Abstract:
A reference plate for irradiating a reference mark pattern with observation light, detecting the reflected light, and obtaining the position of the reference mark pattern has a position where the reference mark pattern is not directly exposed to the observation light.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a reference plate, an exposure apparatus using the reference plate, a device manufacturing system, a device manufacturing method, a semiconductor manufacturing factory, and an exposure apparatus maintenance method.  
         BACKGROUND OF THE INVENTION  
         [0002]    Measurement precision calibration of an exposure apparatus such as baseline measurement or best focus position measurement conventionally uses a reference plate mounted on a stage. The reference plate bears reference mark patterns formed from a chromium or aluminum film on a glass for X/Y- or Z-direction measurement. These reference mark patterns are observed by a microscope using light of the same wavelength as that of exposure light.  
           [0003]    The exposure light of the exposure apparatus is decreasing in wavelength in order to increase the resolution of a projection optical system and expose a finer pattern.  
           [0004]    [0004]FIG. 4 is a view for explaining a conventional reference plate. In FIG. 4, the upper views are schematic sectional views of the reference plate. Reference numeral  1  denotes a glass substrate;  2 , a reference mark pattern formed from a chromium or aluminum film; and  4 , a deposit on the surface of the reference mark pattern  2 . The lower views show the wavelength of an observation signal.  
           [0005]    When short-wavelength observation light from an ArF excimer laser or F 2  excimer laser is used to detect the reference mark pattern  2  by a microscope using the conventional reference mark as shown in FIG. 4, long-time irradiation of illumination light deteriorates the pattern film of the reference mark pattern  2  or forms a deposit on the reference mark pattern  2 . The image contrast then gradually decreases, finally failing observation.  
           [0006]    If the deposit  4  is formed on the surface of the reference mark pattern  2 , as shown in FIG. 4, and decreases the contrast, the surface of the reference mark pattern  2  must be periodically cleaned. However, if a deposit  4  is formed at a step on the surface of the reference mark pattern  2 , it is difficult to clean the surface.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention has been made to overcome the conventional drawbacks, and has as its object to provide a long-service-life reference plate which enables stable high-precision mark detection even with short-wavelength observation light, an exposure apparatus using the reference plate, a device manufacturing system, a device manufacturing method, a semiconductor manufacturing factory, and an exposure apparatus maintenance method.  
           [0008]    To achieve the above object, a reference plate according to the present invention has following features. A reference plate used to irradiate a reference mark pattern with observation light, detect the reflected light, and obtain a position of the reference mark pattern, wherein the reference mark pattern is formed at a position where the reference mark pattern is not directly exposed to the observation light.  
           [0009]    To achieve the above object, an exposure apparatus according to the present inventions has following features. An exposure apparatus for exposing a wafer to a mask pattern, comprising reference plates having reference patterns formed at positions where the reference patterns are not directly exposed to observation light, as a mask reference plate formed on a mask stage for supporting a mask and a wafer reference plate formed on a wafer stage for supporting the wafer.  
           [0010]    To achieve the above object, a device manufacturing method according to the present invention has following features. A device manufacturing method comprising the steps of installing, in a semiconductor manufacturing factory, manufacturing apparatuses for various processes including an exposure apparatus which exposes a wafer to a mask pattern and uses reference plates having reference patterns formed at positions where the reference patterns are not directly exposed to observation light, as a mask reference plate formed on a mask stage for supporting a mask and a wafer reference plate formed on a wafer stage for supporting the wafer, and manufacturing a semiconductor device by using the manufacturing apparatuses in a plurality of processes.  
