Abstract:
A substrate processing system for processing a substrate in accordance with a photolithographic process, comprising a cassette section, a process section having a plurality of process units each processing a substrate, main transfer arm mechanism arranged in a transfer space surrounded by the process section and the cassette section, for transporting substrates one by one not only between a cassette of the cassette section and each of the plurality of process units but also between the plurality of process units, and a loop transfer path movably supporting the main transfer arm means in a lower portion of the transfer space and guiding the main transfer arm means so as to face each of the process units and the cassette section.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-162562, filed Jun. 9, 1999; and No. 11-350144, filed Dec. 9, 1999, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a substrate processing system for processing a substrate such as a semiconductor wafer in accordance with a photo-lithographic process. 
     In a manufacturing process of a semiconductor device, a semiconductor wafer is coated with a resist, and then the resist coating film is baked, exposed to light, and developed. Such a manufacturing process is carried out by using a substrate processing system (coating/developing system) disclosed in U.S. Pat. No. 5,664,254. In this system, resist coating, baking, and developing treatments excluding a light-exposure treatment are applied to a wafer. The process units are vertically stacked in multiple stages. A wafer is transferred to each of the process units by a main transfer arm mechanism which moves up and down along a transfer space arranged at the center of the system. 
     In the near future, the diameters of the wafers are planned to be changed from 8-inches to 12-inches (300 mm). When a large-size wafer is processed in accordance with a conventional system, the apparatus having quite a large footprint is required. In addition, the transfer arm must be moved horizontally for a long distance to transfer the large-size wafer, in other words, the moving stroke of the transfer arm becomes excessively long. As a result, the main transfer arm mechanism itself is enlarged more than required. Furthermore, the conventional system has a problem of a low maintainability since a maintenance operation must be applied from the outside the system. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a substrate processing system for processing a large substrate with a high throughput, characterized in that a transfer mechanism has a compact size with a small footprint, and excellent maintainability. 
     According to the present invention, there is provided a substrate processing system for processing a substrate in accordance with a photolithographic process, comprising: 
     a cassette section; 
     a process section having a plurality of process units each processing a substrate; 
     main transfer arm means arranged in a transfer space surrounded by the process section and the cassette section, for transporting substrates one by one not only between a cassette of the cassette section and each of the plurality of process units but also between the plurality of process units; and 
     a loop transfer path movably supporting the main transfer arm means in a lower portion of the transfer space and guiding the main transfer arm means so as to face each of the process units or the cassette section. 
     According to the present invention, the distance from the main transfer arm mechanism to each of the process units is shortened by a radius of the loop transfer path. It is therefore possible to smoothly load a large substrate into the process unit. As a result, the throughput increases. In addition, since the foot print of the system is reduced, the main transfer arm means is prevented from being enlarged. 
     Furthermore, according to the present invention, it is possible to increase the transfer space itself. Therefore, the maintainability of the main transfer arm mechanism and the process unit can be improved. 
     In the case where the cassette section has a plurality of cassette tables vertically stacked in multiple stages and the process section has a plurality of process units vertically stacked in multiple stages, the main transfer arm means comprises 
     a holder for holding the substrate; 
     a loop moving mechanism for moving the holder along the loop transfer path; 
     an up-and-down moving mechanism for moving the holder up and down; and 
     a back-and-forth moving mechanism for moving the holder back and forth. 
     The loop transfer path has a pair of support guide rails; and 
     a monorail having a rectangular sectional shape and interposed between the pair of support guide rails. 
     The loop moving mechanism comprises a cart having an upside-down U-letter sectional shape; 
     a plurality of wheels attached to the lower portion of the cart and driven to rotate on the support guide rails; 
     at least one pair of moving rollers attached to a depressed portion of the cart in contact with a side surface of the monorail; 
     a plurality of follower rollers driven to rotate on the monorail; and 
     a motor for initiating rotation of the driving roll. 
     The main transfer arm means comprises 
     a cylindrical support; 
     a plurality of holders for holding the substrate; 
     an up-and-down moving mechanism for moving the plurality of holders up and down in the cylindrical support; 
     a loop moving mechanism for moving the plurality of holders together with the cylindrical support along the loop transfer path; and 
     a plurality of back-and-forth moving mechanisms for independently moving the holders back and forth. 
