Abstract:
A non-linear modification to telecentric object space together with alteration of working distance provides a distortion adjustment feature. The modification to telecentric object space can be manifest as a spherical aberration in an entrance pupil. The change in working distance can be made by relatively translating the imaged object through the modified telecentric object space. The distortion adjustment can be made to compensate for distortions accompanying changes in ambient or operating conditions. Distortions accompanying magnification corrections can also be corrected.

Description:
TECHNICAL FIELD 
   The invention is directed to quasi-telecentric lenses subject to variations in image distortion with use and is particularly directed to distortion adjustment features of such lenses to compensate for such variations during use. 
   BACKGROUND OF THE INVENTION 
   Environmental factors such as temperature and pressure, as well as other factors such as component heating during use, can affect the refractive indices or spacing of optical components within lenses, and these changes can result in changes in magnification and image distortion. Such dynamic changes are apparent in many types of lenses including doubly-telecentric lenses. 
   Magnification adjustments have been made by axially translating certain optical elements of projection lenses. However, other optical aberrations including image distortions can accompany such magnification adjustments. 
   SUMMARY OF THE INVENTION 
   The invention contemplates a solution to the problem of radial distortion accompanying the use of telecentric lenses. The solution has two main parts. First, telecentric object space is deliberately altered in a non-linear fashion, which can be manifest, for example, as a spherical aberration in an entrance pupil. Second, the imaged object, together with its object plane, is relatively translated axially through the altered telecentric object space for adjusting radial distortion of the lens. The adjustments can be made dynamically to correct distortion errors caused by environmental influences or other factors accompanying the operation of the lens. Such distortion adjustments can also be paired with magnification adjustments to manage both dynamically. 
   In true telecentric object space, the chief rays emanating from the object plane all extend parallel to the optical axis. In one example of an altered telecentric space exploited here for purposes of adjustment, the chief rays preferably follow a pattern in which the chief paraxial and full-field rays extend parallel to the optical axis but chief intermediate rays vary in angle with respect to the optical axis by amounts that tend to increase with radial distance from both the chief paraxial and the full-field rays. The chief intermediate rays are preferably inclined slightly toward the optical axis. 
   Although the modified lens departs slightly from telecentricity, no significant distortion is evident in the image plane. In addition, the lens preferably remains uniformly telecentric at the image plane. Although telecentricity is not a requirement for good imaging, telecentricity does impose additional design constraints, generally for the purpose of reducing unwanted magnification changes with changes in working distance. The alteration to telecentric object space is incorporated into the lens design so that at a given position of the object plane no significant radial distortion is evident in the image plane. However, if the object plane is axially shifted in either direction along the optical axis (i.e., a change in working distance), positive or negative radial distortion can be introduced into the image. Preferably, the lens design remains sufficiently telecentric so that changes in working distance do not significantly alter magnification, but the lens design departs sufficiently from ideal telecentricity so that the changes in working distance produce radial distortion. The radial distortion adjustments, which can be made by axially translating the imaged object through the modified telecentric object space, can be determined in advance and recorded in a lookup table to make automatic corrections accompanying monitored changes in temperature or pressure. 
   Magnification adjustments can be made by axially translating one of the powered optical components of the lens. The chosen powered optical component is preferably one whose axial translation has the least effect on other distortions (i.e., beyond radial distortion or magnification). Good candidates are the first and last optical components of the lens adjacent to telecentric image or object space. In addition to changes in magnification, radial distortion can also be produced by such translations. However, the imaged object defining the object plane can be moved in addition to the chosen lens component to isolate the magnification correction. For example, the imaged object can be axially translated together with the chosen lens component closest to the object plane for correcting magnification independently of radial distortion. Compound changes in radial distortion and magnification can also be made by translating both the object and the chosen lens component. 
   The translation of the imaged object and the chosen lens component can also affect the location of the image plane. To restore the image plane to its initial location, the entire lens together with the imaged object can be translated. Alternatively, the receptor (not shown) on which the image is formed can be similarly translated to accommodate the altered location of the image plane. 
   To exploit more fully the imaging and adjustment possibilities of the subject invention, particularly in the form of a projection lens system, an illuminator is preferably matched to the quasi-telecentric projection lens envisioned for the invention. For example, the chief ray pattern emitted from the illuminator (e.g., at the image plane of the illuminator) can be matched to the non-linear chief ray pattern at the object plane of the projection lens so that the entrance pupil of the projection lens is at least partially filled according to the design. This allows the light patterns through which the object points are projected onto the image plane to be matched throughout the field. Preferably, the centroids of light energy associated with each of the points are aligned with the chief rays and oriented parallel to the optical axis at the image plane. The illuminator can be coupled directly to the projection lens or through a relay lens, which can either transmit or participate in forming the matching chief ray illumination pattern. For example, the relay could participate in forming the desired illumination pattern by converting a telecentric output from a conventional illuminator into the quasi-telecentric input required for matching the chief ray pattern of the projection lens. 
