Abstract:
In a method of manufacturing projection objectives including defining an initial design for a projection objective and optimizing the design using a merit function, a set of related projection objectives including a first projection objective and at least one second projection objective is defined. Further, a plurality of merit function components, each of which reflects a particular quality parameter, is defined. One of these merit function components defines a common module requirement requiring that the first projection objective and the second projection objective each include at least one common optical module that is constructed to be substantially identical for the first and the second projection objective. The method results in a set of projection objectives having at least one common optical module. Employing the method in the manufacturing of complex projection objectives, such as projection objectives for microlithography, facilitates the manufacturing process and allows substantial cost savings.

Description:
[0001]     This application claims benefit of provisional application U.S. Ser. No. 60/687,877 filed on Jun. 7, 2005. The complete disclosure of this provisional application is incorporated into the present application by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the invention  
         [0003]     The present invention relates to a method of manufacturing projection objectives including defining an initial design for a projection objective and optimizing the design using a merit function. The method is used in the manufacturing of projection objectives, for example those used in a microlithographic process of manufacturing miniaturized devices.  
         [0004]     2. Brief Description of the Related Art  
         [0005]     Microlithographic processes are commonly used in the manufacture of miniaturized devices, such as integrated circuits, liquid crystal elements, micro-patterned structures and micro-mechanical components. In that process, a projection objective serves to project patterns of a patterning structure (usually a photo mask (mask, reticle)) onto a substrate (usually a semiconductor wafer). The substrate is coated with a photosensitive layer (resist) which is exposed with an image of the patterning structure using projection radiation.  
         [0006]     In order to create even finer structures, it is sought to both increase the image-side numerical aperture (NA) of the projection objective and to employ shorter wavelength, preferably ultraviolet radiation with wavelength less than about 260 nm. As a consequence, increasingly high demands are placed on the complexity of the projection objective. A projection objective usually has a plurality of at least 10 or 20 or even 25 optical elements, such as lenses, curved mirrors and the like. Each single optical element as well as the entire structure containing the plurality of optical elements arranged in a certain way must be designed and manufactured to a high accuracy to provide an imaging of the patterning structure onto the substrate within a large image field and with a low level of aberrations.  
         [0007]     Generating a new design of a projection objective is a complicated task involving an optimization of structural parameters and quality parameters of the projection objective. The structural parameters include refractive indices of materials of which the lenses are formed, surface shape parameters of lenses and mirrors (if applicable), distances between first and second surfaces of each lens, distances between surfaces of different optical elements, a distance between the object plane of the projection objective and an entry surface of the object-side front element of the projection objective, a distance between an exit surface of an image-side front element of the projection objective and the image plane, refractive indices of media disposed between adjacent optical elements, between the object plane and the object-side front element and between the image plane and the image-side front element.  
         [0008]     Quality parameters include parameters describing the optical performance of the projection objective e.g. in terms of selected aberrations, image-side numerical aperture, magnification of the projection objective and the like.  
         [0009]     In the patent U.S. Pat. No. 5,067,067 a method of manufacturing optical systems is disclosed where manufacturing considerations, such as design simplicity, glass cost, lens centerability, and manufacturability of aspheric surfaces are taken into account in the design process.  
         [0010]     The optimization of a design to conform to a desired specification of the optical performance and other quality features of the projection objective nowadays involves computational methods such as ray tracing to optimize the parameters of the projection objective while observing certain boundary conditions. CODE V, a lens analysis and design program sold by Optical Research Associates, Inc., is a commonly used software tool employed for that purpose. The optimization includes minimizing or maximizing a suitably chosen merit function depending on the parameters of the design. Typically, the merit function construction is done by utilizing several merit function components, which may represent optical aspects, manufacturability aspects and other aspects describing the optimization goal of the specific design.  
         [0011]     Due to the high number of parameters of the design, the solution space of the optimization process has high dimension, and there are many local minima and maxima in that solution space where a computational method might get trapped yielding a result far away from a design fulfilling the required specification. Therefore, an optics designer designing a projection objective for microlithography has to fulfill a sophisticated task to determine principles of a new design suitable for a certain application based on his or her intuition. A designer will therefore specify an “initial design” serving as a potentially successful “starting point” for a computer based optimization and will then improve the design based thereon by computational optimization. Typically, one or more results will still be insufficient with respect to a desired overall specification such that many efforts will have to be tried until a satisfactory solution is found. Therefore, the costs of a new design in the phase of computational manufacturing may be high.  
         [0012]     Once a suitable design has been found, the optical elements of the projection objective have to be manufactured and assembled in order to obtain the actual product of the manufacturing process. Typically, in complex optical systems, such as projection objectives for microlithography, each optical element is mounted in a separate mount and the mounts are then assembled to obtain a barrel or casing containing the optical elements of the optical system in the specified arrangement. Typically, assembly of an optical system becomes more difficult with increasing complexity of the optical system in terms of components which have to be mounted together to obtain the complete optical system. Also, it becomes more difficult to obtain a desired optical performance the more single mounting steps are involved in manufacturing an optical system, since typically each mounting step will introduce a certain amount of inaccuracy contributing to optical aberrations.  
       SUMMARY OF THE INVENTION  
       [0013]     It is one object of the invention to provide a method of manufacturing projection objectives that allows to manufacture complex projection objectives for microlithography, in a cost effective way while maintaining high standards with respect to optical performance.  
         [0014]     As a solution to this and other objects, this invention, according to one formulation, provides a method of manufacturing projection objectives including the steps of defining an initial design for a projection objective and optimizing the design using a merit function comprising: 
    defining a set of related projection objectives including a first projection objective and at least one second projection objective;     defining a plurality of merit function components, each of which reflects a particular quality parameter,     wherein one of the merit function components defines a common module requirement requiring that the first projection objective and the second projection objective each include at least one common optical module that is constructed to be substantially identical for the first and the second projection objectives,     where an optical module is a structure including at least two optical elements combined to perform a defined optical function;     computing a numerical value for each of the merit function components based on a corresponding feature of a preliminary design of the projection objectives;     computing from the merit function components an overall merit function expressible in numerical terms that reflect quality parameters;     successively varying at least one structural parameter of the projection objectives and recomputing a resulting overall merit function value with each successive variation until the resulting overall merit function reaches a predetermined acceptable value;     obtaining the structural parameters of the optimized projection objectives having the predetermined acceptable value for the resulting overall merit function; and     implementing the parameters to make at least one of the first and the second projection objectives.    
 
