Abstract:
In a lithographic projection system, a corrective optic in the form of one or more deformable plates is mounted within telecentric image or object space for making one-dimensional or two-dimensional adjustments to magnification. The deformable plate, which can be initially bent under the influence of a preload, contributes weak magnification power that influences the magnification of the projection system by changing the effective focal length in object or image space. An actuator adjusts the amount of curvature through which the deformable plate is bent for regulating the amount of magnification imparted by the deformable plate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under 35 U.S.C. §119(e) of U.S. Provisional Application Ser. No. 61/263,178 filed on U.S. Nov. 20, 2009. 
    
    
     TECHNICAL FIELD 
     The invention concerns the lithographic projection of patterns onto substrates for such purposes as the manufacture of semiconductor devices or integrated circuits including flat panel displays and particularly concerns the management of the magnification of the projected patterns. 
     BACKGROUND OF THE INVENTION 
     Microlithographic projection systems project patterns onto substrates for selectively exposing photosensitive layers at multiple stages during the manufacture of microcircuits and microdevices. Often, the patterns must be stitched together to expose extended areas or registered with underlying patterns to build the desired circuits or devices. Image magnification of the projected patterns must be finely controlled to compensate for variations in operating conditions, such as changes in ambient temperature or pressure, to properly relate the patterns in successive exposures. Stepped lithography, which requires the stitching together of adjacent patterns, generally requires magnification control in two orthogonal directions within the image plane of the projection system. Scanning lithography, which regulates exposure times in the scanning direction, generally requires magnification control in only one direction that is orthogonal to the scan direction. 
     Magnification control is typically administered by relatively translating either (a) an object conjugate (e.g., reticle) to vary a ratio of object to image distances or (b) an object field lens to relatively vary a ratio of corresponding focal distances. Both approaches require the projector systems to be non-telecentric in object space so that the component shifts change magnification. However, the same projection systems are required to be telecentric in image space so that small shifts in focus to not affect the magnification of the projected image. Illumination and projection systems combined under conditions of partial coherence further complicate the angular distribution of rays in object space required to maintain telecentricity in the image space. As a result, the component shifts within object space can, in addition to changing magnification, also distort the images projected into image space or produce wavefront aberrations. A combination of counteracting component shifts can be required to make magnification corrections with a minimum of distortion. Projection systems with telecentric object space have used corrective optics with specially shaped surfaces, variations in air pressure between lens components, and variations in beam frequency for adjusting combinations of magnification and distortion. 
     SUMMARY OF THE INVENTION 
     The invention, which is particularly applicable to doubly telecentric lithographic projection systems, features a corrective optic in the form of one or more deformable plates for making one-dimensional or two-dimensional adjustments to magnification (e.g., anamorphic magnification adjustments or radially symmetric magnification adjustments). The deformable plate contributes weak magnifying power that influences the magnification of the projection system by changing the effective focal length in object or image space. An actuator adjusts the amount of curvature through which the deformable plate is bent for regulating the amount of magnification imparted by the deformable plate. 
     Preferably, the deformable plate remains under a constant overall direction of loading throughout the predetermined range of curvature variation so that the deformable plate is continuously adjustable throughout the range. For example, the deformable plate can be initially preloaded and the subsequent loads on the deformable plate can increase or decrease with respect to the initial preload, but within its range of preferred operation, the plate is not allowed to transition through a relaxed state. The projection system is preferably designed to accommodate the initially curved condition of the deformable plate under preload and its associated contribution to the magnifying power of the projection system. 
     Changes in magnification associated with the operation of the projection system can be monitored indirectly by measuring changes in temperature or pressure in or around the projection system or directly by measuring the size of the projected pattern. A controller controls the actuator to change the curvature of the deformable plate and thereby compensate for the monitored changes in magnification. 
