00986224e-12 2.68200572e-12

C21 -4.27010051 e-17 -3.61671448e-16 1.03589706e-15

C23 -7.7882641 1 e-17 1.71334057e-15 -2.82633589e-15

C25 -9.1 1967025e-17 -1.2382258e-15 4.6651 1761 e-15

C27 -3.08060418e-17 3.99850272e-14 8.44666964e-15

C29 8.77951791 e-20 -2.12325806e-18 1.12276048e-19

C31 1.771691 17e-19 1.74659086e-18 2.08872559e-17

C33 1.34766609e-19 -6.31367756e-17 3.21976285e-17

C35 2.03490892e-20 8.78301001 e-17 1.83443084e-17

C36 -3.19683784e-23 2.327021 14e-21 2.52757672e-21

C38 -2.04574776e-22 -6.28599598e-21 9.68622943e-21

C40 -2.71616731 e-22 7.86319294e-20 1.47383978e-20

C42 -2.35280835e-22 -2.5703768e-19 8.20492642e-20

C44 -6.20833545e-23 1.91 106883e-19 2.10433981 e-20

C46 -1.56150681 e-26 9.08862194e-24 -5.04005572e-24

C48 3.48982966e-25 -3.65624507e-23 1.19741441 e-23

C50 3.37807257e-25 1.70169986e-22 1.98008305e-22

C52 1.74667593e-25 -3.60091364e-22 1.73954473e-22 Coefficient M10 M9 M8

C54 1.73003933e-26 -1.41369846e-21 -4.64572764e-24

C55 -9.14974685e-29 -2.1067628e-27 1.75351809e-27

C57 -1.38158184e-28 6.42122467e-26 5.63336949e-26

C59 -5.04027539e-28 4.30777188e-26 2.48606491 e-25

C61 -6.42124688e-28 1.08929859e-24 6.98967803e-26

C63 -3.96873549e-28 2.27314455e-24 1.76228481 e-25

C65 -9.69514873e-29 1.32345147e-24 -3.71019497e-26

C67 2.08984524e-31 0 0

C69 5.02882666e-31 0 0

C71 1.02647652e-30 0 0

C73 8.42552583e-31 0 0

C75 2.72643186e-31 0 0

C77 1.0041 1079e-32 0 0

C78 -1.29738103e-34 0 0

C80 -1.03141007e-33 0 0

C82 -2.90640927e-33 0 0

C84 -4.91820062e-33 0 0

C86 -4.59378867e-33 0 0

C88 -2.19237133e-33 0 0

C90 -3.82974968e-34 0 0

Table 3a

Coefficient M7 M6 M5

KY 0.00000000 0.00000000 0.00000000 KX 0.00000000 0.00000000 0.00000000 RX -756.35134020 -1417.76901700 -5516.94410400

C7 1.98220318e-07 -7.69616538e-08 6.05224345e-08

C9 6.00603819e-08 -3.90780933e-08 3.12018629e-08

C10 6.02350889e-12 -1.86964749e-1 1 -5.72002104e-1 1

C12 -1.27668681 e-10 4.77340782e-1 1 -4.47369532e-1 1

C14 -3.15080226e-10 9.12140764e-1 1 -5.83538751 e-1 1

C16 2.54093551 e-13 -8.88703214e-14 8.6392774e-14

C18 3.7613193e-13 -2.09563713e-13 6.30738356e-14

C20 4.79136055e-13 -1.68864122e-13 4.02478525e-14

C21 1.32777524e-16 -7.60979967e-17 9.14405018e-17

C23 -3.66667319e-16 2.06771 154e-17 -1.917001 1 e-17

C25 -9.07083339e-16 3.94667017e-16 -9.53595736e-18

C27 -1.49225078e-15 -2.21726735e-17 -4.66848683e-17

C29 3.31 159671 e-19 3.57673037e-19 1.27524055e-19

C31 1.15480822e-18 -4.54354127e-19 9.35232931 e-20

C33 2.05720734e-18 2.1247835e-20 -4.46137732e-20

C35 1.96729763e-18 1.07285249e-18 7.76796903e-20

