Abstract:
A stage assembly and support system are provided to stabilize a stage base, such as a wafer stage base or a reticle stage base, minimizing forces transmitted from the stage assembly to a stationary surface, such as the ground, and thereby preventing vibration of other parts or systems in a wafer manufacturing process. Depending of the applicable photolithography system, a reticle stage and/or a wafer stage are accelerated in response to a wafer manufacturing control system to position the semiconductor substrates. The jerking motions of the reticle stage and/or wafer stage cause reaction forces acting on the reticle stage base and/or wafer stage base. The reaction forces induce vibration to the stationary surface and surrounding parts of the photolithography system. The wafer stage assembly and support system according to this invention allow the reticle stage base and/or wafer stage base to move relative the stationary surface. The base, acting as a massive reaction mass, stores a kinetic energy from the reaction force and gradually dissipates such energy by applying small forces to the reaction mass. The stage assembly and support system according to this invention are also capable of canceling any disturbance forces acting on the base.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a stage assembly, a support system, and method for stabilizing the stage assembly in a photolithography process to manufacture semiconductor wafers. More particularly, this invention relates to the stage assembly, support system, and method for stabilizing the stage assembly to prevent ground vibration. 
   2. Description of the Related Art 
   In manufacturing integrated circuits using photolithography, light is transmitted through non-opaque portions of a pattern on a reticle, or photomask, through a projection exposure apparatus, and onto a wafer of specially-coated silicon or other semiconductor material. The uncovered portions of the coating, that are exposed to light, are cured. The uncured coating is then removed by an acid bath. Then, the layer of uncovered silicon is altered to produce one layer of the multi-layered integrated circuit. Conventional systems use visible and ultraviolet light for this process. Recently, however, visible and ultraviolet light have been replaced with electron, x-ray, and laser beams, which permit smaller and more intricate patterns. 
   As the miniaturization of a circuit pattern progresses, the focus depth of the projection exposure apparatus becomes very small, making it difficult to align accurately the overlay of circuit patterns of the multi-layered integrated circuit. As a result, a primary consideration for an overall design of the photolithography system includes building components of the system that achieve precision by maintaining small tolerances. Any vibration, distortion, or misalignment caused by internal, external or environmental disturbances must be kept at minimum. When these disturbances affect an individual part, the focusing properties of the photolithography system are collectively altered. 
   In a conventional exposure apparatus of a photolithography system, a wafer stage assembly is used in combination with a projection lens assembly to manufacture semiconductor wafers. The wafer stage assembly includes a wafer table to support the wafer substrates, a wafer stage to position the wafer substrates as the wafer stage is being accelerated by a force generated in response to a wafer manufacturing control system, and a wafer stage base to support the wafer stage. The wafer manufacturing control system is the central computerized control system executing the wafer manufacturing process. To permit smaller and more intricate circuit pattern, the projection lens assembly must accurately focus the energy beam to align the overlay of circuit patterns of the multi-layered integrated circuit. 
   The conventional exposure apparatus generally includes an apparatus frame which rigidly supports the wafer stage assembly, the projection lens assembly, the reticle stage assembly, and an illumination system. In operation, the exposure apparatus transfers a pattern of an integrated circuit from a reticle onto the wafer substrates. The exposure apparatus can be mounted to a base, such as the ground or via a vibration isolation system. 
   There are several different types of photolithography devices, including a scanning type and a step-and-repeat type. In the scanning type photolithography system, the illumination system exposes the pattern from the reticle onto the wafer with the reticle and the wafer moving synchronously. The reticle stage moves the reticle on a plane which is generally perpendicular to an optical axis of the lens assembly, while the wafer stage moves the wafer on another plane generally perpendicular to the optical axis of the lens assembly. Scanning of the reticle and wafer occurs while the reticle and wafer are moving synchronously. 
   Alternately, in the step-and-repeat type photolithography system, the illumination system exposes the reticle while the reticle and the wafer are stationary. The wafer is in a constant position relative to the reticle and the lens assembly during the exposure of an individual field. Subsequently, between consecutive exposure steps, the wafer is consecutively moved by the wafer stage perpendicular to the optical axis of the lens assembly so that the next field of the wafer is brought into position relative to the lens assembly and the reticle for exposure. Following this process, the images on the reticle are sequentially exposed onto the fields of the wafer. 