   One example of an optical imaging system arranged in accordance with the invention includes a quasi-telecentric lens assembly in which chief rays emanating from an object plane include paraxial rays and reference rays that are located at a given radial distance from the paraxial rays. Both the reference rays and the paraxial rays extend parallel to an optical axis of the lens assembly, and other of the chief rays vary in inclination to the optical axis of the imaging system substantially as a function of the radial distance of the other chief rays from the closer of the paraxial and the reference rays. A stage relatively translates an object intended for imaging by the imaging system with respect to the lens assembly along the optical axis to compensate for distortion otherwise apparent in an image plane of the lens assembly. 
   Preferably, the chief reference rays include chief full-field rays. In addition, the chief rays are preferably arranged to express a spherical aberration within an entrance pupil of the lens assembly. The other chief rays between the chief paraxial and full-field rays preferably include chief intermediate rays that are variously inclined with respect to the optical axis. For example, the chief intermediate rays are preferably variously inclined toward the optical axis in the direction of propagation with substantial axial symmetry. The chief intermediate rays preferably include intermediate rays that are inclined to the optical axis by at least one degree. 
   Movement of the object in one direction along the optical axis contributes toward a positive radial distortion in the image plane of the lens assembly, and movement of the object in an opposite direction along the optical axis contributes toward a negative radial distortion in the image plane of the lens assembly. However, the movement of the object in opposite directions along the optical axis preferably produces minimal magnification and non-orthogonal aberration effects in the image plane. 
   An environmental monitor can be used for monitoring environmental condition of the lens assembly, and a processor can be arranged to receive information from the environmental monitor and determine an amount of stage translation required to compensate for an expected distortion accompanying changes in the environmental conditions. 
   A lens assembly monitor can be used for monitoring operating conditions of the lens assembly, and a processor that receives information from the lens assembly monitor can be arranged to determine an amount of stage translation required to compensate for an expected radial distortion accompanying changes in the lens assembly. The changes in the lens assembly can include a change in the temperature or temperature distribution within one or more components of the lens assembly. The changes can also include a change in the size or shape of one or more components of the lens assembly. The lens assembly monitor can be used to detect changes in the object. An infrared imager, for example, can be used to produce infrared images of the object as a way to anticipate the distortion appearing at the image plane. The infrared imager can be coupled to a relay system that relays an illumination pattern to the object plane. The coupling allows the infrared imager to acquiring an image of the object. 
   The referenced stage can be a first of a plurality of stages, and a second of the stages can be used to translate a lens component of the lens assembly along the optical axis to vary magnification of the object in the image plane. A processor relates movements of the first and second stages to compensate for distortions accompanying the variation in magnification. The lens component translated by the second stage exhibits optical power and is preferably located adjacent to the object plane. Alternatively, the lens component translated by the second stage can be located adjacent to the image plane. A third of the stages can be arranged to translate the lens assembly together with the imaged object with respect to an image-receiving part for appropriately positioning the image plane of the lens assembly on a surface of the image-receiving part. 
   An illumination system is preferably arranged to output an illumination pattern having chief rays substantially matching the non-linear chief ray pattern at the object plane of the quasi-telecentric lens assembly. The illumination system can include an illuminator and a relay lens for optically coupling the illuminator to the quasi-telecentric lens assembly. The relay lens can transmit the desired illumination pattern from the illuminator to the quasi-telecentric lens assembly or can participate in forming the desired illumination pattern. For example, the relay lens can be arranged with a conventional telecentric object space but with a non-linear telecentric image space matching the non-linear telecentric object space of the quasi-telecentric lens. The relay lens can also be used to relay an image of a field stop, such as a cropping mask, onto the object plane of the quasi-telecentric lens assembly. 
   A method of influencing radial distortion in a quasi-telecentric lens in accordance with the invention includes directing light through a quasi-telecentric lens having a non-linear modification to telecentric object space. The object plane is axially translated through the non-linearly modified object space for increasing or decreasing radial distortion in an image plane of the telecentric lens without significantly varying magnification in the image plane. 
   The method can also be used to influence magnification in the image plane by axially translating a powered lens component of the quasi-telecentric lens. At least a portion of the axial translation of the object plane compensates for radial distortion accompanying the axial translation of the powered lens component. The powered lens component is preferably located among the powered lens components of the quasi-telecentric lens closest to one of the object plane and the image plane. For example, the powered lens component can be located closest to the object plane. The quasi-telecentric lens together with the object plane can be axially translated to maintain a desired external location of the image plane. The conditions that produce radial distortion errors in the image plane of the quasi-telecentric lens can be monitored and responded to by making the relative axial translation of the object plane. 
   In addition, the object plane of the quasi-telecentric lens is preferably illuminated by a quasi-telecentric illuminator having a non-linear modification to telecentric image space that matches the non-linear modification to the telecentric object space of the quasi-telecentric lens. This assures that, even under conditions of partial coherence illumination, the centroids of light energy through which the object points of the quasi-telecentric lens are projected onto the image plane of the quasi-telecentric lens correspond to the intended telecentric chief rays at the image plane of the quasi-telecentric lens. 

