Patent Publication Number: US-7210982-B2

Title: Method and apparatus for polishing a substrate

Description:
This is a Divisional application of Ser. No. 11/045,089 filed Jan. 31, 2005 now U.S. Pat. No. 7,115,022 which is a CON of PCT/JP03/09745 filed Jul. 31, 2003 and claims priority to Japan 2002-223001 filed Jul. 31, 2002, the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a method and device for polishing a substrate. In particular, it relates to a method and device for polishing a glass substrate to manufacture a glass substrate for liquid crystal display. 
     BACKGROUND ART 
     A glass substrate used for liquid crystal display has minute recesses and projections or undulation in its surfaces, which causes a deformed picture image. Accordingly, such minute recesses and projections or undulation should be eliminated with a polishing device. As such polishing device, there has generally been known a polishing device in which a glass substrate held by a carrier is pressed to a polishing cloth disposed on a polishing surface-plate while the polishing surface-plate and the carrier are rotated relative to each other to polish the glass substrate. 
     Further, in the polishing device disclosed in JP-A-9-141550, a flexible film is disposed at a lower portion of the carrier and pressurized air is supplied between the flexible film and the carrier so that the pressure of the pressurized air urges the substrate attached to the flexible film to the polishing cloth for polishing. According to this polishing device, there is an advantage that the pressurized air in the space between the flexible film and the carrier applies pressure uniformly to each part of the substrate whereby the substrate can be polished flat, and minute recesses and projections in the substrate surface can be eliminated. 
     However, in the conventional polishing device, there is no proposal about a discharging means for discharging a glass substrate which has been polished and removed from the carrier, from a polishing stage. Particularly, in a case of a large-sized glass substrate, the length of a side of which is, for example, beyond 1,000 mm, the removal and handling of it in the polishing stage and the discharge of it from the polishing stage were very difficult and took a long time to thereby reduce productivity. 
     With the increase of the size of a liquid crystal display screen in recent years, a polishing device for a large-sized glass substrate, which can solve the above-mentioned problem of discharging a glass substrate after being polished and can improve productivity, has been expected. 
     The present invention has been made in consideration of the above-mentioned circumstances, and it is an object of the present invention to provide a method and device for polishing a glass substrate suitable for polishing a large-sized glass substrate. 
     DISCLOSURE OF THE INVENTION 
     In order to achieve the above-mentioned object, the method for polishing a substrate of the present invention is characterized by comprising a process for attaching a substrate to a frame with a film on which the film capable of attaching the substrate is stretched and installing the frame on a carrier, or a process for installing a frame on which a film capable of attaching a substrate is stretched on a carrier and attaching the substrate to the frame; a process for bringing the carrier holding the frame and a polishing surface-plate closer relative to each other and polishing a surface to be polished of the substrate attached to the film by pressing the substrate to the polishing surface-plate; and a process for removing the frame from the carrier after the completion of the polishing of the substrate and removing the substrate from the frame, or a process for removing the substrate from the frame after the completion of the polishing of the substrate and removing the frame from the carrier. 
     Preferably, the present invention is characterized by comprising a process for attaching a glass substrate to a frame on which a film capable of attaching a glass substrate is stretched, a process for installing on a carrier the frame to which the glass substrate is attached, a process for bringing the carrier with the frame and a polishing surface-plate closer relative to each other and polishing a surface to be polished of the glass substrate attached to the film by pressing the glass substrate to the polishing surface-plate, a process for removing the frame from the carrier after the completion of the polishing of the glass substrate, and a process for removing the polished glass substrate from the frame. 
     Further, in order to achieve the above-mentioned object, the polishing device of the present invention is characterized by comprising a substrate attaching stage for attaching a substrate to a frame on which a film capable of attaching the substrate is stretched; 
     a frame installing stage for installing the frame on a carrier; a polishing stage for polishing the substrate by bringing the carrier and a polishing surface-plate closer relative to each other after the installation of the frame on the carrier and pressing a surface to be polished of the substrate attached to the frame, to the polishing surface-plate; a substrate removing stage for removing the frame from the carrier, and a substrate removing stage for removing the polished substrate from the frame. 
     Preferably, the polishing device is characterized by comprising a glass substrate attaching stage for attaching a glass substrate to a frame on which a film capable of attaching the glass substrate is stretched, a polishing stage for polishing a surface to be polished of the glass substrate attached to the film by bringing the carrier and a polishing surface-plate closer relative to each other after the installation of the frame on the carrier and pressing the substrate to the polishing surface-plate, and a glass substrate removing stage for conveying the frame removed from the carrier after the completion of the polishing of the glass substrate and removing the polished glass substrate from the frame. 
     Further, according to the present invention, an unpolished glass substrate is attached to the film of a frame in the glass substrate attaching stage. Then, the frame to which the glass substrate is attached is installed on the carrier in the frame installing stage. In this case, the frame may be installed on the carrier in the frame installing stage and then, the unpolished glass substrate may be attached to the film of the frame in the glass substrate attaching stage. 
     Then, in the polishing stage, the carrier on which the frame is installed and the polishing surface-plate are brought closer relative to each other and the polishing is performed by pressing the surface to be polished of the glass substrate attached to the film to the polishing surface-plate. 
     Then, after the completion of polishing the glass substrate, the frame is conveyed from the polishing stage to the frame removing stage in which the frame is removed from the carrier, and thereafter, the polished glass substrate is removed from the frame in the glass substrate removing stage. In this case, the frame may be removed from the carrier in the frame removing stage after the polished glass substrate is removed from the frame in the glass substrate removing stage. 
     Thus, in the present invention, the glass substrate is attached to the frame capable of being attached to and detached from the carrier, and after the completion of the polishing, the polished glass substrate is removed from the frame in the glass substrate removing stage remote from the polishing stage, instead of removing the glass substrate from the frame in the polishing stage. With this measures, the present invention can solve the problem inherent in conveying a large-sized glass substrate and can improve productivity. 
     Further, in a preferred embodiment of the present invention, the frame is washed in the washing stage after the glass substrate is removed, and this frame can be used repeatedly for the attachment of another glass substrate. Accordingly, the number of frames to be prepared can be minimized, and accordingly, the present invention can contribute to resource saving. 
     According to another preferred embodiment of the present invention, pressurized fluid is supplied between the carrier and the film of the frame from a supply means for supplying pressurized fluid for polishing to create a pressure of pressurized fluid therebetween whereby the glass substrate is pressed for polishing to the polishing surface-plate. Since the pressure of pressurized fluid is applied uniformly to each part of the glass substrate, the glass substrate can be polished flat. Incidentally, the glass substrate is not influenced by the surface profile of the polishing surface-plate, i.e., even though the polishing surface-plate has some undulation in its surface. Therefore, the undulation is not transferred to the glass substrate. Accordingly, a strict requirement of precision to the polishing surface-plate is unnecessary, and cost for the polishing surface-plate can be reduced. 
     The film used preferably in the present invention has a three-layer structure comprising an air-tightness retention layer having a outer circumferential portion adhered tightly to the carrier to retain air-tightness between the film and the carrier, a strength retention layer holding the air-tightness retention layer and having a predetermined tensile stress durable to a tension for stretching the film, and a smooth layer to which the glass substrate is attached. Accordingly, the glass substrate can be held stably by the film whereby the glass substrate can be polished with accuracy. 
     In another embodiment of the present invention, the strength retention layer of the film is made of aramid fibers, a mesh of stainless steel, a mesh of steel, carbon fibers, glass fibers, nylon fibers or a material having the same tensile strength as these materials. Accordingly, the strength of the film can be assured when the glass substrate is pressed to the polishing surface-plate with a pressing force suitable for the polishing. 
     Further, according to another embodiment of the present invention, fluid is supplied from a supply means for supplying fluid for separating to the boundary between the film of the frame and an edge portion of the substrate in the substrate removing stage, whereby the substrate can be separated from the frame due to a separating function produced by the supply of the fluid. When the substrate is to be separated from the frame, it is possible to separate the substrate by its own weight. However, it takes much time. According to the present invention, the separating function is produced forcibly by supplying the fluid whereby the substrate can be separated from the frame in a shorter time to thereby increase productivity. 
