WO2011039261A2

WO2011039261A2 - Illumination system for microlithography

Info

Publication number: WO2011039261A2
Application number: PCT/EP2010/064467
Authority: WO
Inventors: Marc Kirch; Damian Fiolka; Gerhard-Wilhelm Ziegler; Markus DEGÜNTHER; Markus Schwab
Original assignee: Carl Zeiss Smt Gmbh
Priority date: 2009-09-30
Filing date: 2010-09-29
Publication date: 2011-04-07
Also published as: WO2011039261A3; DE102009045219A1

Abstract

Microlithographic projection exposure apparatus comprising an illumination device and ex projection objective), wherein, during the operation of the projection exposure apparatus, the illumination device an least partly illuminates a reticle in an object plane or the projection objective and the projection objective images this illuminated part of this object plane with a scale M onto at least one part of the wafer in the image plane, and wherein the wafer can be moved synchronously with the reticle perpendicular to the optical axis and providing a fly' s eye condenser for illuminating a plane.

Description

Illumination system for microlithography

BACKGROUND OF THE INVENTION

Field of the Invention The invention relates to an illumination system for microlithography .

Prior Art icrolithographic projection exposure apparatuses are used for producing microstructured components such as, for example, integrated circuits or LCDs. Such a projection exposure apparatus has an illumination device and a projection objective. In the microlithography process, the image of a reticle illuminated with the aid of the illumination device is projected by means of the projection objective onto a substrate (e.g. a silicon wafer) that is coated with a light-sensitive layer (photoresist) and is arranged in the image plane of the projection objective, in order to transfer the reticle structure to the light-sensitive layer.

The performance of the projection exposure apparatuses used is determined not only by the imaging properties of the projection objective but also by an illumination system that illuminates the reticle. In this case, the individual light beams have to have specific properties that are generally coordinated with the projection objective and the reticle. These properties include, inter alia, the illumination angle distribution of light beams. The term illumination angle distribution describes how the total intensity of a light beam is dis- tributed among the different directions from which the individual rays of the light beam impinge on the relevant point in the reticle plane. If the illumination angle distribution is specifically adapted to the pattern contained in the reticle, then said pattern can be imaged with higher imaging quality onto the wafer covered with photoresist.

It is often the case that the illumination angle distribution is not described directly in the reticle plane into which the reticle to be projected is introduced, but rather as an intensity distribution in a pupil plane that is in a Fourier relationship with the reticle plane. This makes use of the fact that each angle with respect to the optical axis at which a light ray passes through a field plane, in a Fourier-transformed pupil plane, can be assigned a radial distance measured from the optical axis. In the case of a so-called conventional illumination setting, by way of example, the region illuminated in such a pupil plane is a circular disk that is concentric with respect to the optical axis. Consequently, light rays are incident on each point in the reticle plane at angles of incidence of between 0° and a maximum angle given by the radius of the circular disk. In the case of so-called non-conventional illumination settings, e.g. angular field, dipole or quadrupole, the region illuminated in the pupil plane has the form of a ring that is concentric with respect to the optical axis or of a plurality of individual regions (poles) arranged at a distance from the optical axis. Consequently, the reticle to be projected is illuminated exclusively obliquely in the case of these non-conventional illumination settings. In the case of conventional illumination settings and annular field illumination, the illumination angle distribution is ideally rotationally symmetrical. In the case of quadrupole illumination, although the illumination angle distribution is ideally not rotationally symmetrical, the poles in the pupil plane are ideally illuminated such that the illumination angle distribution has a four-fold symmetry. Consequently, when stated in a simplified manner, an identical amount of light impinges on a field point in the reticle plane from all four directions. These symmetry properties of the respective illumination angle distribution are of great importance for a dimensionally accurate imaging of the structures contained on the reticle. In the case of deviations from these symmetry properties it can happen, for example, that structures that have the same width but are oriented differently (e.g. vertically or horizontally) on the reticle are imaged with different widths onto the photoresist. This can adversely affect the completely satisfactory function of the microlithographically produced components.

In the illumination system, therefore, filters {for example neu- tral density or polarization-altering filters) and diaphragms of a wide variety of types and forms are often used in order to influence the optical properties of the system, that is to say the desired illumination of the reticle. This can be, for example, the intensity distribution in the field or else the pupil.

One important diaphragm in many illumination systems is the so- called reticle masking diaphragm (REMA diaphragm for short) . In microlithography an essential requirement made of the illumination system is that the reticle to be imaged is illuminated ho- mogenously with respect to intensity distribution. For so-called stepper systems, the entire illuminated field has to meet the requirements, while in scanning systems the intensity along the scanning direction is firstly integrated and the variation of this integral along the direction perpendicular to the scanning direction is the crucial variable.

At the same time as the requirements made of the homogeneity of the illumination, it is necessary for the intensity at the edge in the reticle plane to decrease to almost zero within a narrow region (typically a few tenths of a millimeter) . This decrease is required in order to prevent an undesired illumination of an adjacent region on the substrate (the wafer) before or after the virtual exposure. For this purpose, a movable diaphragm is usually used for sharply delimiting the region to be illuminated. Since there is no structural space in the region of the reticle for such a diaphragm in conventional illumination systems, this sharp intensity decrease is realized in present-day systems by virtue of the fact that REMA diaphragms arranged in or close to an intermediate field plane are imaged onto the reticle with the aid of an objective, the REMA objective. Known REMA objectives are constructed in a very complex manner from many optical elements in order to ensure an exact imaging of the REMA diaphragm. The above described diaphragms and filters are usually arranged in the pupil or field plane in order there to influence intensity or angle distributions over the entire plane in a targeted manner. In this case, such elements are often designed to be ma- nipulatable in terms of form and position. The choice with regard to number and position of the manipulators is usually restricted since parts of the elements which project into the light path lead to shading or to undesired reflections.

In the illumination device, in order to obtain light intermixing the use of so-called fly's eye condensers is customary, these comprising raster arrangements composed of a multiplicity of ray-deflecting elements (e.g. lenses having dimensions in the millimeters range). The fly's eye condenser can be used both for field homogenization and for pupil homogenization. A customary fly's eye condenser comprises at least two optical elements, having first and second raster elements, between which a multi- plicity of optical channels are generally produced. The homogenization effect is achieved in the case of the fly's eye condenser by virtue of the fact that the optical channels form a multiplicity of images of the light source, so-called secondary light sources, the light of which is subsequently superimposed. This superimposition leads to a certain compensation of spatial luminance fluctuations of the light source. In this case, over and above the homogenization of the laser light, a further important task of the fly's eye condenser consists in stabilization, which means that the position of the illumination in a specific plane of the illumination device remains unchanged in relation to variations of location and, in particular, direction of the beams of rays emerging from the laser light source.

Conventional fly's eye condensers are constructed from two ras- ter arrangements of ray-deflecting lenses, wherein, in order to obtain the stabilization described above, the first raster arrangement in the light propagation direction must necessarily be arranged at a distance from the second raster arrangement in the light propagation direction, which distance corresponds to the focal length of the ray-deflecting elements or lenses of the second raster arrangement.

DE 10 2007 026 730 Al discloses a device for producing a homogenous angle distribution of laser radiation, which has, in addi- tion to a first homogenization stage comprising a first substrate having a first lens array and a second substrate having a second lens array, a third substrate having a third lens array, wherein, in particular, the distance between the first substrate and the second and/or third substrate can also be altered in or- der to alter as required the angle distribution or the size of the illuminated region in the so-called working plane.

JP 2285628 A likewise discloses, inter alia, the construction of an optical integrator made from three successive lens arrays.

As will be explained in even greater detail foelow, the use of fly's eye condensers constructed from at least three arrays of ray-deflecting elements makes it possible to circumvent restric- tions with regard to the location and the construction of diaphragms and filters and at the same time to achieve the desired effects with reduced outlay.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a fly's eye condenser, in particular for a microlithographic projection exposure apparatus, which at least substantially avoids the disadvantages explained above and, in particular, enables improved homogenization and stabilization of the illumination light. This object is achieved by means of a fly's eye condenser comprising a first optical element having a plurality of first raster elements, which is illuminated by a light source, and wherein the light beam incident from the light source is split by the first raster elements into convergent light beams with a respec- tive focal point, a second optical element having a plurality of second raster elements, wherein each light beam formed by the first raster element is assigned a second raster element and raster element pairs composed in each case of a raster element of the first optical element and a raster element of the second optical element predefine a plurality of first illumination channels. Furthermore, provision is made of a third optical element having third raster elements, wherein each light beam formed fay the second raster element is assigned a third raster element and raster element pairs composed in each case of a raster element of the second optical element and a raster element of the third optical element predefine a plurality of second illumination channels. In this case, the second raster elements image the first raster elements with an imaging scale into at least one plane P, wherein the size of the illuminated region of the second illumination channel in the plane P is less than or equal to the size of the illuminated region directly upstream of the first raster elements, and a transfer optical unit is disposed downstream of the third raster elements and the third ras- ter elements image all the illuminated regions of the planes P into a plane F in a superimposing fashion by means of the transfer optical unit.

In one advantageous configuration, the transfer optical unit has a condenser lens.

In a further configuration, the transfer optical unit has, in this order:

a fourth optical element having fourth raster elements, wherein each light beam formed by the third raster element is assigned a fourth raster element; a fifth optical element having fifth raster elements, wherein each light beam formed by the fourth raster element is assigned a fifth raster element; a condenser lens, which images the light beams into the plane F in a superimposing fashion proceeding from the fifth raster elements of the optical element.

This has the advantage of avoiding a parceling of the intensity distribution downstream of the fly's eye condenser.

In a further embodiment, at least one raster element or the condenser is arranged such that it is displaceable along the optical axis. This makes it possible to achieve an adaptation of the imaging to conditions deviating from the ideal case, for example a correction of the telecentricity .

Advantageously, an assigned filter device for the manipulation of the illumination light guided in the respective second illu- ruination channel is arranged in or in the vicinity of the plane P in at least one of the second illumination channels.

In addition, a first filter device can be arranged in the illumination light of the second illumination channel and at least one second filter device is kept outside the illumination light of the second illumination channel and can be introduced into the illumination light guided in the second illumination channel.

Different parameters of the illumination light for example of an illumination device of a microlithographic projection exposure apparatus can thus be influenced.

Advantageously, the at least second filter device is different from the first filter device in order that different filters can thus be rapidly introduced into the fly's eye condenser. In further advantageous embodiments, the filter device of the fly's eye condenser comprises at least one diaphragm for limit- ing the illumination light and is movable along the optical axis or in at least one direction perpendicular to the optical axis.

Particularly advantageously, the aperture of the diaphragm lim- its the size and shape of the illumination light guided in the respective second illumination channel in the plane P.

Intensity distributions in the plane F can thus be manipulated in a targeted manner. In a further embodiment, a multiplicity of the second illumination channels have the diaphragms, wherein all the diaphragms are arranged in a diaphragm raster, and in that all the diaphragms can thereby be moved jointly in the same way. A large number of illumination channels can thus be manipulated simulta- neously in a synchronous manner.

In a further embodiment, the apertures of the diaphragms can be altered in terms of their shape and size in order to obtain further manipulation possibilities.

In one advantageous configura ion of the fly's eye condenser, the filter device has at least one filter element which can be introduced into the illumination light guided in the second illumination channel, herein the filter element has an actuating device, such that the filter element can be brought to different positions in the second illumination channel with the aid of the actuating device. In this case, the filter device can comprise a multiplicity of filter elements.

Thus, in an illumination channel, different manipulations of the illumination light in the channel can be achieved dynamically in a targeted manner. In this case, the filter elements can be embodied as linear or locally varying neutral filter structures, dielectric layer structures, polarization-altering filters, switchable liquid crystal elements or phase-altering elements. In one development, the filter elements are arranged on one or a plurality of filter substrates .

A wide variety of parameters of the illumination light can thus be influenced in an advantageous manner.

In a further embodiment, the filter substrate is advantageously movable in at least one direction perpendicular to the optical axis in such a way that the at least second filter element can be introduced into the illumination light guided in the second illumination channel.

In a further con iguration, the filter substrates are movable independently of one another in a direction perpendicular to the optical axis, as a result of which the at least second filter element can be introduced into the illumination light guided in the second illumination channel.

This means that the manipulation possibilities available are even more variable.

In a further advantageous embodiment, at least one of the ray-deflecting optical elements of the fly's eye condenser, in particular all of said ray-deflecting optical elements, is or are embodied as a mirror. Light can thus be manipulated in par- ticular for applications in microlithography in the EUV range.