   
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       FIG. 1  is a diagram in side view of a doubly telecentric projection system having a relay lens and objective lens in which an illuminated reticle located in an object plane is projected onto an image plane. 
       FIG. 2  is an enlarged cutaway view of the projection system near the reticle. 
       FIG. 3  is a graph showing an angular variation (radians) in the inclination of the chief rays passing through the reticle as a function of displacement (millimeters) from the center of the object field. 
       FIG. 4  depicts exemplary paraxial, intermediate, and full-field rays in telecentric object space. 
       FIG. 5  is an enlarged cutaway view of telecentric object space showing axial adjustment possibilities for the reticle. 
       FIG. 5A-5C  plot distortions (microns) in the image plane as a function of normalized radial field position associated with the radial distortion adjustment possibilities for the reticle. 
       FIG. 6  is an enlarged cutaway view of telecentric object space showing axial adjustment possibilities for a first optical component of the objective lens. 
       FIG. 6A-6C  plot distortions (microns) in the image plane as a function of normalized radial field position associated with the magnification adjustment possibilities for the first optical component. 
       FIG. 7  depicts a mobile photolithographic imaging system incorporating a projection system in accordance with the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In  FIG. 1 , a projection system  10  includes (a) a relay lens  12 , which receives light from an illuminator (not shown) and relays a nearly uniform light plane bordered by cropping blades  22  to a reticle  16  (i.e., imaged object) at the object plane and (b) a quasi-doubly telecentric objective lens  14 , which projects an image of a reticle  16  in a magnified size onto an image plane  18 . A relay stop  24  within the relay lens  12  is arranged conjugate to the objective stop  26  within the objective lens  14 , which can also be considered as an entrance pupil of the objective lens  14 . 
   The reticle  16 , which includes patterns intended for projection onto the image plane  18 , can be sized larger than the field of view of the objective lens  14 , and the cropping blades  22  mask the portions of the reticle  16  that are not intended for a particular projection. An image of the cropping blades  22  is relayed to the reticle  16  so that the blades remain within the depth of field of the objective lens  14 . Alternatively, the cropping blades  22  could be located immediately adjacent to the reticle  16 . However, required offsets for protecting the reticle  16  and other considerations such as cropping blade thickness can result in depth of field blurring. The problem is more acute for objective lenses having higher numerical apertures at the object plane, i.e., at the reticle  16 . Thus, instead of mounting the cropping blades  22  next to the reticle  16 , the relay lens  12  relays an image of the cropping blades  22  directly onto the reticle  16 . This also moves a heat source away from the reticle  16  and allows thicker cropping blades  22  to be used. 
   The objective lens  14  is quasi-doubly telecentric; i.e., true telecentric adjacent to the image plane  18  but only quasi-telecentric adjacent to the object plane at the reticle. As better seen in the enlarged cutaway view of  FIG. 2 , both chief paraxial rays  32  and chief full-field rays  34  passing through the reticle  16  extend parallel to an optical axis  30  of the projection system  10 . However, chief intermediate rays  36  tip slightly toward the optical axis  30  within the same substantially telecentric object space  38 , such as through an angle of up to approximately 1.25 degrees (0.22 radians). The variation in the inclination of the chief intermediate rays  36  to the optical axis  30  is preferably modeled after a second or other even ordered function, such as plotted in the graph of  FIG. 3 , in which the inclination variation of the intermediate chief rays  36  increases with their radial distance from the closer of the chief paraxial or the chief full-field rays  32  or  34 . This telecentric variation appears as a spherical aberration in the entrance pupil  26  of the objective lens  14 . 
