Abstract:
Disclosed is technology for holding a substrate and, specifically, an object holding apparatus including a chuck for holding an object, a holding unit for holding the chuck, a generating unit provided in the holding unit, for generating a field related to an attraction force, a member provided in the chuck and attracted by the generating unit in accordance with the field, and a supporting unit for supporting one of the generating unit and the member, for movement at least in a direction nearing the other and in a direction away from the other.

Description:
FIELD OF THE INVENTION AND RELATED ART  
       [0001]     This invention relates generally to technology for holding a thin plate-like substrate such as a reticle or a silicon wafer, for example, in a semiconductor manufacturing procedure or any other precision microprocessing procedures, for example.  
         [0002]     As a projection exposure apparatus for projecting and transferring a reticle pattern onto a silicon wafer, there is an EUV (extreme ultraviolet) exposure apparatus that uses, as a light source, exposure light of a wavelength of about 13-14 nm (extreme ultraviolet light) and that is arranged to project and photoprint a reticle pattern onto a silicon wafer in a vacuum environment and through a mirror optical system.  
         [0003]     Referring to  FIG. 8 , such EUV exposure light source will be explained in detail. Denoted in the drawing at  101  is a mirror reduction optical system (projection optics), and a plurality of reflection mirrors are disposed and supported precisely inside this projection optical system  101 .  
         [0004]     The projection optical system  101  is supported by a projection optical system base table  106 , and this base table  106  is supported by means of a supporting mechanism  108 . The supporting mechanism  108  comprises an anti-vibration table that supports the weight thereof while suppressing external vibration applied to the projection optical system base table  106 , and a metal bellows (not shown). It is so arranged that, when the load of a structure inside a vacuum chamber  107  (i.e., projection optical system  101  and base table  106 ) is supported from outside the chamber  107 , the vacuum level inside the vacuum chamber can be maintained while, on the other hand, any positional deviation between the vacuum chamber and the thus supported structure can be resiliently absorbed.  
         [0005]     There is a mask  103  above the projection optical system  101 , and the whole of the bottom face of the mask  103  is held by means of a mask chuck  115 . The mask chuck  115  is mounted to a mask stage  102  above it. The mask  102  stage can be driven by means of an actuator (not shown) for repeated scan exposure of the mask  103  pattern. Denoted in the drawing at  104  is a portion of mask stage measurement light, taking the projection optical system base table  106  as the reference of measurement. In the exposure apparatus of  FIG. 8 , the position of the mask stage  102  is measured with respect to multiple axes, by means of interferometers using laser light, and the mask stage  102  is positioned on the basis of it. Disposed above the mask stage  102  is a mask stage guide  113  that guides the mask stage  102  for multiple-axis motions. The mask stage guide  113  is supported by a mask stage damper base table  114 .  
         [0006]     Disposed below the projection optical system  101  is a wafer stage  109  being movable while holding a wafer (substrate to be exposed)  105 . Denoted at  110  is a portion of wafer stage measurement light, taking the projection optical system base table  106  as the reference of measurement, like for the mask stage  102 . The position of the wafer stage  109  is measured with respect to multiple axes, by means of interferometers using laser light, and the wafer stage  109  is positioned on the basis of it.  
         [0007]     Disposed below the wafer stage  109  is a wafer stage guide  111  that guides the wafer stage  109  for multiple-axis motions. As regards the guiding method, a static pressure arranged for use in a vacuum may be used, for example. The wafer stage guide  111  is supported by a wafer stage damper base table  112  which is arranged to support the flatness of the guiding surface of the wafer stage guide  111  very precisely. The wafer stage damper base table  112  is supported by an anti-vibration table or the floor on which the apparatus is mounted.  
