WO2009090007A2

WO2009090007A2 - Illumination system of a microlithographic projection exposure apparatus

Info

Publication number: WO2009090007A2
Application number: PCT/EP2009/000049
Authority: WO
Inventors: Artur HÖGELE
Original assignee: Carl Zeiss Smt Ag
Priority date: 2008-01-16
Filing date: 2009-01-08
Publication date: 2009-07-23
Also published as: GB0800677D0; WO2009090007A3

Abstract

An illumination system of a microlithographic projection exposure apparatus (10) has a pupil plane (54), an object plane (62) and a mask plane (68) in which a mask (16) to be illuminated can be arranged. The illumination system has an optical system (170; 270; 370) consisting of a condenser (60; 160; 260; 360) that produces a Fourier relationship between the pupil plane (54) and the object plane (62). The system further has a field stop objective (66; 166; 266; 366) that optically conjugates the object plane (62) to the mask plane (68). According to the invention the optical system (170; 270; 370) has a negative Petzval sum with an absolute value of less than 0.0032 1/mm and preferably of less than 0.0026 1/mm. This ensures small telecentricity errors and a good pole balance.

Description

ILLUMINATION SYSTEM OF A MICROLITHOGRAPHIC PROJECTION EXPOSURE APPARATUS

BACKGROUND OF THE INVENTION

1. Field of the invention

The invention relates to an illumination system for a mi- crolithographic projection exposure apparatus. Such apparatuses are used in the manufacture of integrated circuits and other microstructured devices.

2. Description of Related Art

Microlithography (also referred to as photolithography) is a technology for the fabrication of integrated circuits, liquid crystal displays and other microstructured devices. More particularly, the process of microlithogra- phy, in conjunction with the process of etching, is used to pattern features in thin film stacks that have been formed on a substrate, for example a silicon wafer. At each layer of the fabrication, the wafer is first coated with a photoresist which is a material that is sensitive to radiation, such as very deep ultraviolet (VUV) light. Next, the wafer with the photoresist on top is exposed to projection light through a mask in a projection exposure apparatus. The mask contains a circuit pattern to be projected onto the photoresist. After the exposure, the photoresist is developed to produce an image corresponding to the circuit pattern contained in the mask. Then an etch process transfers the circuit pattern into the thin film stacks on the wafer. Finally, the photoresist is re- moved.

In current projection exposure apparatus a distinction can be made between two different types of apparatus. In one type each target portion on the wafer is irradiated by exposing the entire mask pattern onto the target por- tion in one go; such an apparatus is commonly referred to as a wafer stepper. In the other type of apparatus, which is commonly referred to as a step-and-scan apparatus or scanner, each target portion is irradiated by progressively scanning the mask pattern under the projection beam in a given reference direction while synchronously scanning the substrate table parallel or anti-parallel to this direction. The ratio of the velocity of the wafer and the velocity of the mask is equal to the magnification of the projection lens, which is usually smaller than 1, for example 1:4.

A projection exposure apparatus typically includes an illumination system, a mask alignment stage, a projection objective and a wafer alignment stage. The illumination system illuminates a region of the mask that is to be projected onto the photoresist. Usually the illumination system contains a pupil plane in which secondary light sources are produced with the help of an optical raster element, for example a fly-eye lens. The divergence of the light produced by the secondary light sources influences the geometry of the region that is illuminated on the mask. The light intensity distribution in the pupil plane determines the angular distribution of the projection light impinging on the mask. For modifying the intensity distribution in the pupil plane, various optical elements, for example axicon elements, diffractive optical elements or micro-mirror arrays, may be used in the illumination system.

A condenser, which usually comprises a plurality of lenses, transforms the pupil plane into a field plane. This means that the condenser images an object positioned at infinity on the field plane. Often a field stop com^¬ prising a plurality of adjustable blades is positioned in the field plane. The field stop ensures sharp edges of the region that is illuminated on the mask. To this end, a field stop objective images the field stop onto the mask plane in which the mask is positioned.

The illumination system has to ensure a very uniform ir- radiance in the mask plane. The uniformity of the irradi- ance is often expressed in terms of the relative change of the irradiance over 1 mm in an arbitrary direction.

This gradient of the irradiance in the mask plane should not exceed a certain value that may be as low as 0.1 %/mm or even 0.015%/mm.

Furthermore, the illumination system should produce a chief ray distribution in its exit pupil that matches the chief ray distribution of the subsequent projection objective. Usually it is desired that the chief rays are collimated, i.e. the exit pupil is positioned at infinity. In this case the illumination system is said to be telecentric on the image side.

Another property of highly advanced illumination systems is a good pole balance. The pole balance denotes the ability of an illumination system to energetically transform an intensity distribution in the pupil plane correctly into an angular distribution in the mask plane. For example, if only two poles are illuminated in the pupil plane with perfect symmetry, a perfect pole balance (PB = 0) means that the irradiance at an arbitrary point in the mask plane results from equal contributions from both poles. If PB ≠ 0 in the case of a dipole illumina- tion, the light impinging from one side on a field point is more intense than the light impinging from the opposite side.

These properties should be achieved with an illumination system having a short overall length, containing few lenses with a small diameter and maintaining a certain minimum distance between the last lens and the mask plane.

Meeting these tight specifications has become more difficult in illumination systems that do not comprise a light homogenization rod. Such a rod, which is known, for example, from US 6,285,443, is used to homogenize the illumination light bundle. Since the rod does not maintain the polarization state of the illumination light bundle, its use is restricted to illumination systems without polari- zation control.

From US 6,583,937 Bl a condenser of a rod-less illumination system is known that comprises five lenses.

US 2002/0171944 Al discloses a condenser of a rod-less illumination system that comprises four lenses, namely a negative meniscus lens having an aspherical concave front surface, two bi-convex lenses and a flat convex lens having an aspherical convex rear surface.

US 6,680,803 B2 discloses a field stop objective for a rod-less illumination system comprising a total of 9 lenses.

From DE 196 53 983 Al another field stop objective is known comprising only 7 lenses with at least three aspherical surfaces. In one embodiment, this objective ensures a telecentricity error of less than 0.3 mrad. Very sophisticated combinations of a condenser and a field stop objective with an image side numerical aper^¬ ture NA= 0.3 are known from WO 2006/114294 A2. The field stop objective partly corrects residual pupil aberrations of the condenser, for example telecentricity errors. This makes it possible to keep telecentricity errors below 0.3 mrad. In some embodiments deviations from the sine condi^¬ tion are kept below +0.004.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an illumination system of a microlithographic projection ex^¬ posure apparatus which ensures excellent illumination conditions in the mask plane.

In accordance with the present invention this object is achieved by an illumination system comprising a pupil plane, an object plane and a mask plane in which a mask to be illuminated can be arranged. The illumination system further comprises an optical system consisting of a condenser that produces a Fourier relationship between the pupil plane and the object plane, and a field stop objective that optically conjugates the object plane to the mask plane. According to the invention the optical system has a negative Petzval sum with an absolute value of less than 0.0032 I/mm, preferably of less than 0.0028 I/mm, and even more preferably of equal to or less than 0.0026 I/mm. Expressed in relative terms, the optical system has, in accordance with the present invention, a negative Petzval sum P, wherein the ratio P_x = | P | / (NA- h_max) is below 1.5-10^"4 I/mm², preferably 1.3- ICT⁴ I/mm², still more pref- erably below 1.2-10^"4 I/mm², with NA being the image side numerical aperture and h_max the maximum image height of the optical system.

The invention is based on the surprising discovery that field curvature, which is a third order aberration usu- ally described by the Petzval sum, has a very strong influence on the telecentricity error and the pole balance. The latter are pupil related quantities that do not describe if or where light rays of a converging light bundle intersect (this is the subject of optical aberra- tions) . Instead, these pupil related quantities are concerned with the direction and energy distribution of such light bundles.