           [0011]    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  
       [0012]    [0012]FIGS. 1A to  1 C are schematic views showing a reference plate according to an embodiment of the present invention;  
         [0013]    [0013]FIG. 2 is a view for explaining an exposure apparatus using the reference plate of the present invention in FIGS. 1A to  1 C as mask and wafer reference plates;  
         [0014]    [0014]FIG. 3 is a view for explaining mask alignment in the exposure apparatus of FIG. 2;  
         [0015]    [0015]FIG. 4 is a schematic view showing a conventional reference plate;  
         [0016]    [0016]FIG. 5 is a view showing the concept of a semiconductor device production system when viewed from a given angle;  
         [0017]    [0017]FIG. 6 is a view showing the concept of the semiconductor device production system when viewed from another given angle;  
         [0018]    [0018]FIG. 7 is a view showing an example of a user interface;  
         [0019]    [0019]FIG. 8 is a flow chart for explaining the flow of a device manufacturing process; and  
         [0020]    [0020]FIG. 9 is a flow chart for explaining a wafer process. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    &lt;Embodiment of Reference Plate&gt; 
         [0022]    An embodiment of a reference plate according to the present invention will be described with reference to FIGS. 1A to  1 C.  
         [0023]    In FIGS. 1A to  1 C, reference numerals  1  and  5  denote glass substrates;  2 , reference marks formed from a chromium pattern; and  3 , an SiO 2  film. In this embodiment, a thickness d of the glass substrate  1  is adjusted to 30 nm or more which satisfies nd=λ/2×m (m=1, 2, 3, . . . ) where n is the refractive index of the material of the glass substrate with respect to observation light, and λ is the wavelength of observation light. At this time, the thickness of the glass substrate  1  has a given allowable range in accordance with the performance necessary for an exposure apparatus.  
         [0024]    Since the reference marks  2  are formed on a surface opposite to the observation light irradiation surface in the example shown in FIG. 1A, observation light does not directly strike the reference marks  2  formed from the chromium pattern, suppressing deterioration of the reference marks  2 . Since a deposit  4  is uniformly formed on the glass substrate  1 , the deposit  4  hardly causes contrast changes of a signal waveform, facilitating cleaning.  
         [0025]    In FIG. 1B, the glass substrate  5  is identical to the glass substrate  1 , and adjusted to the same thickness as that of the glass substrate  1  in FIG. 1A.  
         [0026]    Since the glass substrate  5  is stacked on the reference marks  2  in the example shown in FIG. 1B, observation light does not directly hit the reference marks  2  formed from the chromium pattern, suppressing deterioration of the reference marks  2 . Since the deposit  4  is uniformly formed on the glass substrate  5 , the deposit  4  hardly causes contrast changes of a signal waveform, facilitating cleaning.  
         [0027]    In FIG. 1C, the SiO 2  film  3  is a protective film. A thickness d from the substrate  1  to the surface of the protective film is adjusted to 30 nm or more which satisfies nd=λ/2×m (m=1, 2, 3, . . . ) where n is the refractive index of the material of the protective film  3  with respect to observation light, and λ is the wavelength of observation light, similar to FIGS. 1A and 1B. At this time, the thickness of the glass substrate  1  has a given allowable range in accordance with the performance necessary for an exposure apparatus.  
         [0028]    &lt;Embodiment of Exposure Apparatus&gt; 
         [0029]    An exposure apparatus using the reference plates of the embodiment as mask and wafer reference plates will be described with reference to FIGS. 2 and 3.  
         [0030]    The present invention will be explained in detail on the basis of the embodiment shown in FIGS. 2 and 3. FIG. 2 is a schematic view showing a projection exposure apparatus using as an exposure light source an F 2  excimer laser to which the present invention is applied. A mask  13  bearing an original image is supported on the apparatus main body by a mask stage  16  which is driven in the X and Y directions by a laser interferometer (not shown) and driving control unit  103 . A wafer  15  as a photosensitive substrate is supported on the apparatus main body by a wafer stage  17  which is also driven in the X and Y directions by the laser interferometer (not shown) and driving control unit  103 . The mask  13  and wafer  15  are set at optically conjugate positions via a projection optical system  14 . Projection exposure is performed by illuminating the mask  13  with an exposure beam from an illumination system (not shown) and projecting the optical image of the mask  13  onto the wafer  15  at a size proportional to the optical magnification of the projection optical system  14 .  