C36 -1.01035392e-22 -2.86859982e-22 -5.35868247e-23

C38 -9.3366137e-22 3.82880588e-22 4.26827946e-22

C40 -1.73635173e-21 9.41295218e-22 -6.4176409e-23

C42 -4.12763021 e-21 -2.34899679e-21 -8.86880044e-23

C44 -9.7707508e-21 -5.61062446e-22 -1.73529402e-22

C46 5.23570404e-25 -8.69056492e-25 -4.39387485e-25

C48 -5.14805032e-25 -3.99864655e-24 -9.89421 191 e-25

C50 -3.62299272e-24 1.16686643e-24 -1.02164133e-25

C52 2.79625697e-23 -3.15598564e-24 4.1 1571954e-25 Coefficient M7 M6 M5

C54 8.63301477e-23 -1.09955675e-23 2.28682815e-25 C55 3.83909963e-28 3.48469972e-28 -4.15214892e-28 C57 3.87820551 e-28 4.784881 12e-27 7.65885169e-28 C59 6.17515464e-27 1.00474213e-27 -7.64939976e-29 C61 2.17592246e-26 1.76244813e-27 1.98832884e-28 C63 -1.27629678e-25 1.96371307e-26 -3.96054581 e-28 C65 -2.51085462e-25 2.4859618e-26 -1.20255428e-28

Coefficient M4 M3 M2

KY 0.00000000 0.00000000 0.02969487 KX 0.00000000 0.00000000 0.00000000 RX -80255.93172000 2865.00625200 3837.75824200

C7 6.84371 172e-08 6.46268825e-09 -1.05057834e-07 C9 3.05405131 e-08 1.1 141 1088e-07 -9.66596781 e-08 C10 8.68997619e-1 1 -5.22442392e-1 1 -1.51263499e-10 C12 2.1969297e-12 -1.46806264e-10 -4.59402492e-10 C14 1.40081074e-10 -1.22800751 e-10 9.8916743e-1 1 C16 1.5287661 1 e-13 1.84203798e-13 -4.54004845e-14 C18 -7.69717861 e-14 4.86612535e-13 1.58845105e-12 C20 4.00159137e-13 1.9467882e-13 1.28084536e-13 C21 1.46361577e-16 1.07865954e-16 4.38481837e-17 C23 2.69089086e-16 -5.33034271 e-16 3.00718483e-15 C25 -6.04995808e-16 5.12880944e-16 -1.80290226e-15 C27 3.04634382e-16 5.44487089e-16 -5.80699627e-16 C29 1.63669377e-19 2.69599038e-19 1.2772278e-18 C31 5.71 139265e-19 -2.77021052e-18 -1.12674253e-17 C33 -2.0569781 e-18 -2.68401626e-19 -1.47419704e-18 C35 -3.76959861 e-18 1.85847569e-18 -6.35049596e-19 C36 7.41332873e-22 -1.69651914e-21 8.1242866e-22 C38 -5.26804588e-22 1.47913706e-21 -1.02729033e-20 C40 2.29138809e-21 -2.23206068e-21 2.05904697e-20 C42 2.53005421 e-21 -4.92753784e-23 7.36265223e-21 C44 -1.38378144e-20 -5.03266549e-21 1.04244628e-20 C46 -9.98595148e-25 -2.29016325e-25 -3.78523909e-24 C48 -2.62255637e-24 -1.03009976e-23 2.48506394e-23 C50 4.63243161 e-24 -1.27800452e-23 -1.23509829e-23 C52 2.79922972e-23 1.51095825e-25 -4.17262005e-24 C54 1.42491041 e-23 -2.20603372e-23 -2.85772948e-23 C55 -5.25786519e-27 7.14725502e-27 -6.43766455e-28 C57 5.80142861 e-28 6.470951 15e-27 1.5593196e-26 C59 -1.721031 13e-26 -3.10095736e-26 -1.88777446e-26 C61 -2.52341494e-26 -4.78198882e-26 3.68931638e-27 C63 3.78238932e-27 6.05955815e-26 -6.34223347e-28 C65 1.13278648e-25 1.8284345e-26 2.68127617e-26