         [0024]     In this method, the first projection objective and second projection objective are designed to perform distinctly different optical functions. Therefore, the sets of quality parameters related to the optical function vary significantly between the first and the second projection objectives.  
         [0025]     Preferably, the first projection objective and the second projection objective are both configured as projection objectives suitable for micro-lithography for imaging a pattern provided in an object surface of the projection objective onto an image surface of the projection objective.  
         [0026]     For example, the first projection objective may be specified as a “dry system” or “dry objective”, where in the image space between the exit surface of a last optical element and the image plane there is a finite working distance which, during operation, is filled with air or another suitable gas, such as Helium or Nitrogen, having a refractive index n≈1. The second projection objective, in contrast, may be specified as an “immersion system” or “immersion objective” suitable for immersion lithography. In one variant of this type an immersion medium with a refractive index substantially larger than 1 is introduced into an interspace between the exit surface of a last optical element of the projection objective and the image plane, where an entry surface of the substrate can be placed.  
         [0027]     Whereas in dry objectives the image side numerical aperture is limited to values NA≦1, for example 0.8≦NA≦0.95, immersion lithography allows to obtain image side numerical apertures NA&gt;1, for example NA=1.1 or 1.2 or 1.3 or larger. Alternatively, or in addition, the image field size may differ significantly between the first optical system and the second optical system.  
         [0028]     When designing sets of projection objectives for different purposes, the invention allows to use synergy effects in the computational phase of the manufacturing process as well as in the manufacturing and assembly of the optical elements once the desired optical design has been found.  
         [0029]     The first and second projection objective of the set of related projection objectives are related in that each of that projection objectives includes at least one optical module that is also present in the other projection objective of the set. This optical module is denoted “common optical module” in this specification. Generally, an “optical module” is a structure including at least two optical elements combined in a predefined arrangement to perform a defined optical function.  
         [0030]     Although the physical structure of the optical module is substantially (essentially) the same in both projection objectives, the optical function of the optical module will generally differ between the projection objectives depending on the design and arrangement of the other optical elements of the respective projection objectives. Although the common optical module will typically have different optical functions in different optical environments, i.e. in different projection objectives of the set, the same mechanical mounting technique can be used for mounting the optical elements. Moreover, the same technologies can be used to manufacture the optical surfaces of the optical elements (spheric or aspheric) and for testing the single optical elements of the modules (component testing) as well as the entire optical module (system testing). Further, if identical modules can be used in different projection objectives of a set, logistic aspects, such as packaging, transport and so on can be facilitated. The overall costs for providing the projection objectives can therefore be drastically reduced.  
         [0031]     In preferred embodiments the common optical module includes three or more consecutive optical elements, for example four, five, six, seven, eight, nine or ten optical elements. The optical elements may be lenses only. It is also possible that the optical elements include one or more reflective components, such as at least one concave mirror and/or another curved or planar mirror.  
         [0032]     The term “common optical module” as used here is intended to encompass optical modules where the corresponding optical elements (e.g. lenses or mirrors) differ from each other no more than would be expected as a result of manufacturing tolerances, e.g. regarding surface shape, thickness of lenses, variations in refractive index etc. If aspheric surfaces are present in the common optical module, the correspnding aspheric surfaces should be similar in a sense that they can be tested using the same testing system.  
         [0033]     With regard to absolute and relative positions of optical elements in a “common optical module”, a common optical module has “substantially the same construction” in two projection objectives of a set particularly if distances between corresponding optical elements do not differ by more than 2 mm between the projection objectives.  
         [0034]     A common optical module may include at least one adjustable optical element intended and designed as a manipulator to adjust optical properties of the module. The manipulator may be used to at least partly adjust the common optical module to different installation environments and/or to different functions within the different projection objectives of a set. The manipularor may include at least one of at least one optical element displaceable parallel to the optical axis, at least one optical element displaceable transverse to the optical axis, particularly perpendicular thereto, at least one optical element tiltable about a tilting axis transverse, particularly perpendicular to the optical axis, and at least one deformable optical element associated to a driving system to provide a force or torque to actively deform that optical element such that the optical effect of that optical element is significantly changed.  
         [0035]     Typically, the potential savings in costs and efforts are higher the higher the number of optical elements within a common optical module is when compared to the overall number of optical elements in an optical system. In preferred embodiments, the common optical module includes at least 20% of all optical elements of the projection objectives, or even at least one third of all optical elements.  
         [0036]     Unlike in zoom objectives, where optical modules including one or more lens are necessary to allow relative movement of optical elements of the optical system with respect to each other, the common optical module is preferably mounted at a fixed position in the projection objective such that the relative position of the common optical module with respect to the other optical elements or the projection objective is fixed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0037]      FIG. 1  shows a schematic representation of a catadioptric projection objective having a first, refractive subsystem, a second catadioptric subsystem and a third refractive subsystem (R-C-R type) in various combinations of subsystems forming a dry objective with NA&lt;1 in  1 ( a ) and an immersion objective with NA&gt;1 in  1 ( b ) to  1 ( d );  
         [0038]      FIG. 2  shows a schematic lens section through a refractive two-belly projection objective having a sequence of negative (N) and positive (P) lens groups;  
         [0039]      FIG. 3  shows a schematic representation of a refractive projection objective consisting of two consecutive groups of lenses, where  3 ( a ) shows a dry objective with NA&lt;1 and  3 ( b ) shows an immersion objective with NA&gt;1;  
         [0040]      FIG. 4  shows diagrams indicating contributions of the lens groups of the system shown in  FIG. 2  to spherical aberration in  4 ( a ), coma in  4 ( b ) and image field curvature in  4 ( c ); and  