     According to another embodiment of the present invention, a substrate is placed on a table in the substrate attaching stage, and then, the film of a frame is placed on the substrate on the table, and then, a press roller is pressed to the film placed on the substrate while the table and the press roller are moved relatively along the surface of the film by a moving means, whereby the substrate is attached to the film by the press roller. 
     The present invention can effectively be applied to a method and device for polishing a substrate, particularly, for polishing a substrate having a large surface area. In the production of a substrate having a small surface area, the substrate can be attached to a film without causing air bubbles between the substrate and the film by pressing simply the substrate to the film. The presence of air bubbles reduces the attaching strength. In order to obtain assured attaching, the amount of air bubbles should be minimized as possible. If the substrate having a large surface area is simply pressed to the film, a large amount of air bubbles exists because the degree of flatness of each of the film and the substrate is high. According to the present invention, the substrate and the film can be attached by pressing them with the press roller to discharge forcibly air bubbles existing between the film and the substrate. With this, the substrate of large surface area can certainly and firmly be attached to the film. 
     According to another preferred embodiment of the present invention, the frame is connected detachably to the carrier by means of a plurality of pins wherein a predetermined number of pins among the plurality of pins are fitted to be swung to the frame and the remaining pins are fixed thereto so as to be used for determining the position to the carrier. 
     The above-mentioned preferred embodiment of the present invention is also effective to the method and device for polishing a substrate, particularly, a substrate of large surface area. In the case that the frame and the carrier are connected, to determine mutual positions, by fitting a plurality of pins mounted on the frame to a plurality of openings formed in the carrier and that the frame is a small-sized frame, all the pins can be fitted to the openings even though these pins are mounted fixedly on the frame because accuracy in mounting the pins can easily be obtained. On the other hand, in the case of a large-sized frame to which a substrate of large surface area is to be attached, it is difficult to mount pins with accuracy. Accordingly, if all the pins are mounted fixedly, it is difficult to fit all the pins into the openings. On the other hand, if all the pins are mounted on the frame so that each pin can be swung with respect to its axis, an error of mounting can be absorbed by their swinging movement. Accordingly, all the pins can be fitted to the openings. However, if all the pins are mounted so as to be swung, it is impossible to determine the mutual positions because the frame can not be stable with respect to the carrier. Further, the pins have to resist against the shearing force of the polishing surface-plate at the time of the polishing. Accordingly, there is a possibility that they can not withstand against the shearing force. 
     According to the present invention, a predetermined number of pins among the plurality of pins are mounted on the frame so that they can be swung with respect to their axes, to absorb error in mounting each pin. The remaining pins are mounted fixedly on the frame to resist the shearing force to each of these pins applied from the polishing surface-plate. Accordingly, the large-sized frame can stably be connected to the carrier with accurate positional relation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view showing the entire structure of the polishing device according to a first embodiment. 
         FIG. 2  is a side view showing polishing heads and polishing stages as an embodiment. 
         FIG. 3  is a perspective view of a polishing head disassembled. 
         FIG. 4  is diagram showing the three-layer structure of a film to be attached to a frame. 
         FIG. 5  is an enlarged cross-sectional view of an important portion showing an attaching/detaching structure for the frame to a slide-contact ring. 
         FIG. 6  shows enlarged cross-sectional views of important portions showing other attaching/detaching structures for the frames to slide-contact rings. 
         FIG. 7  shows enlarged views of important portions showing other attaching/detaching structures for the frames to slide-contact rings. 
         FIG. 8  is a schematic structural view of a conveying device for a glass substrate. 
         FIG. 9  is a diagram showing a glass substrate attaching process as well as a frame and a carrier. 
         FIG. 10  is a diagram showing a separating process for separating a glass substrate from a frame. 
         FIG. 11  is a front view of the polishing device according to a second embodiment. 
         FIG. 12  is a diagram showing an operation of the polishing device shown in  FIG. 11 . 
         FIG. 13  is a diagram showing an operation of the polishing device shown in  FIG. 11 . 
         FIG. 14  is a diagram showing an operation of the polishing device shown in  FIG. 11 . 
         FIG. 15  is a diagram showing an operation of the polishing device shown in  FIG. 11 . 
         FIG. 16  is a diagram showing an operation of the polishing device shown in  FIG. 11 . 
         FIG. 17  is a diagram showing an operation of the polishing device shown in  FIG. 11 . 
         FIG. 18  is a diagram showing an operation of the polishing device shown in  FIG. 11 . 
         FIG. 19  is a diagram showing an operation of the polishing device shown in  FIG. 11 . 
         FIG. 20  is a diagram showing an operation of the polishing device shown in  FIG. 11 . 
         FIG. 21  is a diagram showing an operation of the polishing device shown in  FIG. 11 . 
         FIG. 22  is a diagram showing an operation of the polishing device shown in  FIG. 11 . 
         FIG. 23  is a diagram showing an operation of the polishing device shown in  FIG. 11 . 
         FIG. 24  is a diagram showing an operation of the polishing device shown in  FIG. 11 . 
         FIG. 25  is a diagram showing an operation of the polishing device shown in  FIG. 11 . 
         FIG. 26  is a diagram showing an operation of the polishing device shown in  FIG. 11 . 
         FIG. 27  is a diagram showing an operation of the polishing device shown in  FIG. 11 . 
         FIG. 28  is a diagram showing an operation of the polishing device shown in  FIG. 11 . 
         FIG. 29  is a diagram showing an operation of the polishing device shown in  FIG. 11 . 
         FIG. 30  is a diagram showing an operation of the polishing device shown in  FIG. 11 . 
         FIG. 31  is a diagram showing an operation of the polishing device shown in  FIG. 11 . 
         FIG. 32  is a diagram showing an operation of the polishing device shown in  FIG. 11 . 
         FIG. 33  is a diagram showing an operation of the polishing device shown in  FIG. 11 . 
         FIG. 34  is a diagram showing an operation of the polishing device shown in  FIG. 11 . 
         FIG. 35  is a perspective view of an important portion showing a position determining structure for a frame to a carrier. 
         FIG. 36  is a plan view of a hook to be engaged with a pin in the position determining structure shown in  FIG. 35 . 
         FIG. 37  is a side view showing the structure of a press roller with a balloon. 
     
    
    
     EXPLANATION OF NUMERALS 
       10 ,  300 : polishing device,  12 : conveyer,  14 : frame,  16 : stage (glass substrate attaching stage),  18 : first polishing stage,  20 : second polishing stage,  22 : stage (glass substrate removing stage),  24 : glass substrate discharging conveyer,  26 : frame washing stage,  28 : frame drying stage,  30 : frame returning conveyer,  32 : robot,  33 : arm,  34 : suction pad,  36 : conveyer,  38 : film,  40 : upper frame,  42 : lower frame,  44 : air-tightness retention layer,  46 : strength retention layer,  48 : smooth layer,  50 ,  50 A,  50 B: polishing head,  51 : casing unit,  52 : carrier,  53 : lower peripheral ring,  54 : air chamber,  56 : spindle,  58 : polishing pad,  60 : polishing pad,  62 : polishing surface-plate,  64 : rotary shaft,  66 : polishing surface-plate,  68 : rotary shaft,  70 : rectilinear guide,  72 : guide rail,  74 : maintenance stage,  76 : maintenance stage,  78 : suspender ring,  80 : penetration hole,  82 : slide-contact ring,  84 : slide-contact ring suspender,  86 : upper spring,  88 : spring for lifting,  90 : penetration hole,  92 : screw jack,  94 : stopper pin,  96 : line shaft,  98 : jet orifice,  100 : air chamber,  102 : air supply channel,  104 : valve,  106 : air pump,  108 : pin,  110 : head portion,  112 : hook,  114 : pin,  116 : recess,  118 : stopper plate,  120 : air passage,  122 : clamper,  124 : clamping plate,  126 : pole,  128 : penetration hole,  130 : penetration hole,  132 : pin supporting member,  134 : penetration hole,  136 : stopper pin,  138 : conveyer,  140 : robot,  142 : arm,  144 : suction head,  146 : conveyer,  150 ,  152 ,  154 : conveying device,  160 : guide rail,  162 : holder,  164 : small-sized robot,  166 : arm,  168 : guide block,  170 : guide rail,  200 : table,  202 : jack,  204 : table,  206 : air nozzle,  208 : jack,  302 : rail,  304 : frame installing stage,  306 : frame removing stage,  308 : table,  310 : plate attaching shuttle,  312 : press roller,  314 : plate separating shuttle,  316 : elevating device,  320 : table,  322 : elevating device,  324 : shuttle main body,  326 : conveying table,  330 : air nozzle (means for supplying fluid for separation),  340 : pin,  342 : opening,  344 : tip portion,  346 : thin portion,  350 : hook,  352 : fitting portion,  360 : film pressing balloon,  362 : head,  364 : supporter,  366 : cylinder unit 
     BEST MODE FOR CARRYING OUT THE INVENTION 
     In the following, preferred embodiments of the method and device for polishing a glass substrate of the present invention will be described with reference to the attached drawings. 