     Each of the plurality of process units has a substrate loading/unloading port formed facing up so as to face the transfer space. 
     The process section comprises 
     a coating unit for applying a resist solution to the substrate; 
     a developing unit for developing a resist film applied on the substrate; and 
     a thermal processing unit for applying a heat treatment to the substrate. 
     It is preferable that the system of the present invention should further comprise a clean-air supply mechanism for supplying a down-flow of clean air into a space formed between adjacent process units. As the clean air supply mechanism, it is desirable to use an air cleaning unit having a fan filter unit (FFU) and an alkaline substance removing mechanism. 
     The system of the present invention may further comprise an interface section for transferring the substrate to/from a light exposure apparatus and for transferring the substrate to/from a washing apparatus. 
     The interface section is desirably arranged near the transfer space and in a position accessible by the main transfer arm means. 
     FIG. 1 shows a schematic structure of a conventional substrate transfer system. A main transfer arm mechanism  200  has a transfer table  203  having two holders  201 ,  202  capable of holding the wafer W in upper and lower portions and a liftable rotating mechanism  204  for moving the transfer table  203  up and down and rotating it by an angle of θ. The holders  201 ,  202  can be moved back and forth by a moving mechanism (not shown) housed in the transfer table  203 , in the direction indicated by a double-headed arrow  210 . 
     However, since a single main transfer arm mechanism  200  transports the wafer W between various process units and loads/unloads the wafer W into/from various process units in the conventional system, the wafer W is not transferred between the process units  206  at the same time as the wafer W is loaded/unloaded into/from the various process units  206 . As a result, it is impossible to reduce the time required for coating/developing the wafer W. 
     Furthermore, if the up-and-down movement, rotation of the transfer table  203 , and back-and-forth movement of the holders  201 ,  202  are performed by the main transfer arm mechanism  200 , the burden on the main transfer arm mechanism becomes significantly high, with the result that the transfer of the wafer W is delayed. 
     When the wafer is exposed to light in a light-exposure apparatus, the wafer is first mounted on the delivery table, and then, the wafer is transferred to a wafer holder used exclusively for transferring the wafer from the delivery table to the light-exposure apparatus. While the wafer remains on the delivery table, if another wafer is delivered there, the wafer holder cannot transfer the newly transferred wafer to the delivery table. Therefore, the transfer of the wafer is further delayed. 
     The present inventors conducted intensive studies to solve the aforementioned problems. As a result, they made the present invention. 
     According to the present invention, there is provided a substrate processing system for processing a substrate in accordance with a photolithographic process, comprising: 
     a cassette section; 
     a process section having a plurality of process units vertically stacked in multiple stages; 
     a plurality of circularly moving main transfer arm mechanisms arranged in a transfer space surrounded by the process section and the cassette section, and arranged at different heights corresponding to positions of the process units vertically stacked in multiple stages, for transferring substrates one by one not only between a cassette of the cassette section and each of the plurality of process units but also between the plurality of process units; and 
     a loop transfer path movably supporting the circularly moving the main transfer arm mechanisms and guiding the circularly moving main transfer arm mechanisms so as to face each of the process units and the cassette section; 
     a plurality of delivery tables arranged in a middle region of the transfer space and arranged at different heights corresponding to positions of the process units stacked in the multiple stages; and 
     a vertical transfer arm mechanism arranged at the middle region of the transfer space, for transferring the substrates one by one to/from each of the circularly moving transfer arm mechanisms via the delivery table. 
     Each of the circularly moving transfer arm mechanisms comprises 
     a holder for holding the substrate; 
     a loop moving mechanism for moving the holder along the loop transfer path; 
     a θ rotary moving mechanism for rotating the holder about a vertical shaft; and 
     a back-and-forth moving mechanism for moving the holder back and forth. 
     The vertical transfer arm mechanism can possess one or two or more holders. It is preferable that the vertical transfer arm mechanism should have a plurality of holders. This is because the throughput can increase. 
     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention. 