         [0041]      FIG. 5  shows lens sections through two optical systems of a set of a related optical systems sharing a common optical module (shaded), where  5 ( a ) shows an immersion objective having NA=1.05 and  5 ( b ) shows a dry objective having NA=0.93. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0042]     Some principles of the invention will now be explained with respect to  FIG. 1 , which shows schematic representations of related projection objectives of a set of projection objectives, where the projection objective is designed as a catadioptric projection objective for microlithography. The optical system is designed to project an image of a pattern on a reticle arranged in the planar object surface OS onto the planar image surface IS oriented parallel to the object surface on a reduced scale (e.g. 4:1) while creating exactly two real intermediate images IMI 1 , IMI 2 . The projection objective consists of three consecutive imaging subsystems SS 1 , SS 2  and SS 3  concatenated at the intermediate images and arranged in the sequence R-C-R, where “R” represents a refractive (dioptric) subsystem, “C” represents a catadioptric (or catoptric) subsystem and “-” represents the connection between the image subsystems at the intermediate image.  
         [0043]     The first subsystem SS 1  is a refractive (dioptric) subsystem (denoted R 1  or R 1 *) designed to create the first intermediate image IMI 1  from the object field such that the first intermediate image has a desired correction status, position and size suitable for further imaging by the subsequent imaging subsystems. In this respect, the first subsystem SS 1  is a “relay system”. The second subsystem SS 2  (designated C or C*) is a catadioptric or catoptric subsystem including exactly one concave mirror arranged optically between the first and second intermediate images close to or at a pupil surface. At least one additional lens is typically arranged within the second subsystem, providing negative refractive power close to the concave mirror. Positive refractive power optically closer to an intermediate image may also be provided. The second subsystem is designed to provide the major part of correction for image field curvature (Petzval sum) and longitudinal chromatic aberration (axial color, CHL). The second subsystem SS 2  forms the second intermediate image IMI 2  serving as the object of the third, refractive subsystem SS 3  (denoted R 2  or R 2 * in the figure). The third subsystem provides the major contribution to the overall reduction, thereby increasing the numerical aperture such that the substrate placed in the image surface IS is exposed with radiation, which, in the case of high aperture microlithographic projection objectives shown here, is typically in the range of NA&gt;0.8.  
         [0044]     The projection objective of  FIG. 1 ( a ) is a “dry objective” designed with respect to image aberration such that an image with low aberrations at image-side numerical aperture 0.8&lt;NA&lt;1 is obtained if an image-side working distance (finite gap between the exit surface of the projection objective and the image surface) is filled with a gas having refractive index n≈1. In contrast, the variants shown in  FIG. 1 ( b ) to ( d ) are “immersion objectives” providing image-side numerical aperture NA&gt;1 if an immersion medium with refractive index no substantially larger than 1 is present in the space adjacent to the image surface. If a liquid immersion medium, such as pure water) is used as immersion medium, a small, finite image-side working distance is provided. The lens may also be designed as a “solid immersion lens” where a planar exit surface of the projection objective is placed either in contact with an entry surface of the substrate to be exposed or within a very small distance typically smaller than the wavelength of the projection radiation in order to allow image formation using evanescent fields exiting the projection objective (so called “near field lithography”).  
         [0045]     Catadioptric projection objectives of type R-C-R consisting of a catadioptric subsystem arranged between an entry side and an exit side refractive subsystem are disclosed, for example, in U.S. application with a Ser. No. 60/573,533 filed on May 17, 2004 by the applicant. The disclosure of that application is incorporated into this application by reference. Other examples of R-C-R-Systems are shown in US 2003/0011755, WO 03/036361 or US 2002/0197946.  
         [0046]     Intensive studies by the inventor revealed that it is possible to design dry objectives on the one hand and immersion objectives on the other hand in such a way that particular groups of subsequent optical elements can be used in identical form and arrangement in a dry objective (as shown in (a)) as well as in an immersion objective (as shown in (b) to (d)). For example, the projection objective of (a) and (b) are considered as first and second optical systems of a set of related optical systems. The difference in optical function of the projection objectives is brought about by replacing the second refractive subsystem R 2  of the dry objective by a refractive subsystem of different design (designated R 2 *) in the immersion objective of (b). It has been found that the first refractive subsystem R 1  (serving as relay optics) as well as the catadioptric subsystem (denoted “C”) can be left unchanged such that the first subsystem R 1  as well as the second subsystem C each form a common optical module of the projection objectives shown in (a) and (b). In another view, the combination of the first refractive subsystem R 1  and the subsequent catadioptric subsystem C having an intermediate image IMI 1  therebetween can be regarded as one common optical module (which includes two immediately successive imaging subsystem linked at an intermediate image arranged therebetween).  
         [0047]     In a transition from the dry objective of (a) to the variant of an immersion objective shown in (c) the catadioptric second subsystem (denoted C) is the common optical module present in both projection objectives, whereas the first, refractive subsystem R 1  as well as the second, refractive subsystem R 2  have different design in the dry objective and the immersion objective (denoted R 1 * and R 2 *, respectively).  
         [0048]     In another variant shown in (d) the transition between the dry objective of (a) and the immersion objective of (d) is effected by exchanging the second, catadioptric subsystem C by subsystem C* and by exchanging the second refractive subsystem R 2  by the refractive subsystem R 2 * having different design. Here, the relay system R 1  forms the common optical module.  
         [0049]     It has been found that the object-side first, refractive subsystem SS 1  can normally be used as a common optical module for a dry system and a related immersion system. The main function of that relay system is to define the properties of the first intermediate image IMI 1  with regard to position, size and correction status in such a way that the first intermediate image can be imaged onto the image surface by the subsequent subsystems. The second, catadioptric subsystem is basically responsible for providing a major contribution to the correction of image field curvature and longitudinal chromatic aberration. In the variants of (b) and (c) the catadioptric subsystem C is identical to the corresponding subsystem in the dry objective of (a), thereby forming a common optical module. The changing requirements for image field curvature and axial color correction caused by the change in numerical aperture NA can be compensated by modifying the image side refractive subsystem R 2  when a transition is made from the dry objective to the immersion objective. Typically, one or more lenses having negative refractive power positioned appropriately in R 2  are suitable for that purpose.  