     In a first embodiment, a polishing device  10  is shown in  FIG. 1 , which is to polish a single surface of a large-sized glass substrate G (having, for example, a side exceeding 1,000 mm and a thickness of from 0.3 mm to 1.1 mm) to have a flatness necessary for a glass substrate used for liquid crystal display. 
     This polishing device  10  comprises mainly a conveyer  12  for conveying an unpolished glass substrate G, a stage  16  for attaching the glass substrate G to a frame  14  (glass substrate attaching stage), a first polishing stage  18 , a second polishing stage  20 , a stage  22  for removing the polished glass substrate G from the frame  14  (glass substrate removing stage), a glass substrate discharging conveyer  24 , a frame washing stage  26 , a frame drying stage  28  and a frame returning conveyer  30 . 
     Further, the polishing device  10  is provided with a conveying device  150  for conveying the frame  14  from the stage  16  to the first polishing stage  18 , a conveying device  152  for conveying the frame  14  from the first polishing stage  18  to the second polishing stage  20  and a conveying device  154  for conveying the frame  14  from the second polishing stage  20  to the stage  22 . The number of polishing stages may be only one or more than two, which depends on intended use. In consideration of efficiency and cost, it is preferred to install two stages of a rough polishing stage and a fine polishing stage. However, if the case requires, the fine polishing stage may be added to obtain high quality. 
     An unpolished glass substrate G conveyed by the conveyer  12  is sucked and held by a suction pad  34  provided on the arm  33  of a robot  32 , and it is transferred from the conveyer  12  to a conveyer  36  by a turning motion of the arm  33 . Then, it is conveyed by the conveyer  36  to the stage  16 . In the stage  16 , the glass substrate G is attached to a frame  14 . Description will be made as to the method of attaching. In the stage  16 , the frame  14  is held on an elevating device (not shown) as a glass substrate attaching means. When the glass substrate G is positioned below the frame  14 , the frame  14  is moved downward by means of the elevating device so that a film (see  FIG. 3 ) stretched on the frame  14  is pressed to the glass substrate G. By this pressing force, the glass substrate G is attached to the film  38 . Then, the frame  14  is held on the conveying device  150  in  FIG. 1  and is conveyed to the first polishing stage  18  shown in  FIG. 2 , at which the frame is installed on a carrier  52 . The glass substrate attaching means is not limited to the elevating device but any suitable means may be used as long as the glass substrate G can be attached to the frame  14 . Here, the frame  14  described herein means the entirety including the stretched film  38 . 
     As shown in  FIG. 3 , the frame  14  is constituted by stretching the film  38  which is adhesive to the glass substrate G between an upper frame  40  and a lower frame  42  and by fastening the upper frame  40  and the lower frame  42  by means of bolts (not shown). 
     The frame  14  and the film  38  are not limited to have a circular shape but they may have a rectangular shape. 
     The film  38  has a three-layer structure comprising an air-tightness retention layer  44 , a strength retention layer  46  and a smooth layer  48  as shown in  FIG. 4 . The air-tightness retention layer  44  is a sheet material having its outer peripheral portion being adhered tightly to a lower peripheral ring  53  in the carrier  52  so as to maintain air-tightness of an air chamber  54  formed between the layer and the carrier  52 . As the material for the sheet material, rubbers, silicons, fluorine resin, vinyls such as polyvinyl chloride (PVC), nylons and urethane may be mentioned. However, polyvinyl chloride or urethane is preferred from the standpoint of manufacturing. In particular, such one made of urethane is preferred. The strength retention layer  46  in  FIG. 4  is a sheet material which can hold the air-tightness retention layer  44  and has a predetermined tensile strength durable to a tensile force for stretching the film  38 . 
     Here, the tensile strength required for the strength retention layer  46  is calculated on the basis of a frictional force acting on the glass substrate G at the time of the polishing. When the glass substrate G have a size L, the frictional force acting on the glass substrate G at the time of the polishing is presented by “a friction coefficient of a polishing tool to the glass substrate G at the time of the polishing”×“a surface area per a unit width (cm) of the glass substrate G”×“pressure of polishing”=μ×Lm×10 −2 ×kPa. 
     For instance, when μ=0.3, L=1 m and p=3 kPa, 0.3×10 −2 ×3×10 3 =9N. 
     Accordingly, the tensile strength required for the strength retention layer  46  needs to have a tensile force strong enough to the frictional force. Accordingly, in terms of a strip-like region having a unit width (1 cm) in the strength retention layer  46 , a tensile strength of more than 9 N is required. 
     Assuming that a glass substrate having a large surface area is subjected to a high pressure of polishing, for example, when μ=0.5, L=1.8 m and p=20 kPa, the tensile strength required for the strength retention layer  46  in this embodiment needs to have a tensile strength of at least 180 N in terms of a strip-like region having a unit width (1 cm) in the strength retention layer  46 . 
     Rubber or resins are generally considered as the material for the strength retention layer  46 . However, the strength retention layer is made of a material such as alamide fibers, a mesh of stainless steel, a mesh of steel, carbon fibers, glass fibers, nylon fibers, a metallic sheet, a resin sheet or the like so as not to cause the deformation in practical use wherein the tensile strength is at least 9 N/cm even in a case of L=100 cm and a pressure of pressing of about 3 kPa, particularly, the tensile strength is at least 180 N/cm in a case of L=180 cm from practical use and in addition, in consideration of an impact load. The particularly preferred material is alamide fibers because they have very small elongation to the tensile force. 
     Since the glass substrate G is rotated when it is polished actually, the maximum tensile force applied to the strength retention layer  46  is calculated based on the length of a diagonal line of the glass substrate G. In this embodiment, the calculation was made based on the length of a longer side of the glass substrate G in order to simplify the calculation. 
     The smooth layer  48  is constituted by bonding a glass-holding sheet used commonly to attach the glass substrate G. However, if the surface irregularity of the smooth layer  48  is large, there causes the problem that the surface irregularity is transferred to the glass substrate G at the time of polishing. Accordingly, the smooth layer  48  has to be flat and smooth. However, when resin or a rubber layer is applied by using a coating technique such as gluing, a local surface irregularity may take place. If this can not be avoided, a flat sheet can be formed by bonding a thin sheet according to a laminating process. The thin sheet may be of, for example, urethane, PVC, PET, PP as long as smoothness can be maintained. Urethane or PVC is preferred because a common laminating process can be used. In particular, a thin sheet of urethane is preferred. Specifically, the flatness of the smooth layer  48  be at most 0.1 mm per 100 mm 2  in terms of surface irregularity. In order to obtain a sufficient flatness, a plurality of smooth layers  48  may be overlaid. Further, the sheet thickness of the film  38  is preferably from about 0.1 mm to 5 mm in order to provide flexibility. Further, the thin sheet may be a porous sheet having a sucking function to the glass substrate G. In this case, the sucking function can be improved by forming previously a water film on the surface of the glass substrate G or the surface of the sheet. 
     The polishing pad of the polishing stage is generally subjected previously to truing to remove a minute undulation in the surface layer. For this purpose, a grinding unit for truing is generally installed in the polishing device. It is naturally for the grinding unit for truing to have a high precision because it provides the standard for the polished surface. 
     In this embodiment, the truing is carried out by attaching a commercially available sheet containing polishing powder to the film  38  of the frame  14  installed on the carrier  52 . Namely, in the same manner as the polishing of the glass substrate G, the commercially available sheet attached to the film  38  of the frame  14  is pressed to the polishing pad of the polishing stage under the application of a uniform pressure by pressurized fluid, which is described later, while the sheet and the pad are moved relatively, whereby the truing of the polishing pad is carried out. This provides the advantage of eliminating a highly precise grinding unit. Incidentally, since the frame  14  attached with the polishing sheet instead of the glass substrate G can be put into the production line with a minimum interference to the production cycle, the interference to the production due to the truing can be controlled to the minimum. 
