Abstract:
The present invention relates to a lithography apparatus and method using catadioptric exposure optics that projects high quality images without image flip. The apparatus includes means for illuminating a reticle stage to produce a patterned image. The apparatus also includes means for receiving the patterned image at each of a plurality of wafer stages. Each of the wafer stages has an associated data collection station. The apparatus also includes means for positioning the reticle stage substantially orthogonal to each of the plurality of wafer stages as well as means for directing the patterned image through a catadioptric exposure optics element between the reticle stage and each wafer stage to cause an even number of reflections of the patterned image and to project the patterned image onto each wafer stage in a congruent manner. The invention can also be combined with a dual isolation system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This patent application is a continuation of U.S. patent application Ser. No. 10/156,005, filed May 29, 2002, now U.S. Pat. No. 6,757,100, the disclosure of which is incorporated herein by reference in its entirety. 
   This patent application is related to the following commonly-owned U.S. patent applications: U.S. patent application Ser. No. 09/449,630, to Roux et al., entitled “Dual Stage Lithography Apparatus and Method,” filed Nov. 30, 1999, now abandoned, and U.S. patent application Ser. No. 09/794,133, to Galburt et al., for “Lithographic Tool with Dual Isolation System and Method for Configuring the Same,” filed Feb. 28, 2001, now U.S. Pat. No. 6,538,720. The foregoing U.S. patent applications are hereby incorporated by reference in their entirety. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to an improved lithography system and method. More specifically, this invention relates to a lithography system and method using catadioptric exposure optics that projects high precision images without image flip. 
   2. Background Art 
   Lithography is a process used to create features on the surface of substrates. Such substrates can include those used in the manufacture of flat panel displays, circuit boards, various integrated circuits, and the like. A frequently used substrate for such applications is a semiconductor wafer. While this description is written in terms of a semiconductor wafer for illustrative purposes, one skilled in the art would recognize that this description also applies to other types of substrates known to those skilled in the art. During lithography, a wafer, which is disposed on a wafer stage, is exposed to an image projected onto the surface of the wafer by exposure optics located within a lithography apparatus. The image refers to the original, or source, image being exposed. The projected image refers to the image which actually contacts the surface of the wafer. While exposure optics are used in the case of photolithography, a different type of exposure apparatus may be used depending on the particular application. For example, x-ray or photon lithographies each may require a different exposure apparatus, as is known to those skilled in the art. The particular example of photolithography is discussed here for illustrative purposes only. 
   The projected image produces changes in the characteristics of a layer, for example photoresist, deposited on the surface of the wafer. These changes correspond to the features projected onto the wafer during exposure. Subsequent to exposure, the layer can be etched to produce a patterned layer. The pattern corresponds to those features projected onto the wafer during exposure. This patterned layer is then used to remove exposed portions of underlying structural layers within the wafer, such as conductive, semiconductive, or insulative layers. This process is then repeated, together with other steps, until the desired features have been formed on the surface of the wafer. 
   Exposure optics comprise refractive and/or reflective elements, i.e., lenses and/or mirrors. Currently, most exposure optics used for commercial manufacturing consist only of lenses. However, the use of catadioptric (i.e., a combination of refractive and reflective elements) exposure optics is increasing. The use of refractive and reflective elements allows for a greater number of lithographic variables to be controlled during manufacturing. The use of mirrors, however, can lead to image flip problems. 
   Image flip occurs when an image is reflected off of a mirror.  FIG. 1  shows an example of image flip. In this example, if one were to hold up plain English text to a mirror, one would notice that the text, viewed in the mirror, would appear to be written backwards. Thus, an image of the letter “F” would be seen as “           ” in the mirror. This shows that when an image is reflected off of a mirror, the projected image results in an incorrect image orientation, i.e., the image transfer produces image flip. Of course, if the image is reflected off of two mirrors, the image orientation of the projected image would be correct because the image is flipped twice. Thus, an image of the letter “F” would be seen as “F” after the second reflection. Therefore, it can be seen that image flip results when an image is reflected an odd number of times. Conversely, it can be seen that image flip does not result when the image is reflected an even number of times.
