Patent Publication Number: US-2010108564-A1

Title: Clean device with clean box-opening/closing device

Description:
CROSS REFERENCE 
     This application is a division of and is based upon and claims the benefit of priority under 35 U.S.C. §120 for U.S. Ser. No. 10/556,723, filed Nov. 16, 2006, the entire contents of each which are incorporated herein by reference, which is a National Stage of PCT/JP04/06604, filed May 11, 2004, and claims the benefit of priority under 35 U.S.C. §119 from Japanese Patent Application No. 2003-137026, filed May 15, 2003, and Japanese Patent Application No. 2003-154078, filed May 30, 2003. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an opening/closing mechanism for opening and closing a lid of an SMIF-type clean box, and to a load port portion of a clean device having the opening/closing mechanism in a substrate processing device, in which a substrate, such as a substrate of a semiconductor product or the like as an object for a processing requiring high cleanliness, is accommodated in the clean box and sealed up by its lid and main body so as to ensure high cleanliness inside. The substrate processing device loads/unloads the substrate into/from the clean box. In loading and unloading the substrate, the lid is vertically moved to be opened and closed. 
     The present invention also relates to an article accommodating container for accommodating an article to be processed in a highly clean environment such as a semiconductor, a panel for a flat panel display, or an optical disk, and various articles used together with that article, during a manufacturing process thereof. More specifically, the present invention also relates to the structure of a main body of the article accommodating container having an opening portion located at vertical side and to the structure of a lid for closing the opening portion. 
     BACKGROUND ART 
     The processing of a substrate of a semiconductor product or the like needs to be carried out in an environment in which high cleanliness is ensured. In general, the processing is carried out in a clean room that is entirely kept highly clean. However, heavy investment in facilities and immense expenses of maintenance are required in order to keep the entire room having a large cubic volume highly clean. Even after an investment in facilities has been made, further heavy investment in facilities would be needed in changing the layout of the room associated with a change in manufacturing process, which is not economical. 
     Further, substrates such as silicon wafers have been increasing in size, so such a measure is problematic in terms of the cost to ensure a required clean environment. 
     In view of the above, a method as disclosed in the specification of Japanese Patent No. 3167970 has been known in recent years, according to which the inside of a substrate processing device (hereinafter referred to as a clean device) for processing a substrate such as a semiconductor is kept highly clean as a micro environmental space (hereinafter referred to as a mini-environment portion), instead of keeping the entire room highly clean, thereby achieving the same effect as in the case where the entire room is kept highly clean. 
     That is, the substrate processing device is laid out in a room where substrates are manufactured, and a substrate storing container (hereinafter referred to as a clean box) whose inside is kept highly clean is used to transfer substrates into and from the clean device. Then, the clean box is coupled to a predetermined substrate gateway provided in the substrate processing device so as to prevent the entrance of dust from the outside. If substrates are transferred via the predetermined gateway, the entire environment to which those substrates are exposed can be kept highly clean without enhancing the cleanliness of the room where those substrates are manufactured. Thus, the same effect as in the case where the entire room is turned into a clean room can be achieved. As a result, an efficient production process can be realized by cutting down on the amount of investment in facilities and the expense of maintenance. In this specification, a substrate should be construed to include, for example, an exposure mask (reticle), a semiconductor wafer. Therefore, a substrate processing device should be construed to include a reticle processing device and a semiconductor wafer processing device. 
     A pod having an opening portion in a vertically lower side as described above and adapted to open and close the opening portion by vertically moving a lid is generically referred to as a standard mechanical interface (SMIF) type pod. The present invention relates to this SMIF type pod. As described above, an efficient production process is realized while reducing the amount of investment in facilities and the expense of maintenance and achieving the same effect as in the case where an entire plant is turned into a clean room, by adopting a so-called mini-environment method in which only limited space is kept highly clean. 
     A clean device  1  will be described with reference to  FIG. 9 .  FIG. 9  is a view showing a cross-section of the entire clean device  1 . The clean device  1  is provided with a processing room  60 , a transfer room  50 , and a load port portion  10 . 
     Various substrate processings to be carried out in the clean device  1  are carried out in the processing room  60 . 
     The transfer room  50  has therein a sealed-up space shut off from the outside. A robot arm  55  for transferring substrates is arranged in the transfer room  50 . 
     A clean box  2  is laid on the load port portion  10  to transfer substrates into the processing room  60  of the clean device  1 . The load port portion  10  has a function of removing a lid  2   b  from a main body  2   a  of the clean box  2 . 
     A port door  3  that is substantially horizontally held is arranged in the load port portion  10 . The port door  3  is raised and lowered vertically (see, Japanese Patent Application Laid-open No. 2001-203253). Referring to  FIG. 9 , the port door  3  is in its lowered state. The port door  3  is surrounded by wall surfaces surrounding the port door  3  on all four sides and a bottom portion located substantially parallel to a lower face of the port door  3 . The wall surfaces and the bottom portion constitute a buffer chamber  6  inside the load port portion  10 . The buffer chamber  6  is open at its top, thus constituting an access opening  5  that is substantially equal in size to the port door  3 . Therefore, when viewed from the access opening  5 , there is formed the buffer chamber  6  having a predetermined depth. The size of the access opening  5  is substantially equal to or smaller than that of an envelope region of an opening of the clean box  2 . The port door  3  is raised and lowered along the wall surfaces of the buffer chamber  6 . The access opening  5  is covered with the main body  2   a  of the clean box  2  as shown in  FIG. 9  when the clean box  2  is laid on the load port portion  10 . The buffer chamber  6  of the load port portion  10  remains sealed up even when the lid  2   b  is removed. 
     In this example, a pod  2  accommodates, instead of a substrate, a photomask called a reticle used in a semiconductor processing process. The inside of the pod  2  is filled with a gas such as dry nitrogen which is usually kept highly clean, when an article is accommodated therein. Using this gas, the pressure inside the pod  2  is thus held equal to or higher than an atmospheric pressure to thereby reduce the possible internal contamination resulting from an ambient environment. 
     The buffer chamber  6  in the load port portion  10  and an inside  50   a  of the transfer room  50  communicate with each other through a transfer opening  51 . The inside  50   a  of the transfer room  50  and an inside  60   a  of the processing room  60  communicate with each other through a transfer opening  52 . The inside of the load port portion  10 , the inside  50   a  of the transfer room  50 , and the inside of the processing room  60  are sealed up to be shut off from the external environment, thus forming a mini-environment portion. 
     Further, the transfer opening  51  is opened and closed by an opening/closing door  53  driven by an opening/closing gate valve  53   a . On the other hand, the transfer opening  52  is opened and closed by an opening/closing door  54  driven by an opening/closing gate valve  54   a.    
     Referring now to  FIG. 10 , the load port portion  10  will be described in detail.  FIG. 10  is a view showing the load port portion  10  of  FIG. 9  on an especially enlarged scale. As shown in  FIG. 10 , the port door  3  is in its raised state unlike in the case of  FIG. 9 . Referring to  FIG. 10 , the lid  2   b  is laid on the port door  3 . Note that, the port door  3  in its lowered state is indicated by a chain double-dashed line in  FIG. 10 . Raising/lowering means  4  is connected to the port door  3 . The raising/lowering means  4  is provided with a latch opening/closing shaft  4   a , a frame  4   b  for holding an actuator within the latch opening/closing shaft, a raising/lowering shaft  4   c , and an electric actuator  7 . The latch opening/closing shaft  4   a  is a vertically extending rod-like member that is joined at one end thereof to the lower face as an inner face of the port door  3 , thus serving to directly transmit a raising/lowering movement of the raising/lowering means  4  to the port door  3 . The latch opening/closing shaft  4   a  is joined at the other end thereof, which is located on the side opposite to the port door  3 , to the frame  4   b . The frame  4   b  is connected to the raising/lowering shaft  4   c . The raising/lowering shaft  4   c  is connected to the electric actuator  7 . Thus, the raising/lowering means  4  causes a raising/lowering movement of the port door  3 . A through-hole through which the latch opening/closing shaft  4   a  extends is arranged at a lower center of the buffer chamber  6 . The size of the through-hole is substantially equal to or smaller than that of the latch opening/closing shaft  4   a.    
     A rotary shaft  33  rotatable around a center of the latch opening/closing shaft  4   a  is mounted therein. Rod-like latch pins  32  arranged so as to protrude vertically from the surface of the port door  3  are arranged at a tip of the rotary shaft  33 . The latch pins  32  are arranged at arbitrary positions on a circumference of a circle spreading around a rotation axis of the rotary shaft  33 . It is preferable that the latch pins  32  be circular holes arranged point-symmetrically on the circumference of the circle. 