         [0031]    This embodiment concerns a scanning exposure apparatus. Slit-like exposure light traveling in the Y direction in FIG. 2 illuminates the mask  13 , and the mask stage  16  and wafer stage  17  are moved in, the X direction with respect to the slit-like exposure light at a speed ratio corresponding to the optical magnification of the projection optical system  14 , thus scanning the mask  13  and wafer  15 . The entire surface of a device pattern  21  on the mask  13  is transferred in a transfer region (pattern region)  22  on the wafer  15 .  
         [0032]    This embodiment has exemplified the projection optical system  14  comprised of only a refraction element. However, the same effects of the present invention can be obtained even with a projection optical system made up of a reflecting element and refraction element, a reduction projection optical system, like this embodiment, or an equal-magnification projection optical system.  
         [0033]    Mask reference plates  10  and  11  are fixed on the mask stage  16  in the X direction as a scanning direction with respect to the mask  13 . A wafer reference plate  12  is fixed on the wafer stage  17 .  
         [0034]    Each of the mask reference plates  10  and  11  has reference marks  50  and  51 . The wafer reference plate  12  has reference marks  60  and  61  at transfer positions corresponding to the positions of the reference marks  50  and  51  via the projection optical system  14 . The reference marks  50  and  51  on each of the mask reference plates  10  and  11  are flush with the pattern-drawn surface of the mask  13 , whereas the reference marks  60  and  61  on the wafer reference plate  12  are almost flush with the exposure surface of the wafer  15 .  
         [0035]    Observation microscopes  9 L and  9 R enable observing the reference marks  50  and  51  on each of the mask reference plates  10  and  11  and an object (mark) on the pattern-bearing surface of the mask  13 , and at the same time observing the reference marks  60  and  61  on the wafer reference plate  12  and an object (mark) on the wafer  15 . Photoelectrically observed image signals are processed by a mark detection unit  101 , and relative position relationship information is sent to a calculation processing circuit  102 .  
         [0036]    For simultaneous observation, an F 2  excimer laser beam used for projection exposure is used as observation light, which conveniently obviates the need for a new optical system for correcting chromatic aberration generated in the projection optical system  14 .  
         [0037]    The wafer stage  17  is so driven as to move the reference marks  60  and  61  on the wafer reference plate  12  to the observation positions (exposure positions) of the observation microscopes  9 L and  9 R under the projection optical system  14 . Similarly, the mask stage  16  is moved similarly to scanning exposure so as to position the reference marks  50  and  51  on the mask reference plate  11  within the observation region of the observation microscopes  9 L and  9 R.  
         [0038]    In this state, relative misalignments between the reference marks  50  and  60  and between the reference marks  51  and  61  are observed via the observation microscopes  9 L and  9 R. This relative position relationship means the position of a currently projected/exposed mask image on the wafer stage  17 . In this case, the F 2  excimer laser is used as the light source of an exposure apparatus, but an ArF excimer laser may be used as the light source of an exposure apparatus.  
         [0039]    Alignment of the mask  13  on the mask stage  16  by using the mask reference plates  10  and  11  in FIG. 2 will be explained with reference to FIG. 3.  
         [0040]    In this embodiment, as shown in FIG. 3, the mask  13  is aligned by fixing a stationary reference plate (not shown) to a holding member for holding the projection optical system  14 , and using marks  75   a  and  75   b  formed on the stationary reference plate. The reference plate of the present invention can also be applied as the stationary reference plate.  
         [0041]    The mask stage  16  driven in the X direction by laser interferometers  80   a  and  80   b  and the driving control unit  103  is moved to move the reference marks  50  and  51  (FIG. 3) on the mask reference plate  10  (or  11 ) onto the marks  75   a  and  75   b  on the stationary reference plate. Then, the relative position relationship between these marks ( 50 ,  51 ,  75   a , and  75   b ) is measured via a reticle alignment microscope  8 . The relative position relationship between a plurality of alignment reference marks on the mask reference plate  10  (or  11 ) and a plurality of alignment marks on the stationary reference plate is detected, and the relationship between a coordinate system determined by the plurality of alignment marks on the mask reference plate  10  (or  11 ) and a coordinate system determined by the plurality of alignment marks on the stationary reference plate is detected. The position relationship between the marks  75   a  and  75   b  on the stationary reference plate and the reference marks  50  and  51  on the mask reference plate  10  (or  11 ) need not be measured every time the mask is exchanged as long as the positions of the marks  75   a  and  75   b  on the stationary reference plate are stable.  