Table 3c

Coefficient M1

KY 0.00000000 KX 0.00000000 RX -3810.86664300 Coefficient M1

C7 -3.07724748e-08 C9 -1.1092234e-09 C10 5.42603668e-12 C12 4.34272696e-10 C14 5.20715764e-1 1 C16 -5.91448696e-14 C18 2.99993389e-13 C20 7.92455179e-13 C21 2.77299977e-18 C23 8.44040962e-17 C25 1.72365307e-15 C27 2.96867047e-15 C29 -9.37461721 e-20 C31 9.48636629e-19 C33 1.51 121919e-17 C35 -6.94799531 e-17 C36 5.56491 129e-24 C38 -1.14082819e-21 C40 -7.851 13088e-21 C42 6.16008871 e-20 C44 -3.69867602e-19 C46 1.38831435e-25 C48 -5.29874848e-24 C50 -1.13734657e-23 C52 -8.97248374e-23 C54 9.80001404e-22 C55 -1.0656534e-28 C57 -3.06386065e-28 C59 -2.94379006e-27 C61 -1.47445886e-25 C63 -2.04830046e-24 C65 1.39915328e-23

Table 3d

Surface DCX DCY DCZ

Image field 0.00000000 0.00000000 0.00000000 M10 0.00000000 0.00000000 726.26825857 AS 0.00000000 1 14.99787753 222.43108435 M9 0.00000000 136.95980546 126.20986754 M8 0.00000000 -102.28561601 1 172.14414151 M7 0.00000000 1.951 19662 1533.55503523 M6 0.00000000 606.64992938 2158.01874657 M5 0.00000000 1053.47672037 2341 .26818301 M4 0.00000000 2075.95201296 2321 .98264847 M3 0.00000000 2479.49763735 2134.64912748 M2 0.00000000 2704.66987413 1852.70145894 M1 0.00000000 2888.73001061 1221 .70644087

Object field 0.00000000 3021 .79508673 2868.97685767

Table 4a

Surface TLA[deg] TLB[deg] TLC[deg]

Image field -0.00000000 0.00000000 -0.00000000 M10 6.42858928 0.00000000 -0.00000000 Surface TLA[deg] TLB[deg] TLCrdeg]

AS -17.14246277 180.00000000 0.00000000 M9 192.87063810 -0.00000000 -0.00000000 M8 88.39783563 0.00000000 -0.00000000 M7 59.91640627 -0.00000000 -0.00000000 M6 34.1 102031 1 -0.00000000 0.00000000 M5 10.60930228 -0.00000000 -0.00000000 M4 -12.99109198 -0.00000000 -0.00000000 M3 -38.14483096 -0.00000000 -0.00000000 M2 -62.56308442 0.00000000 0.00000000 M1 185.82179813 -0.00000000 -0.00000000

Object field 0.38172435 0.00000000 0.00000000

Table 4b

Surface AOI[deg] Reflectivity

M10 6.42858928 0,647 M9 0.01345953 0,291 M8 75.51373800 0,764 M7 76.00483264 0,763 M6 78.18896421 0,767 M5 78.31013496 0,776 M4 78.08947079 0,770 M3 76.75679022 0,773 M2 78.82495632 0,774 M1 10.44007378 0,629

Overall transmission 0,020

X[mm] Y[mm] Z[mm]

0.00000000 132.80229462 0.00000000 -34.55713145 131.35951691 0.00000000 -68.29061856 127.02179719 0.00000000 -100.38643567 1 19.76879342 0.00000000 -130.05397146 109.59066928 0.00000000 -156.54719905 96.51757053 0.00000000 -179.19248193 80.64902007 0.00000000 -197.41654143 62.17477925 0.00000000 -210.76616416 41.38135861 0.00000000 -218.91636786 18.64429089 0.00000000 -221.67132151 -5.58642687 0.00000000 -218.96468570 -30.79671678 0.00000000 -210.86176036 -56.40803396 0.00000000 -197.56060372 -81.76967486 0.00000000 -179.38857244 -106.15490156 0.00000000 -156.79392006 -128.77181569 0.00000000 -130.33439869 -148.79395729 0.00000000 -100.66380815 -165.40937807 0.00000000 -68.51564422 -177.88300337 0.00000000 -34.68350686 -185.62426280 0.00000000 -0.00000000 -188.24913322 0.00000000 34.68350686 -185.62426280 0.00000000 68.51564422 -177.88300337 0.00000000 100.66380815 -165.40937807 0.00000000 130.33439869 -148.79395729 0.00000000 X[mm] Y[mm] Z[mm]