     Next, the polishing heads  50  shown in  FIG. 2  will be described. The polishing head  50  of the first polishing stage  18  had the same structure as the polishing head  50  of the second polishing stage  20 . Accordingly, the same reference numeral is used for these polishing heads. 
     Each polishing head  50  comprises a casing unit  51  including a motor, the output shaft of the motor being connected to a spindle  56  extending in a vertical direction. A carrier  52  is connected to the spindle  56 . The casing unit  51  is connected to a slider  158  by a elevating devices  156 . The elevating devices  156  move each casing unit  51  vertically with respect to each slider  158  whereby carriers  52  are advanced to or retracted from the polishing pad  58  of the first polishing stage  18  and the polishing pad  60  of the second polishing stage  20 , and glass substrates G attached respectively to frames  14  can be pressed to respective polishing pads  58 ,  60  with a predetermined pressure of polishing. 
     The structure of an attaching/detaching means for attaching or detaching the frame  14  to the carrier  52  and the method for attaching or detaching are described later. 
     The polishing pad  58  is bonded to an upper face of a polishing surface-plate  62 , and a lower portion of the polishing surface-plate  62  is connected with a rotary shaft  64  rotated by a motor not shown. The polishing pad  60  is bonded to an upper face of a polishing surface-plate  66 , and a lower portion of the polishing surface-plate  66  is connected with a rotary shaft  68  rotated by a motor not shown. Here, the motors are not always necessary because there is a case that the polishing pads  58 ,  60  need not to be rotated. Instead, the polishing pads  58 ,  60  may be swung. In the description of the present invention, “polishing surface-plate” includes a combination of the polishing surface-plate  62  and the polishing pad  58  or a combination of the polishing surface-plate  66  and the polishing pad  60  in this embodiment. 
     Further, each casing unit  51  is connected to an orbital driving mechanism (not shown) so as to revolve with a predetermined radius of revolution. The orbital driving mechanism may include a planetary gear mechanism in the casing unit  51  so that the output shaft of the planetary gear mechanism is connected to the spindle  56 . Specifications of the first polishing stage  18  and the second polishing stage  20  are described below. 
     Pressure of polishing: from 2 kPa to 25 kPa 
     Number of rotation of carrier  52 : from 0 to 25 rpm, radius of orbital revolution: 100 mm (from 50 to 200 mm), number of orbital revolution: from 20 to 150 rpm or from 20 to 200 rpm 
     Number of rotation of polishing surface-plates  62 ,  66 : from 0 to 15 rpm 
     Polishing slurry: an aqueous solution of cerium oxide is supplied through slurry supplying holes of the polishing surface-plates. 
     Polishing pad  58 : made of urethane foam with grooves for feeding slurry in its front surface (groove pitch of from 5 to 10 mm, groove width of from 2 to 6 mm, groove depth of from 1 to 5 mm) 
     Polishing pad  60 : made of suede-like flexible urethane with grooves for feeding slurry in its front surface (groove pitch of from 5 to 10 mm, groove width of from 2 to 6 mm, groove depth of from 1 to 5 mm) 
     Polishing time: from 1 to 10 min for both the first and the second polishing stages  18 ,  20   
     Swing motion of carriers  52  to polishing surface-plates  62 ,  66 : from 0 to 700 mm in relative movement in a horizontal direction 
     Thickness of glass substrate G: from 0.3 mm to 3.0 mm 
     Shape of glass substrate G: rectangular glass sheet having a side exceeding 1,000 mm 
     Surface without subjecting the polishing of a glass substrate G: held air-tightly with suction pads of polyurethane (glass holding sheets) attached to film  38   
     The above-mentioned are the specifications of each of the polishing stages  18 ,  20  by which the glass substrates G are polished and minute recesses and projections and undulation in the front surface of the glass substrates G can be removed. 
     Rectilinear guides  70 ,  70  are attached to the slider  158  of the first polishing stage  18 . These rectilinear guides  70 ,  70  are respectively fitted to guide rails  72 ,  72 . The guide rails  72 ,  72  are extended into a maintenance stage  74  in which the spindle  56  and the carrier  52  of the first polishing stage  18  undergo maintenance, as shown in  FIG. 1 . 
     Similarly, rectilinear guides  70 ,  70  are attached to the slider  158  of the second polishing stage  20  as shown in  FIG. 2 . These rectilinear guides  70 ,  70  are respectively fitted to guide rails  160 ,  160 . The guide rails  160 ,  160  are extended into a maintenance stage  76  in which the spindle  56  and the carrier  52  of the second polishing stage  20  undergo maintenance, as shown in  FIG. 1 . 
     The structure of the carrier  52  will be described. A suspender ring  78  is provided at an upper peripheral portion of the carrier  52  and is fixed thereto by means of bolts (not shown) as shown in  FIG. 3 . In a flange portion of the suspender ring  78 , which projects beyond the outer peripheral portion of the carrier  52 , a plurality of penetration holes  80 ,  80  . . . are formed with equal intervals on a concentric circle, and slide-contact ring suspenders  84  provided on an upper face of the slide-contact ring  82  are penetrated upward into these penetration holes  80 ,  80  . . . as shown in  FIG. 5 . Further, each of the slide-contact ring suspenders  84  is inserted into a lifting spring assembly  88  disposed between the suspender ring  78  and a lifting disc spring  86 ; is also inserted into a penetration hole  90  of the lifting disc spring  86 , and is connected to a screw jack  92 . 
     Accordingly, when the screw jack  92  is operated to lift upward the slide-contact ring suspender  84  against the urging force of the suspender ring  88 , the slide-contact ring  82  is lifted with respect to the carrier  52  whereby the frame  14  which is mounted on the slide-contact ring  82  so as to be attached or detached, is lifted so that a predetermined tensile force is exerted to the film  38 . 
     In order to exert a tensile force to each film  38  automatically, a plurality of frames  14  and films  38  are prepared. In this case, there must consider that there is individual difference among initial tensile forces of films  38  with respect to frames  14 , and there is difference among initial tensile forces of the films  38 ,  38  . . . , which are resulted from difference in time of use. Accordingly, it is difficult to exert the same tensile force to every film  38  having an individual difference of tensile force. Further, if an excessive tensile force is applied to a film  38 , the film  38  or a peripheral device may be broken. In order to solve this, the quantity of shrinkage of the lifting spring assembly  88  (the distance between the suspender ring  78  and the lifting disc spring  86 ) should be monitored. Namely, the tensile force applied actually to the film  38  is measured by observing not only the quantity of lifting by the screw jack  92  but also the quantity of shrinkage of the lifting spring assembly  88 . The provision of this lifting spring assembly  88  can solve simultaneously problems that a constant tensile force is applied to the film  38  and that an excessive tensile force is not applied to the film  38 . In order to obtain a constant tensile force, it is necessary to measure the quantity of shrinkage of the lifting spring assembly  88 . As one of techniques, the tensile force applied to the film  38  can be observed by calculating a torque of the screw jack  92  based on a current of the motor (not shown) connected to the screw jack via a line shaft  96  to obtain indirectly the lifting force of the screw jack  92  and by controlling the torque. The line shaft  96  is a shaft for transmitting the driving force of the motor to the screw jack  92 . Reference numeral  94  designates a stopper pin which bears the reaction force of the lifting spring assembly  88 , the reaction force generating between the suspender ring  78  and the lifting disc spring  86 . 
     A plurality of jet orifices  98 ,  98  . . . for discharging compressed air into the air chamber  54  are formed in the carrier  52 . These jet orifices  98 ,  98  . . . are communicated with an air supply channel  102 , indicated by a broken line in  FIG. 2 , via an air chamber  100  formed in an upper face of the carrier  52 . The air supply channel  102  is extended to the outside of each polishing head  50  via a rotary joint (not shown) attached to the polishing head  50  and is connected to an air pump  106  through a valve  104 . Accordingly, when the value  104  is opened, compressed air is supplied from the air pump  106  to the air chamber  54  through the air supply channel  102 , the air chamber  100  and the jet orifices  98 . Thus, the pressure of the compressed air is transmitted to the glass substrate G through the film  38  whereby the glass substrate G is pressed to the polishing pad  58  ( 60 ) to be polished. 