         [0050]     The invention can also be implemented in purely refractive projection objectives. Some refractive projection objectives suitable for immersion lithography have recently become known. Purely refractive projection objectives known from the international patent applications WO 03/077036 and WO 03/077037 A1 (corresponding to US 2003/3174408) of the applicant are designed as so-called “single-waist systems” or “two-belly systems” with an object-side belly, an image-side belly and a waist situated therebetween, that is to say a constriction of the beam bundle diameter. Image side numerical apertures up to NA=1.1 have been achieved in the mentioned embodiments.  FIG. 2  shows a schematic lens section through a purely refractive, rotationally symmetric reduction objective designed for projecting a pattern, arranged in the object surface OS, of a reticle or the like onto the image surface IS on a reduced scale of e.g. 4:1 or 5:1. The single-waist system has five consecutive lens groups (represented by double-arrows) that are arranged along one straight optical axis OA which is perpendicular to the planar object surface and image surface. A first lens group N 1  directly following the object surface has negative refractive power (symbolized by a double-arrow with arrow heads facing inside). A second lens group P 1  following directly thereon has positive refractive power (symbolized by a double-arrow with arrow heads facing outside). A third lens group N 2  following directly thereon has negative refractive power. A fourth lens group P 2  following directly thereon has positive refractive power. A fifth lens group P 3  following directly thereon has positive refractive power. The planar image surface (image plane) IS directly follows the fifth lens group such that the projection objective has no further lenses or lens groups apart from the first to fifth lens group. This distribution of refractive power provides a two-belly system that has an object side first belly B 1 , an image-side second belly B 2 , and a waist W lying therebetween, in which a constriction with minimum beam bundle diameter is positioned. In a transition region from the fourth lens group to the fifth lens group the system aperture is positioned in a region of relatively large beam diameters. An aperture stop AS is positioned in that region for adjusting the numerical aperture.  
         [0051]     It is known that projection objectives of this type have potential for very high image side numerical apertures, where dry systems with 0.8&lt;NA&lt;1 as well as immersion objectives with NA&gt;1 can be realized. Intensive studies of the inventor have revealed that it is possible to design a set of related projection objectives including a dry objective with 0.8&lt;NA&lt;1 as well as an immersion objective with NA&gt;1 such that both objectives have a “common optical module”, i.e. a group of consecutive optical elements which are designed substantially the same in the dry objective and in the immersion objective.  
         [0052]      FIG. 3  shows a schematic representation showing the dry objective in (a) and the related immersion objective (b). It has been found useful to design the objective such that the first two lens groups N 1  and P 1  on the object-side can be left unchanged in a transition from a dry objective to a immersion objective (or vice versa). These lens groups, identical in both objectives constitute common optical module R 1  in  FIG. 3 . The remainder three lens groups N 2 , P 2 , P 3  form a second optical module denoted R 2  for the dry objective and R 2 * for the immersion objective. The type and sequence and/or number of lenses in the second optical module differ between the dry objective and immersion objective.  
         [0053]     Considerable efforts were made to establish whether a common optical module can be designed at all and, if so, where an optimum interface position between a common optical module (identical in both objectives) and the variable optical modules (differing between both types of objectives) should be. In this embodiment, it has been found advantageous to position the interface such that maximum flexibility with respect to correction of spherical aberration, coma and image field curvature can be obtained. Analysis shows that these are the major image aberrations which differ significantly between an immersion objective having NA&gt;1 and a dry objective having NA&lt;1. For the purpose of demonstration,  FIG. 4  shows the schematic representation of the single-waist system of  FIG. 2  together with diagrams showing contributions of lenses and lens groups to spherical aberration (a), coma (b), and image field curvature (represented by the Petzval sum) in (c).  
         [0054]     The diagrams in  FIG. 4 ( a ) to ( b ) show the lens contributions of spherical aberration (SA 3 ), coma (COM 3 ) and Petzval sum (PTZ) for both types of objectives at the smallest numerical aperture NA=0.93. It has been found that these are the aberrations which are most strongly effected by a transition between a dry objective and an immersion objective.  
         [0055]     As  FIG. 4 ( a ) shows, the major contribution to spherical aberration correction originates from the three image side lens groups N 2 , P 2  and P 3  forming module R 2 . In contrast, there is almost no contribution to spherical aberration correction from the two image side lens groups N 1  and P 1 . The situation is quite similar with regard to the correction of coma, where the lenses positioned around the waist W and the lenses around the system aperture provide the major contribution for correction. With regard to Petzval sum correction it is evident from  FIG. 4 ( c ) that a major contribution is generated in the region of the waist to counterbalance opposite contributions on the image side and on the object side thereof. Therefore, it was established that the two lens groups N 1  and P 1  closest to the object surface are preferred candidates for forming a common optical module, whereas lenses closer to the image surface and placed in the waist region must be modified in a transition between a dry objective and an immersion objective of this type.  
         [0056]      FIG. 5  shows operative examples of two objectives of a set of related objectives, where an immersion objective IO is shown in (a) and a corresponding dry objective DO shown in (b). Both objectives are designed for λ=248 nm operating wavelength and have 2 mm image side working distance. The image field size of the rectangular field is 26·10.5 mm 2  in both cases (differing image field sizes are also possible). The immersion objective in (a) is operated with an immersion liquid IM (water) inserted between a planar exit surface of the projection objective and the planar image surface IS at NA=1.05. In contrast, the finite gap between the exit surface of the objective and the image surface is filled air in (b) allowing numerical aperture NA=0.93.  
         [0057]     The specifications of the designs are summarized in tabular form in tables 1(IM) and 1A(IM) for the immersion system and in table 1(DRY) and 1A(DRY) for the dry objective. In tables 1(IM) and 1(DRY) the leftmost column lists the number of the refractive, reflective, or otherwise distinguished surface, the second column lists the radius, r, of that surface [mm], the third column lists the distance, d [mm], between that surface and the next surface, a parameter that is referred to as the “thickness”, the fourth column lists the material employed for fabricating that optical element, the fifth column lists the refractive index of the material employed for its fabrication, and the sixth column lists the optically utilizable, clear, semi diameter [mm] of the optical component.  
         [0058]     In both embodiments, a number of surfaces are aspherical surfaces. Tables 1A(IM) and 1A(DRY) list the associated data for those aspherical surfaces, from which the sagitta or rising height p(h) of their surface figures as a function of the height h may be computed employing the following equation: 
 