   The reticle  16  is preferably mounted on an adjustable stage or other translating mechanism such as voice coils (not shown) for translating the reticle  16  limited distances along the optical axis  30  as shown in  FIG. 5  by double arrow  40 . At a given design position, no radial distortion is apparent in the image plane  18  as shown by the graph of  FIG. 5B . However, translation of the reticle  16  in either direction along the optical axis  30  through the telecentric object space  38  has an effect of varying distortions of the projection system  10 . Translation of the reticle  16  in the direction of the relay lens  12  has the effect of producing a positive radial distortion as plotted in  FIG. 5A , and translation of the reticle  16  in the opposite direction toward the objective lens  14  has the effect of producing a negative radial distortion as plotted in  FIG. 5C . A controller (not shown) can be connected to the reticle mount for adjusting distortion in response to changing conditions. For example, the distortion itself can be monitored and corrections made for reducing the monitored distortion, or related conditions can be monitored, such as temperature, and corrections made based on predictable effects of the changing conditions on distortion. 
   The same telecentric alteration at the object plane can be further exploited to support magnification adjustments, which like distortion, can be altered by environmental influences or other changing conditions. The magnification correction can be made as shown in  FIG. 6  by translating a first optic (i.e., “first glass”)  42  of the objective lens  14  along the optical axis  30  as shown by the double arrow  44  in concert with a translation of the reticle  16  (as shown in  FIG. 5 ) to undo any unwanted radial distortion created by the translation of the first optic  42 . At a given design position, a desired amount of magnification is apparent in the image plane  18  as shown on the graph of  FIG. 6B . Translation of the first optic  42  in the direction of the relay lens  12  has the effect of producing a positive magnification as plotted in  FIG. 6A . Translation of the first optic  42  in the opposite direction toward the objective lens  14  has the effect of producing a negative magnification as plotted in  FIG. 6C . 
   The first optic  42  can be mounted on a stage or other translating mechanism such as piezoelectric transducers (not shown). Alternatively, one stage could be arranged for translating both the reticle  16  and the first optic  42  and another stage could be arranged for further translating one or the other of the reticle  16  and the first optic  42 . The same or a different controller (not shown) can be used to monitor the amount of magnification reduction produced in the image plane  18  or other conditions predictably related to the magnification reduction and adjust the positions of the reticle  16  and first optic  42  accordingly. Translations of the reticle  16  and the first optic  42  can also have the effect of axially displacing the location of the image plane  18 . This can be corrected by translating the entire objective lens  14  on another stage having lifts for raising and lowering the objective lens  14  together with the reticle  16 . 
   Alternatively, one or more powered optical components of the objective lens  14  can be translated for making the desired magnification corrections, particularly powered optical components in the vicinity of the telecentric image or object space. Movement of the chosen optical component preferably has the least effect introducing distortions beyond radial distortion or magnification. That is, the chosen component is preferably forgiving with respect to its axial position for introducing other errors, such as non-orthogonal errors. Any unwanted radial distortion can be corrected by moving the reticle/object plane. For example, a last optic (i.e., “last glass”)  46  of the projection lens  14  closest to the image plane  18  can be translated along the optical axis  30  for making similar changes to magnification, while having a minimal effect on the location of the image plane  18 . 
   Other chief ray patterns can be used to render the design sensitive to other distortions with changes in working distance. For example, a fifth order distortion sensitivity can be created by orienting chief mid-field rays also parallel to the optical axis and varying the inclination of the other rays as a function of their radial distance from the closest of the paraxial, midfield, or full-field rays that all extend parallel to the optical axis. However, the alternative ray patterns preferably preserve at least the paraxial and full-field rays parallel to the optical axis to distinguish distortion sensitivity from changes in magnification. 
   While telecentric object space  38  can be configured with various nonlinear chief ray patterns, the objective lens  14  preferably remains truly telecentric in image space. Both good placement and low telecentricity errors are evident at the image plane  18 , where the chief rays remain parallel to the optical axis. 
   The following tables listing design specifications for an exemplary relay lens  12  and a matched objective lens  14 . The design is quasi-telecentric and is substantially balanced on either side of the aperture stops in element form and material to reduce odd order aberrations such as coma and to limit the number of different elements within the design. 
   