156 79392006 128 77181569 0 00000000 179 38857244 106 15490156 0 00000000 197 56060372 -81 76967486 0 00000000 210 86176036 -56 40803396 0 00000000 218 96468570 -30 79671678 0 00000000 221 67132151 -5 58642687 0 00000000 218 91636786 18 64429089 0 00000000 210 76616416 41 38135861 0 00000000 197 41654143 62 17477925 0 00000000 179 19248193 80 64902007 0 00000000 156 54719905 96 51757053 0 00000000 130 05397146 109 59066928 0 00000000 100 38643567 1 19 76879342 0 00000000 68 29061856 127 02179719 0 00000000 34 55713145 131 35951691 0 00000000

Table 6

An etendue of the projection optical unit 7 is 6.32 mm². The etendue fined as image field surface x NA².

A pupil obscuration of the projection optical unit 7 is 18% of the numerical aperture of the projection optical unit 7. Hence, a surface portion of 0.18² of a pupil of the projection optical unit 7 is obscured. The projection optical unit 7 is telecentric on the object side and image side. Thus, the chief rays 16 extend parallel to one another between the object field 4 and the mirror Ml on the one hand and between the mirror M10 and the image field on the other hand, wherein an angle deviation over the entire field is negligibly small, in particular less than 0.1°. An object-image offset dois is approximately 3000 mm. The mirrors of the projection optical unit 7 can be housed in a cuboid with xyz-edge lengths of 693 mm x 3285 mm x 2292 mm.

The object plane 5 extends at an angle of 0.4° in relation to the image plane

9. A working distance between the mirror M9 closest to the wafer and the image plane 9 is 102 mm. A mean wavefront aberration rms is 15.74 ml, i.e. it is defined as dependent on the design wavelength. The mirrors Ml, M4, M5, M7 and M10 have negative values for the radius, i.e. they are, in principle, concave mirrors. The mirror M2 has positive values for the radius, i.e. it is, in principle, a convex mirror.

The mirrors M3, M6, M8 and M9 have different signs in respect of their x- radius value and y-radius value, i.e. they have a saddle-shaped basic form.

In order to produce a microstructured or nanostructured component, the projection exposure apparatus 1 is used as follows: First, the reflection mask 10 or the reticle and the substrate or the wafer 1 1 are provided. Sub- sequently, a structure on the reticle 10 is projected onto a light-sensitive layer of the wafer 1 1 with the aid of the projection exposure apparatus 1. Then, a micro structure or nanostmcture on the wafer 1 1 , and hence the microstructured component, is produced by developing the light-sensitive layer.

Claims

Patent claims

1. Projection optical unit (7) for EUV projection lithography

comprising a plurality of mirrors (Ml to M10) for imaging an ob- ject field (4) into an image field (8) with illumination light (3), wherein at least one of the mirrors (Ml, M9, M10) is embodied as an NI mirror and arranged in such a way that a reflection surface of the NI mirror (Ml, M9, M10) is impinged upon with a maximum angle of incidence (AOI) of a chief ray (16) of a central field point, said maximum angle of incidence being less than 45°, wherein a ray portion of the chief ray (16) incident on the reflection surface and a ray portion of the chief ray (16) emerging from the reflection surface lie in a plane of incidence (yz),

wherein a mirror dimension Dx of the at least one NI mirror (Ml, M9, M 10) in a plane of extent (xz) perpendicular to the plane of incidence (yz) satisfies the following relationship:

4 LLWx/IWPVmax < Dx,

where the following applies:

- LLWx: etendue of the projection optical unit (7) in the plane of extent (xz);

IWPVmax : maximum difference between a maximum angle of incidence and a minimum angle of incidence of the illumination light (3), respectively at the same location and determined on the entire reflection surface of the NI mirror (Ml, M9, M10).