     Next, the structure of the attaching/detaching means for attaching the frame  14  to the slide-contact ring  82  or detaching the frame  14  from the slide-contact ring  82  will be described. 
     As shown in  FIG. 3 , a plurality of pins  108 ,  108  . . . are projected from an upper frame  40  of the frame  14  with equal intervals on a concentric circle. At the upper edge portion of each of the pins  108 , a large-sized head portion  110  is formed. Each head portion  110  is engaged with each hook  112  fixed to a lower portion of the slide-contact ring  82  whereby the frame  14  is attached to the slide-contact ring  82  as shown in  FIG. 5 . The engaging force between the head portion  110  and the hook  112  is increased by the reaction force of the film  38  when the film  38  is stretched by the screw jack  92 . Accordingly, there is no danger of disengaging of the head portion  110  from the hook  112  by the resistance of polishing given by the film  38  at the time of polishing. 
     The attaching/detaching structure of the frame  14  with respect to the slide-contact ring  82  is not limited to the structure as shown in  FIG. 5 , but it may have such a structure that the slide-contact ring  82  is made of a magnetic material, the upper frame  40  of the frame  14  is made of a magnet, and the frame  14  is attracted to the slide-contact ring  82  and held thereto by a magnetic force, for example, as shown in  FIG. 6(A) . In this structural example, a pin  114  is provided on the upper frame  40  so as to be inserted in a hole  116  formed in a lower face of the slide-contact ring  82  whereby a horizontal movement of the frame  14  to the slide-contact ring  82  is prevented. 
     In the structural example shown in  FIG. 6(B) , a frame  14  is attracted to a slide-contact ring  82  and is held thereto by a magnetic force in the same manner as  FIG. 6(A) . An inner peripheral surface of an upper frame  40  of the frame  14  is made contact with a stopper plate  118  attached to a lower surface of the slide-contact ring  82  whereby a horizontal movement of the frame  14  to the slide-contact ring  82  is prevented. 
     In the structural example shown in  FIG. 6(C) , an air passage  120  is formed in a slide-contact ring  82  and a suction pump is connected to the air passage  120 . The frame  14  is attracted to and held by the slide-contact ring  82  by sucking the upper frame  40  of the frame  14  through the air passage  120 . 
     In the structural example shown in  FIG. 6(D) , a frame  14  is held to a slide-contact ring  82  by a sucking force in the same manner as  FIG. 6(C) . A pin  114  of an upper frame  40  is inserted into a recess  116  in the slide-contact ring  82  whereby a horizontal movement of the frame  14  to the slide-contact ring  82  is presented. 
     In the structural example shown in  FIG. 6(E) , a clamper  122  is disposed in an outer peripheral portion of a frame  14  and an outer peripheral portion of a slide-contact ring  82  is clamped between the clamping plate  124  of the clamper  122  and the frame  14  whereby the frame  14  is attached to the slide-contact ring  82 . 
     In the structure shown in  FIGS. 7(A) and 7(B) , a pole  126  is provided on an upper frame  40  of a frame  14 . This pole  126  is inserted in a penetration hole  128  formed in a slide-contact ring  82 . A penetration hole  130  is formed in an upper end portion of the pole  126 . A pair of pin supporters  132 ,  132  each having a penetration hole  134  are fixed on an upper face of the slide-contact ring  82 . A stopper pin  136  is inserted in the penetration hole  130  of the pole and penetration holes  134 ,  134  of the pin supporters. Thus, the frame  14  is held by the slide-contact ring  82 . 
     In  FIG. 7 , the frame  14  is lifted upward along with the slide-contact ring  82  with a predetermined tensile force by an urging force of a lifting spring  88 . Even though a creep elongation generates in the film  38 , the film  38  is always subjected to a predetermined tensile force by the urging force of the lifting spring. The lifting spring  88  may be replaced by a unit such as hydraulic cylinder, air cylinder, disc spring, leaf spring or the like as long as a tensile force is applied to the film  38  automatically even though a creep elongation generates in it. For the purpose of automation, an actuator such as cylinder, motor or the like may be used. 
     The polishing of the glass substrate G is carried out by conveying the glass substrate G from the stage  16  to the first polishing stage  18  by the conveying device  150 , and by a conveying sequentially the glass substrate G from the first polishing stage  18  to the second polishing stage  20  by the conveying device  152 . When the polishing of the glass substrate G is finished in the second polishing stage  20 , the frame  14  is removed from the carrier  52 , and it is conveyed to the stage  22  by the conveying device  154 . The method for removing the frame  14  from the carrier  52  is described. First, the screw jack  92  as shown in  FIG. 5  is operated to reduce the tensile force of the film  38 . Then, the frame  14  is turned by a predetermined angle with respect to the carrier  52  to disengage the head portion  110  from the hook  112 . Thus, the frame  14  can be removed from the carrier  52 . 
       FIG. 8  shows an example of the conveying device  150  ( 152 ,  154 ). This conveying device  150  has holders  162 ,  162  for holding the upper frame  40  and the lower frame  42  of the frame  14 . These holders are arranged at both sides of the conveying route for the frame  14  and they are connected respectively to arms  166  of small robots  164  so that the holders are moved vertically and horizontally by the movement of the arms  166 . A guide block  168  is fixed to a lower portion of each small robot  164 , and this guide block  168  is fitted to each guide rail  170  which is arranged at each side of the conveying route for the frame  14 . Further, the feed screw of a feed screw unit (not shown) is engaged with each of the guide blocks  168  whereby the glass substrate G is held by the conveying device  150  ( 152 ,  154 ) and is conveyed to a predetermined position. 
     On the other hand, in the stage  22  shown in  FIG. 1 , the glass substrate G to which the polishing is finished is removed from the frame  14  conveyed by the conveying device  154 . The removed glass substrate G is conveyed by a conveyer  138  and is sucked to a suction head  144  attached to an arm  142  of a robot  140 . The robot  140  transfers the glass substrate onto the glass substrate discharging conveyer  24  to be discharged outside the polishing device  10 . 
     The frame  14  from which the glass substrate G is removed is conveyed to the frame washing stage  26  by means of a conveyer  146  to be washed with water. The washed frame  14  is conveyed to the frame drying stage  28  by a conveyer  148 , in which it is heated and dried. Then, the dried frame  14  is conveyed to the stage  16  by the frame returning conveyer  30  to be used again for attaching another glass substrate G. 
     According to the polishing device  10  for the glass substrate G, constructed as mentioned above, after the completion of the polishing of the glass substrate G in the second polishing stage  20 ′, the frame  14  is conveyed from the second polishing stage  20  to the stage  22  by the conveying device  154 , and in the stage  22 , the polished glass substrate G is removed from the frame  14 . Namely, the polishing device  10  of this embodiment is not constituted so that the glass substrate G is attached to the frame  14  to be attached to or detached from the carrier  52 , and after the completion of the polishing, the glass substrate G is removed from the frame  14  in the second polishing stage  20 , but is constituted so that the polished glass substrate G is removed from the frame  14  in the stage  22  located apart from the second polishing stage  20 . Accordingly, it is possible to solve the problem of discharging a special glass substrate G such as a large-sized glass substrate having, for example, a side exceeding 1,000 mm (the problem that it is very difficult to removing the glass substrate in the polishing stage, handling and discharging it, whereby it takes a long time, and therefore, productivity is decreased). Thus, productivity can be improved. 
     Further, in the polishing device  10 , the frame  14  from which the glass substrate G is removed is washed in the frame washing stage  26 , is dried in the frame drying stage  28 , then, is conveyed to the stage  16 , and is used repeatedly for attaching glass substrates G. Accordingly, it is enough to prepare the minimum necessary number of frames  14 . This contributes resource saving. 
     Further, according to the polishing device  10 , compressed air is supplied from the air pump  106  to the space between the carrier  52  and the film  38  of the frame  14  so that the glass substrate G is pressed to the polishing pad  58  ( 60 ) for polishing by the pressure of the compressed air. Accordingly, each portion of the glass substrate G is applied with a uniform pressure whereby the glass substrate G can be polished flat. Further, the polishing is not influenced by the surface configuration of the polishing pad  58  ( 60 ). Namely, even though the front surface of the polishing pad  58  ( 60 ) has more or less undulation, there is no danger that the undulation is transferred to the glass substrate G. Accordingly, it is unnecessary to finish precisely the polishing pads  58  ( 60 ), and therefore, cost for the polishing pads  58  ( 60 ) can be suppressed. 
