Abstract:
A container for storing substrates capable of shortening the cycle time of the production, improving the production efficiency and reducing the production cost is provided. The container for storing substrates is composed of a box for accommodating the substrates, and a closure member for sealingly closing the box by tightly fixing the closure member to the opening of the box. The container for storing substrates is provided with means for temporarily storing a sealing gas and introducing the sealing gas into the box. Also, the container for storing substrates is provided with means for means for temporarily forming a low pressure space for the purpose of evacuating the gas inside of the box by transferring the gas to the low pressure space.

Description:
CROSS REFERENCE TO THE RELATED APPLICATION 
   The subject application is related to subject matter disclosed in the Japanese Patent Application No.Hell-186768 filed in Jun. 30, 1999 in Japan, to which the subject application claims priority under the Paris Convention and which is incorporated by reference herein. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention is related generally to a transportable container for storing substrates such as a semiconductor wafer transportation pod for accommodating a stack of semiconductor wafers. In particular, the present invention is related to a SMIF (Standard Mechanical Interface)-type semiconductor wafer transportation system for accommodating a stack of semiconductor wafers in a SMIF-type box and transporting the stack of semiconductor wafers between the process chambers. 
   2. Description of the Related Art 
   It is a very important gist in the semiconductor production line to improve the device yield. The major causes of lessening the device yield is the existence of contaminant particles consisting of dust, organic substances and so forth. In the prior art technique, it is the measure for meeting the contaminant particles problem to conduct the LSI production processes within a clean room. However, the size of the contaminant particles to be eliminated has been decreased along with the miniaturization of LSIs and the rapidly increasing packing densities and therefore it is difficult to furthermore purify the clean room environment itself in view of avoiding an increase in costs. It is therefore proposed to make use of an SMIF-type system provided with a sealed wafer pod in place of an open cassette which has been used in the prior art technique of the semiconductor wafer transportation. By means of the wafer pod, it is possible to maintain dust-free wafers because the wafers can be accepted, transported and stored in a sealed box implemented with the wafer pod. Furthermore, even if the environment around the process chambers is not so purified, it is possible to conduct the wafer transportation between the process chambers with the wafers free from contaminant particles. 
     FIG. 1A  is a schematic diagram showing the wafer transportation by means of a semiconductor wafer transportation pod which is placed on a wafer pod table  20  for carrying in or out the semiconductor wafers  10 . As illustrated in  FIG. 1A , in the case of the prior art semiconductor wafer transportation pod, the pod lid  14   b  is detached from the wafer pod body  12  when the wafers  10  are carried out from the semiconductor wafer transportation pod and carried in an semiconductor process chamber (not shown in the figure). The detachment of the pod lid  14   b  is performed by means of a lid opening/closing control means  22  provided with a pod lid shutting device  16   b . Inversely, when the wafers  10  are carried in the wafer pod body  12  after the wafers  10  have been processed in the semiconductor process chamber, the lid opening/closing control means  22  then serves to attach the pod lid  14   b  to the wafer pod body  12  in order to sealably close the wafer pod body  12 . 
   On the other hand, in the recent years, there have been demands for protecting the surface of the semiconductor wafers from the generation of natural oxide films by means of the semiconductor wafer transportation pod in addition to demands for excluding contaminant particles. The natural oxide films are undesirable resulting in unexpected troubles during a process so that it is desirable to be able to avoid the formation thereof. Particularly, substantial adverse effects are likely in the case of highly miniaturized LSIs. Because of this, for the purpose of avoiding the generation of natural oxide films, it is proposed to fill the wafer pod with an inactive gas such as nitrogen (N 2 ), argon (Ar) and so forth and to transport the wafer pod as it is. 
   Namely, as illustrated in  FIG. 1B , an inactive gas such as nitrogen is injected into the wafer pod body  12  through the attachment  18  after sealing and fixing the pod lid  14   b  to the wafer pod body  12 . The wafer pod is then transported with the atmosphere of the inactive gas inside of the wafer pod body  12 . The surfaces of the semiconductor wafers  10  shall not be exposed to oxygen but only be exposed to nitrogen during the transportation between the process chambers. Accordingly, it is possible to protect the surfaces of the wafers  10  from the generation of natural oxide films. The semiconductor wafers  10  are also protected from the generation of natural oxide films even in the case that the wafer pod is temporarily stored in a stocker together with the semiconductor wafers  10  therein. 
