WO2008080537A1

WO2008080537A1 - Lithographic projection lens

Info

Publication number: WO2008080537A1
Application number: PCT/EP2007/010962
Authority: WO
Inventors: Olaf Conradi; Dirk Juergens
Original assignee: Carl Zeiss Smt Ag
Priority date: 2006-12-29
Filing date: 2007-12-13
Publication date: 2008-07-10
Also published as: DE102007062265A1

Abstract

Disclosed is a lithographic projection lens (10) comprising an optical array (30) of optical elements (32) between an object plane (O) and an image plane (B) along a direction of diffusion of the light. The optical array (30) has at least one first pupil plane (P1, P2) as well as at least one first and second corrective element (38a, b) for correcting thermally induced optical aberrations, each of which is located in an area that is at least optically close to the at least one first pupil plane (P1, P2).

Description

Projection objective for lithography

The invention relates to a projection objective for lithography.

The invention further relates to a method for correcting thermally induced aberrations of a projection objective for lithography.

Such a projection lens is known from US 6,262,793 Bl.

Such a projection lens is used, for example, in semiconductor lithography for the production of optical components. It has an optical arrangement of optical elements, for example lenses, plane-parallel plates, and / or mirrors, which has a structure of an object-level object (reticle) on a photosensitive layer of a substrate (wafer) arranged in an image plane of the projection objective is, depict. Light rays generated by a light optic pass through the structure during the exposure process and transfer it to the photosensitive layer of the substrate which is subsequently developed thereon, whereby the structure to be imaged is formed.

Due to a high integration density of the structures to be imaged on the substrate, increasing demands are placed on the projection lens, so that it may have largely no aberrations. The aberrations of a projection lens may, for example, be intrinsically conditioned to be caused during the manufacturing or assembly process of the optical elements. Furthermore, aberrations occur during operation of the projection lens, as at least one optical element of the optical arrangement is heated by the light rays passing through the projection lens and the optical properties of the at least one optical element, for example its shape and / or its material properties (refractive index, etc.). , change. These operational aberrations can occur briefly or reversibly, so that the optical properties of the at least one optical element are not permanently influenced. Furthermore, lifetime effects have a lasting effect on the optical properties, so that the optical elements are thereby irreversibly changed (compacification, dilution).

It is well known that aberrations can lead to different field gradients in the image plane of the projection objective. The field profile of a wavefront has field-dependent and field-constant components, so that both types of wavefront characteristics must be corrected effectively.

To compensate for production-related or temperature-induced aberrations, in particular magnification errors and distortions due to aberrations, the projection objective known from US Pat. No. 6,262,793 B1 has two correction elements arranged immediately adjacent in the form of cylindrical lenses whose surfaces have a non-rotationally symmetric aspherization. In order to effectively correct the aberrations, the surfaces of the lenses are appropriately processed prior to installation, for example, in or near the pupil plane of the projection lens, and the lenses can be additionally rotated about the optical axis and translated along the optical axis.

A disadvantage of this projection lens is that a correction effect based on a rotation of the two lenses is limited, since only specific imaging errors can be effectively corrected. In particular, complex higher-wave field courses of aberrations are, for example, during operation of the Projection lens can occur due to the arrangement of two lenses or their rotation about the optical axis only limited correctable.

Another disadvantage of the projection lens is the use of cylindrical lenses as correction elements, since these are relatively expensive to handle due to processing their surface and their high centering accuracy when installed in the projection lens, thereby significantly increasing the manufacturing and maintenance costs of the known projection lens.

It is also disadvantageous that a common arrangement of the two lenses in or near the pupil plane is often not possible due to the design of the projection lens whose optical arrangement in the area of the pupil plane particularly many optical elements, and / or due to the space requirement of the two lenses. Thus, a correction option using the two lenses is only applicable to those projection objectives that have sufficient space in the area of the pupil plane.

Another disadvantage of the known projection lens is that the lens surfaces are not optically changeable during operation of the projection exposure apparatus. Consequently, a corrective effect of the two lenses is often insufficient because, in particular, unpredictable aberrations based on heating of the optical elements can not be achieved by rotating the two correction elements.

It is therefore an object of the invention to improve the projection lens described above to the effect that it allows a precise imaging of a structure of a reticle on a photosensitive layer of a wafer with little technical effort.

It is also an object of the invention, the above-mentioned method for correcting thermally induced aberrations of a projection lens for the To improve lithography so that it corrects temperature-induced aberrations particularly effective and flexible.

According to the invention, the object is achieved by a projection objective for lithography, which has an optical arrangement of optical elements along a light propagation direction between an object plane and an image plane, wherein the optical arrangement has at least a first pupil plane, wherein the optical arrangement comprises at least a first and a second correction element for correcting thermally induced aberrations and wherein the at least first and second correction elements are each arranged in a region which is at least optically close to the at least first pupil plane.

