Abstract:
A magnetic levitation lithography machine having a low spring stiffness to minimize disturbances of the first structure and which is capable of dynamically controlling the first structure in one or more degrees of freedom. The machine includes a radiation source, a patterning element configured to define a pattern, a projection element, the projection element configured to project the pattern onto a substrate when radiation from the radiation source is projected through the projection element; and a substrate take configured to support the substrate. The substrate take includes a second structure, a fine stage, and a magnetic support configured to support the fine stage adjacent the second structure. The magnetic support includes a first magnet element, coupled to the fine stage, having a first magnet polarization, a second magnet element, coupled to the course stage, having a second magnet polarization, the first magnet element being separated from the second magnet element by a gap, and an adjustment mechanism configured to adjust the magnetic force used to support the fine stage by varying the gap between the first magnet element and the second magnet element.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority on Provisional Application Ser. No. 60/580,468 filed on Jun. 17, 2004 and entitled “Permanent Magnet Gravity Compensation Device”. The contents of Provisional Application Ser. No. 60/580,468 are incorporated herein by reference for all purposes. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to lithography, and more particularly, to a magnetic levitation lithography apparatus and method that uses magnets to provide a static, gravity opposing force to support a fine stage over a coarse stage and to dynamically control the position of the fine stage in one or more degrees of freedom. 
         [0003]    A typical lithography machine includes a radiation source, a patterning element, a projection system, and a wafer table to support a wafer. A radiation-sensitive material, such as resist, is coated onto the wafer surface prior to placement onto the wafer table. During operation, radiation energy from the radiation source is used to project the pattern defined by the patterning element through the projection system onto the wafer. 
         [0004]    The projection area during an exposure is typically much smaller than the wafer. The wafer therefore has to be moved relative to the projection system to pattern the entire surface. 
         [0005]    In the semiconductor industry, two types of lithography machines are commonly used. With so-called “step and repeat” machines, the entire pattern is projected at once in a single exposure onto a target area of the wafer. After the exposure, the wafer is moved or “stepped” in the x and/or y direction and a new target area is exposed. This step and repeat process is performed over and over until the entire wafer surface is exposed. With scanning type lithography machines, the target area is exposed in a continuous or “scanning” motion. The patterning element is moved in one direction while the wafer is moved in either the same or the opposite direction during exposure. The wafer is then moved in the x and y direction to the next scan target area. This process is repeated until all the desired areas on the wafer have been exposed. 
         [0006]    With either type of machine, the wafer substrate table is used to move the wafer substrate. Wafer tables typically have two stages, a coarse stage and a fine stage. The coarse stage is used to move the wafer in the x and/or y directions from one target area to the next. The fine stage is used for minute adjustments and is capable of positioning the wafer in six degrees of freedom (x, y, z, ⊖n, ⊖y and ⊖z. Magnetic levitation is one known way to support the fine stage over the coarse stage. For more details on magnetic levitation, see U.S. Pat. Nos. 4,952,858, 5,157,296, 5,294,854, 3,935,486, 5,623,853, U.S. Patent Publications 2003/0173833A1, 2003/0052284 and British Patent Specification 1,424,413, each incorporated by reference herein for all purposes. 
         [0007]    Ideally, a magnet levitation fine stage should have no vertical weight. In other words, the upward magnetic force completely offsets or compensates for the effects of gravity, resulting in a static vertical mass of zero for the fine stage. In the real world, a certain amount of stiffness will always be present between the fine and coarse stages. This stiffness, which is analogous to a spring, is problematic for several reasons. Any disturbances in the coarse stage are transmitted to the fine stage through the spring. The force of these disturbances can be modeled using equation [1] below. 
         [0008]    [1] F=mg+kz, where
       m=mass of the fine stage;   g=gravity;   k=the stiffness of the spring; and   z=the displacement of the fine stage in the vertical direction.       Based on equation [1], it is clear that the smaller the stiffness of the spring, the smaller the displacement force.   
 
         [0014]    A magnetic levitation lithography machine having a low spring stiffness to minimize disturbances of the fine stage and which is capable of dynamically controlling the fine stage in one or more degrees of freedom is therefore needed. 
