Abstract:
An exposure method exposes a substrate arranged on a stage, which holds the substrate and moves, to light through an original and a projection optical system. The method includes steps of a first measurement of measuring a first drive characteristic of the stage by detecting a position of a pattern on the stage using a first detection system which detects a position of a pattern on the substrate through an optical system which does not include the projection optical system, a second measurement of measuring a second drive characteristic of the stage by detecting the position of the pattern on the stage using a second detection system which detects the position of the pattern on the stage through the projection optical system, and aligning the original and the substrate based on the first and second drive characteristics.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to an exposure method and apparatus. More particularly, though not exclusively, the present invention relates to an exposure method and apparatus which align an original such as a mask or reticle with a substrate such as a semiconductor wafer accurately to expose the substrate to light through the original.  
       BACKGROUND OF THE INVENTION  
       [0002]     In recent years, as semiconductor integrated circuits such as ICs or LSIs or a liquid crystal panel micronize and their integration degree increases, the accuracy and function of an exposure apparatus such as a semiconductor exposure apparatus improve. In particular, in alignment of an original such as a mask or reticle and a substrate such as a semiconductor wafer, a technique which overlays the original and substrate on the order of several nm to be promising is expected. As an exposure apparatus used in the manufacture of devices such as semiconductor integrated circuits, an apparatus called a stepper or step &amp; scan is used often.  
         [0003]     This apparatus sequentially transfers a pattern formed on an original (e.g., a reticle) to a plurality of portions of the substrate (e.g., a semiconductor wafer). An apparatus that performs this transfer is collectively called a stepper, and an apparatus that performs this transfer while scanning a stage is called a step &amp; scan.  
         [0004]     Alignment of the original and substrate in the exposure apparatus will be described.  
         [0005]     An example of alignment of the original and substrate in the exposure apparatus includes a die-by-die alignment scheme which performs alignment by measuring the exposure position for each exposure. A global alignment scheme is also available which performs position measurement at an appropriate number of measurement points in advance and creates a correction equation of the exposure position from the measurement result to perform alignment.  
         [0006]     The global alignment scheme is an excellent scheme with which a high throughput and high accuracy can be obtained. According to the global alignment scheme, alignment is performed according to one correction equation for the entire area of the substrate. Hence, the state of alignment can be judged by examining several points of the substrate, leading to an advantage in usage as well. To perform alignment, the alignment target itself or an alignment mark arranged in its vicinity must be detected. An example of a detection scheme for this includes the following two schemes:  
         [0007]     1. The TTL (Through The Lens) scheme with which the position of the alignment mark is measured through a projection optical system.  
         [0008]     2. The OA (Off Axis) scheme with which the position of an alignment mark is measured directly and not through a projection optical system.  
         [0009]     When the original and substrate are to be aligned by the OA scheme, the base line amount as the gap between the measurement center of an alignment detection system and the projection image center (exposure center) of the original pattern must be known.  
         [0010]     More specifically, the substrate must be moved to a position which is obtained by correcting the position of a target exposure region (also called a shot region), which is measured by using the alignment detection system, with the base line amount, so that the center of the shot region is correctly aligned with the exposure center. During use of the exposure apparatus, sometimes the base line amount gradually fluctuates. When fluctuation in base line amount occurs, the alignment accuracy (overlaying accuracy)-decreases.  
         [0011]     To prevent this, conventionally, the base line amount is measured periodically.  
         [0012]     So far the conventional exposure apparatus and alignment with the exposure apparatus have been described briefly.  
         [0013]     A prior art (first prior art) of alignment of a wafer and reticle in a semiconductor exposure apparatus will be described with reference to  FIG. 2 .  
         [0014]     Referring to  FIG. 2 , reference numeral  1  denotes an illumination optical system;  2 , a reticle serving as an original;  3 , a projection optical system; and  4 , a wafer serving as a substrate. The image of the reticle  2  illuminated by the illumination optical system  1  is projected onto the wafer  4  through the projection optical system  3 . Reference numeral  5  denotes a wafer stage;  6 , a wafer chuck; and  7 , a wafer stage controller. The wafer  4  is placed on the wafer chuck  6  on the wafer stage  5  by a wafer transport device (not shown). The wafer stage  5  is positioned by the wafer stage controller  7 . Reference numerals  8   a  and  8   b  denote TTL alignment detection systems, respectively;  9 , an OA alignment detection system;  10 , a height detection unit; and  11 , a controller or processor which controls the exposure apparatus and executes various calculations.  
         [0015]      FIG. 7  is a view of the wafer stage  5  seen from the direction of the projection optical system  3 . The wafer stage  5  has a reference mark  12  equivalent to an alignment mark formed on the surface of the wafer  4 , or a reference member  12  having such a reference mark, at a position where it does not interfere with the wafer  4 , as shown in  FIG. 7 .  
         [0016]     The reticle  2  has marks RMa and RMb at positions symmetrical with reference to a center C, as roughly shown in  FIG. 8 . The reticle  2  is held on a reticle stage (not shown). The reticle stage moves the reticle  2  to a position where the center C coincides with an optical axis AX of the projection optical system  3 .  
         [0017]     The wafer stage  5  is positioned such that the reference mark on the wafer stage  5  falls on a predetermined position in the projection field of the projection optical system  3 . Then, the TTL alignment detection system  8   a  provided above the reticle  2  can detect the mark RMa of the reticle  2  and the reference mark simultaneously. When the wafer stage  5  is moved to another position, the TTL alignment detection system  8   b  can detect the mark. RMb of the reticle  2  and the reference mark simultaneously. The OA alignment detection system  9  is fixed outside the projection optical system  3  (outside the projection field). An optical axis OX of the OA alignment detection system  9  is parallel to the optical axis AX of the projection optical system  3 .  
         [0018]     The exposure method of the first prior art exposure apparatus will be described with reference to  FIG. 9 .  
         [0019]     Referring to  FIG. 9 , step S 301  is a base line measurement step. The position of the wafer stage  5  obtained when the mark RMa of the reticle  2  and the reference mark on the reference member  12  are aligned by using the TTL alignment detection systems  8   a  and  8   b  is measured by an interferometer such as a laser interferometer (not shown).  
         [0020]     Similarly, the position of the wafer stage  5  obtained when the mark RMb of the reticle  2  and the reference mark on the reference member  12  are aligned by using the TTL alignment detection systems  8   a  and  8   b  is measured by the interferometer such as the laser interferometer described above.  
         [0021]     The reference mark on the reference member  12 , obtained when the wafer stage  5  is located at the central position (average value) of the position of the wafer stage  5  with respect to the marks RMa and RMb, is on the optical axis AX of the projection optical system  3 , and located at a position conjugate with the center C of the reference member  12 .  
         [0022]     Similarly, the position of the wafer stage  5 , obtained when the reference mark on the reference member  12  is aligned with the OA alignment detection system  9 , is measured by the interferometer such as the laser interferometer described above. A base line amount BL is obtained by calculating the difference between the central position (position of the optical axis AX) (described above) detected by the TTL alignment detection systems  8   a  and  8   b  and the position (position of the optical axis OX) (described above) detected by the OA alignment detection system  9 .  
         [0023]     Step S 302  is a wafer pattern position measurement step. In the wafer pattern position measurement step, the position error amount of the pattern (wafer pattern) on the wafer  4  is measured with reference as an origin to the position to which the wafer stage  5  has been moved from the exposure center position by the base line amount BL measured in the base line measurement step.  
         [0024]     More specifically, the positions of a plurality of alignment marks on the wafer  4  are measured by the OA alignment detection system  9  to create a correction equation for global alignment. Namely, the shift, magnification offset, rotation, and the like of the wafer pattern are measured. As a conventional example of the wafer pattern position measurement step, for example, one proposed by Japanese Patent Laid-Open No. 9-218714 is available.  
         [0025]     Japanese Patent Laid-Open No. 9-218714 proposes an example of the global alignment scheme. Particularly, a high-order error factor is also corrected to improve the alignment accuracy. A simple example of the correction equation includes the following equations (1) and (2): 
 