In a further advantageous embodiment, at least one of the ray-deflecting optical elements of the fly's eye condenser, in particular all of said ray-deflecting optical elements, is or are embodied as a refractive lens.

Advantageously, the fly's eye condenser is designed for an operating wavelength of less than 200 nm, more particularly less than 160 nm, and more particularly of less than 15 nm .

This has the particular advantage that the fly's eye condenser can be used for microlithography in a wide wavelength range.

Advantageously, at least one fly's eye condenser is arranged at least in direct proximity to a pupil plane or a field plane of an illumination device of a microl thographic projection exposure apparatus.

This makes it possible to influence both the angle distribution and the intensity distribution on the reticle of a microlitho- graphy projection exposure apparatus.

The object is furthermore achieved by means of an illumination device of a microlithographic projection exposure apparatus com- prising a fly's eye condenser according to the invention.

The object is furthermore achieved by means of a microlitho- graphic projection exposure apparatus comprising an illumination device and a projection objective, wherein, during the operation of the projection exposure apparatus, the illumination device illuminates an object plane of the projection objective and the projection objective images said object plane onto an image plane, wherein the illumination device has a fly's eye condenser according to the invention.

The object is furthermore achieved by means of a microlithographic projection exposure apparatus comprising an illumination device and a projection objective, wherein, during the operation of the projection exposure apparatus, the illumination device at least partly illuminates a reticle in an object plane of the projection objective and the projection objective images this illuminated part of this object plane with a scale M onto at least one part of the wafer in the image plane, and wherein the wafer can be moved synchronously with the reticle perpendicular to the optical axis. In this case, the illumination device has a fly's eye condenser according to the invention having a diaphragm raster and in that the diaphragm raster can be moved perpendicular to the optical axis synchronously with the movement of the reticle.

The object is furthermore achieved by means of a method for producing a microstructured component, wherein, an illumination device at least partly illuminates a reticle in an object plane of a downstream projection objective with an illumination light and the projection objective images this illuminated part of the reticle with a scale M onto at least one part of the wafer. In this case, the reticle with a mask structure is moved in at least one first direction, the scanning direction, relative to the illumination light, wherein the wafer is moved synchronously with the reticle at a speed which is in a ratio M with respect to the speed of the reticle. In addition, a diaphragm raster arranged in an illumination device in a fly's eye condenser in or near a field plane that is optically conjugate with respect to the reticle plane is moved synchronously with the movement of the reticle, wherein the wafer is exposed in a scanning fashion in such a way that the diaphragm raster completely blocks the illumination light at the beginning and at the end of the exposure process and that, during the exposure process, the illumi- nation light is released at the beginning and blocked again at the end, synchronously with the movement of the reticle.

Further configurations of the invention can be gathered from the description and the dependent claims. The invention is explained in greater detail below on the basis of exemplary embodiments illustrated in the accompanying figures ,

BRIEF DESCRIPTION OF THE DRAWINGS

In the figures

Figure 1 shows a schematic illustration for elucidating the mode of operation of a conventional two-stage fly's eye condenser;

Figure 2a shows a fly's eye condenser in a schematic illustration in accordance with a first embodiment of the invention;

Figure 2b shows a fly's eye condenser in a schematic illustration in accordance with a second embodiment of the invention;

Figure 3 shows a fly's eye condenser in a schematic illustration in accordance with a third embodiment of the invention;

Figure 4a shows a schematic illustration of an exemplary construction of an illumination device of a mi- crolithographic projection exposure apparatus from the prior art;

Figure 4b shows a schematic illustration of essential components of an embodiment of a pupil shaping unit from the prior art Figure 5 shows a highly schematic illustration of the most important elements of an illumination device

Figure 6 schematically shows the functioning of the REMA diaphragms

Figure 7 shows a fly's eye condenser with raster diaphragm in a schematic illustration Figure 8 shows a schematic illustration of an exemplary construction of an illumination device of a mi- crolithographic projection exposure apparatus comprising the fly's eye condenser according to the invention

Figure 9 shows a schematic illustration of a raster diaphragm

Figures lOa-b show an embodiment of a raster-type filter ele- ment in accordance with a fourth embodiment of the invention

Figure 11 shows a further embodiment of a raster-type filter element in accordance with a fifth embodiment of the invention

Figures 12a~b show a further embodiment of a raster-type filter element in accordance with a sixth embodiment of the invention

Figures 12c-e show different embodiments of an individual filter element Figures 13a-c show a further embodiment of a raster-type correction filter element in accordance with a seventh embodiment of the invention Figures 14, 15 show schematic illustrations of the correction parameters

Figure 16 shows a fly's eye condenser in a schematic illustration in accordance with an eighth embodiment of the invention;

Figures 17, 18 show a fly's eye condenser in a schematic illustration in accordance with a ninth embodiment of the invention;

Figure 19 shows a fly's eye condenser element in a schematic illustration in accordance with a tenth embodiment of the invention; Figure 20 show a fly's eye condenser element in a schematic illustration in accordance with an eleventh embodiment of the invention;

Figures 21, 22 show a fly's eye condenser in a schematic illus tration in accordance with a twelfth embodiment of the invention; DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 shows a conventional fly's eye condenser in combination with a condenser lens such as is known from the prior art .

The fly's eye condenser comprises two raster arrangements 10 and 15 arranged one behind the other in the z-direction, having first and second raster elements, between which a multiplicity of optical channels are generally produced. The homogenization effect is achieved in the case of a fly's eye condenser by virtue of the fact that the optical channels form a multiplicity of images of the light source, so-called secondary light sources, the light of which is subsequently superimposed by the condenser lens K spanning all the raster elements. This superimposition leads to a certain compensation of spatial luminance fluctuations of the light source.

The raster elements can have a round or rectangular cross section, for example. The raster elements are arranged

two-dimensionally in an x-y plane perpendicular to the optical axis, which extends in the z-direction, in such a way that one first raster element in each case exactly illuminates one second raster element. This prevents channel crosstalk, in the case of excessively high illumination, or underfilling of the channels, in the case of excessively low illumination. The channel diameter d thus corresponds to the diameter, here in the y-direction, for example, of the raster elements. The raster elements are usually strung together without any gaps, such that the corresponding channels are therefore also arranged without any gaps. In order to ensure this property even in the case of varying angles of incidence, for example as a result of fluctuations in the laser divergence, on the raster elements of the first optical element 10, the raster arrangement 10 and 15 and the condenser lens K have to be arranged in the manner indicated in figure 1. The raster elements of the raster arrangement 10 are arranged in the front focal plane of the raster arrangement 15. The condenser lens is usually arranged such that its front focal plane coincides with the rear side of the raster arrangement 15.

If there is then a desire to introduce between the raster arrangements 10 and 15 for example light-manipulating optical elements such as diaphragms or filters with, for example, a raster arrangement corresponding to that of the channels, this is in- evitably associated with a loss of light or an undesired manipulation of light . Parts of the elements, for example supporting structures, or filter regions always project into the channels since there are no lightless regions between the individual channels.

The inventors have now recognized that a fly's eye condenser constructed from at least three raster arrangements having raster elements can be designed such that the channel diameter between a second and a third raster arrangement is less than the diameter of the channel between the first and the second raster arrangement and in this case is independent of the angle of incidence on the first raster arrangement. Illumination-free structural space is thus obtained, into which, for the targeted influencing of individual channels, by way of example, dia- phragms or filters can be introduced in order to keep these available for manipulation.

Figures 2a and 2b schematically illustrate a fly's eye condenser according to the invention comprising three raster arrangements in accordance with a first and second embodiment. Even though only one lens respectively for each of the raster arrangements can be discerned in the side view in the schematic illustration, the number of ray-deflecting raster elements per raster arrangement is typically significantly greater. One typical number merely by way of example can be approximately 40*40 or more ray-deflecting raster elements per raster arrangement, where typical dimensions can be in the millimeters range, e.g. 0.5 mm to 4 mm {without the invention being restricted thereto) .

A raster element can also consist of a group of ray-deflecting optical elements instead of an individual ray-deflecting optical element, for example a lens.

By way of example, the raster element can be composed of two planoconvex lenses instead of one biconvex lens. All other com- binations of ray-deflecting optical elements which are deemed to be suitable by the person skilled in the art are likewise conceivable .

Thus, the ray-deflecting optical elements can be embodied as mirrors. Light can thus be manipulated in particular for appli- cations in microlithography in the EUV range.

Furthermore, it is possible for the ray-deflecting elements to be embodied as diffractive optical elements, for example as grating structures or computer generated holograms. The fly's eye condenser has three raster arrangements Rl, R2, R3 situated one behind another in the light propagation direction (corresponding to the z-direction in the coordinate system depicted) , said raster arrangements each having a multiplicity of ray-deflecting raster elements 21-23 which, in the exemplary era- bodiment, are configured in each case as refractive biconvex lenses and are in each case strung together without gaps in each raster arrangement. Figure 2a illustrates a more general arrangement of the raster elements, whereas figure 2b illustrates a special case of the embodiment according to figure 2a. The raster elements 21, 22 and 23 have the focal lengths fi, f.2 and f3« The light distribution on the raster element 21 is imaged into the plane P foy the raster element 22 with an imaging scale fi∞dVd. The diameter of the light distribution on the raster element 21 is d, and the diameter of the light distribution in the plane P is d' . d corresponds to the channel diameter upstream of the fly's eye condenser according to the invention, and d* corresponds to the channel diameter between the second and third raster elements. On account of the imaging, the channel diameter d* is always less than or equal to the channel di- ameter d since β ≤ 1.

The raster element 23, together with a downstream condenser k having the focal length f4, images the light distribution in the plane P into the plane F. In this case, condenser lens k ac- quires the images of all the raster elements 23 and images them in a superimposing fashion into the plane F. This means that the light distributions in the plane P of all the raster elements 23 are superimposed in the plane F to form a single light distribution. This advantageously takes place in such a way that light distributions are all superimposed congruously. The size of the superimposed light distribution in the plane F is then d' ' .

At the first raster element 21, the light beams for each point impinge with a specific divergence angle a, which corresponds to a numerical aperture of the light beams in the far field of a/2. The divergence can fluctuate over time, for example as a result of thermal influences, by the value a, for example in a manner instigated by fluctuations of laser divergences or disturbances in the upstream optical system. The aim of the design of the channels of the fly's eye condenser according to the invention is for the diameter d* of the illuminated surface in the plane P to be less than the channel diame- ter d at the entrance upstream of the first raster element 21. In this case, the focal lengths are intended to be specified in a manner dependent on the divergence a. For a system with unknown or fluctuating divergence a, this can be interpreted as maximum or minimum divergence and the system can be designed ac~ cordingly. In the first case, a divergence variation would result in the parceling becoming greater (the light-free regions expand) , and, in the second case, light would change over to one of the adjacent channels and thus lead to loss of light. Therefore, it is important for the field illumination and the illumi- nation in the plane P always to be independent of a.

In figure 2a, the raster elements 21,22,23 and the condenser K are arranged in such a way that there is a distance z< between raster elements 21 and 22, a distance 22 between raster element 22 and the plane P, and a distance z between raster element 23 and the plane P. The distance between raster elements 22 and 23 is then 22+2;»' · The distance between condenser K and raster element 23 is %i, and the distance between condenser K and the plane F is 24.

The following then holds true for the absolute value of the imaging scale : i i=d'/d«iz7; zi!< 1 (1)

Furthermore, the following must hold true as imaging conditions: l/fi∞l/z2-l/z_' l~ β)/ζ₂ (2) It holds true for the absolute value of the imaging scale β' that:

IP' |=d"/d' (3) z₃=f₃ 2₂'/(f3 +2₂')-f« z«/{f₄ -z«) (4)

In the most general case it is possible to choose the focal lengths fx to f< and the distances z* to z< such that the focal lengths or the additions thereof do not correspond to the distances z\ to Zi, but rather deviate by distances Vj.. This is illustrated by the distances vi to Vs in figure 2a. This can be understood as defocusing, which can be achieved, for example, by the raster elements 21-23 and the condenser K being arranged such that they are displaceable along the optical axis. It is thus possible to achieve an adaptation of the imaging to conditions deviating from the ideal case, for example a correction of the telecentricity. By way of example, the distance v_s represents a defocusing of the imaging from the plane F. Equations (1) - (4) also hold true for the case where the ν_λ are not equal to zero.

