# Patent

## Title
Lithography projection objective, and a method for correcting image defects of the same

## Abstract

The disclosure provides a microlithography projection objective which includes a plurality of optical elements along the optical axis of the projection objective. The plurality of optical elements includes a last optical element and a penultimate optical element. A distance between the last optical element and the penultimate optical element is variable. The disclosure also provides a microlithography projection exposure machine including such a projection objective, and a method of making semiconductor components using such a projection exposure machine.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
The present application is a continuation of U.S. patent application Ser. No. 12/715,473, filed Mar. 2, 2010, now U.S. Pat. No. 8,054,557, which is a continuation of U.S. patent application Ser. No. 12/265,090, filed on Nov. 5, 2008, now U.S. Pat. No. 7,692,868, which is a continuation of U.S. patent application Ser. No. 11/955,662 filed on Dec. 13, 2007, now U.S. Pat. No. 7,463,423, which is a continuation of International Patent application PCT/EP2006/005059 filed on May 26, 2006, which claims to U.S. provisional application No. 60/690,544, filed Jun. 14, 2005.


BACKGROUND OF THE INVENTION
The invention relates to a lithography projection objective for imaging a pattern arranged in an object plane of the projection objective onto a substrate to be arranged in an image plane of the projection objective.
The invention further relates to a method for correcting image defects in the case of a lithography projection objective that can be tuned to immersion operation.
A projection objective of the type mentioned at the beginning is preferably used for microlithography projection exposure machines for producing semiconductor components and other finely structured subassemblies. A projection objective serves the purpose of projecting patterns from photomasks or graticules, which are also designated as masks or reticles, onto an object, that is to say a substrate, coated with a photosensitive layer, or onto a semiconductor wafer coated with photoresist, with very high resolution.
The resolution of the imaging of the pattern by the projection objective is proportional to the wavelength of the light used, and inversely proportional to the image-side numerical aperture of the projection objective. The resolution can therefore be improved with the aid of shorter wavelengths and higher numerical apertures. The numerical aperture NA is given by NA=n·sin Θ, n being the refractive index of the medium between the substrate and the last optical element of the projection objective.
Hitherto, use has predominantly been made of projection objectives in the case of which there exists in the image space between the exit surface of the last optical element of the projection objective and the image plane a finite working distance that is filled during operation with air or another suitable gas. Such systems are designated as “dry systems” or “dry objectives”. The working distance between the last optical element and the substrate is generally filled in this case with helium, nitrogen or another gas or a gas mixture with a refractive index n of approximately 1.
It follows from the previously mentioned relationship between the resolution and the image-side numerical aperture that the resolution can be raised when an immersion medium of high refractive index is introduced into the working distance between the exit surface of the last optical element and the substrate. This technique is designated as immersion lithography. A projection objective of this type is also designated as an “immersion system” or “immersion objective”. Some refractive projection objectives that are suitable for immersion lithography and have image-side numerical apertures NA>1 are disclosed in the patent applications DE 102 10 899 and PCT/EP 02/04846 of the same applicant.
A further advantage of an immersion objective consists in the possibility of obtaining a larger depth of field of the imaging in conjunction with the same numerical aperture as for a dry objective. This advantage is used in the projection objectives according to the invention.
In the case of an immersion objective, instead of being filled with a gas, the space between the exit surface of the last optical element of the projection objective and the substrate, which determines the working distance, is filled with an immersion medium of a refractive index substantially greater than 1. An immersion medium normally used at present is water, but it is possible, particularly within the scope of the present invention, to select other immersion media in accordance with needs and suitability.
Document EP 1 431 826 A2, which stems from the same applicant, describes how simple design means and manipulations can be used to tune a projection objective between a dry operation (dry configuration) and an immersion operation (immersion configuration). The projection objective described there has a multiplicity of optical elements that are arranged along an optical axis of the projection objective, the optical elements comprising a first group, following the object plane, of optical elements and a last optical element that follows the first group, is next to the image plane and defines an exit surface of the projection objective that is arranged at a working distance from the image plane. The last optical element is substantially free from refractive power and has no sag or only a slight one. The tuning method described there comprises varying the thickness of the last optical element, changing the refractive index of the space between the exit surface of the last optical element and the substrate by introducing or removing an immersion medium, and moreover preferably an axial displacement of the last optical element for the purpose of setting a suitable working distance in the dry operation of the projection objective. Moreover, it is provided to refine the tuning to the dry configuration or the immersion configuration by changing the air spaces between individual optical elements of the first group or by providing or varying aspheres.
The projection objective of the present invention can likewise be tuned between a dry configuration and an immersion configuration.
However, the present invention is based on a further aspect of such a projection objective that can be tuned between the dry configuration and the immersion configuration.
A temperature change usually occurs during operation of a projection objective. This can be global, homogenous or else local. For example, the air around the projection objective, the projection objective housing, the individual mounts of the optical elements, the optical elements themselves and the air or the gas inside the projection objective and, during immersion operation, the immersion liquid can heat up.
It has emerged that temperature changes have a different effect with regard to spherical image defects on a projection objective during immersion operation than on a projection objective in the dry configuration. In other words, dry objectives and immersion objectives differ from one another with regard to their sensitivity to temperature changes.
In the case of a projection objective in dry configuration, such spherical aberrations induced by temperature changes can be at least largely compensated even in the relatively high order by simply refocusing in which only the position of the substrate is adjusted in the direction of the optical axis. Specifically, a change in the working distance between the exit surface of the last optical element and the substrate leads in the case of a projection objective in dry configuration to very similar aberrations such as heating up of the projection objective, and so the aberrations induced by the heating up can be at least largely compensated by an appropriately directed displacement of the substrate, usually in conjunction with heating up, in a direction away from the last optical element.
It came out that this mode of procedure, specifically a correction of image defects on the basis of temperature changes solely by adjusting the position of the substrate does not lead in the case of a projection objective in immersion configuration to the result as in the case of a projection objective in dry configuration, that is to say in the case of such a focusing correction in which the Zernike coefficient Z4 is compensated to zero, higher spherical Zernike coefficients Z9, Z16, Z25, . . . remain and impair the imaging properties of the projection objective in immersion configuration.
SUMMARY OF THE INVENTION
It is the object of the invention to improve a projection objective that can be or is tuned to immersion operation with regard to its imaging properties or with regard to the correctability of image defects that are caused by a disturbance during immersion operation, such as a change in temperature, for example.
It is also the object of the invention to specify a method for correcting image defects of a projection objective that can be or is tuned to immersion operation, which can be carried out with the aid of simple means.
According to the invention, a lithography projection objective is provided for achieving the first mentioned object.
According to the invention, a method for correcting aberrations in the case of a projection objective that can be, or is, tuned to immersion operation is specified for the purpose of achieving the object mentioned in the second instance.
A lithography projection objective according to the invention for imaging a pattern to be arranged in an object plane of the projection objective onto a substrate to be arranged in an image plane of the projection objective has a multiplicity of optical elements that are arranged along an optical axis of the projection objective. The optical elements comprise a first group, following the object plane, of optical elements, and a last optical element, which follows the first group and is next to the image plane and which defines an exit surface of the projection objective and is arranged at a working distance from the image plane. The projection objective can be or is tuned with respect to aberrations for the case that the volume between the last optical element and the image plane is filled by an immersion medium with a refractive index substantially greater than 1. The position of the last optical element can be adjusted in the direction of the optical axis. A positioning device is provided that positions at least the last optical element during immersion operation such that aberrations induced by a disturbance caused by the operation of the projection objective are at least partially compensated.
The method according to the invention for correcting image defects in the case of a lithography projection objective that can be, or is, tuned to immersion operation comprises the step, in the event of a disturbance arising during immersion operation of the projection objective, of positioning at least the last optical element such that aberrations induced by the disturbance are at least partially compensated.
A disturbance in the case of the abovementioned projection objective or the abovementioned method is, for example, a change in temperature. The present invention is based on the finding that in the event of a change in temperature owing to heating up of the projection objective the working distance between the exit surface of the last optical element and the substrate is varied by the thermal expansion of the projection objective. However, since the immersion medium is located between the last optical element and the substrate during immersion operation, this change in the working distance leads to other sensitivities of the projection objective during immersion operation than by comparison with dry operation. In dry operation of the projection objective, the change in working distance has no influence on the aberrations, while the changed working distance, and thus the changed layer thickness of the immersion liquid during immersion operation, induces additional aberrations. These additional aberrations during immersion operation cannot be compensated solely by displacing the substrate in the direction of the optical axis, as in the case of the dry objective.
An instance of “disturbance” in the meaning of the present invention can also be one that is not caused by temperature, but is based, for example, on bubble formation in the immersion liquid, unevenness of the wafer surface, a locally differing wafer thickness or other geometry errors, and which renders refocusing necessary. This refocusing can be accomplished by displacing the wafer stage and/or displacing optical elements in the direction of the optical axis.
The inventive solution to this problem now consists, in the event of a disturbance, in positioning at least also the last optical element such that aberrations induced by the disturbance are at least partially compensated via the positioning of the last optical element. In particular, and preferably, by means of positioning of the last optical element the volume filled with the immersion medium, which can change in the event of disturbance such as a thermal expansion, can be set by means of the positioning device such that the aberrations induced by the disturbance, in particular aberrations of higher order, are at least largely compensated. By contrast with refocusing solely by adjusting the position of the substrate in the direction of the optical axis in the case of a projection objective during dry operation, now at least also the position of the last optical element is adjusted in the direction of the optical axis in order to keep the working distance, and thus the layer thickness of the immersion medium, preferably at a nominal value, while the gas-filled or air-filled space between the last optical element and the penultimate optical element of the projection objective is kept variable.
It is preferably also possible to adjust the position of the substrate in the direction of the optical axis, and the positioning device adjusts the last optical element in a ratio correlated with the adjustment of the position of the substrate. In particular, the ratio between the adjustment of the position of the substrate and the adjustment of the position of the last optical element can be selected to be 1:1.
With this type of “alternative focusing” in the immersion system by comparison with focussing in the dry system, the same focussing sensitivities are achieved in the immersion objective as in the case of focusing in the dry objective, in which only the substrate is displaced without adjusting the position of the last optical element in the direction of the optical axis.
Depending on requirement and degree of optimization, the ratio between the adjustment of the position of the substrate and the adjustment of the position of the last optical element can also be selected to be greater than or less than 1:1.
For the purpose of further optimizing the imaging properties of the projection objective during immersion operation, it is preferred in a first step to adjust only the position of the last optical element in the direction of the optical axis in order to restore a predetermined desired working distance, and in a second step the position of the last optical element and the position of the substrate are adjusted in the direction of the optical axis, preferably in the ratio of 1:1.
It is also possible here to interchange the first step and the second step in the sequence, or it can be provided to carry out these two steps in an interlocking fashion.
It has emerged that optimum corrections of the imaging properties, in particular even in higher orders of the spherical aberrations, that correspond to the achievable corrections in the dry configuration can be achieved by controlling the working distance filled with immersion medium to a nominal value that corresponds, for example, to the optimum value which is pre-calculated in the cold state of the projection objective, and the refocusing, as mentioned above, by simultaneously adjusting the position of the substrate and of the last optical element in the ratio of preferably 1:1.
The working distance is preferably measured before and/or during operation of the projection objective, in order to enable permanent control of the working distance. The respective measurement results are then used to adjust the position of the last optical element and/or of the substrate.
The measuring device preferably cooperates with an actuator in order to regulate the working distance to a nominal value. This enables unchanging optimum imaging properties of the projection objective during operation of the projection objective, that is to say the projection objective is capable of reacting to any sort of disturbance, for example changes in temperature, without manipulations from outside.
In a preferred alternative, it is also possible to proceed such that the position of the last optical element is adjusted so that aberrations can subsequently be at least largely compensated solely by adjusting the position of the substrate.
In this mode of procedure, the temperature sensitivities of the projection objective are therefore adapted during immersion operation such that, as in dry operation, they are again compatible with the sensitivities that exist from solely adjusting the substrate.
In the case of the projection objective, the last optical element is preferably assigned at least one actuator for adjusting the position of the last optical element in the direction of the optical axis.
Alternatively or cumulatively, the positioning device can have a mount for the last optical element that, upon heating up, moves the last optical element in a direction running counter to the thermal expansion of the projection objective.
This type of mounting technique for the last optical element with the use of materials with various coefficients of thermal expansion advantageously ensures that despite thermal expansion of the projection objective the working distance between the last optical element and the substrate can be kept at least approximately at the nominal value. This renders it possible even without additional actuators to compensate the aberrations induced by disturbance, or these are already avoided from the beginning.
In accordance with further preferred measures specified in the claims, the projection objective according to the invention can be tuned between dry operation and immersion operation.
Further advantages and features emerge from the following description and the attached drawing.
It is self-evident that the abovementioned features which are still to be explained below can be used not only in the combination respectively specified, but also in other combinations or on their own without departing from the scope of the present invention.