Thus far it has been assumed that optical aberrations and pupil related quantities are more or less independent from each other. However, the inventor has developed a new mathematical formalism which reveals that there is a strong physical link between the aberration field curvature on the one hand and telecentricity error and pole balance as typical pupil related quantities on the other hand. The improvement of the pupil related quantities has up to now been a process which has mainly been dominated by try and error approaches and which strongly relies on the experience of the optics designer. By establishing a link between these illumination related properties on the one hand and the field curvature as an imaging aberration on the other hand, it is now possible to strongly improve the performance of illumination systems by employing known approaches that have been developed for correcting the field curvature in optical systems. By reducing the absolute value of the Petzval sum to the values indicated above, an optical system for the illumination system is obtained which has superior properties with regard to the telecentricity error and also the pole balance.

For reducing the absolute value of the Petzval sum, the field stop objective may comprise a lens triplet, i. e. a combination of a positive lens, a negative lens and a positive lens. Alternatively or additionally, the field stop objective may have lenses with a negative refractive power which are arranged close to the pupil plane of the objective .

Superior pupil related properties are obtained if not only the field stop objective, but also the condenser has a very small absolute value of the Petzval sum, which should be less than 0.0014 I/mm, and preferably less than 0.0010 I/mm. The inventor has furthermore designed various embodiments of such an optical system which attain such low absolute value of the Petzval sums in spite of their large numerical aperture NA > 0.38 towards the mask plane and their maximum field radius on the mask plane of more than 50 mm. This corresponds to a geometrical optical flux of more than 19 mm. Nevertheless the optical system has an overall axial length of less than 1200 mm, a maximum clear optical diameter of the lenses of less than 350 mm or even 310 mm, and uses not more than 8, in some embodiments not more than 6, aspherical lenses.

The new designs of the optical system provide nevertheless an axial distance between the condenser and the object plane of more than 50 mm, and an axial distance be- tween the field stop objective and the mask plane of more than 50 mm.

In one embodiment the axial distance between an objective pupil plane within the field stop objective and the closest optical element exceeds 40 mm. This makes it possible to arrange a variety of optical elements, for example absorptive filter elements or polarizers, in the objective pupil plane.

In another embodiment the field stop objective has an objective pupil plane, in which light rays form a maximum angle to an optical axis of the field stop objective of less than 15°, preferably of less than 12°. Small angles in the objective pupil plane improve the function of optical elements that may be arranged in or in close proximity to this plane.

The optical designs also provide for a folding mirror or any other beam folding element (e.g. prism) having an at least substantially flat reflective surface which may be arranged such that the optical axis is tilted by 90°. In the context of the present application a beam folding element denotes a device which is capable of tilting the optical axis of the illumination system. In one embodiment the axial length of the portion of the field stop objective formed by all lenses arranged between the flat reflective surface and the mask plane is less than 350 mm, and in another embodiment this length is even below 120 mm. In this embodiment no lens at all is arranged between the folding mirror and the mask plane. This makes it possible to arrange the optical system such that all lenses are aligned along a horizontal optical axis. Therefore this embodiment is particularly suitable for use in projection exposure apparatus where the overall height of the apparatus is restricted, but a very high projection objective is to be used.

As a result of the small absolute value of the Petzval sum, the condenser has a maximum telecentricity error an- gle α_c and the field stop objective has an image side maximum telecentricity error angle α_o < 0.6 α_c, preferably < 0.5 α_c, and even more preferably < 0.3 α_c, wherein α_o may be smaller than 1.2 mrad.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features and advantages of the present invention may be more readily understood with reference to the following detailed description taken in conjunction with the accompanying drawing in which:

FIG. 1 is a perspective and simplified view of a projection exposure apparatus comprising an illu- mination system and a projection objective;

FIG. 2 is a simplified meridional section through the illumination system shown in FIG. 1 containing a condenser and a field stop objective;

FIG. 3 is a meridional section through a condenser and a field stop objective according to a first embodiment of the invention;

FIG. 4 is a meridional section through a condenser and a field stop objective according to a second embodiment of the invention;

FIG. 5 is a meridional section through a condenser and a field stop objective according to a third embodiment of the invention. DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a perspective and highly simplified view of a projection exposure apparatus 10 that comprises an illumination system 12 for producing a projection light bun- die. The projection light bundle illuminates a field 14 on a mask 16 containing minute structures 18. In this embodiment, the illuminated field 14 has approximately the shape of a ring segment. However, other shapes of the illuminated field 14, for example rectangles of various as- pect ratios, are contemplated as well.

A projection objective 20 images the structures 18 within the illuminated field 14 onto a light sensitive layer 22, for example a photoresist, which is deposited on a sub^¬ strate 24. The substrate 24, which may be realized as a silicon wafer, is arranged on a wafer stage (not shown) such that the light sensitive layer 22 is precisely located in an image plane of the projection objective 20. The mask 16 is positioned by means of a mask stage (not shown) in an object plane of the projection objective 20. Since the absolute value of the magnification of the projection objective 20 is usually smaller than 1, a minified image 14' of the structures 18 within the illuminated field 14 is formed on the light sensitive layer 22.

During the projection, the mask 16 and the substrate 24 move along a scan direction which coincides with the Y- direction. Thus the illuminated field 14 scans over the mask 16 so that structured areas larger than the illuminated field 14 can be continuously projected. Such a type of projection exposure apparatus is often referred to as "step-and-scan tool" or simply a "scanner". The ratio be- tween the velocities of the mask 16 and the substrate 24 is equal to the magnification of the projection objective 20. If the projection objective 20 inverts the image, the mask 16 and the substrate 24 move in opposite directions, as this is indicated in FIG. 1 by arrows Al and A2. How- ever, the present invention may also be used in stepper tools in which the mask 16 and the substrate 24 do not move during projection.

In the embodiment shown, the illuminated field 14 is not centered with respect to the optical axis OA of the pro- jection objective 20. Such an off-axis illuminated field 14 may be necessary with certain types of projection objectives 20, for example objectives that contain one or more truncated mirrors. It is to be understood, however, that the present invention may also be used in apparatus in which the illuminated field 14 is centered with respect to the optical axis OA.

FIG. 2 is a more detailed meridional section through the illumination system 12 shown in FIG. 1. For the sake of clarity, the illustration of FIG. 2 is also considerably simplified and not to scale. This particularly implies that different optical units are represented by very few optical elements only. In reality, these units may com- prise significantly more lenses and other optical elements .

The illumination system 12 comprises a housing 28 and a light source that is, in the embodiment shown, realized as an excimer laser 30. The excimer laser 30 emits projection light that has a wavelength of about 193 ran. Other wavelengths, for example 248 nm or 157 nm, are also contemplated.

The projection light emitted by the excimer laser 30 en- ters a beam expansion unit 32 in which the light bundle is expanded. After passing through the beam expansion unit 32, the projection light impinges on a first optical raster element 34. The first optical raster element 34 is received in a first exchange holder 36 so that it can easily be replaced by other optical raster elements having different properties. The first optical raster element 34 comprises, in the embodiment shown, one or more diffraction gratings that deflect each incident ray such that a divergence is introduced. This means that at each location on the optical raster element 34, light is diffracted within a certain range of angles. This range may extend, for example, from -3° to +3°. In FIG. 2 this is schematically represented for an axial ray that is split into two diverging rays 38, 40. The first optical raster element 34 thus modifies the angular distribution of the projection light and influences the far field intensity distribution. Other kinds of optical raster elements, for example micro-lens or micro-mirror arrays, may be used instead or additionally.