   Current lithographic systems typically include a reticle stage that is parallel to a wafer stage, such that the image from the reticle stage is projected downward onto the wafer stage. In addition, current lithographic systems typically include catadioptric exposure optics that require a magnifying mirror, such as a concave asphere. This mirror enhances the projected image and enables better exposure of the wafer. The parallel wafer and reticle stages together with the geometry of a magnifying mirror, however, makes it difficult for the catadioptric exposure optics to perform an even number of reflections. 
   To illustrate this point,  FIG. 2  shows a simplified example lithographic system  200 . System  200  shows a parallel reticle stage  202  and wafer stage  204  using catadioptric exposure optics  212 , having a first mirror  206 , a beam splitter  208 , a quarter wave plate  209 , and a magnifying mirror element group  210 . In this example system  200 , an image is projected from reticle stage  202  using P polarized light. This polarized light is reflected by first mirror  206  directly into magnifying mirror element group  210 . It should be noted that quarter wave plate  209  can rotate the polarization angle of the light. The reflected image from first mirror  206  passes through beam splitter  208 . This is due to the P polarization of the light being transmitted by beam splitter  208 . The reflected image from magnifying mirror element group  210  has its polarization angle rotated 90°. This light is reflected at the beam splitter surface onto wafer  204 . Thus, S polarization is not transmitted by beam splitter  208 . Subsequently, the image is reflected directly out of magnifying mirror element group  210  that contains quarterwave plate  209 . Besides flipping the image, magnifying mirror element group  210  also reverses the polarization of the image. Thus, the image reflected out of magnifying mirror element group  210  is then reflected by beam splitter  208 , since the image now has the opposite polarization as beam splitter  208 . The image is then projected onto parallel wafer stage  204 . Using this configuration, an odd number of reflections occur. As a result, image flip problems occur. 
   Several alternative lithographic system designs, however, have attempted to overcome the image flip obstacle. One such design is a centrally obscured optical system design.  FIG. 3  shows an example lithographic system  300  with a centrally obscured optical system design. System  300  shows a parallel reticle stage  302  and wafer stage  304  using catadioptric exposure optics  312  with a first mirror  306  and a magnifying mirror  308 . In this example system  300 , an image is projected from reticle stage  302  directly into magnifying mirror  308 . It should be noted that the image projected from reticle stage  302  passes through first mirror  306 . This is because first mirror  306  is polarized (in the same way as beam splitter  208  above). The image is then reflected directly out of magnifying mirror  308  and onto first mirror  306 . Besides flipping the image, magnifying mirror  308  also reverses the polarization of the image. The image is then reflected downwards by first mirror  306 , through a small hole  310  in magnifying mirror  308  and onto wafer stage  304 . In this configuration, magnifying mirror  308  is in the path of the projected reflection of first mirror  306 , which is why small hole  310  exists within magnifying mirror  308 . The projected reflection of first mirror  306  travels through small hole  310  in magnifying mirror  308  to reach wafer stage  304 . Using this configuration, an even number of reflections occur. Thus, there is no image flip problem. However, this configuration has its drawbacks. As the image is reflected by magnifying mirror  308 , some of the image information (namely the portion of the image that passes through small hole  310  in magnifying mirror  308 ) is lost. This can produce aberrations or inconsistencies in the projected image. 
   Another lithographic system that has attempted to overcome the image flip obstacle is an off-axis design.  FIG. 4  shows an example lithographic system  400  with an off-axis design. System  400  shows a parallel reticle stage  402  and wafer stage  404  using catadioptric exposure optics  412  with a first mirror  406  and a magnifying mirror  408 . In this example system  400 , an image is projected from reticle stage  402  onto a first mirror  406 , reflected from first mirror  406  and into magnifying mirror  408 , reflected out of magnifying mirror  408  and onto wafer stage  404 . In this configuration, reticle stage  402  is off-axis from wafer stage  404 . This is because the image is reflected away from the reticle stage in order to magnify it using magnifying mirror  408 . As shown, there is a small angle  410  between first mirror  406  and wafer stage  404 . Using this configuration, an even number of reflections occur. However, this configuration has its drawbacks. Magnifying mirror  408  does not directly (i.e., perpendicularly) receive the reflected image from first mirror  406 . This is because magnifying mirror  408  must be able to receive a reflected image from first mirror  406  and reflect that image through a small angle  410  onto wafer stage  404 . Further, magnifying mirror  408  does not directly reflect the image onto wafer stage  404 . As a result, aberrations and perspective warping of the image can occur. 