BRIEF DESCRIPTION OF THE DRAWINGS
Exemplary embodiments of the invention are illustrated in the drawing and explained in yet more detail here with reference thereto. In the drawing:
FIG. 1 shows a schematic projection objective in immersion configuration;
FIG. 2 shows the projection objective in FIG. 1 in dry configuration;
FIG. 3 shows a bar diagram for illustrating the influence of a displacement of the substrate in the direction of the optical axis on a wavefront change in a comparison between the projection objective in FIG. 2 (dry configuration) and the projection objective in FIG. 1 (immersion configuration);
FIG. 4 shows a bar diagram in which the fractions of higher spherical aberrations (Z9, Z16, Z25, Z36) in relation to the Z4 fraction of the spherical aberration are illustrated by comparison with the projection objective in FIG. 2 and the projection objective in FIG. 1;
FIG. 5 shows a bar diagram that shows the temperature sensitivities of the projection objective in FIG. 2 in comparison with the temperature sensitivities of the projection objective in FIG. 1;
FIG. 6 shows a bar diagram that illustrates the temperature sensitivities of the projection objective in FIG. 2 in comparison with those of the projection objective in FIG. 1 with and without correction of the Z4 fraction of the spherical aberration to the value zero;
FIGS. 7a) and b) show a detail of the projection objective in FIG. 1 in two different states;
FIG. 8 shows a bar diagram similar to FIG. 6 although aberrations of higher order are illustrated after an identical displacement of the last optical element and the substrate for the projection objective in FIG. 1 in accordance with FIG. 7b) (the ratio between the adjustment of the position of the substrate and the adjustment of the position of the last optical element being equal to 1:1);
FIG. 9 shows a bar diagram, comparable to the bar diagram in FIG. 8, after a further error correction of the projection objective in FIG. 1 (the ratio between the adjustment of the position of the substrate and the adjustment of the position of the last optical element not being equal to 1:1);
FIG. 10 shows a schematic of a mount for the last optical element that compensates or overcompensates a temperature-induced change in the working distance;
FIG. 11 shows an embodiment of a projection objective in immersion configuration, in which the present invention can be used; and
FIG. 12 shows a further embodiment of a projection objective in immersion configuration in which the present invention can likewise be implemented.



DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
FIG. 1 illustrates a projection objective, provided with the general reference numeral 10, in immersion configuration.
The projection objective 10 is used for the microlithographic production of semiconductor components and other finely structured subassemblies. The projection objective operated with ultraviolet light from the deep UV region (for example 193 nm) serves to image onto a substrate 14, which is arranged in an image plane 15 of the projection objective 10, a pattern 12 of a photomask (reticle) that is arranged in an object plane 13 of the projection objective.
The projection objective 10 has a multiplicity of optical elements in the form of lenses, but can also have both lenses and mirrors.
The optical elements are arranged along an optical axis 16 of the projection objective 10.
The optical elements comprise a first group 18 of optical elements that follow the object plane 13 or the pattern 12. Three optical elements 18a, 18b and 18c of the first group 18 are illustrated by way of example in FIG. 1.
The optical elements further comprise a last optical element 20 that follows the first group 18 and is closest to the substrate 14 or the image plane 15.
The last optical element 20 is illustrated in FIG. 1 as a plane-parallel plate. However, the last optical element 20 can also respectively have on the entrance side and exit side a radius of curvature that are, however, only so large that aspheric aberrations induced by the displacement of the optical element 20 in the direction of the optical axis 16 are sufficiently small.
Like the optical elements of the first group, the last optical element 20 can be made from synthetic quartz glass. Furthermore, the last optical element 20 can also comprise a number of components in the direction of the optical axis.
An exit surface 22, facing the image plane 15, of the last optical element 20 also simultaneously forms the exit surface of the projection objective 10.
A distance between the exit surface 22 of the last optical element 20 and the surface of the substrate 14 defines a working distance 24.
The last optical element 20 is spaced sufficiently far away, for example, by a few millimeters, from the first group 18 of optical elements, such that the position of the last optical element 20 can be adequately adjusted in the direction of the optical axis 16.
The working distance 24 between the last optical element 20 and the substrate 14 is filled with an immersion medium 26. The immersion medium 26 is, for example, an immersion liquid, for example water, that has a refractive index of n≈1.437 given an operating wavelength of λ=193 nm.
In the configuration illustrated in FIG. 1, the projection objective 10 is designed for immersion operation, that is to say, with reference to the aberrations produced, it is designed for, that is to say tuned to, the presence of the immersion medium 26 at the working distance 24.
FIG. 2 shows the projection objective 10 in FIG. 1 in its dry configuration. The transition of the projection objective 10 in FIG. 1 (immersion configuration) to its dry configuration in FIG. 2 will firstly be described.
Starting with FIG. 1, the projection objective 10 is transformed as follows into its dry configuration. The immersion medium 26 is removed from the image space in a first step. This measure does not change the correction state before entry into the terminal element or into the last optical element 20 and at the exit of the terminal element 20. However, by removing the highly refractive, plane-parallel layer made from the immersion medium 26 from the image space, the overcorrecting effect thereof is taken away such that the correaction state in the image plane 15 corresponds to the undercorrected correction state at the exit surface 22.
In a further step, the thickness of the last optical element 20 is enlarged. In this case, the overcorrecting effect thereof increases with the rising thickness. In accordance with the refractive index of the plate material, the thickness is selected to be so wide that the overcorrection effected by the thicker plate, which now forms the last optical element 20, largely compensates the undercorrected correction state at the entrance to the last optical element 20.
In two further steps, a larger working distance 24 by comparison with the immersion configuration in FIG. 1 is set by axially displacing the last optical element 20 in the direction of the first group 18. This can be performed by axially displacing the last optical element 20 with the aid of a z-manipulator that can be driven electrically or in another way. It is also possible to mount the last optical element 20 individually and to use spacers to set a suitable spacing between the mounts of the first group 18 and the mount of the last optical element 20 by removing and/or installing spacers. Since the plane-parallel plate 20 is as free from refractive power as possible and does not sag, this axial displacement can be carried out without this having a measurable influence on the aberrations of the projection objective 10.
Furthermore, at least one of the lenses, for example the negative lens 18b, in the first group 18 is mounted such that it can be displaced axially with the aid of a z-manipulator. A residual error can be compensated in this case by slightly displacing the lens 18b in the direction of the object plane such that the completely tuned projection objective 10 in dry configuration has a sufficiently good correction state at the light exit.
The last-mentioned step, specifically the fine tuning with the aid of at least one manipulatable or variable optical element of the first group 18 can frequently be required in order to be able to meet tight specifications. In the event of lesser requirements, the first-mentioned steps (changing the refractive index in the image space by introducing or removing an immersion medium, varying the thickness of the last element 20, and displacing the last element 20 in order to change the working distance 24) can suffice in order to achieve a reconfiguration between immersion configuration and dry configuration (or vice versa).
It is described below how a disturbance or interference in the form of a temperature change affects the projection objective 10 in dry configuration (FIG. 2), and how the same disturbance affects the projection objective 10 in immersion configuration (FIG. 1), and how aberrations induced by the disturbance can be corrected.
Firstly, the fact is that the response of the projection objective 10 to an identical disturbance in the dry configuration and in the immersion configuration is virtually identical if, firstly, the presence of the immersion medium 26 is discounted. Such disturbance is encountered with the projection objective 10 in the dry configuration by adjusting the position of the substrate 14 in the direction of the optical axis 16 in order thereby to carry out a focus correction such that the Zernike coefficient Z4 vanishes in the middle of the field.
A displacement of the substrate 14 in the direction of the optical axis 16 by the amount ΔZ (compare FIGS. 1 and 2) leads in both systems to a wavefront change OPD for which it holds that:

OPDΔz(ρ)=Δz·n√{square root over (1−(NA/n)2π2)}.  (1)

Here, n is the refractive index at the working distance 24, that is to say n≈1.000 for air in the dry configuration, or n≈1.437 for water in the immersion configuration for a given wavelength λ=193 nm. ρ is the normalized radial pupil coordinate.
The wavefront change OPD Δz in accordance with equation (1) can be developed in the customary way using Zernike polynomials:

OPDΔz(ρ)=Δz·(f4(NA,n)·Z4(ρ)+f9(NA,n)·Z9(ρ)+f16(NA,n)·Z16(ρ)+f25(NA,n)·Z25(ρ)+f36(NA,n)·Z36(ρ))  (2)

The following Zernike coefficients Δz·fi(NA, n) with NA′=NA/n are then yielded analytically in this expansion:




  
    
      
        
          
        
        ⁢
        
          
            
              f
              4
            
            ⁡
            
              (
              
                NA
                ,
                n
              
              )
            
          
          =
          
            n
            ·
            
              
                4
                -
                
                  NA
                  ′2
                
                -
                
                  
                    
                      1
                      -
                      
                        NA
                        ′2
                      
                    
                  
                  ⁢
                  
                    (
                    
                      4
                      -
                      
                        3
                        ⁢
                        
                          NA
                          ′2
                        
                      
                      -
                      
                        NA
                        ′4
                      
                    
                    )
                  
                
              
              
                
                  5
                  /
                  2
                
                ⁢
                
                  NA
                  ′4
                
              
            
          
        
      
    
    
      
        (
        3
        )
      
    
  
  
    
      
        
          
        
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              9
            
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            n
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                      48
                      -
                      
                        84
                        ⁢
                        
                          NA
                          ′2
                        
                      
                      +
                      
                        35
                        ⁢
                        
                          NA
                          ′4
                        
                      
                      -
                    
                  
                
                
                  
                    
                      
                        
                          1
                          -
                          
                            NA
                            ′2
                          
                        
                      
                      ⁢
                      
                        (
                        
                          48
                          -
                          
                            60
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                              NA
                              ′2
                            
                          
                          +
                          
                            11
                            ⁢
                            
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                  21
                  /
                  2
                
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                  NA
                  ′6
                
              
            
          
        
      
    
    
      
        (
        4
        )
      
    
  
  
    
      
        
          
        
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              f
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            ·
            
              
                
                  
                    
                      320
                      -
                      
                        740
                        ⁢
                        
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                          ′2
                        
                      
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                        504
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                          ′4
                        
                      
                      -
                    
                  
                
                
                  
                    
                      
                        
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                          320
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                            560
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                  45
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                  ′8
                
              
            
          
        
      
    
    
      
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                      1792
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                        4928
                        ⁢
                        
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                        4752
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                      -
                    
                  
                
                
                  
                    
                      
                        1848
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                        231
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                  77
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                  NA
                  ′10
                
              
            
          
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                  1792
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                    4032
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                      ′2
                    
                  
                  +
                  
                    2960
                    ⁢
                    
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                      ′4
                    
                  
                  -
                  
                    760
                    ⁢
                    
                      NA
                      ′6
                    
                  
                  +
                  
                    39
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                  +
                  
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                )
              
              
                
                  77
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                      9216
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                        29952
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                        36608
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                      -
                    
                  
                
                
                  
                    
                      
                        20592
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                          NA
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                        5148
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                          ′8
                        
                      
                      -
                      
                        429
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                          ′10
                        
                      
                    
                  
                
              
              
                
                  117
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                  9216
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                      ′2
                    
                  
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                    25088
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                      ′4
                    
                  
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                    10640
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                    1740
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                    59
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        7
        )
      
    
  




It is to be seen from equations (3) to (7) that the Zernike coefficients Δz·fi, that is to say the induced spherical aberrations both of order Z4 and of higher orders Z9, Z16, Z25, Z36 are a function both of the numerical aperture and, in particular, of the refractive index n in the working distance 24.
FIG. 3 illustrates this state of affairs with reference to a numerical example. The bar diagram illustrates the wavefront changes, coded according to the Zernike coefficients Z4, Z9, Z16, Z25 and Z36 for a displacement of the substrate 14 by Δz=1 μm given a numerical aperture NA=0.93 for the projection objective in dry configuration (FIG. 2) and for the projection objective 10 in immersion configuration (FIG. 1). Of each pair of bars, the left-hand bar relates to the dry configuration, and the right-hand bar to the immersion configuration.
FIG. 4 illustrates the relative wavefront changes in the orders Z9, Z16, Z25 and Z36 referred to Z4. It follows in particular from FIG. 4 that a displacement of the substrate 14 in the direction of the optical axis 16 by the amount Δz has a lesser effect on the wavefront changes in the higher orders Z9, Z16, Z25, Z36 with the projection objective 10 in immersion configuration than in the dry configuration. That is to say, the sensitivity of the projection objective 10 to the z-displacement of the substrate 14 in the higher Zernike coefficients is less in immersion configuration than in the dry configuration. The consequence of this is that the method of focus correction by displacing the substrate 14 in the direction of the optical axis 16 that is applied in the dry configuration of the projection objective 10 has less influence on the wavefront changes or aberrations of higher order.
While previously the different focus sensitivities of the projection objective 10 in the dry configuration have been considered by comparison with the immersion configuration, in the following the sensitivity of the projection objective 10 in both configurations is explained with regard to a disturbance in the form of a temperature change.
In a simulation of aberrations induced by a global, homogeneous temperature change, for example in the air (or another gas) around the projection objective 10, in the projection objective housing with the individual mounts, in the gas inside the projection objective 10, in the lenses and in the immersion liquid 24, the sensitivities of the following effects were considered:

    1. Change in the lens geometries—that is to say the thicknesses and radii—through the thermal expansion of the lens material;
    2. Changes in spacings through the thermal expansion of the projection objective housing (metal mounts):
    
        a. between the lenses (“air spaces”),
        b. between the pattern 12 (reticle) and a first optical element of the first group 18 of optical elements,
        c. between the last optical element 20 and the substrate 14;
    
    
    3. Changes in refractive index Δn=dn/dT ΔT of the lens material (quartz, CaF2);
    4. Changes in refractive index Δn=dn/dT ΔT
    
        a. of the gas between the individual optical elements of the first group 18,
        b. of the air (or the other gas) between the pattern 12 and the first optical element of the group 18,
        c. in the immersion liquid 24 between the last optical element 20 and the substrate 14 in the immersion system or in the air (or the other gas) in the case of the dry system.
    
    