     Further, the film  38  of the frame  14  has a three-layer structure comprising the air-tightness retention layer  44 , the strength retention layer  46  and the smooth layer  48 . Accordingly, the glass substrate G can be held stably on the film  38 , and therefore, the glass substrate G can be polished with precision. 
     Further, the strength retention layer  46  is made of alamide fibers, a mesh of stainless steel, a mesh of steel, carbon fibers, glass fibers, nylon fibers, a metal sheet, a resin sheet or a material having the same tensile strength as these materials. Accordingly, when the glass substrate G is pressed to the polishing pads  58  ( 60 ) with a pressing force suitable for the polishing, the strength of the film  38  can be assured. 
     Here, the tensile strength described herein indicates a tensile strength ruled in JIS L1096 (1999) or the standard pursuant thereto, when the strength retention layer  46  is made of fabric, and indicates a tensile strength used commonly when it is made of a resin sheet or metal sheet (for example, JIS K7161 (1994) in a case of plastics, or a standard pursuant thereto, the same as in the case of metal). 
       FIG. 9  shows another example of the process for attaching a glass substrate G to a frame  14  with respect to a carrier  52 . This attaching process is carried out in the stage  16 . 
     As shown in  FIG. 9(   a ), an unpolished glass substrate G is placed on a table  200  provided in the stage  16 , and the frame  14  is supported above by means of jacks  202 ,  202 . On the other hand, the carrier  52  is above the frame  14  in a standby state. This state is an initial state of attaching.  FIG. 9(   b ) shows a state that the carrier  52  is moved downward from the initial state of attaching to contact the frame  14 . This state is a state of initiating the attachment of the frame  14  by utilizing screw jacks  92  or the like. 
     Then, as shown in  FIG. 9(   c ), the head portion  110  of the pin  108  (see  FIG. 5)  of the frame  14  is engaged with the hook  112  fixed to the lower portion of the slide-contact ring  82 . Then, the screw jacks  92  are driven to stretch the film  38  of the frame  14  to have a predetermined tensile force. Thus, the frame  14  is attached to the carrier  52 . 
       FIGS. 9(   d ) and  9 ( e ) show the process for attaching the glass substrate G to the film  38  of the frame  14 . First, as shown in  FIG. 9(   d ), air is supplied to the air chamber  54  via the air supply channel  102  to inflate the film  38  so that the film  38  is attached to the entire surface of the glass substrate G. When the attaching is completed, air in the air chamber  54  is released through the air supply channel  102  to shrink the film  38  as shown in  FIG. 9(   e ). Thus, both the operation of attaching the frame  14  to the carrier  52  and the operation of attaching the glass substrate G to the frame  14  can be carried out in a single stage  16 . 
       FIG. 10  shows the process for removing a polished glass substrate G from a frame  14 , the process being carried out in the stage  22 . 
     As shown in  FIG. 10(   a ), when the carrier  52  is located above a table  204  located in the stage  22 , air is supplied to an air chamber  54  via an air supply channel- 102  to inflate the film  38 . This state is an initial state for separating the glass substrate G. By causing this state, the glass substrate G can easily be separated from the film  38  due to a relative change of position between the glass substrate G and the film  38  and the elastic force of glass substrate G by which the glass substrate tends to be flat. Namely, the process for separating the substrate, which conventionally imposed a burden to the equipment for separating, can be easy by inflating the film  38 . 
     In this embodiment, an attempt is made to shorten the tact. Namely, as shown in  FIG. 10(   b ), water and air, or only water, or only air (fluid) is injected through a plurality of air jet nozzles  206 ,  206  (which may be water jet nozzles, as supply means for supplying fluid for separation) which are arranged at opposed positions with respect to edge portions of the glass substrate G, to the boundary between the edge portions of the glass substrate G and the film  38 . Thus, the glass substrate G is separated from the film  38  by the energy of the injection as shown in  FIG. 10(   c ) although the nozzles  206  are omitted in  FIG. 10(   c ). 
       FIG. 10(   d ) shows a state that the glass substrate G is separated completely from the film  38  and is placed on the table  204 . Then, the glass substrate G is conveyed by the conveyer  138  shown in  FIG. 1 , is transferred on the glass substrate discharging conveyer  24  by means of a robot  140 , and is discharged outside the polishing device  10 . 
     On the other hand, when the glass substrate G is separated completely from the film  38  as shown in  FIG. 10(   d ), the frame  14  is removed from the carrier  52  by means of a removing device to place it on jacks  208 ,  208  as shown in  FIG. 10(   e ). This frame  14  is conveyed to the frame washing stage  26  by the conveyer  146  shown in  FIG. 1 . 
       FIG. 11  is a front view of a polishing device  300  according to a second embodiment wherein the same reference numerals designate the same or similar parts as the polishing device  10  according to the first embodiment shown in  FIGS. 1 to 10 . 
     The characteristic feature of the polishing device  300  shown in  FIG. 11  resides in that two polishing heads  50 A,  50 B are moved horizontally along a rail  302  to transfer the frame  14  (see  FIG. 3 ) to not only from the first polishing stage  18  to the second polishing stage  20  but also from a frame installing stage  304  to the first polishing stage  18  and from the second polishing stage  20  to a frame removing stage  306 . With this, the tact for manufacture can be improved. 
     The polishing device  300  comprises mainly a plate attaching shuttle  310  with a table  308  on which an unpolished glass substrate G is placed, a glass substrate attaching stage  16  having a press roller  312 , a frame installing stage  304  for installing the frame  14  on the carrier  52 , a first polishing stage  18 , a second polishing stage  20  and a frame removing stage  306  for removing the frame  14  from the carrier  52 . The frame removing stage  306  serves as a glass substrate removing stage  22  in which the polished glass substrate G is removed from the frame  14 . Reference numeral  314  designates a plate separating shuttle for discharging the polished glass substrate G from the glass substrate removing stage  22 . The polishing device  300  is also provided with a frame washing stage, a frame drying stage and a frame returning conveyer in the same manner as the polishing device  10  although these elements are omitted in  FIG. 11 . 
     In the following, the sequence of polishing the glass substrate G by the polishing device  300  will be described. 
     On the table  308  of the plate attaching shuttle  310  in the glass substrate attaching stage  16  in a standby state, a glass substrate G conveyed by a robot (not shown) is placed so that the surface to be polished faces downward. The table  308  is mounted on the plate attaching shuttle  310  by interposing an elevating device  316 . When the glass substrate G is placed on the table, the elevating device is elongated so that the table projects slightly from an upper edge portion  311  of the shuttle on which the frame  14  is placed. The upper edge portion  311  has the shape corresponding to the shape of the frame  14 . Namely, when the frame  14  is rectangular, it has also a rectangular shape. 
     Then, the plate attaching shuttle  310  is moved from the glass substrate attaching stage  16  to the frame installing stage  304  and the table  308  is moved lower than the upper edge portion  311  of the plate attaching shuttle  310  so as not to interfere the positioning of the frame  14  as shown in  FIG. 12 . Then, in the frame installing stage  304 , the frame  14  conveyed by the frame returning conveyer (not shown) is placed on the upper edge portion  311  of the plate attaching shuttle  310  so that the film  38  of the frame  14  is positioned above the glass substrate G. In this case, it is preferable to provide a plurality of guide rollers on the upper edge portion  311  in order to make the positioning of the frame  14  easy. 
     When the plate attaching shuttle  310  receives the frame  14 , the shuttle  310  is moved to the glass substrate attaching stage  16  as shown in  FIG. 13 . In association with this moving action, the press roller  312  positioned above the glass substrate attaching stage  16  in a standby state is descended by the extension of a cylinder unit  313  to press the film  38  to the glass substrate G. This press roller  312  has a longer width than the width of the glass substrate G (the length in a direction perpendicular to the moving direction). The operational timing of the attaching is controlled by a controller (not shown) so that the film  38  is pressed to the glass substrate G on the moving plate attaching shuttle  310  just before the front edge portion of the moved glass substrate G passes just below the press roller  312 . Further, the press roller  312  continues the pressing operation until the rear edge portion of the moved glass substrate G on the plate attaching shuttle  310  passes away as shown in  FIG. 14 . The operational timing of the press roller is controlled by the controller so that it is retracted upward from the pressing position to the film  38  as shown in  FIG. 15 . 