The following then hold true:

Z_x-f,+ i (6)

Z₂«f₂+v₂ (7)

Z₂'~f₃+v₃ (8)

Z₃=f4+ ₄ (9)

Z^fs+vj (10) Figure 2b illustrates the special case in which all v< apart from v₂ are zero. The position of the plane P is determined here from the image distance a' of the system composed of the two raster elements 21 and 22.

The object distance a is (fi+fj) and the image distance a" is β· (fi+fz) . Therefore, the focal length f2 and image distance a' are generally not identical.

According to the invention, the following relationship therefore arises for the focal lengths: f₂~{B"fl-v₂)/U-ft) {11} where β is the absolute value of the imaging scale of the illumination of the lens 1 with respect to the plane P.

Moreover, it holds true that: (fi+f₂) ·α = d/2- U-β) (12) and f₃-d/2-fi^« (l-β) /a (13) and β - dVd (14)

It is thus ensured that in the plane P the channel diameter can never become greater than d even if there is a fluctuation in the divergence angle a at the input of the fly's eye condenser according to the invention at the entrance surface of the first raster element 21. 23

Between the second and third raster elements 22 and 23, a smaller channel diameter d', called channel constriction hereinafter, has thus been created, which allows optical elements to be kept in the light-free regions outside the channel, which optical elements can be introduced as required into the optical channel in order to be able to individually manipulate each channel of the fly's eye condenser.

Since, on account of the design of the fly's eye condenser ac- cording to the invention, it is ensured that the channel diameter d' is not exceeded, the optical elements can be kept available without shading the light path. As indicated in figures 2a and 2b, this can be effected by means of a diaphragm 27, for example. As shown further below, the diaphragm 27 can be embodied as a raster diaphragm, for example, wherein each diaphragm aperture of the raster diaphragm corresponds to a channel of the fly's eye condenser.

The channel constriction in the plane P is therefore advanta- geously suitable for introducing an optical element for the manipulation of individual channels of an illumination system without disturbing the light path and thus for setting optical parameters of the illumination system flexibly and in a targeted manner.

Figure 3 schematically illustrates a fly's eye condenser comprising five raster arrangements R1-R5 in a third embodiment of the invention. In the embodiment from figures 2a and 2b, the angles a* downstream of the channel are greater than the angles a upstream thereof by the factor 1 /& . For this reason {etendue maintenance) the local distribution downstream of the last raster element is parceled, which ultimately results in a parceled intensity dis- tribution in the pupil, for example. With appropriate channel dimensioning the parceling generally does not constitute a problem. By adding two further refractive powers, however, it is also possible to design the channel in such a way that the angles upstream and downstream are identical and parceling is avoided.

The fly's eye condenser has five raster arrangements R1-R5 situated one behind another in the light propagation direction (corresponding to the z-direction in the coordinate system de- picted) , said raster arrangements each having a multiplicity of ray-deflecting raster elements 21-25, which, in the exemplary embodiment, are in each case configured as refractive biconvex lenses and are in each case strung together without any gaps in each raster arrangement. The raster elements 31 to 35 have the focal lengths fj. to f₅.

The following holds true for the focal lengths: f₂=(S-f_;i-v₂)/{l-fi) (15)

where β is the absolute value of the imaging scale of the ill ination of the lens 31 with respect to the plane P.

Moreover, it holds true that:

(fi+fa) -a « d/2- (1-β) (16)

(17) f«»(fi+f;:)/2 (18) f_b«-d/2 (19)

On account of this design, in figure 3 the angles a and * are now identical, such that parceling no longer occurs. In addition, this embodiment requires fewer strong refractive powers than in the embodiment according to figure 2 with three raster arrangements.

The construction of the channel in figures 2a, 2b and 3 should be understood only as a principle. It goes without saying that imaging steps which do not change the principle but may be advantageous with regard to technical embodiment can be imple- mented into this channel. By way of example, the distance fz between lens 22 or 32 and a diaphragm for a typical design can be of the order of magnitude of just 1 mm. If this distance between micro-optical unit and a movable mechanical part appears to be too small, then e.g. the plane P can be imaged to a more easily accessible location by means of an additional optical unit with a correspondingly larger working distance.

In addition, it is possible, in a fly's eye condenser according to the invention, to provide more than one region having a chan- nel constriction, by arranging further raster arrangements in a suitable manner. This can be done, for example, by using the raster element downstream of the channel constriction, raster element 23 in the example of the three-stage fly's eye condenser and raster element 35 in the example of the five-stage fly's eye condenser, as first raster element of a further three-or five-stage fly's eye condenser. It is thereby possible to provide a plurality of planes having channel constrictions and thus space for further channel-wise light-manipulating optical elements .

In order to afford a better understanding of the various possibilities for use of the fly's eye condenser, firstly a typical construction of a microlithography projection exposure apparatus will be explained. Figure 4a shows a microlithography projection exposure apparatus in accordance with the prior art, which can foe used in the production of semiconductor components and other finely structured components and operates with light or electromagnetic radiation from the deep ultraviolet range (DUV) in order to achieve resolutions down to fractions of micrometers. The primary light source 102 used is an ArF excimer laser having an operating wavelength of approximately 193 nm, the linearly polarized laser beam of which is coupled into the illumination system coaxiaily with respect to the optical axis OA of the illumination system. Other UV light sources, for example f2 lasers having an operating wavelength of 157 nm, ArF excimer lasers having an operating wavelength of 248 nm or mercury vapor lamps, e.g. having an op- erating wavelength of 368 nm or 436 nm, and also primary light sources having wavelengths of less than 157 nm are likewise possible.

The light from the light source 102 firstly enters into a beam expander 104, which can be embodied for example as a mirror arrangement in accordance with US 5,343,489 and serves for reduction of coherence and enlargement of the beam cross section.

The expanded laser beam has a specific cross-sectional area con- taining an area for example in the range of between 100 mm² and 1000 mm² and a specific cross-sectional shape, for example a square cross-sectional shape. The divergence of the expanded laser beam is generally less than the very small divergence of the laser beam prior to beam expansion. The divergence can be e.g. between approximately 0.3 mrad and approximately 3 mrad.

The expanded laser beam enters into a pupil shaping unit 150, which contains a multiplicity of optical components and groups and is designed to generate, in a downstream pupil surface 110 of the illumination system, a defined, local (two-dimensional) illumination intensity distribution, which is sometimes also referred to as secondary light source or as "illumination pupil". The pupil surface 110 is a pupil plane of the illumination system.

The pupil shaping unit 150 can be set in variable fashion, such that different local illumination intensity distributions (that is to say differently structured secondary light sources) can be set depending on the driving of the pupil shaping unit. Various illuminations of the circular illumination pupil are possible, for example a conventional setting with a centered, circular illumination spot, a dipole illumination or a quadrupole illumina- tion.

An optical raster element 109 is arranged in direct proximity to the pupil surface 110. A coupling-in optical unit 125 arranged downstream of said raster element transfers the light to an in- ter ediate field plane 121, in which a reticle masking system (REMA) 122 is arranged, which serves as an adjustable field stop.

The optical raster element 109 has a two-dimensional arrangement of diffractive or refractive optical elements and has a number of functions. Firstly, the raster element shapes the entering radiation such that the latter illuminates a rectangular illumination field after passing through the downstream coupling-in optical unit 125 in the region of the field plane 121. The raster element 109, which is also referred to as a field-defining element (FDE) , with a rectangular emission characteristic in this case produces the main portion of the geometrical etendue and adapts it to the desired field size and field shape in the field plane 121, which is optically conjugate with respect to the reticle plane 165. The raster element 109 can be embodied as a prism array in which individual prisms arranged in a two-dimensional array introduce locally specific angles in order to illuminate the field plane 121 as desired. The Fourier transformation produced by the coupling-.in optical unit 125 has the effect that each specific angle at the exit of the raster element corresponds to a location in the field plane 121, while the location of the raster element, that is to say its position with respect to the optical axis 103, determines the illumination angle in the field plane 121. In this case, the beams of rays emerging from the individual raster elements are superimposed in the field plane 121. It is also possible for the field-defining element to be configured in the manner of a multistage fly's eye condenser with micro-cylindrical lenses and diffusing screens. What can be achieved by designing the raster element 109 or its individual elements in a suitable manner is that the rectangular field is illuminated substantially homogeneously in field plane 121. The raster element 109 thus serves as field shaping and homogenizing element also for homogenizing the field illumination. The downstream masking objective 140 (also called REMA objective) images the intermediate field plane 121 with the field stop 122 onto the reticle 160 (mask) on a scale which can be between 2:1 and 1:5, for example. The imaging is effected without an intermediate image in the example, such that exactly one pu- pil plane 145, which is a Fourier-transformed surface with respect to the exit plane 165 of the illumination system, lies between the intermediate field plane 121, corresponding to the object plane of the masking objective 140, and the image plane 165 of the masking objective, which image plane is optically conju- gate with respect to said object plane and corresponds to the exit plane of the illumination system and simultaneously to the object plane of a downstream projection objective 170. Those optical components which receive the light from the laser 102 and shape from the light illumination radiation that is directed onto the reticle 160 belong to the illumination system of the projection exposure apparatus. A device 171 for holding and manipulating the reticle 160 is arranged downstream of the illumination system in such a way that the pattern arranged on the reticle lies in the object plane 165 of the projection objective 170 and can be moved in this plane for scanner operation in a scanning direction perpendicular to the optical axis OA with the aid of a scanning drive.

Downstream of the reticle plane 165 there follows the projection objective 170, which acts as a reducing objective and images an image of the pattern arranged on the reticle 160 onto a wafer 180 coated with a photoresist layer on a reduced scale, for example on a scale of M = 1:2, M - 1:4 or M ~ 1:5, the

light-sensitive surface of said wafer lying in the image plane 175 of the projection objective 170. Refractive, catadioptric or catoptric projection objectives are possible. Other reduction scales, for example greater demagnifications of up to M = 1:20 or M = 1:200, are possible.

The substrate to be exposed, which is a semiconductor wafer 180 in the case of the example, is held by a device 181 comprising a scanner drive in order to move the wafer synchronously with the reticle 160 perpendicular to the optical axis. Depending on the design of the projection objective 170 (e.g. refractive, catadioptric or catoptric, without intermediate image or with intermediate image, folded or unfolded) , these movements can be ef- fected parallel or antiparallel to one another. The device 181, which is also referred to as "wafer stage", and the device 171, which is also referred to as "reticle stage", are part of a scanner device controlled by means of a scanning control device. The pupil surface 110 lies at or near a position which is optically conjugate with respect to the nearest downstream pupil plane 145 and with respect to the image-side pupil plane 172 of the projection objective 170. Consequently, the spatial (local) light distribution in the pupil 172 of the projection objective is determined by the spatial light distribution (spatial distribution) in the pupil surface 110 of the illumination system. Lying between the pupil planes 110, 145, 172 there are in each case field surfaces in the optical beam path, which are Fou~ rier-transformed surfaces relative to the respective pupil planes. This means, in particular, that a defined spatial distribution of illumination intensity in the pupil surface 110 produces a specific solid angle distribution of the illumination radiation in the region of the downstream field surface 121, which in turn corresponds to a specific solid angle distribution of the illumination radiation incident on the reticle 160.

Essential components of a possible embodiment of a pupil shaping unit 150 are shown schematically in figure 4b. The entering, ex- panded laser radiation beam 105 is deflected by a plane deflection mirror 151 in the direction of a fly's eye condenser 152, which splits the arriving radiation beam into partial illumination radiation beams, which are subsequently transferred through a Fourier optical system 500 onto a lens array 155, that is to say onto a two-dimensional array arrangement of lens systems . The lens array 155 concentrates the partial illumination radiation beams 156 onto individually drivable mirror elements of a multi-mirror array 300 (MMA) . The partial illumination radiation beams issuing f om the individual mirrors are passed through a diffusing screen 157 and imaged into the pupil surface 110 by means of a downstream condenser optical unit 158. The lens array 155 and/or the micromirror array 300 can essentially be constructed in the manner described i US 2007/0165202 Al in the name of the present applicant. The disclosure in this regard in said patent application is incorporated by reference in the content of this description. Transmissive light modulation devices are also possible. The more mirror elements the multi-mirror array 300 has, the more accurately it is possible to set a desired intensity distribution in the pupil surface 110 and hence the illumination solid angle distribution on the reticle 160.