       SUMMARY 
       [0015]    A magnetic levitation lithography machine having a low spring stiffness to minimize disturbances of the fine stage and which is capable of dynamically controlling the fine stage in one or more degrees of freedom is disclosed. The machine includes a radiation source, a patterning element configured to define a pattern, a projection element, the projection element configured to project the pattern onto a substrate when radiation from the radiation source is projected through the projection element; and a substrate table configured to support the substrate. The substrate table includes a coarse stage, a fine stage, and a magnetic support configured to support the fine stage adjacent the coarse stage. The magnetic support includes a first magnet element, coupled to the fine stage, having a first magnet polarization, a second magnet element, coupled to the course stage, having a second magnet polarization, the first magnet element being separated from the second magnet element by a gap, and an adjustment mechanism configured to adjust the magnetic force used to support the fine stage by varying the gap between the first magnet element and the second magnet element. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0016]      FIG. 1  is a diagram of a lithography machine according to the present invention. 
           [0017]      FIG. 2  is an enlarged view of the fine stage and coarse stage of the lithography machine of the present invention; 
           [0018]      FIG. 3  is a model diagram of a magnet support used in the lithography machine of the present invention; 
           [0019]      FIGS. 4A and 4B  are a top-down views of a diagram of a magnet support according to a second embodiment of the present invention; 
           [0020]      FIG. 5  is a cross sectional view of one embodiment of a first magnet assembly of the present invention. 
           [0021]      FIG. 6A  is a diagram of a second magnet assembly used in the magnet support of the Present invention; 
           [0022]      FIG. 6B  is a cross section diagram showing the magnet support for supporting a fine stage over a course stage according to the present invention. 
           [0023]      FIGS. 7A-7C  are various arrangements of the first and second magnets according to various embodiments of the invention. 
           [0024]      FIGS. 8A and 8B  are two more arrangements of magnet supports according to other embodiments of the invention. 
           [0025]      FIG. 9  is a flow chart outlining a process for manufacturing a semiconductor device consistent with the principles of the present invention; and 
           [0026]      FIG. 10  is a flow chart outlining the process of  FIG. 9  in more detail. 
       
    
    
     DESCRIPTION 
       [0027]    Referring to  FIG. 1 , a photolithography apparatus  10  according to the present invention is shown. The apparatus  10  includes an illumination system  12  that projects radiation energy through a patterning element  14  that is supported using a patterning stage  16 . Patterning stage  16  is supported by frame  18 . Frame members  19  are provided to support the illumination system  12  over the patterning element  14 . The apparatus  10  also includes an optical projection system  20  that is supported by another frame  22 . Frame members  24  support the projection system  20  below the patterning element  14 . The frame  22  is anchored to ground through support members  26 . 
         [0028]    The apparatus  10  also includes a wafer table  28  that is suspended from frame  22  below the projection system  20 . The wafer table  28  includes a fine stage  30  and a coarse stage  32 . The fine stage  30  is used to support a wafer  34 . The fine stage  30  is limited in travel to fine movements, for example 500 microns in total stroke, in one or more of the six degrees of freedom directions. The coarse stage  32  is used to support the fine stage  30  and is used for coarse positioning. For example, the coarse stage has a capability of traveling 300 mm in the X, and Y directions. The coarse stage may be moved by linear motors that include a fixed member (not shown) and a moving member  38  and positions the coarse stage in three degrees of freedom (in the X, Y directions and about the Z direction). The fine stage  30  may be moved by one or more actuators. The actuators may be, in different embodiments, linear motors, voice coil motors, or a combination thereof. Such actuator may include a fixed member (not shown) connected to the coarse stage  32  and a moving member connected to fine stage  30 . The exposure area on the wafer  34  can therefore be precisely controlled by controlling the fine  30  and coarse  32  stages respectively. 
         [0029]    Referring to  FIG. 2 , an enlarged view of the fine stage  30  and coarse stage  32  is shown. The coarse stage is capable of moving in the Y direction along a guide beam  36  and the X direction with guide of the guide member  39 . The coarse stage  32  is supported on a base (not shown) and is capable of moving in the Z direction using some type of moving device such as an actuator or bearing to support and move the coarse stage  32  in the Z direction. The fine stage  30  is mounted onto the coarse stage  32  and positioned by three sets of magnetic supports  40 . The magnetic supports  40  are capable of controlling the position of the fine stage  30  in the X, Y and Theta Z (i.e., rotation in the X-Y plane). 