     With the pressing operation of the press roller  312  and the movement of the plate attaching shuttle  310 , the film  38  is attached to the glass substrate G in the glass substrate attaching stage  16  without causing air bubbles between the film  38  and the glass substrate G. 
     The attaching of the glass substrate G with use of the press roller  312  is effective for a polishing device for polishing, in particular, a large-sized glass substrate. In the case of a small-sized glass substrate, the glass substrate can be attached to the film  38  without causing air bubbles between the glass substrate and the film  38  by pressing simply the film  38  to the glass substrate. The presence of air bubbles reduces the attaching strength. Accordingly, the quantity of air bubbles should be reduced as possible in order to assure the attaching. On the other hand, in the case of a glass substrate having a large surface area, if the glass substrate is simply pressed to the film  38 , the quantity of air bubbles increases because both the glass substrate and the film have a high flatness. Accordingly, the film  38  is pressed to the glass substrate G by the aid of the press roller  312  to attach them while air bubbles existing between the film  38  and the glass substrate G are discharged outside forcibly. Thus, the glass substrate G can certainly and strongly be attached to the film  38  even in the case of glass substrate G of large surface area. In this embodiment, the attaching is carried out by moving the frame  14  and the glass substrate G with respect to the press roller  312 . However, the attaching may be carried out by moving the press roller  312  with respect to the frame  14  and the glass substrate G. Further, the press roller is preferably made of a flexible material without causing the damage of the film  38 , such as plastic, rubber, urethane or the like. It goes without saying that the pressing force of the press roller  312  is determined so as not to damage the glass substrate G. 
     The frame  14  with the film  38  attached with the glass substrate G is conveyed by the plate attaching shuttle  310  to the position just below the frame installing stage  304  as shown in  FIG. 16 . Then, the elevating device  316  of the plate attaching shuttle  310  is driven to raise the frame  14  toward the carrier  52  of the polishing head  50 A so that the frame  14  is installed on the carrier  52 . Then, the screw jacks  92  are operated to lift the frame  14  so that the film  38  has a predetermined tensile force. Thus, the installation of the frame  14  on the carrier  52  of the polishing head  50 A is completed. 
     Here, when the film  38  is stretched by the operations of the screw jacks  92 , a local portion of the film  38  may deviate with respect to the glass substrate G to reduce the attaching strength. In order to avoid such disadvantage, the table  308  is raised slightly by the elevating device  316  so that the glass substrate G is pressed to the film  38  by the table  308  as shown in  FIG. 18 . Thus, the secondly attaching of the glass substrate G to the film  38  prevents the frame  14  from dropping from the polishing head  50 A when the frame  14  is conveyed by the polishing head  50 A. 
     The film  38  may be attached to the glass substrate G in the glass substrate attaching stage  16  after the frame  14  is installed on the polishing head  50 A in the frame installing stage  304 . 
     When the installation of the frame  14  is finished in the frame installation stage  304 , the plate attaching shuttle  310  is returned to the glass substrate attaching stage  16  as shown in  FIG. 19 , and the shuttle is remained on standby at this position until another glass substrate G is placed on the table  308 . 
     On the other hand, the polishing head  50 A on which the frame  14  is installed is moved along the rail  302  to the first polishing stage  18 , and the first glass substrate G attached to the frame  14  is pressed to the polishing pad  58  of the first polishing stage  18  and is subjected to rough polishing, as shown in  FIG. 20 . During the rough polishing, the second glass substrate G is placed on the table  308  of the plate attaching shuttle  310  and the glass substrate is conveyed by the plate attaching shuttle  310  to the frame installation stage  304  as shown in  FIG. 20 . Then, a frame  14  is placed on the plate attaching shuttle  310 . 
     When the second frame  14  is placed on the plate attaching shuttle  310 , the film  38  of the first frame  14  is conveyed from the rough polishing process in the first polishing stage  18  as shown in  FIGS. 21 to 25  to the second polishing stage  20 . In the meantime, the film is pressed to a second glass substrate G by means of the press roller  312  to perform the attaching. Explanation of the attaching process by the press roller  312  is omitted because it is the same as that shown in  FIGS. 13 to 15 . The second glass substrate G in a standby state in that it is attached completely to the film  38 . When the rough polishing is finished in the first polishing stage  18 , the polishing head  50 A is moved along the rail  302  to the second polishing stage  20 . 
     After the movement to the second polishing stage  20 , the screw jacks  92  of the polishing head  50 A are relaxed in the state that the glass substrate G is placed on the polishing pad  60 , and the frame  14  is removed from the polishing head  50 A. Then, the polishing head  50 A is raised in the state that the frame  14  is placed on the polishing pad  60  as shown in  FIG. 26 . During this time, the second glass substrate G is attached to the frame  14  and is in a standby state in the frame installing stage  304 . 
     Then, the polishing head  50 A is moved to the frame installing stage  304 , and the polishing head  50 B which is in a standby state in the substrate removing stage  22  (frame removing stage  306 ) is moved to the second polishing stage  20  in which the frame  14  on the polishing pad  60  is installed on the polishing head  50 B. In this case, the position of the film  38  with respect to the glass substrate G may deviate to cause a reduction of the attaching force since tensile force is again imparted to the relaxed film  38  by the screw jacks  92 . To avoid this, compressed air (see  FIG. 5 ) is supplied to the space between the carrier  50  of the polishing head  50 B and the film  38  after the film is stretched by the screw jacks  92 , so that the film  38  can be pressed to the glass substrate G as shown in  FIG. 28 . Accordingly, the secondary attaching of the film to the glass substrate G is performed whereby the dropping of the glass substrate from the polishing head  50 B can be prevented. Then, the glass substrate G is subjected to fine polishing by the polishing pad  60  of the second polishing stage  20  in the state that the glass substrate is attached to the side of the polishing head  50 B. On the other hand, another frame  14  is attached to the polishing head  50 A. 
     When the next frame  14  is attached to the polishing head  50 A, the polishing head  50 A is moved to the first polishing stage  18  and the second glass substrate G is subjected to rough polishing in the stage  18  as shown in  FIG. 29 . During the rough polishing, the plate separating shuttle  314  is moved to the substrate removing stage  22  (frame removing stage  306 ) to be in a standby state. Then, the polishing head  50 B is moved to the substrate removing stage  22  (frame removing stage  306 ) as shown in  FIG. 30 . The plate separating shuttle  314  has a table  320  for the glass substrate G and the table  320  is provided on the shuttle main body  324  by interposing an elevating device  322 . 
     When the plate separating shuttle  314  is moved to the substrate removing stage  22  (frame removing stage  306 ), the screw jacks  92  of the polishing head  50 B are relaxed so that the frame  14  is removed from the polishing head  50 B and is placed on the upper edge portion  328  of a conveying table  326  as shown in  FIG. 31 . 
     Then, air (water: fluid) is injected from a plurality of air jet nozzles (which may be water jet nozzles: a supply means for supplying fluid for separation) provided on the conveying table  326  to the boundary between edge portions of the glass substrate G and the film  38  to separate the glass substrate G by utilizing the energy of the injected fluid as shown in  FIG. 32 . The separated glass substrate G is placed on the table  320  of the plate separating shuttle  314  as shown in  FIG. 33 . During the separating operation of the glass substrate G, the second glass substrate G is conveyed to the second polishing stage  20  by means of the polishing head  50 A. The frame  14  is removed from the polishing head  50 A, and the polishing head  50 A is moved to the frame installing stage  304 . Then, the polishing head  50 B is moved to the second polishing stage  20 . Then, the glass substrate G is subjected to fine polishing by the polishing pad  60  of the second polishing stage  20  in the state that it is attached to the side of the polishing head  50 B. 
     Instead of separating forcibly the glass substrate G from the film  38  by utilizing the fluid in the substrate removing stage  22  (frame removing stage  306 ), the glass substrate G can be separated from the film  38  by its own weight, without using fluid. Then, the separated glass substrate G is placed on the carriage  320  of the plate separating shuttle  314  and is conveyed from the substrate removing stage  22  (frame removing stage  306 ) to a product storage space as shown in  FIG. 34 . By repeating the above-mentioned series of operations, glass substrates G can continuously be polished with good efficiency. 