The first optical raster element 34 is positioned in a front focal plane 42 of a zoom lens group 46 which colli- mates the diverging light rays emerging from the first optical raster element 34. By adjusting the zoom lens group 46 it is thus possible to vary the diameter of the projection light bundle. This at least substantially col- limated light bundle then enters a pair 48 of axicon ele- merits 50, 52 having opposing conical faces. If both axicon elements 50, 52 are in contact, the axicon pair 48 has the effect of a plate having parallel plane surfaces. If both elements 50, 52 are moved apart, the spacing between the axicon elements 50, 52 results in a shift of light energy radially outward. A light bundle having a cross section of a circular disk will thus be transformed into a light bundle having the cross section of a ring. Since axicon elements are known as such in the art, these will not be explained here in further detail. The zoom lens group 46 and/or the axicon pair 48 may be completely dispensed with, particularly if the first optical raster element 34 is formed by an array of individually controllable elements, for example tiltable micro-mirrors.

Reference numeral 54 denotes a pupil plane of the illumi- nation system 12. Immediately in front of the pupil plane 54 a second optical raster element 56 is arranged, which may comprise a plurality of micro-lens arrays. The second optical raster element 56 produces a plurality of secon^¬ dary light sources in the pupil plane 54. The secondary light sources may produce light with different divergences along the X and Y directions. For example, if the illuminated field 14 has the shape of a curved slit as is shown in FIG. 1, the exit side numerical aperture of the second optical raster element 56 may be in the range from 0.28 to 0.35 in the X-direction and in the range from 0.07 to 0.09 in the Y-direction. The divergence intro- duced by the second optical raster element 56 is schematically represented in FIG. 2 by divergent rays 38a, 38b and 40a, 40b emerging from two different secondary light sources.

The diverging rays 38a, 38b and 40a, 40b emerging from the second optical raster element 56 enter a condenser 60. The front focal plane of the condenser 60 coincides with the pupil plane 54, and the back focal plane will be referred to in the following as object plane 62. Thus a diverging light bundle emerging from a particular secon- dary light source in the pupil plane 54 leaves the condenser 60 as parallel light bundles and completely illuminates the object plane 62. On the other hand, all light rays emerging from the secondary light sources under the same angle will converge to a single point in the object plane 62 (see dotted area in FIG. 2) .

In or in close proximity to the object plane 62 a field stop 64 is positioned. A field stop objective 66 opti- cally conjugates the object plane 62 to an image plane in which the mask 16 is positioned during the exposure operation. This image plane will therefore be referred to in the following as mask plane 68. The field stop objec- tive 66 thus images the field stop 64 arranged in the object plane 62 onto the mask 16 and ensures sharp edges of the illuminated field 14 at least for the short lateral sides extending along the Y-direction.

In the following various embodiments of the condenser 60 and the field stop objective 66 will be described with reference to FIGS. 3 to 5.

1. First embodiment

FIG. 3 is a meridional section through a condenser 160 and a field stop objective 166 according to a first em- bodiment of the invention. Since the condenser 160 and the field stop objective 166 are the result of a common design process, certain optical properties may be better described with reference to the combination of the condenser 160 and the field stop 166, and not separately for these constituents as such. For that reason the combination of the condenser 160 and the field stop objective 166 will be referred to in the following also as optical system 170.

The optical system 170 is designed for a wavelength λ= 193.380 nm and contains a total of 16 lenses made of quartz glass (SiO₂) , from which 6 lenses make up the con^¬ denser 160, and the remaining 10 lenses make up the field stop objective 166. The design data and the aspheric con^¬ stants of the optical system 170 are listed in appendices Ia and Ib, respectively, at the end of this description.

In the table of appendix Ia, the first column lists a surface number S# of all components of the optical system 170 in the order in which light propagates through the optical system 170 from the pupil plane 54 to the mask plane 68. The second column lists the radius of curvature (in mm) for each surface S#. The third column lists the spacing between successive surfaces (in mm) along the optical axis OA. The fourth column indicates the material of those optical media having an index of refraction dis- tinct from 1. The fifth column lists the refractive index of all media between successive surfaces at the design wavelength λ. The sixth column lists the ^ diameter of the optical surfaces.

The abbreviation AS after a radius listed in column 2 in- dicates that this surface is aspherical. The aspherical surfaces are described by the following equation:

ch² 10 z = + C_λh^Λ + C₂h⁶ + C₃h* + CJi

where z is the height of a surface point in a direction parallel to the optical axis OA, and c = 1/R is the spherical component of the curvature of the respective surface. The conical constant K and the aspherical coef^¬ ficients C], C₂, C₃ and C₄ are given in the tables of appendix Ib.

From the design data it becomes clear that the axial distance between the condenser 160 and the object plane 62, and also the axial distance between the field stop objective 166 and the mask plane 68, is above 55 mm. This leaves enough space for arranging the field stop 64 in the object plane 62, and a mask stage in the mask plane 68, respectively.

The condenser 160 establishes a Fourier relationship between the pupil plane 54 having a diameter of 125 mm and the object plane 62 having a maximum field radius r_f = 55 mm. The maximum object light angle α_max, which is formed between the optical axis OA and a light ray which still can be received by the condenser 160, is α_max = 20°, and the numerical aperture NA_C of the condenser 160 in the object plane 62 is 0.39. This results in a geometrical optical flux L = NA_C • r_F = 21.45 mm.

The field stop objective 166 has a magnification M =-1.0 and thus produces an inverted and identically sized image of the field stop 64 on the mask 16. Since |M| = 1, the image side numerical aperture NA₀ of the field stop ob- jective 166 is also 0.39 (NA₀ = NA_C) . The shaded area in FIG. 3 represents a light bundle 172 that emerges from the pupil plane 54 as a parallel light bundle with the maximum angle α_max = 20^o. This light bundle 172 converges in the object plane 62 to a point at the maximum object height of 55 mm. The light bundle 172 emerging from this point in the object plane 62 passes, again as a parallel light bundle, through an objective pupil plane 174 which corresponds to surface S126 in the table of appendix Ia. The objective pupil plane 174 is optically conjugate to the pupil plane 54. The light bundle 172 then converges again to an image point at a maxi^¬ mum image height of 55 mm in the mask plane 68.

A plane folding mirror 176 is arranged in the objective pupil plane 174, i. e. between the optical surfaces S125 and S128. The folding mirror 176 corresponds to optical surfaces S126 and S127 in the table of appendix Ia. The folding mirror 176 is arranged such that a normal on a flat reflective mirror surface forms an angle of 45° with respect to the optical axis OA. In order to make the de- signs of the optical system 170 better comparable to the optical systems shown in FIGS. 4 and 5, the folding mirror 176 is not shown in its real tilted position, and thus the optical axis OA is not tilted by 90° in the illustration of FIG. 3.

If the optical axis OA in front of the folding mirror is arranged horizontally, the folding mirror 176 tilts the optical axis OA after the folding mirror 176 so that it runs vertically. Such a folded arrangement is often advantageous in illumination systems 12 of microlitho- graphic projection exposure apparatus 10, because the available space above the projection objective 20 is usu- ally very limited. With a folding mirror at the position of the objective pupil plane 174, the portion of the field stop objective 166 having a vertical optical axis has a total length of about 500 mm, which is about one half of the total length of the field stop objective 166 of 1010 mm. The total length of the condenser 160 in this embodiment is 479 mm.

The Petzval sums of the condenser 160 and the field stop objective 166 are about -0.0005 I/mm and -0.0020 I/mm (i.e. the absolute values of the Petzval sums are below 0.001 I/mm and 0.0025 I/mm, respectively). Thus the optical system 170 as a whole has an absolute value of the Petzval sum of 0.0025 I/mm which is less than 0.0032 and even less than 0.0026 I/mm. In relation to the large geometrical optical flux L = NA_C • r_F = 21.45 mm this is a very low value. More specifically, the relative Petzval sum P_x = I P I /L < 1.17-10^'4 1/mm² which is well below 1.5-10^"4 I/mm² and even below 1.2- 10^~4 I/mm².