         [0008]     In exposure operation, EUV light projected from an illumination system (not shown) is reflected by the exposure pattern surface of the mask  103  and then is reflected along an optical path (not shown) inside the projection optical system  101 , whereby it is projected upon the silicon wafer  105 . While the wafer  105  is held by the wafer stage  109 , the wafer stage  109  and the mask stage  102  having a mask  3  mounted thereon are measured with respect to multiple axes by using laser light and then they are positioned. Then, the wafer  105  and the mask  103  are scanningly moved in synchronism with each other or, alternatively, one of them is held stationary and sequential exposure is carried out. As regards the position of the mask stage  102 , as an example, the position in a vertical direction (Z direction) of the mask reflection surface, the position with respect to two orthogonal directions (X and Y directions) along a plane (X-Y plane) perpendicular to that vertical direction, and rotations about the three orthogonal axes (X, Y and Z axes) may be measured.  
         [0009]      FIG. 9  is an enlarged view of the mask chuck  115  and the mask stage  102  described above. There is a possibility that a foreign particle such as at  116  is sandwiched between the chucking surface of the mask chuck  115  and the mask  103 , and it adversely influences the flatness of the mask  103 . In consideration of it, the mask chuck  115  is demountably mounted to the mask stage  102 , and the cleaning operation for the mask chuck  115  is carried out outside the vacuum chamber  107 .  
         [0010]     As a fixing device for attracting and holding a thin plate-like member in a vacuum environment, Japanese Patent No. 3076727 discloses a technique according to which electrostatic attracting means arranged to attract and hold, upon a stage and through an electrostatic force, an electrically conductive cassette for holding a sample such as a glass mask or a wafer, provided for electron beam irradiation, is mounted to the stage. Also, as an exposure apparatus in which a wafer is held fixed, Japanese Laid-Open Patent Application, Publication No. 2003-142393 discloses a technique according to which a pallet has a wafer electrostatic chuck for fixing a wafer. Further, as an exposure apparatus having a mask holding member for mountably and demountably holding an exposure mask, Japanese Laid-Open Patent Application, Publication No. 11-288099 discloses a technique according to which an exposure mask is positioned by manually pressing it against a positioning pin of a mask holding member and, in this state, the mask is held by a toggle clamp.  
         [0011]     In a mechanism for demounting and clearing a mask chuck, chucking (attracting and holding) the mask chuck from the stage causes degradation of the mask chuck flatness. Also, a positional deviation of the mask chuck with respect to the mask stage leads to degradation of the mask holding precision. Moreover, an electricity supplying system for mounting and demounting a mask to and from the mask chuck has a complicated structure.  
       SUMMARY OF THE INVENTION  
       [0012]     It is accordingly an object of the present invention to provide a substrate holding technique by which a substrate can be held at high surface precision, in a vacuum environment.  
         [0013]     In accordance with an aspect of the present invention, there is provided an object holding apparatus, comprising: a chuck for holding an object; a holding unit for holding said chuck; a generating unit provided in said holding unit, for generating a field related to an attraction force; a member provided in said chuck and attracted by said generating unit in accordance with the field; and a supporting unit for supporting one of said generating unit and said member, for movement at least in a direction nearing the other and in a direction away from the other.  
         [0014]     In accordance with another aspect of the present invention, there is provided an object holding apparatus, comprising: a chuck for holding an object; a holding unit for holding said chuck; and a measuring unit for measuring relative displacement between said chuck and said holding unit.  
         [0015]     In accordance with a further aspect of the present invention, there is provided an object holding apparatus, comprising: a chuck for holding an object; and a holding unit for holding said chuck, wherein said chuck includes a first electrode for attracting the object with an electrostatic force and a second electrode for attracting said holding unit with an electrostatic force.  
         [0016]     Thus, the present invention can provide unique and useful substrate holding technology for holding a substrate at high surface precision.  
         [0017]     These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  is a schematic view of attracting means in a first embodiment of the present invention.  
         [0019]      FIG. 2  is a fragmentary and enlarged view of the attracting means of  FIG. 1 .  
         [0020]      FIG. 3  is a schematic view of attracting means in a second embodiment of the present invention.  
         [0021]      FIG. 4  is a schematic view of attracting means in a third embodiment of the present invention.  
         [0022]      FIG. 5  is a schematic view of a fourth embodiment of the present invention, wherein a mask stage having attracting means is provided with a sensor.  
         [0023]      FIG. 6  is a flow chart for explaining the sequence of device manufacture.  