According to the invention, the object is achieved by a method for correcting thermally induced aberrations of a projection objective for lithography, the projection objective having an optical arrangement of optical elements along a light propagation direction between an object plane and an image plane, the optical arrangement having at least a first pupil plane, wherein the optical arrangement has at least a first and a second correction element for correcting the thermally induced aberrations, wherein the at least first and second correction element are each arranged in a region which is at least optically close to the at least first pupil plane, and wherein a correction position of the at least two correction elements determined is corrected in the predominantly field-constant and / or field-dependent portions of the aberrations.

In the projection objective according to the invention, whose optical arrangement of optical elements between the object plane and the image plane has at least one first pupil plane, at least two correction elements are arranged in those regions which are at least optically close to the at least first pupil plane of the projection objective in order to effectively correct aberrations based on heating at least one of the optical elements of the projection lens. According to the invention, an "arrangement in an area at least optically close to a pupil plane" is to be understood as meaning an arrangement of a correction element within the projection objective whose optical effect is approximately equal to an optical effect of a correction element arranged in the pupil plane. This term also includes the placement of a correction element exactly in the pupil plane of the projection lens and the arrangement of a plurality of optical elements between the correction element and the pupil plane.

A criterion for classifying whether a selected position of the correction element is at least optically close to a pupil plane is a ratio of principal ray height to marginal ray height in this position. If this ratio is zero or approximately zero, for example less than 1/4, then one speaks of a position at least optically close to the pupil plane. Here, "main beam height" is to be understood as meaning the beam height of the main beam of a field point of the object plane with the maximum field height in terms of magnitude. The term "edge beam height", however, denotes the beam height of a beam with maximum aperture, starting from the center of the field of the object plane.

It is generally known that an optical element arranged in a pupil plane has an influence on the field constant progression of the wavefront in the image plane of the projection lens, while an optical element provided in the vicinity of the pupil plane influences the field-dependent component of the field profile. The arrangement of the at least two correction elements in at least optically near-pupil areas therefore advantageously allows not only a correction of a field-constant course of the aberrations but also an effective correction of remaining field-dependent portions of the aberrations.

A further advantage of the projection objective is that it offers different possible arrangements of the at least two correction elements, which are flexibly adaptable to the respective correction requirements depending on the design of the projection objective and the space requirement of the correction elements. This allows the occurring Abnormal aberration also independent of external influences, for example. An illumination of the projection lens, be corrected without further technically complex measures effectively.

In a preferred embodiment, the at least two correction elements are each an optical element, preferably a plane parallel plate, a mirror and / or a lens, each with suitably optically effective surfaces.

This measure has the advantage that the correction elements, which are likewise designed as optical elements, are particularly easy to integrate into the optical arrangement of the optical elements and thus into the light path of the projection objective. The configuration of the correction elements as plane-parallel plates, mirrors and / or lenses, each with suitably optically effective surfaces, advantageously provide various design options for the correction elements, which can be implemented depending on the design of the projection objective. In this case, the correction elements can each be configured differently from one another. According to the invention, an "optically active surface" is to be understood as meaning a surface which is used by the light in the installed state of the associated correction element in the projection lens.

In a further preferred embodiment, the optical elements have a non-exchangeable lens and / or a mechanically deformable lens.

This measure advantageously represents a particularly frequently occurring embodiment of the projection lens whose image errors based on heating of its optical elements are compensated by the correction elements.

In a further preferred embodiment, the first correction element and / or the second correction element are optically variable. In this context, an "optical change" of the at least first and / or second correction element means a change in its optical properties, in particular its shape and / or material properties (refractive index, thermal expansion coefficient, etc.).

This measure advantageously enables an additional correction of the thermally induced aberrations which can be carried out very quickly. For this purpose, the first and / or second correction element have mechanical or thermal manipulators, the actuators of which act on the surface of the correction elements in order to exert a mechanical or thermal force on them.

In a further preferred embodiment, the first correction element and / or the second correction element are adjustable in position, in particular designed to be decentered.

This measure allows a further, particularly rapid correction of the thermally induced aberrations by changing the arrangement of the at least first and / or second correction element in the projection objective. "Positional adjustability" generally means a change in the position of the correction elements, so that the first and / or second correction element are rotatable about an optical axis, tiltable with respect to the optical axis and slidable along or transverse to the optical axis.

In a further preferred embodiment, the first correction element and / or the second correction element are exchangeable for at least one other correction element.

This measure effects a replacement of the first and / or second correction element by at least one other correction element, which can advantageously support the correction of thermally induced aberrations. For this purpose, the projection lens on a fast changer device, in the preferably several exchange elements with different Oberflächenasphärisie- ments are kept.

In a further preferred embodiment, the first and / or second correction element can be heated for correction.