The Petzval sum is a measure for the field curvature, which is a well-known third order optical aberration. In the case of field curvature, a plane object plane arranged orthogonal to an optical axis of an objective is imaged onto a curved optical surface having a vertex cur- vature which is referred to as Petzval curvature. This curvature is given by the product of the Petzval sum and the refractive index of the optical material of the last optical surface of the objective. In the approximation of the third order imaging aberrations, the Petzval sum P of an optical system containing k optical surfaces with radii r, and refractive indices «,^■ is given by the following eguation:

Up to now the design objectives for the condenser 160 and the field stop objective 166 have been defined solely in terms of certain pupil related quantities. Important quantities of this kind are telecentricity, pole balance and sine condition.

A telecentricity error occurs if a central ray, which forms the energetic center of a light bundle converging towards a point in the mask plane 68, is not parallel to the optical axis OA, but forms an angle therewith. This (maximum) angle is usually, and also in the context of the present description, used as a measure for the telecentricity error. The central ray may be determined from the intensity distribution in the exit pupil for this particular point in the mask plane 68. It should be noted that, at least in the general case, it is not possible to determine the central ray (and thus the telecentricity error) on the basis of the intensity distribution in the pupil plane 54. This is because the optical system 170 is usually not an ideal system, and therefore the pupil plane 54 is subject to distortion and other pupil aberra- tions. The portion of the telecentricity error which is caused by such pupil aberrations, but does not take into account the different intensities, is sometimes referred to as geometrical telecentricity error.

The pole balance denotes the ability of the illumination system to correctly transform an intensity distribution in the pupil plane into an angular distribution in the mask plane. For example, if only two poles are illuminated in the pupil plane 54 with perfect symmetry, a perfect pole balance (PB = 0) means that the irradiance at an arbitrary point in the mask plane 68 results from equal contributions from both poles. If PB ≠ 0 in the case of a dipole illumination, the light impinging from one side on a field point is more intense than light impinging from the opposite side.

The sine condition relates to the ability of a condenser to correctly transform heights in the pupil plane 54 into angles in a Fourier related field plane, here the object plane 62.

However, in contrast to projection objectives, the opti- cal systems in illumination systems have heretofore not been optimized with respect to reducing the classical third order aberrations. This is because only the field stop 64 is imaged by the field stop objective 166, but for various reasons the image of this field stop 64 does not have to be extremely sharp and aberration-free. Thus the correction of classical aberrations has not been an issue in the development of optical systems in illumination systems. Instead, all efforts and system costs have been allotted to the optimization of pupil related illumination quantities, particularly telecentricity, pole balance and sine condition.

In the context of the present invention, however, it has been found out that the field curvature as a classical aberration has surprisingly a very strong effect on certain pupil related illumination quantities, namely the telecentricity and the pole balance. Thus a good correction of the field curvature automatically results in small telecentricity errors and a good pole balance.

A significant advantage of this approach is that some concepts how to reduce field curvature are known in the art. These concepts may now be applied to the condenser 160 and the field stop 166, and their application will automatically result in low telecentricity errors and a good pole balance. In this embodiment, the telecentricity error of the condenser 160 is below 5 mrad. The field stop objective 166 further reduces the telecentricity error to a value below 1 mrad. In the condenser 160 the good correction of the field curvature (|P| < 0.001 I/mm) has been achieved with a variety of measures. One of these measures is the use of lenses having a negative refractive power in the vicinity of the pupil plane 54 and the object plane 62. More specifically, the first and the last lens of the condenser 160 are meniscus lenses having a relatively strong negative refractive power.

The same approach has been used in the field stop objec- tive 166, in which the first and also the last lens have a relatively strong negative refractive power. Also the lenses adjacent the objective pupil plane 174 have a negative refractive power. Generally, it is difficult to reduce field curvature whilst keeping the overall length of an optical system small. In the embodiment shown in

FIG. 3, however, this has been achieved with an optimized design, but nevertheless with few lenses and only eight aspherical lenses distributed over the optical system 170.

This embodiment thus combines a variety of advantages, such as large geometrical optical flux, short overall length, good accessibility of field and pupil planes, low field curvature and thus good telecentricity and pole balance properties, and also reasonable production costs because the total number and size of the lenses is kept low. 2. Second embodiment

FIG. 4 is a meridional section through a condenser 260 and a field stop objective 266 according to a second embodiment of the invention. Since also the condenser 260 and the field stop objective 266 are the result of a common design process, certain optical properties may be better described with reference to the combination of the condenser 260 and the field stop 266, and not separately for these constituents as such. For that reason the com- bination of the condenser 260 and the field stop objective 266 will be referred to in the following as optical system 270.

The optical system 270 is designed for a wavelength λ= 193.380 nm and contains a total of 16 lenses made of quartz glass (SiO₂) from which 6 lenses make up the condenser 260, and the remaining 10 lenses make up the field stop objective 266. The design data and the aspheric con^¬ stants of the optical system 270 are listed in appendices 2a and 2b, respectively, at the end of this description. In this embodiment the gas filling the spaces between the lenses is nitrogen (N₂) having, at the wavelength of λ= 193.380 nm and a pressure of 975 Pa, a refractive index of 1.000308.

With regard to the quantities listed in the appendices 2a and 2b, reference is made to the explanations given in the description of the first embodiment above. From the design data it becomes clear that the axial dis^¬ tance between the condenser 260 and the object plane 62, and also the axial distance between the field stop objec^¬ tive 266 and the mask plane 68, is above 55 mm. This leaves enough space for arranging the field stop 64 in the object plane 62, and a mask stage in the mask plane 68, respectively.

The condenser 260 establishes a Fourier relationship between the pupil plane 54 having a diameter of 125 mm and the object plane 62 having a maximum field radius r_f = 55 mm. The maximum object light angle α_max, which is formed between the optical axis OA and a light ray which still can be received by the condenser 260, is α_max = 20°, and the numerical aperture NA_C of the condenser 260 in the object plane 62 is 0.39. This results in a geometrical optical flux L = NA_C • r_F = 21.45 mm.

The field stop objective 266 has a magnification M = -1.0 and thus produces an inverted and identically sized image of the field stop 64 on the mask 16. Since |M| = 1, the image side numerical aperture NA₀ of the field stop objective 266 is also 0.39 (NA₀ = NA_C) .

The shaded area in FIG. 4 represents a light bundle 272 that emerges from the pupil plane 54 as a parallel light bundle with the maximum angle α_maχ ⁼ 20°. This light bun- die 272 converges in the object plane 62 to a point at the maximum object height of 55 mm. The light bundle 272 emerging from this point in the object plane 62 passes, again as a parallel light bundle, through an objective pupil plane 274 which corresponds to surface S226 in the table of appendix 2a. The objective pupil plane 274 is optically conjugate to the pupil plane 54. The light bundle 272 then converges again to an image point at a maximum image height of 55 mm in the mask plane 68.

A plane folding mirror 276 is arranged between the optical surfaces S231 and S235. The plane mirror 276 corre- sponds to optical surfaces S233 and S234 in the table of appendix 2a. The folding mirror 276 is arranged such that a normal on a reflective mirror surface forms an angle of 45° with respect to the optical axis OA. In order to make the designs of the optical system 270 better comparable to the optical systems shown in FIGS. 3 and 5, the fold^¬ ing mirror 276 is not shown in its real tilted position, and thus the optical axis OA is not tilted by 90° in the illustration of FIG. 4.

If the optical axis OA in front of the folding mirror is arranged horizontally, the folding mirror 276 tilts the optical axis OA after the folding mirror 276 so that it runs vertically. Such a folded arrangement is often advantageous in illumination systems 12 of microlitho- graphic projection exposure apparatus 10, because the available space of the projection objective 20 is often very limited. With the folding mirror 276 arranged between the optical surfaces S231 and S235, the portion of the field stop objective 266 having a vertical optical axis will have a total length of only 340 mm, which is about one third of the total length of the field stop ob^¬ jective 266 of 1150 mm. The total length of the condenser 260 in this embodiment is 480 mm.