 d   wx   =M   wx   *x+θ   wx   *y+S   wx   (1) 
 
 d   wy   =θ   wy   *x+M   wy   *y+S   wy   (2) 
 
 where d wx  and d wy  are the position error amounts at a coordinate point (x, y) on the wafer  4 . An X-direction magnification offset M wx , Y-direction magnification offset M wy , X-direction rotation θ wx , Y-direction rotation θ wy , X-direction shift S wx , and Y-direction shift S wy  of the pattern on the wafer  4  as the respective coefficients can be obtained by the method of least squares. 
 
         [0026]     Step S 303  is an exposure step. In the exposure step, the wafer stage  5  is driven on the basis of the base line amount and the position error amount of the pattern on the wafer  4  which is measured in the wafer pattern position measurement step, to transfer the pattern of the reticle  2  onto the wafer  4 .  
         [0027]     So far the exposure apparatus and alignment of the wafer and reticle according to the first prior art have been described.  
         [0028]     An exposure apparatus and alignment of the wafer and reticle according to another prior art (second prior art) will be described.  
         [0029]     As described above, the ICs and LSIs shrink in feature size acceleratingly, and each year a higher apparatus performance is demanded for a semiconductor manufacturing apparatus. In recent years, an improvement in productivity is strongly sought for to accompany the increasing demands for semiconductors represented by DRAMs. Thus, not only an increase in accuracy but also an increase in throughput is demanded for the semiconductor manufacturing apparatus.  
         [0030]     In view of this, Japanese Patent Laid-Open No. 1-49007 separately has a function (to be referred to as a measurement station hereinafter) for measuring a pattern position on a wafer and a function (to be referred to as an exposure station hereinafter) for exposing the wafer to light. More specifically, an exposure apparatus which performs a measurement process and exposure process simultaneously is proposed. As an example of this exposure apparatus, the second prior art will be described with reference to  FIG. 5 .  
         [0031]     The exposure apparatus according to the second prior art includes a measurement station  13 , exposure station  14 , wafer supply unit  15 , and controller  11 . The measurement station  13  measures the relative positional relationship between a wafer chuck serving as a wafer support and a pattern on a wafer. After the relative positional relationship between the reticle and wafer chuck is measured, the exposure station  14  projects the pattern of the reticle to the wafer and exposes the wafer to light. The wafer supply unit  15  transfers the wafer and wafer chuck between the measurement station  13  and exposure station  14 . The controller  11  controls the measurement station  13 , exposure station  14 , and wafer supply unit  15 .  
         [0032]     In the measurement station  13 , reference numeral  9  denotes an OA alignment detection system;  4   a , a wafer serving as a target exposure substrate;  6   a , a wafer chuck;  5   a , a wafer stage; and  10 , a height detection unit. The wafer chuck  6   a  serves as a substrate support which mounts and holds the wafer  4   a  on it. The wafer stage  5   a  mounts the wafer chuck  6   a  on it and its position is measured by a stage controller  7   a  to position the wafer  4   a.    
         [0033]     In the exposure station  14 , reference numeral  3  denotes a projection optical system;  8   a  and  8   b , TTL alignment detection systems;  1 , an illumination optical system; and  5   b , a wafer stage. The projection optical system  3  projects the image of a reticle  2  onto a wafer  4   b . The position of the wafer stage  5   b  is measured by a stage controller  7   b  which positions a wafer chuck  6   b  on which the wafer  4   b  is mounted.  
         [0034]      FIG. 10  is a view of the wafer chuck  6   b  seen from the direction of the projection optical system  3 . Reference members  12   a  and  12   b  are fixed to each of the wafer chucks  6   a  and  6   b , respectively having reference marks equivalent to the alignment marks formed on the surfaces of the corresponding wafers  4   a  and  4   b , at positions where they do not interfere with the wafer  4   a , as shown in  FIG. 10 .  
         [0035]     According to this prior art, the pattern of the reticle is exposed to the wafer in the following procedure.  
         [0036]     First, in the measurement station  13 , the alignment mark positions on the wafer chuck  6   a  and wafer  4   a  are measured by using the OA alignment detection system  9  to measure the relative positional relationship between the wafer chuck  6   a  and the pattern on the wafer  4   a . At this time, in the exposure station  14 , the wafer  4   b  is exposed to light simultaneously with the procedure to be described hereinafter.  
         [0037]     Subsequently, the exposed wafer  4   b  and wafer chuck  6   b  are unloaded from the exposure station  14  by using the wafer supply unit. The wafer  4   a  and wafer chuck  6   a  of the measurement station  13  are supplied to the exposure station  14 .  
         [0038]     In the exposure station  14 , the alignment mark position on the wafer chuck  6   b  is measured by the TTL alignment detection systems  8   a  and  8   b  through the reticle  2  to measure the relative positional relationship between the pattern on the reticle  2  and the wafer chuck  6   b . In addition, the relative positional relationship between the patterns on the reticle  2  and wafer  4   b  is calculated by using the relative positional relationship between the wafer chuck  6   a  and the pattern on the wafer  4   a  measured in the measurement station  13 . Finally, the pattern of the reticle  2  is exposed onto the wafer  4   b  on the basis of the calculated relative positional relationship between the calculated patterns on the reticle  2  and wafer  4   b.    
         [0039]     According to this prior art, the process of the measurement station  13  and that of the exposure station  14  can be performed simultaneously, so that the total processing time of accurate alignment and wafer exposure can be shortened.  
         [0040]     A case has been described wherein the wafer chuck is used as a substrate support which supports the wafer when the wafer is to be moved between the measurement station  13  and exposure station  14 . However, the present invention is not limited to this. For example, the wafer stages  5   a  and  5   b  can be used as substrate supports when the wafer is to be moved. In this case, in place of detecting the alignment mark on the wafer chuck, the alignment marks on the wafer stages are detected in the same manner.  
         [0041]     The exposure method of the exposure apparatus according to the second prior art will be described with reference to  FIG. 11 .  
         [0042]     Referring to  FIG. 11 , step S 401  is a measurement position chuck mark position measurement step. In step S 401 , the reference mark positions on the reference members  12   a  and  12   b  on the wafer chuck  6   a  are measured by using the OA alignment detection system  9 . As shown in  FIG. 10 , the wafer chuck  6   a  has, as alignment marks, reference marks at least on the two reference members  12   a  and  12   b . These reference marks are measured by the OA alignment detection system  9 . Thus, the position and rotation amount of the wafer chuck  6   a  with respect to the OA alignment detection system  9  are measured.  
         [0043]     Step S 402  is a wafer pattern position measurement step. In step S 402 , the alignment mark position on the wafer chuck  6   a  is measured in the measurement station  13  by using the OA alignment detection system  9 . Thus, the position of the pattern (wafer pattern) on the wafer  4   a  is measured. The wafer pattern position measurement step is identical to that of the first prior art described above, and a detailed description thereof will be omitted. The relative positional relationship between the wafer chuck  6   a  and the pattern on the wafer  4   a  is measured by the measurement position chuck mark position measurement step and the wafer pattern position measurement step.  
         [0044]     Step S 403  is an exposure position chuck mark position measurement step. In step S 403 , the positions of the reference marks on the reference members  12   a  and  12   b  of the wafer chuck  6   b  are measured in the exposure station  14  by the TTL alignment detection systems  8   a  and  8   b  through the reticle  2 . Thus, the relative positional relationship (position and rotation amount) between the pattern on the reticle  2  and the wafer chuck  6   b  is obtained.  