   Therefore, it is difficult to create a lithographic system with catadioptric exposure optics that can produce a high quality image without image flip. Consequently, most lithographic systems today use a design similar to the design of FIG.  1 . This design performs an odd-number of reflections that result in image flip problems. As a result, when exposing an image using these catadioptric exposure optics, it must be kept in mind that the projected image is the reverse of the desired image. This can lead to increased processing time and preparation. This problem is further compounded by the fact that most lithographic systems used today do not result in image flip. As a result, manufacturers that use both catadioptric exposure optics and non-catadioptric exposure optics (i.e., systems that have the image flip problem and systems that do not have the image flip problem) must use two reticle plates-one with each image orientation. This can lead to higher production costs. 
   In view of the above, what is needed is a lithographic system and method, using catadioptric exposure optics, which produces a high precision image without image flip. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention relates to a lithography system and method using catadioptric exposure optics that projects high quality images without image flip. 
   In embodiment(s) of the invention, the apparatus includes means for illuminating a reticle stage to thereby produce a patterned image. The apparatus also includes means for receiving the patterned image at each of a plurality of wafer stages, each wafer stage having an associated data collection station. In embodiment(s) of the invention, the apparatus includes means for exchanging the plurality of wafer stages between the associated data collection station and an exposure station. For example, in one embodiment, the apparatus includes means for alternately moving each of the plurality of wafer stages during operation form the associated data collection station to the exposure station such that data collection of one wafer stage can occur at the same time as exposure of another wafer stage. The apparatus also includes means for positioning the reticle stage substantially orthogonal to each of the plurality of wafer stages. Additionally, the apparatus includes means for directing the patterned image through a catadioptric exposure optics element between the reticle stage and the wafer stage to cause an even number of reflections of the image and to project the image onto the wafer stage in a congruent manner. The invention can also be combined with a dual isolation system. Method embodiments involving the apparatus embodiments are also presented. 
   The catadioptric exposure optics projects an image from the reticle stage onto the wafer stage. The projected image has the same image orientation as the image from the reticle stage. In other words, the catadioptric exposure optics does not perform image flip. The resulting projected image is of high precision and lacks aberrations such as perspective warping and obscured areas. 
   An advantage of the present invention is the use of catadioptric exposure optics that does not perform image flip. This allows a manufacturer to use the same image with catadioptric and non-catadioptric lithographic systems. This increases compatibility and reduces production costs. 
   Another advantage of the present invention is projection of a high precision image onto the wafer stage. Unlike the prior art which uses alternative catadioptric exposure optics designs, the present invention projects a high quality image without aberrations such as perspective warping and obscuration areas in the optics pupil. This produces a higher quality product. 
   Another advantage of the present invention is maximization of the use of the exposure optics. This is due to wafer data collection and exposure steps occurring in parallel. The parallel nature of the present invention allows for greater data collection without a corresponding decrease in throughput. This increases the efficiency of the manufacturing process. 
   Another advantage of the present invention is the reduction of relative motion between critical elements of the lithography apparatus. The present invention uses multiple isolated systems to reduce motion loads, and relative motion between critical components, including components such as those included in a wafer stage, a reticle stage, and exposure optics. By reducing motion loads, and relative motion between one or more lithography system components, semiconductor wafers may be more precisely and repeatedly etched according to tighter tolerances. 
   Further features and advantages of the invention as well as the structure and operation of various embodiments of the present invention are described in detail below with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
     The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit of a reference number identifies the drawing in which the reference number first appears. 
       FIG. 1  is a picture illustrating the image flip problem, in an embodiment of the present invention. 
       FIG. 2  is a diagram illustrating a typical lithographic system using catadioptric exposure optics, parallel reticle and wafer stages and a magnifying mirror. 
       FIG. 3  is a diagram illustrating a lithographic system using the centrally obscured optical system design. 
       FIG. 4  is a diagram illustrating a lithographic system using the off-axis design. 
       FIG. 5  is a diagram illustrating a lithographic system using orthogonal reticle and wafer stages, in an embodiment of the present invention. 
       FIG. 6  is a diagram illustrating the catadioptric exposure optics of a lithographic system using orthogonal reticle and wafer stages, in an embodiment of the present invention. 