     FIG. 1 is a schematic perspective view of a conventional apparatus; 
     FIG. 2 is a perspective sectional view of an inner structure of a substrate processing apparatus according to an embodiment of the present invention, as viewed from above; 
     FIG. 3 is a schematic perspective view of a substrate processing apparatus according to the embodiment of the present invention; 
     FIG. 4 is a schematic front view showing a thermal process unit group; 
     FIG. 5 is a schematic front view showing a cassette section; 
     FIG. 6 is a cross-sectional view showing a main transfer arm mechanism; 
     FIG. 7 is a schematic plan view showing a wafer holder of the main transfer arm mechanism; 
     FIG. 8 is a perspective sectional view of a substrate processing apparatus according to another embodiment of the present invention, as viewed from above; 
     FIG. 9 is a perspective side sectional view of an inner structure of a substrate processing apparatus according to another embodiment of the present invention, as viewed from side; 
     FIG. 10 is a perspective view showing an vertical transfer arm mechanism according to another embodiment; 
     FIG. 11 is a perspective view showing a circularly-moving transfer arm mechanism according to another embodiment; and 
     FIG. 12 is a vertical transfer arm mechanism according to another embodiment. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Now, various preferred embodiments of the present invention will be explained with reference to the accompanying drawings. In the first place, a substrate processing system according to a first embodiment of the present invention will be explained with reference to FIGS. 2-7. 
     Reference numeral  1  denotes a substrate processing system which is surrounded by an exterior jacket  8  made of a metal plate. The substrate processing system has a cassette section  4 , process section  5 , and first and second interface sections  6 ,  7  and a main transfer arm mechanism  10 . A side door  80  is formed in the exterior jacket  8 . A cassette  9  is loaded/unloaded into/from the cassette section  4  by opening the side door  80 . The cassette section has a receipt portion  4 A and a deliver section  4 B. A cassette  9  storing unprocessed wafers W is loaded into the receipt portion  4 A. A cassette  9  storing processed wafers W is unloaded from the deliver portion  4 B. 
     The process section  5  has four process unit groups G 1 , G 2 , G 3 , G 4 , which are arranged so as to surround a transfer space  2  of the center of the system  1 . Process units of each of the process unit groups G 1 , G 2 , G 3 , G 4  are vertically stacked in multiple stages. 
     The system  1  is connected to a light-exposure apparatus  40  via the first interface section  6 . The wafer W is transferred between a transfer unit (not shown) and the main transfer arm mechanism  10 . The system  1  is connected to a washing apparatus  50  via the second interface section  7 . The wafer is transferred between a transfer unit (not shown) and the main transfer arm mechanism  10 . 
     As shown in FIG. 2, the first process section G 1  and the second process section G 2  are arranged next to each other. The third process section G 3  and the fourth process section G 4  are arranged next to each other. The first interface section  6  is arranged between the cassette section  4  and the second process section G 2 . The second interface section  7  is arranged between the first process section G 1  and the fourth process section G 4 . Clean air is downwardly supplied from a fine filter unit  99  (shown in FIG. 4) to the transfer space  2  and dead spaces  88   a ,  88   b ,  88   c ,  88   d ,  88   e ,  88   f ,  88   g . An exhaust apparatus (not shown) is arranged at a floor portion of the system  1 , for exhausting air which has passed through the system  1 . Note that various connecting lines and pipes may be arranged in the dead spaces  88   a ,  88   b ,  88   c ,  88   d ,  88   e ,  88   f ,  88   g.    
     Each of the process units of the process unit groups G 1 , G 2 , G 3 , G 4  has a loading/unloading port for loading and unloading the wafer W. The loading/ unloading port faces the transfer space  2 . 
     A loop transfer path  3  is arranged in the center of a lower portion of the transfer space  2 . A main transfer arm mechanism  10  moves on the loop transfer path  3 . The loop transfer path  3  is arranged so as to keep substantially the same distance from the main transfer arm mechanism  10  to each of the process units. 
     As shown in FIG. 3, a door  82  is attached at the lower portion of the exterior jacket  8 . An operator can enter the transfer space  2  by opening the door  82 . A resist solution tank  83  and a developing liquid tank  84  are arranged at the lower portion of the transfer space  2 . 
     The first process section G 1  has two developing units (DEV) stacked one upon the other. The second process section G 2  has a developing unit (DEV) and a resist coating unit (COT) stacked one upon the other. In each of the developing unit and the resist-coating unit (COT), a nozzle (not shown) and a cup  90  are arranged. A spin chuck (not shown) is arranged in the cup  90 . 