         [0045]     Step S 404  is an exposure step. In step S 404 , the relative positional relationship between the pattern on the reticle  2  and the pattern on the wafer  4   b  is calculated by using the relative positional relationship between the wafer chuck  6   a  and the pattern on the wafer  4   a  which is measured in steps S 401  and S 402  and the relative positional relationship between the pattern on the reticle  2  and the wafer chuck  6   b  which is measured in step S 403 . The wafer stage  5   b  is driven on the basis of the calculated relative positional relationship to transfer the pattern of the reticle  2  onto the wafer  4   b.    
         [0046]     So far the exposure apparatus and alignment of the wafer and reticle according to the second prior art have been described.  
         [0047]     These prior arts are excellent schemes that enable highly accurate alignment of the reticle and wafer with a high throughput.  
         [0048]     In recent years, a further demand has arisen for an improvement in alignment accuracy, and accordingly an error component which is conventionally regarded an infinitesimal amount has become non-negligible. For example, if the wafer stage drive characteristic differs between the measurement position and exposure position of the first prior art, an alignment error can occur. Similarly, if the wafer stage drive characteristic differs between the measurement station and exposure station of the second prior art, an alignment error can occur. Such a difference in wafer stage drive characteristic will be referred to as a stage drive characteristic difference.  
         [0049]     Conventionally, in the manufacture of the exposure apparatus, the stage drive characteristic at the measurement position or measurement station and that at the exposure position or exposure station are adjusted such that the error component becomes an infinitesimal amount. In addition, the error component including the stage drive characteristic difference is measured in advance and corrected as an offset.  
         [0050]     If, however, the stage drive characteristic difference changes because, e.g., the stage drive characteristic changes over time, an alignment error can occur, if infinitesimal. Such an error can become non-negligible in meeting the future demand for an improvement in alignment accuracy.  
       SUMMARY OF THE INVENTION  
       [0051]     The present invention has been made in view of the above background. It is an exemplary object of the present invention to improve the alignment accuracy.  
         [0052]     According to the present invention, the foregoing object is attained by providing an exposure method of exposing a substrate arranged on a stage, which holds the substrate and moves, to light through an original and a projection optical system, the method comprising steps of:  
         [0053]     a first measurement of measuring a first drive characteristic of the stage by detecting a position of a pattern on the stage using a first detection system which detects a position of a pattern on the substrate through an optical system which does not comprise the projection optical system;  
         [0054]     a second measurement of measuring a second drive characteristic of the stage by detecting the position of the pattern on the stage using a second detection system which detects the position of the pattern on the stage through the projection optical system; and  
         [0055]     aligning the original and the substrate based on the first and second drive characteristics.  
         [0056]     In a preferred embodiment, the first and second measurement steps measure positions with respect to a same reference mark on the stage, respectively.  
         [0057]     In a preferred embodiment, the first measurement step is performed at a measurement station, the second measurement step is performed at an exposure station, and the first and second measurement steps measure positions with respect to a same reference mark on either one of a substrate chuck and the stage, respectively.  
         [0058]     In a preferred embodiment, the apparatus further comprises a step of storing a difference between the first and second drive characteristics in a storage medium, wherein the aligning step aligns the original and the substrate based on the difference stored in the storage medium.  
         [0059]     In a preferred embodiment, the first and second measurement steps are performed with respect to each of the substrate.  
         [0060]     In a preferred embodiment, the second measurement step is performed if a change amount of the first drive characteristic exceeds a tolerance.  
         [0061]     In a preferred embodiment, the drive characteristic comprises at least one of a drive magnification offset and a drive rotation.  
         [0062]     According to the present invention, the foregoing object is attained by providing an exposure method of exposing a substrate arranged on a movable stage to light through an original and a projection optical system, the method comprising steps of:  
         [0063]     a first measurement of measuring positions of a plurality of reference marks on the movable stage by using a first measurement system which sequentially measures the positions of the plurality of reference marks through the projection optical system;  
         [0064]     a first determination of determining a first relationship to approximately obtain the plurality of positions measured in the first measurement step from set positions of the plurality of reference marks;  
         [0065]     a second measurement of measuring the positions of the plurality of reference marks by using a second measurement system which sequentially measures the positions of the plurality of reference marks through an optical system which does not include the projection optical system;  
         [0066]     a second determination of determining a second relationship to approximately obtain the plurality of positions measured in the second measurement step from the set positions of the plurality of reference marks;  
         [0067]     a third measurement of measuring positions of a plurality of marks on the substrate held by the movable stage by using the second measurement system;  
         [0068]     a third determination of determining a third relationship to approximately obtain the plurality of positions measured in the third measurement step from set positions of the plurality of marks on the substrate; and  
         [0069]     a calculation of calculating positions of regions on the substrate to be exposed to the light based on set positions of the regions, the third relationship, and a difference between the first and second relationships.  
         [0070]     In a preferred embodiment, the plurality of reference marks on the movable stage comprise a plurality of marks formed on a chuck which supports the substrate.  
         [0071]     According to the present invention, the foregoing object is attained by providing an exposure apparatus for exposing a substrate to light through an original, the apparatus comprising:  
         [0072]     a projection optical system configured to project a pattern of the original onto the substrate;  
         [0073]     a stage configured to hold the substrate and to move;  
         [0074]     a first measurement unit configured to measure a position of a pattern on the substrate and a position of a pattern on the stage, the first measurement unit comprising an optical system which does not comprise the projection optical system; and  
         [0075]     a second measurement unit configured to measure the position of the pattern on the stage through the projection optical system,  
         [0076]     wherein the original and the substrate are aligned based on a measurement result by the first measurement unit, a measurement result by the second measurement unit, a drive characteristic of the stage for measurement by the first measurement unit, and a drive characteristic of the stage for measurement by the second measurement unit.  
         [0077]     According to the present invention, the foregoing object is attained by providing an exposure apparatus for exposing a substrate to light through an original, the apparatus comprising:  