         [0024]      FIG. 7  is a flow chart for explaining a wafer process in the procedure of  FIG. 6 , in detail.  
         [0025]      FIG. 8  is a schematic view of exposure apparatus.  
         [0026]      FIG. 9  is an enlarged view a mask stage and a mask chuck having a mask mounted thereon. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]     Preferred embodiments of the present invention will now be described with reference to the attached drawings.  
       Embodiment 1  
       [0028]     A first embodiment of the present invention will be described with reference to  FIGS. 1 and 2 .  FIGS. 1 and 2  illustrate, in enlarged magnification, a mask stage and a mask chuck portion, disposed above a projection optical system of an exposure apparatus such as shown in  FIG. 8 . In  FIG. 1 , denoted at  1  is a mask chuck (substrate holding member), and denoted at  2  is a mask stage (stage) movable in a predetermined direction. The mask chuck has targets formed thereon, for measurement of position, angle and focus of the mask stage  2 . The scan direction of the mask stage  2  is in Y-axis direction in  FIG. 1 . The mask chuck  1  having a mask (substrate)  3  held thereon is mounted to the mask stage  2 . The mask chuck  1  and the mask stage  2  are provided with attracting means for mountably and demountably supporting the mask chuck  1  on the mask stage  2 . The attracting means comprises a coil ion core  7  (second member) provided at the mask stage  2  side and a ferromagnetic material member (first member) provided at the mask chuck  1  side. In  FIG. 1 , actually there are two sets of attracting means disposed along X direction.  
         [0029]     Each coil iron core  7  has an exciting coil  4  wound around the core, and the coil  7  is supported on the mask stage  2  with freedoms in Z direction, around Y axis (small freedom) and around X axis in  FIG. 1 , by means of a leaf spring (resilient material)  6 . In this example, the rigidity of the leaf spring  6  is lower than that of the mask chuck  1 . Namely, the leaf spring  6  has a low rigidity only with respect to a vertical direction of the mask reflection surface. The ferromagnetic material member  5  is a plate-like member made of metal, and it is embedded at such position where the coil ion core  7  can contact thereto against the force of the leaf spring  6 , in the manner that the member  5  surface becomes approximately coplanar with the upper surface of the mask chuck  1 .  
         [0030]     The mounting structure for the coil ion core  7  will be described in greater detail, with reference to  FIG. 2 . At a nominal position of the leaf spring  6 , the coil iron core  7  is placed inwardly, inside the mask stage  2 , of the contact surface between the mask stage  2  and the mask chuck  1 , that is, the surface of the ferromagnetic material member  5 . With this arrangement, the free end face of each leg of the coil iron core  7  can be opposed to the ferromagnetic material member  5  with a clearance. For attraction of the coil iron core  7  and the ferromagnetic material member  5 , while the leaf spring  6  deforms, the coil iron core  7  is attracted toward the ferromagnetic material  5  side and is brought into contact with it, whereby the mask chuck  1  is held. In this case, since the leaf spring  6  can absorb displacement, there is no possibility that, due to the surface precision matching between the contact surfaces of the coil iron core  7  and the ferromagnetic material member  5 , a force is applied to the mask chuck  1  to cause deformation thereof.  
         [0031]     In the attracting means of the first embodiment, the leaf spring  7  is mounted on the coil iron core  7  side to support the same. However, the invention is not limited to this. The leaf spring  6  may be mounted on the ferromagnetic material member  5  side to support the same. It is to be noted here that, regarding the attracting means, there are two sets of attracting means also with respect to the Y-axis direction.  