     One version of the invention as a magnification adjustable lithographic projection system includes a telecentric imaging system having a telecentric object or image space and a deformable plate located within the telecentric object or image space for contributing a limited amount of magnification power to the telecentric imaging system as a function of an amount of curvature of the deformable plate. An actuator adjusts the curvature of the deformable plate through a range of curvature variation for adjusting a magnification of the imaging system. 
     Preferably, the actuator provides for both increasing and decreasing curvature of the deformable plate with respect to the initially curved condition of the deformable plate. In addition, the deformable plate preferably remains under a constant overall direction of loading throughout the range of curvature variation. The actuator can be arranged to preload the deformable plate in the initially curved condition. The telecentric imaging system can be designed to a nominal state that incorporates a certain amount of magnification power imparted by the deformable plate in its initially curved condition. 
     The deformable plate preferably has an optical axis coincident with the optical axis of the imaging system in which it is mounted. For purposes of anamorphic magnification adjustment, the deformable plate is preferably bent around a single transverse axis that extends normal to the common optical axis of the deformable plate and imaging system. As such, the deformable plate can be arranged to contribute a weak amount of cylindrical magnification power. 
     The deformable plate can be a first of a plurality of deformable plates that are deformable through a predetermined range of curvature variation for adjusting a magnification of the imaging system. Each of the deformable plates preferably remains under a constant overall direction of loading throughout the predetermined range of curvature variation. The actuator can be one of a plurality of actuators for bending the deformable plates in at least two different directions, or the actuator can collectively deform the plurality of deformable plates in the same or different directions. For example, one deformable plate can be bent about a first transverse axis and another deformable plate can be bent about a second transverse axis. For purposes of increasing magnification power, the first and second transverse axes of the deformable plates can be oriented in parallel. For purposes of providing radially symmetric magnification adjustments, the first and second transverse axes of the deformable plates can be oriented orthogonally and both deformable plates can contribute equal amounts of magnification power. For purposes of anamorphic magnification adjustments, the deformable plates can contribute different amounts of magnification power or can be oriented about non-orthogonal axes. 
     Another version of the invention involves a magnification corrector for a lithographic projection system. A deformable plate is preloaded in an initially curved condition. An actuator relatively increases and decreases the curvature of the deformable plate through a range of curvatures with respect to the nominal curvature. The deformable plate remains under a constant overall direction of loading throughout the predetermined range of curvature variation. 
     The actuator preferably preloads the deformable plate in the initially curved condition. The preferred deformable plate, which can have a nominal radius of curvature of greater than 10 meters, has anterior and posterior surfaces that are bent about a transverse axis such that one of the anterior and posterior surfaces is under compression in the initially curved condition and the other of the anterior and posterior surfaces is under tension in the initially curved condition. In addition, one of the surfaces remains under compression and the other of the surfaces remains under tension throughout the predetermined range of curvature variation. 
     If the initially curved condition of the deformable plate departs from a nominal circular arcuate shape, an optical thickness of the plate can be varied to compensate for the departure from the nominal circular arcuate shape to avoid producing distortion in the imaging system. The deformable plate can include an optical region for transmitting light through the projection system and a mounting region in engagement with the actuator for imparting bending loads to the deformable plate. The actuator engages the mounting region of the deformable plate for imparting bending loads to the deformable plate. For example, the actuator can include rotatable elements in engagement with the mounting region for imparting bending moments to the deformable plate. 
     Alternatively, the deformable plate can be sealed together with a backing plate forming a sealed cavity between the deformable plate and the backing plate and the actuator regulates pressure within the sealed cavity for deforming the deformable plate through a predetermined range of curvature variation. Also possible, the deformable plate can have an orientation that subjects the deformable plate to deformation under a force of gravity. The actuator adjustably supports the deformable plate through different spans for deforming the deformable plate through the predetermined range of curvature variation. Either anamorphic or radially symmetric distortion can be effected by forces acting generally over the exposed surfaces of the deformable plates depending at least in part on the placement of the supports for the deformable plates. For example, parallel supports can be used for adjusting cylindrical magnification power and radially symmetric supports can be used for adjusting spherical magnification power. 