 p ( h )=[((1 /r ) h   2 )/(1+ SQRT (1−(1+ K )(1 /r ) 2   h   2 ))]+ C 1 ·h   4   +C 2 ·h   6 + . . . , 
 
 where the reciprocal value (1/r) of the radius is the curvature of the surface in question at the surface vertex and h is the distance of a point thereon from the optical axis. The sagitta p(h) thus represents the distance of that point from the vertex of the surface in question, measured along the z-direction, i.e., along the optical axis. The constants K, C 1 , C 2 , etc., are listed in Tables 1A(IM) and 1A(DRY). 
 
         [0059]     Both systems can be physically and optically subdivided into two parts, wherein in object-side common optical module R 1  is identical in both systems, whereas the lenses following the common optical module towards the image surface form refractive optical modules R 2  and R 2 * respectively, differing significantly in construction. The common optical module consists of the first, most object wise lens group N 1  with negative refractive power and subsequent lens group P 1  with positive refractive power. Lens group N 1  consists of an image side negative lens L 1  with almost planar entry surface and concave exit surface, followed by a biconcave negative lens L 2 . Positive lens group P 1  consists of an entry side positive meniscus lens L 3  with object side concave surface, a subsequent positive meniscus lens L 4  with object side concave surface, two subsequent biconvex positive lenses L 5 , L 6 , a positive meniscus lens L 7  having image-side concave surface and a meniscus lens L 8  having image side concave surface and weak negative refractive power.  
         [0060]     The subsequent module R 2 * in the immersion system IO has, in that sequence, a negative meniscus lens L 9  having image side concave surface, a negative lens L 10  near the position of minimum beam diameter, a biconcave negative lens L 11 , a positive meniscus lens L 12  having an object side concave surface, another positive meniscus lens L 13  having object side concave surfaces, a biconvex positive lens L 14  immediately ahead of the system aperture AS, a positive lens L 15  having spherical entry surface and aspheric exit surface, two biconvex positive lenses L 16 , L 17 , a positive meniscus lens L 18  having image-side concave surface, and a piano-convex lens L 19  having spherical entry surface and planar exit surface immediately upstream of the image surface IS.  
         [0061]     With regard to the optical function, the lenses of the common optical module R 1  are predominately designed for correcting distortion and telecentricity. In the following optical module R 2 , the lenses of negative group N 2  in waist area serve primarily to correct field curvature, coma and spherical aberration. Remarkably, all lenses L 15  to L 19  between the system aperture AS and the image surface have positive refractive power, thereby effecting large convergence angle of radiation on the image side allowing NA&gt;1 at low aberration values.  
         [0062]     In contrast, in the dry objective DO of  FIG. 5 ( b ) the optical module R 2  designed for receiving radiation coming from the common optical module R 1  and to form the image in the image surface opens with four lenses L 9 , L 10 , L 11 , L 12 , being of the same type as lenses L 9 , L 10 , L 11 , L 12  in the immersion lens, but having different curvatures of their entry and exit side when compared to the lenses of the immersion objective. A biconvex positive lens L 13  having aspheric entry surface and spherical exit surface is then followed by a biconvex positive lens L 14  immediately ahead of the system aperture, which is positioned closer to the waist as in the corresponding immersion objective. Fifth lens group P 3  opens with three consecutive biconvex positive lenses L 15 , L 16 , L 17 . A biconcave negative lens L 18  following this positive refractive power serves primarily for correcting higher order of spherical aberration, coma and astigmatism. Note that no negative lens is present between the system aperture and the image surface in the corresponding immersion objective. A positive meniscus lens L 19  having image side concave surface and a plano-convex lens L 20  having spherical entry surface and planar exit surface are provided between negative lens L 18  and the image surface.  
         [0063]     A direct comparison of the structural features of the image side optical modules R 2  and R 2 *, respectively reveals some characteristic differences. In the immersion objective of  FIG. 5 ( a ) it is evident that only positive lenses are present between the waist region (where the beam bundle diameter attains a local minimum at the negative lenses L 9 , L 10 , L 11 ) and the image surface IS. This appears characteristic of immersion objectives with moderate numerical aperture, e.g. close to NA=1 Immersion systems sharing this feature are disclosed in international patent application PCT/EP03/111677 filed on Oct. 22, 2003 by the applicant. The disclosure of that application is incorporated herein by reference. In contrast, high aperture dry objectives, such as shown in  FIG. 5 ( b ) require correction means for correcting higher order spherical aberration, astigmastism and coma, partly induced by high incidence angles on the last lens element adjacent to the image surface (plano-convex lens L 20 ). A suitable means for correcting these aberrations is a negative lens with high incidence angles and exit angles of radiation positioned at a location with relatively large marginal ray height and non-zero chief ray height. In the embodiment of  FIG. 5 ( b ) the biconcave negative lens L 19  is provided for that purpose at a distance both from the image surface IS and from the pupil surface where the aperature stop AS is positioned. Further, the aspherical lens surfaces have a tendency towards stronger deformations in order to provide sufficient aspherical correction contributions.  