     
       
             
           
             
             
             
             
             
           
             
             
             
             
             
             
             
           
             
             
             
             
             
             
           
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
           
             
             
             
             
             
           
         
             
                 
             
             
               Relay Lens Fabrication Data 
             
           
        
         
             
                 
               Radius of Curvature 
                 
               Aperture Diameter 
                 
             
           
        
         
             
               Element 
               Front 
               Back 
               Thickness 
               Front 
               Back 
               Material 
             
             
                 
             
           
        
         
             
               OBJECT 
               INF 
               44.1379 
                 
                 
                 
             
           
        
         
             
               1 
               INF 
               INF 
               4.3000 
               165.8307 
               166.2155 
               SIO2 
             
           
        
         
             
                 
                 
                 
                 
                 
               46.8816 
                 
                 
                 
             
             
               2 
               −104.0409 
               CC 
               2226.9485 
               CC 
               25.6403 
               166.8749 
               224.4487 
               SIO2 
             
             
                 
                 
                 
                 
                 
               17.8014 
             
             
               3 
               −677.5359 
               CC 
               −178.7235 
               CX 
               51.1400 
               231.6797 
               244.0225 
               PBM18Y 
             
             
                 
                 
                 
                 
                 
                 
                 
                 
               Ohara 
             
             
                 
                 
                 
                 
                 
               1.0000 
             
             
               4 
               703.1659 
               CX 
               −299.7709 
               CX 
               60.0792 
               273.6760 
               276.0145 
               SIO2 
             
             
                 
                 
                 
                 
                 
               213.6768 
             
             
               5 
               355.7864 
               CX 
               −2050.6270 
               CX 
               32.4361 
               215.4036 
               210.7433 
               SIO2 
             
             
                 
                 
                 
                 
                 
               128.8237 
             
             
               6 
               139.9641 
               CX 
               111.6454 
               CC 
               55.0000 
               123.9744 
               88.4198 
               SIO2 
             
             
                 
                 
                 
                 
                 
               94.0830 
             
           
        
         
             
                 
                 
                 
                 
                 
               APERTURE 
                33.2957 
                 
             
             
                 
                 
                 
                 
                 
               STOP 
             
           
        