   Regardless of the type of photolithography system being used, to focus accurately the image transferred from the reticle onto the wafer, the exposure apparatus must align a position of an exposure point on the wafer with a position of the focal point of the projection lens assembly. 
   To maximize throughput of wafer production, the reticle stage and the wafer stage must move at high acceleration rates. To generate high acceleration rates, the force generating motors must produce large stage forces F in  over short durations to move the reticle stage or the wafer stage, such as diagrammatically shown in  FIG. 2A . The stage forces move either the reticle stage or wafer stage according to the graph shown in  FIG. 3A . 
   According to Newton&#39;s second law, these types of impulses generate reaction forces on the base, which cause the reticle stage base or a wafer stage base to move according to the graph shown in  FIG. 3B . Since both the reticle base and wafer stage base are rigidly connected to the apparatus frame of the exposure apparatus, the reaction forces are transmitted to the apparatus frame and the ground, causing a detrimental vibration to the photolithography system. 
   Therefore, there is a need for an improved stage assembly, stage support system, and method to eliminate or substantially reduce the vibration. 
   SUMMARY OF THE INVENTION 
   The advantages and purposes of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages and purposes of the invention will be realized and attained by the elements and combinations particularly pointed out in the appended claims. 
   To attain the advantages and consistent with the principles of the invention, as embodied and broadly described herein, one aspect of the invention is a support system for stabilizing and supporting a base on a stationary surface. The base supports a device which is moved by a predetermined force. The support system comprises a set of bearings and a set of actuators. The set of bearings supports the base allowing the base to move relative to the stationary surface. The base moves due to at least one of a reaction force and a disturbance force acting on the base. The reaction force is responsive to the predetermined force acting on the device supported by the base. The set of actuators controls movement of the base in at least one degree of freedom. 
   Another aspect of the present invention is a stage assembly for manufacturing semiconductor wafers, comprising a stage and a base supporting the stage. The stage positions at least one substrate, and is being moved by a first member of a force generator in response to a wafer manufacturing control system. The base is being allowed to move in response to a reaction force generated by a second member of the force generator. The stage assembly also comprises a set of bearings to support the base allowing the base to move relative to a stationary surface, and a set of actuators to control movement of the base, the movement being caused by a disturbance force. 
   A further aspect of the present invention is a stage assembly for manufacturing semiconductor wafers, comprising a stage and a base supporting the stage. The stage positions at least one substrate, and is being moved in accordance with a wafer manufacturing control system. The base is being allowed to move in response to a reaction force generated by a movement of the stage. The stage assembly also comprises a set of bearings to allow the base to levitate above a stationary surface, and a set of actuators to control movement of the base. The movement may be caused by any disturbance force. 
   Yet a further aspect of the present invention is a method for reducing a vibration force transmitted by a base to a stationary surface. The method comprises the steps of supporting the base and levitating the base above the stationary surface so that the base can move relative to the stationary surface, and controlling movement of the base in at least one degree of freedom, the movement being caused by a disturbance force. 
   It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed. Additional advantages will be set forth in the description which follows, and in part will be understood from the description, or may be learned by practice of the invention. The advantages and purposes may be obtained by means of the combinations set forth in the attached claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings, 
       FIG. 1  is a schematic elevation view of an exposure apparatus having a conventional wafer stage assembly; 
       FIG. 2A  is a graph illustrating the profile of a force accelerating a conventional stage; 
       FIG. 2B  is a graph illustrating the profile of a force acting on the ground produced by a stage consistent with the principles of the present invention; 
       FIG. 3A  is a graph illustrating a trajectory profile of a stage; 
       FIG. 3B  is a graph illustrating a trajectory profile of a base in response to the position profile of the stage shown in  FIG. 3A ; 
       FIG. 4  is a schematic view of a stage assembly consistent with the principles of the present invention; 
       FIGS. 5A and 5B  are diagrams illustrating the concept of conservation of momentum applied to the stage assembly consistent with the principles of the present invention; 
       FIG. 6  is a perspective view of an embodiment of the base consistent with the principles of the present invention; 
       FIGS. 7 and 8  are schematic elevation views of an air bearing supporting the base consistent with the principles of the present invention; 
       FIG. 9  is a block diagram of a control system to monitor the base consistent with the principles of the present invention; 
       FIG. 10  is a schematic of the exposure apparatus having the wafer stage assembly consistent with the principles of the present invention; 
       FIG. 11  is a flow chart outlining a process for manufacturing a semiconductor wafer consistent with the principles of the present invention; and 
       FIG. 12  is a flow chart outlining the semiconductor manufacturing process in further detail. 