     As shown in FIG. 4, eight thermal process system units are stacked in multiple stages in each of the third and fourth process sections G 3 , G 4 . Each unit has a mounting table  92  on which a wafer W is mounted. The cooling unit (COL) has a mechanism for cooling the wafer W. An adhesion unit has a mechanism for applying an adhesion treatment to the wafer W. An alignment unit (ALIM) has a mechanism for aligning the wafer W. An extension unit (EXT) has a mechanism for placing the wafer W in a stand-by status. An extension/cooling unit (EXTCOL) has a mechanism for cooling the wafer W while placing the wafer W in a stand-by status. A hot plate unit (HP) has a mechanism for heating the wafer W. 
     Note that a cooling unit (COL) having an alignment mechanism may be arranged in place of the alignment unit (ALIM). 
     Since the cooling unit (COL) and the extension/cooling unit (EXTCOL) whose processing temperatures are low, are arranged in lower stages, and the hot plate units (HP) whose processing temperatures are high, are arranged in higher stages, it is possible to minimize mutual thermal interference between the process units. Since the unit groups G 1 , G 2  of a spinner type are arranged at a distance from the unit groups G 3 , G 4  of the oven type, substantially no thermal influence is exerted upon the unit group G 1 , G 2  of a spinner type by the units G 3 , G 4  of an oven type. 
     As shown in FIG. 5, the cassette section  4  has the receipt portion  4 A and the deliver portion  4 B. Upper and lower stage mounting tables  41 ,  42  are arranged in the receipt portion  4 A. The cassette  9  storing unprocessed wafers W is loaded into each of the mounting tables  41 ,  42 . On the other hand, upper and lower stage mounting tables  43 ,  44  are arranged in the deliver portion  4 B. The cassette  9  storing processed wafers W is loaded into each of the mounting tables  43 ,  44 . 
     In the first interface section  6 , a pick-up cassette and a buffer cassette (not shown) are arranged. Furthermore, a peripheral light-exposure apparatus (not shown) and a cooling plate (not shown) are arranged in the interface section  6 . Note that the pick-up cassette (not shown) and the buffer cassette (not shown) are also arranged in the second interface section  7 . 
     Furthermore, to the extension unit (EXT) of the third process section G 3 , a film-thickness measuring device  60  can be connected by way of a transfer unit  61 . To the extension unit (EXT) of the fourth process section G 4 , a particle measuring device  70  can be connected by way of a transfer unit  71 . 
     As shown in FIG. 6, the main transfer arm mechanism  10  has a wafer transfer unit  20  for movably supporting three holders  22 ,  23 ,  24 . The wafer transfer unit  20  is movably supported by an up-and-down moving mechanism  19  in a cylindrical support  11 . The cylindrical support  11  is further movably supported by a loop moving mechanism  30  and a rotary moving mechanism  13 . The holders  22 ,  23 ,  24  are movably supported on a base  21 . The base  21  has a back-and-forth moving mechanism (not shown) for moving each of the holders  22 ,  23 ,  24  independently forward and backward. The back-and-forth moving mechanism of this type is disclosed in, for example, U.S. Pat. No. 5,664,254. 
     The cylindrical support  11  has vertical walls  11   a ,  11   b . A side opening  11   c  is formed between the vertical walls  11   a  and  11   b . The wafer transfer unit  20  moves the holders  22 ,  23 ,  24  back and forth through the side opening  11   c.    
     The up-and-down moving mechanism  19  has a motor  14 , a belt  15 , a driving pulley  16 , a follower pulley  17  and a connecting member  18 . The driving pulley  16  is engaged in a driving shaft of the motor  14  via another member. The driving pulley  16  is fitted at the lower portion of the vertical wall  11   b . The follower pulley  17  is fixed at the upper portion of the vertical wall  11   b . The belt  15  is stretched between the driving pulley  16  and the follower pulley  17 . The wafer transfer unit  20  is connected to the belt  15  by way of the connecting member  18 . 
     The rotary moving mechanism (motor)  13  is fitted to the same shaft as the cylindrical support  11 . The wafer transfer unit  20  is rotated about a Z-axis together with the cylindrical support  11 . 