The principle of an illumination system for optical lithography, consisting of a pupil-defining element PDE (corresponding to the pupil shaping unit 150 from figure 4a) , a field-defining element FDE (corresponding to the raster element 109 from figure 4a), a condenser K, an intermediate image plane F, which is optically conjugate with respect to a reticle plane R, and the reticle masking unit 140 (REMA), which images a REMA diaphragm in the intermediate image plane F onto the reticle in the reticle plane R, is greatly simplified in figure 5.

A fly's eye condenser according to the invention, as described above, can be arranged at the location of the pupil-defining element or field-defining element, depending on the desired task. As outlined above, at these locations with optical elements it is possible to manipulate either the intensity distribution or the angle distribution at the location of the reticle R. If the fly's eye condenser according to the invention is used, these manipulations can be carried out very flexibly and, moreover, in a channel-related manner.

A particularly advantageous embodiment with the fly's eye condenser according to the invention is described below with refer- ence to figures 6 to 9, which embodiment can replace a conventional REMA unit. As discussed further above, the REMA unit serves for limiting the field as sharply and dynamically as possible on the reticle in scanning systems, the so-called "step~and-scan" systems.

In a "step-and-scan" system, only one slotted illumination field (illumination slot) is used to expose the wafer. The illumination slot is guided {scan) over the reticle by the reticle 660 being moved through the illumination slot. At the same time, the wafer 680 moves in the same or an opposite direction, depending on the design of the projection system. The wafer 680, with closed REMA diaphragms 622 and 623, is then moved to a new position (step) . The illumination slot can therefore be narrow in the scanning direction and, perpendicular thereto, can utilize the full size of the illumination field of the illumination system.

Since the projection objective usually, as described above, effects demagnify ng imaging, the scanning speed of the reticle and also of the REMA diaphragms has to be greater than that of the wafer on the same scale M. Figure 6 shows, in a greatly simplified manner, how conventional REMA diaphragms operate in the interplay with the movement of the reticle 660 and of the wafer 680 to be exposed by means of the projection objective 670. At the instant t-ti, the "front edge" of the wafer 680 to be exposed just reaches the illumination slot, and the REMA diaphragms 622 and 623 that are imaged onto the reticle 660 via the REMA objective 640 start to open. While the wafer 680 continues to move, the REMA diaphragms 622 and 623 have to open further at a speed scaled according to the imaging scale (t=t2) , and the left-hand REMA diaphragm 622 moves toward the left. As soon as the illumination slot is fully open (t=t3> , the REMA diaphragm 622 stops, but wafer 680 and reticle 660 continue to move

(scan), of course. Once the "back edge" of the wafer 680 to be exposed reaches the illumination slot, the right-hand REMA diaphragm 623 in the above imaging has to foe moved with this "back edge" in the same manner that previously the left-hand REMA diaphragm 622 was moved with the "front edge" of the wafer 680. It is ensured in this way that only the region of the wafer 680 which is intended to receive the pattern of the reticle 660 is exposed .

Very stringent requirements are made of a REMA objective 640 with regard to the optical imaging quality. Therefore, firstly REMA objectives are relatively costly, and secondly they require a large amount of structural space in comparison with the rest of the illumination system. In addition, the REMA diaphragms have to be moved over large distances at a high speed.

With the aid of the fly's eye condenser according to the invention together with the use of a specially constructed diaphragm it is now possible to replace the REMA objective and the conventional REMA diaphragms.

For this purpose, the fly's eye condenser according to the invention is used as a field-defining element (FDE) in the iilumi- nation system of a microlithography projection exposure apparatus, for example at the position designated by FDE in figure 5 or at the place of the optical raster element 109 in figure 4. What is important is that the plane P, the channel constriction, of the fly's eye condenser is situated in or near a field plane that is optically conjugate with respect to the reticle plane.

Figure 7 illustrates an excerpt from a three-stage fly's eye condenser in accordance with the embodiment according to figure 2b, with a movable diaphragm raster 727 at the location of the plane P. For simplification, the first raster elements of the first raster arrangement have been omitted in the illustration. The diaphragm raster 727 is illustrated schematically in plan view in figure 9, wherein a raster of four by three diaphragm apertures 728 is illustrated merely by way of example. The diaphragm raster consists of a non-transparent carrier substrate with the diaphragm apertures 727. Bach diaphragm aperture 728 in the diaphragm raster 727 corresponds at most to the diameter d' of a channel of the field-defining fly's eye condenser, a is the size of the diaphragm apertures 728 in the y-direction. The size of the diaphragm aperture is advantageously chosen such that it corresponds to the largest aperture width after the imaging onto the plane R of the reticle, b advantageously corresponds to the diameter of the illumination-free space between the channels in the plane F. It can be ensured by means of a ≤ b that the entire light can be blocked by displacement of the diaphragm raster 727. d corresponds to the channel diameter upstream of the fly's eye condenser as described with regard to figure 2, for example. The size of the diaphragm apertures 728 in the x-direction cor- responds at most to the diameter of the channel in the

x-direction, but advantageously, after the imaging into the plane R, to the aperture width of a conventional REMA diaphragm perpendicular to the scanning direction. The diaphragm raster 727 consists of many individual diaphragm apertures 728, each per se representing a luminous field diaphragm. The diaphragm raster 727 can have, for example, 50x50, 200x200 or 500x500 diaphragm apertures 728 of this type. In one embodiment, the value for a can be approximately 0.2 mm, and the distance b can be 0.8 mm.

The imaging by the condenser K must produce an imaging of the individual diaphragm apertures 782 into a single location and a single size. The imaging of all the diaphragm apertures 728 in the plane P then corresponds in terms of shape and size to a desired REMA diaphragm in the plane F.

The functioning will now be explained in greater detail below.

The field illuminated by the condenser K is trimmed by corresponding movement of the diaphragm raster 727. If the diaphragm raster 727 moves from its position shown for example downward (indicated by the arrow in plane P) , then firstly all rays de- picted in dashed fashion are blocked, as a result of which "the lower" part of the field illuminated by the condenser is cut off .

Afterward, the rays depicted in dotted fashion and, finally, the rays depicted in solid fashion are blocked. If the diaphragm raster 727 moves further downward, the rays are gradually released again until the full field is illuminated again. The diaphragm raster 727 is imaged in a superimposing fashion into the plane F. This means that, in the plane F, the superimposed rays are blocked and released again from the bottom toward the top (indicated by the arrow at plane F) . The movement of the diaphragm raster 727 is effected synchronously with the movement of the reticle and the wafer analogously to the description of the conventional REMA system from figure 6. It follows from this that an illumination system comprising the fly's eye condenser according to the invention already has its full functionality in the plane designated as "intermediate image plane F" in figure 5 and a further imaging by the REMA objective is no longer necessary, and the REMA objective can therefore be obviated. The diaphragm raster 827 only has to be moved very small distances in the range of the channel diameter, such that the distances of the REMA diaphragms, which distances are larger by one to two orders of magnitude in comparison, with the higher speeds required therefore are avoided. In addition, smaller masses are moved.

An illumination system 800 comprising a fly's eye condenser 809 according to the invention is illustrated in figure 8, The illumination system 800 is a development according to the invention of the illumination system from figure 4a. The designations, as far as comparable elements are concerned, correspond to those from figure 4a increased by 700.

A light source 802 is coupled into the illumination system coaxially with respect to the optical axis 803 of the illumination system. The light from the light source 802 firstly enters into a beam expander 804. The expanded laser beam enters into a pupil shaping unit 850, which contains a multiplicity of optical components and groups and is designed to generate a defined, local (two-dimensional) illumination intensity distribution in a downstream pupil surface 810 of the illumination system. The pupil surface 810 is a pupil plane of the illumination system.

The pupil shaping unit 850 can be set in a variable fashion, such that different local illumination intensity distributions (that is to say differently structured secondary light sources) can be set depending on the driving of the pupil shaping unit. Various illuminations of the circular illumination pupil are possible, for example a conventional setting with a centered, circular illumination spot, a dipole illumination, a quadrupole illumination or any freely shaped illumination distribution of the illumination pupil .

The fly's eye condenser 809 according to the invention, here in a three-stage variant in accordance with the embodiment according to figure 7, is arranged with its plane P in direct proximity to the pupil surface 810. The fly's eye condenser 809 also serves here, in addition to the function as field shaping and homogenizing element, as an adjustable field stop with simultaneous imaging onto the reticle plane 865. The REMA function is as it were integrated into the fly's eye condenser. The function of the coupling- n optical unit 125 from figure 4 is now performed by the condenser K, which belongs to the fly's eye condenser 827 according to the invention. It performs the Fourier transformation and superim- poses the beams of rays in the field plane 865, which is now simultaneously the reticle plane, as already explained above.

The fly's eye condenser 827 is arranged in such a way that the front plane of the first raster elements 821 is arranged in or in the vicinity of the pupil plane 810, corresponding to the pupil surface 110 from figure 4, in order to receive the light from the pupil shaping unit 850. The diaphragm raster 827 is arranged in the plane 821.

A REMA objective is no longer necessary since now the reticle 860 can be arranged directly in the field plane 865, which thus corresponds to the reticle plane 165 from figure 4, and the entire REMA function is nevertheless fulfilled.

Those optical components which receive the light from the laser 802 and form from the light illumination radiation that is directed onto the reticle 860 belong to the illumination system of the projection exposure apparatus.

Downstream of the reticle plane 865 there follows again the pro- jection objective 870, which acts as a reducing objective and images an image of the pattern arranged on the reticle 860 onto a wafer 880 covered with a photoresist layer on a reduced scale, for example on a scale of 1:2, 1:4 or 1:5, the light-sensitive surface of said wafer lying in the image plane 875 of the pro- jection objective 870. In this case, too, refractive, catadiop- tric or catoptric projection objectives are possible. Other reduction scales, for example greater demagnifications up to 1:20 or 1:200, are possible.

The substrate to be exposed, which is a semiconductor wafer 880 in the case of the example, is held by a device 881 comprising a scanner drive in order to move the wafer synchronously with the reticle 860 and the diaphragm raster 827 perpendicular to the optical axis. Depending on the design of the projection objective 870 (e.g. refractive, catadioptric or catoptric, without intermediate image or with intermediate image, folded or unfolded) , these movements can be effected parallel or antiparal- lel to one another. The device 881, which is also referred to as "wafer stage", and the device 871, which is also referred to as "reticle stage", are part of a scanner device controlled by means of a scanning control device.

The projection exposure apparatus described above should be con- sidered as merely by way of example. The raster elements can be configured as refractive or diffractive optical elements and can be produced e.g. from quartz glass (Si02) or calcium fluoride <CaF2), production from calcium fluoride being advantageous particularly with regard to improved light resistance (avoidance of compaction effects, etc.). Corresponding refractive lenses for forming the ray-deflecting elements can be, for example, biconvex lenses, planoconvex lenses, cylindrical lenses, lenses having aspherical surfaces, etc. Furthermore, individual or all of the ray-deflecting elements can also be embodied as reflective elements (mirrors) . Consequently, the invention is also suitable, in particular, in the EUV range (that is to say at wavelengths of less than 15 nm, in particular approximately 13 nm or approximately 7 nm) . The raster arrangements are then usually embodied as facet mirrors.

The fly's eye condenser according to the invention can also be used to set optical parameters of the illumination system in a targeted manner.

Different optical parameters of the illumination system can be influenced depending on whether the plane P is situated in a pu- pil plane or field plane.

By way of example, one parameter may be the uniformity of the illumination of the field in the field plane (in the reticle plane) . In order to avoid aberrations during the lithography process it is necessary to achieve as uniform as possible illumination of the field in the field plane. On account of the optical components in the beam path between the light source of the illumination system and the illuminated field, a complete uniformity of the field illumination is generally not provided. In order to be able to minimize the field-dependent intensity profile of the illumination by means of filters, in this case the plane P has to be situated in a field plane that is conjugate with respect to the reticle plane. A manipulation at this location influences the intensity profile in the reticle plane.

A further setting possibility concerns the so-called pupil el- lipticity. In order that deviations from the abovementioned ideal symmetry properties of the illumination angle distributions can be better registered quantitatively, the term pupil ellipticity is often used. Expressed in a simplified form, the pupil ellipticity corresponds to the ratio of the quantities of light which are incident from orthogonal directions during an exposure onto a field point onto the reticle. The greater the extent to which the pupil ellipticity deviates from one, the more asymmetrical the illumination angle distribution.