         [0078]     a projection optical system configured to project a pattern of the original onto the substrate;  
         [0079]     a chuck configured to hold the substrate;  
         [0080]     a stage configured to hold the chuck and to move;  
         [0081]     a first measurement unit configured to measure a position of a pattern on the substrate and a position of a pattern on the chuck, the first measurement unit comprising an optical system which does not comprise the projection optical system; and  
         [0082]     a second measurement unit configured to measure the position of the pattern on the chuck through the projection optical system,  
         [0083]     wherein the original and the substrate are aligned based on a measurement result by the first measurement unit, a measurement result by the second measurement unit, a drive characteristic of the stage for measurement by the first measurement unit, and a drive characteristic of the stage for measurement by the second measurement unit.  
         [0084]     According to the present invention, the foregoing object is attained by providing an exposure apparatus for exposing a substrate to light through an original, the apparatus comprising:  
         [0085]     a projection optical system configured to project a pattern of the original onto the substrate;  
         [0086]     a stage configured to hold the substrate and to moves;  
         [0087]     a first measurement unit configured to sequentially measure positions of a plurality of reference marks on the stage through the projection optical system;  
         [0088]     a measurement optical system which does not comprise the projection optical system;  
         [0089]     a second measurement unit configured to sequentially measure any of the positions of the plurality of reference marks and positions of a plurality of marks on the substrate held by the stage through the measurement optical system; and  
         [0090]     a processor configured to determine a first relationship to approximately obtain the positions of the plurality of reference marks measured by the first measurement unit from set positions of the plurality of reference marks, to determine a second relationship to approximately obtain the positions of the plurality of reference marks measured by the second measurement unit from the set positions of the plurality of reference marks, to determine a third relationship to approximately obtain the positions of the plurality of marks on the substrate measured by the second measurement unit from set positions of the plurality of marks on the substrate, and to calculate positions of regions on the substrate to be exposed to the light based on set positions of the regions, the third relationship, and a differences between the first and second relationships.  
         [0091]     According to the present invention, the foregoing object is attained by providing a method of manufacturing a device, the method comprising steps of:  
         [0092]     exposing a substrate to light through an original using an exposure apparatus as defined in claim  10 ;  
         [0093]     developing the exposed substrate; and  
         [0094]     processing the developed substrate to manufacture the device.  
         [0095]     According to the present invention, the foregoing object is attained by providing a method of manufacturing a device, the method comprising steps of:  
         [0096]     exposing a substrate to light through an original using an exposure apparatus as defined in claim  11 ;  
         [0097]     developing the exposed substrate; and  
         [0098]     processing the developed substrate to manufacture the device.  
         [0099]     According to the present invention, the foregoing object is attained by providing a method of manufacturing a device, the method comprising steps of:  
         [0100]     exposing a substrate to light through an original using an exposure apparatus as defined in claim  12 ;  
         [0101]     developing the exposed substrate; and  
         [0102]     processing the developed substrate to manufacture the device.  
         [0103]     Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0104]     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the description, serve to explain the principles of the invention.  
         [0105]      FIG. 1  is a flowchart showing an exposure method according to the first embodiment of the present invention;  
         [0106]      FIG. 2  is a view showing the structure of an exposure apparatus to which the first embodiment of the present invention is applied;  
         [0107]      FIG. 3  is a view showing the arrangement of reference members according to the first embodiment of the present invention;  
         [0108]      FIG. 4  is a flowchart showing an exposure method according to the second embodiment of the present invention;  
         [0109]      FIG. 5  is a view showing the structure of an exposure apparatus to which the second embodiment of the present invention is applied;  
         [0110]      FIG. 6  is a view showing the arrangement of reference members according to the second embodiment of the present invention;  
         [0111]      FIG. 7  is a view showing the arrangement of a reference member according to the first prior art;  
         [0112]      FIG. 8  is a view showing the arrangement of reticle marks according to the first prior art;  
         [0113]      FIG. 9  is a flowchart showing an exposure method according to the first prior art;  
         [0114]      FIG. 10  is a view showing the arrangement of reference members according to the second prior art;  
         [0115]      FIG. 11  is a flowchart showing an exposure method according to the second prior art;  
         [0116]      FIG. 12  is a flowchart showing the flow of an overall semiconductor device manufacturing process; and  
         [0117]      FIG. 13  is a flowchart showing flow of the wafer process of  FIG. 12  in detail. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0118]     Preferred embodiment(s) of the present invention will be described in detail in accordance with the accompanying drawings.  
       First Embodiment  
       [0119]     The first embodiment of the present invention will be described.  
         [0120]     The first embodiment is an improvement over the exposure apparatus according to the first prior art of  FIG. 2 .  
         [0121]     According to the first embodiment, the stage drive characteristic is measured at a measurement position in substrate pattern position measurement which measures the pattern position on a substrate (wafer), and at an exposure position in an exposure step of projecting the pattern of an original (reticle) onto the substrate and exposing the substrate to light. The stage drive characteristic difference is obtained from the measurement results, and a process based on the stage drive characteristic difference is performed during wafer pattern measurement or exposure. More specifically, a plurality of reference members each having a reference mark are arranged on a wafer stage  5 . The respective reference marks of the plurality of reference members are measured at the measurement position and exposure position by using one detection system to obtain a stage drive characteristic difference.  
         [0122]     For example, assume that the stage drive characteristic (stage drive characteristic difference) with respect to the exposure position includes an X-direction magnification M sx , Y-direction magnification M sy , X-direction rotation θ sx , and Y-direction rotation θ sy . In this case, an alignment error of M sx *x+θ sx *y in the X direction and an alignment error of θ sy *x+M sy *y in the Y direction occur.  
         [0123]     Note that x and y indicate the designed position of each shot on the wafer. In the first embodiment, M sx , θ sx , M sy , and θ sy  are measured in the following manner.  
         [0124]     First, the reference mark positions on the plurality of reference members are measured by using an OA alignment detection system  9 . Then, drive magnification offsets M s1x  and M s1y , drive rotations θ s1x  and θ s1y , and shift amounts S s1x  and S s1y , which are the stage drive characteristics at the measurement position, are measured.  
         [0125]     These drive characteristics can be calculated with the method of least squares in the same manner as with the correction equations for global alignment by calculating, from the plurality of reference mark measurement positions, the coefficients of the following equations (3) and (4): 
 