     The port door  3  is a rectangular flat plate substantially corresponding in shape to the access opening  5 . When being raised, the port door  3  is fittingly inserted into the access opening  5  and closes it as shown in  FIG. 10 , thus sealing up the buffer chamber  6  and shutting it off from the external world. A positioning pin  3   c  as a protrusion, which protrudes from a top face of the port door  3  substantially perpendicularly thereto, is arranged on the top face side of the port door  3  corresponding to the outer face side of the load port portion  10  so as to position the lid  2   b  of the clean box  2 . A hole corresponding to the positioning pin  3   c  extends through the lid  2   b  of the clean box  2 . When the clean box  2  is laid on the load port portion  10  and the port door  3  is raised to abut on the lid  2   b  of the clean box  2 , the positioning pin  3   c  is fittingly inserted into the hole so that the lid  2   b  is located at a right position with respect to the port door  3 . 
     A lower portion of the port door  3  constitutes a flange-like brim  3   a  that is larger than the access opening  5 . A sealing member  3   b  is fitted in the brim  3   a . When the electric actuator  7  is driven to raise the latch opening/closing shaft  4   a  to thereby fittingly insert the port door  3  into the access opening  5 , the brim  3   a  comes into abutment with an edge portion  5   a  of the access opening  5 , thereby sealing up the buffer chamber  6 . On the other hand, conversely, when the electric actuator  7  is driven to lower the latch opening/closing shaft  4   a  to thereby lower the port door  3 , the access opening  5  opens widely. 
     A bellows  31  is so fitted as to range from a lower face of the port door  3  to at least an outer periphery of the latch opening/closing shaft  4   a  in the buffer chamber  6  (e.g., see Japanese Patent Application Laid-open No. 2001-203253 or Japanese Patent Application Laid-open No. 06-268046). When the electric actuator  7  is driven to raise the latch opening/closing shaft  4   a , the bellows  31  expands because the port door  3  moves away from the bottom face. When the electric actuator  7  is driven to lower the latch opening/closing shaft  4   a , the bellows  31  contracts because the port door  3  moves toward the bottom face. 
     A measure against falloff of the lid  2   b  from the main body  2   a  of the clean box  2  during transfer is taken by means of a latch mechanism.  FIG. 11  shows a latch mechanism inside the lid  2   b.    
     A conventional latch mechanism typically has the following structure. A rotatably arranged circular rotary cam plate  21  is rotatably located substantially at a central position of the lid  2   b . Latch holes  21   a  located at arbitrary positions on a circumference of a circle spreading around a center of the rotary cam plate  21  are formed therethrough. Note that the latch holes  21   a  are preferably circular holes arranged point-symmetrically on the circumference of the circle. The latch pins  32  engage the latch holes  21   a . The latch holes  21   a  are shaped so as to receive the latch pins  32  therein, and are so arranged as to correspond in position to the latch pins  32 . 
     Arranged outside the latch holes  21   a  of the rotary cam plate  21  are two cam grooves  23 , which are point-symmetrical to each other with respect to the center of the rotary cam plate  21 . Given that each of the cam grooves  23  has one end as a starting point  23   a  and the other end as an end point  23   b , the distance between the starting point  23   a  of the cam groove  23  and the center of the rotary cam plate  21  is the shortest, whereas the distance between the center of the cam groove  23  on the end point  23   b  side of the cam groove  23  and the center of the rotary cam plate  21  is the longest. On the other hand, the lid  2   b  has a latch member  26  movable parallel to the plane of the lid  2   b . A driven pin  24  is arranged on the rotary cam plate  21  side of the latch member  26 . The driven pin  24  is engaged with the cam groove  23 . The latch member  26  includes a tip portion protruding from a lateral face of the lid  2   b.    
     Now, when the latch pins  32  arranged at the tip of the rotary shaft  33  in the latch opening/closing shaft  4  of the port door  3  on which the lid  2   b  is laid are fittingly inserted into the latch holes  21   a  and the rotary cam plate  21  is rotated by rotating the rotary shaft  33 , the driven pin  24  of the latch pin  26  moves along the cam groove  23   b  from its starting point  23   a  toward its end point  23   b . In accordance therewith, the position of the driven pin  24  moves from the center of the rotary cam plate  21  toward the outside thereof. In accordance with a moving distance of the driven pin  24 , a tip portion  22   a  of the latch member  26  moves toward the outside of the lid  2   b . The latch member  26  is set to be confined within the lid  2   b  when the driven pin  24  is located at the starting point  23   a , and to protrude from the lid  2   b  when the driven pin  24  is located at the end point  23   b . On the other hand, a latch hole  30  for engagement with the latch member  26   a  is arranged at the position where the latch hole  30  abuts on the lid  2   b  for the main body  2   a  of the clean box  2 , so the lid  2   b  can be fixed to the clean box  2  by rotating the rotary cam plate  21 . 
     The rotatable latch pins  32  for engaging the cam grooves  23  of the rotary cam plate  21  are arranged as an opening/closing mechanism on the top face of the port door  3 . The latch pins  32  are coupled to the rotary shaft  33  arranged within the latch opening/closing shaft  4   a . The rotary shaft  33  is coupled to a rotary actuator  34  as rotation means. 
     Next, how a substrate  9  is exchanged between the load portion  10 , the transfer room  50 , and the processing room  60  in the clean device  1  will be described. 
     The clean box  2  is first laid on the load port portion and fixed as shown in  FIG. 9 . At this moment, the substrate  9  is laid on the lid  2   b . When the latch opening/closing shaft  4   a  is raised by driving the electric actuator  7 , the port door  3  is raised while the bellows  31  expands, and the latch pins  32  protruding from the top face of the port door  3  are fittingly inserted into the latch holes  21   a . Then, the port door  3  comes into abutment with the lid  2   b  of the clean box  2 . When the rotary actuator  34  is rotated at this stage, the rotary shaft  33  rotates. In response thereto, the latch pins  32  press the edges of the latch holes  21   a , thus causing the rotary cam plate  21  to rotate. When the rotary cam plate  21  rotates, the driven pin  24  rotates and the latch member  26  is confined within the door  2   b . In this state, the lid  2   b  fixed to the main body  2   a  of the clean box  2  is then released therefrom. 
     When the electric actuator  7  is then driven to lower the latch opening/closing shaft  4   a , the port door  3  is also lowered while the bellows  31  contracts. The lid  2   b  moves due to its own weight away from the main body  2   a  of the clean box  2  as the port door  3  is lowered. After the port door  3  has been completely lowered, the lid  2   b  on which the substrate  9  is laid is located on a bottom portion of the buffer chamber  6 . In this state, the robot arm  55  can then perform a transfer operation. 
     The buffer chamber  6  in the load port portion  10  and the inside  50   a  of the transfer room  50  communicate with each other through the transfer opening  51 , and the inside  50   a  of the transfer room  50  and the inside  60   a  of the processing room  60  communicate with each other through the transfer opening  52 . The inside of the load port portion  10 , the inside  50   a  of the transfer room  50 , and the inside of the processing room  60  are sealed up and shut off from the external environment, thus forming a mini-environment portion. 
     When the opening/closing gate valve  53   a  is driven to open the opening/closing door  53 , the buffer chamber  6  in the load port portion  10  and the inside  50   a  of the transfer room  50  communicate with each other. The substrate  9  is transferred from the buffer chamber  6  in the load port portion  10  by operating the robot arm  55 . Furthermore, the inside  50   a  of the transfer room  50  and the inside  60   a  of the processing room  60  communicate with each other by driving the opening/closing gate valve  54   a  to open the opening/closing door  54 . The substrate  9  is transferred from the transfer room  50  into the processing room  60  by operating the robot arm  55 . 
     Note that included in related art documents about the above-described constructions are Japanese Patent No. 3084827 and Japanese Patent No. 2960540 as well as the aforementioned Japanese Patent Application Laid-open No. 2001-203253 and Japanese Patent Application Laid-open No. 06-268046. 
     In an SMIF type container, a latch member arranged on a lid or a tip portion of the latch member engages a hole or a groove formed in a main body of a pod, so that the lid is fixed to the main body of the pod. That is, this fixation is accomplished when the latch member comes into contact with a latch member receiving face formed on the main body, and a load toward a central portion of the lid and a load toward the main body are applied from the latch member receiving face to the latch member. In this case, as described in Japanese Patent No. 3167970 as well, a physical “rub” occurs between the surface of the latch member and the latch member receiving face so as to obtain the aforementioned loads, which may result in generation of particles. As far as a single operation is concerned, such particles are generated with very low frequency. However, in a working process consisting of several tens of steps or more, a considerable amount of particles may be generated. 