     The loop transfer path  3  has a monorail  33   a , and a pair of support guide rails  33   b . The monorail  33   a  having a rectangular sectional shape is placed between the pair of support guide rails. The right and left support guide rails are arranged at an equal distance from the monorail  33   a . It is preferable that the radius of the loop transfer path  3  should fall within the range of 300-600 mm. 
     The loop moving mechanism  30  movably supports the entire main transfer arm mechanism  10 . The loop moving mechanism  30  has a cart  34 , a plurality of wheels  30   b , a plurality of moving rollers  31   a , a plurality of follower rollers  31   b , and a motor  32 . The cart  34  of an upside-down U-letter sectional shape has a depressed portion  34   a . The moving roller  31   a  is fitted at one side of the wall surrounding the depressed portion  34   a  and rotated by the motor  32 . The follower roller  31   b  is fixed at the other side of the wall and the upper wall. These moving roller  31   a  and the follower roller  31   b  are in contact with the monorail  33   a . When the driving force is transmitted from the motor  32  to the driving roll  31   a , the cart  34  moves along the monorail  33   a.    
     The moving roller  31   a  and the follower roller  31   b  are made of a material rarely producing particles. Note that a plurality of wheels  33   b  are fixed at both sides of the lower portion of the cart  34 . The wheel  33   b  is placed on the support guide rails  33   b . The wheel  33   b  supports the weight of the cart  34  and the wafer transfer unit  20  and prevents the cart  34  from leaving the rails  33   b.    
     As shown in FIG. 7, the wafer transfer unit  20  has a base  21  and three holders  22 ,  23 ,  24 . The three holders  22 ,  23 ,  24  are arranged in the order mentioned from top. The first and second holders  22 ,  23  have C-letter tip portions  22   a  and  23   a , respectively. The second holder  23  has three projections  23   b  for directly holding the wafer W. The third holder  24  (not shown) also has three projections  24   b  for directly holding the wafer W. These three holders  22 ,  23 ,  24  are independently moved back and forth in the direction indicated by an arrow shown in the FIG. 7, by a back-and-forth moving mechanism (not shown) housed in the base  21 . The back-and-forth moving mechanism has a motor, pulley, and belt. The stroke of each of the holders by the back-and-forth moving mechanism is 330-370 mm in the case of an 8-inch wafer, and 550-650 mm in the case of a 12-inch wafer. 
     Now, how to operate the system  1  will be explained. 
     The main transfer arm mechanism  10  moves the wafer transfer unit  20  circularly together with the cylindrical support  11  along the loop transfer path  3 . Consequently, the holder  22  is allowed to face the cassette section  4 . The main transfer arm mechanism  10  moves the holder  22  forward and the holder  22  then picks up a single wafer W. Then, the main transfer arm mechanism  10  moves the wafer transfer unit  20  circularly along the loop transfer path  3 . In this manner, the holder  22  is allowed to face the interface section  7 . Then, the holder  22  is moved forward and transfers the wafer W to the interface section  7 . Furthermore, the transfer unit (not shown) transfers the wafer W from the interface section  7  to the washing device  50 . The wafer W is scrub-washed by the washing device  50  and returned to the main transfer arm mechanism  10  by way of the interface section  6 . 
     The main transfer arm mechanism  10  transfers the water W to the adhesion process unit (AD) of the third process section G 3 . Adhesion treatment is applied to the wafer W in the adhesion unit (AD). The main transfer arm mechanism  10  takes out the wafer W from the adhesion process unit (AD) and transfers to any one of the cooling units of the third and fourth process sections G 3 , G 4 . The wafer W is cooled to room temperature in the unit (COL). 
     Then, the main transfer arm mechanism  10  transfers the wafer W to the resist coating unit (COT). In the resist coating unit (COT), a resist is applied onto the wafer W in accordance with a spin-coating method. Subsequently, the main transfer arm mechanism  10  transfers the wafer W to any one of hot plate units (HP) of the third and fourth process sections G 3 , G 4 . The wafer W is heated by a hot plate unit (HP), with the result that the resist coating film is baked. Thereafter, the main transfer arm mechanism  10  transfers the wafer W to any one of the cooling plate unit (COL) of the third and fourth process sections G 3 , G 4 . The wafer W is cooled to room temperature in the cooling plate unit (COL). At this time, if necessary, the wafer W may be transferred to the film-thickness measuring device  60  by way of the extension unit (EXT) of the third process section G 3  in order to measure the thickness of the resist film. Alternatively, if necessary, the wafer W is transferred to the particle measuring device  70  by way of the extension unit (EXT) of the fourth process section G 4  in order to count the number of particles on the resist film. 