By heating one of the two correction elements or both correction elements, the already mentioned above optical change of the correction or the correction elements can be achieved in a simple manner, wherein at least one of the correction elements corresponding to a heating / cooling is assigned.

In a further preferred embodiment, the at least two correction elements are arranged directly adjacent.

This measure has the advantage that the aberrations can be corrected particularly easily, since no additional optical elements arranged between the two correction elements influence the beam path of the light and must be taken into account for the overall correction effect of the two correction elements.

In a further preferred embodiment, the at least two correction elements are arranged at optically conjugate positions.

"Optically conjugate positions" of at least two correction elements are to be understood as meaning those positions whose ratios of principal ray height to marginal ray height are approximately equal.

This measure advantageously ensures that the respective optical effects of the individual correction elements are superimposed on the field profile in order to optimally correct the aberrations that occur. In a further preferred embodiment, the at least two correction elements are arranged at a distance from each other.

This measure has the advantage that, in contrast to a non-spaced arrangement of the at least two correction elements, for example. By a different choice of spacing, a variety of beam guidance options of the light can be provided in the projection lens, which can be utilized for the correction of thermally induced aberrations ,

The configuration of the projection objective according to the invention can be used particularly advantageously if the optical arrangement of the projection objective has at least two pupil planes, in which case the at least first and second correction element is optically close to the first and / or second pupil plane.

The two correction elements can thus be distributed to correction positions in both and / or near both pupil planes, which for reasons of space, which are caused by the design of the projection lens, allows a higher correction potential than if only one pupil plane is present, in which both correction elements may be off Space reasons can not be arranged.

In a further preferred embodiment, the first correction element in the at least first pupil plane and the second correction element in the at least second pupil plane are arranged.

This measure has the advantage that by arranging the at least two correction elements in each case one pupil plane, field-constant portions of the aberrations can be corrected particularly effectively, since the respective correction effects of the at least two correction elements overlap. In a further preferred refinement, the first correction element is arranged in a pupil plane and the second correction element is arranged at least optically close to a pupil plane of the at least first and second pupil planes.

This measure advantageously ensures a particularly effective correction of field-constant and field-dependent profiles of the aberrations in the image plane of the projection lens that can be adapted to the respective projection objective and the aberrations that occur.

In a further preferred embodiment, as seen in the light propagation direction, the first correction element is arranged in front of a pupil plane and the second correction element is arranged behind a pupil plane of the at least first and second pupil planes.

This measure has the advantage that the optical effect of the correction elements arranged near a pupil plane in the image plane of the projection lens shows a field-dependent course, so that advantageously the field-dependent portion of the thermally induced aberrations can be corrected particularly well by the additive effect of the at least two correction elements.

In a further preferred embodiment, the two correction elements are arranged symmetrically with respect to the at least first pupil plane.

This measure has the advantage that the correction elements spaced equidistant from the first pupil plane have an additive effect on the field-constant component and an at least reduced effect on the field-dependent component of the imaging errors. In this case, the desired correction effect can be influenced by the respective configuration of the correction elements. In a further preferred refinement, a distance of the first correction element from the at least first pupil plane is not equal to a distance of the second correction element from the at least first pupil plane.

This measure advantageously makes it possible, depending on the choice of the distances of the two correction elements to the first pupil plane, to predominantly correct the field-constant or field-dependent components of the aberrations.

In a further preferred embodiment, as seen in the light propagation direction, the at least two correction elements are arranged in front of the at least first pupil plane.

In a further preferred embodiment, as seen in the light propagation direction, the at least two correction elements are arranged behind the at least first pupil plane.

The arrangement of the correction elements outside of pupil planes advantageously corrects a field-dependent course of the aberrations in the image plane of the projection objective. Further, the arrangement of the correction elements on one side of a pupil plane enables independent intervention in the course of upper and lower marginal rays of the projection lens.

In a further preferred refinement, if the aberrations are predominantly caused close to the at least first pupil plane, the at least two correction elements are arranged at least optically close to the at least second pupil plane.

This measure has the advantage that the aberrations generated optically close to the at least first pupil plane can be corrected at the optically conjugate location, namely optically in the vicinity of the at least second pupil plane. Is the second pupil plane in the light propagation direction seen before the arranged at least first pupil plane, so first an aberration is induced in the projection lens by the correction elements, which is compensated by the actual aberration.

In a further preferred embodiment, the optical arrangement has exactly two correction elements.

This measure has the advantage that correcting aberrations with exactly two correction elements is easier to carry out than correcting with three or more correction elements. In this case, the first correction element can be used to correct field-constant portions of the aberrations, while the second correction element compensates for a field-dependent course of the aberrations.

In a preferred embodiment of the method according to the invention, the correction position of the at least two correction elements is determined by selecting different positions for the at least two correction elements between two optical elements adjacent to the correction elements and an influence of the arrangement of the at least two correction elements in these positions on the aberrations is determined.