     In order to reduce the factors for generation of such particles, according to the aforementioned Japanese Patent No. 2960540, two cam faces acting in different directions are provided for a latch member. That is, a latch tip portion moves without coming into contact with a latch receiving face in advancing or retreating with respect to an inside of a main body portion such as a groove. The latch tip portion moves substantially perpendicularly to the latch receiving face in the process of engagement. Therefore, in the construction disclosed in the above document, the latch tip portion and the latch receiving face seldom rub each other. Accordingly, with this construction, it seems possible to suppress the generation of particles resulting from the rubbing of the latch tip portion which has been conventionally deemed problematic. However, the latch tip portion usually operates as a fulcrum for pressing the entire lid against the main body portion. Therefore, as is the case with the foregoing construction, loads tend to converge on a contact point when this contact point is obtained by a movement of the latch tip portion in the direction substantially perpendicular to the latch receiving portion. As a result of the convergence of the loads, there may occur a serious local abrasion. In this case, the generation of particles due to a cause slightly different from those of conventional cases seems to raise a problem. 
     Note that, the pressure inside a pod and the pressure inside a buffer chamber in a load port are generally held equal to or higher than an atmospheric pressure by means of a clean gas. Thus, even when the aforementioned particles and the like are generated, they hardly enter the inside of the pod or the like. Thus, even with the construction disclosed in Japanese Patent No. 2960540, it is possible to achieve an effect of reducing the amount of particles to some extent. However, in the case of an SIMF type container used for a specific purpose such as accommodation of a reticle, the inside of a pod is usually maintained in a depressurized state, and an operation of taking out the reticle as an accommodated article is also performed with the inside of a buffer chamber depressurized. In this case, generated particles are extremely likely to enter the inside of the pod or the like. 
     In consideration of the foregoing circumstances, there is known a construction in which a vacuum space is formed on a lid face on a main body side instead of employing a latch mechanism and the atmospheric pressure applied to the lid due to the existence of the vacuum space is used to ensure tight contact between the lid and the main body and seal up of an inner space. This construction eliminates the necessity of a latch mechanism, so it is absolutely unnecessary to consider the generation of particles resulting from the mechanism. In this construction, the lid is unlikely to fall off even when the pressure in the vacuum space has become equal to the atmospheric pressure for some reason, as long as the construction is applied to a container having an opening in its lateral face, such as a so-called FOUP. It is also relatively easy to cope with such a situation. However, a vacuum break in the space can cause the lid to fall off when the above-described construction is applied to a container having an opening in its vertically lower face, such as an SMIF type pod, so it is desirable to take an appropriate measure. In this case, when the above-mentioned latch mechanism is employed as a corresponding measure, the amount of the aforementioned particles needs to be reduced as well. 
     DISCLOSURE OF INVENTION 
     As described above, the conventional clean device  1  has the following problems. 
     (1) Although the opening/closing mechanism arranged on the port door  3  of the load port portion  10  in the conventional clean device  1  releases the latch mechanism serving as a device for fixing the lid  2   b , it simply holds the lid  2   b  itself and does not forcibly remove the lid  2   b  from the main body  2   a  of the clean box  2  while keeping the lid  2   b  fixed to the port door  3 . The lid  2   b  is supposed to move spontaneously, due to its own weight away from the main body  2   a  of the clean box  2 . 
     This is because of the following reasons. Usually, the internal pressure of the clean box  2  is substantially equal to the atmospheric pressure, even in the state in which the inside of the clean box  2  is filled with an inactive gas. Also, the lid  2   b  itself, including the substrate  9 , is heavy enough to move spontaneously away from the clean box  2   a  owing to the gravity. 
     However, in the case of processing a substrate, in particular a reticle, the entire clean device  1  including the processing room  60  and the transfer room  50  needs to be kept not only highly clean but also vacuum. In addition, the inside of the clean box  2  also needs to be kept vacuum. In such a case, the weight of the lid  2   b  may not allow the lid  2   b  to move away from the main body  2   a  of the clean box  2 . Further, as the sealing effect of a sealing material arranged at a joint between the main body  2   a  and the lid  2   b  of the clean box  2  for maintaining a vacuum state increases, the tightness of contact between the sealing member and the clean box  2  improves and the lid  2   b  becomes more unlikely to fall off the clean box  2 . This tendency is noticeable particularly, for example, in the case where the substrate  9  is not laid. 
     (2) In the load port portion  10  in the conventional clean device  1 , the bellows  31  is mounted in the buffer chamber  6  between the lower face of the port door  3  and the bottom portion of the buffer chamber  6 . The buffer chamber  6  is evacuated when the port door  3  is lowered. However, abrasion of the bellows  31  resulting from its expansion/contraction produces dust, which causes a problem of a decrease in the degree of cleanliness in the buffer chamber  6 . 
     To solve the above-mentioned problems, the present invention provides a clean device including a lid and a main body and having an inside environment kept cleaner than an outside environment to receive a substrate from a clean box, which is kept highly clean inside and has the substrate stored in the inside, and process the substrate, characterized in that: the clean device includes a load port portion equipped with an opening/closing mechanism having a turnable latch pin to separate the lid from the main body or couple the lid to the main body with the clean box laid thereon; the lid of the clean box has: a cam plate capable of engaging with the latch pin and actuating in accordance with a turning movement of the latch pin; and a latch member protruding to an outside of the lid to engage a latch hole of the main body of the clean box or being confined within the lid to be released from the latch hole of the main body of the clean box in accordance with an actuation of the cam plate; the lid of the clean box further includes a non-circular receiving hole; the opening/closing mechanism further includes a protrusion that can be fittingly inserted into the receiving hole; the latch pin becomes capable of engaging the cam plate and the protrusion of the opening/closing mechanism is fittingly inserted into the lid of the clean box when the clean box is laid on the load port; and the protrusion and the receiving hole become capable of engaging with each other in accordance with a turning movement of the latch pin. This makes it possible for the port door to fix the lid in the clean device. Thus, the lid can be positively moved away from the main body of the clean box not solely due to the weight of the lid itself. 
     Further, to solve the above-mentioned problems, the present invention provides a clean device including a lid and a main body and having an inside environment kept cleaner than an outside environment to receive a substrate from a clean box, which is kept highly clean inside and has the substrate stored in the inside, and process the substrate, characterized in that: the clean device includes a load port portion for separating the lid from the main body or coupling the lid to the main body with the clean box laid thereon, to receive the substrate from the clean box; the load port portion includes: a port door that is raised and lowered and has one face on which the lid is laid; a buffer chamber defined by wall surfaces arranged surrounding an outer periphery of the port door in a region where the port door is raised and lowered, and by a bottom face arranged opposed to the other face of the port door; raising/lowering means joined to the port door, for raising and lowering the port door along a direction perpendicular to the face of the port door; and a bellows arranged along an outer periphery of the raising/lowering means; the bellows is coupled at one end thereof to the bottom face of the buffer chamber; and the bellows is fixed at the other end thereof to the raising/lowering means outside the buffer chamber. That is, the port door can be raised and lowered in the clean box without producing dust. 
     Further, the present invention also provides a method in which a clean device including a lid and a main body and having an inside environment kept cleaner than an outside environment to receive a substrate from a clean box, which is kept highly clean inside and has the substrate stored in the inside, and process the substrate, is used to separate the lid from the main body of the clean box to prepare for extraction of the substrate, characterized in that: the clean device includes a load port portion equipped with an opening/closing mechanism having a turnable latch pin to separate the lid from the main body or couple the lid to the main body with the clean box laid thereon; the load port portion includes: a port door capable of being raised and lowered and having one face on which the lid is laid with an outer face of the lid being in contact with the one face; and a buffer chamber defined by wall surfaces arranged surrounding an outer periphery of the port door in a region where the port door is raised and lowered, and by a bottom face arranged opposed to the other face of the port door; the lid of the clean box has: a cam plate capable of engaging with the latch pin and actuating in accordance with a turning movement of the latch pin; and a latch member protruding to an outside of the lid to engage a latch hole of the main body of the clean box or being confined within the lid to be released from the latch hole of the main body of the clean box in accordance with an actuation of the cam plate; the lid of the clean box further includes a non-circular receiving hole; the opening/closing mechanism further includes a protrusion that can be fittingly inserted into the receiving hole; the clean device includes a first exhaust port arranged close to the port door in the buffer chamber and a second exhaust port arranged apart from the first exhaust port of the buffer chamber; and the method includes: making the latch pin capable of engaging with the cam plate when the clean box is laid on the load port, and fittingly inserting the protrusion of the opening/closing mechanism into the lid of the clean box; evacuating an interface portion where the port door and the lid are joined to each other, from the first exhaust port; evacuating the buffer chamber from the second exhaust port; and lowering the port door and transferring the substrate into the buffer chamber. Owing to this method, in a clean device whose internal environment is kept cleaner than an external environment to receive a substrate from a clean box so as to process the substrate, the cleans device having a lid and a main body, being kept highly clean inside, and having the substrate stored in the inside, the substrate can be taken out easily and reliably by separating the lid from the main body of the clean box. 