       FIG. 7  is a diagram illustrating the image path in a lithographic system using orthogonal reticle and wafer stages, in an embodiment of the present invention. 
       FIG. 8  is a chart illustrating the orientation of an image during processing within the catadioptric exposure optics, in an embodiment of the present invention. 
       FIG. 9  is an illustration of a dual wafer stage, in an embodiment of the present invention. 
       FIG. 10  is an illustration of a dual isolation system, in an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Table of Contents 
   I. Overview 
   A. Definitions 
   B. General Considerations 
   II. System Orientation 
   III. Exposure Optics 
   A. Image Path 
   B. Projected Image 
   IV. Dual Wafer Stage 
   V. Dual Isolation System 
   VI. Conclusion 
   I. Overview 
   The present invention relates to a lithography system and method using catadioptric exposure optics that projects high quality images without image flip. The present invention allows for a more efficient and timely production of semiconductors. 
   A. Definitions 
   The following definitions are provided for illustrative purposes only. Alternative definitions for the listed terms will be apparent to persons skilled in the relevant art(s) based on the discussion contained herein, and fall within the scope and spirit of embodiments of the invention. 
   The term “catadioptric” refers to the use of reflective and refractive elements (i.e., mirrors and lenses). 
   B. General Considerations 
   The present invention is described in terms of the examples contained herein. This is for convenience only and is not intended to limit the application of the present invention. In fact, after reading the following description, it will be apparent to one skilled in the relevant art(s) how to implement the following invention in alternative embodiments. 
   II. System Orientation 
     FIG. 5  is a diagram illustrating a lithographic system  500 , in an embodiment of the present invention. The figure shows a reticle stage  502 , a wafer stage  504  and catadioptric exposure optics  506 . During operation of system  500 , an image (not shown) is associated with reticle stage  502 . Subsequently, the image is projected into catadioptric exposure optics  506 , which processes the image and projects the image onto wafer stage  504 . Alternatively, the image can be reflected into catadioptric exposure optics  506 . Heretofore, any reference to the projection of the image from reticle stage  502  into catadioptric exposure optics  506  will be interchangeable with the reflection of the image into the same. 
   In an embodiment of the present invention, reticle stage  502  is orthogonal to wafer stage  504 . To illustrate this configuration, using  FIG. 5  as an example, reticle stage  502  is situated on a first plane while wafer stage  504  is situated on a second plane, wherein the first plane is orthogonal to the second plane. This feature allows for the image orientation of the image projected onto wafer stage  504  to be congruent to the image orientation of the original image (i.e., the image is not flipped). Image orientation is explained in greater detail below. 
   III. Exposure Optics 
     FIG. 6  is a diagram illustrating a more detailed view of a catadioptric exposure optics  600 , in an embodiment of the present invention.  FIG. 6  shows entrance lenses  602 , beam splitter  604 , concave asphere  606  (i.e., magnifying mirror) and exit lenses  610 .  FIG. 6  is shown for illustrative purposes only and does not seek to limit the present invention to the illustrated configuration. The highly sophisticated catadioptric exposure optics  600  includes such components as may be necessary in, for example, step-and-scan type lithographic tools. An example of catadioptric exposure optics is described in commonly-owned U.S. Pat. No. 5,537,260 to Williamson, entitled “Catadioptric Optical Reduction System with High Numerical Aperture.” The foregoing U.S. Patent is hereby incorporated by reference in its entirety. 
   Entrance lenses  602  are situated upon the entrance of catadioptric exposure optics  600 . As an image enters catadioptric exposure optics  600 , lenses  602  magnify and/or align the image. In addition, entrance lenses  602 , or any other component situated upon the entrance of catadioptric exposure optics  600 , can perform any task known to one of skill in the art. 
   Beam splitter  604  is a polarized mirror. Thus, light of the same polarity as beam splitter  604  can pass through it, while light of a different polarity is reflected by it. It should also be noted that beam splitter  604  is situated at a 45 degree angle from the incidence of the angle of an incoming image. Using  FIG. 6  as an example, beam splitter  604  is situated at a 45 degree angle from the horizontal plane. This feature allows an incoming image to be reflected directly into concave asphere  606 , due to Snell&#39;s Law (i.e., the angle of incidence is equal to the angle of reflection). 