         
             
                 
                 
                 
                 
                 
               94.0830 
                 
                 
                 
             
             
               7 
               −111.6454 
               CC 
               −139.9641 
               CX 
               55.0000 
               88.3915 
               123.9313 
               SIO2 
             
             
                 
                 
                 
                 
                 
               128.8237 
             
             
               8 
               2050.6270 
               CX 
               −355.7864 
               CX 
               32.4361 
               210.6429 
               215.3071 
               SIO2 
             
             
                 
                 
                 
                 
                 
               213.6768 
             
             
               9 
               299.7709 
               CX 
               −703.1659 
               CX 
               60.0792 
               275.8684 
               273.5220 
               SIO2 
             
             
                 
                 
                 
                 
                 
               1.0000 
             
             
               10 
               178.7235 
               CX 
               677.5359 
               CC 
               51.1400 
               243.9200 
               231.5508 
               PBM18Y 
             
             
                 
                 
                 
                 
                 
                 
                 
                 
               Ohara 
             
             
                 
                 
                 
                 
                 
               17.8014 
             
             
               11 
               −2226.9485 
               CC 
               104.0409 
               CC 
               25.6403 
               224.3043 
               166.8064 
               SIO2 
             
           
        
         
             
                 
                 
                 
               91.0196 
                 
                 
                 
             
             
               12 
               INF 
               INF 
               4.3000 
               160.3002 
               159.9416 
               SIO2 
             
           
        
         
             
               IMAGE 
               INF 
                 
               159.9416 
             
             
                 
             
           
        
       
     
   
   
     
       
             
           
             
             
             
             
             
           
             
             
             
             
             
             
             
           
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
             
           
             
             
             
             
             
           
         
             
                 
             
             
               Objective Lens Fabrication Data 
             
           
        
         
             
                 
               Radius of Curvature 
                 
               Aperture Diameter 
                 
             
           
        
         
             
               Element 
               Front 
               Back 
               Thickness 
               Front 
               Back 
               Material 
             
             
                 
             
           
        
         
             
               OBJECT 
               INF 
               98.8673 
                 
                 
                 
             
           
        
         
             
               1 
               1602.5020 
               CX 
               −202.3611 
               CX 
               38.8682 
               178.7816 
               180.1374 
               SIO2 
             
             
                 
                 
                 
                 
                 
               7.0000 
             
             
               2 
               347.6276 
               CX 
               2949.4535 
               CC 
               29.2046 
               166.3521 
               158.2304 
               SIO2 
             
             
                 
                 
                 
                 
                 
               20.6023 
             
             
               3 
               199.8183 
               CX 
               94.4280 
               CC 
               40.0000 
               139.6297 
               110.9390 
               SIO2 
             
             
                 
                 
                 
                 
                 
               48.8757 
             
             
               4 
               793.1909 
               CX 
               124.3330 
               CC 
               19.7476 
               101.6115 
               95.1142 
               SIO2 
             
             
                 
                 
                 
                 
                 
               133.3812 
             
             
               5 
               −158.1986 
               CC 
               674.5769 
               CC 
               17.0000 
               99.6948 
               107.2745 
               PBM18Y 
             
             
                 
                 
                 
                 
                 
                 
                 
                 
               Ohara 
             
             
                 
                 
                 
                 
                 
               9.9549 
             
             
               6 
               −1889.7778 
               CC 
               −170.0924 
               CX 
               21.4065 
               111.3332 
               116.1943 
               SIO2 
             
             
                 
                 
                 
                 
                 
               23.4885 
             
             
               7 
               1255.2681 
               CX 
               −159.0652 
               CX 
               26.7841 
               125.3039 
               127.0018 
               SIO2 
             
             
                 
                 
                 
                 
                 
               21.0000 
             
           
        
         
             
                 
                 
                 
                 
                 
               APERTURE 
               119.9009 
                 
             
             
                 
                 
                 
                 
                 
               STOP 
             
           
        
         
             
                 
                 
                 
                 
                 
               21.0000 
                 
                 
                 