     The main transfer arm mechanism  10  transfers the wafer W to the alignment unit (ALIM) of the third process section G 3 . The wafer W is aligned with the system  1  by the alignment unit (ALIM). Then, the main transfer arm mechanism  10  transfers the wafer W to the interface section  6 . 
     In the interface section  6 , the wafer W is transfers to the peripheral light exposure apparatus (not shown) by a transfer unit (not shown). In the peripheral light exposure apparatus, the resist coating film of the peripheral portion of the wafer is exposed to light. Then, the wafer W is cooled by a cooling plate (not shown) and transferred to the transfer unit (not shown). The transfer unit (not shown) loads the wafer W into the light exposure apparatus  40 , in which the resist coating film is exposed to light with a pattern as a mask. 
     The wafer W is returned to the interface section  6  by the transfer unit (not shown) from the light exposure apparatus  40 . The main transfer arm mechanism  10  transfers the wafer W from the interface section  6  to the hot plate unit (HP), in which the resist coating film is baked (this step is called post-exposure bake (PEB)). Subsequently, the main transfer arm mechanism  10  transfers the wafer W to the cooling unit (COL), in which the wafer W is cooled to room temperature. 
     The main transfer arm mechanism  10  transfers the wafer W to any one of the developing units (DEV) of the first and second process sections G 1  and G 2 . In the developing unit (DEV), a pattern latent image on the resist coating film is developed. Subsequently, the main transfer arm mechanism  10  transfers the wafer W to the hot plate unit (HP), in which the wafer W is heated. In this way, the resist coating film is baked (Post baking). Thereafter, the main transfer arm mechanism  10  transfers the wafer W to a cooling unit (COL), in which the wafer W is cooled. The wafer W is loaded into a cassette  9  of the cassette section  4  by the main transfer arm mechanism  10 . The wafer W is finally unloaded from the system  1  together with the cassette  9 . 
     According to this embodiment, since the main transfer arm mechanism is moved along the loop transfer path, the back-and-forth moving stroke (horizontal moving distance) of the holder is suppressed so as not to become too long. As a result, the holder is supported by a small and light member. In particular, the small and light feature of the support member is helpful in transferring a large-size wafer by the main transfer arm mechanism. 
     Furthermore, a plurality of process units can be arranged without mutual interference, so that the footprint of the apparatus can be reduced. 
     Moreover, the transfer space is increased compared to the conventional one. Therefore, the maintenance operation of the main transfer arm mechanism and the process units can be easily performed. 
     Furthermore, if an interface unit is provided in the process section, a large apparatus (light-exposure apparatus, washing apparatus) can be externally connected to the system. The system is therefore expandable. 
     Note that the monorail moving system is applied to the loop transfer mechanism in the aforementioned embodiment. However, a linear-motor moving system may be employed in place of the monorail moving system. 
     The system of the present invention can be applied to a case where an LCD substrate is employed in place of a semiconductor wafer, as the substrate. 
     Now, referring to FIGS. 8-12, a second embodiment of the present invention will be explained. 
     The substrate process system  100  has a process section  101 , a cassette section  102 , a vertical transfer arm mechanism  107 , four circularly-moving transferring arm mechanisms  110 ,  111 ,  112 ,  113 , and four delivery tables  115 ,  116 ,  117 ,  118 . The system  100  is surrounded by an exterior jacket (not shown) having an open/shut door (not shown). The open/shut door is positioned immediately outside the cassette section  102 . An operator or an automatic transfer robot opens the door and loads and unloads the cassette  9  into/from the cassette section  102 . The cassette section  102  has a receipt portion and a deliver portion. The cassette  9  storing unprocessed wafers W is loaded into the receipt section. The cassette  9  storing processed wafers W is unloaded from the deliver section. 
     A transfer space  170  is formed at the center of the system  100 . A vertical transfer arm mechanism  107  is arranged in the transfer space  170 . The wafer W is vertically transferred in a z-axis direction. 