Precisely in the case of small apertures or settings, a

field-dependent pupil ellipticity occurs, which can be caused by optical elements, for example. In order to influence this parameter, the plane P has to be situated in a pupil plane that is in a Fourier relationship with a field plane. An influencing of the intensity distribution in a pupil plane has an influence on the angle distribution in the reticle plane and thus on the pu- pil ellipticity.

The light beams which are assigned to individual field points in the reticle plane generally cover different distances through the optical elements of the illumination system. Since the illumination system does not have the same total transmissivity for all distances, the pupil ellipticity is very generally

field-dependent. This means that the pupil ellipticity can assume different values depending on the field point considered. A further value for the symmetry of the illumination angle distribution is the so-called pole balance. In this case, pole bal- ance is understood to mean the quotient of the difference between the intensities of two poles (for example in the case of quadrupole illumination) and the sum of the intensities in the poles . A further property of the light beams impinging on an optical element is the telecentricity . Telecentric illumination is the term employed if the - in respect of energy ~ central rays of the light beams, which are generally referred to as centroid rays, impinge on the optical element parallel to the optical axis. In the case of non-telecentric illumination, the entire light beams impinge obliquely to a certain extent. The telecentricity of the light beams can uary here over the entrance surface of the optical element. In other words, this means that, at each impingement point of the optical element, the centroid rays of the light beams can have a different angle with respect to the optical axis.

A telecentricity error can also be corrected with the aid of a filter used according to the invention.

A further advantageous embodiment of the invention is described below with reference to figures 10 and 11.

Figure 10a illustrates raster elements 1022 upstream of the plane P, which raster elements correspond to the raster elements 22 and 32 from the three- and four-stage fly's eye condensers from figures 2 and 3, respectively. These raster elements 1022 produce the channel constriction in the plane P. This is illustrated in the side view along the optical axis OA.

If the channels in the plane P are then considered in the view in the direction of the optical axis OA, as illustrated in figure 10b, the channels in this example are seen as in this case rectangular light spots 1028. The shape of the channels is mentioned merely by way of example and can also be round or arcu- ate, for example, depending on the design of the illumination system and of the raster elements. The regions between said light spots 1023 are lightless.

In the embodiment described, the lightless regions are used for keeping filters 1029a-d arranged in a raster-type fashion on a filter substrate 1027 there in or near the plane P, which filters can be introduced into the channels as necessary by the movement of the filter substrate 1027 perpendicularly to the optical axis OA, in x- and y-directions. In the example, a filter 1029 is actually assigned to each light spot 1028, that is to say to the respective channel of the fly's eye condenser. In this example, the filter region is depicted as smaller than the light spot 1028, for the sake of better clarity. Advantageously, however, the filter 1029a-d is the same size or larger, in order to achieve an optimum effect. The filters 1029a-d can be arranged, for example, as optical elements on a diaphragm raster as filter substrate 1027, as shown in figure 9, for example, in diaphragm apertures.

In the example, four different filter types 1029a-d are provided, which can be introduced into the channels by the movement of the filter substrate 1027. In order to introduce the filters 1029d, for example, into the channels, the filter substrate 1027 has to be displaced along the y-direction. The filter change can take place on a time scale of milliseconds because only very short distances of the order of magnitude of the channel diameters, typically of the order of magnitude of 1 mm or less, have to be covered in order to change between the filter functions.

The filters can be, for example, uniformly linear or locally varying neutral filter structures, or dielectric layer structures {which have transmission dependent on the angle of incidence) . The filters can also be embodied as switchable filters, for ex- ample as switchable liquid crystal elements. The filters can likewise have polarization- and phase-altering elements. The filters can also be used in combination.

By way of example, the filter change can take place simultane- ously with a setting change in the context of a double exposure in so-called double patterning systems.

An advantageous development of the filter substrate is described in figure 11. In order to make the filter even more flexible, the filter substrate can be subdivided into partial substrates 1127 that can be displaced independently of one another along an axis along the raster elements of the fly's eye condenser. In figure 11, by way of example, three partial substrates 1127a-c can be displaced in the y-direction. Identical or different fil- ter types can be applied on the partial substrates 1127a-c. The number of partial substrates 1127 should be understood as merely by way of example here. Thus, it is also possible to provide a dedicated partial substrate 1127 for each series of raster ele- ments in the x- or y-direction. With the aid of these filters it is possible, as described further above, to influence different optical parameters of the illumination system depending on the position of the plane P in the field or pupil plane. If the plane P is not situated exactly in a field or pupil plane, then it is possible to influence a plurality of parameters simultaneously.

Figures 12a-c show a further embodiment of a filter element that can be used in the plane P of a fly's eye condenser according to the invention and is suitable for the manipulation of optical parameters of the illumination system.

Figure 12a shows a non-transparent carrier plate 1237 having transparent openings 1232. The shape and position of the open- ings 1232 correspond to the channels of the channel constriction in the plane P in the x- and y-directions of a fly's eye condenser according to the invention such as has been described in figure 2 or figure 3 for example. Small movable rods 1231 are arranged around said openings 1232. The rods 1231 are cylindri- cal in the example. However, they can also be embodied as narrow, thin rectangular strips. The rods 1231 should be understood here as representative of all types of movable elements which can be introduced into the channel and which are able to shade or absorb the light.

The opening 1232 and the rods 1231 form together in each case a filter element 1233 for the variable shading of the light in the individual channel. The rods 1231 absorb or shade the light in the channel, which light is directed from a light source in the direction of the reticle, as soon as they are introduced into the channel. In figure 12a, all the rods 1231 are in a neutral position, in which no influencing of the channel takes place. Figure 13b shows how the rods 1231 are pivoted into the openings 1232 in an operating position and thus remove light in the chan- nel in a targeted manner. In this example, the rods 1231 are rotated around a pivot 1235 at one end of the rods 1231 and thereby brought into the region of the openings 1232.

Figure 12c illustrates that in greater detail on the basis of an individual filter element 1233. A rod 1231 is mounted such that it can be rotated around a pivot 1235 at one end of the rod 1231 about an axis parallel to the optical axis and can thus be pivoted into the region of the opening 1232 from a neutral position. At each pivot 1235, a drive 1234 connected to the rod 1231 is arranged on the carrier plate 1237, by means of which drive the rod 1231 can be moved rotatably around the pivot. Each rod 1231 of a raster of filter elements 1233 on a carrier plate 1237 can be driven and pivoted individually, for example. This is possible because enough structural space for the mechanism and the control lines has been obtained with the aid of the fly's eye condenser according to the invention.

The number and position of rods 1231 per filter element 1233 is here merely by way of example, but can encompass any expedient number and position permitted by the structural space.

Figure 12d shows a further embodiment of the filter element 1233 with eight rods 1231. Here the rods 1231 are moved along their longitudinal axis into the opening 1232 with the aid of a drive 1236 fixed on the carrier plate 1237. In the example, the rods 1231 are moved radially toward and away again from the midpoint of the opening 1232 in order thus to achieve the desired variable shading of the light. In this case, too, the number and po~ sition can vary as desired and the rods 1231 can again be driven individually.

The shape and size of the rods 1231 are intended to be merely by way of example. The rods serve very generally for influencing the light of the channel. Thus, it is also possible to embody the rods 1231 such that they are partly transparent or have a neutral filter effect. Using the same principle, other filter types, as described further above, for example, can also be in- troduced into the channel in a targeted manner.

Figure 12e shows a variant of a filter element 1233a having adjustable diaphragms 1230a-d. The diaphragms 1230a-d can be displaced along the x- and y-directions in order thus to reduce the si2e of the diaphragm aperture 1228 in a targeted manner. On the left in figure 12e, the diaphragms 1230a-d have been fully opened, and on the right they have been displaced in the direction of the center of the diaphragm aperture 1228 and thus reduce the latter.

These filter elements 1233 and 1233a are advantageously suitable for correcting or influencing a field-dependent pupil elliptic- ity and also the pole balance, as has been described further above .

For this purpose, the filter elements 1233 have to be arranged in a pupil plane of the illumination system. If the intensities are influenced in a location-dependent manner there, then this influences the field-dependent angle distribution in the reticle plane. The intensities are removed in a location-dependent manner for each channel of the fly's eye condenser in the pupil plane. Since the channels are brought together and superimposed by the condenser K at the output of the fly's eye condenser in a, in this case, field plane, this results in a possibility of highly variable influencing of the field-dependent angle distribution. A combination of different filter types in a single filter substrate or carrier element is also possible. Moreover, it is also possible to use a plurality of fly's eye condensers according to the invention in the illumination system, for example one re- spectively with its respective plane P of the channel constriction in a pupil plane and in a field plane. If corresponding filters are used there, a plurality of optical parameters of the illumination system can be manipulated simultaneously and/or cumulatively. Figures 13a-c show a further embodiment of a filter element that can be used in the plane P of a fly's eye condenser according to the invention and is suitable for the manipulation of optical parameters of the illumination system. As described above in the descriptions to Fig. 7, the imaging by the condenser K must produce an imaging of the individual diaphragm apertures 782 into a single location and a single size. The imaging of all the diaphragm apertures 728 in the channel constriction in the plane P then corresponds in terms of shape and size to a desired REMA diaphragm in the plane F.

A homogenization effect is achieved in the case of a fly's eye condenser by virtue of the fact that the optical channels form a multiplicity of images of the light source, so-called secondary light sources, the light of which is subsequently superimposed by the condenser lens K spanning all the raster elements. The superimposition has to be very precise in order to produce a sharp image of the desired REMA diaphragm in the plane F.

For that reason the condenser lens K has to be distortion-free as good as possible. This requires high optical efforts to achieve this goal. Usually a condenser lens consists not only of a single lens but of several lenses, often called field lens group. Such a field lens group is complex and expensive. This embodiment discloses an alternative solution for the problem of a distorted condenser lens K. Fig. 13a shows the ideal situation of similar individual apertures 1328 arranged on a movable diaphragm raster 1327 as raster elements .

The individual apertures 1328 are equally spaced in a raster with raster coordinates i in x-direction and j in y-direction. Bach location of a raster element can be described in this coordinates .

An ideal condenser lens images the individual apertures 1328 superimposed in the plane F to form the desired REMA diaphragm 1330. The imaging by the condenser K produces an imaging of the individual diaphragm apertures 1382 into a single location and a single size and a magnification given by the geometry of the fly's eye condenser.

Fig. 13b shows schematically the situation in which a condenser lens K' is not ideal. The condenser lens K' may exhibit for example distortions, spherical or coma aberrations. Such a, not distortion corrected, condenser lens K' produces images of the individual diaphragm apertures 1328 which are not superimposed exactly or show distortions in shape and size. Fig. 13b shows exemplary four images 1330a-d of the individual diaphragm apertures 1328. In this example the images are only displaced to each other due to the distortions. One can easily understand that this will result in a diffuse and distorted overall image of a desired REMA diaphragm 1330' (dashed line) .

The general idea is now to use the individual diaphragm apertures as correction elements in addition to their aforementioned function. Fig. 13c illustrates schematically how this can foe realized . The raster elements 1328' are now no longer arranged equidis- tantly and do not have the same size and shape.

Each raster element 1328' at a raster position is shifted by

a correction vector from the original position in an equi-

distantly arranged raster and is distorted in shape and size by an shape correction factor c_iikerr from the original shape and size

More generally speaking, a raster element can be described by a position and a shape factor c_l} . This can be abstracted in a

general {and multidimensional) shape vector In the case of an

ideal condenser lens K a raster element has a rectangular shape and is arranged in an equidistant raster as for example shown in Fig. 9.

To correct the effects of a non-ideal condenser lens K' the individual raster elements 1328' have to be transformed as described above in position and shape. This results in a new shape vector This is illustrated in Fig. 14.

To evaluate the new shape vectors one has to measure the effect (distortion, displacement etc.) of a non ideal condenser lens K' and calculate for each raster element 1328' the correction vector and the shape correction factor c^_ierT,to get an image

1330 of a raster element 1328' which corresponds to an image with an ideal condenser lens K. With this data a new movable diaphragm raster 1327 is designed. With this new movable diaphragm raster 1327 the effects of an non-ideal condenser lens 1328' are corrected and a sharp image of the desired REMA diaphragm in the plane F is produced. In a further embodiment of this invention optical or mechanical filters can be introduced in the openings of the raster elements 1328' to correct radiance errors of a non-ideal condenser lens K' . This is achieved by a change of the position dependant transmission in the opening of the raster elements 1328' by optical or mechanical filters. This could be filter elements as described above to the embodiments of the Figs. 10a to 12d or any other transmission influencing filters for the effective wavelength known to the person skilled in the art. The filter elements could be the same type of filter elements in each opening of the raster elements 1328' . It is also possible to use two or more different types of filter elements to be more flexible in influencing the radiance errors. Analogous to the above described calculation for the position and shape of a raster element 1328 for each point with the local coordinates x and y inside the opening of a raster element 1328' from a shape and transmission factor c_i}aey a shape and transmis- sion change factor c_iJxyk9rr has to be calculated. A raster element is now described by its position, shape and location dependant transmission by a new multidimensional shape and transmission vector .