   

   DESCRIPTION OF THE INVENTION 
   Reference will now be made in detail to an embodiment of the apparatus, system, and method consistent with the principles of the present invention, examples of which are illustrated in the accompanying drawings. The invention will be further clarified by the following examples, which are intended to be exemplary of the invention. 
   The apparatus, system, and method consistent with the principles of the present invention are useful to minimize forces transmitted from a moving object, such as a wafer stage assembly of a photolithography system, to a stationary surface, such as the ground or an exposure apparatus frame. Therefore, vibrations from the wafer stage assembly to other parts of the photolithography system can be prevented. The principles of this invention are similarly applicable to other parts of the photolithography system, such as a reticle stage assembly. Thus, this invention is not limited to any particular application. Rather, the stage assembly, support system, and method disclosed herein could be used in any system configured to embody similar elements disclosed which require stabilization as the system is being accelerated. 
     FIG. 1  illustrates an exposure apparatus  21  of a photolithography system having a wafer stage assembly  100  used in combination with a projection lens assembly  78  to manufacture semiconductor wafers  68 . A wafer table  104  supports wafer  68 , while a wafer stage  66  positions a semiconductor wafer  68  as wafer stage  66  is accelerated by a stage force (not shown) generated in response to a wafer manufacturing control system (not shown). The wafer manufacturing control system is the central computerized control system executing the wafer manufacturing process. To permit smaller and more intricate circuit patterns, projection lens assembly  78  must accurately focus the energy beam to align the overlay of circuit patterns of the multi-layered integrated circuit. 
   In operation, exposure apparatus  21  transfers a pattern of an integrated circuit from a reticle  80  onto semiconductor wafer  68 . Exposure apparatus  21  can be mounted to a the ground  82 , or a vibration isolation system (not shown). An apparatus frame  72  is rigid and supports the components of exposure apparatus  21 , including a reticle stage  76 , wafer stage  66 , lens assembly  78 , and an illumination system  74 . 
   Illumination system  74  includes an illumination source  84  to emit a beam of light energy. Illumination system  74  also includes an illumination optical assembly  86  to guide the beam of light energy from illumination source  84  to lens assembly  78 . The beam selectively illuminates different portions of reticle  80  and exposes wafer  68 . 
   Lens assembly  78  projects and/or focuses the light passing through reticle  80  to wafer  68 . Lens assembly  78  may magnify or reduce the image illuminated on reticle  80 . Lens assembly  78  may also be a 1× magnification system. 
   Reticle stage  76  holds and positions reticle  80  relative to lens assembly  78  and wafer  68 . Similarly, wafer stage  66  holds and positions wafer  68  with respect to the projected image of the illuminated portions of reticle  80 . Wafer stage  66  and reticle stage  76  are moved by a plurality of motors  10 . 
   Consistent with the principles of the present invention and as illustrated in  FIG. 4 , a stage assembly  200  is schematically illustrated for manufacturing semiconductor wafers. A base  202  supports stage  201  via a first set of bearings  204 . Stage  201  may represent reticle stage  76  or wafer stage  66  shown in  FIG. 1 . Stage  201  levitates above base  202  on first bearings  204 . First bearings  204  could be any types of bearings which allow stage  201  to move linearly along the x and y axes as well as rotationally around the z axis. Thus, first bearings  204  have three degrees of freedom. For example, first bearings  204  could be a pneumatic system, such as air bearings, or magnetic levitation, mechanical support, or any equivalent support system. 
   Stage  201  is accelerated by a stage force F in  produced by a force generator (not shown), such as a motor  10  shown in  FIG. 1 . Stage force F in  is generated as a result of the wafer manufacturing control system. Motor  10  could be a planar motor, a linear motor, or any types of commercially available force generator to move stage  201 . 