   However, it takes, for example, about 10 minutes to completely fill the wafer pod body  12  with the inactive gas in the case that the semiconductor wafer transportation pod has been designed to accommodate  25  wafer having a diameter of 300 mm. 
   Because of this, (1) the wafer pod can not be transported to the next semiconductor process chamber just after collecting and transferring the semiconductor wafers  10  into the wafer pod. Namely, the transportation of the wafer pod is delayed by the gas filling time. At the present time, the manufacture process of a semiconductor device is composed of a large number of manufacturing steps in the order of 200 steps, and therefore, if 10 minutes is required for each manufacturing step, it takes about total 33 hours required of the gas filling time for the entire 200 manufacturing steps. Accordingly, there is a problem that the cycle time required for completing all the manufacturing steps is elongated by the gas filling time resulting in deteriorating the effectiveness of the manufacture process, and then an increase in costs. 
   Furthermore, (2) the next wafer pod can not be placed on the wafer pod table  20  during the period that the previous wafer pod is being filled with the gas. Namely, the process of the next wafer pod is therefore delayed by the gas filling time of the previous wafer pod. On the other hand, the semiconductor process chamber of the subject manufacturing step is left idling during the period that the previous wafer pod is being filled with the gas so that the process chamber is used in an ineffective manner. The accumulated loss time is considered to be substantial. Furthermore, even if there are a plurality of the wafer pod tables  20  available in the system, it is the case that all the wafer pod tables  20  are in use. In this case, the process of a wafer pod as transported is delayed until one of the wafer pods has been completely filled with the gas. Accordingly, in the same manner as the above (1), it results in elongating the cycle time required for completing all the manufacture process and deteriorating the effectiveness of the manufacture process, and then an increase in costs. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in order to solve the shortcomings as described above. It is an object of the present invention therefore to provide a container for storing substrates capable of shortening the cycle time of the production, improving the production efficiency and reducing the production cost is provided. 
   In order to accomplish the above and other objects, in accordance with the first aspect of the present invention, a transportable container for sealingly enclosing substrates, the container comprises a box having an opening and receiving the substrates therein; a removable closure member received by the box and capable of closing the box; and a sealing gas introduction system temporarily having a source of a sealing gas to be introduced to purge an interior of the box. 
   In accordance with the first aspect of the present invention, for example, the closure member is provided with a gas holding vessel in which the sealing gas has been injected in advance. The sealing gas is then introduced into the box in order to purge the interior of the box. Namely, in accordance with the first aspect of the present invention, the sealing gas is injected to the gas holding vessel during the period after the substrates are carried out from the box and before the substrates are carried again in the box. The sealing gas as held in the gas holding vessel is then introduced into the box after starting transportation of the box. By this configuration, the sealing gas introduction step to the box can be recognized to virtually disappear. Accordingly, there is no need for an extra time as required to inject the sealing gas to the box so that the transportation of the wafer pod can be accelerated by the extra time which has been dispensed with. As a result, the cycle time required for completing all the manufacture process can be shortened to realize the improvement of the production efficiency and the reduction of the production cost. 
   The second aspect of the present invention resides in a transportable container for sealingly enclosing substrates, the container comprising a box having an opening and receiving the substrates therein; a removable closure member for received by the box and capable of closing the box; and an exhaustion system temporarily having a low pressure space whose pressure is lower than a pressure of a surrounding environment outside the container for exhausting a gas from an interior of the box by connecting the low pressure space to the interior of the box. 
   In accordance with the second aspect of the present invention, for example, the closure member is provided with a vacuum chamber which is evacuated to a pressure which is lower than the pressure of the atmosphere to some extent, i.e., “in a vacuum condition”, in order to evacuate the interior of the box by connecting the vacuum chamber to the interior of the box, which is therefore in a vacuum condition thereafter. Namely, in accordance with the second aspect of the present invention, the vacuum chamber is evacuated in advance during the period after the substrates are carried out from the box and before the substrates are carried in the box. The box is then evacuated by means of the vacuum chamber during the transportation of the box. By this configuration, the evacuation step of the box can be recognized to virtually disappear. Accordingly, there is no need for an extra time as required for the evacuation of the box. As a result, the cycle time required for completing all the manufacture process can be shortened to realize the improvement of the production efficiency and the reduction of the production cost. Furthermore, in accordance with the second aspect of the present invention, it is possible to maintain the sealed structure of the box for a longer time and therefore the substrates as stored in the box can be maintained in a highly purified environment for a longer time. 