 d   s1x   =M   s1x   *x+θ   s1x   *y+S   s1x   (3) 
 
 d   s1y   =θ   s1x   *x+M   s1y   *y+S   s1y   (4) 
 
 where d s1x  and d s1y  are the error amounts of each reference mark position from its designed position (x, y). 
 
         [0126]     Subsequently, the plurality of reference mark positions are measured by using TTL alignment detection systems  8   a  and  8   b . Then, drive magnification offsets M s2x  and M s2y , drive rotations θ s2x  and θ s2y , and shift amounts S s2x  and S s2y , which are the stage drive characteristics at the exposure position, are measured. These drive characteristics can also be calculated with the method of least squares in the same manner as with the correction equations for global alignment by calculating, from the plurality of reference mark measurement positions, the coefficients of the following equations (5) and (6): 
 
 d   s2x   =M   s2x   *x+θ   s2x   *y+S   s2x   (5) 
 
 d   s2y =θ s2y   *x+M   s2y   *y+S   s2y   (6) 
 
 where d s2x  and d s2y  are the error amounts of each reference mark position from its designed position (x, y). 
 
         [0127]     Finally, the stage drive characteristic difference between the two measurement positions is calculated from the respective stage drive characteristics at the measurement position and exposure position by using the following equations (7), (8), (9), and (10): 
 
 M   sx   =M   s1x   /M   s2x   (7) 
 
 M   sy   =M   s1y   /M   s2y   (8) 
 
θ sx =θ s1x −θ s2x   (9) 
 
θ sy =θ s1y −θ s2y   (10) 
 
         [0128]     Note that S sx  and S xy  which can be calculated by the following equations (11) and (12) indicate the base line error amounts (differences between a base line amount BL with which the stage has been driven at the time of measurement and the measured base line amount) in the X and Y directions: 
 
 S   sx   =S   s1x   −S   s2x   (11) 
 
 S   sy   =S   s1y   −S   s2y   (12) 
 