   In either a planar or linear motor or other types of motors, the force generator commonly has a moving member (not shown), such as a set of magnets, and a stationary member (also not shown), such as a set of coils. In one embodiment, the moving member is attached to an underside of stage  201 , and the stationary member attached to an upperside of base  202 . Conversely, the moving member may be attached to the upperside of base  202 , and the stationary member attached to the underside of stage  201 . 
   Consistent with the principles of the present invention, the second set of bearings  240  is provided to allow base  202  to move relative the stationary surface or ground  82 . Base  202  levitates above stationary surface, such as ground  82 , on second bearings  240 . Second bearings  240  could be any types of bearings which allow base  202  to move in any directions necessary to reduce reaction forces on the ground  82 . In one embodiment, base  202  may move linearly along the x and y axes as well as rotationally around the z axis. Thus, second bearings  240  may have three degrees of freedom. In other embodiments, base  202  may move in more or less than three degrees of freedom. 
   Second bearings  240  could be a pneumatic system, such as air bearings, or magnetic levitation, mechanical support, or an equivalent support system. In one embodiment shown in  FIG. 6 , second bearings  240  are a set of three air bearings. Only air bearings  240   a  and  240   b  are shown. In the illustrated embodiment, air bearings  240   a  and  240   b  are disposed on an undersurface  202   b  of base  202  adjacent to a front face  202   c  parallel to the x axis. The third air bearing (not shown) could be positioned on underside  202   b  near the mid-section of a rear face  202   d.    
   Undersurface  202   b  of base  202  may have a plurality of base paddings  206  (shown in  FIG. 8 ) positioned to interface with second bearings  240 . As shown in  FIG. 7 , each air bearing  240  produces a first planar layer of pressurized air  242  to allow base  202  to move linearly along the x and y axes, and to rotate around the z axis. Each air bearing  240  also produces a second spherical layer of pressurized air  244  to allow a top flat surface  246  of bearing  240  to pivotally conform to the contour of undersurface  202   b  of base  202 . The pivoting action of second bearings  240  compensate for circumstances when the surfaces of base paddings  206  are not perfectly aligned as illustrated in exaggeration for exemplary purposes on  FIG. 8 . Other types of pivoting supports, for example, flexure mounts, can also be used. 
   In accordance with Newton&#39;s third law, stage force F in  acts in an equal magnitude but in opposite directions on stage  201  and base  202 . Whatever motion stage  201  makes, base  202  will make the exact opposite motion scaled by the ratio of masses between stage  201  and base  202 . In the photolithography system, generally base  202  weighs more than stage  201 . Generally, stage  201  and base  202  move synchronously in opposite directions with the motion of stage  201  having a bigger amplitude. Thus, a trajectory or motion profile of stage  201  and base  202  can be determined and follows a pattern such as shown in  FIGS. 3A and 3B , respectively. For example, as illustrated in  FIG. 5A , if stage  201  weighs 50 kg and base  202  weighs 500 kg, when stage  201  moves 100 mm to the left along the x axis, base  202  will move 10 mm to the right along the x axis, and accordingly base  202  will be accelerated at a rate of 1/10 th  of the acceleration rate of stage  201 . 
   Consistent with the principles of the present invention and as illustrated in  FIG. 4 , base  202  is allowed to move thereby reducing or substantially eliminating the amplitude of reaction forces F in  acting on base  202 . Due to its large size in comparison with stage  201 , base  202  acts as a massive reaction mass to store the energy of reaction force F in  acting on base  202  as kinetic energy. The impulse (I) of stage force F in  acting on both stage  201  and base  202  is a mathematical integration of F in  with respect to time and equals to the change in momentum of stage  201  and base  202 , according to the following formula:
 
 I   stage   =m   stage   ·Δv   stage   =∫F   in   dt=−m   base   ·Δv   base 
 
As shown in  FIG. 2A , the area bounded by the force profile with the x axis also represents the value of impulse | stage .
 
   According to a first principle of the present invention involving the theory of conservation of momentum, the combined center of gravity of stage  201  and base  202  remains substantially stationary as illustrated in  FIGS. 5A and 5B . For example, as shown in  FIG. 5A , when stage  201  weighing 50 kg travels 100 mm (0.1 m) to the left along the x axis, then base  202  weighing 500 kg travels 10 mm (0.01 m) to the right along the x axis. However, as shown in  FIG. 5B , the combined center of gravity of the system comprising stage  201  and base  202  remains stationary along vertical axis l cg . Therefore, the stage assembly and support system consistent with the principles of the present invention produce minimal, if any, vibration or disturbances. 