         [0032]     At a lower portion inside the mask chuck  1 , opposed to the mask  3 , there are tow sets of plate-like electrostatic chuck electrodes  8  for holding the mask  3 . Each electrostatic chuck electrode  8  is connected to the ferromagnetic material member  5  through a wire or a metal plate, while on the other hand the coil iron core  7  contacted to the ferromagnetic material member  5  is connected to an electricity supplying unit (not shown) through a wire or the like. In this example, the contact surface between the coil iron core  7  and the ferromagnetic material member  5 , producing an electromagnetic force, is defined or functions as a portion of an electricity supplying path for the electrostatic chuck electrode  8  of the mask chuck  1 . In this embodiment, as described above, the contact surface between the coil iron core  7  and the ferromagnetic material member  5  is included in the electricity supplying path for the electrostatic chuck electrode  8 . However, the invention is not limited to this. Along a different path, electricity can be supplied to the electrostatic chuck electrode  8 . Furthermore, in this embodiment, the contact surface that produces an electromagnetic force functions as a heat transfer path for cooling the mask chuck  1  and the mask  3 . In this case, any produced heat can flow from the contact surface to the coil iron core and the wire, for example, and is heat-exchanged. If the contact surface between the coil iron core  7  and the ferromagnetic material member  5  is not used as the electricity supplying path, as the ferromagnetic material member  5  a material having low electric conductivity, such as ferrite, may be used.  
         [0033]     In the first embodiment, for holding of the mask chuck  1  by the mask stage  2 , the exciting coil  4  is energized and, in response, a magnetic field is produced from the coil iron core  7  by which the ferromagnetic material member  5  embedded in the mask chuck  1  is magnetized and whereby the mask chuck  1  is attracted. After the attraction and even after the voltage supply to the exciting coil  4  is discontinued, since the ferromagnetic material member  5  has already been magnetized, the coil iron core  7  and the ferromagnetic material member  5  are mutually attracted to each other, such that the mask chuck  1  can be continuously held on the mask stage  2 . For demounting the mask chuck  1  from the mask stage  2 , an electric current is applied in an opposite direction to the exciting coil  4  and thus an opposing magnetic field is applied to the ferromagnetic material member  5 , whereby it is demagnetized. Further, when the coil iron core  7  and the ferromagnetic material member  7  are attracted to each other, owing to the electricity supplying path extending through the contact surface therebetween producing an electromagnetic force, an electric potential is applied to the two, left-hand side and right-hand side electrostatic chuck electrodes  8 . By means of electric charges in that occasion, the mask chuck  1  can electrostatically attract approximately the entire surface of the mask bottom face and hold the same tightly.  
       Embodiment 2  
       [0034]     A second embodiment of the present invention will be described with reference to  FIG. 3 . In  FIG. 3 , like reference numerals are assigned to components corresponding to those of the  FIG. 1  embodiment, and description therefor will be omitted. Only distinctive features will be explained.  
         [0035]     In the second embodiment, the second member at the mask stage  2  side (i.e., coil iron core  7 ) and the first member at the mask chuck  1  side (i.e., ferromagnetic material member  5 ) are disposed close to each other with a clearance, like the structure shown in  FIG. 2 . By disposing the coil iron core  7  and the ferromagnetic material member  5  opposed to each other with a clearance as described above, unwanted deformation of the mask chuck  1  due to their mutual surface precision can be avoided. Furthermore, each coil iron core  7  is provided with a piezoelectric actuator  10  or, alternatively, a distance adjusting mechanism (not shown), such that the flatness of the mask chuck  1  can be corrected thereby.  
         [0036]     For the flatness correction, the gap distance (clearance) between the coil iron core  7  and the ferromagnetic material member  5  may be adjusted by means of the piezoelectric actuator  10  or the like, while the flatness is measured by using an external interferometer or any other measuring device. As an alternative, distortion sensors  11  may be embedded in the mask chuck  1 , at plural locations, and the adjustment may be done while measuring the surface shape by use of these distortion sensors  11 . As for such adjustment, measurement and adjustment may be done at start of the exposure apparatus, for example, or it may be made in various ways. It should be noted that, to each electrostatic chuck electrode  8 , an electricity supplying path such as wire or metal plate, for example, is connected, and this electricity supplying path is in turn connected to an electricity supplying unit, not shown. In this case, the contact between the mask chuck  1  and the mask stage  2  in the electricity supplying path is accomplished by means of a brush member, for example, which is provided on at least one of or each of the mask chuck  1  side and the mask stage  2  side. The attraction of the mask  3  is similar to that of the first embodiment. In this case, by means of the electrostatic chuck electrodes  8 , approximately the whole surface of the mask  3  bottom face can be held tightly.  