   Concave asphere  606  increases the magnitude of an incoming image reflected by beam splitter  604 . In addition, concave asphere  606  reverses the polarity of light carrying an incoming image reflected by beam splitter  604 . Concave asphere  606  performs these tasks, as well as any other potential tasks, in a manner which is known to those skilled in the art of the present invention. 
   Exit lenses  610  are situated upon the exit of catadioptric exposure optics  600 . As an image exits catadioptric exposure optics  600 , lenses  610  magnify and/or align the image. In addition, exit lenses  610 , or any other component situated upon the exit of catadioptric exposure optics  600 , can perform any task known to one of skill in the art. 
   A. Image Path 
     FIG. 7  is a diagram illustrating the path taken by an image within example catadioptric exposure optics  700 , in an embodiment of the present invention. In this embodiment, an image  702  enters catadioptric exposure optics  700  through a designated entrance. As image  702  enters catadioptric exposure optics  700 , lenses  602  magnify and/or align image  702 . 
   Subsequently, image  702  enters beam splitter  604 . The light carrying image  702  through the entrance of catadioptric exposure optics  700  is of opposite polarity as beam splitter  604 . Thus, image  702  is reflected by beam splitter  604 . Due to the orientation of beam splitter  604  (i.e., its 45 degree angle), image  702  is reflected directly into concave asphere  606 . 
   Next, image  702  is reflected off of concave asphere  606 . Concave asphere  606  then increases the magnitude of image  702  and reverses the polarity of image  702 . In addition, concave asphere  606 , as known to one of skill in the art, flips the image around both axes. As a result, after being reflected by concave asphere  606 , the light carrying image  702  is of the equal polarity as beam splitter  604 . 
   Since the light carrying image  702  is now of equal polarity as beam splitter  604 , image  702  passes through beam splitter  604 . Then, image  702  is projected toward the exit of catadioptric exposure optics  700 . In doing so, the image passes through exit lenses  610 . As image  702  exits catadioptric exposure optics  700 , lenses  610  magnify and/or align image  702 . Subsequently, image  702  is projected onto wafer stage  504 . 
   B. Projected Image 
     FIG. 8  is a chart  800  illustrating the orientation image  702  during processing within the catadioptric exposure optics, in an embodiment of the present invention. It should be noted that a rotation of the image of 180° is not a permanent problem, as this requires a simple rotation of the wafer 180° to correct.  FIG. 8  shows how image  702  changes during processing by catadioptric exposure optics  700 , as described in  FIG. 7  above. The left column of chart  800  provides a description of the processing stage of image  702 , as well as the viewing perspective. In other words, the left column describes where in the process image  702  is currently located, and how image  702  should be viewed. The right column of chart  800  shows a representation of image  702  from the defined viewing perspective and at the defined processing stage. 
   The first row of chart  800  shows that image  702  is originally an image of the letter “F” if viewed from the perspective of a person standing behind catadioptric exposure optics  700  and looking into the entrance. The image of the second row of chart  800  is basically the image of the first row, rotated. The image of the second row is significant because it represents how the wafer will be viewed. 
   As explained above, it can be seen that, using the lithographic system and method of the present invention, an original image of the letter “F” will be projected as the image “           ” onto wafer stage  504 . It can be shown that the original image “F” is congruent to the projected image “         .” This assertion becomes more clear when the projected image “         ” is rotated one hundred and eighty (180) degrees clockwise. After the rotation, the projected image “         ” becomes identical to the original image “F.” In contrast, an image that has undergone one image flip is not congruent to the original image. This is because there are no number of rotations of the flipped image that will render the flipped image identical to the original image.
   Further, the lithographic system of the present invention does not possess the problems associated with alternative lithographic system designs (as described above), such as the centrally obscured optical system design (see  FIG. 3 ) and the off-axis design (see FIG.  4 ). One reason for this is because the lithographic system of the present invention does not utilize a configuration using a magnifying mirror with a small hole, through which the image passes. Thus, the lithographic system of the present invention does not exhibit obscured areas. 
   Another reason why the lithographic system of the present invention does not possess the problems associated with alternative lithographic system designs is because of the use of the magnifying mirror. The lithographic system of the present invention projects images directly (i.e, perpendicularly) into the magnifying mirror (i.e., the concave asphere). In addition, the lithographic system of the present invention projects images directly out of the magnifying mirror and directly onto another surface, such as the wafer stage. Thus, the lithographic system of the present invention does not exhibit perspective warping and related problems. 