         [0042]    The mask stage  16  is moved to position mask alignment marks  42   a  and  42   b  on the mask  13  to the marks  75   a  and  75   b . Masks are exchanged near this position.  
         [0043]    The relative position relationship between these marks ( 42   a ,  42   b ,  75   a , and  75   b ) is measured via the reticle alignment microscope  8 . The relative position relationship between the plurality of alignment marks on the mask  13  and the plurality of alignment marks on the stationary reference plate is detected, and the relationship between a coordinate system determined by the plurality of alignment marks on the mask  13  and a coordinate system determined by the plurality of alignment marks on the stationary reference plate is detected. The mask  13  is rotated with respect to the mask stage  16  in consideration of the relationship between the coordinate system determined by the plurality of alignment reference marks on the mask reference plate  10  and the coordinate system determined by the plurality of alignment marks on the stationary reference plate. Alternatively, the driving control unit  103  controls the scanning direction of the mask stage  16  so as to make the scanning direction of the mask  13  coincide with that of the mask stage  16 .  
         [0044]    This effect can also be attained by arranging the marks  75   a  and  75   b  on the stationary reference plate below the mask alignment mark  42   b  on the mask stage  16  when the mask  13  is at the exposure position.  
         [0045]    More specifically, the mask is aligned by moving the mask stage  16  and positioning the reference marks  42   a  and  42   b  (or marks  75   a  and  75   b ) at observation positions of the reticle alignment microscope  8 . At this time, the position relationship between the marks  75   a  and  75   b  and the reference marks  50  and  51  can be measured via the observation microscopes  9 R and  9 L or the reticle alignment microscope  8  while the mask  13  is set. Also, this position relationship need not be measured every time the mask is exchanged as long as the positions of the marks  75   a  and  75   b  on the stationary reference plate are stable.  
         [0046]    (Comparative Example)  
         [0047]    As a comparative example, a reference plate identical to that of the embodiment shown in FIG. 1C except that no SiO 2  film was formed on a chromium pattern was prepared and subjected to a comparison test.  
         [0048]    The reference plates prepared as the embodiment (FIG. 1C) and comparative example underwent durability irradiation using an ArF excimer laser beam (4.0 mj/cm 2 , 1.3×10 6  pulses), and changes in reflectivity before and after durability irradiation were measured. Table 1 shows the results.  
                                             TABLE 1                                   Embodiment   Comparative Example                                        Reflectivity Before   39%   40%           Durability Irradiation           Reflectivity After   39%   24%           Durability Irradiation                      
 
         [0049]    As is apparent from Table 1, the reference mark in the comparative example decreases in reflectivity after durability irradiation, while the reference mark in the embodiment does not decrease in reflectivity before and after irradiation.  
         [0050]    Since the glass or SiO 2  film tightly contacts chromium (or aluminum film) on the reference plate of the embodiment, the film does not change even by irradiation, and an observation image does not change. Even a deposit on the upper surface of the glass (SiO 2  film) does not decrease the contrast, and a pattern can be observed. Further, the upper surface of the glass can be easily cleaned of a substance deposited on it.  
         [0051]    &lt;Embodiment of Semiconductor Production System&gt; 
         [0052]    A production system for a semiconductor device (semiconductor chip such as an IC or LSI, liquid crystal panel, CCD, thin-film magnetic head, micromachine, or the like) will be exemplified. A trouble remedy or periodic maintenance of a manufacturing apparatus installed in a semiconductor manufacturing factory, or maintenance service such as software distribution is performed by using a computer network outside the manufacturing factory.  