       Embodiment 3  
       [0037]     A third embodiment of the present invention will be described with reference to  FIG. 4 . In  FIG. 4 , like reference numerals are assigned to components corresponding to those of the embodiments of  FIGS. 1-3 , and description therefor will be omitted. Only distinctive features will be explained.  
         [0038]     In the third embodiment, in order that a mask chuck  1  is held on a mask stage  3  by electrostatic attraction force, mask-chuck electrostatic chuck electrodes (electrostatic attracting means)  9  are provided above the mask chuck  1 . Each electrostatic chuck electrode  8  is connected to an electricity supplying unit (not shown) through an electricity supplying path such as wire or metal plate, for example. In this example, a connecting member such as a brush, for example, is used at the connection of electricity supplying path, between the mask chuck  1  and the mask stage  2 . With this structure, when the mask chuck  1  is mounted to the mask stage  2 , from an electricity supplying unit (not shown), an electric potential is applied to the mask-chuck electrostatic chuck electrodes  9  and, in response to it, the mask chuck  1  itself is attracted to the mask stage  2  by electrostatic attraction force, and it is held thereby. Since high-precision flat plane is obtainable with an electrostatic chuck (attraction by electrostatic), application of unwanted deformation to the mask chuck  1  can be avoided assuredly. As an alternative, the electrostatic chuck electrodes  9  may be provided on the mask stage  2  side to attract and hold the mask chuck  1 . The attraction of the mask  3  is similar to that of the first embodiment. Also in this case, approximately the entire surface of the mask  3  bottom face can be attracted and held tightly, by means of the electrostatic chuck electrodes  8 .  
       Embodiment 4  
       [0039]     A fourth embodiment of the present invention will be described with reference to  FIG. 5 . In  FIG. 5 , like reference numerals are assigned to components corresponding to those of the embodiments of  FIGS. 1-4 , and description therefor will be omitted. Only distinctive features will be explained.  
         [0040]     In the fourth embodiment, at the bottom surface portion of the mask stage  2 , avoiding the mask chuck  1 , a chuck position measuring device (interferometer)  12  which is a displacement measuring sensor for detecting any positional deviation between the mask stage  2  and the mask chuck  1 , is provided. In case there occurs a positional deviation between the mask stage  2  and the mask chuck  1 , the exposure sequence is stopped and alignment of the mask  3  is carried out again.  
         [0041]     In the forth embodiment, the chuck position measuring device  12  is provided on the mask stage  2  of the first embodiment ( FIG. 1 ). However, the invention is not limited to this. It may be mounted to the mask stage  2  of the second embodiment or of the third embodiment. Further, in place of the mechanism for measuring a relative displacement, from the mask stage  2  side, a mask stage measurement reference may be used and displacement of the mask chuck  1  may be measured directly.  
         [0042]     Where a stage system such as described above is used as a mask stage of a projection exposure apparatus such as shown in  FIG. 8 , when the mask chuck is chucked, deformation of the mask chuck resulting from the surface shape of the contact area, including a foreign particle, if any, can be prevented effectively and, in turn, the surface precision of the mask as well as the performance of the apparatus can be improved significantly.  
         [0043]     Although in the foregoing description the invention has been described with reference to embodiments wherein it is applied to a mask stage system, the present invention is applicable also to a wafer stage system, as a matter of course.  
       Embodiment 5  
       [0044]     Next, an embodiment of a device manufacturing method which uses an exposure apparatus such as described above, will be explained.  
         [0045]      FIG. 6  is a flow chart for explaining the procedure of manufacturing various microdevices such as semiconductor chips (e.g., ICs or LSIs), liquid crystal panels, CCDs, thin film magnetic heads or micro-machines, for example. Step  1  is a design process for designing a circuit of a semiconductor device. Step  2  is a process for making a mask on the basis of the circuit pattern design. Step  3  is a process for preparing a wafer by using a material such as silicon. Step  4  is a wafer process which is called a pre-process wherein, by using the thus prepared mask and wafer, a circuit is formed on the wafer in practice, in accordance with lithography. Step  5  subsequent to this is an assembling step which is called a post-process wherein the wafer having been processed at step  4  is formed into semiconductor chips. This step includes an assembling (dicing and bonding) process and a packaging (chip sealing) process. Step  6  is an inspection step wherein an operation check, a durability check an so on, for the semiconductor devices produced by step  5 , are carried out. With these processes, semiconductor devices are produced, and they are shipped (step  7 ).  