FIG. 5 shows the temperature sensitivities without focus correction, that is to say without displacement of the substrate 14 in the direction of the optical axis with reference to the spherical Zernike coefficients in the center of the field in a comparison between the projection objective 10 in the dry configuration and the projection objective 10 in the immersion configuration, once again the left-hand bar of each pair of bars referring to the dry configuration, and the right-hand bar referring to the immersion configuration.
It emerges from FIG. 5 that the dry configuration and the immersion configuration of the projection objective 10 differ considerably from one another with regard to the temperature sensitivities, at least in the orders Z4 and Z9. These differences between the dry configuration and the immersion configuration result from the above-mentioned contributions 2.c and 4.c to the temperature effects, that is to say the differences are a consequence of the presence of the immersion liquid 26 at the working distance 24 between the last optical element 20 and the substrate 14. Of the two contributions 2.c and 4.c, the contribution 2.c, that is to say the change in the working distance 24, is the dominating additional contribution to the aberrations in the immersion configuration. This can be explained in that the temperature-induced thermal expansion of the projection objective 10 displaces the last optical element 20 in the direction of the substrate 14. The working distance 24 is consequently reduced. Whereas this has no influence on the aberrations in the dry configuration, the change in the working distance 24 in the immersion configuration induces a changed layer thickness of the immersion liquid 26 that induces additional aberrations. All other above-mentioned contributions to the temperature effects yield virtually identical sensitivities in the two systems.
FIG. 6 illustrates with the aid of a further bar diagram the extent to which the previously described aberrations induced by a temperature change can be compensated only by adjusting the position of the substrate 14 in the direction of the optical axis 16.
FIG. 6 shows the wavefront changes OPD/T, caused by temperature changes, for the dry configuration and for the immersion configuration, respectively without and with focus correction solely by displacing the substrate 14 in the direction of the optical axis, in a fashion split up with reference to the Zernike coefficients Z9, Z16, Z25, Z36 (Z4=0 after the focus correction).
Of the four bars relating to each of the coefficients Z9, Z16, Z25, Z36, the first bar relates to the dry configuration without focus correction, the second bar to the dry system with focus correction (Z4=0), the third bar to the immersion configuration without focus correction, and the fourth bar to the immersion configuration with focus correction (Z4=0) solely by displacing the substrate 14 in the direction of the optical axis.
It is clear from FIG. 6 that in the dry configuration the higher spherical sensitivities Z9, Z16, Z25, Z36 relating to a homogeneous temperature change have a similar ratio to the Z4 fraction as the focus sensitivities in the case of adjusting the position of the substrate 14 in the direction of the optical axis 16. As a result of this circumstance, a focus correction, that is to say a correction such that Z4=0 in the middle of the field, solely by adjusting the position of the substrate 14 in the direction of the optical axis simultaneously also adequately corrects substantial contributions of the higher spherical aberrations Z9, Z16, Z25, Z36 in the dry configuration. By contrast, in the immersion configuration the crosstalk in the higher spherical Zernike coefficients is substantially smaller in the case of Z4 correction solely by adjusting the position of the substrate 14, as has been explained above with reference to FIGS. 3 and 4. The consequence of this is that in the case of a complete compensation of Z4 in the immersion configuration it is still only small fractions of the higher Zernike coefficients Z9, Z16, Z25, Z36 that are also compensated, and therefore large fractions of these aberrations of higher order remain as residual errors. Consequently, it is not sufficient to correct aberrations simply by adjusting the position of the substrate 14 in the direction of the optical axis, that is to say nothing but a focus correction to Z4=0 in the immersion configuration. This means that in the immersion configuration as contrasted with the dry configuration for the case of an identical temperature change there remains a residual error Z9 that is larger by a factor of approximately 7 and residual errors that are approximately four to five times larger for the other spherical Zernike coefficients of higher order when only one focus correction is performed by adjusting the position of the substrate 14.
With reference to FIGS. 7a) and b), it is described below how the residual errors of the projection objective 10 can be reduced in immersion configuration by means of an alternative type of focusing.
FIG. 7a) shows the projection objective 10 in accordance with FIG. 1 in the region of the last optical element 20 and of the penultimate optical element 18c that forms the last optical element of the first group 18 of optical elements of the projection objective 10. The space between the penultimate optical element 18c and the last optical element 20 is filled with a gas having a refractive index n of approximately 1.
In accordance with FIG. 7b), the projection objective 10 has a positioning device 28 that comprises an actuator 30 and a measuring device 32. The actuator 30 is capable of positioning the last optical element 20 in the direction of the optical axis 16 (z direction) as is indicated by an arrow 30a. The actuator 30 is further capable of likewise positioning the substrate 14 in the direction of the optical axis 16, as indicated by an arrow 30b. 
The actuator 30 is capable, in particular, of adjusting the position of the last optical element 20 and of the substrate 14 in a mutually correlated ratio in the direction of the optical axis 16.
The aim firstly is to discuss what is the result of a common adjustment of the position of the last optical element 20 and of the substrate 14 in the same direction in a ratio of 1:1 as is illustrated in FIG. 7b) by comparison with FIG. 7a).
Adjusting the position of the last optical element 20 enlarges the air space 34 between the penultimate optical element 18c and the last optical element 20 by the amount ΔzLR when the optical element 20 is displaced by the amount Δz (just like the substrate 14).
The wavefront change OPDΔz,LR owing to the enlargement of the air space 34 is then given by

OPDΔz,LR(ρ)=Δz·n′√{square root over (1−(NA/n′)2ρ2)}  (8)

Here, n′ is the refractive index of the gas in the air space 34 upstream of the last optical element 20. Comparing equation (8) with equation (1) shows that this type of focusing in the projection objective 10 in immersion configuration leads to the same change in the wavefront as does a corresponding sole displacement of the substrate 14 in the dry configuration, since the refractive index n′ ̃1 in the last air space 34 upstream of the last optical element 20 is virtually identical to the refractive index n ̃1 of the air in the dry system. Consequently, the projection objective 10 in the dry configuration and in the immersion configuration then have the same focus sensitivities (equations (2) to (7)) with the same crosstalk to the higher spherical Zernike coefficients Z9, Z16, Z25, Z36.
FIG. 8 shows a similar illustration to that in FIG. 6, the fourth bar in relation to each of the Zernike coefficients Z9, Z16, Z25, Z36 showing the residual aberrations for the projection objective 10 in immersion configuration after an identical displacement of the last optical element 20 and of the substrate 14.
Comparing this respective fourth bar with the respective fourth bar in FIG. 6 shows that the residual aberrations in the higher Zernike coefficients Z9, Z16, Z25, Z36 are substantially reduced, and differ from the residual aberrations in the dry configuration only by factors of approximately 1.7 to 2.7.
It is described below how the residual aberrations of the projection objective 10 in the immersion configuration can be yet further reduced.
A further reduction in the residual aberrations of the projection objective 10 in immersion configuration is achieved by setting the working distance 24 between the last optical element 20 and the substrate 14 solely by adjusting the position of the last optical element 20 to a nominal value (nominal working distance), something which can likewise be carried out with the aid of the actuator 30. The nominal value can in this case be the originally set optimum working distance in immersion configuration if no disturbance such as a temperature-induced expansion of the system is present.
The wavefront change OPDΔz,LLE owing to displacement of the last optical element 20 by the path Δz in the direction of the optical axis is then yielded as the difference between the wavefront change OPDΔz,LR by enlarging the last air space 34 (FIG. 7b)) and the wavefront change OPDΔz,S by adjusting the position of the substrate 14 in the direction of the optical axis 16:

OPDΔz,LLE(ρ)=OPDΔz,LR(ρ)−OPDΔz,S(ρ)=Δz[n′√{square root over (1−(NA/n′)2ρ2)}−n√{square root over (1−(NA/n)2ρ2)}]  (9)