         [0064]     The invention allows an economic manufacturing process for optical systems, where large economic benefits can be particularly obtained for complex projection objectives for microlithography, which usually include at least 15 or 20 or even more lenses which have to be mounted relative to another with high accuracy. Optical modules can be designed to form elements of a building set for projection objectives such that a projection objective can be assembled using a small number of optical modules rather than a considerably larger number of single optical elements to construct a projection objective of desired function. Projection objectives can be analyzed to identify corresponding lens groups which are identical or quite similar in construction between objectives designed for different functions. Then, an optical module can be selected and different projection objectives of a set can be reoptimized such that each of that projection objective contains at least one common optical module and the remainder of the optical elements of the projection objectives are designed such that they perform a complementary optical function which, in addition to the optical function of the optical module, provide the desired optical function of the entire optical system. A platform principle is thereby introduced into the manufacture of projection objectives. Optical modules which may be inserted into different types of projection objectives can, for example, be designed such that they provide, as a consequence of the layout and arrangement of optical elements integrated therein, a certain correcting function, e.g. by providing strong means for image field curvature correction or strong means for correction of chromatic aberrations. Based on optical modules, modular objective systems can be designed economically. Software routines allowing to identify and/or implement optical modules in the design of more complex optical systems, such as projection objectives for microlithography, will facilitate future manufacture of complex optical systems.  
         [0065]     The above description of the preferred embodiments has been given by way of example. The individual features may be implemented either alone or in combination as embodiments of the invention, or may be implemented in other fields of application. Further, they may represent advantageous embodiments that are protectable in their own right, for which protection is claimed in the application as filed or for which protection will be claimed during pendency of the application. From the disclosure given, those skilled in the art will not only understand the present invention and its attendant advantages, but will also find apparent various changes and modifications to the structures and methods disclosed. The applicant seeks, therefore, to cover all such changes and modifications as fall within the spirit and scope of the invention, as defined by the appended claims, and equivalents thereof.  
                                                                   TABLE 1                           (IM)            Sur-                   ½       face   Radius   Thickness   Material   248.413 nm   Diameter                    1   0.000000   −0.072693   AIR   1.00000000   64.573       2   −1568.789661   7.997574   SIO2V248   1.50885281   64.576       3   179.307329   28.903394   N2VP950   1.00027962   68.537       4   −239.139497   12.365315   SIO2V248   1.50885281   71.344       5   240.999846   29.475445   N2VP950   1.00027962   87.908       6   −295.435206   18.864653   SIO2V248   1.50885281   91.687       7   −222.704490   0.995368   N2VP950   1.00027962   100.305       8   −487.550219   59.663902   SIO2V248   1.50885281   110.866       9   −140.510438   0.996298   N2VP950   1.00027962   116.884       10   1032.321269   37.461425   SIO2V248   1.50885281   138.690       11   −548.511138   0.998331   N2VP950   1.00027962   140.110       12   386.191635   57.490161   SIO2V248   1.50885281   144.024       13   −622.506816   0.997700   N2VP950   1.00027962   143.235       14   132.978383   37.383993   SIO2V248   1.50885281   117.701       15   163.622598   0.996878   N2VP950   1.00027962   111.190       16   114.712308   37.102128   SIO2V248   1.50885281   101.271       17   76.476917   51.643602   N2VP950   1.00027962   73.679       18   316.074243   8.841198   SIO2V248   1.50885281   72.421       19   124.873355   33.181993   N2VP950   1.00027962   66.802       20   −225.913541   7.995634   SIO2V248   1.50885281   66.330       21   −1327.805953   34.931398   N2VP950   1.00027962   66.776       22   −88.113887   8.049540   SIO2V248   1.50885281   66.984       23   174.578294   39.260889   N2VP950   1.00027962   87.783       24   −222.318895   53.924677   SIO2V248   1.50885281   91.654       25   −125.994492   1.002701   N2VP950   1.00027962   105.238       26   −2199.468630   37.301168   SIO2V248   1.50885281   132.598       27   −278.591993   1.002786   N2VP950   1.00027962   136.431       28   773.924176   46.632587   SIO2V248   1.50885281   152.754       29   −581.071531   3.645363   N2VP950   1.00027962   154.105       30   0.000000   0.000000   N2VP950   1.00027962   155.423       31   0.000000   −2.518406   N2VP950   1.00027962   155.423       32   408.098313   43.702061   SIO2V248   1.50885281   159.975       33   −1966.854092   27.972966   N2VP950   1.00027962   159.696       34   560.565495   54.864023   SIO2V248   1.50885281   160.030       35   −506.420373   0.976063   N2VP950   1.00027962   159.071       36   301.425947   59.017885   SIO2V248   1.50885281   143.308       37   −771.109601   0.996421   N2VP950   1.00027962   139.750       38   00.000000   0.000000   SIO2V248   1.50885281   128.777       39   00.000000   0.000000   N2VP950   1.00027962   128.777       40   124.354764   38.279833   SIO2V248   1.50885281   94.285       41   144.861269   1.410713   N2VP950   1.00027962   79.139       42   126.842984   84.340472   SIO2V248   1.50885281   74.643       43   0.000000   2.000000   H2OV248   1.37831995   16.375       44   0.000000   0.000000   AIR   0.00000000   14.020                  
 