         [0046]      FIG. 7  is a flow chart for explaining details of the wafer process. Step  11  is an oxidation process for oxidizing the surface of a wafer. Step  12  is a CVD process for forming an insulating film on the wafer surface. Step  13  is an electrode forming process for forming electrodes upon the wafer by vapor deposition. Step  14  is an ion implanting process for implanting ions to the wafer. Step  15  is a resist process for applying a resist (photosensitive material) to the wafer. Step  16  is an exposure process for printing, by exposure, the circuit pattern of the mask on the wafer through the exposure apparatus described above. Step  17  is a developing process for developing the exposed wafer. Step  18  is an etching process for removing portions other than the developed resist image. Step  19  is a resist separation process for separating the resist material remaining on the wafer after being subjected to the etching process. By repeating these processes, circuit patterns are superposedly formed on the wafer.  
         [0047]     With these processes, high density microdevices can be manufactured.  
         [0048]     Although some preferred embodiments of the present invention have been described in the foregoing, in different aspects, the present invention can be embodied as follows.  
         [0049]     (1) In an exposure apparatus wherein a pattern formed on an original is projected, in a vacuum environment, onto an exposure substrate to be exposed, through a projection optical system, wherein, while moving both of the original and the exposure substrate or only the exposure substrate relative to the projection optical system by use of a stage system, the pattern of the original is repeatedly photoprinted on the exposure substrate, characterized by an original mounting and holding member for mounting the original to the stage system, wherein at least one of attracting and holding means provided at the original mounting and holding member side and attracting and holding means provided at the stage system side is mounted through a resilient member having a rigidity lower than that of the original mounting and holding member.  
         [0050]     (2) In an exposure apparatus according to Item (1) above, the resilient member is a resiliency member having a low rigidity only in a vertical direction to the mask reflection surface.  
         [0051]     (3) In an exposure apparatus according to Item (1) or (2) above, attracting and holding means having a clearance is provided between the original attracting and holding member and the attracting and holding means at the stage system side, wherein the flatness of the original mounting and holding member is measured and the clearance distances at plural locations of the attracting and holding means are adjusted.  
         [0052]     (4) In an exposure apparatus according to Item (3) above, measuring means for measuring the surface precision of the original mounting and holding member uses a distortion sensor.  
         [0053]     (5) In an exposure apparatus according to Item (4) above, the clearance distance between a ferromagnetic material member and a coil iron core is controlled by means of an actuator and on the basis of an output value of the distortion sensor or on the basis of pre-measured value.  
         [0054]     (6) In an exposure apparatus according to any one of Items (1) to (5), the attracting mechanism of the attracting and holding means uses an electromagnetic force or an electrostatic attraction force.  
         [0055]     (7) In an exposure apparatus according to any one of Items (1)-(6), a displacement measuring sensor is provided between the original mounting and holding member and the stage system.  
         [0056]     (8) In an exposure apparatus according to any one of Items (1)-(7), the original mounting and holding member is provided with a target for measurement of position, angle, or focus of the stage system.  
         [0057]     (9) In an exposure apparatus according to any one of Items (1)-(8), the contact surface for generating an electromagnetic force functions as an electricity supplying path to the original mounting and holding member.  
         [0058]     (10) In an exposure apparatus according to any one of Items (1)-(9), the contact surface for generating an electromagnetic force functions as a heat transfer path for cooling the original mounting and holding member and the mask.  
         [0059]     (11) A device manufacturing method characterized by manufacturing a device by use of an exposure apparatus as recited in any one of Items (1)-(10).  
         [0060]     While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.  
         [0061]     This application claims priority from Japanese Patent Application No. 2003-324214 filed Sep. 17, 2003, for which is hereby incorporated by reference.