Here, n is the refractive index of the immersion medium 26, and n′ is the refractive index of the gas in the air space 34 upstream of the last optical element 20.
The (sole) adjustment of the position of the last optical element 20 can now be used to fully compensate again the displacement of the last optical element 20 in the direction of the substrate 14 induced by the thermal expansion of the projection objective 10.
The result of this mode of procedure is illustrated in FIG. 9.
FIG. 9 shows for the first bar (seen from the left) relating to each Zernike coefficient Z9, Z16, Z25, Z36 the aberrations of a projection objective 10 in dry configuration due to a disturbance in the form of a temperature change, no focus correction yet having been performed. (The Zernike coefficient Z4, which is not shown in this figure, does not vanish here.)
The respective second bar in FIG. 9 shows the residual aberrations of the projection objective 10 in dry configuration after a focus correction solely by displacing the substrate 14 in the direction of the optical axis 16. (The Zernike coefficient Z4, which is not shown in this figure, vanishes here.)
The respective third bar in FIG. 9 shows in relation to each Zernike coefficient Z9, Z16, Z25, Z36 the aberrations of the projection objective 10 in immersion configuration due to a disturbance in the form of a temperature change without focus correction, the fourth bar shows the aberrations after setting the working distance 24 between the last optical element 20 and the substrate 14 to a desired working distance that corresponds, or can correspond, to the originally set working distance before commissioning of the projection objective 10, and the fifth bars show the residual aberrations after additional common adjustment of the position of the last optical element 20 and of the substrate 14 in the direction of the optical axis in the ratio of 1:1.
Comparing the first and fourth bars relating to each Zernike coefficient in FIG. 9 reveals that restoring the desired working distance between the last optical element 20 and the substrate 14 yields sensitivities that are virtually identical to the not refocused sensitivities of the projection objective 10 in dry configuration.
Comparing the second and fifth bars in relation to each Zernike coefficient in FIG. 9 reveals that these show identical residual aberrations for the projection objective 10 in dry configuration after focus correction, and identical residual aberrations for the projection objective 10 in immersion configuration after adjusting the position of the last optical element 20 in order to set a desired working distance, and identical adjustment of the position of the last optical element 20 and of the substrate 14 in the direction of the optical axis 16.
The focus correction (Z4=0) is carried out by correlated adjustment of the position of the last optical element 20 and the substrate 14. This now results in the same corrective action as in the case of the projection objective 10 in dry configuration (identical focus sensitivities), and virtually identical and sufficiently small residual errors of the higher spherical aberrations are achieved.
During operation of the projection objective 10 in immersion configuration, the working distance 24 can be controlled by means of the measuring device 32, and it is then possible on the basis of the respective measurement results to use the actuator 30 to keep the working distance 24 at the desired working distance, in the manner of a control loop.
FIG. 10 illustrates diagrammatically an embodiment with the aid of which, on the basis of a specific mounting technique for the last optical element 20, it is already possible to keep the working distance 24 between the last optical element 20 and the substrate 14 with reference to temperature changes at the set point, or to position the last optical element 20 for the purpose of minimizing aberrations.
The last optical element 20 is held in a mount 20a that is connected to a mount 19 of an optical element of the first group 18 of optical elements of the projection objective 10 at a point 21. The mount 20a has, in particular, a thermal expansion coefficient that is large by comparison with the thermal expansion coefficient of the mount 19.
If, by heating up, the mount 19 now expands in the direction of an arrow 23, this would reduce the working distance 24. However, owing to the heating up the mount 20a also expands, but in the opposite sense to the expansion of the mount 19 in accordance with an arrow 25, the result being not to diminish the working distance 24 but to keep it substantially constant. It is thereby possible to keep the working distance 24 at the nominal value.
However, it is also possible to provide not to keep the working distance 24 at the nominal value by means of the previously described mounting technique, but to fashion the mount 20a for the last optical element 20 such that it not only compensates the change in the working distance 24, but overcompensates it in such a way that the above-described customary focus correction, that is to say solely adjusting the position of the substrate 14, leads again to the same results for the correction of aberrations. Thus, with this mode of procedure the temperature sensitivities of the projection objective are adapted in terms of design in such a way that they are once again compatible with the focus sensitivities as in the dry configuration.
The following measures are provided with reference, again, to FIGS. 1 and 2, which show the projection objective 10 in immersion configuration and in dry configuration, respectively, in order to tune the projection objective 10 between the dry configuration and the immersion configuration.
A large distance that enables a substantial axial displacement of the last optical element 20 exists between the first group 18 and the last optical element 20.
The tunability between the immersion configuration in FIG. 1 and the dry configuration in FIG. 2 of the projection objective 10 is preferably achieved with the aid of a variation in the thickness of the last optical element 20, preferably in conjunction with a displacement of the last optical element 20 relative to the image plane 15, it being necessary, however, not to confuse this method with the previously described method for correcting aberrations of the projection objective 10 in the immersion configuration.
The last optical element 20 is, furthermore, exchangeable.
The last optical element 20 can have a variable thickness, the last optical element 20 preferably having a thickness that can be varied without removing material or adding material. This is preferably achieved by virtue of the fact that the last optical element 20 comprises a number of mutually detachable components that are arranged at a spacing from one another or are neutrally interconnected in optical terms, it being preferred for components of the last optical element 20 to consist of different optical materials, preferably at least one component consisting of fluoride crystal, in particular of lithium fluoride or calcium fluoride.
The optical material, adjacent to the exit surface 22, of the last optical element 20 preferably has a refractive index nE that is close to the refractive index nI of the immersion medium 26, it being preferred for a ratio nI/nE to be more than 0.8, in particular more than 0.9.
Furthermore, the first group 18 of optical elements also has at least one displaceable optical element, but preferably a number of, in particular at least five, displaceable optical elements, at least one of the displaceable optical elements being displaceable along the optical axis 16.
A free space upstream of the previously mentioned displaceable element and/or downstream of the displaceable element is in this case preferably dimensioned to be so large that displacing the at least one displaceable optical element renders it possible to correct at least a fraction of aberrations that result from adapting the last optical element 20 to the immersion medium 26. The projection objective 10 can be assigned at least one exchangeable optical correction element that preferably has at least one aspheric surface. Furthermore, at least one optical element of the first group 18 can have at least one optical surface with a surface curvature that can be varied reversibly or permanently.
The projection objective 10 is designed such that, when use is made of the immersion medium 26, that is to say in the immersion configuration, it has an image-side numerical aperture NA<1 between exit surface 22 and image plane 15, the image-side numerical aperture preferably being between approximately 0.7 and 1.0, in particular between 0.8 and 1.0.
It is further provided that the last optical element 20 can be removed from the projection objective 10 and be replaced by a plane-parallel plate that is large by comparison with the exit surface of the projection objective 10 and can be laid over a large area of the substrate 14 to be exposed.
FIGS. 11 and 12 demonstrate particular exemplary embodiments of projection objectives in the case of which the present invention can be implemented.
FIG. 11 shows by way of example a purely refractive, rotationally symmetrical projection objective 40 for high-resolution microlithography, in particular in the DUV wavelength region. In FIG. 11, 41 designates the optical axis of the projection objective 40, 42 denotes the object plane, 43 denotes the image plane, 44 denotes the first group of optical elements, 45 denotes the last optical element, and 46 denotes the immersion medium. Table 1 (appended) summarizes the specification of the design of the projection objective 40 in tabular form. In this case, column 1 specifies the number of refractive surfaces or surfaces otherwise distinguished, column 2 specifies the radius of the surfaces (in mm), column 3 specifies the distance, designated as thickness, of the surface from the subsequent surface (in mm), column 4 specifies the material, column 5 specifies the refractive index of the material at the operating wavelength, and column 6 specifies the maximum useful radius (half the free diameter). The total length L between the object plane and image plane is approximately 1.166 mm. All curvatures are spherical. FIG. 11 shows the projection objective 40 in immersion configuration, and the data in table 1 likewise correspond to the immersion configuration. Table 2 contains the data of the projection objective in dry configuration.
FIG. 12 illustrates a catadioptric projection objective 50 in the case of which the present invention can likewise be used. The catadioptric projection objective 50 with geometric beam splitter 52 is provided for the purpose of imaging a pattern lying in its object plane 53 into the image plane 56 to the scale 4:1 while producing a real intermediate image 54 in the image plane 56. The optical axis 58 is folded at the geometric beam splitter 52 in order to be able to make use when imaging of a concave mirror 60 that facilitates the chromatic correction of the overall system. FIG. 12 and table 3 reproduce the properties of the projection objective 50 in the immersion configuration. Table 4 contains the data of the corresponding dry configuration.
The data of the projection objective 50 are listed in table 5, the surface 32 being formed by a nanosphere.