   IV. Dual Wafer Stage 
   In an embodiment of the present invention, a dual wafer stage is used to make the manufacturing process more efficient. A dual wafer stage includes the use of two, separate wafer stages operating in tandem, such that one wafer may be exposed while the other is loading. This embodiment of the present invention increases lithography tool throughput while simultaneously increasing the volume of alignment data collected through the use of two substrate stages. Each substrate stage has associated load/unload and data collection stations. The load/unload and data collection stations are located on either side of an exposure station. The substrate stages are mounted on a common rail such that as a first stage moves away from the exposure station, a second stage can immediately move in to take its place under the exposure apparatus. Through this arrangement, use of the exposure apparatus is maximized. Because wafer data collection and exposure steps occur in parallel in the instant invention, the compromised wafer alignment strategies sometimes employed to increase throughput need not be used. In fact, the parallel nature of the instant invention allows for greater data collection without a corresponding decrease in throughput. 
   In another embodiment of the present invention, the lithography apparatus comprises an exposure station and a plurality of substrate stages, each of the substrate stages having an associated data collection station separate from a data collection station associated with other of the plurality of substrate stages. Each of the plurality of substrate stages is movable from the associated data collection station to the exposure station. 
   During operation, each of the plurality of substrate stages is alternately moved from its associated data collection station to the exposure station such that data collection of a first of the plurality of substrate stages can occur at the same time a second of the plurality of substrate stages is undergoing exposure at the exposure station. 
   The lithography apparatus can further be characterized as including first and second data collection cameras disposed over first and third positions within the apparatus. The exposure apparatus being disposed over a second position within the lithography apparatus. The first and second substrate stages being movable from the first position to the second position and from the third position to the second position, respectively. 
     FIG. 9  illustrates a dual wafer stage, in an embodiment of the present invention. Data collection and exposure structure  900  includes a first wafer stage  910  and a second wafer stage  920 . The first and second wafer stages are depicted in the figures as having wafers  911  and  921  mounted thereon. Wafer stage  910  is mounted via sub-stages  912  and  913  to rail  930 . Sub-stage  913  is movably mounted to sub-stage  912  to permit stage movement in a direction perpendicular to rail  930 . Though not shown, substages  912  and  913  can include components of a linear brushless motor of the type known to those skilled in the art to effectuate this movement. Motors  931  and  932  propel sub-stage  913  along the rail  930 . Motors  931  and  932  can also be linear brushless motors of the type known to those skilled in the art. Likewise, wafer stage  920  is mounted to rail  930  via sub-stages  922  and  926 . Motors  931  and  932  also propel sub-stage  926  along rail  930 . As with sub-stages  912  and  913 , additional motor components are included within sub-stages  922  and  926  to effectuate stage movement in a direction perpendicular to rail  930 . Furthermore, interferometers (not shown) are disposed within the structure to accurately determine the location of wafer stages  910  and  920  on rail  930  and along an axis perpendicular to  930 . These interferometers work together with a control system to control stage movement. 
   Data collection and exposure structure  900  works together with first and second data collection cameras  940  and  950 , respectively. These cameras are mounted to a structure separate from the data collection and exposure apparatus. These data collection cameras are of the type known to those skilled in the art as being capable of data gathering for calibration functions such as wafer alignment target mapping and wafer flatness mapping. The first and second data collection cameras are mounted above regions referred to herein respectively as first and second data collection stations. The term data collection station is meant to refer to a region along rail  930  where wafer data collection occurs during operation and is not meant to be limited to a single particular wafer stage location within the structure. The data collection station associated with each data collection camera is larger in area than its associated wafer stage since each wafer stage moves within its associated data collection station during the data collection process. Data collection cameras  940  and  950  communicate with a control system. 