         [0129]     To obtain the coefficients of equations (3), (4), (5), and (6), three or more reference mark measurement values (d s1x , d s1y , d s2x , and d s2y ) are necessary at least at each stage position. To measure the stage drive characteristics, three or more reference marks must be measured.  
         [0130]     Note that the difference in drive magnification offset and that in drive rotation between the X and Y directions are constant and known (M s1x =M s1y +C 1 , θ s1x =θ s1y +C 2 , M s2x =M s2y +C 3 , θ s2x =θ s2y +C 4 , where C 1 , C 2 , C 3 , and C 4  are known constants). In this case, the stage drive characteristics can be calculated by measuring only two or more reference marks.  
         [0131]     The first embodiment will be described in detail.  
         [0132]     The outline of an exposure apparatus according to the first embodiment is the same as that of the exposure apparatus of the first prior art shown in  FIG. 2  except for the arrangement of the reference members having reference marks.  
         [0133]     The layout of the reference members having reference marks of the first embodiment will be described with reference to  FIG. 3 .  
         [0134]      FIG. 3  schematically shows a wafer stage of the first embodiment seen from the direction of a projection optical system.  
         [0135]     According to the first embodiment, reference members  12   a  to  12   d  each having a reference mark are arranged on a wafer stage  5 .  FIG. 3  shows a case wherein four reference members each having a reference mark are arranged. The number of reference members having reference marks is not limited to four but can be any number equal to 2 or more. A plurality of reference marks can be formed on one reference member.  
         [0136]     An exposure method according to the first embodiment will be described with reference to  FIG. 1 .  
         [0137]     Step S 101  is a measurement position stage drive characteristic measurement step. In step S 101 , the wafer stage  5  is driven to measure the respective reference marks on the plurality of reference members  12   a  to  12   d  by the OA alignment detection system  9 . Then, the stage drive characteristics M s1x , M s1y , θ s1x , and θ s1y , and the shift amounts S s1x  and S s1y  at the measurement position are measured. The stage drive characteristics are calculated in the same manner as described above.  
         [0138]     Step S 102  is an exposure position stage drive characteristic measurement step. In step S 102 , the wafer stage  5  is driven to measure the respective reference marks on the plurality of reference members  12   a  to  12   d  by TTL alignment detection systems  8   a  and  8   b . Then, the stage drive characteristics M s2x , M s2y , θ s2x , and θ s2y , and the shift amounts S s2x  and S s2y  at the exposure position are measured. The stage drive characteristics are calculated in the same manner as described above.  
         [0139]     Step S 103  is a wafer pattern position measurement step. In step S 103 , an alignment mark on a wafer  4  is measured by the OA alignment detection system  9 , in the same manner as in the prior art, to measure the position error amount of a pattern on the wafer  4 .  
         [0140]     Step S 104  is an exposure step. In step S 104 , the stage drive characteristic difference is calculated from the measurement position stage drive characteristics measured in step S 101  and the stage drive characteristics at the exposure position measured in step S 102 . Then, the wafer stage  5  is driven on the basis of a value which is obtained by correcting the position error amount of the pattern on the wafer  4  measured in step S 103  by the calculated stage drive characteristic difference, to transfer the pattern of a reticle  2  onto the wafer  4 .  
         [0141]     The measurement position stage drive characteristic measurement step and exposure position stage drive characteristic measurement step need not always be performed for each exposure. The stage drive characteristic difference may be stored in a storage medium (e.g., a memory in a controller  11 ), and after that the measured values may be used.  
         [0142]     For example, the measurement position stage drive characteristic measurement step and exposure position stage drive characteristic measurement step may be performed when a predetermined number of wafers are processed, at a lapse of a predetermined period of time, or non-periodically to acquire a stage drive characteristic difference, and the acquired difference may be stored in a storage medium (e.g., the memory in the controller  11 ). After that, each stored stage drive characteristic difference may be used. The wafer pattern position measurement step and exposure step need not always be performed after the measurement position stage drive characteristic measurement step and exposure position stage drive characteristic measurement step are performed.  
         [0143]     The reference marks on all the reference members need not be measured each time. For example, only some reference marks may be measured. Only when the stage drive characteristic difference is supposed to have changed, the reference marks on all the reference members may be measured to update the stored stage drive characteristic difference.  
         [0144]     For example, usually, the base line measurement step may be performed in the same manner as in the prior art to update only the base line amount BL. Only when a change in base line amount BL exceeds a preset value, the stage drive characteristic difference may be measured and updated. The stage drive magnification can be calculated by measuring only two reference marks. Thus, the stage drive characteristic differences may be measured and updated only when the change amount of the drive magnification exceeds a preset value.  
         [0145]     In this manner, when the timing for measuring the stage drive characteristic difference and the number of reference marks to be measured are changed in accordance with the device manufacturing process and product, a decrease in throughput can be minimized.  
         [0146]     While the first embodiment is exemplified by a case wherein the stage drive characteristic difference is corrected in the exposure step, the present invention is not limited to this. For example, when a stage drive characteristic difference measured in advance is to be used, the wafer stage position in alignment mark measurement of the wafer pattern position measurement step may be corrected by using the stage drive characteristic difference. Alternatively, the wafer stage position may be corrected in both the exposure step and wafer pattern position measurement step.  
         [0147]     In addition, although the prior art describes a case wherein the drive characteristic difference between the stages is approximated by an equation of the first degree, the drive characteristic difference may be approximated by other equations including a polynomial.  
         [0148]     For example, when an equation of the third degree is employed, the safer stage position can be corrected even if the stage drive characteristic shows a curve (is arcuate). When the stage drive characteristic is approximated by a polynomial, it can be calculated by calculating the respective coefficients by the method of least squares in the same manner as in Japanese Patent Laid-Open No. 9-218714 described above.  
         [0149]     As described above, according to the first embodiment, an overlapping error caused by a change over time or the like of the stage drive characteristic difference can be suppressed by measuring and correcting the stage drive characteristic difference between the measurement position and exposure position.  
       Second Embodiment  
       [0150]     The second embodiment of the present invention will be described.  
         [0151]     The second embodiment is an improvement over the exposure apparatus according to the second prior art of  FIG. 5 .  
         [0152]     According to the second embodiment, the stage drive characteristic is measured at a wafer stage  5   a  (to be referred to as a measurement stage hereinafter) of a measurement station  13  and at a wafer stage (to be referred to as an exposure stage hereinafter) of an exposure station  14 , and the difference between the two characteristics is corrected during exposure.  
         [0153]     More specifically, a plurality of reference members each having a reference mark are arranged on each of wafer chucks  6   a  and  6   b , and the plurality of reference marks are measured on the measurement stage and exposure stage. Thus, the drive characteristic difference between the stages is measured and corrected. The basic idea of how to measure the stage drive characteristic difference is similar to that of the first embodiment but is different from the first embodiment in the following respects.  
         [0154]     According to the first embodiment, the reference marks of the reference members on the wafer stage are measured by the OA alignment detection system and TTL alignment detection systems. In contrast to this, according to the second embodiment, the reference marks of reference members on the wafer chucks serving as wafer supports are measured by an OA alignment detection system and TTL alignment detection systems. Also, the stage drive characteristic difference is calculated in a manner slightly different from that of the first embodiment, which will be described hereinafter.  
         [0155]     First, the reference mark positions on the plurality of reference members are measured by using an OA alignment detection system  9 . Then, drive magnification offsets M s1x  and M s1y , drive rotations θ s1x  and θ s1y , chuck position error amounts S c1x  and S c1y , and a chuck rotation amount θ c1 , which are the stage drive characteristics at the measurement stage, are measured. These drive characteristics can be calculated with the method of least squares in the same manner as with the correction equations for global alignment by calculating, from the respective reference mark measurement positions on the plurality of reference members, the coefficients of the following equations (13) and (14): 
 