     Further, the frame  14  may be removed from the polishing head  50 B after the glass substrate G is separated from the film  38  in the substrate removing stage  22  (frame removing stage  306 ). 
       FIGS. 35 and 36  are diagrams showing the structure for determining the position of the frame  14  with respect to the slide-contact ring  82  of the carrier  52 . In  FIG. 35 , a plurality of pins  340 ,  340  . . . (only two pins are shown in  FIG. 35 ) are provided on the frame  14  and openings  342 ,  342  . . . to be fitted with these pins  340 ,  340  . . . are formed in the slide-contact ring  82 . By fitting the pins  340 ,  340  . . . to the openings  342 ,  342  . . . , the position of the frame  14  with respect to the slide-contact ring  82  is determined. 
     A predetermined number of pins  340  among the plurality of pins  340 ,  340  . . . are attached to the frame  14  so as to be swung as shown in  FIG. 35 , and the remaining pins  340  are fixed firmly to the frame  14  in order to determine the position of the frame with respect to the carrier. 
     The attachment of the pins  340  to the frame  14  so as to be swung is effective for the polishing device for polishing, in particular, a glass substrate G having a large surface area. In the case of connecting the frame  14  to the slide-contact ring  82  (i.e., the carrier  52 ) for determining mutual positions by fitting the plurality of pins  340 ,  340  . . . provided on the frame  14  to the plurality of openings  342 ,  342  . . . formed in the slide-contact ring  82 , if the frame is a small-sized frame, the pins  340  can be attached with high precision. Accordingly, all the pins  340 ,  340  . . . can be fitted to the openings without any difficulty even though the all pins  340 ,  340  . . . are attached fixedly to the frame. 
     On the other hand, in the case of using a large-sized frame  14  for attaching a glass substrate G having a large surface area, it is difficult to attach the pins  340  with higher precision. Accordingly, if all the pins  340 ,  340  . . . are attached fixedly to the frame  14 , it is difficult to fit all the pins  340 ,  340  . . . into the openings  342 ,  342  . . . . On the other hand, if all the pins  340 ,  340  . . . are attached to the frame  14  so as to be swung, the fitting of the pins  340 ,  340  . . . can be easy because error in the attachment can be absorbed by the swinging movement of the pins. In this case, however, if the all the pins  340 ,  340  . . . are provided so as to be swung, the position of the frame  14  becomes unstable because there is a possibility of shift of the frame  14  with respect to the carrier  52 . Further, there is a possibility that the pins  340  can not withstand the shearing force applied by the polishing pad  58  ( 60 ) at the time of polishing. 
     Accordingly, in the embodiment as shown in  FIG. 35 , a predetermined number of pins  340  among the plurality of pins  340 ,  340  . . . are attached to the frame  14  so as to be swung so that error in the attachment can be absorbed by these swing pins  340 . The remaining pins (e.g., two pins)  340 ,  340  are attached fixedly to the frame  14  so that these pins  340 ,  340  . . . can withstand the shearing force applied from the polishing pad  58  ( 60 ). Accordingly, the large-sized frame  14  can be positioned precisely to the carrier  52  and a steady connection can be assured. 
     Further, each pin  340  has a tapered portion at its tip portion  344  so as to make the fitting of the pin  340  to the opening  342  easy, and further, a thin portion  346  is formed at the boundary between the tip portion  344  and a cylindrical main body portion  341 . The thin portion  346  projects from the opening  342  when the pin  340  is fitted to the opening  342 . Further, the thin portion is fitted to a circular-arc-like fitting portion  352  of a hook  350  shown in  FIG. 36 . This hook  350  is attached to the carrier  52  so as to be rotatable around a fixed support O. When the hook is rotated in a counterclockwise direction from the state shown in  FIG. 36  (A), the hook is fitted to the thin portion  346  of the pin  340 . Thus, the frame  14  can be held on the carrier  52  by engaging the pin  340  with the hook  350 . 
       FIG. 37  is a diagram showing another embodiment of the glass substrate attaching stage  16  shown in  FIG. 11 , in which a film pressing balloon  360  is provided in addition to the press roller  312 . 
     The film pressing balloon  360  is made of rubber and is formed to have a circular shape. The balloon is disposed to close the opening at a lower portion of a head  362 . The balloon  360  is inflated by supplying compressed air from an air supply source (not shown) into the space between the head  362  and the film pressing balloon. 
     The head  362  is attached to a support frame  364  for supporting the press roller  312  via a cylinder unit  366  so as to be ascended and descended, namely, the head is advanced and retracted with respect to the frame  14  disposed above the glass substrate G. 
     An example of the attaching method using the film pressing balloon  360  will be described. First, before the attaching by using the press roller  312 , the film pressing balloon  360  inflated is pressed to the central portion of the film  38  to contact closely the central portion of the film  38  to the glass substrate G. Then, the film pressing balloon  360  is retracted upward from the frame  14 , and then, the attaching by the press roller  312  is initiated. Thus, it is possible to carry out the stable attaching without air bubbles between the film  38  and the glass substrate G. 
     INDUSTRIAL APPLICABILITY 
     As described above, in the method and device for polishing a substrate according to the present invention, a substrate is attached to a frame which can be attached to or detached from a carrier, and after the completion of the polishing in a polishing stage, the polished substrate is removed from the frame in a substrate removing stage which is remote from the polishing stage. Accordingly, it is possible to solve the problems of the reduction of productivity due to the stopping of the polishing machine when a large-sized substrate is removed and discharged. Therefore, productivity can be improved remarkably. Namely, when a substrate is polished, another substrate can be attached to a frame or another substrate having been subjected to polishing can be removed. Accordingly, stable working can be assured and a large-sized substrate can safely be polished with stable quality. 
     Further, in the present invention, the frame from which a substrate is removed is washed in a washing stage and then, the frame can be used for attaching another substrate. Accordingly, it is enough to prepare a necessary minimum number of frames, and therefore, it serves resource saving. 
     In addition, in the present invention, pressurized fluid is supplied from a supply means for supplying pressurized fluid for polishing between the carrier and the film of a frame so that the substrate is pressed for polishing to a polishing surface-plate by the pressure of the pressurized fluid. Accordingly, each portion of the substrate is applied with uniform pressure and therefore, the substrate can be polished flat. 
     Further, the film of the present invention has a three-layered structure comprising an air-tightness retention layer having its outer peripheral portion in contact hermetically with the carrier to thereby maintain air-tightness with respect to the carrier, a strength retention layer holding the air-tightness retention layer and having a predetermined tensile strength durable to a tensile force for stretching the film and a smooth layer to which the substrate is attached. Accordingly, the substrate can stably be held by the film and the substrate can be polished with high precision. 
     In addition, the strength retention layer of the film is made of alamide fibers, a mesh of stainless steel, a mesh of steel, carbon fibers, glass fibers, nylon fibers or a material having the same tensile strength as these materials. Accordingly, it is possible to guarantee the strength of the film when the substrate is pressed to the polishing surface-plate with a pressing force suitable for polishing. 
     Further, in the present invention, the substrate can be separated from the frame by a separating function which is obtained by supplying fluid from a supply means for supplying fluid for separation to the boundary between the film of the frame and edge portions of the substrate. Accordingly, the substrate can be separated from the frame in a shorter time to thereby improve productivity. 
     Further, in the present invention, the substrate is placed on a table in a substrate attaching stage, and then, the film of a frame is put on the substrate placed on the table, and then, a press roller is pressed to the film on the substrate while the table and the press roller are moved relatively along the surface of the film by a moving means whereby the substrate is attached to the film by the press roller. Accordingly, the substrate can certainly and firmly attached to the film even when the substrate has a large surface area. 
     Further, in the present invention, the frame and the carrier are attached to or detached from each other by means of a plurality of pins wherein a predetermined number of pins among the plurality of pins are attached to the frame so as to be swung, and the remaining pins are attached fixedly to the frame so as to serve the determination of the position with respect to the carrier. Accordingly, the position of a large-sized frame to the carrier can be correct and they can stably be connected. 
     The entire disclosure of Japanese Patent Application No. 2002-223001 filed on Jul. 31, 2002 including specification, claims, drawings and summary is incorporated herein by reference in its entirety.