To correct now the effects of a non-ideal condenser lens K' the individual raster elements 1328' have to be transformed as described above in position, shape and transmission. This results in a new shape and transmission vector \ This is illus-

trated in Fig. 15. To evaluate the new shape and transmission vectors one has to measure the effect (distortion, displacement, radiance etc.} of a non ideal condenser lens K' and calculate for each raster ele- ment 1328' a correction vector and the shape and trans

mission correction factor ^^y_k4trrto get an image 1330 of a raster element 1328' which corresponds to an image with an ideal condenser lens K. With this data a new movable diaphragm raster 1327 is designed.

With this new movable diaphragm raster 1327 the effects of an non-ideal condenser lens 1328' are corrected and a sharp image of the desired REMA diaphragm in the plane F with a homogenous radiance is achieved.

A further advantageous embodiment is described together with Fig. 16. A fly's eye condenser according to this invention as described for example together with the Figs. 2a and 2b or Fig. 7 homogenizes the light in a pupil or field plane and simultaneously providing space for in each channel for light influencing elements in a channel constriction. The diameter of this channel constriction is limited by the pitch of the individual raster elements. This embodiment provides an advantageous solution to introduce filter elements with a greater diameter than the channel constriction without loss of light and by preserving the number of light mixing channels.

Figure 16 schematically illustrate a fly's eye condenser according to the embodiment comprising three raster arrangements in a side view. Two channels of a fly's eye condenser are shown exemplary to illustrate the invention.

Three raster elements 1621a, 1622a, 1623a and 1621b, 1622b and 1623b are each arranged one behind the other in the z-direction, having first, second and third raster elements, between each of the two arrangements an optical channel is produced.

The raster element 1623a, 1623b together with a downstream con- denser , images the light distribution in the plane P into the plane F. In this case, condenser lens K acquires the images of all the third raster elements and images them in a superimposing fashion into the plane F. This means that the light distributions in the plane P of all the raster elements are superimposed in the plane F to form a single light distribution. This advantageously takes place in such a way that light distributions are all superimposed congruously.

To achieve now a greater diameter of a channel constriction while maintaining the channel superimposition two pairs of prisms 1631a, 1631b and 1632a, 1632b are introduced downstream between each second and third raster element 1622a, 1622b and 1623a, 1623b. The first pair of prisms 1631a, 1631b is positioned close to the second raster elements in adjacent channels. The second pair of prisms 1632a, 1632b is positioned close to the third raster elements in adjacent channels.

Without prisms the light distribution on the raster element 1621a, 1621b is imaged into the plane P by the raster element 1622a, 1622b in each channel as shown for example in Figure 2a. Introducing the prisms arranged in pairs in adjacent channels combines the images of two adjacent channels in one image in the plane P. The prisms of the first pair of prisms 1631a and 1631b are shaped such that the images of two channels are exactly im- aged at the same position in the plane P spanning over two channels of the fly's eye condenser. The prisms of the second pair of prisms 1632a and 1632b are shaped such that the image in the plane P is then redistributed in the two adjacent channels as illustrated in Figure 16. This results in a virtual channel be- t een the second and third raster elements with a channel constriction with a greater diameter which is now greater than the diameter of a single channel . This makes it possible to use a raster diaphragm with greater openings or filter elements with a greater diameter. In this example the pairs of prisms are arranged along the y-direction of the fly's eye condenser and therefore to expand the channel constriction in the y-direction. It also possible to arrange the pairs of prisms along the x- direction and then expanding the channel constriction in x- direction. It is also possible to combine pairs of prisms in x- and y-direction to expand the channel constriction in both directions. It is also possible to introduce the pairs of prisms between the first and second raster elements. Any other order of raster elements and prisms which results in an expanded channel constriction is also suitable.

It is further possible to use the pairs of prisms in embodiments with more than three raster elements in a row as described for example in conjunction with figure 3.

In a further development of the invention one raster element and one prism can integrally formed in a single optical element.

The raster elements 1622a, 1622b and/or the raster elements 1623a, 1623b can be for example substituted by such an integrally formed element and no additional prisms are necessary.

The shape of the prisms 1631a, 1631b and 1632a, 1632b is only by way of example. It is possible to use any other optical element which images two channels are exactly at the same position in the plane P. 53

It is advantageous to use the prism pairs of this embodiment together with a microlithography projection exposure apparatus without a RE A objective which is for example described in conjunction with the figures 6 to 8.

Further advantageous embodiments of fly's eye condenser according to the invention are described below with reference to figures 17 to 22. As discussed further above, the REMA unit of a microlithography projection exposure apparatus can be replaced by a fly's eye condenser according to the invention.

It is desirable to design such a fly's eye condenser to be easily producible and which has reduced requirements to adjustment accuracy.

This is for example achieved by an embodiment according to the figures 17 and 18. Figure 17 shows a schematic 3-dimensional presentation of a fly's eye condenser with cylindrical lenses whereas figure 18 shows a schematic view of the y-channel of this embodiment to explain the design data. The necessary condenser lens is not shown here for the sake of simplicity.

The general idea of this embodiment is the breakup of the channel of a fly' s eye condenser, as described for example in con- junction with figure 2a, in two separate channels. Each of these channels has optical elements with refractive power either only in the x-direction or only in the y-direction of a microlithography projection exposure apparatus. This can be realized by cylindrical lenses which have only refractive power in one di- rection and no refractive power in a direction perpendicular to that direction. A further advantage of such an arrangement is that the plane P in which the channel constriction occurs can now be separated in two planes, one for each channel.

A further advantage is that the refractive powers and the pitch of the cylindrical lenses can be chosen separately.

A cylindrical lens with refractive power in x-direction is called y-cylindrical lens and a cylindrical lens with refractive power in y-direction is called x-cylindrical lens in the follow- ing description.

To form a raster arrangement for a fly's eye condenser the cylindrical lenses are arranged side by side and evenly spaced side by side along their axes with no refractive power , The cy- lindrical lenses are arranged two-dimensionally in an x-y plane perpendicular to the optical axis, which extends in the

z-direction. The cylindrical lenses are usually strung together without any gaps, such that the corresponding channels are therefore also arranged without any gaps.

Advantageously x-cylindrical lenses and y-cylindrical lenses are arranged on a single optical element as shown in figure 17, for example the optical element 1703.

With such an arrangement it is possible to design the lens systems for the x- and y-channel separately which makes it

to reach the optimal geometry for each channel.

Such elements can be produced relatively easy for example by a fly cut manufacturing process .

In this embodiment five optical elements 1703-1707 with arrange- ments of cylindrical lenses are arranged along the optical axis (z-axis) of a microlithography projection exposure apparatus. Each optical element has one surface an arrangement of x- cylindrical lenses and on the opposite surface an arrangement of y-cylindrical lenses. In this example the plane P in which the channel constriction occurs is separated in z-direction in two planes IIPx and IXPy in the same space between the two optical elements 1705 and 1706.

This has the advantage that filters and diaphragms can now be related separately to the x- and the y-channel .

If this fly's eye condenser is used for a system as described with figures 6 to 9 the diaphragm raster 727 of figure 9 can be replaced for example by two diaphragm rasters with strip-like openings in y- or x-direction respectively. For example the openings for the diaphragm for the y-channel have to be exactly dimensioned in the y-direction and can extend for example in the x-direction across the whole optical element. Only this diaphragm positioned in the plane IXPy has to be moved in the y- direction to achieve the desired function of a reticle masking system. Because of the aspect ratio of the illuminated field on the reticle it is advantageous that the x- and the y-cylindrical lenses are arranged with a different pitch. This is illustrated in fig re 20 which show an optical raster element 2010 with cylindrical lenses on opposite sides of the element. The x- cylindrical lenses 2020 are arranged side by side with a pitch pi which corresponds in this case to the diameter of the x- cylindrical lens in the x-direction. The y-cylindrical lenses 2030 have a different pitch p2 which corresponds to the diameter of the y-cylindrical lens in the y-direction.

Figure 18 shows a schematic view of a lens section of this embodiment to explain the design data of an advantageous embodiment of a fly's eye condenser designed for a microl ithography projection exposure apparatus without RE A-ob ective . is particular design is optimized for optimal uniformity and arp imaging of the edges of a diaphragm. The numbers in figure identify the different surfaces. ble 1: Design Data

The cylindrical lenses have aspherica^'l surfaces defined as follows :

The design data are: 5

59

Surface =- 10 Radius y «· 0 Kappa y = 0

Axial distance Surface 10 .. 11 3.604568041512489 Surface = 11 Y4 BRZ - 1.00031

Surface - 11 Radius x = 0 Kappa x - 0

Surface = 11 Radius y ^» -8.638749763120426 Kappa y « -

0.009731338875194865

Surface - 11 yCl - 2.816688497124621e-10

Surface - 11 yC2 = 1. 39653326735906e-15

Surface - 11 yC3 - 5.205265283986975e-21

Surface = 11 yC4 = -2.316566925566638e~25

Axial distance Surface 11 .. 12 = 0.8333193575264085 Surface ∞ 12 X5 BRZ - 1.50136

Surface = 12 Radius x ^« 5.884879289328342 Kappa x - - 5.018298554737907

Surface = 12 xCl = -7.561584558679483e-05

Surface - 12 xC2 ^« 2.804001393116185e-07

Surface = 12 xC3 = 3.677463782531965e-09

Surface - 12 xC4 ^« 2.180686948134901e-ll

Surface ^« 12 Radius y = 0 Kappa y - 0

Axial distance Surface 12 .. 13 = 10.22641507110422

Surface - 13 Y5 BRZ = 1.00031

Surface = 13 Radius κ - 0 Kappa x ~ 0

Surface ^« 13 Radius y ^« -7.796586865376083 Kappa y ■ - 0.06380570134892251

Surface - 13 yCl - 1.37031303431526e-09

Surface - 13 yC2 = 9.499125828226893e~15

Surface - 13 yC3 - 5.399927340753975e-20

Surface - 13 yC4 = 1.213852022558055e-25

Axial distance Surface 13 .. 14 » 3.54398

Surface - 14

Axial distance Surface 14 .. 15 - 0

Term Description Surface = 5 Serial surface number (5) and surface labeling, Y

Y3 ~ y-channel , 3 - 3. y-surface

BRZ Refractive index, 1.00031 match 2, 1.50136 match

CaF₂

Pitch x/y x/y channel width

NAOx/y Numerical Aperture at the first fly's eye-x/y- surface

x- channel channel, which span the long side of the field with refractive power in x-direction

y~ channel channel, which span the short side of the field with refractive power in y-direction

Diff Diffusing plate

The exit pupils of both channels (x and y) of the fly's eye condenser have to be close to the entrance pupil of the condenser lens. The condenser lens is not necessarily a single lens. To achieve a good imaging quality the condenser lens is designed as a group of lenses and/or mirrors and is often called "field lens group" .

The term condenser lens in this application includes therefore the field lens groups as well.

Advantageously the exit pupil of the x-channel coincidences with the entrance pupil of the condenser lens.

To achieve a good imaging of the aperture edges each channel of the fly' s eye condenser has to transform a field position in the intermediate image plane P according to the sine condition into angles in the exit pupil of the fly's eye condenser. The ideal condenser lens transforms then the angles at its entrance pupil into positions at the reticle plane. The change of uniformity at the reticle plane by the fly' s eye condenser and the condenser lens should be minimal, advantageously < 0.5%. It is possible to control the uniformity distribution within small limits and adapt it to special conditions. For example a constant intensity distribution or a quadratic increase at the field limits at the reticle plane is possible. To achieve this, the sine condition between the entrance pupil of the fly's eye condenser and its exit pupil has to be fulfilled:

SW.(CC_Ep)_FljCt ~ $UI((XAP FDS ~ ^X Sniram* f ffDS

Where sin( is the sine of the angle at the entrance pupil of the condenser lens, sini(X_Ap)p_DE the sine of the angle at the exit pupil of the fly's eye condenser, な_i)WW<> the position at the entrance of the fly' s eye condenser and f_FDB the total focal length of the fly's eye condenser.