 d   s1x   =M   s1x   *x +(θ s1x +θ c1 )* y+S   c1x   (13) 
 
 d   s1y =(θ s1x +θ c1 )* x+M   s1y   +S   s1y   (14) 
 
 where d s1x  and d s1y  are the error amounts of each reference mark position from its designed position (x, y). 
 
         [0156]     Subsequently, the respective reference mark positions of the plurality of reference members are measured by using TTL alignment detection systems  8   a  and  8   b . Then, drive magnification offsets M s2x  and M s2y , drive rotations θ s2x  and θ s2y , chuck position error amounts S c1x  and S c1y , and chuck rotation amounts θ c2 , which are the stage drive characteristics at the exposure stage, are measured. These drive characteristics can also be calculated with the method of least squares in the same manner as with the correction equations for global alignment by calculating, from the plurality of reference mark measurement positions, the coefficients of the following equations (15) and (16): 
 
 d   s2x   =M   s2x   *x +(θ s2x +θ c2 )* y+S   c2x   (15) 
 
 d   s2y =(θ s2x +θ c2 )* x+M   s2y   +S   c2y   (16) 
 
 where d s2x  and d s2y  are the error amounts of each reference mark position from its designed position (x, y). 
 
         [0157]     Finally, the stage drive characteristic difference between the two measurement positions is calculated from the respective stage drive characteristics at the measurement position and exposure position by using the following equations (17), (18), (19), and (20): 
 
 M   sx   =M   s1x   /M   s2x   (17) 
 
 M   sy   =M   s1y   /M   s2y   (18) 
 
θ sx =θ s1x −θ s2x   (19) 
 
θ sy =θ s1y −θ s2y   (20) 
 
         [0158]     Note that the chuck position error amounts S c1x , S c1y , S c2x  and S c2y  and the rotation amounts θ c1  and θ c2  are the same as the chuck position error amounts and rotation amounts of the prior art.  
         [0159]     To obtain the coefficients of equations (13), 
        (14), (15), and (16), four or more reference mark measurement values (d s1x , d s1y , d s2x , and d s2y ) are necessary at least at each stage position. To measure the stage drive characteristics, four or more reference marks must be measured.        
 