This measure has the effect that different arrangement possibilities of the two correction elements are determined by calculation and from these the arrangement is selected whose optical effect on the thermally induced aberrations is greatest. Thus, the best correction of the aberrations without actually changing the arrangement of the correction elements can, for example, be calculated and optimally adapted to the design of the projection objective and the aberrations that occur.

In a further preferred embodiment, the suitable positions are selected in mutually equidistant intervals. This measure advantageously makes possible a systematic determination of the optimal arrangement positions of the correction elements.

In a further preferred embodiment, an illumination mode of the projection objective is taken into account when determining the optimum position.

The heating of the optical elements is determined in particular by the illumination of the projection lens, so that the thermally induced aberrations can be advantageously corrected particularly effective when the respective illumination of the projection lens is taken into account.

Further advantages and features will become apparent from the following description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the specified combinations but also in other combinations or alone, without departing from the scope of the present invention.

The invention will be described below with reference to some selected embodiments in conjunction with the accompanying drawings and described. Show it:

1 shows a schematic representation of a projection exposure apparatus with an illumination system and a projection objective according to the invention;

Fig. 2 is a detailed embodiment of the projection lens in Fig. 1;

FIGS. 3A-3F show various arrangements of two correction elements with respect to a first pupil plane of the projection objective in FIG. 2; FIG. 4 shows different illumination modes of the projection objective in FIG. 2; FIG.

FIG. 5 shows various arrangement positions of the correction elements in FIG. 2; FIG.

FIG. 6A shows position-dependent RMS values of wavefront curves of the projection objective in FIG. 2 as a function of the illumination modes in FIG. 4, wherein the projection objective has only a first correction element;

6B wavefront profiles of the projection objective in FIG. 2, which shows the RMS

Associated with values in Fig. 6A;

FIG. 6C are cross sections through the wavefront profiles in FIG. 6B; FIG.

FIG. 7A wavefront course of the projection objective in FIG. 2 as a function of the illumination modes in FIG. 4, wherein the projection objective has the first correction element in a first position;

FIG. 7B cross sections through the wavefront profiles in FIG. 7A; FIG.

FIG. 7C wavefront profile of the projection objective in FIG. 2 as a function of the illumination modes in FIG. 4, wherein the projection objective has a second correction element in a second position; and

7D are cross sections through the wavefront profiles in FIG. 7C.

In Fig. 1 is provided with the general reference numeral 10 projection lens of a projection exposure apparatus 12 is shown. Further details of the projection lens 10 are shown in FIG.

The projection exposure apparatus 12 is, for example, in semiconductor microlithography for the production of finely structured components, for example. Transistors, switches, etc., used to arranged on a holder 14 structure of a reticle 16, which is arranged in an object plane O of the projection lens 10, on a arranged on a holder 18 photosensitive layer of a substrate 20 (wafer), which is arranged in an image plane B of the projection lens 10 is to picture. For this purpose, the projection exposure apparatus 12 has a light source 22 and an illumination optical system 24 arranged between the light source 22 and the reticle 16. Light rays 26 emitted from the light source 22 pass through the illumination optics 24, the reticle 16 and the projection objective 10 and strike the photosensitive layer of the substrate 20. After developing the substrate 20, the structure to be imaged is formed thereon.

The projection objective 10 has an optical arrangement 30 of optical elements 32, here illustrated four optical elements 32a-d in the form of four lenses 34a-d, which are respectively received on both sides by means of a clamping mechanism in a socket 36a-d.

In addition to intrinsic imaging aberrations, temperature-induced aberrations due to heating of at least one optical element 32a-d, in this case the optical element 32d, are produced in the projection objective 10 during operation of the projection exposure apparatus 12. This local heating leads to a local change in the optical properties of the optical element 32d, for example, to a change in its shape and / or its material properties (refractive index, thermal expansion coefficient, etc.).

The aberrations that occur as a result during operation show different field profiles in the image plane B of the projection lens 10, each of which has a field-constant and field-dependent component.

In order to effectively correct predominantly field-constant and / or field-dependent portions of the total wave front profile of the thermally induced aberrations, the optical arrangement 30 has at least two further optical elements 37 trained correction elements 38, here exactly two correction elements 38a, b, which are formed as plane-parallel plates 40a, b and positively received in sockets 42a, b. The two correction elements 38a, b are further arranged directly adjacent to each other and slightly spaced in areas which is at least optically close to a pupil plane Pi of the projection lens 10.

An arrangement in an area "at least optically close to the first pupil plane Pi" is to be understood as meaning not only an arrangement in the first pupil plane Pi or in an area spatially close to the first pupil plane Pi two correction elements 38a, b whose effect is optically approximately equal to an arrangement in the first pupil plane Pi, so that, for example, a plurality of optical elements 32 between the two correction elements 38a, b may be arranged.