     Another version of the invention involves a method of adjusting magnification of a lithographic projection system. A deformable plate is mounted within a telecentric object or image space of the lithographic projection system. Magnification changes of the projection system are monitored, and the curvature of the deformable plate is adjusted through a predetermined range of curvature variation to compensate for the monitored changes in the magnification of the projection system. 
     Preferably, the deformable plate is preloaded for imparting an initial amount of curvature to the deformable plate for contributing a limited amount of magnification power to the projection system. In one or more of its various forms, the invention (a) provides independent control over magnification in two orthogonal directions, (b) has minimal impact on aberrations of imaging systems, (c) requires relatively simple mechanics for operation, (d) allows for precisely matching optical imaging systems from one lithographic tool to another, and (e) allows for precisely matching multiple optical systems within a single lithographic tool. 
     The projection system is preferably designed to incorporate the limited amount of magnification power imparted by the deformable plate in the preloaded condition. Preferably, the deformable plate is maintained under a constant overall direction of loading throughout the predetermined range of curvature variation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         FIG. 1  is a diagram of a lithographic projection system with a deformable plate within telecentric object space for purposes of magnification adjustment. 
         FIG. 2  is a side view of the deformable plate in a preloaded condition and showing depicting apparatus for preloading and otherwise bending the plate 
         FIG. 3  is a perspective view of the deformable plate depicting the plate in both its preloaded and further bent conditions in an overall cylindrical form. 
         FIG. 4  is a perspective view of two overlapping deformable plates each arranged for bending in a different orthogonal direction. 
         FIG. 5  is a cross-sectional perspective view of a sealable lens barrel for mounting a deformable plate between two independently controllable pressure chambers for spherically deforming the plate. 
         FIG. 6  is a cross-sectional view depicting a deformable plate having an aspheric surface and a varying thickness to compensate for bending forces that would otherwise distort the plate out of a desired form such as a cylindrical or spherical form. 
         FIG. 7  is a plan view of a deformable plate having slots within a mounting surface of the plate to facilitate bending the plate into a spherical form. 
         FIG. 8  is a side view of a pair of deformable plates that are simultaneously deformed into desired shapes by a common actuator. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A microlithographic projection system (tool)  10 , as an example of a projection system capable of benefitting from the invention, includes a light source  12 , an illuminator  14 , and a projection lens  16  for projecting an image of a reticle  18  onto a substrate  20 . A horizontal X-Y-axis stage  22 , which is translatable in two orthogonal directions normal to a common optical axis  24  of the illuminator  14  and the projection lens  16 , provides for relatively moving the substrate  20  with respect to the projection lens  16  for exposing successive areas of the substrate  20 . A vertical Z-axis stage  26  provides for relatively translating the projection lens  16  with respect to the substrate  20  along the optical axis  24  to provide for appropriately focusing the image of the reticle  18  onto the substrate  20 . 
     The light source  12  emits radiation in the form of a beam of light  28  appropriate for developing the photosensitive substrate  20 . A variety of known devices can be used to for the light source  12  including a lamp source, such as a high-pressure mercury arc lamp targeting certain spectral lines, or a laser source, such as an excimer laser, particularly for operating within the deep ultraviolet spectrum. 
     The illuminator  14  provides for shaping and spatially distributing the light beam  28  and targeting angular and spatial irradiance profiles set for both the pupil and image plane of the projection lens, the latter coinciding with the substrate  20 . Although not shown in detail in  FIG. 1 , typical illuminators for microlithographic operations include a profiler for collecting and shaping the beam  28 , a uniformizer (e.g., a kaleidoscope or fly&#39;s eye array) for integrating the light into a uniform irradiance field, and a relay lens for relaying an image of the output of the uniformizer to the reticle  18 , where an image plane of the illuminator  14  coincides with an object plane of the projection lens  16 . 
     The projection lens  16 , which preferably has an entrance numerical aperture larger than an exit numerical aperture of the illuminator  14  for providing partial coherent imaging, projects an image of the reticle  18  onto the substrate  20 . That is, a pupil (not shown) of the projection lens  16 , which is typically conjugate to a pupil (also not shown) in the illuminator  14 , is preferably underfilled by the image of the illuminator pupil but is sized to collect angularly divergent light from illuminated features of the reticle  18  to produce a high resolution image of the reticle  18  on the substrate  20 . The projected image of the reticle  18  can be enlarged or reduced as required. The projection lens  16  can include reflective or diffractive elements as well as refractive elements or combinations of such elements, such as in catadioptric optics. 