Advantageously the numerical aperture at the image side of the fly's eye condenser NAI should be less than 0.15 to achieve a good uniformity and imaging of the edges of the diaphragm.

The diameter of the fly' s eye condenser multiplied by NAI is coupled to the etendue of the system, which is always constant. To satisfy this requirement in known micro!ithography projection exposure apparatus the fly's eye condenser as alternative for a REMA-group has to have a greater diameter.

One possibility to achieve this is to assemble the raster elements of the fly' s eye condenser from smaller raster elements in the xy-plane. Another advantageous embodiment of the invention is described in connection with the figures 21 and 22. Figure 21 shows a schematically 3-dimensional view of a fly's eye condenser according to this embodiment .

Analogous to the embodiment described with figure 17 the x- and y-channels are separated with the use of cylindrical lenses. In this embodiment four optical elements 2103-2107 with arrangements of cylindrical lenses are arranged along the optical axis (z-axis) of a microlithography projection exposure apparatus. Three of the optical elements 2103 (y-cylindrical lenses), 2106 {x-cylindrical lenses ) and 2107 (x-cylindrical lenses )have on both surfaces an arrangement of cylindrical lenses in the same direction. One surface of optical element 2104 has an arrangement of y-cylindrical lenses and on the opposite surface a diffusing plate 2105. This diffusing plate 2105 can be integrally formed on the surface of the optical element 2104 or which may be designed as a separate element located close to the surface of the optical element 2104. The advantages of a diffuser plate will be described below.

In this example the plane P in which the channel constriction occurs is separated in z-direction in two planes IIPx and IlPy in different spaces between two optical elements. The diaphragms and/or filters are situated in these two planes.

This has the advantage that there is more space for inserting filters and diaphragms for each channel separately. The mechanical decoupling of the movement of diaphragms in the two planes IIPx and IlPy is facilitated. For example the diaphragm in the IIPx plane is static and the diaphragm in the IlPy plane is mo- 63

veable. It is also possible to make the diaphragms exchangeable by an interchangeable holder.

This embodiment is optimized for matching the etendue to the as- pect ratio x:y at the reticle. The reason is, that at the entrance pupil of the fly's eye condenser the etendue ratio x:y is 1 and at the reticle the etendue ratio is for example Etendue_x : Etendue_y ~ 5:1. One solution for this problem is a diffuser plate 2105 which only influences the x-channel. This is achieved for example by a diffuser plate which only diffuses the light in x-direction and leaves the y-direction unchanged. Such a diffuser plate increases the solid angle only in x-direction and therefore the Etendue_x only in the x-channel. As a result the etendue ratio Etendue* : Etendue_y is increased.

Another solution is to fit the pitch of the channels to the aspect ratio. This has the disadvantage of problems with the de- sign of the elements because of the ratio. A third solution is to "underfill" the phase space in x-direction according to the aspect ratio, this means the angles downstream of the channel are greater than the angles upstream which leads to a parceling of the pupil as a disadvantage.

In this embodiment these three options are combined and optimized to minimize the disadvantages of these three options.

The arrangement of the diffuser plate 2105 in this embodiment minimizes the influence to the y-channel to fulfill the above mentioned condition.

Figure 22 shows a schematic view of a lens section this embodiment to explain the design data of an advantageous embodiment of a fly's eye condenser designed for a icrolithography projection exposure apparatus without REMA-objective . The numbers in figure 22 identify the different surfaces. Surfaces 7 and 8 are not shown in the figure. Table 2: Design Data

Pitch x-cylindrical lenses = 1.5 MI

Pitch y-cylindrical lenses * 1.5 nan

NAOx - 0.062

NAOy = 0.02

Fx_FDE « 5.12

Fy_FD£ « 23.8

NAIx = 0.142

NAIy - 0.031

The terms and definitions are the same as for table one above . wavelength - 193.38 nm

Surface = 1 BRZ - 1.00031 HMAX ^« 1.061

Axial distance Surface 1 .. 2 - 0

Surface - 2 Yl BRZ - 1.50136 HMAX = 0

Surface = 2 Radius x = 0 Kappa x - 0

Surface » 2 Radius y « 9.043208999999999 Kappa y =

91.21785717

Surface - 2 yCl - -0.007379259517

Surface - 2 yC2 » -4.451293438e~07

Surface - 2 yC3 - -7.562283258e-12

Surface - 2 yC4 =^» -2.621739084e-13

Axial distance Surface 2 .. 3 = 27.408

Surface ^« 3 Y2 BRZ ^« 1.00031 HMAX = 0

Surface ~ 3 Radius x - 0 Kappa x ~ 0

Surface ^« 3 Radius y = -2.771246 Kappa y - -0.06529588338

Surface = 11 Radius x ~ -3.029172 Kappa

2.6441S5771

Surface - 11 xCl - 0.0004332058097

Surface = 11 xC2 = 2.706602144e-06

Surface - 11 xC3 - 4.413073778e-09

Surface = 11 xC4 « 1.320045913e~12

Surface = 11 Radius y ~ 0 Kappa y - 0

Axial distance Surface 11 .. 12 = 1

Surface - 12 X3 BRZ - 1.50136 HMAX - 0

Surface = 12 Radius x = -9.296051 Kappa

3.478007226

Surface = 12 xCl = 0.0005033107805

Surface - 12 xC2 « -7.970447917e-07

Surface ^« 12 xC3 - -1.309285409e-09

Surface = 12 xC4 = -4.235122093e-12

Surface ^« 12 Radius y - 0 Kappa y = 0

Axial distance Surface 12 .. 13 ~ 4

Surface ~ 13 X4 BRZ « 1.00031 HMAX = 0

Surface - 13 Radius x ^«· -3.737553 Kappa

0.7092175762

Surface - 13 xCl - ~1.144959351e-05

Surface = 13 xC2 = -3.219942801e-07

Surface - 13 xC3 - -2.454931721e-10

Surface = 13 xC4 = -1.614785366e-13

Surface - 13 Radius y - 0 Kappa y = 0

Axial distance Surface 13 .. 14 ∞ 3.55817

Surface - 14 BRZ = 1 HMAX = 0

Axial distance Surface 14 .. 15 ~ 0

Figure 19 illustrates another advantageous embodiment of the invention. When producing the components of a fly's eye condenser, for example micro-lens arrays or micro-cylindrical lens arrays, due to production limitations a periodical micro-roughness oc- curs on the surface of the components. This periodic micro- roughness causes disturbances of the field intensity distribution at the reticle. In a conventional ra crolithography projection exposure apparatus this effect is smoothed by a diffuser plate situated downstream behind the fly's eye condenser. In a microlithography projection exposure apparatus in which the fly's eye condenser according to the invention replaces a conventional RE A-system this is not possible because a diffuser plate will increase the spot size at the reticle and therefore decreases for example the sharpness of the diaphragm image. The homogenizing effect of a fly's eye condenser will not smooth this disturbance because of the periodicity of the micro- roughness .

One solution is to produce the cylindrical lenses not in a straight line but to give them a wavy line as it is depicted in figure 19. This causes a wavelike displacement of the images at the reticle which will smooth the disturbances. The optical element 1910 shows on one surface an arrangement of straight cylindrical lenses and on the opposite surface an arrangement of wavy deformed cylindrical lenses. The contour lines 1930 of the cylindrical lenses are in this example equidistantly spaced. This has the advantage that this form can be easily produced by an fly cut process.

The wave line of figure 19 is only by way of example. Any suit- able contour of the cylindrical lenses which satisfy the smoothing effect, are possible.

Another alternative is to arrange the optical elements with the cylindrical lenses slightly rotated around the optical axis against each other. Another alternative is to displace the optical elements along the x- and/or y-axis.

This will also result in a decrease of the effect of the periodicity of the micro-roughness on the surface of the optical elements . It is possible to combine this embodiment with the other embodiments of the invention to further optimize the optical quality of the fly's eye condenser.

Even though the invention has been described on the basis of specific embodiments, numerous variations and alternative embodiments are evident to the person skilled in the art/ e.g.

through combination and/or exchange of features of individual embodiments. Accordingly, for the person skilled in the art it goes without saying that such variations and alternative embodiments are concomitantly encompassed by the present invention, and the scope of the invention is restricted only within the meaning of the accompanying patent claims and the equivalents thereof.

According to decision J 0015/88 the following clauses which show preferred embodiments are not part of the patent claims.

1. Fly's eye condenser for illuminating a plane (F) comprising a. a first optical element (Rl) having a plurality of first raster elements (21), which is illuminated by a light source (102), and wherein the light beam incident from the light source (102) is split by the first raster elements (21) into convergent light beams with a respective focal point; b.a second optical element (R2) having a plurality of second raster elements (22), wherein each light beam formed by the first raster element (21) is assigned a second raster element (22) and raster element pairs (21, 22) composed in case of a raster element (21) of the first optical element and a raster element (22) of the second optical element predefine a plurality of first illumination channels; c. a third optical element (R3) having third raster elements (23), wherein each light beam formed by the second raster element (21) is assigned a third raster element (23) and raster element pairs (22, 23) composed in each case of a raster element (22) of the second optical element and a raster element (23) of the third optical element predefine a plurality of second illumination channels;

characterized in that d. the second raster elements (22) image the first raster elements (21) with an imaging scale (β) into at least one plane (P) , wherein the size of the illuminated region (d^l) of the second illumination channel in the plane (P) is less than or equal to the size (d) of the illuminated region directly upstream of the first raster elements (21) , and e.a transfer optical unit is disposed downstream of the third raster elements (23) and the third raster elements (23) image all the illuminated regions of the planes (P) into a plane (F) in a superimposing fashion by means of the transfer optical unit . Fly's eye condenser according to clause 1, characterized in that the transfer optical unit has a condenser lens (K) .

Fly's eye condenser according to clause 1, characterized in that the transfer optical unit has, in this order: a fourth optical element (R4 ) having fourth raster elements (24), wherein each light beam formed by the third raster element (23) is assigned a fourth raster element (24), a fifth optical element {R5) having fifth raster elements (25) , wherein each light beam formed by the fourth raster element (24) is assigned a fifth raster element (25), a condenser lens (K) , which images the light beams into the plane (F) in a superimposing fashion proceeding from the fifth raster elements (25) of the optical element (R5) .

Fly's eye condenser according to any of the preceding

clauses, characterized in that at least one raster element (21,22,23,24,25) or the condenser (K) is arranged such that it is displaceable along the optical axis OA.

Fly's eye condenser according to any of the preceding clauses, characterized in that an assigned filter device (728, 1029a-d, 1233, 1233a) for the manipulation of the illumination light guided in the respective second illumination channel is arranged in or in the vicinity of the plane (P) in at least one of the second illumination channels.

Fly's eye condenser according to clause 5, characterized in that a first filter device (728, 1029a-d, 1233,1233a) is arranged in the illumination light of the second illumination channel and at least one second filter device (728, 1029a-d, 1233,1233a) is kept outside the illumination light of the second illumination channel and can be introduced into the illumination light guided in the second illumination channel.

Fly's eye condenser according to clause 6, characterized that the at least second filter device (728, 1029a-d,

1233,1233a) is different from the first filter device (728_f 1029a-d, 1233,1233a).

Fly's eye condenser according to clause 5, 6 and 7, characterized in that the filter device comprises at least one dia- phragm (728) for limiting the illumination light. Fly's eye condenser according to clause 8, characterized in that the diaphragm (728) is movable along the optical axis (OA) . Fly's eye condenser according to clause 8, characterized in that the diaphragm (728) is movable in at least one direction perpendicular to the optical axis (OA) .

Fly's eye condenser according to clause 9 or 10, characterized in that the aperture of the diaphragm (728) limits the size and shape of the illumination light guided in the respective second illumination channel in the plane (P) . Fly's eye condenser according to any of clauses 8 to 11, characterized in that a multiplicity of the second illumination channels have the diaphragms (728} , wherein all the dia~ phragms (728) are arranged in a diaphragm raster (727), and in that all the diaphragms (728) can thereby be moved jointly in the same way. Fly's eye condenser according to any of clauses 8 to 12, characterized in that the apertures of the diaphragms (728) can be altered in terms of their shape and size. Fly's eye condenser according to clause 5 or 6, characterized in that the filter device (1233, 1233a) has at least one filter element (1230a-d, 1231) which can be introduced into the illumination light guided in the second illumination channel, wherein the filter element {1230a-d, 1231) has an actuating device (1234, 1236),

such that the filter element (1230a-d, 1231) can be brought to different positions in the second illumination channel with the aid of the actuating device (1234, 1236) .