   A set of ground actuators  260  (only one is schematically shown in  FIG. 4 ) acts between base  202  and a stationary surface, such as ground  82  or apparatus frame  72 , to counteract any disturbances acting on the base  202 . Theoretically, the stage  201  and base  202  move with perfect conservation of momentum, and no force is required from the ground actuators  260 . In practice, however, there are always disturbances to the base  202  which must be corrected by the ground actuators  260 . 
   According to a second principle of the present invention, actuators  260  may act like a passive spring and/or damper. In one embodiment according to the second principal, a plurality of passive springs and/or dampers (not shown) indeed may be used as actuators  260 . Particularly, according to the second principal, the combined center of gravity of stage  201  and base  202  does move, and thus, actuators  260  do apply ground force F g  on the ground  82  or apparatus frame  72 . However, the stage assembly  200 , due to its movable base  202 , reduces the magnitude of the motion of the combined center of gravity and the magnitude of ground force F g , which thereby makes the stage assembly  200  consistent with the second principal of the present invention operate smoother. 
   Also, according to the second principle of the present invention, the set of ground actuators  260  acts between base  202  and a stationary surface, such as ground  82  or apparatus frame  72 , to dissipate the kinetic energy by applying small forces to the reaction mass or base  202 . To remove the momentum of base  202  as calculated using the above equation from base  202 , actuators  260  must produce an equal impulse according to the following formulae: 
               I   base     =     I     stage   ⁢           ⁢   assembly                   =           m   base     ·   Δ     ⁢           ⁢     v   base       =     ∫       F   g     ⁢     ⅆ   t                     
 
Because of the massive weight of base  202 , its velocity is relatively low, and its momentum can be cancelled by a small force F g  (also referred to as a trim force) acting over a longer duration, as shown in  FIG. 2B . Thus, trim force F g  has a smoother profile and smaller amplitude, thereby inducing less, if any, vibration to ground  82  or apparatus frame  72  than if base  202  were rigidly attached to ground  82  or apparatus frame  72 .
 
   Further consistent with both principles of the present invention, the ground actuators  260  (shown in  FIG. 4 ) can cancel out any force(s) created by disturbances to base  202 . Alternatively, ground actuators  260  may be connected to apparatus frame  72  or connected to both ground  82  and apparatus frame  72 . One advantage of connecting base  202  to ground  82  is that the disturbance forces are dissipated to and absorbed by ground  82 , thus reducing disturbances to exposure apparatus  21  and the lithography system. 
     FIG. 6  shows one embodiment whereby a set of three ground actuators  260   x ,  260   y , and  260   θz  is provided. Ground actuator  260   x  controls the linear motion of base  202  along the x axis, while ground actuator  260   y  controls the motion along the y axis. Ground actuator  260   θz  controls the rotational motion of base  202  around the z axis. In one embodiment, ground actuator  260   x  is positioned so that it generates a correction force F gx  acting through the center of gravity of base  202  along the x axis. Similarly, ground actuator  260   y  is positioned so that it generates a correction force F gy  acting through the center of gravity of base  202  along the y axis. Therefore, by generating correction forces F gx  and F gy  passing through the center of gravity of base  202 , ground actuators  260   x  and  260   y  do not generate any torque that will imbalance base  202 . In the embodiment discussed above, ground actuator  260   Θz  is positioned not passing through the center of gravity of base  202  so that it produces a correction torque T Θz  about the z axis to counter any rotational imbalance acting on base  202 . 
   Ground actuators  260   x ,  260   y , and  260   Θz  can be any types of actuators, such as voice-coil motors (VCM) that utilizes a magnetic field for generating a driving force (Lorentz force) as shown in  FIG. 6 , or they can also be planar motors, linear motors, rotary motors with linkages, a combination thereof, or any equivalent mechanism. Alternatively, ground actuators  260   x ,  260   y , and  260   Θz  can be any types of passive components, such as springs, dampers, a combination thereof, or any equivalent mechanism. 