         [0066]    
       
         
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1A 
               
               
                   
               
               
                   
               
               
                 (IM) 
               
               
                 Aspheric Constants 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 SRF 
                 2 
                 5 
                 6 
                 13 
                 21 
               
               
                   
               
               
                 K 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C1 
                 1.762082e−07 
                 −9.183634e−08 
                 −3.408842e−08 
                 −1.500515e−08 
                 1.127039e−07 
               
               
                 C2 
                 −2.759343e−11 
                 −1.102652e−11 
                 −3.329749e−13 
                 2.780276e−13 
                 1.111238e−12 
               
               
                 C3 
                 2.019270e−15 
                 1.690219e−15 
                 7.575864e−17 
                 7.828638e−18 
                 −3.911416e−16 
               
               
                 C4 
                 −2.728143e−19 
                 −1.904109e−19 
                 1.115585e−21 
                 −2.049366e−22 
                 −7.973208e−20 
               
               
                 C5 
                 1.912846e−23 
                 1.250178e−23 
                 3.086727e−25 
                 7.458985e−28 
                 −2.663011e−26 
               
               
                 C6 
                 −8.094791e−28 
                 −4.350273e−28 
                 −3.363604e−29 
                 6.905378e−32 
                 −2.455555e−27 
               
               
                   
               
               
                 SRF 
                 23 
                 26 
                 33 
                 35 
                 41 
               
               
                   
               
               
                 K 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C1 
                 −1.732944e−07 
                 −2.550983e−08 
                 3.634681e−10 
                 5.751410e−09 
                 −6.234011e−08 
               
               
                 C2 
                 7.577403e−12 
                 6.612947e−13 
                 4.221634e−13 
                 3.010024e−14 
                 7.109989e−13 
               
               
                 C3 
                 −4.469153e−16 
                 2.051494e−18 
                 −2.553884e−18 
                 −2.922458e−19 
                 2.225044e−16 
               
               
                 C4 
                 2.812559e−20 
                 1.694020e−22 
                 −1.591737e−22 
                 1.024859e−23 
                 9.462190e−21 
               
               
                 C5 
                 −1.483815e−24 
                 −9.918545e−27 
                 5.564228e−27 
                 −4.178737e−28 
                 −1.041202e−24 
               
               
                 C6 
                 3.233356e−29 
                 −4.711136e−32 
                 −7.404837e−32 
                 1.770091e−32 
                 1.697312e−28 
               
               
                   
               
             
          
         
       
     
         [0067]    
       
         
               
             
               
               
               
               
               
               
             
               
             
               
               
             
               
               
               
               
               
               
             
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1A 
               
               
                   
               
               
                   
               
               
                 (DRY) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Surface 
                 Radius 
                 Thickness 
                 Material 
                 248.413 nm 
                 ½ Diameter 
               
               
                   
               
               
                  1 
                 0.000000 
                 −0.072693 
                 AIR 
                 1.00000000 
                 63.657 
               
               
                  2 
                 −1568.789661 
                 7.997574 
                 SIO2V248 
                 1.50885281 
                 63.660 
               
               
                  3 
                 179.307329 
                 28.903394 
                 N2VP950 
                 1.00027962 
                 67.093 
               
               
                  4 
                 −239.139497 
                 12.365315 
                 SIO2V248 
                 1.50885281 
                 70.138 
               
               
                  5 
                 240.999846 
                 29.475445 
                 N2VP950 
                 1.00027962 
                 85.099 
               
               
                  6 
                 −295.435206 
                 18.864653 
                 SIO2V248 
                 1.50885281 
                 89.422 
               
               
                  7 
                 −222.704490 
                 0.995368 
                 N2VP950 
                 1.00027962 
                 97.768 
               
               
                  8 
                 −487.550219 
                 59.663902 
                 SIO2V248 
                 1.50885281 
                 107.211 
               
               
                  9 
                 −140.510438 
                 0.996298 
                 N2VP950 
                 1.00027962 
                 114.432 
               
               
                 10 
                 1032.321269 
                 37.461425 
                 SIO2V248 
                 1.50885281 
                 133.267 
               
               
                 11 
                 −548.511138 
                 0.998331 
                 N2VP950 
                 1.00027962 
                 134.835 
               
               
                 12 
                 386.191635 
                 57.490161 
                 SIO2V248 
                 1.50885281 
                 137.838 
               
               
                 13 
                 −622.506816 
                 0.997700 
                 N2VP950 
                 1.00027962 
                 136.683 
               
               
                 14 
                 132.978383 
                 37.383993 
                 SIO2V248 
                 1.50885281 
                 113.546 
               
               
                 15 
                 163.622598 
                 0.996878 
                 N2VP950 
                 1.00027962 
                 105.837 
               
               
                 16 
                 114.712308 
                 37.102128 
                 SI02V248 
                 1.50885281 
                 97.416 
               
               
                 17 
                 76.476917 
                 51.643602 
                 N2VP950 
                 1.00027962 
                 71.636 
               