The optical system 270 is therefore perfectly suited for microlithographic projection exposure apparatus 10 in which the projection objective 20 arranged in an upright position is very long, and simultaneously the overall maximum height of the apparatus is limited. In such a case it is important that the portion behind the folding mirror 276 is very short, as is the case with the optical system 270 shown in FIG. 4.

The Petzval sums of the condenser 260 and the field stop objective 266 are about -0.0008 I/mm and -0.0017 I/mm

(i.e. the absolute values of the Petzval sums are below 0.001 I/mm and 0.002 I/mm, respectively). Thus the optical system 270 as a whole has an absolute value of the Petzval sum of 0.0025 I/mm which is less than 0.0032 I/mm and even less than 0.0026 I/mm. In relation to the large geometrical optical flux L = NA_C • r_F = 21.45 mm this is a very low value. More specifically, the relative Petzval sum P_x = I P| /L « 1.17-10^"4 I/mm² which is well below 1.5-10^"4 1/mm² and even below 1.2-10^"4 I/mm².

As a result of the small absolute value of the Petzval sum, the telecentricity error of the condenser 260 is be- low 5 mrad. The field stop objective 266 further reduces the telecentricity error to a value below 1 mrad.

In the condenser 266 the good correction of the field curvature (|P| < 0.001 I/mm) has been achieved with a va- riety of measures. One of these measures is the use of lenses having a negative refractive power in the vicinity of the pupil plane 54 and the object plane 62. More spe^¬ cifically, the first and the last lens of the condenser 260 are meniscus lenses having a relatively strong nega- tive refractive power.

In the field stop objective 266, a lens triplet arranged between the object plane 62 and the objective pupil plane 274 significantly contributes to the low absolute value of the Petzval sum. The lens triplet is formed by the fourth, fifth and sixth lens of the field stop objective 266 and comprises optical surfaces S221 to S226. Generally a lens triplet is characterized by a sequence of a first lens having a positive refractive power, a second lens having a negative refractive power (usually a bi- concave lens) , and a third lens having a positive refractive power.

Generally, it is difficult to reduce field curvature whilst keeping the overall length of an optical system small. In the embodiment shown in FIG. 4, however, this has been achieved with an optimized design, but neverthe- less with few lenses and only six aspherical lenses distributed over the optical system 270.

Another advantage of the optical system 270 shown in FIG. 4 is that the objective pupil plane 274 is spaced apart by a distance d > 45 mm from the adjacent lenses (lens surfaces S228 and S230) . This makes it possible to arrange other optical elements, for example absorptive filters such as rotatable grey filter elements, in the objective pupil plane 274. Instead of or in addition to ab- sorptive filters, optical elements influencing the state of polarization of the projection light may be arranged in or in close proximity to the pupil plane 274. For example, polarizers such as known from US 2005/0140958 Al or elements that rotate the polarization direction of po- larized light such as described in US 2002/0176166 Al may be envisaged in this context.

A still further advantage of the optical system 270 is that the objective pupil plane 274 is almost perfectly flat, whereas in other field stop objectives known in the prior art the pupil plane is not really a "plane", but is considerably curved. The flatness of the objective pupil plane 274 has a positive effect on the function of optical elements arranged in the objective pupil plane 274, or at least makes their arrangement simpler.

From a comparison of FIGS. 3 and 4 it also becomes clear that the maximum angles occurring in the objective pupil plane 274 are significantly smaller in the optical system 270 shown in FIG. 4 than in the optical system 170 shown in FIG. 3. More specifically, in the optical system 270 the maximum angle formed between light rays and the opti- cal axis OA is about 12 °, and in the optical system 170 shown in FIG. 3 this angle is about 16°. Having small angels in the objective pupil plane 274 also has a positive effect on the function of optical elements that may be arranged at that axial position.

3. Third embodiment

FIG. 5 is a meridional section through a condenser 360 and a field stop objective 366 according to a third embodiment of the invention. Since also the condenser 360 and the field stop objective 366 are the result of a com- mon design process, certain optical properties may be better described with reference to the combination of the condenser 360 and the field stop 366, and not separately for these constituents as such. For that reason the combination of the condenser 360 and the field stop objec- tive 366 will be referred to in the following as optical system 370.

The optical system 370 is designed for a wavelength λ= 193.380 nm and contains a total of 15 lenses made of quartz glass (SiO₂) from which 6 lenses make up the con- denser 360, and the remaining.9 lenses make up the field stop objective 366. The design data and the aspheric con- stants of the optical system 370 are listed in appendices 3a and 3b, respectively, at the end of this description.

With regard to the quantities listed in the appendices 3a and 3b, reference is made to the explanations given in the description of the first embodiment above.

From the design data it becomes clear that the axial dis^¬ tance between the condenser 360 and the object plane 62, and also the axial distance between the field stop objective 366 and the mask plane 68, is above 50 mm. This leaves enough space for arranging the field stop 64 in the object plane 62, and a mask stage in the mask plane 68, respectively.

The condenser 360 establishes a Fourier relationship between the pupil plane 54 having a diameter of 125 mm and the object plane 62 having a maximum field radius rf = 55 mm. The maximum object light angle α_max, which is formed between the optical axis OA and a light ray which still can be received by the condenser 360, is α_max = 20°, and the numerical aperture NA_C of the condenser 360 in the object plane 62 is 0.39. This results in a geometrical optical flux L = NA_C • r_F = 21.45 mm.

The field stop objective 366 has a magnification M = -1.0 and thus produces an inverted and identically sized image of the field stop 64 on the mask 16. Since |M| = 1, the image side numerical aperture NA₀ of the field stop objective 366 is also 0.39 (NA₀ = NA_C) .

The shaded area in FIG. 5 represents a light bundle 372 that emerges from the pupil plane 54 as a parallel light bundle with the maximum angle α_max = 20°. This light bundle 372 converges in the object plane 62 to a point at the maximum object height of 55 mm. The light bundle 372 emerging from this point in the object plane 62 passes, again as a parallel light bundle, through an objective pupil plane 374 which corresponds to surface S327 in the table of appendix 3a. The objective pupil plane 374 is optically conjugate to the pupil plane 54. The light bundle 372 then converges again to an image point at a maximum image height of 55 mm in the mask plane 68.

A folding mirror 376 having a flat reflective surface is arranged between the optical surface S333 and the mask plane 68. The folding mirror 376 corresponds to optical surfaces S334 and S335 in the table of appendix 3a. The folding mirror 376 is arranged such that a normal on its reflective surface forms an angle of 45° with respect to the optical axis OA. In order to make the designs of the optical system 370 better comparable to the optical systems shown in FIGS. 3 and 4, the folding mirror 376 is not shown in its real tilted position, and thus the opti- cal axis OA is not tilted by 90° in the illustration of FIG. 5. If the optical axis OA in front of the folding mirror 376 is arranged horizontally, the folding mirror 376 tilts the optical axis OA after the folding mirror 376 so that it runs vertically. Such a folded arrangement is often advantageous in illumination systems 12 of microlitho- graphic projection exposure apparatus 10, because the available space of the projection objective 20 is often very limited. With the folding mirror 376 arranged immediately in front of the mask plane 68, the portion of the field stop objective 366 having a vertical optical axis will have a total length of only 112 mm, which is about one ninth of the total length of the field stop objective 366 of 1010 mm. The total length of the condenser 360 in this embodiment is 485 mm.

The optical system 370 is therefore perfectly suited for microlithographic projection exposure apparatus 10 in which the projection objective 20 arranged in an upright position is very long, and simultaneously the overall maximum height of the apparatus is limited. In such a case it is important that the portion behind the folding mirror 376 is as short as possible, as is the case with the optical system 370 shown in FIG. 5.