     The reticle  18 , also referred to as a “mask”, includes one or more patterns intended for projection onto the substrate  20  and can be sized within or beyond the field captured by the projector lens  16 . Reticles with larger patterns can be relatively translated with respect to the projection lenses to expose different parts of the reticle patterns in succession. 
     The photosensitive substrate  20  generally takes the form of a flat plate, such as a semiconductor wafer or glass panel treated with a photoresist to react to exposures of light. Often, the entire substrate  20  cannot be imaged at once, so the horizontal X-Y-axis translational stage  22  on a base  30  provides for translating the substrate  20  through a range of positions for collectively illuminating a desired working area of the substrate  20 . The projection lens  16  is supported on the vertical Z-axis translational stage  26  above the base  30  for adjusting the image distance of the projection lens  16  from the substrate  20  along the optical axis  24 . A controller  32  coordinates relative motions among the projection lens  16 , the reticle  18 , and the substrate  20  as well as the exposure of the projection system  10 . 
     A deformable plate  40  is located adjacent to the reticle  18  within a telecentric object space  36  of the projection lens  16 . The deformable plate  40  is preloaded into an initially deformed condition, which contributes a limited amount of magnification power to the projection lens  16 . As such, projection lens  16 , including the prescriptions of its other components, is designed to compensate for the limited magnification power contribution of the deformable plate in its initially deformed (preloaded) condition to preserve a nominally desired magnification of the projection lens  16 . Although shown in telecentric object space  36 , the deformable plate  40  could also be located in telecentric image space  38  adjacent to the substrate  20 . The choice can be made largely on the basis of space and access considerations. In either or both locations, the deformable plate can the control magnification in a lithographic system that is telecentric in both image and object space. 
       FIG. 2  shows the deformable plate  40  in an initially deformed (preloaded) condition bent about a single transverse axis  60 . The preload is generated by an actuator  50  acting at one end  42  of the deformable plate  40  through a pair of fulcrum supports  54  and  56  and an anchor  52  at the other end  44 . The deformation places an anterior surface  46  of the deformable plate  40  in compression and a posterior surface  48  of the deformable plate  40  in compression. 
     Prior to preloading, the deformable plate  40  is preferably a thin plane-parallel plate with the anterior and posterior surfaces  46  and  48  both flat and parallel. The deformable plate  40  is preferably made of optical glass in either an amorphous or crystalline form to provide for the transmission of light without generating unnecessary wavefront aberrations or departures from uniformity. The deformable plate  40  is also made thin enough in relation to its length between ends  42  and  44  to effect the desired bending. For example, a plate having an overall length of 90 millimeters is preferably 5 millimeters or less in thickness. 
     In its preloaded condition, the deformable plate  40  is preferably only slightly bent so that any induced wavefront aberrations are negligible. Preferably, the deformable plate is preloaded to an initially curved condition with a nominal curvature of less than 0.1 meters. However, the deformable plate  40  is sufficiently bent in its preloaded condition to accommodate a range of bending that includes both partially unloading and further loading the deformable plate  40  to provide a corresponding range of magnification adjustment from lesser magnification to greater magnification. Thus, the deformable lens  40  is not adjusted from or into an unloaded condition to avoid instabilities associated with transitions between loaded and unloaded conditions of the deformable lens  40 . 
       FIG. 3  shows the deformable plate  40  being bent from the initially bent (preloaded) condition (shown in phantom) to a further bent condition designated  40 A as imposed by moments  62  and  64  produced by the actuator  50  between each end  42  and  44  and the respective fulcrum supports  54  and  56 . The further bending about the transverse axis  60  produces an anamorphic change in magnification in one orthogonal direction of the image field at the substrate  20 . The moments  62  and  64  can be imposed by linear or angular displacements of the ends  42  and  44 . 
     The table reproduced below illustrates the sensitivity of deformable plates of different thickness, all having a length of approximately 90 millimeters (mm). The abbreviation “μm” refers to microns, the abbreviation “mm” refers to millimeters, the abbreviation “m” refers to meters, the abbreviation “ppm” refers to parts per million, and the abbreviation “deg” refers to degrees. A measure of “sag” is illustrated in  FIG. 2 . 
     