         [0030]    Referring to  FIG. 3 , a model diagram of a single magnetic support  40  is shown. The magnetic support  40  includes a first magnet  50  and a second magnet  52  that is annular in shape and surrounds the first magnet  50 . The first magnet  50  generates a magnetic force designated by the arrow  51  in the general direction to support the fine stage  30  above or adjacent to the coarse stage  32 . In other words, the first magnet  50  is configured to move in the vertical direction in this embodiment. The second magnet  52  has a magnetic polarization that is orthogonal to that of the first magnet  50 , as designated by arrow  53 . The magnetic force used to support the fine stage  30  is created by the magnetic interaction of the first magnet  50  and the second magnet  52 . For example, the first magnet (magnetic member)  50  and the second magnet (magnetic member)  52  might be made of a rare earth magnet, such as NdFeb. 
         [0031]    A gap  56  is provided between the first magnet  50  and the second magnet  52 . By varying the gap  56 , the magnetic force applied to the fine stage  30  is controlled. As the gap  56  decreases, the force increases, and vice-versa. 
         [0032]    Referring to  FIGS. 4A and 4B , a top-down view of a diagram of a magnetic support  40  is shown. In this view, the first magnet  50  is shown in the center of the annular shaped second magnet  52 . The gap  56  separates the two magnets. In the embodiment shown, the second magnet  52  is made up of a plurality of magnetic segments  52   a - 52   d  that are symmetrically arranged around the first magnet  50 . By radially moving or adjusting the magnet segments  52   a - 52   d , the gap  56  can be varied. In  FIG. 4A , the segments  52   a - 52   d  are radially adjusted inward. The gap  56  is therefore minimized. In  FIG. 4B , the segments  52   a - 52   d  are radially adjusted outward, increasing the size of the gap  56 . 
         [0033]    Referring to  FIG. 5 , a diagram of an assembly  201  including the first magnet  50  is shown according to one embodiment. The first magnet  50  includes a ring-shaped flat top surface  60 , a bottom surface  203 , a ring  204  arranged laterally around the bottom of the top surface  60 , and a center plunger  62 . The inner surface of the ring is defined by reference numeral  204   a . The first magnet  50 , as described below, forms a moving “plunger” designated by reference numeral  201 , with respect to the second magnet  52 . 
         [0034]    Referring to  FIG. 6A , a diagram of an assembly  202  including the second magnet  52  is shown. The assembly  202  includes an annular ring  64  with a center opening to receive the center plunger  62  of the first magnet  50 . In this view of the figure, only the plunger  62  of the first magnet  50  is illustrated. The ring shaped top surface  60  and the ring  204  are purposely not shown so that the features of the second magnet  52  can be illustrated. The annular ring  64  includes plurality of gap adjustment grooves  66 . Each of the grooves  66  are designed to engage an adjustment pin  68  of a magnet segment  52   a - 52   f  of the second magnet  52 . Each adjustment pin  68  is connected to a mount  207   a - 207   f  that is mounted to one of the magnet segments  52   a - 52   f  respectively. By rotating the annular ring  64 , each of the adjustment pins  68  slides within the gap adjustment grooves  66 . When the ring  64  is rotated clockwise, the pins are pulled inward within the grooves  66 . As a result, the magnet segments  52   a - 52   f  are moved inward, decreasing the gap  56 . Alternatively, the gap  56  is increased by rotating the ring  64  counter-clockwise, causing the pins  68  and magnet segments  52   a - 52   f  to be pulled outward. The magnet segments  52   a - 52   f , ring  64 , grooves  66 , pins  68  and mounts  207   a - 207   f  thus provide an adjustment mechanism that can control the magnetic force used to support the fine stage  30  by varying the gap  56  between the first magnet  50  and the second magnet  52 . A clamping mechanism, such as a clamp or screws, is used to clamp the ring  64  in place once the desired gap  56  is achieved. 