   Further consistent with the principles of the present invention, one or more sensors  282 , as schematically shown in  FIG. 4 , is/are provided to detect any disturbance forces acting on base  202 . Sensors  282  keep track of the motion, lateral or rotational, of base  202  in all directions to assure that base  202  follows the predetermined trajectory motion as illustrated in  FIG. 3B . Sensors  282  may be one or more position sensors, velocity sensors, or acceleration sensors. In the block diagram of  FIG. 9 , sensors  282  are position sensors. 
   As illustrated in  FIG. 9 , a base control system  280  is provided to determine the amount of correction forces F gx , F gy , and correction torque T Θz  to be generated by ground actuators  260   x ,  260   y , and  260   Θz , respectively, corresponding to the measurements detected by sensor  282 . Alternatively, a plurality of base control systems may be provided, each is similar to base control system  280 , corresponding to the measurement detected by each of a plurality of sensors  282 . 
   In either alternatives of control system  280 , reference number  284  represents the actual position of base  202  which may be affected by any disturbance forces as measured by sensor  282 . A summing junction  286  compares the measured position of base  202  with a calculated trajectory  288  or desired position of base  202  as determined from the trajectory shown in  FIG. 3B . Summing junction  286  calculates a position error signal  290  based on the difference between actual position  284  and calculated position  288 . Based on position error signal  290 , a controller  292  generates a correction force signal  294  for at least one of actuators  260 , which then generates the corresponding correction force F g  to be applied to the reaction mass or base  202 . 
     FIG. 10  shows stage assembly  200  consistent with the principles of the present invention and incorporated with an exposure apparatus  21  shown in  FIG. 1  of a photolithography system to manufacture semiconductor wafers. Second bearings  240  allow base  202  to move relative to the stationary surface, such as ground  82  or apparatus frame  72 . In addition, actuators  260  counteract any disturbance forces or vibration acting on base  202  which cause position error of stage assembly  200  relative to projection lens assembly  78 . Therefore, stage assembly  200  substantially reduces the vibration from stage  201  to transmit to apparatus frame  72 , other parts of exposure apparatus  21 , and subsequently to ground  82 . 
   However, the use of exposure apparatus  21  provided herein is not limited to a photolithography system for a semiconductor manufacturing. Exposure apparatus  21 , for example, can be used as an LCD photolithography system that exposes a liquid crystal display device pattern onto a rectangular glass plate or a photolithography system for manufacturing a thin film magnetic head. Further, the present invention can also be applied to a proximity photolithography system that exposes a mask pattern by closely locating a mask and a substrate without the use of a lens assembly. Additionally, the present invention provided herein can be used in other devices, including other semiconductor processing equipment, machine tools, metal cutting machines, and inspection machines. 
   The illumination source  84  can be g-line (436 nm), i-line (365 nm), KrF excimer laser (248 nm), ArF excimer laser (193 nm) and F 2  laser (157 nm). Alternatively, illumination source  84  can also use charged particle beams such as x-ray and electron beam. For instance, in the case where an electron beam is used, thermionic emission type lanthanum hexaboride (LaB 6 ) or tantalum (Ta) can be used as an electron gun. Furthermore, in the case where an electron beam is used, the structure could be such that either a mask is used or a pattern can be directly formed on a substrate without the use of a mask. 
   With respect to lens assembly  78 , when far ultra-violet rays such as the excimer laser is used, glass materials such as quartz and fluorite that transmit far ultra-violet rays is preferably used. When the F 2  type laser or x-ray is used, lens assembly  78  should preferably be either catadioptric or refractive (a reticle should also preferably be a reflective type), and when an electron beam is used, electron optics should preferably comprise electron lenses and deflectors. The optical path for the electron beams should be in a vacuum. 
   Also, with an exposure device that employs vacuum ultra-violet radiation (VUV) of wavelength 200 nm or lower, use of the catadioptric type optical system can be considered. Examples of the catadioptric type of optical system include the disclosure Japan Patent Application Disclosure No. 8-171054 published in the Official Gazette for Laid-Open Patent Applications and its counterpart U.S. Pat. No, 5,668,672, as well as Japan Patent Application Disclosure No. 10-20195 and its counterpart U.S. Pat. No. 5,835,275. In these cases, the reflecting optical device can be a catadioptric optical system incorporating a beam splitter and concave mirror. Japan Patent Application Disclosure No. 8-334695 published in the Official Gazette for Laid-Open Patent Applications and its counterpart U.S. Pat. No. 5,689,377 as wall as Japan Patent Application Disclosure No. 10-3039 and its counterpart U.S. patent application Ser. No. 873,606 (Application Date: Jun. 12, 1997) also use a reflecting-refracting type of optical system incorporating a concave mirror, etc., but without a beam splitter, and can also be employed with this invention. The disclosures in the abovementioned U.S. patents, as well as the Japan patent applications published in the Official Gazette for Laid-Open Patent Applications are incorporated herein by reference. 