Fly's eye condenser according to clause 14, characterized in that the filter device (1233, 1233a) comprises a multiplicity of filter elements <1230a-d, 1231) .

Fly's eye condenser according to any of clauses 5-7, characterized in that the filter elements <1029a~d) is/are embodied as one or a plurality of the following elements: a. linear or locally varying neutral filter structures, fo. dielectric layer structures c. polarization-altering filters d. switchable liquid crystal elements e. phase-altering elements

Fly's eye condenser according to clause 16, characterized in that the filter elements (1029a-d) are arranged on one or a plurality of filter substrates (1027, 1027a-c) .

Fly's eye condenser according to clause 17, characterized in that the filter substrate (1027) is movable in at least one direction perpendicular to the optical axis (OA) in such a way that the at least second filter element (1029a-d) can be introduced into the illumination light guided in the second illumination channel. Fly's eye condenser according to clause 17, characterized in that the filter substrates (1027a~c) are movable independently of one another in a direction perpendicular to the optical axis (OA) , as a result of which the at least second filter element (1029a-d) can be introduced into the illumina tion light guided in the second illumination channel.

Fly's eye condenser according to any of the preceding clauses characterized in that at least one of the ray-defleeting optical elements, in particular all of said ray-deflecting optical elements, is or are embodied as a mirror.

Fly's eye condenser according to any of the preceding clauses characterized in that at least one of the ray-deflecting optical elements, in particular all of said ray-deflecting optical elements, is or are embodied as a refractive lens.

Fly's eye condenser according to any of the preceding clauses characterized in that at least one of the ray-deflecting optical elements, in particular all of said ray-deflecting optical elements, is or are embodied as a d ffractive optical element .

Fly's eye condenser according to any of the preceding clauses, characterized in that it is designed for an operating wavelength of less than 200 nm, more particularly less than 160 nm, and more particularly of less than 15 nm.

Illumination device of a microlithographic projection exposure apparatus, characterized in that the illumination device has at least one fly's eye condenser according to any of the preceding clauses.

Illumination device according to clause 24, characterized in that at least one fly's eye condenser is arranged at least in direct proximity to a pupil plane.

Illumination device according to clause 25, characterized in that at least one fly's eye condenser is arranged at least in direct proximity to a field plane.

Microlithographic projection exposure apparatus comprising an illumination device and a projection objective, wherein, during the operation of the projection exposure apparatus, the illumination device illuminates an object plane of the projection objective and the projection objective images said object plane onto an image plane, characterized in that the illumination device is embodied according to any of clauses 23 to 26.

Microlithographic projection exposure apparatus comprising an illumination device (800) and a projection objective (870), wherein, during the operation of the projection exposure apparatus, the illumination device (800) at least partly illuminates a reticle (860) in an object plane (865) of the projection objective (870) and the projection objective (870) images this illuminated part of this object plane (865) with a scale M onto at least one part of the wafer (880) in the image plane (875),

and wherein the wafer (880) can be moved synchronously with the reticle (860) perpendicular to the optical axis, characterized in that the illumination device (800) has a fly's eye con denser (809) having a diaphragm raster (827) according to clause 12 or 13, and in that the diaphragm raster (827) can be moved perpendicular to the optical axis synchronously with the movement of the reticle (860) . 29. Method for producing a microstructured component, characterized in that, an illumination device (800) at least partly illuminates a reticle (860) in an object plane (865) of a downstream pro- jection objective (870) with an illumination light and the projection objective (870) images this illuminated part of the reticle (860) with a scale M onto at least one part of the wafer (880), the reticle (870) with a mask structure is moved in at least one first direction, the scanning direction, relative to the illumination light, wherein the wafer (880) is moved synchronously with the reti cle (860) at a speed which is in a ratio M with respect to the speed of the reticle (870) , and in that a diaphragm raster (827) arranged in an illumination device (800) in a fly's eye condenser (809) according to clause 12 or 13 in or near a field plane that is optically conjugate with respect to the reticle plane (865) is moved synchronously with the movement of the reticle (860), wherein the wafer (880) is exposed in a scanning fashion in such a way that the diaphragm raster (827) completely blocks the illumination light at the beginning and at the end of the exposure process and that, during the exposure process, the illumination light is released at the beginning and blocked again at the end, synchronously with the movement of the re- tide {860) .

Claims

Patent Claims 1. icrolithographic projection exposure apparatus comprising an illumination device (800) and a projection objective (870),

wherein, during the operation of the projection exposure apparatus, the illumination device (800) at least partly illuminates a reticle (860) in an object plane (865) of the projection objective (870) and the projection objective (870) images this illuminated part of this object plane (865) with a scale M onto at least one part of the wafer (880) in the image plane (875) and wherein the wafer (880) can be moved synchronously with the reticle (860) perpendicular to the optical axis, characterized in that the illumination device (800) has a fly's eye condenser (809) for illuminating a plane (F) comprising a. a first optical element (Rl) having a plurality of first raster elements (21), which is illuminated by a light source (102), and wherein the light beam incident from the light source (102) is split by the first raster elements (21) into convergent light beams with a respective focal point / b. a second optical element (R2) having a plurality of second raster elements (22), wherein each light beam formed by the first raster element (21) is assigned a second raster element (22) and raster element pairs (21, 22) composed in each case of a raster element (21) of the first optical element and a raster element (22) of the second optical element predefine a plurality of first illumination channels; c. a third optical element (R3) having third raster elements (23), wherein each light beam formed by the second raster element (21) is assigned a third raster element (23) and raster element pairs (22, 23) composed in each case of a raster element (22) of the second optical element and a raster element (23) of the third optical element predefine a plurality of second illumination channels;

d. the second raster elements (22) image the first raster elements (21) with an imaging scale (β) into at least one plane (P) , wherein the size of the illuminated region (d') of the second illumination channel in the plane (P) is less than or equal to the size (d) of the illuminated region directly upstream of the first raster elements (21), and a transfer optical unit is disposed downstream of the third raster elements (23) and the third raster elements (23) image all the illuminated regions of the planes (P) into a plane (F) in a superimposing fashion by means of the transfer optical unit and a multiplicity of the second illumination channels have diaphragms (728) , wherein all the diaphragms (728) are arranged in a diaphragm raster (727, 827), and in that all the diaphragms (728, 827) can thereby be moved jointly in the same way and the diaphragm raster (727, 827) arranged in or in the vicinity of the plane (P) in at least one of the second illumination channels and that the diaphragm raster (727, 827) can be moved perpendicular to the optical axis synchronously with the movement of the reticle (860) .

2. Microlithographic projection exposure apparatus according to claim 1, characterized in that the transfer optical unit has, in this order: a. a fourth optical element (R4) having fourth raster elements (24), wherein each light beam formed by the third raster element (23) is assigned a fourth raster element

(24) , b. a fifth optical element (R5) having fifth raster elements (25), wherein each light beam formed by the fourth raster element (24) is assigned a fifth raster element

(25) , c. a condenser lens ( ), which images the light beams into the plane (F) in a superimposing fashion proceeding from the fifth raster elements (25) of the optical element <R5) .

3. Microlithographic projection exposure apparatus according to any of the preceding claims characterized in that at least one of the raster elements, in particular all of said raster elements is or are embodied as a refractive lens.

4. MicroIithographic projection exposure apparatus according to any of the preceding claims character zed in that at least one of the raster elements, in particular all of said raster elements is or are embodied as a cylindrical lens .

5. Microlithographic projection exposure apparatus according to claim 4 characterized in that the cylindrical lenses on at least one optical element (1703, 1704, 1705, 1706, 1707,2103, 2105, 2106, 2107,) are all arranged in the same direction perpendicular to the optical axis {OA) .

6. Microlithographic projection exposure apparatus according to claim 4 characterized in that the cylindrical lenses are arranged on opposite sides of the same optical element (1703, 1704, 1705, 1706, 1707, 2103, 2105, 2106, 2107) in the direction of the optical

7. Microlithographic projection exposure apparatus according to claim 6 characterized in that the cylindrical lenses on one side of the optical element (1703, 1704, 1705, 1706, 1707) are aligned along a first direction perpendicular to the optical axis and the cylindrical lenses on the opposite side of the optical element (1703, 1704, 1705, 1706, 1707) are aligned along a second direction perpendicular to the optical axis and perpendicular to the first direction.

8. Microlithographic projection exposure apparatus according to claim 6 characterized in that the cylindrical lenses on one side of the optical element (2103, 2106, 2107) are aligned along a first direction perpendicular to the optical axis and the cylindrical lenses on the opposite side of the optical element (2103, 2106, 2107) are aligned along a second direction perpendicular to the optical axis and parallel to the first direction.

9. Microlithographic projection exposure apparatus according to claim 5 characterized in that the pitch of the cylindrical lenses on a first optical (1703, 1704, 1705, 1706, 1707, 2103, 2105, 2106, 2107, 2010) element is different to the pitch of the cylindrical lenses on an at least second optical element (1703, 1704, 1705, 1706, 1707, 2103, 2105, 2106, 2107, 2010).

10. Microlithographic projection exposure apparatus according to any of the claims 6 to 8 characterized in that the pitch of the cylindrical lenses on one side of an optical element (2010) is different to the pitch of the cylindrical lenses on the opposite side of the optical element (2010) .

11. Microlithographic projection exposure apparatus according to any of the preceding claims characterized in that the numerical aperture NAI at the image side of the fly's eye condenser is < 0.15

12. Microlithographic projection exposure apparatus comprising an illumination device (800) and a projection objective (870), wherein, during the operation of the projection exposure apparatus, the illumination device (800) at least partly illuminates a reticle (860) in an object plane (865) of the projection objective (870) and the projection objective (870) images this illuminated part of this object plane (865) with a scale M onto at least one part of the wafer (880) in the image plane (875), and wherein the wafer (880) can be moved synchronously with the reticle (860) perpendicular to the optical axis, characterized in that the illumination device (800) has a fly's eye condenser (809) in which the incident light is guided in illumination channels and the illumination channels are separated in first illumination channels with first raster elements and second illumination channels with second raster elements and the first and second raster elements comprise refractive power only in a direction perpendicular to the optical axis (OA) and comprise no refractive power in a direction perpendicular to that direction.

13. Microlithographic projection exposure apparatus comprising according to claim 12 characterized in that the direction of the refractive power of the first raster elements is perpendicular to the direction of the refractive power of the second raster elements.

14. Microlithographic projection exposure apparatus comprising according to claim 12 characterized in that the first and second illumination channels comprise an image plane ( (IIPx, IlPy) and each image plane { (IlPx, IlPy) is imaged in the object plane (865) in a superimposing fashion.

15. Microlithographic projection exposure apparatus according to claim 14 characterized in that the image plane (IIPx) of the first illumination channel and the image plane (IlPy) of the second illumination channel differ in their position along the optical axis (OA) .

16. Microlithographic projection exposure apparatus according to claim 14 characterised in that the image plane (IIPx) of the first illumination channel and the image plane (IlPy) of their second illumination channel coincidence in the position along the optical axis (OA) .

17. Microlithographic projection exposure apparatus according to any of the claims 14 to 16 characterized in that at least one diaphragm raster (827) is positioned in the image plane {IIPx, IlPy) of the fly's eye condenser (809) and in that the diaphragm raster (827) can be moved perpendicular to the optical axis synchronously with the movement of the reticle (860) .

18. Microlithographic projection exposure apparatus according to any of the preceding claims characterized in that between to raster elements (1622a, 1623a, 1622b, 1623b) two optical elements (1631a, 1632a, 1631b, 1632b) are positioned so that the images of two adjacent channels are superimposed between the raster elements (1622a, 1623a, 1622b, 1623b) in one image in a plane (P) to form an expanded channel constriction.

19. Microlithographic projection exposure apparatus according to claim 13 characterized in that two pairs of prisms (1631a, 1631b, 1632a, 1632b) are in troduced between each second and third raster element (1622a, 1622b, 1623a, 1623b) in adjacent illumination channels .

20. Microlithographic projection exposure apparatus according to any of the claims 12-19 characterized in that the fly's eye condenser comprises a diffuser plate (2105) which influences the light guided in an illumina tion channel only in a direction perpendicular to the optical axis (OA) .