TABLE 1







j29o
















REFRACTIVE INDEX
1⁄2 FREE


SURFACE
RADII
THICKNESSES
LENSES
248.38 nm
DIAMETER















0
0.000000000
32.000000000

1.00000000
54.410


1
0.000000000
10.587540450
L710
0.99998200
61.093


2
−2417.351767120
13.126300000
SUPRA1
1.50833811
63.132


3
−248.195466920
7.359264018
L710
0.99998200
63.945


4
−168.131361870
10.000000000
SUPRA1
1.50833811
64.202


5
328.986124739
7.907519166
L710
0.99998200
70.046


6
671.742152743
22.614900000
SUPRA1
1.50833811
71.945


7
−219.346865952
1.054978296
L710
0.99998200
73.402


8
351.854459479
21.378800000
SUPRA1
1.50833811
77.449


9
−417.329819985
0.748356148
L710
0.99998200
77.668


10
266.259242017
26.426700000
SUPRA1
1.50833811
76.971


11
−418.068287643
0.747164758
L710
0.99998200
75.964


12
195.049526899
10.000000000
SUPRA1
1.50833811
69.816


13
112.784218098
27.264697553
L710
0.99998200
64.221


14
−548.976305020
10.000000000
SUPRA1
1.50833811
63.660


15
167.581609987
25.042515270
L710
0.99998200
61.992


16
−203.629259785
10.000000000
SUPRA1
1.50833811
62.349


17
360.120642869
28.995838980
L710
0.99998200
66.965


18
−127.653905514
12.696400000
SUPRA1
1.50833811
68.153


19
−1103.725724970
17.018787360
L710
0.99998200
81.984


20
−225.898831342
23.521200000
SUPRA1
1.50833811
84.684


21
−171.063497139
1.574450554
L710
0.99998200
92.606


22
−22770.163604600
38.438000000
SUPRA1
1.50833811
109.997


23
−229.816390281
0.749282985
L710
0.99998200
113.270


24
1170.594630540
38.363100000
SUPRA1
1.50833811
123.579


25
−320.184892150
0.749629640
L710
0.99998200
124.514


26
335.012872058
39.596800000
SUPRA1
1.50833811
124.658


27
−764.462984962
2.214257730
L710
0.99998200
123.947


28
270.136227728
25.935800000
SUPRA1
1.50833811
112.963


29
1248.618077510
4.352014987
L710
0.99998200
110.825


30
177.098661261
18.578800000
SUPRA1
1.50833811
96.632


31
131.459110961
48.405871098
L710
0.99998200
84.997


32
−254.431714105
10.000000000
SUPRA1
1.50833811
83.694


33
149.734192113
49.515509852
L710
0.99998200
77.858


34
−137.204786283
10.000000000
SUPRA1
1.50833811
78.232


35
1410.223675540
43.391488727
L710
0.99998200
89.345


36
−134.825941720
35.292100000
SUPRA1
1.50833811
91.736


37
−168.418502871
3.480235112
L710
0.99998200
110.924


38
−350.805989269
24.010800000
SUPRA1
1.50833811
123.372


39
−244.301424027
6.015284795
L710
0.99998200
128.258


40
4941.534628580
43.549100000
SUPRA1
1.50833811
147.192


41
−357.889527255
2.367042190
L710
0.99998200
149.417


42
1857.663670230
40.932000000
SUPRA1
1.50833811
156.043


43
−507.091567715
−0.213252954
L710
0.99998200
156.763


44
0.000000000
0.962846248
L710
0.99998200
155.516


45
637.188120359
28.431900000
SUPRA1
1.50833811
156.869


46
−4285.746531360
0.749578310
L710
0.99998200
156.617


47
265.928249908
45.432900000
SUPRA1
1.50833811
152.353


48
1127.170329670
57.049328626
L710
0.99998200
150.272


49
−273.057181282
24.571800000
SUPRA1
1.50833811
149.389


50
−296.450446798
2.401860529
L710
0.99998200
150.065


51
−317.559071036
23.847600000
SUPRA1
1.50833811
148.110


52
−297.103672940
0.819938446
L710
0.99998200
148.158


53
223.869192775
28.117900000
SUPRA1
1.50833811
122.315


54
548.591751129
0.749776549
L710
0.99998200
120.110


55
123.937471688
34.861300000
SUPRA1
1.50833811
99.291


56
211.883788830
0.738299719
L710
0.99998200
93.879


57
121.391085072
21.109500000
SUPRA1
1.50833811
82.929


58
178.110541498
13.722409422
L710
0.99998200
77.266


59
314.102464129
10.000000000
SUPRA1
1.50833811
71.524


60
60.563892001
10.471596266
L710
0.99998200
49.697


61
71.706607533
10.069000000
SUPRA1
1.50833811
48.032


62
53.184242317
0.713865261
L710
0.99998200
40.889


63
48.728728866
24.194000000
SUPRA1
1.50833811
39.865


64
325.049018458
16.249640231
L710
0.99998200
35.979


65
0.000000000
3.000000000
SUPRA1
1.50833811
16.879


66
0.000000000
2.000000000
IMMERS
1.40000000
14.998


67
0.000000000
0.000000000

1.00000000
13.603
















TABLE 2







j30o
















REFRACTIVE INDEX
1⁄2 FREE


SURFACE
RADII
THICKNESSES
LENSES
248.38 nm
DIAMETER















0
0.000000000
32.000000000

1.00000000
54.410


1
0.000000000
10.283889256
L710
0.99998200
61.093


2
−2417.351767120
13.126300000
SUPRA1
1.50833811
63.069


3
−248.195466920
7.293007084
L710
0.99998200
63.884


4
−168.131361870
10.000000000
SUPRA1
1.50833811
64.137


5
328.986124739
8.273191790
L710
0.99998200
69.971


6
671.742152743
22.614900000
SUPRA1
1.50833811
72.045


7
−219.346865952
0.447882685
L710
0.99998200
73.489


8
351.854459479
21.378800000
SUPRA1
1.50833811
77.419


9
−417.329819985
0.643718463
L710
0.99998200
77.636


10
266.259242017
26.426700000
SUPRA1
1.50833811
76.935


11
−418.068287643
1.297611013
L710
0.99998200
75.923


12
195.049526899
10.000000000
SUPRA1
1.50833811
69.627


13
112.784218098
26.146948060
L710
0.99998200
64.049


14
−548.976305020
10.000000000
SUPRA1
1.50833811
63.646


15
167.581609987
26.480913850
L710
0.99998200
61.963


16
−203.629259785
10.000000000
SUPRA1
1.50833811
62.465


17
360.120642869
28.474843347
L710
0.99998200
67.077


18
−127.653905514
12.696400000
SUPRA1
1.50833811
68.070


19
−1103.725724970
17.347391549
L710
0.99998200
81.856


20
−225.898831342
23.521200000
SUPRA1
1.50833811
84.765


21
−171.063497139
1.525859924
L710
0.99998200
92.671


22
−22770.163604600
38.438000000
SUPRA1
1.50833811
110.016


23
−229.816390281
0.449372011
L710
0.99998200
113.280


24
1170.594630540
38.363100000
SUPRA1
1.50833811
123.463


25
−320.184892150
0.449220757
L710
0.99998200
124.404


26
335.012872058
39.596800000
SUPRA1
1.50833811
124.508


27
−764.462984962
0.448529485
L710
0.99998200
123.785


28
270.136227728
25.935800000
SUPRA1
1.50833811
113.275


29
1248.618077510
4.599063715
L710
0.99998200
111.173


30
177.098661261
18.578800000
SUPRA1
1.50833811
96.787


31
131.459110961
48.903368693
L710
0.99998200
85.123


32
−254.431714105
10.000000000
SUPRA1
1.50833811
83.644


33
149.734192113
49.544589669
L710
0.99998200
77.792


34
−137.204786283
10.000000000
SUPRA1
1.50833811
78.174


35
1410.223675540
43.113042129
L710
0.99998200
89.233


36
−134.825941720
35.292100000
SUPRA1
1.50833811
91.558


37
−168.418502871
4.049119334
L710
0.99998200
110.696


38
−350.805989269
24.010800000
SUPRA1
1.50833811
123.308


39
−244.301424027
5.341877309
L710
0.99998200
128.188


40
4941.534628580
43.549100000
SUPRA1
1.50833811
146.729


41
−357.889527255
4.028668923
L710
0.99998200
148.997


42
1857.663670230
40.932000000
SUPRA1
1.50833811
155.818


43
−507.091567715
−1.371361371
L710
0.99998200
156.540


44
0.000000000
2.120040201
L710
0.99998200
155.343


45
637.188120359
28.431900000
SUPRA1
1.50833811
156.764


46
−4285.746531360
0.447699567
L710
0.99998200
156.510


47
265.928249908
45.432900000
SUPRA1
1.50833811
152.266


48
1127.170329670
56.966580248
L710
0.99998200
150.172


49
−273.057181282
24.571800000
SUPRA1
1.50833811
149.291


50
−296.450446798
2.661459751
L710
0.99998200
149.961


51
−317.559071036
23.847600000
SUPRA1
1.50833811
147.915


52
−297.103672940
0.449161173
L710
0.99998200
147.956


53
223.869192775
28.117900000
SUPRA1
1.50833811
122.290


54
548.591751129
1.339172987
L710
0.99998200
120.081


55
123.937471688
34.861300000
SUPRA1
1.50833811
99.087


56
211.883788830
0.952940583
L710
0.99998200
93.588


57
121.391085072
21.109500000
SUPRA1
1.50833811
82.604


58
178.110541498
13.676325222
L710
0.99998200
76.860


59
314.102464129
10.000000000
SUPRA1
1.50833811
71.076


60
60.563892001
10.077651049
L710
0.99998200
49.477


61
71.706607533
10.069000000
SUPRA1
1.50833811
47.911


62
53.184242317
0.732248727
L710
0.99998200
40.780


63
48.728728866
24.194000000
SUPRA1
1.50833811
39.753


64
325.049018458
4.167687088
L710
0.99998200
35.772


65
0.000000000
5.000000000
SUPRA1
1.50833811
32.831


66
0.000000000
12.000000000
L710
0.99998200
29.694


67
0.000000000
0.000000000

1.00000000
13.603
















TABLE 3





j31o
























REFRACTIVE







INDEX
1⁄2 FREE


SURFACE
RADII
THICKNESSES
LENSES
157.63 nm
DIAMETER





 0
0.000000000
38.482288093

1.00000000
85.333


 1
304.292982078
22.168809366
CAF2HL
1.55840983
92.476


 2
2741.794481050
96.128678854

1.00000000
92.204


 3
0.000000000
0.000000000

−1.00000000
131.930


REFL


 4
0.000000000
−467.095641350

−1.00000000
90.070


 5
199.893955036
−10.268444544
CAF2HL
−1.55840983
91.280


 6
486.702942680AS
−26.734713685

−1.00000000
96.529


 7
186.738998389
−10.064297945
CAF2HL
−1.55840983
99.240


 8
447.975139348
−19.001496621

−1.00000000
111.362


 9
243.529966034
19.001496621

1.00000000
114.369


REFL


10
447.975139348
10.064297945
CAF2HL
1.55840983
112.384


11
186.738998389
26.734713685

1.00000000
102.903


12
486.702942680AS
10.268444544
CAF2HL
1.55840983
101.523


13
199.893955036
464.738613843

1.00000000
96.499


14
0.000000000
0.000000000

−1.00000000
115.398


REFL


15
0.000000000
−100.235657635

−1.00000000
92.746


16
−536.442986965
−25.379215206
CAF2HL
−1.55840983
94.306


17
629.049380815
−7.436012624

−1.00000000
93.787


18
0.000000000
−118.304806660

−1.00000000
91.342


19
−312.177007433AS
−24.720749191
CAF2HL
−1.55840983
94.928


20
−734.696609024
−220.443381712

−1.00000000
94.168


21
−277.004238298AS
−15.426909916
CAF2HL
−1.55840983
96.206


22
−460.130899964
−73.782961291

−1.00000000
95.245


23
−158.318468619
−30.586960517
CAF2HL
−1.55840983
91.460


24
−162.867000225
−41.632945268

−1.00000000
84.793


25
419.508310212
−20.539965049
CAF2HL
−1.55840983
84.016


26
−238.581080262
−31.955227253

−1.00000000
85.006


27
−430.197019246
−30.182066783
CAF2HL
−1.55840983
92.237


28
691.939037816AS
−23.703096035

−1.00000000
93.527


29
−241.462660758AS
−10.000000000
CAF2HL
−1.55840983
97.681


30
−182.472613831
−25.656103361

−1.00000000
96.159


31
−420.041190250
−36.705938298
CAF2HL
−1.55840983
98.541


32
324.867666879
−43.586137768

−1.00000000
99.096


33
−44866.873107000
36.893151865

−1.00000000
93.979


34
−149.830817441
−28.311419778
CAF2HL
−1.55840983
94.246


35
−315.631878253AS
−18.939811826

−1.00000000
91.369


36
−172.862510793
−12.271843841
CAF2HL
−1.55840983
87.996


37
−115.635345524
−27.567353538

−1.00000000
81.847


38
−229.213645994AS
−32.436472831
CAF2HL
−1.55840983
82.617


39
474.721571790
−3.611495525

−1.00000000
81.971


40
−152.435372054
−30.802088433
CAF2HL
−1.55840983
75.907


41
−530.778945822
−8.465514650

−1.00000000
70.966


42
−159.504999222
−41.060952888
CAF2HL
−1.55840983
63.576


43
3040.455878600
−4.225976128

−1.00000000
51.729


44
−226.630329417AS
−24.123224774
CAF2HL
−1.55840983
44.179


45
897.778633917
−8.617797536

−1.00000000