     Further, to solve the above-mentioned problems, the present invention provides a substrate processing device load port on which a clean box including a main body and a lid, which is laid with a substrate and fitted to the main body, is laid, for extracting the substrate from an inside of the cleaning box, including: a port door having an outer face on which the lid is laid; a buffer chamber defined by wall surfaces arranged surrounding an outer periphery of the port door, and by a bottom face arranged opposed to an inner face of the port door; raising/lowering means joined to the inner face of the port door, for raising and lowering the port door along a direction perpendicular to the face of the port door; and a bellows arranged along an outer periphery of the raising/lowering means, the substrate processing device load port being characterized in that: the bellows is coupled at one end thereof to the bottom face of the buffer chamber; and the bellows is fixed at the other end thereof to the raising/lowering means outside the buffer chamber. That is, the port door can be raised and lowered without producing dust. 
     Further, to solve the above-mentioned problems, the present invention provides an opening/closing mechanism arranged in a substrate processing device to extract a substrate from a clean box and process the substrate by means of the substrate processing device, the cleaning box having: a lid which has a cam plate and a latch member that moves to protrude from the lid or to be confined within the lid by means of the cam plate, and on which the substrate can be laid; and a main body that is coupled to the lid by means of a latch hole for receiving a tip of the latch member when the latch member protrudes from the lid, characterized in that: the opening/closing mechanism includes a rotatable latch pin for engaging the cam plate; the lid further includes a non-circular receiving hole; the opening/closing mechanism includes a protrusion that can be fittingly inserted into the receiving hole; and the opening/closing mechanism and the lid are coupled to each other through engagement between the protrusion and the receiving hole to remove the lid from the clean box. That is, the port door becomes thereby capable of fixing the lid, so the lid can be positively moved away from the main body of the clean box not solely due to the weight of the lid itself. 
     Further, the present invention has been made in view of the above-described circumstances, and it is an object of the present invention to provide an article accommodating container for accommodating an article such as a pod, for example, an SMIF type pod, in which a lid is prevented from falling off etc. at the time of a vacuum break and the generation of particles resulting from a latch mechanism is suppressed. More specifically, it is an object of the present invention to provide an article accommodating container capable of suppressing the generation of particles resulting from a latch mechanism and also preventing particles or the like from entering the inside of the container when the pressure in the container is lower than an atmospheric pressure (i.e., when the inside of the container is depressurized). 
     To solve the above-mentioned problems, an article accommodating container according to the present invention relates to an article accommodating container including: a main body having an inner space capable of accommodating an article and an opening provided vertically below the inner space; and a lid for sealing the inner space by closing the opening, characterized in that: the main body and the lid have a depressurized space arranged therebetween; the lid has a falloff preventing member capable of protruding from an outer periphery of the lid; the main body has a depressed portion for accommodating the falloff preventing member without coming into contact with the falloff preventing member when the falloff preventing member protrudes from the outer periphery of the lid; and the falloff preventing member comes into contact with an inner periphery of the depressed portion when a depressurized state of the depressurized space for sealing the inner space by means of the lid is broken with the falloff preventing member protruding from the outer periphery of the lid. 
     In the aforementioned article accommodating container, it is preferable that the depressurized space be either identical to or different from the internal space. In the aforementioned article accommodating container, it is preferable that the main body and the lid have horizontally opposed first and second planes respectively, and that the falloff preventing member protrude horizontally from the second plane, and that the depressed portion be formed in the first plane. It is preferable that the internal space be circular or rectangular in its horizontal cross-section, and that four corners of the internal space belong to an arc of a circle having a predetermined radius. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a side view of a load port portion of a clean device according to the present invention. 
         FIG. 1B  is a top view of the load port portion of the clean device according to the present invention. 
         FIG. 2  is a view showing a lid of the clean box according to the present invention. 
         FIG. 3A  is a view showing a rotary cam plate of the lid of the clean box according to the present invention. 
         FIG. 3B  is a sectional view showing in detail a positional relationship between the rotary cam plate of the lid of the clean box according to the present invention and a port door of the load port portion, taken along the line  3 B- 3 B in  FIG. 3A . 
         FIG. 4A  is a view showing the rotary cam plate of the lid of the clean box according to the present invention. 
         FIG. 4B  is a sectional view showing in detail a positional relationship between the rotary cam plate of the lid of the clean box according to the present invention and the port door of the load port portion, taken along the line  4 B- 4 B in  FIG. 4A . 
         FIG. 5A  is a view showing the load port portion according to the present invention with the port door in its lowered state. 
         FIG. 5B  is a view showing the load port portion according to the present invention with the port door in its raised state. 
         FIG. 6  is a flow chart showing a loading operation in the load port portion according to the present invention. 
         FIG. 7  is a flow chart showing an unloading operation in the load port portion according to the present invention. 
         FIG. 8A  is a view showing a positional relationship of the port door in the flow of the loading operation and the unloading operation performed in the load port portion according to the present invention. 
         FIG. 8B  is a view showing a positional relationship of the port door in the flow of the loading operation and the unloading operation performed in the load port portion according to the present invention. 
         FIG. 8C  is a view showing a positional relationship of the port door in the flow of the loading operation and the unloading operation performed in the load port portion according to the present invention. 
         FIG. 8D  is a view showing a positional relationship of the port door in the flow of the loading operation and the unloading operation performed in the load port portion according to the present invention. 
         FIG. 9  is a view showing a relationship between a load port portion and an entire clean device according to a conventional art and the present invention. 
         FIG. 10  is a view showing a load port portion of the conventional art. 
         FIG. 11  is a view showing an example of a clean box of the conventional art. 
         FIG. 12  is a view showing an example of a clean device in the case where a common vacuum pump is employed. 
         FIG. 13  is a schematic sectional view showing a pod according to another embodiment of the present invention. 
         FIG. 14  is a bottom view of a main body of the pod shown in  FIG. 13 . 
         FIG. 15  is a bottom view showing the main body of the pod of  FIG. 13  with a lid fitted thereto, and further showing a part relating to a falloff preventing mechanism formed inside the lid. 
         FIG. 16A  is an enlarged sectional view of a main part of a pod according to still another embodiment of the present invention. 
         FIG. 16B  is an enlarged sectional view of a main part of a pod according to still another embodiment of the present invention. 
     
    
    
     BEST MODES FOR CARRYING OUT THE INVENTION 
     Referring to  FIGS. 1A and 1B  to  FIG. 6 , an embodiment of a load port portion  10  of a clean device  1  of the present invention will be described.  FIG. 1A  is an enlarged view of the load port portion  10  of the present invention. The overall construction of the load port portion  10  in the clean device  1  is the same as the construction described as the conventional art referring to  FIG. 9 . The clean device  1  and that of  FIG. 9  have the following respects in common. The clean device  1  is provided with a processing room  60 , a transfer room  50 , and the load port portion  10 . A clean box  2  is laid on the load port portion  10  so as to transfer a substrate  9  into a semiconductor device. The load port portion  10  has a function of removing a lid  2   b  from a main body  2   a  of the clean box  2 . In other words, as is the case with the conventional clean device  1 , the load port portion  10  is connected to the transfer room  50  via a transfer opening  51 , and the load port portion  10  and the transfer room  50  are separated from each other by an opening/closing door  53 . A substantially horizontally held port door  3  is arranged within the load port portion  10 . 
     The load port portion  10  has a buffer chamber  6 , which is surrounded by wall surfaces surrounding the port door  3  on all four sides and a bottom portion located substantially parallel to a lower face of the port door  3 . As is the case with the conventional device, the buffer chamber  6  is classified into two parts for the sake of convenience. That is, one of the parts is an interface space  6   a  on an upper face side of the port door, the other part is the buffer chamber  6  on a lower face side of the port door  3 . 
     The lower face of the port door  3  is connected to a latch opening/closing shaft  4   a  arranged below the port door  3 . The latch opening/closing shaft  4   a  is arranged so as to extend outward and downward through a hole arranged through a bottom face of the buffer chamber  6 . The latch opening/closing shaft  4   a  is connected to an electric actuator  7  as raising/lowering means via a frame  4   b . The frame  4   b  is connected to the electric actuator to raise and lower the latch opening/closing shaft  4   a  vertically. A rotary shaft  33  is arranged within the latch opening/closing shaft  4   a  in a penetrating manner. Unlike the conventional device, the rotary shaft  33  performs a raising/lowering operation as well as a rotating operation. In order to perform the raising/lowering and rotating operations, a rotary actuator  8   a  for rotating the rotary shaft  33  and a raising/lowering cylinder  8   b  for raising/lowering the rotary shaft  33  in the latch opening/closing shaft  4   a  are arranged within the frame  4   b . A substrate detecting sensor  77  is arranged in the load port portion  10  so as to face the wall surfaces surrounding the port door  3  on all four sides. The substrate detecting sensor  77  is composed of emitters  77   a  for radiating infrared rays from loopholes and detectors  77   b  for receiving infrared rays emitted from the emitters. The emitters  77   a  and the detectors  77   b  are arranged on opposed wall surfaces respectively.  FIG. 1B  is a vertical top view of the load port portion  10  shown in  FIG. 1A , showing a positional relationship between the emitters  77   a  and the detectors  77   b . The substrate detecting sensor  77  is not limited to an infrared sensor. As shown in  FIG. 1B , the emitters  77   a  and the detectors  77   b  are arranged such that the substrate  9  crosses optical axes of rays emitted from the emitters  77   a  and reaches the detectors  77   b  when the substrate  9  is raised and lowered. Therefore, if the optical axes are interrupted at a position where the substrate  9  is supposed to cross them when the port door  3  is raised or lowered, it turns out that the substrate  9  is laid on the lid  2   b.    