       
         
               
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                   
               
               
                   
                 thickness of 
               
               
                   
                 the bent plate (mm) 
               
             
          
           
               
                   
                 1.25 
                 2.5 
                 5 
               
               
                   
               
             
          
           
               
                 sag for 20 ppm (um) 
                 29.4 
                 14.7 
                 7.3 
               
               
                 radius of curvature (m) 
                 20.0 
                 39.9 
                 79.9 
               
               
                 max slope or tilt at edge of plate (deg) 
                 0.006 
                 0.012 
                 0.025 
               
               
                   
               
             
          
         
       
     
     As illustrated by the table, both the bending range and sensitivity of the bent plate varies approximately linearly with the thickness of the plate. A more direct comparison is made in the table below comparing a 2.5 millimeter (mm) thick plate to a 5.0 millimeter (mm) thick plate, each made of fused silica and having a common target magnification. 
     
       
         
               
               
               
             
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                   
                 Plate Thickness 
               
             
          
           
               
                   
                   
                 2.5 mm 
                 5.0 mm 
               
               
                   
               
             
          
           
               
                   
                 Sag 
                 14.683 
                 μm 
                 7.342 
                 μm 
               
               
                   
                 Radius of Cylinder 
                 39945.7 
                 mm 
                 79887.1 
                 mm 
               
               
                   
               
             
          
         
       
     