33.827


46
0.000000000
−8.000000000
CAF2HL
−1.55840983
22.352


47
0.000000000
−2.000000000
IMMERS
−1.39000000
18.217


48
0.000000000
0.000000000

−1.00000000
17.067










ASPHERIC CONSTANTS





SURFACE NO. 6










K
0.0000



C1
3.87858881e−009



C2
−1.57703627e−013



C3
1.62703226e−017



C4
−1.12332671e−021



C5
−1.51356191e−026



C6
8.57130323e−031







SURFACE NO. 12










K
0.0000



C1
3.87858881e−009



C2
−1.57703627e−013



C3
1.62703226e−017



C4
−1.12332671e−021



C5
−1.51356191e−026



C6
8.57130323e−031







SURFACE NO. 19










K
0.0000



C1
3.62918557e−009



C2
6.75596543e−014



C3
5.68408321e−019



C4
−6.78832654e−023



C5
6.78338885e−027



C6
−2.05303753e−031







SURFACE NO. 21










K
0.0000



C1
1.19759751e−008



C2
7.35438590e−014



C3
7.03292772e−019



C4
−1.26321026e−023



C5
−3.01047364e−027



C6
2.08735313e−031







SURFACE NO. 28










K
0.0000



C1
−8.39294529e−009



C2
−3.39607506e−013



C3
8.76320979e−018



C4
−1.43578199e−021



C5
5.59234999e−026



C6
2.01810948e−030







SURFACE NO. 29










K
0.0000



C1
1.74092829e−008



C2
−1.69607632e−013



C3
1.18281063e−017



C4
−3.08190938e−021



C5
1.70082968e−025



C6
−1.68479126e−030







SURFACE NO. 35










K
0.0000



C1
−2.14453018e−008



C2
6.73947641e−013



C3
−4.84677574e−017



C4
5.99264335e−021



C5
−2.87629386e−025



C6
3.90592520e−031







SURFACE NO. 38










K
0.0000



C1
1.60415031e−008



C2
4.78837509e−015



C3
2.08320399e−016



C4
−2.87713700e−020



C5
1.77485272e−024



C6
−1.93501550e−029







SURFACE NO. 44










K
0.0000



C1
−6.56394686e−008



C2
−8.25210588e−012



C3
−1.27328625e−016



C4
−1.16616292e−020



C5
−1.58133131e−023



C6
6.39526832e−027

















TABLE 4





j32o
























REFRACTIVE







INDEX
1⁄2 FREE


SURFACE
RADII
THICKNESSES
LENSES
157.63 nm
DIAMETER





 0
0.000000000
36.500665837

1.00000000
85.333


 1
304.292982078
22.168809366
CAF2HL
1.55840983
92.166


 2
2741.794481050
96.128678854

1.00000000
91.891


 3
0.000000000
0.000000000

−1.00000000
131.415


REFL


 4
0.000000000
−467.820384551

−1.00000000
89.765


 5
199.893955036
−10.268444544
CAF2HL
−1.55840983
91.269


 6
486.702942680AS
−26.059978075

−1.00000000
96.632


 7
186.738998389
−10.064297945
CAF2HL
−1.55840983
99.260


 8
447.975139348
−19.256116633

−1.00000000
111.485


 9
243.529966034
19.256116633

1.00000000
114.609


REFL


10
447.975139348
10.064297945
CAF2HL
1.55840983
112.551


11
186.738998389
26.059978075

1.00000000
103.039


12
486.702942680AS
10.268444544
CAF2HL
1.55840983
101.801


13
199.893955036
465.028501331

1.00000000
96.752


14
0.000000000
0.000000000

−1.00000000
115.771


REFL


15
0.000000000
−100.235657635

−1.00000000
93.044


16
−536.442986965
−25.379215206
CAF2HL
−1.55840983
94.574


17
629.049380815
−8.746601911

−1.00000000
94.056


18
0.000000000
−116.715874811

−1.00000000
91.368


19
−312.177007433AS
−24.720749191
CAF2HL
−1.55840983
94.620


20
−734.696609024
−220.365529295

−1.00000000
93.861


21
−277.004238298AS
−15.426909916
CAF2HL
−1.55840983
95.944


22
−460.130899964
−74.636127671

−1.00000000
94.984


23
−158.318468619
−30.586960517
CAF2HL
−1.55840983
91.216


24
−162.867000225
−41.086604589

−1.00000000
84.569


25
419.508310212
−20.539965049
CAF2HL
−1.55840983
83.832


26
−238.581080262
−32.443299462

−1.00000000
84.836


27
−430.197019246
−30.182066783
CAF2HL
−1.55840983
92.223


28
691.939037816AS
−22.851030925

−1.00000000
93.515


29
−241.462660758AS
−10.000000000
CAF2HL
−1.55840983
97.602


30
−182.472613831
−25.705407401

−1.00000000
96.085


31
−420.041190250
−36.705938298
CAF2HL
−1.55840983
98.486


32
324.867666879
−7.220642187

−1.00000000
99.044


33
−149.830817441
−28.311419778
CAF2HL
−1.55840983
94.165


34
−315.631878253AS
−11.206528270

−1.00000000
91.678


35
0.000000000
−7.539660426

−1.00000000
92.142


36
−172.862510793
−12.271843841
CAF2HL
−1.55840983
88.327


37
−115.635345524
−27.665363620

−1.00000000
82.122


38
−229.213645994AS
−32.436472831
CAF2HL
−1.55840983
82.891


39
474.721571790
−3.783646156

−1.00000000
82.256


40
−152.435372054
−30.802088433
CAF2HL
−1.55840983
76.122


41
−530.778945822
−8.330902516

−1.00000000
71.200


42
−159.504999222
−41.060952888
CAF2HL
−1.55840983
63.821


43
3040.455878600
−4.484154484

−1.00000000
51.982


44
−226.630329417AS
−24.123224774
CAF2HL
−1.55840983
44.183


45
897.778633917
−0.971829936

−1.00000000
33.797


46
0.000000000
−9.700651756
CAF2HL
−1.55840983
31.743


47
0.000000000
−7.828847134

−1.00000000
26.288


48
0.000000000
0.000446630

−1.00000000
17.067










ASPHERIC CONSTANTS





SURFACE NO. 6










K
0.0000



C1
3.87858881e−009



C2
−1.57703627e−013



C3
1.62703226e−017



C4
−1.12332671e−021



C5
−1.51356191e−026



C6
8.57130323e−031







SURFACE NO. 12










K
0.0000



C1
3.87858881e−009



C2
−1.57703627e−013



C3
1.62703226e−017



C4
−1.12332671e−021



C5
−1.51356191e−026



C6
8.57130323e−031







SURFACE NO. 19










K
0.0000



C1
3.62918557e−009



C2
6.75596543e−014



C3
5.68408321e−019



C4
−6.78832654e−023



C5
6.78338885e−027



C6
−2.05303753e−031







SURFACE NO. 21










K
0.0000



C1
1.19759751e−008



C2
7.35438590e−014



C3
7.03292772e−019



C4
−1.26321026e−023



C5
−3.01047364e−027



C6
2.08735313e−031







SURFACE NO. 28










K
0.0000



C1
−8.39294529e−009



C2
−3.39607506e−013



C3
8.76320979e−018



C4
−1.43578199e−021



C5
5.59234999e−026



C6
2.01810948e−030







SURFACE NO. 29










K
0.0000



C1
1.74092829e−008



C2
−1.69607632e−013



C3
1.18281063e−017



C4
−3.08190938e−021



C5
1.70082968e−025



C6
−1.68479126e−030







SURFACE NO. 34










K
0.0000



C1
−2.14453018e−008



C2
6.73947641e−013



C3
−4.84677574e−017



C4
5.99264335e−021



C5
−2.87629386e−025



C6
3.90592520e−031







SURFACE NO. 38










K
0.0000



C1
1.60415031e−008



C2
4.78837509e−015



C3
2.08320399e−016



C4
−2.87713700e−020



C5
1.77485272e−024



C6
−1.93501550e−029







SURFACE NO. 44










K
0.0000



C1
−6.56394686e−008



C2
−8.25210588e−012



C3
−1.27328625e−016



C4
−1.16616292e−020



C5
−1.58133131e−023



C6
6.39526832e−027

















TABLE 5





j33o
























REFRACTIVE







INDEX
1⁄2 FREE


SURFACE
RADII
THICKNESSES
LENSES
157.63 nm
DIAMETER





 0
0.000000000
38.054423655

1.00000000
85.333


 1
304.292982078
22.168809366
CAF2HL
1.55840983
92.441


 2
2741.794481050
96.128678854

1.00000000
92.171


 3
0.000000000
0.000000000

−1.00000000
131.865


REFL


 4
0.000000000
−467.749539716

−1.00000000
90.082


 5
199.893955036
−10.268444544
CAF2HL
−1.55840983
91.444


 6
486.702942680AS
−25.540971142

−1.00000000
96.627


 7
186.738998389
−10.064297945
CAF2HL
−1.55840983
98.903


 8
447.975139348
−19.398954786

−1.00000000
110.873


 9
243.529966034
19.398954786

1.00000000
114.137


REFL


10
447.975139348
10.064297945
CAF2HL
1.55840983
111.985


11
186.738998389
25.540971142

1.00000000
102.576


12
486.702942680AS
10.268444544
CAF2HL
1.55840983
101.403


13
199.893955036
465.154328539

1.00000000
96.394


14
0.000000000
0.000000000

−1.00000000
115.447


REFL


15
0.000000000
−100.235657635

−1.00000000
92.750


16
−536.442986965
−25.379215206
CAF2HL
−1.55840983
94.346


17
629.049380815
−8.324209221

−1.00000000
93.829


18
0.000000000
−117.663111488

−1.00000000
91.238


19
−312.177007433AS
−24.720749191
CAF2HL
−1.55840983
94.838


20
−734.696609024
−220.431435837

−1.00000000
94.085


21
−277.004238298AS
−15.426909916
CAF2HL
−1.55840983
96.283


22
−460.130899964
−74.271177440

−1.00000000
95.326


23
−158.318468619
−30.586960517
CAF2HL
−1.55840983
91.580


24
−162.867000225
−41.410948173

−1.00000000
84.915


25
419.508310212
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ASPHERIC CONSTANTS





SURFACE NO. 6










K
0.0000



C1
3.87858881e−009



C2
−1.57703627e−013



C3
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SURFACE NO. 12










K
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C2
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SURFACE NO. 19










K
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C1
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SURFACE NO. 21










K
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SURFACE NO. 28










K
0.0000



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C2
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SURFACE NO. 29










K
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C2
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SURFACE NO. 32










K
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C1
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C2
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SURFACE NO. 34










K
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SURFACE NO. 38










K
0.0000



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C2
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C4
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C5
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SURFACE NO. 44










K
0.0000



C1
−6.56394686e−008



C2
−8.25210588e−012



C3
−1.27328625e−016



C4
−1.16616292e−020



C5
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C6
6.39526832e−027

## Claims

1. A system, comprising:
a projection objective configured to image radiation from an object plane to an image plane along a radiation path, the projection objective having an optical axis, the projection objective comprising:
a plurality of optical elements along the optical axis of the projection objective, the plurality of optical elements comprising a last optical element and a penultimate optical element, the last optical element being the optical element of the plurality of optical elements which is closest to the image plane along the radiation path, and the penultimate optical element being the optical element of the plurality of optical elements which is second closest to the image plane along the radiation path,

wherein:
during use of the system, an immersion liquid is present between the last optical element and the image plane;
the system is configured so that, during use of the system, a distance between at least two of the optical elements of the plurality of optical elements of the projection objective is varied to reduce at least one aberration induced by a change in a property of the immersion liquid; and
the projection objective is a microlithography projection objective.