     Then, the following description will focus especially on differences between the load port portion  10  of the present invention and the conventional load port portion. The load port portion  10  of the present invention and the conventional clean device  1  mainly share the following two features. 
     The first feature is that coupling means is provided as an opening/closing mechanism for coupling the port door  3  to the lid  2   b  of the clean box  2  to open and close the lid  2   b . Owing to this feature, the lid  2   b  can be forcibly removed from the main body  2   a  of the clean box  2  without counting on the weight of the lid  2   b.    
     The second feature is that, while in the conventional art the bellows  31  is mounted in the buffer chamber  6  between the lower face of the port door  3  and the bottom portion of the buffer chamber  6 , in the present invention, the bellows  31 , which is coupled at one end  31   a  thereof to the bottom face portion of the buffer chamber  6  and fixed at the other end  31   b  thereof to the raising/lowering means  4 , is mounted outside the buffer chamber  6 . Thus, it is possible to suppress generation of dust in the buffer chamber  6 . 
     In this specification, the term “coupling” means that the lid  2   b  is coupled so as to move in accordance with a raising/lowering movement of the port door. Those features will be described hereinafter. 
     (Coupling Means) 
     The port door  3  is provided with the opening/closing mechanism of the present invention. The opening/closing mechanism has coupling means for coupling the lid  2   b  of the clean box  2  and the port door  3  to each other. Referring first to  FIG. 2 , the clean box  2 , especially the lid  2   b  of the clean box  2  will be described.  FIG. 2  is a top view showing an internal structure of the lid  2   b  of the clean box  2 . As is the case with the conventional rotary cam plate  21 , the lid  2   b  of the clean box  2  is mounted with a latch mechanism. The latch mechanism includes a generally circular rotary cam plate  21  arranged at the center of the lid  2   b , and a latch member  26 . The rotary cam plate  21  is arranged substantially at the center of the lid  2   b  of the conventional clean box  2  rotatably around the center. Latch holes  21   a  arranged on a circle concentric with the rotary cam plate  21  are defined in a central region of the rotary cam plate  21 . 
     Two cam grooves  23 , which are point-symmetrical to each other with respect to the center of the rotary cam plate  21 , are arranged outside the latch holes  21   a  of the rotary cam plate  21 . Given that each of the cam grooves  23  has one end as a starting point  23   a  and the other end as an end point  23   b , the distance between the starting point  23   a  of the cam groove  23  and the center of the rotary cam plate  21  is the shortest, whereas the distance between the center of the cam groove  23  on the end point  23   b  side of the cam groove  23  and the center of the rotary cam plate  21  is the longest. Each of the cam grooves  23  has such a smooth arcuate shape that the distance from the center of the cam plate  21  gradually changes from the starting point  23   a  to the end point  23   b . On the other hand, the lid  2   b  has the latch member  26  movable parallel to a plane thereof. A driven pin  24  is arranged at an end portion  26   b  of the latch member  26  on the rotary cam plate  21  side. This driven pin  24  is in engagement with the cam groove  23 . The latch member  26  also includes a tip portion  26   a  protruding from a lateral face of the lid  2   a . The latch member  26  is slidably held between a guide member  28   a  and a guide member  28   b  in such a manner that the latch member  26  penetrates through guide holes formed therein. The guide holes are substantially identical to the latch member  26  in cross-sectional shape. A spring  27  is fitted between the guide member  28   a  and the guide member  28   b , urging the latch member  26  to expand to the outside of the lid  2   b . The setting of the urging direction of the spring  27  can be modified as required either to the direction in which the latch member  26  expands outwardly or to a direction in which the latch member  26  contracts inwardly. When the rotary cam plate  21  rotates, the cam groove  23  also rotates in response thereto, so the latch member  26  is accommodated inside the lid  2   b  or protrudes outside the lid  2   b . A latch hole  30  is arranged through an edge of the main body  2   a  of the clean box  2  abutting on the lid  2   b , at a position corresponding to the tip portion  26   a  of the latch member  26 . When the latch member  26  protrudes with the tip portion  26   a  protruding outside the lid  2   b , the tip portion  26  of the latch member  26  is received in the latch hole  30  and engaged therewith, so the lid  2   b  is fixed to the clean box  2 . On the other hand, when the latch member  26  is drawn furthest inside the lid  2   b  due to rotation of the rotary cam plate  21 , the tip portion  26   a  of the latch member  26  is accommodated in the lid  2   b , so the lid  2   b  is not coupled to the clean box  2 . The diameter of the latch hole  30  is sufficiently larger than that of the latch member  26  received in the latch hole  30 , thus preventing dust from being generated through sliding friction between the latch hole  30  and the latch member  26 . With this construction as well, since the lid sticks to the clean box  2  in an attractive manner when the clean box  2  is a vacuum, there is no possibility of the lid  2   b  falling off from the main body  2   a  of the clean box  2 . 
     The lid  2   b  and the port door  3  of the present invention are coupled to each other and therefore equipped with coupling means composed of what are called male-side coupling means and female-side coupling means. It is optional which one of the male-side coupling means and the female-side coupling means is arranged on the lid  2   b  side. This embodiment will be described as a representative example on the premise that the female-side coupling means is arranged on the lid  2   b  side and the male-side coupling means is arranged on the port door  3  side. 
     First of all, the female-side coupling means on the lid  2   b  side will be described. A counter boring  42  and a receiving hole  41  as the female-side coupling means are arranged through a central portion of the lid  2   b . The receiving hole  41  is arranged so as to extend through from the face of the lid  2   b  abutting on the port door  3  to a bottom portion of the counter boring  42 . The receiving hole  41  typically assumes a non-circular shape. For instance, the receiving hole  41  may assume a rectangular or elliptical shape. It is appropriate that the counter boring  42  is larger in size than the receiving hole  41 , and that a bearing surface of the counter boring  42  remains as a seat  41   a  of the receiving hole  41 . 
     Then, the coupling means on the port door  3  side will be described with reference to  FIGS. 3A ,  3 B,  4 A, and  4 B. In this state, namely, the latch opening/closing shaft  4   a  has been raised and the port door  3  abuts on the lid  2   b , as described above as to the conventional art. Each of  FIGS. 3A and 4A  is an enlarged view showing the rotary cam plate  21  portion when the port door  3  abuts on the lid  2   b . On the other hand,  FIGS. 3B and 4B  are sectional views taken along a line  3 B- 3 B of  FIG. 3A  and a line  4 B- 4 B of  FIG. 4A , respectively. 
     The male-side coupling means is arranged at a position corresponding to the center of a rotary circular plate  21  at the end portion of the rotary shaft  33  on the lid  2   b  side. A protrusion  45  as the male-side coupling means is equipped with a cylindrical root portion  45   b  extending from an end face of the rotary shaft  33 , and a brim portion  45   a  arranged on a tip portion side of the root portion  45   b . The brim portion  45   a  achieves its effect if it is larger in cross-sectional area than the root portion  45   b . When a projection plane of the brim portion  45   a  is viewed along a center axis of the rotary shaft  33  from the lid  2   b  side toward the plane of the port door  3 , the projection plane of the brim portion  45   a  is substantially similar in shape to and slightly smaller than a through-hole  42  to the extent that the brim portion  45   a  can be fittingly inserted into the receiving hole  41 . When viewed from that direction after having been further rotated, the brim portion  45   a  deviates in shape from the receiving hole  41 , thus creating an overlapping region. This overlapping region enables engagement with the seat  41   a  of the receiving hole  41  as the bearing surface of the counter boring  42 . In this embodiment, the receiving hole  41  is a substantially rectangular long hole, and the brim portion  45   a  has a substantially rectangular shape allowing insertion into the receiving hole  41  and is slightly smaller than it. 
     The rotary shaft  33  arranged inside the latch opening/closing shaft  4   a  can be raised and lowered in such a manner that the rotary shaft  33  slides along a central axis of a raising/lowering shaft  3  within the latch opening/closing shaft  4   a . On the other hand, the latch pins  32  are arranged at the tip of the latch opening/closing shaft  4   a  so as to protrude vertically from the port door  3 . The latch pins  32  are located at positions corresponding to the latch holes  21   a  of the rotary cam plate  21  on a circumference of a circle substantially concentric with the rotary cam plate  21 , and arranged point-symmetrically to each other with respect to the center of the rotary cam plate  21 . 