     Tables  150  vertically arranged in four stages are arranged so as to surround the transfer space  170 . Loop transfer paths  150   a  are arranged respectively on the tables  150 . The circularly moving arm mechanisms  110 ,  111 ,  112 ,  113  move respectively on the loop transfer paths  150   a.    
     The delivery tables  115 ,  116 ,  117 ,  118  are respectively supported by the tables  150  by way of a bracket  160  so as to extend in the peripheral region of the transfer space  170 . The delivery tables  115 ,  116 ,  117 ,  118  are located respectively between circularly-moving transfer arm mechanisms  110 ,  111 ,  112 ,  113  and the vertical transfer arm mechanism  107 . The wafer W is transferred between the mechanisms  110 ,  111 ,  112 ,  113  and  107 . 
     As shown in FIG. 8, the four delivery tables  115 ,  116 ,  117 ,  118  are arranged at equal intervals so as not to overlap with each other in the same plane. This is made to prevent mutual interference between two arm holders  140 ,  141  of the vertical transfer arm mechanism  107  and to improve a transfer efficiency of the wafer W. 
     The process section  101  and the cassette section  102  are arranged further outside the table  150 . The process section  101  has  11  process unit groups  103 . These  11  process unit groups  103  and the cassette section  102  are arranged around the table  150  so as to surround it. 
     As shown in FIG. 9, in each of the process unit groups  103 , a thermal process unit  120 , first liquid-process unit  121 , second liquid-process unit  122 , and third liquid-process unit  123  are stacked in the order mentioned from top. The thermal process unit  120  is placed at the same height as the first circularly-moving transfer arm mechanism  110  mounted on the uppermost table  150 . The first liquid process unit  121  is placed at the same height as the second circularly-moving transfer arm mechanism  111 . The second liquid process unit  122  is placed at the same height as the third circularly-moving transfer arm mechanism  112 . The third liquid process unit  123  is arranged at the same height as the fourth circularly-moving transfer arm mechanism  113  arranged at the lowermost stage. Note that, in the same manner as in the process unit groups, cassette tables are stacked in four stages in the cassette section  102 . One of the process unit groups  103  has an interface section. The wafer W is transferred to a light exposure apparatus (not shown) by way of the interface section. 
     The thermal process unit  120  has at least one of an adhesion mechanism, prebaking mechanism, post exposure baking mechanism, post baking mechanism, alignment mechanism, cooling mechanism and extension (stand-by) mechanism. Each unit  120  has a wafer table  120   a  having a plurality of lift pins  120   b.    
     First to third liquid-processing units  121 ,  122 ,  123  have at least one of a resist coating mechanism, developing mechanism, and anti-reflection film coating mechanism. Each of units  121 ,  122 , and  123  has a cup  125  and a spin chuck  126 . 
     Now, the vertical transfer arm mechanism  107  will be explained with reference to FIG.  10 . 
     The vertical transfer arm mechanism  107  has two liftable rotary mechanisms  135 ,  137 , two support members  136 ,  138 , and two arm holders  140 ,  141 . The arm holders  140 ,  141  are supported by the support members  136 ,  138 , respectively. The support members  136 ,  138  are moved up and down respectively by the liftable rotary mechanisms  135 ,  137  in the z-axis direction and simultaneously rotated about the z-axis. Furthermore, a back and forth moving mechanism (not shown) is provided in each of the support members  136 ,  138 . Each of arm holders  140 ,  141  is moved back and forth in the horizontal direction by the back and forth moving mechanism. Note that the second support member  138  is moved by the second liftable rotary mechanism  137  in a sufficiently long stroke (vertical moving distance) such that the second arm holder  141  delivers the wafer W to the uppermost delivery table  115 . 
     Now, referring to FIG. 11, the circularly-moving transfer arm mechanism  110  ( 111 ,  112 ,  113 ) will be explained. 
     The circularly-moving transfer arm mechanism  110  has a cart  151 , a support shaft  152 , a slide base  153 , and upper and lower holders  156 . The cart  151  houses a loop moving mechanism and a circularly moving mechanism (not shown). The loop moving mechanism employs a monorail moving system having substantially the same structure as in the first embodiment. When the moving roller (not shown) of the loop moving mechanism is in contact with the rail  150   a , the driving force of a motor is transmitted to the moving roller. The circularly-moving mechanism has a rotary moving mean (not shown) for rotating a support shaft  152  about the z-axis. With this mechanism, the holders  156  are moved around the z-axis together with the support shaft  152 . 