         [0035]    Referring to  FIG. 6B , a cross section diagram illustrating a magnet support  40  supporting a fine stage surface  30 . The magnet support  40  includes the first magnet  50  and the second magnet  52 . The first magnet  50  includes the ring shaped top surface  60 , center plunger  62 , bottom surface  203 , and ring  204  with inner surface  204   a . The arrow  51  designates the direction of the magnetic force of the first magnet  50 . The second magnet  52  includes magnet segments (both designated by reference numeral  52 ), annular ring  64 , grooves  66  (not visible), pins  68 , and mounts  207 . The arrows  53  designate the direction of the magnetic force of the magnet segments  52 . Although not visible in the cross section of the figure, the assembly  202  may include a plurality of magnet segments  52 , for example six, more than six, or less than six. 
         [0036]    The annular ring  64  of the second assembly  202  is mounted onto an annular shaped fixed base  205  on the course stage  32 . The course stage  32  also includes a second base  206 , supported above the surface of the course stage  32 , and configured to fit between the ring surface  204 A and the plunger  62  and under the bottom surface  203  of the first magnet  50 . The second base  206  is also annular shaped and is configured to allow the plunger  62  of the first magnet  50  to move up and down with respect to the course stage  32 . The mounts  207  each have an upper pin  207 A configured to engage the second base  206  and a lower pin  207   b  configured to engage the fixed base  205 . Together, the pins  207 A and  207 B allow the mounts  207  to be rotated so that when the annular ring  64  is rotated, the pin  68  can be positioned within the grooves  66  (not illustrated) so that the magnets  52  can be radially moved in and out to vary the size of the gap  56 . 
         [0037]    In an alternative embodiment, the fine stage  30  can be supported by both the magnet structure  40  and an air bearing. With this embodiment, as illustrated in  FIG. 6B , an air bearing surface  210 A is provided on the top surface  60  of the first magnet  50 . The air bearing  210 A is positioned under the surface of the fine stage  30  without contacting the fine stage surface  30 . The air bearing surface  210 A creates sufficient pressure, along with the magnetic force, to support the fine stage  30 . The fine stage can thus be easily moved in the horizontal direction. In addition, air bearing surfaces may be provided along the surface  204 A of magnet  50  and the opposing surface of second base  206 . A journal bearing is thus created between the two opposing air bearing surfaces, for movement of the first magnet  50  along and about the Z axis with respect to the second assembly  202 . 
         [0038]    In yet another embodiment, the second assembly  202  might be coupled to the fine stage  30  instead of the coarse stage  32 . In this case, the flat top surface  60  of the first assembly  201  faces to the coarse stage  32  and an air bearing is formed between the flat top surface  60  and a partial surface of an upper part of the course stage  32  for the horizontal degree of freedom (along the X and Y axes and about the Z axis) of the fine stage  30  relative to the coarse stage  32 . 
         [0039]    Referring to  FIGS. 7A-7C , several different magnet arrangements are illustrated according to various other embodiments of the invention. Each of these embodiments are characterized in having (i) a first magnet element having a first magnet polarity; (ii) a second magnet having a second magnet polarity, perpendicular to the first magnet; and (iii) an adjustment mechanism to adjust the gap between the two magnets to adjust the magnetic force. In  FIG. 7A  for example, a first magnet  50  has a magnetic polarization  51  pointing downward and a second magnet  52  with an orthogonal polarization directed outward. In  FIG. 7B , the first magnet  50  having a polarization  51  directed upward and a second magnet  52  having an orthogonal polarization  53  directed inward. In  FIG. 7B , the first magnet  50  surrounds the second magnet made up of two segments  52   a  and  52   b . The magnet  50  has a polarization that is directed downward. The second magnet  52  has a two segments  52   a  and  52   b  with orthogonal polarizations  53   a  and  53   b  directed in opposite directions. In each embodiment  7 A- 7 C, a gap  56  separates the two magnets. The gap adjustment mechanism illustrated and described above with regard to  FIGS. 5 ,  6 A and  6 B can be used to adjust the gap  56  in each of these embodiments. 