     In this case, when the rotary shaft  33  is raised within the latch opening/closing shaft  4   a  as shown in, for example,  FIG. 3B , the brim portion  45   a  is fittingly inserted into the receiving hole  41 , and the latch pins  32  are fittingly inserted into the latch holes  21   a . At this stage, the shapes of the brim portion  45   a  and the receiving hole  41  projected onto the plane of the rotary cam plate  21  are substantially identical to each other. When the rotary shaft  33  is rotated at this stage, the projections of the brim portion  45   a  and the receiving hole  41  onto the plane of the rotary cam plate  21  are different in shape from each other as shown in  FIG. 4A  and create overlapping regions, respectively. Those overlapping regions correspond to the seat  41   a  of the receiving hole  41 . The port door  3  and the lid  2   b  can be coupled to each other through mutual contact of the overlapping regions. 
     The fragile substrate  9  is laid on the lid  2   b  and thus may be damaged when strong vibrations are transmitted to the lid  2   b . Thus, the brim portion  45   a  and the seat  41   a  of the receiving hole  41  do not engage each other when the rotary shaft  33  is rotated. The projections of the brim portion  45   a  and the receiving hole  41  onto the rotary cam plate  21  are different in shape from each other and create overlapping regions when the rotary shaft  33  is rotated. The influence on the substrate  9  can be reduced by thereafter lowering the rotary shaft  33  to bring the overlapping regions into contact with each other. More specifically, the height between the face of the seat  41   a  of the receiving hole  41  as the bearing surface of the counter boring  42  and the face of the brim portion  45   a  contactable with the seat  41   a  (the lower face in this embodiment) is set to a predetermined height (t) as a backlash. As soon as this predetermined height (t) is ensured, the rotary shaft  33  is operated to be rotated and then moved downward. Then, as soon as the rotary shaft  33  is lowered by the predetermined height (t), the seat  41   a  of the receiving hole  41  as the bearing surface of the counter boring  42  and the face of the brim portion  45   a  contactable with the seat  41   a  engage each other, thus completing the process of coupling. 
     If the rotary shaft  33  is set to become as high as the face of the lid  2   b  when being raised to the highest position, the end face  33   a  of the rotary shaft  33  and the face  3   b  of the port door  3  are substantially equal in height to each other, thus allowing abutment on the face of the lid  2   b . The latch pins  32  are fitted into the latch holes  21   a  and turned by rotating the rotary shaft  33 . The latch member  26  thereby moves with respect to the lid  2   b , thus making it possible to open the lid  2   b  from the main body  2   a  of the clean box  2  and fix the lid  2   b  to the port door  3  at the same time. 
     By combining the aforementioned coupling means with the clean box  2  described with regard to the conventional art, it becomes possible to realize an efficient step of simultaneously performing the operation of fixing/releasing the lid  2   b  to/from the port door  3  and the operation of coupling the lid  2   b  to the port door  3 . This step will be described with reference to  FIGS. 2 ,  3 A,  3 B,  4 A, and  4 B. 
     In this case, a representative example in which the lid  2   b  fixed to the main body  2   a  of the clean box  2  is released from the main body  2   a  will be described. In fixing the lid  2   b  fixed to the main body  2   a  of the clean box  2  to the main body  2   a , the following steps should be carried out in reverse order. At first, the port door  3  is located at the highest position. The end face of the latch opening/closing shaft  4   a  and the end face of the port door  3  are located at the same position. In this state, the clean box  2  is laid on the load port portion  10 . At this moment, the clean box  2  is laid such that the protrusion  45  is fittingly inserted into the lid  2   b  and that the latch pins  32  are fittingly inserted into the latch holes  21   a . At this moment, the protrusion  45  and the latch pins  32  are fittingly inserted into the receiving hole  41  and the latch holes  21   a , respectively. In this state, the latch member  26  protrudes from the lid  2   b  and is received in the latch hole  30  arranged through the lateral face of the clean box  2 , so the lid  2   b  is fixed to the clean box  2 . When the rotary shaft  33  is rotated at this stage, the latch pins  32  press the edges of the latch holes  21   a  to rotate the rotary cam plate  21 . The driven pin  24  moves along the cam groove  23  as the rotary cam plate  21  rotates. In accordance with this movement of the driven pin  24 , the latch member  26   a  moves so as to be accommodated in the lid  2   b  and is released from the latch hole  30  of the clean box  2 . The brim portion  45   a  of the protrusion  45  also rotates as the rotary cam plate  21  rotates by being pressed by the latch pins  32 . The brim portion  45   a  and the receiving hole  41  are positioned so as to create overlapping regions when viewed from the lid  2   b  side in the direction of the plane of the port door  3  along the central axis of the rotary shaft  33 , such that the brim portion  45   a  can be engaged with the seat  41   a  of the receiving hole  41 . As a result, a preparation for coupling is completed (which is referred to as an unlock preparation completion state). Then, when the rotary shaft  33  is lowered by the height t as the backlash, the overlapping regions of the projections of the brim portion  45   a  and the receiving hole  41  abut on each other and engage each other to couple the lid  2   b  to the port door  3 , so the clean box  3  is also fixed to the lid  2   b  (which is referred to as a hold-down preparation completion state). 
     (Arrangement of Bellows) 
     Then, the bellows  31  of the present invention will be described with reference to  FIGS. 1A ,  5 A, and  5 B. 
     The bellows  31  is tightly coupled at one end  31   a  thereof to the bottom face outside the buffer chamber  6 , and is fixed at the other end  31   b  thereof to the frame  4   b  and the latch opening/closing shaft  4   a  for performing raising/lowering operations by means of the electric actuator outside the buffer chamber  6 . Thus, the bellows  31  is always arranged outside the buffer chamber  6 . If this arrangement is adopted, the bellows  31  always performs its expansion/contraction movements outside the buffer chamber  6  both when the port door  3  is lowered as shown in  FIG. 5A  and when the port door  3  is raised as shown in  FIG. 5B . By adopting this arrangement, the clearance between the bellows  31  and the latch opening/closing shaft  4   a  located inside the bellows  31  as well as the buffer chamber  6  can maintain vacuum even when the buffer chamber  6  is evacuated through an exhaust port  58 . Although conventionally the bellows  31  generates dust in the buffer chamber  6 , adoption of the arrangement of the present invention produces effects unachievable by the conventional device. That is, (i) the amount of dust can be limited to that of dust flowing into the buffer chamber  6  from a clearance  31   c  between the inside of the bellows  31  and the buffer chamber  6 , and (ii) the bellows  31  usually falls downward due to the gravity and can be prevented from rising. 
     Then, the operation of the load port portion  10  of the clean device  1  of the present invention will be described with reference to  FIGS. 6 ,  7 , and  8 A to  8 D. 
     First of all, a loading operation will be described with reference to  FIG. 6 . 
     At first, the port door  3  is located in the load port portion  10  with its load port having been raised to the highest position (a state shown in  FIG. 8A ). At this stage, a robot (not shown) or a transfer vehicle (not shown) arranged outside the clean device  1  lays the clean box  2  on the port door  3  of the load port portion  10  of the clean device  1 . In this process, the latch pins  23  and the protrusion  45  are fitted into the latch holes  21   a  and the receiving hole  41 , respectively (S 601 ). Then, the presence or absence of the clean box  2  is confirmed by means of a clean box presence/absence detecting sensor on the port door  3  (S 602 ). Then, the interface space  6   a  is evacuated by carrying out suction and discharge using a first vacuum pump  72  connected to a first exhaust port  81  arranged in the vicinity of the port door  3  that is in its waiting state in the buffer chamber (S 603 ). The interface space  6   a  is theoretically an interface between the port door  3  and the lid  2   b  and practically a narrow clearance created between the port door  3  and the lid  2   b  when the port door  3  is in its raised state. Then, a vacuum pressure of the interface space  6   a  is detected by an interface pressure sensor  71  arranged in the vicinity of the interface space  6   a , and it is confirmed whether or not the detected vacuum pressure has reached a predetermined pressure. When the vacuum pressure has not reached the predetermined pressure, further evacuation is carried out from the first exhaust port  81  using the first vacuum pump  72  (S 604 ). By making the interface space  6   a  itself a vacuum, the port door  3  and the lid  2   b  stick to each other. Subsequently, a vacuum pressure in the buffer chamber  6  is detected by a buffer chamber pressure sensor  74 , and it is confirmed whether or not the detected vacuum pressure has reached a predetermined pressure. When the detected vacuum pressure has not reached the predetermined pressure, the buffer chamber  6  is evacuated by performing suction and discharge from a second exhaust port  82  arranged apart from the first exhaust port  81  at a position most effective for discharge of the volume of the buffer chamber  6 , namely, at a position close to the center or bottom portion of the buffer chamber  6 , using a second vacuum pump  75  connected to the second exhaust port  82  (S 605 ). The rotary shaft  33  is rotated by driving the rotary actuator  8   a . Thus, the unlock preparation completion state is achieved as described above (S 606 ). The steps described hitherto create the state shown in  FIG. 8A . 