     Less bending is required for plates of increased thickness to achieve the same range of magnification adjustment. However, the thicker plates, particularly those substantially greater than 5.0 mm in thickness are more difficult to bend and can produce other unintended effects. 
     A relatively pure magnification change accompanying a cylindrical distortion of the plates can be derived by considering how a tilted plate laterally deviates the telecentric rays. The deviation is a function of the tilt, thickness, and refractive index of the plate. The telecentric rays are the rays that pass through the center of the aperture stop of the imaging lens and are parallel in the telecentric image or object space. A plate bent in a cylindrical shape can be considered on a localized level as a plurality of individually tilted plates whose tilt increases by a sine function with distance from the optical axis, and the relationship between ray deviation and distance from the optical axis is highly linear for small bends. This linearity means that (a) the deviations are proportional to the distance from the optical axis and (b) the deviations have predominately changed only the magnification of the image in the direction of the bend and not the distortion. 
     As an example, if a plate is bent cylindrically, such that the maximum angle of incidence is one degree at the edge of the telecentric rays, then the distortion (i.e., departure from a linear deviation) is approximately 1:15,000 of the magnification. If the maximum angle of incidence is 2 degrees at the edge of the telecentric rays, then the ratio distortion to magnification changes by a factor of 4 to 1:3,750. Thus, the magnification effects of a bent plate in telecentric plate clearly dominate any distortion effects, particularly at small amounts of plate curvature. 
       FIG. 4  depicts a pair of deformable plates  70  and  90  arranged for providing magnification corrections in two orthogonal directions. Actuators  80  and  82 , which are schematically depicted as arrows, act on opposite ends  72  and  74  of the deformable plate  70  against fulcrums  76  and  78  for generating opposing moments resulting in the bending of the deformable plate  70  about transverse axis  84 . Similarly, actuators  100  and  102 , which are also depicted as arrows, act on opposite ends  92  and  94  of the deformable plate  90  against fulcrums  96  and  98  for generating opposing moments resulting in the bending of the deformable plate  90  about transverse axis  94 , which extends orthogonal to the transverse axis  84 . Both axes  84  and  94  preferably extend normal to the optical axes  104  of the deformable plates  70  and  90  as well as the optical axis  24  of the imaging system in which the plates  70  and  90  are mounted. Together, the deformable plates  70  and  90  can produce a range of anamorphic magnification adjustments by relatively adjusting the relative magnitude of adjustments contributed by each of the plates  70  and  90  or by adjusting the relative angular positions of their axes  84  and  94 . A uniform magnification adjustment (i.e., a radially symmetric magnification adjustment) at the substrate  20  can be provided by making equal magnification adjustments with the two plates  70  and  90  about their orthogonal axes  84  and  94 . Preferably, one of the two orthogonal axes  84  or  94  over which magnification control is exercised corresponds to an intended direction for stepping or scanning the projection lens  16  across the substrate  20 . 
       FIG. 5  depicts in cross section a sealed lens barrel  110  for mounting a deformable plate  120  within pressure controlled environment. The deformable plate  120  rests on an annular seat  112 , which functions similar to the fulcrums of the preceding plate mounting systems, and when seated, divides the sealed lens barrel  110  into two independently controllable pressure chambers  114  and  116 . An inert gas, such as nitrogen, is pumped through respective apertures  126  and  128  for adjusting a pressure differential between the two chambers  114  and  116 . Higher pressure in the upper chambers  114  pushes the deformable plate  120  against the annular seat  112  and symmetrically deforms the deformable plate  120  for producing a uniform magnification adjustment across the substrate  20 . Preferably, a pressure differential is maintained even at a nominal operating condition for the projection lens  16  so that the deformable plate  120  remains deformed in a given direction throughout an intended range of magnification adjustment. 
     The deformable plates  40 ,  70 , and  90  of the preceding embodiments are preferably bent into a cylindrical form and the deformable plate  120  is preferably bent into a spherical form for adjusting magnification within either the telecentric object space  36  or the telecentric image space  38  of the projection lens  16  to correct or otherwise adjust magnification while limited unwanted wavefront aberrations or distortions. Predictable or measurable departures from the desired cylindrical or spherical forms can be minimized by adjusting the bending forces or compensated for by varying the thickness from the center to the peripheries of the deformable plates or making other adjustments outside the optical zones of the plates for achieving the desired bending performance. In addition, the deformable plates  40 ,  70 , and  90  can be laterally displaced so that center of curvature of the plates remains centered along the optical axis  24  of the projection lens  16   