A criterion according to which an area which is optically close to a pupil plane can be determined is a ratio of principal ray height to marginal ray height in a selected position which in this case must be approximately zero, for example less than 1/4, in particular less than 1/10 , In this context, the term "main beam height" is to be understood as meaning a beam height of a main beam of a field point of the object plane O with maximum field height and "beam edge height" as the beam height of a beam with maximum aperture starting from the center of the field of object plane O.

In the exemplary embodiment shown, the projection objective 10 additionally has a second pupil plane P2 which, viewed in the light propagation direction, is arranged behind the first pupil plane Pi.

FIG. 2 shows a detailed exemplary embodiment of the projection objective 10 shown schematically in FIG. 1, whose optical arrangement 30 comprises a plurality of optical elements 32 in the form of lenses 34, mirrors 44 and plane-parallel plates 46 has, which are seen along the light propagation direction arranged one behind the other.

The projection objective 10 has three pupil planes P1-P3 and four field planes Fi-F4, the first or last field plane Fi, F4 corresponding to the object plane O or the image plane B of the projection objective 10.

In the region of the first pupil plane Pi, the two correction elements 38a, b are arranged to correct thermally induced aberrations, in this case coma and astigmatism. The first and second correction elements 38a, b are each designed as a plane-parallel plate 40a or curved lens 48a and arranged in the first pupil plane Pi or in the light propagation direction behind the pupil plane Pi immediately adjacent to the first correction element 38a.

The surfaces of the optical elements 32 and the two correction elements 38a, b are designed to be optically effective, wherein for the purposes of the present invention an "optically effective surface" means that this surface in the installed state of the associated optical element or correction element in the projection objective 10th is used by the light. This surface can be, for example, focusing, defocusing or beam guiding (jet folding) and have rotationally symmetric and non-rotationally symmetric fits corresponding to different orders of the Zernike coefficients.

The correction elements 38a, b serve to correct aberrations caused by heating of local regions of the optical elements 32 as a result of, for example, a dipole or quadrupole illumination of the projection lens 10 produced by the illumination optical system 24. In the exemplary embodiment shown, the correction element 38a, since it is arranged in the first pupil plane Pi, corrects a field-constant course of the aberrations in the image plane B, which here assumes, for example, 70% of the total wavefront error profile. A remaining field dependent The proportion of the field profile of 30% is optimally compensated by the second correction element 38b.

The aberrations can occur in front of or behind the correction elements 38a, b in the light propagation direction. If the aberrations occur in optical elements 32, which are arranged in front of the correction elements 38a, b in the light propagation direction, the aberrations are corrected after their formation by the correction elements 38a, b. On the other hand, if the aberrations are caused behind the correction elements 38a, b in the light propagation direction, they are corrected in such a way that corresponding aberrations are first induced by the correction elements 38a, b in the wavefront profile of the projection objective 10, which are then caused by heating behind the first pupil plane Pi arranged optical elements 32 based aberrations can be compensated.

FIGS. 3A-3F show various configurations and arrangements of the two correction elements 38a, b arranged in the region of the first pupil plane Pi between the optical elements 32a, b formed as the lenses 34a, b. Further optical elements 32, which may be provided between the optical elements 32a, b, are not shown for the sake of clarity.

FIG. 3A shows the case shown in FIG. 2 that the correction element 38a is arranged in the pupil plane Pi, while the correction element 38b is arranged behind the pupil plane Pi, viewed in the light propagation direction. In contrast to FIG. 2, the first correction element 38a is designed as a lens 48a and the second correction element 38b as a plane-parallel plate 40b. In FIG. 3B, the correction element 38a designed as a plane-parallel plate 40a is arranged in front of the first pupil plane Pi and the correction element 38b designed as another plane-parallel plate 40b is arranged in the first pupil plane Pi. As shown in FIGS. 3C, 3D, both correction elements 38a, 38b designed as lenses 48a, b or plane-parallel plates 40a, b can be arranged either in front of or behind the first pupil plane Pi as viewed in the light propagation direction. The correction elements 38a, 38b may also be such be arranged such that both are displaced from the first pupil plane Pi in respectively different directions, so that the first correction element 38a is arranged between the optical element 32a and the first pupil plane Pi and the second correction element 38b between the pupil plane Pi and the optical element 32b ( see Fig. 3E, 3F). In this case, a distance di of the first correction element 38a to the pupil plane Pi be non-38b to a distance d ₂ of the second correction element to the first pupil plane Pi, so that the two correcting members 38a, b asymmetrically with respect to the first pupil plane Pi are arranged (see. Fig. 3E ). It is also possible for the two correction elements 38a, 38b to be arranged symmetrically about the first pupil plane Pi (see FIG. 3F). Both embodiments advantageously make it possible to influence upper and lower Komastrahlen independently of each other, both correction elements 38a, b additionally exert an additive effect on the field constant course of aberrations. In FIG. 3E, the correction elements 38a, b are designed as lenses 48a, b and in FIG. 3F as plane-parallel plates 40a, b. Depending on the design of the projection lens 10, the correction elements 38a, b may also be designed as refractive elements instead of transmissive elements, which are additionally suitable for beam deflection. As illustrated in FIG. 2, the correction element 38a, b may be formed as the mirror 44 received in the second pupil plane P2 to simultaneously correct the aberrations and guide the beams 28 of light.