         [0053]    [0053]FIG. 5 shows the overall system cut out at a given angle. In FIG. 5, reference numeral  101  denotes a business office of a vendor (apparatus supply manufacturer) which provides a semiconductor device manufacturing apparatus. Assumed examples of the manufacturing apparatus are semiconductor manufacturing apparatuses for various processes used in a semiconductor manufacturing factory, such as pre-process apparatuses (lithography apparatus including an exposure apparatus, resist processing apparatus, and etching apparatus, annealing apparatus, film formation apparatus, planarization apparatus, and the like) and post-process apparatuses (assembly apparatus, inspection apparatus, and the like). The business office  101  comprises a host management system  108  for providing a maintenance database for the manufacturing apparatus, a plurality of operation terminal computers  110 , and a LAN (Local Area Network)  109  which connects the host management system  108  and computers  110  to build an intranet. The host management system  108  has a gateway for connecting the LAN  109  to Internet  105  as an external network of the business office, and a security function for limiting external accesses.  
         [0054]    Reference numerals  102  to  104  denote manufacturing factories of the semiconductor manufacturer as users of manufacturing apparatuses. The manufacturing factories  102  to  104  may belong to different manufacturers or the same manufacturer (pre-process factory, post-process factory, and the like). Each of the factories  102  to  104  is equipped with a plurality of manufacturing apparatuses  106 , a LAN (Local Area Network)  111  which connects these apparatuses  106  to construct an intranet, and a host management system  107  serving as a monitoring apparatus for monitoring the operation status of each manufacturing apparatus  106 . The host management system  107  in each of the factories  102  to  104  has a gateway for connecting the LAN  111  in the factory to the Internet  105  as an external network of the factory. Each factory can access the host management system  108  of the vendor  101  from the LAN  111  via the Internet  105 . The security function of the host management system  108  authorizes access of only a limited user. More specifically, the factory notifies the vendor via the Internet  105  of status information (e.g., the symptom of a manufacturing apparatus in trouble) representing the operation status of each manufacturing apparatus  106 , and receives response information (e.g., information designating a remedy against the trouble, or remedy software or data, corresponding to the notification, or maintenance information such as the latest software or help information. Data communication between the factories  102  to  104  and the vendor  101  and data communication via the LAN  111  in each factory adopt a communication protocol (TCP/IP) generally used in the Internet. Instead of using the Internet as an external network of the factory, a dedicated network (e.g., ISDN) having high security which inhibits access of a third party can be adopted. Also the user may construct a database in addition to the one provided by the vendor and set the database on an external network, and the host management system may authorize access to the database from a plurality of user factories.  
         [0055]    [0055]FIG. 6 is a view showing the concept of the overall system of this embodiment that is viewed at a different angle from FIG. 5. In the above example, a plurality of user factories having manufacturing apparatuses and the management system of the manufacturing apparatus vendor are connected via an external network, and production management of each factory or information of at least one manufacturing apparatus is communicated via the external network. In the example of FIG. 6, a factory having manufacturing apparatuses of a plurality of vendors and the management systems of the vendors for these manufacturing apparatuses are connected via the external network of the factory, and maintenance information of each manufacturing apparatus is communicated. In FIG. 6, reference numeral  201  denotes a manufacturing factory of a manufacturing apparatus user (semiconductor device manufacturer) where manufacturing apparatuses for various processes, e.g., an exposure apparatus  202 , resist processing apparatus  203 , and film formation apparatus  204  are installed in the manufacturing line of the factory. FIG. 6 shows only one manufacturing factory  201 , but a plurality of factories are networked in practice. The respective apparatuses in the factory are connected to a LAN  206  to build an intranet, and a host management system  205  manages the operation of the manufacturing line. The business offices of vendors (apparatus supply manufacturers) such as an exposure apparatus manufacturer  210 , resist processing apparatus manufacturer  220 , and film formation apparatus manufacturer  230  comprise host management systems  211 ,  221 , and  231  for executing remote maintenance for the supplied apparatuses. Each host management system has a maintenance database and a gateway for an external network, as described above. The host management system  205  for managing the apparatuses in the manufacturing factory of the user, and the management systems  211 ,  221 , and  231  of the vendors for the respective apparatuses are connected via the Internet or dedicated network serving as an external network  200 . If a trouble occurs in any one of a series of manufacturing apparatuses along the manufacturing line in this system, the operation of the manufacturing line stops. This trouble can be quickly solved by remote maintenance from the vendor of the apparatus in trouble via the Internet  200 . This can minimize the stop of the manufacturing line.  