   Data collection and exposure structure  900  further works together with exposure apparatus  960 . While exposure optics are used in the case of photolithography, a different type of exposure apparatus may be used depending on the particular application. For example, x-ray, ion, electron, or photon lithographies each may require a different exposure apparatus, as is known to those skilled in the art. The particular example of photolithography is discussed here for illustrative purposes only. Exposure optics  960  are mounted to the same structure, separate from the data collection and exposure apparatus, to which data collection cameras  940  and  950  are mounted, as discussed above. Exposure optics are of the type known to those skilled in the art as being capable of lithographic exposure functions. These exposure optics can include, for example, components and functionality for use in step-and-scan type tools as well as step and repeat tools where the full reticle field is exposed without scanning. Exposure optics  960  is disposed above a region referred to herein as the exposure station. The term exposure station is meant to refer to a region along rail  930  where wafer exposure occurs during operation and is not meant to be limited to a single particular wafer stage location within the structure. The exposure station is larger in area than a single one of the wafer stages since the wafer stage being exposed moves within the exposure station during the wafer exposure process. The exposure station is located between the first and second data collection stations. 
   The concept of a dual wafer stage is explained in more detail in commonly-owned U.S. patent application Ser. No. 09/449,630, to Roux et al, entitled “Dual Stage Lithography Apparatus and Method,” filed Nov. 30, 1999. The foregoing U.S. patent application is hereby incorporated by reference in its entirety. 
   Referring to  FIG. 5 , a dual wafer stage, as described above, can be interchanged with wafer stage  504 . The combination of a dual wafer stage with lithographic system  500  yields a lithographic system capable of high throughput while using catadioptric exposure optics that produce a high quality image without image flip. 
   V. Dual Isolation System 
   In an embodiment of the present invention, a dual isolation system is used to make the manufacturing process more precise. A dual isolation system includes the isolation of the wafer stage and the reticle stage, such that both stages are protected from environmental motion. In one aspect, an isolated base frame is supported by a non-isolated tool structure. A wafer stage component is supported by the isolated base frame. The wafer stage component provides a mount for attachment of a semiconductor wafer. A reticle stage component is supported by the isolated base frame. The reticle stage component provides a mount for a reticle. An isolated bridge provides a mount for a projection optics. The isolated bridge is supported by the isolated base frame. Radiation from an illumination source passes through a reticle mounted at the provided reticle mount to a surface of an attached semiconductor wafer. A pattern of a mounted reticle is transferred to a surface of an attached semiconductor wafer. 
   In another aspect, an isolated bridge provides a mount for a projection optics. The isolated bridge is supported by a non-isolated base frame. A wafer stage component is supported by the non-isolated base frame. The wafer stage component provides a mount for attachment of a semiconductor wafer. A reticle stage component is supported by the non-isolated base frame. The reticle stage component provides a mount for a reticle. An isolated optical relay is supported by the non-isolated base frame. The isolated optical relay includes at least one servo controlled framing blade. The one or more servo controlled framing blades are configured such that radiation from an illumination source would be framed and imaged onto a reticle mounted at the provided reticle mount. The radiation would pass through the reticle plane to a surface of an attached semiconductor wafer. A pattern of a mounted reticle would be transferred to an attached semiconductor wafer surface. 
     FIG. 10  illustrates a dual isolation system, in an embodiment of the present invention. Lithographic tool apparatus  1100  incorporates an isolation system to minimize motion in the structure supporting critical optical components. Lithographic tool apparatus  1100  includes an isolated bridge  1102 , a projection optics  1104 , a first, second, and third pneumatic isolator  1106 ,  1108 , and  1110 , a non-isolated base frame  1112 , a first and second relative position sensor  1114  and  1116 , a first, second, third, and fourth actuator  1118 ,  1120 ,  1122 , and  1124 , a wafer sub-stage  1126 , a wafer precision stage  1128  with a bracket  1142 , a focus back plate  1130 , one or more flexured spacing rods  1132 , a reticle stage  1134 , a linear motor  1136 , a 1× relay  1138 , and air bars  1140 . These elements of lithographic tool apparatus  1100  are more fully described in the following text and subsections below. 
   The concept of a dual isolation system is explained in more detail in commonly-owned U.S. patent application Ser. No. 09/794,133, to Galburt et al, entitled “Lithographic Tool with Dual Isolation System and Method for Configuring the Same,” filed Feb. 28, 2001. The foregoing U.S. Patent Application is hereby incorporated by reference in its entirety. 
   Referring to  FIG. 5 , a dual isolation system, as described above, can be integrated with wafer stage  504 . The combination of a dual isolation system with lithographic system  500  yields a lithographic system capable of increased operational precision while using catadioptric exposure optics that produce a high quality image without image flip. 
   VI. Conclusion 
   While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant art(s) that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.