Referring again to Fig. 2, the correction elements 38a, b may also be arranged in regions which are at least optically close to different pupil planes Pi-P ₃ , respectively. Here, it is for example. Possible that both correction elements 38a, b in each of a pupil plane P1-P3 or that only the first correction element 38a in a pupil plane Pi-P ₃ and that second correction element 38b at least optically close to another pupil plane P-P ₃ are arranged, wherein seen in the light propagation direction, the second correction element 38b is arranged in front of and behind the respective pupil plane P1-P3. Another possibility for arranging the two correction elements 38a, b in the projection objective 10 is that both correction elements 38a, b are optically close, but outside a pupil plane P1-P3 are arranged, wherein any arrangement with respect to the position with respect to the respective pupil plane P1-P3 and the distance to the respective pupil planes P1-P3 is possible.

It is also possible to arrange the two correction elements 38a, b at optically conjugate positions. "Optically conjugate positions" are to be understood as meaning those positions in the projection objective 10 whose respective ratio of principal ray height to marginal ray height is approximately the same, so that the optical effect of the respectively arranged correction elements 38a, b is also approximately the same.

For better correction of the thermally induced aberrations, furthermore, the first correction element 38a and / or the second correction element 38b are exchangeable during the operation of the projection objective 10, ie. H. The first correction element 38a and / or the second correction element 38b can be partially or fully automatically removed from a light path of the projection lens 10 by means of a rapid changer mechanism or at least one other correction element can be introduced into the light path. It is also possible for the first correction element 38a and / or the second correction element 38b to have a plurality of replacement correction elements in the changer mechanism, which can then best correct any occurring aberration with other optical properties after their respective introduction into the projection objective 10.

The first correction element 38a and / or the second correction element 38b can furthermore be actively optically variable depending on the correction effect of the thermally induced aberrations, so that corresponding mechanical deformation manipulators (not shown) are assigned to them and / or they can also be equipped with thermal manipulators ( not shown) that heat or cool the correction elements 38a, b to set a desired optical correction effect in the correction elements 38a, b. The first correction element 38a and / or the second correction element 38b may additionally be configured so as to be positionally adjustable in order to achieve a specific optical corrective effect of the aberrations based on heating of the optical elements 32, manipulators for positional adjustment (not shown) corresponding to the respective correction elements 38a, b being associated. In this context, "positionally adjustable" means that the respective correction element 38a, b is rotatable about an optical axis A, tiltable with respect to the optical axis A, or displaceable along the optical axis A and / or transversely to the same, ie decentered is.

In addition to the correction elements 38a, b, at least one optical element 32 of the optical arrangement 30 can be embodied as an exchangeable element and / or as an optically variable element and / or as a position-adjustable element, so that the overall correction effect of the projection objective 10 is increased.

The correction effect of thermally induced aberrations by means of an optical correction element 38a and by means of the correction elements 38a, b for different illumination modes of the projection objective 10 will be described below by way of example.

FIG. 4 shows eleven different illumination modes 52a-k, which are recorded as a scan-integrated overall wavefront of an empty exposure of the projection objective 10 with comparatively similar light sources 22. The complex illumination modes 52a-k produce, for example, dipole or quadrupole illuminations, annular or even asymmetrical illumination of the optical elements 32.

If only one correction element 38a, in this case the plane-parallel plate 40a, is arranged at least optically close to the first pupil plane Pi in different positions 54a-e for correcting the aberrations caused by the illumination modes 52a-k, which, as shown in FIG. 5, with respect to the light propagation direction seen before the first correction element 38a arranged optical element 32a Depending on the position, the remaining square mean values (RMS values) 55a-k shown in FIG. 6A result with respect to the total wavefront integrated in the image plane B for the Zernike coefficients Z5-Z36. The associated to the positions 54a-e Distance Xi-X ₅ to the optical element 32a is between 3 mm and 32 mm and increases respectively.

Averaged over all illumination modes 52a-k, position 54b represents the optimal correction position for the correction element 38a since illumination-dependent wavefront peak-to-valley values are between 20 nm and 30 nm. Further, the RMS values 55a-k of position 54b for all illumination modes 52a-k are between 0.8 nm and 5.3 nm, which are the lowest values compared to the other positions 54a, c-d.