     Then, when the rotary shaft  33  is lowered by the raising/lowering cylinder  8   b , the hold-down preparation state is achieved as described above (S 607 ). The port door  3  is lowered by drive means, so the lid  2   b  is separated from the main body  2   a  of the clean box  2 , lowered to a predetermined position, and then stopped (S 608 ). The substrate detecting sensor  77  in the buffer chamber  6  detects the presence/absence of the substrate  9  on the lid  2   b  (S 609 ). The robot arm  55  in the transfer room  50  transfers the substrate  9  to the processing room  60  (S 610 ). The steps described hitherto create a state shown in  FIG. 8B . 
     First of all, an unloading operation will be described with reference to  FIG. 7 . Basically, the loading operation is performed in reverse order. 
     The robot arm  55  in the transfer room  50  fetches the processed substrate  9  from the processing room  60  and lays it at a predetermined position of the lid  2   b  on the port door  3  waiting in the buffer chamber  6  of the load port portion  10  (S 701 ). The substrate detecting sensor  77  confirms whether or not the substrate  9  is appropriately laid on the port door (S 702 ). A vacuum pressure in the buffer chamber  6  is detected by the buffer chamber pressure sensor  74 , and it is confirmed whether or not the detected vacuum pressure has reached a predetermined pressure. When the detected vacuum pressure has not reached the predetermined pressure, further evacuation is carried out from the second exhaust port  82  using the second vacuum pump  75  (S 703 ). It is confirmed whether or not the rotary actuator  8   a  is in the unlock preparation completion state and whether or not the raising/lowering cylinder  8   b  is in the hold-down preparation state (S 704 ). The electric actuator  7  raises the port door  3  and closes the buffer chamber  6 . In this state, the lid  2   b  closes the main body  2   a  of the clean box  2 . Then, when the rotary shaft  33  is raised by the raising/lowering cylinder  8   b , the shape of the brim portion  45   a  and the receiving holes  41  are disengaged from each other. When the rotary actuator  8   a  is driven at this stage to rotate the rotary shaft  33 , the latch member  26  of the lid  2   b  is inserted into the latch hole  30  through rotation of the rotary cam plate  21 . The brim portion  45   a  becomes drawable from the receiving hole  41  (S 705 ). Subsequently, the vacuum interface space  6   a  is charged with high-purity nitrogen gas from an N 2  bomb  73  and purged of the nitrogen gas to be held again at the atmospheric pressure. This is confirmed using the interface space pressure sensor  71  (S 706 ). This step is intended to prevent the port door  3  and the lid  2   b  from remaining stuck to each other as in the case where the interface space  6   a  is a vacuum. The robot (not shown) or the transfer vehicle (not shown) transfers the clean box  2  out from the load port portion  10  of the clean device  1  (S 707 ). 
     Although the foregoing embodiment has been described on the premise that the first vacuum pump  72  and the second vacuum pump  75  are separate from each other, the first vacuum pump  72  and the second vacuum pump  75  can be integrated into a single common vacuum pump. In this case, the second vacuum pump  75  is employed as the common vacuum pump instead of the first vacuum pump  72  as shown in, for example,  FIG. 12 . In this embodiment, the second vacuum pump  75  which is the common vacuum pump is connected to a flow channel  85 . The flow channel  85  is connected to a first flow channel  83  leading to the first exhaust port  81  and a second flow channel  84  leading to the second exhaust port  82 . The first flow channel  83  is provided with a valve  87  for discharging gas from flow channels on the first exhaust port  81  side by means of the vacuum pump. When the valve  87  is opened, it is possible to suck/discharge gas into/from the flow channels of a system on the first exhaust port  81  side including the first flow channel  83 , and thus suck/discharge gas into/from the interface space  6   a . On the other hand, the second flow channel  84  is provided with a valve  86  for discharging gas from flow channels on the second exhaust port  82  side by means of the vacuum pump. When the valve  86  is opened, it is possible to suck/discharge gas into/from the flow channels of a system on the second exhaust port  82  side including the second flow channel  84 , and thus suck/discharge gas into/from the buffer chamber  6 . Thus, the same effect as in the foregoing embodiment in which the first vacuum pump  72  and the second vacuum pump  75  are separate from each other is achieved even when the single common vacuum pump is employed. 
     The present invention achieves the following effect. 
     By coupling the port door of the load port portion to the lid of the clean box and mounting the bellows outside the buffer chamber, the lid and the main body of the clean box can be coupled/decoupled to/from each other while the clean device is kept highly clean. 
     Next, the construction of a pod according to still another embodiment of the present invention will be described with reference to the figures.  FIG. 13  is a schematic sectional view of an article accommodating container according to the present invention, that is, a pod.  FIG. 14  is a bottom view of a main body of the pod with its lid having been removed.  FIG. 15  is a bottom view of the pod with its lid fitted thereto, partially showing an internal structure thereof. In those figures, components performing operations similar to those of the components described in the conventional art will be described using the same reference symbols as used in  FIGS. 9 to 11 . The load port and the like described in the conventional art with reference to  FIG. 10  are employed. 
     (Shape of Pod) 
     The pod  2  according to the present invention is composed of the main body  2   a  and the lid  2   b . The main body  2   a  has an outward appearance of a generally cubic shape having a generally tubular first inner space  111   a  and a generally cubic second inner space  111   b  formed therein. The first inner space  111   a  assumes a circular shape or a generally rectangular shape whose four corners each are formed of a part of a circular arc having an arbitrary diameter when viewed from above. The second inner space  111   b  continues to the first inner space  111   a  below the first inner space  111   a . The first inner space  111   a  has a size large enough to accommodate an article to be held therein, in this case, the reticle (or substrate)  9  having a contour indicated by a chain double-dashed line in the figure. The main body  2   a  has on its lateral portion a brim portion  112  used in transferring the pod. A circular window portion  113  for observing an inner space, to which a glass or the like is fixed to maintain airtightness of the inner space, is arranged on the upper face of the main body  2   a.    
     A plurality of work holding-down pins  114  extending downward from above to restrict the vertical movement of the reticle are arranged at equal intervals in the circumferential direction of the reticle in the first inner space  111   a . The work holding-down pins  114  are in contact at their protruding tip portions with the reticle so as to reduce the area of contact with the reticle. Each of the work holding-down pins  114  is fixed to the main body  2   a  via a support member  114   b  so as to prevent an excessive load from being applied to the reticle. The second inner space  111   b  has a size large enough to accommodate the later-described lid  2   b  and groove portions  115 , which will be described later, formed in two opposed lateral faces of the second inner space  111   b.    
     A work guide  116  and work pins  117  are provided on the upper face of the lid  2   b , which is on the main body  2   a  side in closing the main body  2   a . The work guide  116  has a generally annular shape allowing insertion through the first inner space  111   a . A guide portion  116   a  for guiding an outer periphery portion of the reticle in the inner space on all four sides protrudes from an outer periphery portion of an upper face of the work guide  116 . The work pins  117  are arranged so as to be substantially opposed to the aforementioned work holding-down pins  114 , and their tip portions support the reticle. An O-ring  118  is arranged along an outer periphery of the work guide  116  on the upper face of the lid  2   b . The O-ring  118  is in tight contact with a face  111   c  defining an upper face of the second space  111   b , so the first space  111   a  defined by the main body  2   a  and the lid  2   b  is sealed up. 
     The pod  2  according to the present invention keeps the pressure in the first space  111   a  lower than an ambient pressure (atmospheric pressure), thereby holding the main body  2   a  and the lid  2   b  while ensuring firm contact therebetween. In the pod  2 , the first space  111   a  maintained as a depressurized space has a generally circular cross-sectional shape. As a result, the pod  2  becomes robust against a load resulting from the atmospheric pressure even when there is a great difference between the pressure in the space and the ambient pressure or when the cross-sectional area of the inner space has increased. It is easy to form the pod  2  assuming this shape from a metal such as aluminum, and it is also easy to subject an inner surface thereof to an electrolytic polishing treatment. Generation of particles from the inner surface of the pod or the like can be suppressed by performing the treatment. 