The Petzval sums of the condenser 360 and the field stop objective 366 are about -0.0009 I/mm and -0.0017 I/mm (i.e. the absolute values of the Petzval sums are below

0.001 I/mm and 0.0020 I/mm, respectively). Thus the optical system 370 as a whole has an absolute value of the Petzval sum of 0.0026 I/mm which is less than 0.0032 I/mm and even less than 0.0028 I/mm. In relation to the large geometrical optical flux L = NA_C ^• r_F = 21.45 mm this is a very low value. More specifically, the relative Petzval sum P_x = I P| /L « 1.21- 10^"4 I/mm² which is well below 2.0-10^"4 1/mm² and even below 1.3-10^"4 I/mm².

As a result of the low absolute value of the Petzval sum, the telecentricity error of the condenser 360 is below 5 mrad. The field stop objective 366 further reduces the telecentricity error to a value below 1 mrad.

In the condenser 366 the good correction of the field curvature (|P| < 0.001 I/mm) has been achieved with a variety of measures. One of these measures is the use of lenses having a negative refractive power in the vicinity of the pupil plane 54 and the object plane 62. More specifically, the first and the last lens of the condenser 360 are meniscus lenses having a relatively strong negative refractive power.

A similar approach has been used in the field stop objec- tive 366, in which the first lens has a relatively strong negative refractive power. Additionally, the lenses adjacent the objective pupil plane 374 also have a strong negative refractive power. Generally, it is difficult to reduce field curvature whilst keeping the overall length of an optical system small. In the embodiment shown in

FIG. 5, however, this has been achieved with an optimized design, but nevertheless with few lenses and only seven aspherical lenses distributed over the optical system 370.

This embodiment thus combines a variety of advantages, such as large geometrical optical flux, short overall length, good accessibility of field and pupil planes, low field curvature and thus good telecentricity and pole balance properties, and also reasonable production costs because- the total number and size of the lenses is kept low.

The above description of the preferred embodiments has been given by way of example. From the disclosure given, those skilled in the art will not only understand the present invention and its attendant advantages, but will also find apparent various changes and modifications to the structures and methods disclosed. The applicant seeks, therefore, to cover all such changes and modifications as fall within the spirit and scope of the invention, as defined by the appended claims, and equivalents thereof.

Appendix Ia - Design Data Embodiment: 1

Entrance Pupil Diameter = 125 mm

Object Angle = 20°

Wavelength = 193.380 nm

Numerical Aperture (image side) = 0.39

Height of intermediate image = 55 mm

Magnification between intermediate and final image = -1.0

Height of final image = 55 mm

Surface # Radius Thickness Material Refr . Index H Diameter

SlOl 92 .233557345 1.00000000 62.540

S102 -89. 700000000 29 .679922960 SI02 1.56034000 78.956

S103 -272. 462438385AS 0 .955298052 1.00000000 112.725

S104 -725. 448369464 71 .437326360 SI02 1.56034000 130.148

S105 -167. 694355505 1 .008669622 1.00000000 136.991

S106 -447. 155660016 36 .898792950 SI02 1.56034000 147.384

S107 -242. 866196020 1 .001539643 1.00000000 150.045

S108 163. 849736489AS 67 .433564155 SI02 1.56034000 150.332

S109 1364. 109862141 0 .925331993 1.00000000 147.124

SIlO 162. 104756393 67 .581031005 SI02 1.56034000 127.171

Sill 1887. 620154608 3 .604364887 1.00000000 120.981

S112 610. 048430997 11 .846684677 SI02 1.56034000 108.968

S113 96. 163033983 96 .671112000 1.00000000 78.634

S114 0 .000000000 1.00000000 54.968

S115 75 .872817197 1.00000000 54.968

S116 -83. 789542737 45 .215799660 SI02 1.56034000 70.551

S117 -310. 036905041 0 .824595207 1.00000000 115.298

S118 -535. 352671659 68 .748254532 SI02 1.56034000 123.672

S119 -151. 907325684 0 .835394959 1.00000000 130.004

S120 -1231. 483593390 55 .558272275 SI02 1.56034000 147.744

S121 -209. 503913013AS 0 .824610263 1.00000000 150.399

S122 154. 092521546AS 80 .629744547 SI02 1.56034000 149.947

S123 1065. 917108338 2 .516121503 1.00000000 145.285

S124 265. 109387135AS 22 .236298536 SI02 1.56034000 126.141

S125 114. 547832859 165 .533970841 1.00000000 101.140

S126 0 .000000000 SI02 1.56034000 71.313

S127 128 .127081945 1.00000000 71.313

S128 -110. 044717777 29 .523581666 SI02 1.56034000 94.344

S129 -174. 150784378AS 0 .894954340 1.00000000 118.334

S130-40322. 435844235 73 .195259688 SI02 1.56034000 144.594

S131 -213. 277507038 0 .986210604 1.00000000 148.817

S132 157. 604075517AS 91 .460239170 SI02 1.56034000 150.585

S133 15274. 245301417 3 .242255885 1.00000000 146.299

S134 274. 455520510 44 .999907025 SI02 1.56034000 125.871

S135 1596. 100674430 0 .852705753 1.00000000 115.094

S136 301. 744850001AS 12 .397146898 SI02 1.56034000 106.062

S137 112. 625107823 99 .275036425 1.00000000 82.899

S138 6 .250000000 SI02 1.56034000 56.389

S139 0 .000000000 1.00000000 55.423

S140 0 .000000000 1.00000000 55.423 Appendix Ib - Aspheric Constants Embodiment 1