               
                 18 
                 243.797872 
                 8.221467 
                 SIO2V248 
                 1.50885281 
                 67.859 
               
               
                 19 
                 118.695868 
                 32.198276 
                 N2VP950 
                 1.00027962 
                 62.684 
               
               
                 20 
                 −229.848945 
                 21.449544 
                 SIO2V248 
                 1.50885281 
                 61.674 
               
               
                 21 
                 −17500.763773 
                 33.930639 
                 N2VP950 
                 1.00027962 
                 61.163 
               
               
                 22 
                 −88.133632 
                 9.868811 
                 SIO2V248 
                 1.50885281 
                 61.503 
               
               
                 23 
                 129.878510 
                 38.225149 
                 N2VP950 
                 1.00027962 
                 79.008 
               
               
                 24 
                 −430.176656 
                 48.625825 
                 SIO2V248 
                 1.50885281 
                 90.542 
               
               
                 25 
                 −122.664976 
                 14.863955 
                 N2VP950 
                 1.00027962 
                 97.516 
               
               
                 26 
                 1552.236460 
                 29.760537 
                 SIO2V248 
                 1.50885281 
                 128.434 
               
               
                 27 
                 −507.758891 
                 0.997436 
                 N2VP950 
                 1.00027962 
                 131.180 
               
               
                 28 
                 2202.661441 
                 31.295168 
                 SIO2V248 
                 1.50885281 
                 137.481 
               
               
                 29 
                 −592.000509 
                 −14.590008 
                 N2VP950 
                 1.00027962 
                 139.744 
               
               
                 30 
                 0.000000 
                 0.000000 
                 N2VP950 
                 1.00027962 
                 140.208 
               
               
                 31 
                 0.000000 
                 15.640781 
                 N2VP950 
                 1.00027962 
                 140.208 
               
               
                 32 
                 333.156274 
                 49.531474 
                 SIO2V248 
                 1.50885281 
                 152.296 
               
               
                 33 
                 −3915.908064 
                 0.997316 
                 N2VP950 
                 1.00027962 
                 151.995 
               
               
                 34 
                 606.546299 
                 61.671577 
                 SIO2V248 
                 1.50885281 
                 150.470 
               
               
                 35 
                 −321.412235 
                 0.980027 
                 N2VP950 
                 1.00027962 
                 149.003 
               
               
                 36 
                 215.963312 
                 52.019952 
                 SIO2V248 
                 1.50885281 
                 120.089 
               
               
                 37 
                 −1147.010839 
                 11.149517 
                 N2VP950 
                 1.00027962 
                 115.225 
               
               
                 38 
                 −478.749713 
                 7.984417 
                 SIO2V248 
                 1.50885281 
                 110.866 
               
               
                 39 
                 541.826809 
                 1.013589 
                 N2VP950 
                 1.00027962 
                 98.626 
               
               
                 40 
                 122.099360 
                 35.743898 
                 SIO2V248 
                 1.50885281 
                 84.625 
               
               
                 41 
                 384.307335 
                 1.003817 
                 N2VP950 
                 1.00027962 
                 78.062 
               
               
                 42 
                 160.120700 
                 79.558765 
                 SIO2V248 
                 1.50885281 
                 69.472 
               
               
                 43 
                 0.000000 
                 2.000000 
                 AIR 
                 1.00000000 
                 19.253 
               
               
                 44 
                 0.000000 
                 0.000000 
                 AIR 
                 0.00000000 
                 14.020 
               
               
                   
               
             
          
           
               
                 Aspheric Constants 
               
             
          
           
               
                   
                 SRF 
               
             
          
           
               
                   
                 2 
                 5 
                 6 
                 13 
                 21 
               
               
                   
               
               
                 K 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 C1 
                  1.762082e−07 
                 −9.183634e−08 
                 −3.408842e−08 
                 −1.500515e−08 
                  1.591867e−07 
               
               
                 C2 
                 −2.759343e−11 
                 −1.102652e−11 
                 −3.329749e−13 
                  2.780276e−13 
                  3.825677e−12 
               
               
                 C3 
                  2.019270e−15 
                  1.690219e−15 
                  7.575864e−17 
                  7.828638e−18 
                 −1.796033e−16 
               
               
                 C4 
                 −2.728143e−19 
                 −1.904109e−19 
                  1.115585e−21 
                 −2.049366e−22 
                  2.579256e−20 
               
               
                 C5 
                  1.912846e−23 
                  1.250178e−23 
                  3.086727e−25 
                  7.458985e−28 
                 −2.598003e−23 
               
               
                 C6 
                 −8.094791e−28 
                 −4.350273e−28 
                 −3.363604e−29 
                  6.905378e−32 
                  8.580656e−29 
               
               
                   
               
             
          
           
               
                   
                 SRF 
                   
               
             
          
           
               
                   
                 23 
                 26 
                 35 
                 41 
               
               
                   
               
               
                 K 
                 0 
                 0 
                 0 
                 0 
               
               
                 C1 
                 −2.667246e−07 
                 −1.957192e−08 
                 −1.555637e−10 
                 −1.651093e−08 
               
               
                 C2 
                  1.111079e−11 
                  4.026507e−13 
                  7.732355e−13 
                  3.236859e−12 
               
               
                 C3 
                 −9.349555e−16 
                  9.196348e−18 
                 −2.130155e−17 
                  2.596274e−16 
               
               
                 C4 
                  7.382941e−20 
                  3.358355e−23 
                  5.629071e−22 
                 −5.320359e−20 
               
               
                 C5 
                 −5.553334e−24 
                  1.486969e−26 
                 −1.123450e−26 
                  4.850036e−24 
               
               
                 C6 
                  1.718260e−28 
                 −8.079874e−31 
                  1.213043e−31 
                 −2.301345e−28