2. Projection optical unit (7) according to Claim 1, characterized in that the mirror dimension Dx of the NI mirrors (Ml, M9, M10) is at least 200 mm.

Projection optical unit (7) for EUV projection lithography

comprising a plurality of mirrors (Ml to M10) for imaging an object field (4) into an image field (8) with illumination light (3), wherein at least one of the mirrors (M2 to M8) is embodied as a GI mirror and arranged in such a way that a reflection surface of the mirror (M2 to M8) is impinged upon with a maximum angle of incidence (AOI) of a chief ray (16) of a central field point, said maximum angle of incidence being greater than 45°, wherein a ray portion of the chief ray (16) incident on the reflection surface and a ray portion of the chief ray (16) emerging from the reflection surface lie in a plane of incidence (yz),

wherein a mirror dimension Dy of the at least one GI mirror (M2 to M8) in the plane of incidence (yz) satisfies the following relationship:

4 LLWy/(IWPVmax cos(a)) < Dy,

where the following applies:

LLWy: etendue of the projection optical unit (7) in the plane of incidence (yz);

IWPVmax : maximum difference between a maximum angle of incidence and a minimum angle of incidence of the illumination light (3) on the reflection surface of the GI mirror (M2 to M8), a: angle of incidence of a chief ray (16) of the central field point on the reflection surface of the GI mirror (M2 to M8).

Projection optical unit (7) according to Claim 3, characterized in that the mirror dimension Dy of the at least one GI mirror (M2 to M8) is at least 100 mm.

5. Projection optical unit (7) comprising at least one NI mirror according to Claim 1 or 2 and comprising at least one GI mirror according to Claim 3 or 4.

6. Projection optical unit (7) according to any one of Claims 1 to 5, characterized by a maximum difference IWPVmax between a maximum angle of incidence and a minimum angle of incidence of the illumination light (3) on the reflection surface of the at least one NI mirror (Ml, M9, M10) in the plane of incidence (yz) of at least 3°.

7. Projection optical unit according to Claim 6, characterized by a maximum difference IWPVmax between a maximum angle of incidence and a minimum angle of incidence of the illumination light (3) on the re- flection surface of the at least one NI mirror (Ml, M9, M10) in the plane of incidence (yz) of at most 10°.

8. Projection optical unit according to any one of Claims 1 to 7, characterized by a maximum difference IWPVmax between a maximum angle of incidence and a minimum angle of incidence of the illumination light (3) on the reflection surface of the at least one GI mirror (M2 to M8) in the plane of incidence (yz) of at least 0.25°.

9. Projection optical unit according to Claim 8, characterized by a max- imum difference IWPVmax between a maximum angle of incidence and a minimum angle of incidence of the illumination light (3) on the reflection surface of the at least one GI mirror (M2 to M8) in the plane of incidence (yz) of at most 4°.

10. Projection optical unit according to any one of Claims 1 to 9, characterized in that the projection optical unit (7) is telecentric on the object side.

1 1. Projection optical unit according to any one of Claims 1 to 10, characterized by an image field (8) which is spanned by a coordinate x perpendicular to a plane of incidence (yz) and a coordinate y perpendicular thereto, wherein an aspect ratio Xbf/ybf of the image field (8) is greater than 13.

12. Optical system

- comprising an illumination optical unit (6) for illuminating the object field (4) with the imaging light (3),

- comprising an imaging optical unit (7) according to any one of

Claims 1 to 1 1.

13. Projection exposure apparatus comprising an optical system according to Claim 12 and comprising an EUV light source (2).

14. Method for producing a structured component, comprising the following method steps:

providing a reticle (10) and a wafer (1 1),

projecting a structure on the reticle (10) onto a light-sensitive layer of the wafer (1 1) with the aid of the projection exposure apparatus according to Claim 13,

producing a micro structure or nanostructure on the wafer (1 1).

15. Structured component, produced according to a method according to Claim 14.