   Further, in photolithography systems, when linear motors (see U.S. Pat. Nos. 5,623,853 or 5,528,118) are used in a wafer stage or a reticle stage, the linear motors can be either an air levitation type employing air bearings or a magnetic levitation type using Lorentz force or reactance force. Additionally, the stage could move along a guide, or it could be a guideless type stage which uses no guide. The disclosures in U.S. Pat. Nos. 5,623,853 and 5,528,118 are incorporated herein by reference. 
   Alternatively, one of the stages could be driven by a planar motor or electromagnets, which drives the stage by electromagnetic force generated by a magnet unit having two-dimensionally arranged magnets and an armature coil unit having two-dimensionally arranged coils in facing positions. With this type of driving system, either one of the magnet unit or the armature coil unit is connected to the stage  201  and the other unit is mounted on the base  202 . 
   As described above, a photolithography system according to the above described embodiments can be built by assembling various subsystems, including each element listed in the appended claims, in such a manner that prescribed mechanical accuracy, electrical accuracy and optical accuracy are maintained. In order to maintain the various accuracies, prior to and following assembly, every optical system is adjusted to achieve its optical accuracy. Similarly, every mechanical system and every electrical system are adjusted to achieve their respective mechanical and electrical accuracies. The process of assembling each subsystem into a photolithography system includes mechanical interfaces, electrical circuit wiring connections and air pressure plumbing connections between each subsystem. Needless to say, there is also a process where each subsystem is assembled prior to assembling a photolithography system from the various subsystems. Once a photolithography system is assembled using the various subsystems, total adjustment is performed to make sure that every accuracy is maintained in the complete photolithography system. Additionally, it is desirable to manufacture an exposure system in a clean room where the temperature and purity are controlled. 
   Further, semiconductor devices can be fabricated using the above described systems, by the process shown generally in  FIG. 11 . In step  301  the device&#39;s function and performance characteristics are designed. Next, in step  302 , a mask (reticle) having a pattern is designed according to the previous designing step, and in a parallel step  303 , a wafer is made from a silicon material. The mask pattern designed in step  302  is exposed onto the wafer from step  303  in step  304  by a photolithography system described hereinabove consistent with the principles of the present invention. In step  305  the semiconductor device is assembled (including the dicing process, bonding process and packaging process), then finally the device is inspected in step  306 . 
     FIG. 12  illustrates a detailed flowchart example of the above-mentioned step  304  in the case of fabricating semiconductor devices. In step  311  (oxidation step), the wafer surface is oxidized. In step  312  (CVD step), an insulation film is formed on the wafer surface. In step  313  (electrode formation step), electrodes are formed on the wafer by vapor deposition. In step  314  (ion implantation step), ions are implanted In the wafer. The above mentioned steps  311 – 314  form the preprocessing steps for wafers during wafer processing, and selection is made at each step according to processing requirements. 
   At each stage of wafer processing, when the above-mentioned preprocessing steps have been completed, the following post-processing steps are implemented. During post-processing, initially, in step  315  (photoresist formation step), photoresist is applied to a wafer. Next, in step  316 , (exposure step), the above-mentioned exposure device is used to transfer the circuit pattern of a mask (reticle) to a wafer. Then, in step  317  (developing step), the exposed wafer is developed, and in step  318  (etching step), parts other than residual photoresist (exposed material surface) are removed by etching. In step  319  (photoresist removal step), unnecessary photoresist remaining after etching is removed. 
   Multiple circuit patterns are formed by repetition of these preprocessing and post-processing steps. 
   It will be apparent to those skilled in the art that various modifications and variations can be made in the staggered diffraction pattern, the multi-lens array to form the staggered diffraction pattern, and the methods described, the material chosen for the present invention, and in construction of the multi-lens array, the photolithography systems as well as other aspects of the invention without departing from the scope or spirit of the invention. 
   Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims and their equivalents.