             
             
               8 
               529.1464 
               CX - 
               999.6629 
               CX 
               17.8512 
               126.6781 
               127.9378 
               SIO2 
             
             
                 
                 
                 
                 
                 
               95.9908 
             
             
               9 
               207.8959 
               CX - 
               8081.8685 
               CX 
               25.1353 
               138.2623 
               136.1535 
               SIO2 
             
             
                 
                 
                 
                 
                 
               82.3740 
             
             
               10 
               −520.9933 
               CC 
               173.6855 
               CC 
               18.1895 
               116.4648 
               114.5312 
               PBM18Y 
             
             
                 
                 
                 
                 
                 
                 
                 
                 
               Ohara 
             
             
                 
                 
                 
                 
                 
               88.4088 
             
             
               11 
               −150.1389 
               CC 
               −213.0482 
               CX 
               40.0000 
               136.8564 
               159.8929 
               SIO2 
             
             
                 
                 
                 
                 
                 
               24.4118 
             
             
               12 
               1288.0434 
               CX 
               −298.8531 
               CX 
               29.3711 
               179.3126 
               182.3602 
               SIO2 
             
             
                 
                 
                 
                 
                 
               7.0000 
             
             
               13 
               509.4466 
               CX 
               −637.4366 
               CX 
               27.0839 
               184.5771 
               183.7623 
               SIO2 
             
             
                 
                 
                 
                 
                 
               7.0000 
             
             
               14 
               297.7632 
               CX 
               987.5796 
               CC 
               21.6966 
               177.1968 
               172.8495 
               SIO2 
             
             
                 
                 
                 
                 
                 
               37.9683 
             
             
               15 
               −415.1246 
               CC 
               163.4446 
               CC 
               17.0000 
               160.9247 
               153.5272 
               SIO2 
             
             
                 
                 
                 
                 
                 
               218.2357 
             
             
               16 
               −542.3254 
               CC 
               −194.5365 
               CX 
               37.1022 
               203.4946 
               208.4570 
               SIO2 
             
             
                 
                 
                 
                 
                 
               28.0000 
             
           
        
         
             
               IMAGE 
               INF 
                 
               200.0008 
             
             
                 
             
           
        
       
     
   