     A deformable plate  130  is depicted in  FIG. 6  with radial variation in thickness, which is greatly exaggerated for purposes of illustration. An anterior surface  132  of the deformable plate  130  is depicted as flat, but a posterior surface  134  of the deformable plate  130  is depicted as having an aspheric surface. While symmetrical about an optical axis  136  of the deformable plate, the variation in thickness is intended to compensate for bending forces that are not distributed so as to otherwise result in a cylindrical or spherical shape for the deformable plate  130 . More particularly, the variation in thickness is intended to result in a more nearly cylindrical or spherical shape for the deformable plate  130  in the intended preloaded condition of the deformable plate. Although the just the posterior surface  134  of the deformable plate  130  has an aspheric surface, either or both of the anterior and posterior surfaces  132  and  134  can be formed with aspheric surfaces so that both surfaces  132  and  134  assume more nearly cylindrical or spherical shapes in the preloaded condition. 
     In  FIG. 7 , a deformable plate  140  is formed with slots  142  formed in a mounting region  144  of the deformable plate  140 , which is outside an optical region  146  of the plate  140  as indicated by an optical boundary line  148 . Bending loads for deforming the deformable plate  140  are applied in the mounting region  144  and outside the optical region  146  to avoid interfering with the intended optical performance of the deformable plate. Since the mounting region  144  is not part of the optical system of the projection lens  16  other modifications, including the introduction of the slots  142  or the incorporation of structures for engaging or transmitting forces from the actuator (not shown) can be provided within the mounting region  144 . 
     Not only do the deformable plates exploit telecentric space within projection lenses for adjusting magnification independently of other optical considerations, the deformable plates enable doubly telecentric projection lenses to be adjusted for magnification within a telecentric object space. Other components within the projection lenses including reticles and lens elements, which otherwise require adjustment to carry out magnification adjustments can remain fixed. In addition, the doubly telecentric projections lenses, which are equally telecentric in both image and object space, can be designed with more symmetric components to reduce sources of wavefront errors. Of course, some departure from theoretical telecentricity is evident in any practical optical design, and the tolerance for telecentricity is preferably set so that any unwanted distortion accompanying the intended range of magnification adjustments remains within design limits. 
       FIG. 8  illustrates the collective operation of compound deformable plates  150  and  160  that are deformable together for producing greater amounts of magnification adjustment or such greater amounts of magnification adjustment with thinner plates. Although separately supported on respective fulcrum pairs  152 ,  154 , and  162 ,  164 , actuators  166  and  168  provide for deforming both of the plates  150  and  160  together. Additional deformable plates can be stacked together for making even greater changes to magnification in one or both orthogonal directions. For spherically deforming the plates  150  and  160 , each of the fulcrum pairs  152 ,  154 , and  162 ,  164  can represent respective annular seats for supporting the plates  150  and  160  and the actuators  166  and  168  can be parts of a common annular compression ring for engaging the plates  150  and  160  about their respective circumferences. 
     The various actuators  50 ,  52 ,  80 ,  82 ,  100 ,  102 ,  114 ,  116 ,  166 ,  168  of the preceding embodiments can be connected to the controller  32  for making continuous, intermittent, or otherwise automatic corrections to magnification associated with the operation of the lithographic projection system  10 . Control systems for making automatic magnification adjustments are well known. For example, sensors (not shown) for monitoring operating conditions of the projection system  10  or the substrate  20  can be arranged to provide information to the controller for predicting responses of the projection system  10  or the substrate  20  requiring magnification adjustments, or other instruments can be used for more directly monitoring the magnification of the projection lens  16 , such as by measuring the size of imaged gauge features, to provide the controller  32  with information for controlling the actuators. Continuous closed loop adjustment of magnification is preferred for most lithographic systems. 
     Although depicted with respect to a lithographic projection system designed to project an image of a reticle  18  onto a substrate  20 , the invention is also directly applicable to lithographic projection systems in with the patterns intended for projection are formed by spatial light modulators. The deformable plates are locatable adjacent the object or image conjugates, including in the object space adjacent to the output of a microlens array for producing the pattern intended for projection onto a substrate. 
     The telecentric image and object space of the telecentric lithographic projection systems gradually transitions into pupil space with distance from the object and image conjugates. Preferably, the deformable plates are located as closely as possible to one or the other of the image conjugates to avoid aberration of the imaging system but benefits of the invention can be obtained by locating the deformable plates elsewhere within primarily image or object space where the instantaneous pupil of a point in the image or object field (i.e., the aperture of the cone of light extending from the field point) is substantially smaller than the clear aperture, and preferably one-fourth or less.