FIGS. 6B and 6C show the wavefronts 56a-k associated with the respective illumination modes 52a-k in the image plane B of the projection objective 10 and a cross-section 58a-k through the respective wavefront 56a-k in the horizontal or vertical direction.

In contrast to this, if two correction elements 38a, b designed as plane-parallel plates 40a, b are used to correct the aberrations of the projection lens 10 caused by the illuminations 52a-k shown in FIG. 4 and are arranged at the aforementioned different positions 54a-e, this results averaged over all illumination modes 52a-k, peak-to-valley values of the associated total wavefronts in the image plane B of the projection objective 10 are from 2 nm to 18 nm. This corresponds to a deformation of the wavefronts that is higher by a factor of 1.5-2, so that the imaging aberrations occurring be corrected more effectively than with only one correction element 38a.

FIGS. 7A, 7C and 7B, 7D respectively show the illumination-dependent wavefronts 60a-k and 62a-k for the first correction element 38a arranged in the position 54a and the correction element 38b arranged in the position 54e associated cross-sections 64a-k, 66a-k through the respective wavefronts 60a-k, 62a-k in the horizontal and vertical directions, respectively. The positions 54a, e of the correction elements 38a, b correspond to their optimal correction positions for the desired correction effect. They are determined by choosing a plurality of different positions 54a-e between two optical elements 32a, b adjacent to the correction elements 38a, b, and an influence of any arrangement of the two correction elements 38a, b in these positions 54a-e on the aberrations that occur is determined. In this case, the positions 54a-e can be selected arbitrarily, for example equidistant from one another. In the determination of the optimal positions 54a, e, the respective illumination 52a-k of the projection lens 10 is also taken into account.

Claims

claims

A projection lens for lithography comprising an optical array (30) of optical elements (32) along a light propagation direction between an object plane (O) and an image plane (B), the optical array (30) including at least a first pupil plane (Pi, P ₂ ), the optical assembly (30) comprising at least first and second correction elements (38a, b) for correcting thermally induced aberrations, and wherein the at least first and second correction elements (38a, b) are each disposed in a region, which is at least optically close to the at least first pupil plane (Pi, P2).

2. Projection lens according to claim 1, wherein the at least two correction elements (38a, b) each have an optical element (37), preferably a plane parallel plate (40a, b), a mirror and / or a lens (48a, b) each for the Correction optically effective surfaces.

3. Projection objective according to claim 1 or 2, wherein the first and / or second correction element (38a, b) is deformable for correction.

4. Projection objective according to one of claims 1 to 3, wherein the first correction element (38a) and / or the second correction element (38b) is optically variable.

5. Projection lens according to one of claims 1 to 4, wherein the first correction element (38a) and / or the second correction element (38b) is positionally adjustable, in particular decentered.

6. Projection objective according to one of claims 1 to 5, wherein the first and / or second correction element (38a, b) is heatable for correction.

7. Projection objective according to one of claims 1 to 6, wherein the first correction element (38a) and / or the second correction element (38b) is exchangeable for at least one other correction element.

8. Projection objective according to one of claims 1 to 7, wherein the at least two correction elements (38a, b) are arranged directly adjacent.

9. A projection lens according to any one of claims 1 to 8, wherein the at least two correction elements (38 a, b) are arranged at optically conjugate positions.

10. projection lens according to one of claims 1 to 9, wherein the at least two correction elements (38 a, b) are arranged spaced from each other.

11. The projection objective according to claim 1, wherein the optical arrangement has at least one second pupil plane (Pi, P2), and wherein the at least first and second correction elements (38a, b) are aligned with the first and / or second pupil plane (FIG. Pi, P2) is optically close.

12. Projection objective according to claim 11, wherein the first correction element (38a) in the at least first pupil plane (Pi) and the second correction element (38b) in the at least second pupil plane (P2) is arranged.

13. The projection objective as claimed in claim 11, wherein the first correction element in a pupil plane and the second correction element are arranged at least optically close to a pupil plane of the at least first and second pupil planes.

14. Projection objective according to one of claims 11 to 13, wherein seen in the light propagation direction, the first correction element (38a) in front of a pupil Lanebene and the second correction element (38b) behind a pupil plane of the at least first and second pupil planes (Pi, P2) are arranged.

15. The projection objective according to claim 11, wherein, if the aberrations are predominantly caused close to the at least first pupil plane, the at least two correction elements are arranged at least optically close to the at least second pupil plane.

16. Projection objective according to one of claims 1 to 15, wherein the two correction elements (38a, b) are arranged symmetrically with respect to the at least first pupil plane (Pi).

17. Projection objective according to claim 1, wherein a distance (di) of the first correction element (38a) to the at least first pupil plane (Pi) is not equal to a distance (d2) of the second correction element (38b) to the at least first pupil plane (Pi). is.