   For interpreting the tables, a positive radius indicates the center of curvature is to the right and a negative radius indicates the center of curvature is to the left. All dimensions are given in millimeters, and thickness is the axial distance to next surface. The image diameter is a paraxial value, rather than a ray-traced value. The lens is operated at a reference wavelength of 366.0 nanometers through s spectral region from 363.5 nanometers to 368.5 nanometers. 
   Similar designs having the desired departure from telecentricity can be achieved using conventional lens design software, such as Code 5 by Optical Research Associates, Pasadena, Calif., by specifying the desired orientation pattern of the chief rays. The software accommodates the desired orientation pattern of the chief rays while achieving a design with little or no distortion at the image plane. Other lens design software that can be used for this purpose includes ZMAX optical design code from Focus Software, Tucson, Ariz., and OSLO optical design software from Lambda Research Corporation, Littleton, Mass. The design, however, is more sensitive to the exact placement of the object plane. This sensitivity is exploited to produce controlled amounts of radial distortion. 
     FIG. 7  depicts a mobile photolithographic imaging system  50 , also referred to as a “stepper”, incorporating a projection system  52  similar to the projection system  10  described above. An objective lens  54  supported by a frame  56  projects an image of a reticle  58  onto a panel  60 . Illumination is provided by a light source  62 , such as a high-pressure mercury arc lamp. An illuminator  64  includes a light tunnel that produces a uniform distribution of light. A relay lens  66  receives light from the illuminator  64  through a cropping mask  68 , and transmits an image of the cropping mask  68  bordering the uniform light from the illuminator  64  onto the reticle  58 . 
   The entire panel  60  cannot be imaged at once, so the frame  56  supports an XY-axis translational stage  70  on a base  72  for translating the panel  60  through a range of positions for collectively illuminating a desired working area of the panel  60 . The projection system  52  is supported on a Z-axis translational stage  78  for adjusting the image distance of the projection system  52  from the panel  60  along an optical axis  80  of the projection system  52 . The reticle  58  is supported within the projection system on an XYZ translational stage  82 . The XY component of the XYZ translational stage  82  provides for illuminating different portions of the reticle  58 , which can also be larger than the field of view of the projection system  52 . A controller  84  relates translation of the reticle  58  to the translation of the panel  60  so that a desired pattern on the reticle  58  can be imaged onto the panel  60 . The Z component of the XYZ translational stage  82  adjusts the working distance of the objective lens  54  from the reticle  58  for making radial distortion adjustments. Another Z translational stage  86  translates an optical component  88  of the objective lens  54  along the optical axis  80  for making magnification adjustments. Preferably, the optical component  88  is the powered optical component closest to the reticle  58 . 
   An infrared camera  90  is optically coupled to the relay lens  66  for monitoring a thermal profile of the reticle  58 . Other sensors  92  monitor ambient conditions such as ambient temperature and pressure within the environment of the projection system  52 . Information regarding the thermal profile of the reticle  58  as well as ambient temperature and pressure of the projection system environment reach the controller  84  and based on empirical data relating such information to optical performance of the projection system  52 , adjustments are made to either or both the working distance of the objective lens  54  to counteract image distortion or the axial position of the optical component  88  for adjusting magnification. 
   The projection system  52  is arranged to provide a radial distortion adjustment by making the non-linear alteration to telecentric object space near the reticle  58  and by controlling the XYZ translational stage  82  to alter the working distance between the objective lens  54  and the reticle  58 . A magnification adjustment is provided by the Z translational stage  86  that translates the optical component  88  along the optical axis  80 . Conditions that produce radial distortion or magnification errors are monitored such as by sensors  90  and  92  and empirical knowledge regarding the response of the projection system  52  is used to make compensatory image distortion and magnification adjustments. Dynamic adjustments can be maintained to assure better and more consistent performance of the projection system  52 . 
   The illuminator  64  together with the relay lens  66  convey an illumination pattern to the reticle  58  in a quasi-telecentric form in which the chief rays at the image plane of the relay lens  66  are substantially aligned with the chief rays of the object plane of the objective lens  54  so that the entrance pupil of the objective lens  54  is optimally filled for the objective lens design. The desired ray configuration of the illumination pattern at the reticle  58  can be produced at the image plane of the illuminator  64  and reproduced by the relay lens  66  at the object plane of the objective lens  54 , or the relay lens  66  can be arranged to convert the illumination pattern at the image plane of the illuminator (i.e., the object plane of the relay lens  66 ) to the desired ray configuration at the object plane of the objective lens  54  (i.e., the image plane of the relay lens  66 ). For example, the relay lens  66  can be arranged quasi-doubly telecentric with a true telecentric object space matching a true telecentric image space of the illuminator  64  and a quasi-telecentric image space matching the quasi-telecentric object space of the objective lens  54 . In this way, a conventional illuminator  64  with a telecentric output can be used. 
   The matching alignments of the chief rays at the image plane of the relay lens  66  with the chief rays at the object plane of the objective lens  54  assure that the centers of illumination, also referred to as centroids of light energy, at the image plane of the objective lens  54  remain aligned with the telecentric chief rays of the objective lens  54  at the image plane of the objective lens. With this alignment, various forms of partial coherence illumination can be used while preserving the intended telecentric nature of the illumination at the image plane of the objective lens  54 . 
   Although described with respect to particular embodiments for featuring various capabilities of the invention, those of skill in the art will appreciate the range of modifications that can be made within the overall teaching of this invention. For example, quasi-telecentric lenses used for purposes of the invention can be arranged for magnification or enlargement and the light direction through such lenses can be reversed. The object plane, image plane, or optical component can be translated directly or the remaining lens structure can be translated with respect to any one of them. Other conditions known to affect the performance of optical systems can also be monitored for purposes of correcting distortion or magnification.