SURFACE Sl 03 SURFACE S108

K -2.5748 K -1.5711

Ci -1.19330892e-007 Ci -4.29326717e-009

C₂ 7.04733253e-012 C₂ 5.00511590e-013

C₃ -2.44589399e-016 C₃ -9.78018564e-018

C₄ 6.10706929e-021 C₄ 3.49199291e-023

SURFACE S121 SURFACE S122

K -0.4568 K -0.6323

C₁ 6.11367241e-009 Ci -2.86159265e-009

C₂ 3.40726569e-013 C₂ -2.32170489e-013

C₃ -7.68087411e-018 C₃ 5.81359768e-018

C₄ 1.96451358e-022 C₄ -1.57396672e-022

SURFACE S 124 SURFACE S129

K 2.2865 K 0.1943

C₁ 2.30807796e-008 Ci 1.44760510e-009

C₂ 6.67847615e-013 C₂ -2.48108477e-013

C₃ -4.62329172e-017 C₃ 4.48520578e-018

C₄ 1.53138935e-021 C₄ 2.22291441e-021

Appendix 2a - Design Data Embodiment 2

Entrance Pupil Diameter = 125 mm

Obj ect Angle = 20 °

Wavelength = 193. 380 run

Numerical Aperture (image side) = 0.39

Height of intermediate image = 55 mm

Magnification between intermediate and final image -1.0

Height of final image = 55 mm

N2VP975: nitrogen at 975 Pa

Surface # Radius Thickness Material Refr . Index H Diameter

S201 100.281800000 N2VP975 1.00030800 62.540

S202 -99. 969495554 12.654281340 SIO2VO 1.56081000 82.958

S203 -278. 423497511 12.141235175 N2VP975 1.00030800 106.836

S204 -811. 998741180 65.495728085 SIO2VO 1.56081000 126.847

S205 -144. 775451331AS 0.986911138 N2VP975 1.00030800 133.361

S206 -389. 863076813 51.671208213 SIO2VO 1.56081000 146.368

S207 -195. 526629004 0.956309443 N2VP975 1.00030800 150.119

S208 199. 472030251 53.625329750 SIO2VO 1.56081000 150.065

S209 415. 475814061 14.031454123 N2VP975 1.00030800 145.718

S210 162. 258508450AS 69.646573447 S102VO 1.56081000 130.751

S211 -2282. 239298332 10.691415924 N2VP975 1.00030800 124.926

S212 328. 128631332 12.157582522 S102VO 1.56081000 95.451

S213 86. 801126672 75.661297212 N2VP975 1.00030800 70.956

S214 49.579139452 N2VP975 1.00030800 54.911

S215 -93. 853416516 9.959515113 SIO2VO 1.56081000 64.860

S216 -4570. 893465771 10.136596898 N2VP975 1.00030800 85.617

S217 -762. 133162483 54.902009379 S102VO 1.56081000 92.256

S218 -121. 982367416 0.826328651 N2VP975 1.00030800 98.866

S219 482. 749733535 65.079573509 S102VO 1.56081000 124.610

S220 -207. 758965664AS 0.829002271 N2VP975 1.00030800 126.074

S221 140. 915598124 42.929279245 S102VO 1.56081000 113.049

S222 184. 313439221 63.241603421 N2VP975 1.00030800 104.055

S223 -186. 777426425AS 9.831090942 SIO2VO 1.56081000 100.169

S224 159. 132321249 84.667437111 N2VP975 1.00030800 94.209

S225 -129. 580717792 40.566330002 SIO2VO 1.56081000 97.188

S226 -153. 528148842 0.937210822 N2VP975 1.00030800 115.085

S227 334. 999716941 53.744098498 SIO2VO 1.56081000 140.265

S228 -892. 269414903 49.859769148 N2VP975 1.00030800 140.344

S229 49.754913462 N2VP975 1.00030800 135.590

S230 297. 055477714AS 56.276385365 SI02VO 1.56081000 150.195

S231 -822. 847021409 0.000000000 N2VP975 1.00030800 150.323

S232 166.879709187 N2VP975 1.00030800 149.102

S233 0.000000000 SIO2VO 1.56081000 134.380

S234 165.672064121 N2VP975 1.00030800 134.380

S235 155. 464136122AS 58.994273688 SIO2VO 1.56081000 115.839

S236 -2292. 448501114 1.000000000 N2VP975 1.00030800 112.057

S237 194. 656262132 15.575526906 SIO2VO 1.56081000 95.177

S238 121. 028837383 92.459870982 N2VP975 1.00030800 82.002

S239 6.300000000 S102VO 1.56081000 56.570

S240 0.000000000 N2VP975 1.00030800 55.448

S241 0.000000000 N2VP975 1.00030800 55.448 Appendix 2b - Aspheric Constants Embodiment 2

SURFACE S205 SURFACE S210

K -0.9545 K -0.0643

C₁ -5.37404801e-009 Ci -4.56831698e-009

C₂ -3.60556379e-013 C₂ -1.39578770e-012

C₃ 1.93671836e-017 C₃ 4.58555689e-018

C₄ 1.91453333e-022 C₄ -1.79189818e-021

SURFACE S220 SURFACE S223

K -0.5347 K -6.1311

Ci 1.81509966e-008 C₁ 1.78724119e-011

C₂ -2.23724923e-013 C₂ -7.89769079e-013

C₃ -1.69212208e-017 C₃ 4.00877627Θ-017

C₄ 5.55121003e-022 C₄ 8.23779380e-022

SURFACE S230 SURFACE S235

K -3.4740 K -2.3039

Ci -1.43197495e-009 Ci 4.86636654e-008

C₂ -2.01900332e-013 C₂ -8.82833562e-013

C₃ 5.08762187e-018 C₃ 1.81665181e-017

C₄ -1.64932510e-022 C₄ -8.79578916e-023

Appendix 3a - Design Data Embodiment: 3

Entrance Pupil Diameter = 125 mm

Object Angle = 20°

Wavelength = 193.380 nm

Numerical Aperture (image side) = 0.39

Height of intermediate image = 55 mm

Magnification between intermediate and final image -1.0

Height of final image = 55 mm

Surface # Radius Thickness Material Refr . Index 4 Diameter

S301 90.770800000 1.00000000 62.540

S302 -96.932721386 41.224893761 SI02 1.56034000 80.143

S303 -137.733659044AS 0.980890761 1.00000000 108.614

S304 -207.831568234 51.614059563 SI02 1.56034000 113.964

S305 -157.562924634 0.967027686 1.00000000 127.594

S306 -389.847226924 55.099985222 SI02 1.56034000 142.569

S307 -189.502354230 0.970169042 1.00000000 147.192

S308 194.414880593 47.542915434 S102 1.56034000 147.358

S309 335.032314421 14.631566222 1.00000000 142.954

S310 150.930392026AS 70.091434400 S102 1.56034000 129.677

S311-71007.541817413 0.933581979 1.00000000 124.589

S312 305.483347808 19.972860619 SI02 1.56034000 104.984

S313 90.901781986 89.532610145 1.00000000 75.279

S314 69.716783001 1.00000000 55.127

S315 -86.100779563 36.217510900 SI02 1.56034000 69.550

S316 -818.623419174 0.966260864 1.00000000 113.376

S317 -2747.068390419 68.612964982 SI02 1.56034000 121.346

S318 -163.261840855 0.860917433 1.00000000 127.527

S319 -1295.561456566 63.302210811 SI02 1.56034000 146.964

S320 -196.504445467AS 0.850975994 1.00000000 150.148

S321 174.903053333AS 47.482574771 SI02 1.56034000 149.908

S322 292.845064664 0.910299891 1.00000000 145.478

S323 181.198777679 70.054024846 SI02 1.56034000 138.376

S324 1420.957989288 10.234415156 1.00000000 131.911

S325 851.401931990 38.337251704 SI02 1.56034000 120.159

S326 91.156444436 94.039606899 1.00000000 78.128

S327 98.489011342 1.00000000 71.028

S328 -115.148293517 25.490938157 SI02 1.56034000 93.972

S329 -163.902241668AS 0.932000000 1.00000000 116.005

S330-45666.009768434 90.653830384 SI02 1.56034000 145.738

S331 -159.265088064AS 0.832432600 1.00000000 150.238

S332 241.607578822AS 65.795177318 S102 1.56034000 151.193

S333 36227.938283944 124.222001009 1.00000000 148.211

S334 0.000000000 S102 1.56034000 96.300

S335 95.750000000 1.00000000 96.300

S336 6.250000000 SI02 1.56034000 56.189

S337 0.000000000 1.00000000 55.749

S338 0.000000000 1.00000000 55.749 Appendix 3b — Aspheric Constants Embodiment 3

Surface S303 Surface S310

K 0.1202 K -2.5042

C₁ 4.22249760e-008 Ci 7.43615398e-008

C₂ 4.35088713e-012 C₂ -1.76215253e-012

C₃ -1.27158978e-016 C₃ 5.28817824e-017

C₄ 1.58418236e-020 C₄ -1.75774177e-021

Surface S320 Surface S321

K -0.2177 K -0.6244

Ci 4.53171255e-009 Ci 4.37950131e-009

C₂ 3.97573311e-013 C₂ 3.02466091e-013

C₃ -9.51704348e-018 C₃ -6.36761434e-018

C₄ 3.17811936e-022 C₄ 1.43963558e-022

Surface S329 Surface S331

K -1.4359 K -0.5131

Ci -5.45928819e-009 Ci 8.37988497e-009

C₂ -2.30832239e-012 C₂ -6.96091041e-013

C₃ 8.02589440e-017 C₃ 2.94119281e-017

C₄ -2.93257536e-021 C₄ -3.51950702e-022

Surface S332

K -4.1066

Ci 5.43333139e-008

C₂ -1.84090968e-012

C₃ 5.30531103e-017

C₄ -7.04408341e-022

Claims

1. An illumination system of a microlithographic projection exposure apparatus (10), comprising

a) a pupil plane (54),

b) an object plane (62),

c) a mask plane (68) in which a mask (16) to be illuminated can be arranged,

d) an optical system (170; 270; 370) consisting of a

condenser (60; 160; 260; 360) that pro- duces a Fourier relationship between the pupil plane (54) and the object plane ( 62) , and

a field stop objective (66; 166; 266; 366) that optically conjugates the ob- ject plane (62) to the mask plane (68),

characterized in that the optical system (170; 270; 370) has a negative Petzval sum with an absolute value of less than 0.0032 I/mm.