18. Projection objective according to one of claims 1 to 17, wherein, seen in the light propagation direction, the at least two correction elements (38a, b) are arranged in front of the at least first pupil plane (Pi).

19. Projection objective according to one of claims 1 to 18, wherein seen in the light propagation direction, the at least two correction elements (38 a, b) are arranged behind the at least first pupil plane (Pi).

20. Projection objective according to one of claims 1 to 19, wherein the optical arrangement (30) has exactly two correction elements (38a, b).

21. A method for correcting thermally induced aberrations of a projection objective (10) for lithography, wherein the projection objective (10) comprises an optical arrangement (30) of optical elements (32) along a Light propagation direction between an object plane (O) and an image plane (B), the optical device (30) having at least a first pupil plane (Pi, P2), the optical device (30) comprising at least a first and a second correction elements (38a, b) for correcting the thermally induced aberrations, wherein the at least first and second correction elements (38a, b) are each arranged in a region which is at least optically close to the at least first pupil plane (Pi, P2), and wherein a correction position (54a , e) the at least two correction elements (38a, b) is determined in which predominantly field-constant and / or field-dependent portions of the aberrations are corrected.

22. Method according to claim 21, wherein the correction position (54a, e) of the at least two correction elements (38a, b) is determined by different positions between two optical elements (32a, b) adjacent to the correction elements (38a, b). 54a-e) for the at least two correction elements (38a, b) are selected and an influence of the arrangement of the at least two correction elements (38a, b) in these positions (54a-e) on the imaging errors is determined.

23. The method of claim 22, wherein the different positions (54a-e) are selected at mutually equidistant intervals.

24. The method according to any one of claims 21 to 23, wherein in determining the optimal position (54a, e) a lighting mode (52a-k) of the projection lens (10) is taken into account.

25. The method according to any one of claims 21 to 24, wherein the at least two correction elements (38a, b) are arranged immediately adjacent.

26. The method of claim 19, wherein the at least two correction elements are arranged at optically conjugate positions.

27. The method according to any one of claims 21 to 26, wherein the at least two correction elements (38a, b) are arranged spaced from each other.

28. The method according to any one of claims 21 to 27, wherein the at least two correction elements (38a, b) each have an optical element (37), preferably a plane-parallel plate (40a, b), a mirror and / or a lens (48a, b) each with suitable optically active surfaces.

29. The method according to any one of claims 21 to 28, wherein the first correction element (38a) and / or the second correction element (38b) is deformed for correction.

30. The method according to any one of claims 21 to 29, wherein the first correction element (38a) and / or the second correction element (38b) is optically changed.

31. The method according to any one of claims 21 to 30, wherein the at least first correction element (38a) and / or the at least second correction element (38b) positionally adjusted, in particular decentered.

32. Method according to claim 21, wherein the at least first correction element (38a) and / or the at least second correction element (38b) are heated for correction.

33. The method according to any one of claims 21 to 32, wherein the at least first correction element (38a) and / or the at least second correction element (38b) are replaced by at least one other correction element.

34. Method according to claim 21, wherein the optical arrangement (30) has at least one second pupil plane (Pi, P ₂ ), and wherein the at least first and second correction elements (38a, b) move to the first and / or second pupil plane (Pi, P ₂ ) are arranged optically close.

35. The method of claim 34, wherein the first correction element (38a) in a pupil plane and the second correction element (38b) at least optically close to a pupil plane of the at least first and second pupil planes (Pi, P ₂ ) are arranged.

36. The method of claim 34 or 35, wherein seen in the light propagation direction, the first correction element (38 a) before a pupil plane and the second correction element (38 b) behind a pupil plane of the at least first and second pupil planes (Pi, P ₂ ) are arranged.

37. A method according to any one of claims 34 to 36, wherein if the aberrations predominantly close to the at least first pupil plane (Pi) are caused, at least two correction elements (38a, b) are arranged at least optically close to at least a second pupil plane (P ₂₎ ,

38. The method according to any one of claims 21 to 37, wherein the two correction elements (38a, b) are arranged symmetrically with respect to the at least first pupil plane (Pi).

39. Method according to claim 21, wherein a distance (di) of the first correction element (38a) from the at least first pupil plane (Pi) is not equal to a distance (d ₂ ) of the second correction element (38b) from the at least first pupil plane (Pi ) is selected.

40. Method according to claim 21, wherein, viewed in the light propagation direction, the at least two correction elements (38a, b) are arranged in front of the at least first pupil plane (Pi).

41. Method according to one of claims 21 to 40, wherein, viewed in the light propagation direction, the at least two correction elements (38a, b) are arranged behind the at least first pupil plane (Pi).

42. The method according to any one of claims 21 to 41, wherein exactly two correction elements (38a, b) at least optically close to the at least first and / or second pupil plane (Pi, P ₂ ) are arranged.