     The slide base  153  houses a back-and-forth moving mechanism (not shown). The back-and-forth moving mechanism has a motor, pulley and belt. The holders  156  are independently moved back and forth by these structural elements. 
     Now, how to operate the aforementioned system  100  will be explained. 
     The circularly-moving transfer arm mechanism  113  moves along a loop transfer path  150   a  to position the holder  156  so as to face the cassette section  4 . The circularly-moving transfer arm mechanism  113  loads the holder  156  into the cassette section  4  to allow the holder  156  to take out a single wafer W from the cassette  9 . Then, the circularly-moving transfer arm mechanism  113  moves along the loop transfer path  150   a . As a result, the holder  156  is placed to face the delivery table  118 . Then, the holder  156  is moved forward to transfer the wafer W to the delivery table  118 . 
     The vertical transfer arm mechanism  107  allows the first arm holder  140  to face the delivery table  118  and to take out the wafer W (first wafer) from the delivery table  118 . Subsequently, the arm holder  140  is moved upward and allowed to face the delivery table  115 . The vertical transfer arm mechanism  107  allows the second arm holder  141  to take out another wafer W (second wafer) from the delivery table  115 . Subsequently, the wafer W (first wafer) is transferred to the delivery table  115  by the first arm holder  140 . 
     The circularly-moving transfer arm mechanism  110  takes out the wafer W from the delivery table  115  by the holder  156 . Subsequently, the circularly-moving transfer arm mechanism  110  moves along the loop transfer path  150   a  to place the holder  156  to face the adhesion process unit  120 . Thereafter, the wafer W is loaded into the unit  120  to apply adhesion treatment to the wafer W. Then, the wafer W is taken out from the unit  120  by the circularly-moving transfer arm mechanism  110  and transferred to the delivery table  115 . 
     The vertical transfer arm mechanism  107  allows the second arm holder  141  to face the delivery table  115  and to take out the wafer W from the delivery table  115 . The vertical transfer arm mechanism  107  moves down the second arm holder  141 , rotates, places it to face the delivery table  116 , and allowed it to transfer the wafer W to the delivery table  116 . 
     The circularly-moving transfer arm mechanism  111  takes out the wafer W from the delivery table  116  by use of the holder  156 . Then, the circularly-moving transfer arm mechanism  111  moves along the loop transfer path  150   a  and allowed the holder  156  to face the resist coating unit  121 . Subsequently, the wafer is loaded into the unit  121  to coat the wafer W with a resist. 
     Thereafter, the wafer W is transferred subsequently to the prebaking unit, cooling unit, interface section, the light-exposure apparatus, interface section, post exposure baking unit, cooling unit, developing unit, post baking unit, and cooling unit in the order mentioned. In these units, individual treatments are applied to the wafer. The wafer W is finally loaded into the cassette  9  of the cassette section  4  by any one of the circularly-moving transfer arm mechanisms  110 ,  111 ,  112 ,  113  and stored therein. 
     As shown in FIG. 12, the lower vertical transfer arm mechanism  107 A may be used in combination with the upper vertical transfer arm mechanism  107 B, in place of the vertical transfer arm mechanism  107 . The upper vertical transfer arm mechanism  107 B is supported by a ceiling portion (not shown) of the system  100 . The upper vertical transfer arm mechanism  107 B has a liftable rotation mechanism  135 B, a support member  136 B, a back-and forth moving mechanism (not shown), and a holder  140 B. The lower vertical transfer arm mechanism  107 A is supported by a floor portion (not shown) of the system  100 . The lower vertical transfer arm mechanism  107 A has a liftable rotation mechanism  135 A, a support member  136 A, a back-and forth moving mechanism (not shown), and a holder  140 A. 
     The lower vertical transfer arm mechanism  107 A transfers the wafer W to two delivery tables  117 ,  118  in the lower portion, whereas the upper vertical transfer arm mechanism  107 B transfers the wafer W to two delivery tables  115 ,  116  in the upper portion. Since the lower vertical transfer arm mechanism  107 A and the upper vertical transfer arm mechanism  107 B shares the entire wafer transfer load, the burden applied on each mechanism is reduced. As a result, a failure of the system rarely occurs. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.