2. The illumination system of claim 1, characterized in that absolute value of the Petzval is less than 0.0028 I/mm.

3. The illumination system of claim 2, characterized in that the absolute value of the Petzval sum is equal to or less than 0.0026 I/mm.

4. The illumination system of any of the preceding claims, characterized in that the field stop objective (66; 166; 266; 366) comprises a lens triplet.

5. The illumination system of any of the preceding claims, characterized in that the absolute value of the Petzval sum of the condenser (60; 160; 260; 360) alone is less than 0.0014 I/mm.

6. The illumination system of claim 5, characterized in that the absolute value of the Petzval sum of the condenser (60; 160; 260; 360) alone is less than 0.0010 I/mm.

7. The illumination system of any of the preceding claims, characterized in that the optical system (170; 270; 370) has towards the mask plane (68) a numerical aperture NA > 0.38 and a maximum field radius in the mask plane (68) of more than 50 mm.

8. The illumination system of any of the preceding claims, characterized in that the optical system (170; 270; 370) has an overall axial length of less than 1200 mm.

9. The illumination system of any of the preceding claims, characterized in that the optical system (170; 270; 370) comprises only lenses having a clear optical diameter of less than 350 mm.

10. The illumination system of claim 9, characterized in that the optical system (170; 270; 370) comprises only lenses having a clear optical diameter of less than 310 mm.

11. The illumination system of any of the preceding claims, characterized in that the optical system (170; 270; 370) comprises not more than 8 aspheri- cal lenses.

12. The illumination system of claim 11, characterized in that the optical system (270) comprises not more than 6 aspherical lenses. - A l -

13. The illumination system of claim 11 or 12, characterized in that the condenser (60; 160; 260; 360) alone comprises not more than 2 aspherical lenses.

14. The illumination system of any of the preceding claims, characterized in that the axial distance between the condenser (60; 160; 260; 360) and the object plane (62) exceeds 50 mm.

15. The illumination system of any of the preceding claims, characterized in that the axial distance between the field stop objective (66; 166; 266; 366) and the mask plane (68) exceeds 50 mm.

16. The illumination system of any of the preceding claims, characterized in that the axial distance between an objective pupil plane (174; 274; 374) within the field stop objective (66; 166; 266; 366; and the closest optical element exceeds 40 mm. •

17. The illumination system of any of the preceding claims, characterized in that a field stop (64) is arranged in or in close proximity to the object plane (62) .

18. The illumination system of any of the preceding claims, characterized in that the optical system (170; 270; 370) comprises a beam folding element (176; 276; 376) having an at least substantially flat reflective surface.

19. The illumination system of claim 18, characterized in that the axial length of a portion of the field stop objective (266; 366) formed by all lenses arranged between the flat reflective surface and the mask plane (68) is less than 350 mm.

20. The illumination system of claim 18 or 19, characterized in that the axial length of a portion of the field stop objective (366) formed by all lenses arranged between the flat reflective surface and the mask plane (68) is less than 120 mm.

21. The illumination system of any of claims 18 to 20, characterized in that not more than two lenses are arranged between the beam folding element (276; 376) and the mask plane (68) .

22. The illumination system of claim 21, characterized in that no lens is arranged between the beam folding element (376) and the mask plane (68) .

23. The illumination system of any of the preceding claims, characterized in that the condenser (60; 160; 260; 360) has a maximum telecentricity error angle α_c and the field stop objective (66; 166; 266; 366) has an image side maximum telecentricity error angle α_o < 0.6-α_c.

24. The illumination system of claim 23, characterized in that α_o < 0.5*α_c.

25. The illumination system of claim 24, characterized in that α_o < 0.3-α_c.

26. The illumination system of any of claims 23 to 25, characterized in that α_o < 1.2 mrad.

27. The illumination system of any of the preceding claims, characterized in that the field stop objective (66; 166; 266; 366) has a magnification of -1.

28. The illumination system of any of the preceding claims, characterized in that the field stop objective (266) has an objective pupil plane (274), in which light rays form a maximum angle to an optical axis (OA) of the field stop objective (266) of less than 15°.

29. The illumination system of claim 28, characterized in that the maximum angle is less than 12°.

30. An illumination system of a microlithographic projection exposure apparatus, comprising a) a pupil plane (54),

b) an object plane (62),

c) a mask plane (68) in which a mask (16) to be illuminated can be arranged,

d) an optical system (170; 270; 370) consisting of a

condenser (60; 160; 260; 360) that produces a Fourier relationship between the pupil plane (54) and the object plane (62) , and

a field stop objective (66; 166; 266; 366) that optically conjugates the object plane (62) to the mask plane (68),

wherein the optical system (170; 270; 370) has an image side numerical aperture NA and a maximum image height h_max,

characterized in that

the optical system (170; 270; 370) has a negative Petzval sum P, wherein the ratio P_x= |P|/(NA ^• h_max) is below 1.5- 10^"4 I/mm².

31. The illumination system of claim 30, characterized in that P_x is below 1.3-10^'4 I/mm².

32. The illumination system of claim 31, characterized in that P_x is below 1.2- 10^~4 I/mm².

33. An illumination system of a microlithographic projection exposure apparatus, comprising

a) an object plane (62),

b) a mask plane (68) in which a mask (16) to be illuminated can be arranged,

c) a field stop objective (366) that

optically conjugates the object plane (62) to the mask plane (68),

has an optical axis (OA) ,

has an image side numerical aperture NA > 0.38 and a maximum field radius in the mask plane (68) of more than 50 mm, and

comprises a beam folding element (376) having an at least substantially flat reflective surface, wherein the optical axis (OA) between the object plane (62) and the reflective surface runs at least substantially horizontally, and wherein the optical axis (OA) between the reflective surface and the mask plane (68) runs at least substantially vertically,

characterized in that

the axial distance between the reflective surface and the mask plane (68) is below 150 mm.

34. The illumination system of claim 33, characterized in that the axial distance between the reflective surface and the mask plane (68) is below 115 mm.

35. The illumination system of claim 33 or 34, charac- terized in that an axial distance between the reflective surface and the mask plane (68) is above 50 mm.

36. An illumination system of a microlithographic projection exposure apparatus, comprising

a) an object plane (62),

b) a mask plane (68) in which a mask (16) to be illuminated can be arranged, c) a field stop objective (266; 366) that

optically conjugates the object plane (62) to the mask plane (62),

has an optical axis (OA) ,

- has an image side numerical aperture NA

> 0.38 and a maximum field radius in the mask plane of more than 50 mm, and

comprises a beam folding element (276; 376) having an at least substantially flat reflective surface, wherein the optical axis (OA) between the object plane (62) and the reflective surface runs at least substantially horizontally, and wherein the optical axis (OA) between the reflective surface and the mask plane (68) runs at least substantially vertically,

characterized in that

not more than 2 lenses are arranged between the re- flective surface and the mask plane (68) .

37. The illumination system of claim 36, characterized in that no lens at all is arranged between the reflective surface and the mask plane (68) .

38. A projection exposure apparatus, comprising an il- lumination (12) system of any of the preceding claims and a projection objective (20) .

39. A method of producing microstructured devices, comprising the following steps:

a) providing the apparatus (10) of claim 38;

b) imaging a mask (16) arranged in the mask plane (68) on a light sensitive surface (22) arranged in an image plane of the projection objective (20 ).