         [0161]     Note that the difference in drive magnification offset and that in drive rotation between the X and Y directions are constant and known (M s1x =M s1y +C 1 , θ s1x =θ s1y +C 2 , M s2x =M s2y +C 3 , θ s2x =θ s2y +C 4 , where C 1 , C 2 , C 3 , and C 4  are known constants). In this case, measurement and correction can be performed with three or more reference marks.  
         [0162]     The second embodiment will be described in detail below.  
         [0163]     The outline of an exposure apparatus according to the second embodiment is the same as that of the exposure apparatus of the second prior art shown in  FIG. 5  except for the arrangement of the reference members having reference marks on wafer chucks  6   a  and  6   b  which serve as wafer supports.  
         [0164]     The layout of the reference members having the reference marks on the wafer chucks  6   a  and  6   b  which serve as the wafer supports of the first embodiment will be described with reference to  FIG. 6 .  
         [0165]      FIG. 6  shows a wafer support means chuck according to the second embodiment seen from the direction of a projection optical system.  
         [0166]     According to the second embodiment, a plurality of reference members  12   a  to  12   d  each having a reference mark are arranged on each of the wafer chucks  6   a  and  6   b .  FIG. 6  shows a case wherein four reference members each having a reference mark are arranged. The number of reference members having reference marks is not limited to four but can be any number equal to 3 or more. A plurality of reference marks can be formed on one reference member.  
         [0167]     In addition, the second embodiment also exemplifies a case wherein wafer chucks are used as substrate supports which support wafers when the wafers are to move between the measurement station and exposure station, in the same manner as in the second prior art, but the present invention is not limited to this. For example, the wafer stage  5   a  and a wafer stage  5   b  may be used as substrate supports when the wafers are to be moved. In this case, in place of detecting the alignment marks on the wafer chucks, alignment marks on wafer stages are detected in the same manner.  
         [0168]     An exposure method according to the second embodiment will be described with reference to  FIG. 4 .  
         [0169]     Step S 201  is a measurement stage drive characteristic measurement step. In step S 201 , the wafer stage  5   a  on which a wafer  4   a  and the wafer chuck  6   a  are mounted is driven to measure the reference marks on the plurality of reference members  12   a  to  12   d  by the OA alignment detection system  9 . Then, the stage drive characteristics at the measurement position are measured. The stage drive characteristics are calculated in the same manner as described above.  
         [0170]     Step S 202  is a wafer pattern position measurement step. In step S 202 , on the wafer stage  5   a , alignment mark positions on the wafer  4   a  are measured on the wafer stage  5   a  by using the OA alignment detection system  9 . Thus, the position of a pattern (wafer pattern) on the wafer  4   a  is measured. The wafer pattern position measurement step is identical to that of the prior art described above, and a detailed description thereof will be omitted.  
         [0171]     Step S 203  is an exposure stage drive characteristic measurement step. In step S 203 , the wafer stage  5   b  on which a wafer  4   b  and the wafer chuck  6   b  used in the measurement stage drive characteristic measurement step is driven. Reference marks on the plurality of reference members  12   a  to  12   d  are measured by the TTL alignment detection systems  8   a  and  8   b  to measure the exposure stage drive characteristics. The stage drive characteristics are calculated in the same manner as described above.  
         [0172]     Step S 204  is an exposure step. In step S 204 , the position of a target exposure region is calculated from the measurement stage drive characteristics measured in step S 201 , the position error amount of the pattern on the wafer  4   a  measured in step S 202 , and the exposure stage drive characteristics measured in step S 203 . Then, the wafer stage  5   b  is driven to the calculated position of the target exposure region to transfer the pattern of a reticle  2  onto the wafer  4   b.    
         [0173]     The measurement position stage drive characteristic measurement step and exposure position stage drive characteristic measurement step need not always be performed for each exposure. Each stage drive characteristic difference may be stored in a storage medium (e.g., a memory in a controller  11 ), and may be used for a subsequent exposure process.  
         [0174]     For example, the measurement position stage drive characteristic measurement step and exposure position stage drive characteristic measurement step may be performed when a predetermined number of wafers are processed, at a lapse of a predetermined period of time, or non-periodically to acquire a stage drive characteristic difference, and the acquired difference may be stored in a storage medium (e.g., the memory in the controller  11 ). After that, each stored stage drive characteristic difference may be used. The wafer pattern position measurement step and exposure step need not always be performed after the measurement position stage drive characteristic measurement step and exposure position stage drive characteristic measurement step are performed. For example, the measurement position stage drive characteristic measurement step and exposure position stage drive characteristic measurement step may be performed by using only the wafer chucks serving as the substrate supports, to measure only the stage drive characteristic difference.  
         [0175]     The reference marks on all the reference members need not be measured each time. For example, only some reference marks may be measured. Only when the stage drive characteristic difference is supposed to have changed, the reference marks on all the reference members may be measured to update the stored stage drive characteristic difference.  
         [0176]     For example, usually, three reference marks are measured to calculate the orthogonality (X-Y difference of the drive rotation) of stage drive as one the stage drive characteristic difference. Only when a change in orthogonality exceeds a preset threshold, a larger number of reference marks may be measured to calculate and update the stage drive characteristic difference.  
         [0177]     In this manner, when the timing for measuring the stage drive characteristic difference and the number of reference marks to be measured are changed in accordance with the device manufacturing process and product, a decrease in throughput can be minimized.  
         [0178]     While the second embodiment is exemplified by a case wherein the stage drive characteristic difference is corrected in the exposure step, the present invention is not limited to this. For example, when a stage drive characteristic difference measured in advance is to be used, the wafer stage position in alignment mark measurement of the wafer pattern position measurement step may be corrected by using the stage drive characteristic difference. Alternatively, the wafer stage position may be corrected in both the exposure step and wafer pattern position measurement step.  
         [0179]     In addition, although the prior art describes a case wherein the drive characteristic difference between the stages is approximated by an equation of the first degree, the drive characteristic difference may be approximated by other equations including a polynomial.  
         [0180]     For example, when an equation of the third degree is employed, the wafer stage position can be corrected even if the stage drive characteristic shows a curve (is arcuate). When the stage drive characteristic is approximated by a polynomial, it can be calculated by calculating the respective coefficients by the method of least squares in the same manner as in Japanese Patent Laid-Open No. 9-218714 described above.  
         [0181]     As described above, according to the second embodiment, an overlapping error caused by a change over time or the like of the stage drive characteristic difference can be suppressed by measuring and correcting the stage drive characteristic difference between the measurement stage (measurement position) and exposure stage (exposure position).  
         [0182]     The first and second embodiments are exemplified by the cases wherein the reference members having the reference marks are formed on the wafer stages or wafer chucks. Alternatively, the reference marks themselves may be formed on the wafer stages or wafer chucks.  
         [0000]     [Application of Exposure Apparatus] 
         [0183]     A semiconductor device manufacturing process which uses the exposure apparatus described above will be described.  
         [0184]      FIG. 12  is a flowchart showing the flow of the overall semiconductor device manufacturing process. In step  1  (circuit design), the circuit of a semiconductor device is designed. In step  2  (mask fabrication), a mask is fabricated on the basis of the designed circuit pattern. In step  3  (wafer manufacture), a wafer is manufactured using a material such as silicon. In step  4  (wafer process) called a preprocess, an actual circuit is formed on the wafer in accordance with lithography using the above mask and wafer.  
         [0185]     In the next step  5  (assembly) called a post-process, a semiconductor chip is formed from the wafer fabricated in step  4 . This step includes assembly processes such as assembly (dicing and bonding) and packaging (chip encapsulation). In step  6  (inspection), inspections such as operation check test and durability test of the semiconductor device fabricated in step  5  are performed. A semiconductor device is finished with these steps and shipped (step  7 ).  
         [0186]      FIG. 13  is a flowchart showing the flow of the above wafer process in detail.  
         [0187]     In step  11  (oxidation), the surface of the wafer is oxidized. In step  12  (CVD), an insulating film is formed on the wafer surface. In step  13  (electrode formation), an electrode is formed on the wafer by deposition. In step  14  (ion implantation), ions are implanted in the wafer. In step  15  (resist process), a photosensitive agent is applied to the wafer.  
         [0188]     In step  16  (exposure), the circuit pattern is transferred to the wafer by the above exposure apparatus. In step  17  (development), the exposed wafer is developed. In step  18  (etching), portions other than the developed resist image are removed. In step  19  (resist removal), any unnecessary resist after etching is removed. These steps are repeated to form multiple circuit patterns on the wafer.  
         [0189]     As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.  
       CLAIM OF PRIORITY  
       [0190]     This application claims priority from Japanese Patent Application No. 2004-296689 filed on Oct. 8, 2004, which is hereby incorporated by reference herein.