         [0056]    Each manufacturing apparatus in the semiconductor manufacturing factory comprises a display, a network interface, and a computer for executing network access software and apparatus operating software which are stored in a storage device. The storage device is a built-in memory, hard disk, or network file server. The network access software includes a dedicated or general-purpose web browser, and provides a user interface having a window as shown in FIG. 7 on the display. While referring to this window, the operator who manages manufacturing apparatuses in each factory inputs, in input items on the windows, pieces of information such as the type of manufacturing apparatus ( 401 ), serial number ( 402 ), name of trouble ( 403 ), occurrence date ( 404 ), degree of urgency ( 405 ), symptom ( 406 ), remedy ( 407 ), and progress ( 408 ). The pieces of input information are transmitted to the maintenance database via the Internet, and appropriate maintenance information is sent back from the maintenance database and displayed on the display. The user interface provided by the web browser implements hyperlink functions ( 410  to  412 ), as shown in FIG. 7. This allows the operator to access detailed information of each item, receive the latest-version software to be used for a manufacturing apparatus from a software library provided by a vendor, and receive an operation guide (help information) as a reference for the operator in the factory.  
         [0057]    A semiconductor device manufacturing process using the above-described production system will be explained. FIG. 8 shows the flow of the whole manufacturing process of the semiconductor device. In step  1  (circuit design), a semiconductor device circuit is designed. In step  2  (mask formation), a mask having the designed circuit pattern is formed. In step  3  (wafer manufacture), a wafer is manufactured by using a material such as silicon. In step  4  (wafer process) called a pre-process, an actual circuit is formed on the wafer by lithography using a prepared mask and the wafer. Step  5  (assembly) called a post-process is the step of forming a semiconductor chip by using the wafer manufactured in step  4 , and includes an assembly process (dicing and bonding) and packaging process (chip encapsulation). In step  6  (inspection), inspections such as the operation confirmation test and durability test of the semiconductor device manufactured in step  5  are conducted. After these steps, the semiconductor device is completed and shipped (step  7 ). The pre-process and post-process are performed in separate dedicated factories, and maintenance is done for each of the factories by the above-described remote maintenance system. Information for production management and apparatus maintenance is communicated between the pre-process factory and the post-process factory via the Internet or dedicated network.  
         [0058]    [0058]FIG. 9 shows the detailed flow of the wafer process. In step  11  (oxidation), the wafer surface 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 vapor deposition. In step  14  (ion implantation), ions are implanted in the wafer. In step  15  (resist processing), a photosensitive agent is applied to the wafer. In step  16  (exposure), the above-mentioned exposure apparatus exposes the wafer to the circuit pattern of a mask. In step  17  (developing), the exposed wafer is developed. In step  18  (etching), the resist is etched except for the developed resist image. In step  19  (resist removal), an unnecessary resist after etching is removed. These steps are repeated to form multiple circuit patterns on the wafer. A manufacturing apparatus used in each step undergoes maintenance by the remote maintenance system, which prevents a trouble in advance. Even if a trouble occurs, the manufacturing apparatus can be quickly recovered. The productivity of the semiconductor device can be increased in comparison with the prior art.  
         [0059]    As has been described above, the reference plate of the present invention enables stable detection of a high-precision mark for a long period even with short-wavelength observation light. The plate surface can be easily cleaned of even a deposit.  
         [0060]    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.