         [0040]    Referring to  FIG. 8A , another magnetic support arrangement according to the present invention is shown. The magnetic support  80  includes a first magnet  82  and a second magnet  84  that is annular and surrounds the first magnet  82 . The first magnet  82  generates an upward force, as designated by arrow  83 . The second magnet  84  has a magnetic polarization that is orthogonal to the first magnet  82  polarization, as designated by arrow  85 . A third magnet  86 , with a downward polarization as indicated by arrow  87 , is arranged above magnets  82  and  84 . The third magnet  86  generates an additional force for the same size magnet support. The third magnet  86 , however, generates a greater stiffness. The first magnet  82  is movable in the Z direction relative to the second and the third magnets  84  and  86  as a moving plunger. 
         [0041]    Referring to  FIG. 8B , another magnetic support arrangement is shown. The magnetic support  90  includes a first magnet  92 , which has a polarization directed upward as designated by arrow  93  and a second annular magnet  94  that surrounds the first magnet  92 . The second magnet has a polarization that is orthogonal to the first, as designated by arrow  95 . The magnetic support  90  also has a third annular magnet  96  that surrounds the second magnet  94  with a polarization opposite the second magnet  94 , as designated by arrow  97 . A fourth magnet  98 , provided above the first and second magnets, has a polarization directed down, as designated by arrow  99 . A fifth angular magnet  100  surrounds the fourth magnet  98  and has a polarization orthogonal to the fourth magnet, as designated by the arrow  101 . The first and second magnets  92  and  94  are cylinder and annular shaped and are forced together. The fourth and fifth magnets have the same arrangement. The annular third magnet  96  surrounding the other magnets reduces stiffness within a predetermined operating range. 
         [0042]    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 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 humidity are controlled. Further, semiconductor devices can be fabricated using the above described systems, by the process shown generally in  FIG. 9 . 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 . 
         [0043]      FIG. 10  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. 
         [0044]    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. 
         [0045]    Multiple circuit patterns are formed by repetition of these preprocessing and post-processing steps. 
         [0046]    This invention can be utilized in an immersion type exposure apparatus with taking suitable measures for a liquid. For example, PCT patent application WO 99/49504 discloses an exposure apparatus in which a liquid is supplied to the space between a substrate (wafer) and a projection lens system in exposure process. As far as is permitted, the disclosures in WO 99/49504 is incorporated herein by reference. 
         [0047]    In various embodiments of the invention, the magnets  50  and  52  may be either permanent and/or electromagnetic. The present invention may also be used with an illumination system that projects radiation energy in one of but not limited to the following wavelengths 365, 248, 193, 157, 126 nms or EUV in the 5-20 nm range. Also the patterning element  14  may be either a mask or reticle or a programmable LCD array such as described in U.S. Pat. Nos. 5,296,891, 5,523,193 and PCT applications WO 98/38597 and 98/33096, each incorporated by reference herein. 
         [0048]    Further, this invention can be utilized in an exposure apparatus that comprises two or more substrate and/or reticle stages. In such apparatus, the additional stage may be used in parallel or preparatory steps while other stage is being used for exposing. Such a multiple stage exposure apparatus are described, for example, in Japan patent Application Disclosure No. 10-163099 as well as Japan patent Application Disclosure No. 10-214783 and its counterparts U.S. Pat. No. 6,341,007, No. 6,400,441, No. 6,549,269 and No. 6,590,634. Also it is described in Japan patent Application Disclosure No. 2000-505958 and its counterparts U.S. Pat. No. 5,969,441 as well as U.S. Pat. No. 6,208,407. As far as is permitted, the disclosures in the above-mentioned U.S. patents, as well as the Japan patent applications are incorporated herein by reference. 
         [0049]    This invention can be utilized in an exposure apparatus that has a movable stage retaining a substrate (wafer) for exposing it, and a stage having various sensors or measurement tools for measuring, as described in Japan Patent Application Disclosure No. 11-135400. As far as is permitted, the disclosures in the above-mentioned Japan patent application is incorporated herein by reference. 
         [0050]    It should be noted that the particular embodiments described herein are merely illustrative and should not be construed as limiting. Rather, the true scope of the invention is intended to be determined by the accompanying claims.