     (Falloff Preventing Mechanism) 
     Next, a falloff preventing mechanism, which is a component added to the pod according to the present invention as a countermeasure against a case where the state of tight contact between the main body  2   a  and the lid  2   b  is broken through a loss of the depressurized state in the aforementioned first space  111   a , will be described in detail. A falloff preventing mechanism  120  for preventing the lid  2   b  from falling off is arranged inside the lid  2   b . The falloff preventing mechanism is composed of a cam plate  121  in the shape of a circular plate, falloff preventing plates  124 , and preventing plate holders  126 . The cam plate  121  is turnably arranged substantially at a central position of the lid  2   b . Engagement holes  121   a  arranged on arbitrary positions on a circumference of a circle spreading around the center of the rotary cam plate  121  are formed therethrough. It is preferable that the engagement holes  121   a  are circular holes arranged point-symmetrically on the circumference of the circle. 
     The engagement holes  121   a , with which the latch pins  32  of the load port portion  10  are engaged, are shaped so as to be able to receive the latch pins  32  and arranged so as to correspond in position to the latch pins  32 . Two cam grooves  123  located point-symmetrically with respect to the center of the cam plate  121  are arranged outside the engagement holes  121   a  of the cam plate  121 . Given that each of the cam grooves  123  has one end as a starting point  123   a  and the other end as an end point  123   b , the distance between the starting point  123   a  of the cam groove  123  and the center of the cam plate  121  is the shortest, whereas the distance between the center of the cam groove  123  on the end point  123   b  side of the cam groove  123  and the center of the cam plate  121  is the longest. 
     Each of the falloff preventing plates  124  is constructed of a generally rod-like member extending on a line connecting the center of the cam plate  121  to substantially central portions of the groove portions  115  provided in the main body  2   a . Each of the preventing plate holders  126  is constructed of a plate-like member extending parallel to the direction in which the falloff preventing plates  124  extend. The preventing plate holders  126  are fixed to the lid  2   b  and support the falloff preventing plates  124  via two bushes  125  such that the falloff preventing plates  124  can be driven in the direction in which they extend. Driven pins  127  are fixed to end portions of the falloff preventing plates  124  on the cam plate  121  side. The driven pins  127  are inserted into the cam grooves  123  in a penetrating manner. Spring members  128  are arranged around spaces between the two bushes  125  of the falloff preventing plates  124 . Stoppers  128   a  fixed to the falloff preventing plates  124  restrict the movement of the spring members  128  in the direction in which the falloff preventing plates  124  extend. Owing to loads applied from the spring members  128  in the direction in which the falloff preventing plates  124  extend, the falloff preventing plates  124  are prevented from trembling at respective positions along their movements and causing vibrations or the like. 
     When the lid  2   b  is laid on the load port portion  10 , the latch pins  132  protruding above the surface of the port door  3  are fittingly inserted into the latch holes  121   a . When the rotary shaft  133  is rotated in this state, the cam plate  121  rotates together with the latch pins  132 , and each of the driven pins  127  at the end of the falloff preventing plate  124  moves from the starting point  123   a  toward the end point  123   b  of a corresponding one of the cam grooves  123 . That is, the driven pins  124  move outward from the center of the rotary cam plate  121 , along the direction in which the falloff preventing plates  124  extend. In accordance with the movements of the driven pins  127 , tip portions  124   a  of the falloff preventing plates  124  move toward the outside of the lid  2   b . The tip portions  124   a  are set to be confined within the lid  2   b  when each of the driven pins  127  is located at the cam groove starting point  123   a , and to protrude from the lid  2   b  when each of the driven pins  127  is located at the cam groove end point  123   b.    
     As described above, the groove portions  115  are formed at the positions corresponding to the tip portions  124   a  of the falloff preventing plates  124  in the main body  2   a  of the clean box  2 . The tip portions  124   a  are located within the groove portions  115  when they protrude outside the lid  2   b . The width, height, and depth of the groove portions  115  are set such that the tip portions  124   a  do not come into contact with any part in the inside of the groove portions  115  in performing a normal operation. Accordingly, no particles or the like are generated as a result of the falloff preventing member according to the present invention, especially the tip portions  124   a  of the falloff preventing plates  124 . In other words, only when the depressurized state of a space operating to keep the main body  2   a  and the lid  2   b  in tight contact with each other is broken, the falloff preventing member operates to prevent the tip portions  124   a  and inner walls of the groove portions  115  from being substantially separated from each other through mutual contact and engagement therebetween. 
     Modified Example 
     Next, a modified example of the pod according to another embodiment of the present invention will be described. 
     Components achieving the same operations and effects as those of the components described in the foregoing embodiment will be described using the same reference symbols. Each of  FIGS. 16A and 16B  is an enlarged sectional view showing an essential part of the pod  2  in this embodiment. In this embodiment, the lid  2   b  is kept in tight contact with the main body  2   a  not by depressurizing the inner space  111   a  but by depressurizing a space  119  provided to keep them in tight contact with each other.  FIG. 16A  shows a case where the space  119  is formed in a region of the lid  2   b  opposed to the face  111   c .  FIG. 16B  shows a case where the space  119  is formed in the face  111   c . To seal up the space, O-rings  118  are arranged in inner and outer peripheral portions of the space  119  having a generally annular shape at such positions as to allow tight contact with the face  111   c.    
     By thus providing the dedicated space  119  operating to keep the main body  2   a  and the lid  2   b  in tight contact with each other, it becomes possible to hold the pressure in the first inner space  111   a  substantially equal to or higher than the atmospheric pressure using, for example, dry nitrogen. The lid  2   b  can be prevented from separating from the main body  2   a  due to the operation of the falloff preventing mechanism even if the depressurized state of the space  119  has been broken. Therefore, in comparison with the conventional SMIF type pod, a reticle and the like can be held inside under the condition of a wider pressure range. The present invention also makes it possible to completely eliminate the phenomena of engagement, abrasion, and the like of the latch member and the like as is inevitably the case with the conventional SMIF type pod. Thus, the amount of particles and the like generated at the time when the main body  2   a  and the lid  2   b  are kept in tight contact with each other can be reduced drastically. 
     In the foregoing embodiment, the tip portion of the falloff preventing member is caused to protrude outside the lid  2   b  by rotating the cam plate in the shape of a circular disc and transmitting this rotational movement to the falloff preventing member via a cam mechanism. However, various known mechanisms can be employed as a drive mechanism for the falloff preventing member as long as its tip portion can be driven reciprocally. In other words, the falloff preventing member can adopt various constructions as long as a part of the falloff preventing member can protrude from the outer periphery portion of the lid when the lid is in tight contact with the main body. The groove portions provided on the main body  2   a  side to accommodate the tip portion of the falloff preventing member are not limited in shape to those of this embodiment either. The groove portions can assume various shapes as long as an inner volume for preventing contact between the tip portion of the falloff preventing member and inner peripheral faces of the groove portions is ensured when the falloff preventing member is normally driven. It is also appropriate to arrange elastic members made of rubber or the like on the inner peripheral faces to absorb an impact caused, for example, when the lid falls off. 
     In this embodiment, the falloff preventing member protrudes in such a direction that the falloff preventing member protrudes between the horizontally opposed faces provided on the main body and the lid, respectively, and the groove portions are provided in those opposed faces. However, the embodiment of the present invention is not limited to this construction. It is also acceptable to adopt a construction in which the falloff preventing member protrudes toward a face vertically opposed thereto, for example, the face  111   c  and a protruding portion of the falloff preventing member, after having protruded into a groove portion provided in the face  111   c , can be engaged with a part of the groove portion. More specifically, a hook-like portion may be provided at the tip of the protruding portion to be rotated within the groove portion to allow engagement. Alternatively, the hook-like portion may further protrude from the tip portion after having been arranged within the groove portion. 
     According to the present invention, the depressurized space formed inside the main body of the pod and the lid serves to ensure tight contact therebetween. The falloff preventing mechanism for preventing the lid from falling off usually does not perform engagement accompanied with friction or the like with the main body portion but comes into contact with a part of the main body portion only when the depressurized state of the depressurized space is broken. In addition, it is not absolutely required that the depressurized space is the article accommodating space within the pod. That is, the depressurized space may be formed for the sole purpose of ensuring tight contact. By adopting this construction, it becomes possible to drastically reduce the amount of particles and the like generated as a result of the construction for actually performing the operations of sealing and the like, in performing the operation of sealing or opening the main body of the pod by means of the lid. 
     Since the falloff preventing mechanism has been added, an accident such as falloff of the lid separated from the main body can be prevented even when the depressurized state of the depressurized space has been broken. Moreover, the falloff preventing mechanism according to the present invention can be substantially composed of the same elements as those constituting a so-called latch mechanism used in fixing the lid to the pod in the conventional art, and can be directly applied to the conventional load port or the like. 
     The main body of the pod according to the present invention is structured such that the space for actually accommodating an accommodated article such as a reticle has a generally circular cross-sectional shape. Thus, the resistance against a differential pressure between the outside and inside of the container is enhanced, so the container can be used as a robust vacuum container. It is easy to form the pod assuming this shape from a metal, and it is possible to easily subject the inside thereof to a treatment of suppressing generation of particles, such as an electrolytic polishing treatment.