2. The system of claim 1, wherein the distance between the at least two optical elements is variable along the optical axis of the projection objective.

3. The system of claim 1, further comprising a positioning device configured to move at least one of the plurality of optical elements relative to the image plane.

4. The system of claim 3, wherein the positioning device is configured to move one of the at least two optical elements relative to the image plane.

5. The system of claim 1, further comprising a positioning device configured to move at least one of the optical elements along the optical axis of the projection objective.

6. The system of claim 5, wherein the positioning device is configured to move one of the at least two optical elements along the optical axis of the projection objective.

7. The system of claim 1, further comprising the immersion liquid between the last optical element and the image plane.

8. The system of claim 7, further comprising a positioning device configured to move at least one of the plurality of optical elements relative to the image plane, wherein the positioning device is configured to vary the distance between the at least two of the optical elements along the radiation path to compensate for temperature variations of the immersion liquid or of the environment.

9. The system of claim 1, wherein at least one of the plurality of optical elements is exchangeable.

10. The system of claim 1, wherein the last optical element is exchangeable.

11. The system of claim 1, wherein the system is configured so that, during use of the projection objective, aberrations in the projection objective can be compensated by optical elements other than the last optical element.

12. The system of claim 1, wherein at least one of the optical elements has an aspheric surface.

13. The system of claim 1, wherein at least one of the optical elements has a surface with a surface curvature that can be varied.

14. The system of claim 1, wherein the last optical element is displaceable.

15. The system of claim 1, wherein the last optical element is displaceable along the optical axis of the projection objective.

16. The system of claim 1, wherein the projection objective is a catadioptric projection projective.

17. The system of claim 1, wherein the projection objective has at least one real intermediate image.

18. The system of claim 1, wherein the last optical element comprises a number of mutually detachable components that are spaced from one another or that are interconnected in an optically neutral fashion.

19. The system of claim 18, wherein components of the last optical element comprise different optical materials.

20. The system of claim 19, wherein at least one component of the last optical element comprises fluoride crystal.

21. The system of claim 1, wherein the last optical element has an entrance side radius of curvature and an exit side radius of curvature.

22. The system of claim 1, wherein the last optical element comprises quartz glass.

23. The system of claim 1, wherein the property of the immersion liquid comprises a temperature of the immersion liquid.

24. The system of claim 1, wherein the property of the immersion liquid comprises an amount of bubble formation in the immersion liquid.

25. The system of claim 1, wherein the property of the immersion liquid comprises a degree of evenness of a surface of the immersion liquid.

26. The system of claim 1, wherein one of the at least two optical elements is upstream of the penultimate optical element along the optical axis of the projection objective.

27. The system of claim 1, wherein, during use of the system, a position of an optical element upstream of the penultimate optical element along the optical axis of the projection objective is varied to compensate for a change in temperature of the immersion liquid.

28. The system of claim 1, wherein, during use of the system, a position of an optical element upstream of the penultimate optical element along the optical axis of the projection objective is varied to compensate for a change in a volume of the immersion liquid present between the last optical element and the image plane.

29. The system of claim 1, wherein, during use of the system, a position of an optical element upstream of the penultimate optical element along the optical axis of the projection objective is varied to compensate for a change in an amount of bubble formation in the immersion liquid.

30. The system of claim 1, wherein, during use of the system, a position of an optical element upstream of the penultimate optical element along the optical axis of the projection objective is varied to compensate for a change in a degree of evenness of a surface of the immersion liquid.

31. The system of claim 1, wherein the at least one aberration comprises a spherical aberration.

32. The system of claim 1, further comprising the immersion liquid.

33. The system of claim 1, wherein the plurality of optical elements of the projection objective comprises at least five displaceable optical elements.

34. The system of claim 1, wherein the at least two of the optical elements comprise the last optical element and the penultimate optical element.

35. A projection exposure machine, comprising:
a projection objective configured to image radiation from an object plane to an image plane along a radiation path, the projection objective having an optical axis, the projection objective comprising:
a plurality of optical elements along the optical axis of the projection objective, the plurality of optical elements comprising a last optical element and a penultimate optical element, the last optical element being the optical element of the plurality of optical elements which is closest to the image plane along the radiation path, and the penultimate optical element being the optical element of the plurality of optical elements which is second closest to the image plane along the radiation path,

wherein:
during use of the machine, an immersion liquid is present between the last optical element and the image plane;
the machine is configured so that, during use of the machine, a distance between at least two of the optical elements of the plurality of optical elements of the projection objective is varied to reduce at least one aberration induced by a change in a property of the immersion liquid;
the projection exposure machine is a microlithography projection exposure machine.

36. The machine of claim 35, wherein the last optical element has an entrance side radius of curvature and an exit side radius of curvature.

37. The machine of claim 35, wherein the last optical element comprises quartz glass.

38. The machine of claim 35, wherein the property of the immersion liquid comprises a temperature of the immersion liquid.

39. The machine of claim 35, wherein the property of the immersion liquid comprises an amount of bubble formation in the immersion liquid.

40. The machine of claim 35, wherein the property of the immersion liquid comprises a degree of evenness of a surface of the immersion liquid.

41. The machine of claim 35, wherein one of the at least two optical elements is upstream of the penultimate optical element along the optical axis of the projection objective.

42. The machine of claim 35, wherein, during use of the machine, a position of an optical element upstream of the penultimate optical element along the optical axis of the projection objective is varied to compensate for a change in temperature of the immersion liquid.

43. The machine of claim 35, wherein, during use of the machine, a position of an optical element upstream of the penultimate optical element along the optical axis of the projection objective is varied to compensate for a change in a volume of the immersion liquid present between the last optical element and the image plane.

44. The machine of claim 35, wherein, during use of the machine, a position of an optical element upstream of the penultimate optical element along the optical axis of the projection objective is varied to compensate for a change in an amount of bubble formation in the immersion liquid.

45. The machine of claim 35, wherein, during use of the system, a position of an optical element upstream of the penultimate optical element along the optical axis of the projection objective is varied to compensate for a change in a degree of evenness of a surface of the immersion liquid.

46. The machine of claim 35, wherein the at least one aberration comprises a spherical aberration.

47. The machine of claim 35, further comprising the immersion liquid.

48. The machine of claim 35, wherein the plurality of optical elements of the projection objective comprises at least five displaceable optical elements.

49. The machine of claim 35, wherein the at least two of the optical elements comprise the last optical element and the penultimate optical element.

50. A method, comprising:
using a projection exposure machine to produce semiconductor components, the projection exposure machine comprising a projection objective configured to image radiation from an object plane to an image plane along a radiation path, the projection objective having an optical axis, the projection objective comprising:
a plurality of optical elements along the optical axis of the projection objective, the plurality of optical elements comprising a last optical element and a penultimate optical element, the last optical element being the optical element of the plurality of optical elements which is closest to the image plane along the radiation path, and the penultimate optical element being the optical element of the plurality of optical elements which is second closest to the image plane along the radiation path,

wherein, during the method:
an immersion liquid is present between the last optical element and the image plane; and
a distance between at least two of the optical elements of the plurality of optical elements of the projection objective is varied to reduce at least one aberration induced by a change in a temperature in the machine.

51. The method of claim 50, wherein the last optical element has an entrance side radius of curvature and an exit side radius of curvature.

52. The method of claim 50, wherein the last optical element comprises quartz glass.

53. The method of claim 50, wherein the property of the immersion liquid comprises a temperature of the immersion liquid.

54. The method of claim 50, wherein the property of the immersion liquid comprises an amount of bubble formation in the immersion liquid.

55. The method of claim 50, wherein the property of the immersion liquid comprises a degree of evenness of a surface of the immersion liquid.

56. The method of claim 50, wherein one of the at least two optical elements is upstream of the penultimate optical element along the optical axis of the projection objective.

57. The method of claim 50, wherein, during use of the system, a position of an optical element upstream of the penultimate optical element along the optical axis of the projection objective is varied to compensate for a change in temperature of the immersion liquid.

58. The method of claim 50, wherein, during use of the system, a position of an optical element upstream of the penultimate optical element along the optical axis of the projection objective is varied to compensate for a change in a volume of the immersion liquid present between the last optical element and the image plane.

59. The method of claim 50, wherein, during use of the system, a position of an optical element upstream of the penultimate optical element along the optical axis of the projection objective is varied to compensate for a change in an amount of bubble formation in the immersion liquid.

60. The method of claim 50, wherein, during use of the system, a position of an optical element upstream of the penultimate optical element along the optical axis of the projection objective is varied to compensate for a change in a degree of evenness of a surface of the immersion liquid.

61. The method of claim 50, wherein the at least one aberration comprises a spherical aberration.

62. The method of claim 50, further comprising the immersion liquid.

63. The method of claim 50, wherein the plurality of optical elements of the projection objective comprises at least five displaceable optical elements.

64. The method of claim 50, wherein the at least two of the optical elements comprise the last optical element and the penultimate optical element.