   Other and further objects and features of the present invention will become obvious upon an understanding of the illustrative embodiments about to be described in connection with the accompanying drawings or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employing of the invention in practice. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1A  is a schematic diagram showing the procedure of transferring semiconductor wafers from a semiconductor wafer transportation pod to a semiconductor process chamber in accordance with a prior art technique. 
       FIG. 1B  is a schematic diagram showing the procedure of the injection of a sealing gas to a semiconductor wafer transportation pod in accordance with the prior art technique. 
       FIG. 2  is a schematic diagram showing the procedure of transferring semiconductor wafers from a semiconductor wafer transportation pod in accordance with the present invention to a semiconductor process chamber. 
       FIG. 3A  is a schematic diagram showing the procedure of transferring semiconductor wafers to a semiconductor process chamber from a semiconductor wafer transportation pod in accordance with a first embodiment of the present invention. 
       FIG. 3B  is a schematic diagram showing the semiconductor wafer transportation pod in accordance with the first embodiment of the present invention which is transported between the process chambers. 
       FIG. 4  is a cross sectional view showing the configuration of the pod lid in accordance with the first embodiment of the present invention. 
       FIG. 5  is a plan view showing the configuration of the pod lid shutting device having been used in the prior art technique. 
       FIG. 6A  is a plan view showing the configuration of the pod lid in accordance with the prior art technique. 
       FIG. 6B  is a plan view showing the configuration of the pod lid in accordance with the first embodiment of the present invention. 
       FIG. 7A  is a schematic diagram the procedure of transferring semiconductor wafers to a semiconductor process chamber from a semiconductor wafer transportation pod in accordance with an exemplary modification of the first embodiment of the present invention. 
       FIG. 7B  is a schematic diagram showing the procedure of exhausting the space defined between two rubber gaskets and the contact surface in accordance with the exemplary modification of the first embodiment of the present invention. 
       FIG. 8A  is a plan view showing the configuration of the pod lid shutting device in accordance with the exemplary modification of the first embodiment of the present invention. 
       FIG. 8B  is a plan view showing the configuration of the pod lid in accordance with the exemplary modification of the first embodiment of the present invention. 
       FIG. 9A  is a schematic diagram the procedure of transferring semiconductor wafers to a semiconductor process chamber from a semiconductor wafer transportation pod in accordance with a second embodiment of the present invention. 
       FIG. 9B  is a schematic diagram showing the semiconductor wafer transportation pod in accordance with the second embodiment of the present invention which is transported between the process chambers. 
       FIG. 10  is a graphical diagram showing the leak-proof characteristic in the case of the second embodiment of the present invention in contrast to the leak-proof characteristic in the case of the modification of the first embodiment of the present invention. 
       FIG. 11A  is a cross sectional view showing the configuration of the pod lid in accordance with the second embodiment of the present invention. 
       FIG. 11B  is a plan view showing the configuration of the pod lid in accordance with the second embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Various embodiments of the present invention will be described with reference to the accompanying drawings. It is to be noted that the same or similar reference numerals are applied to the same or similar parts and elements throughout the drawings, and the description of the same or similar parts and elements will be omitted or simplified. 
   First Embodiment 
   As illustrated in  FIG. 2 , a semiconductor wafer transportation pod in accordance with the present invention is placed on a wafer pod table  20  located in front of a semiconductor process chamber  26  when semiconductor wafers  10  are carried out from the semiconductor process chamber  26  or are carried in the semiconductor process chamber  26 . In usual cases, 2 to 4 wafer pod tables  20  are assigned to one semiconductor process chamber  26 . The wafer pod table  20  is used to support the semiconductor wafer transportation pod that is transported from the previous semiconductor process chamber  26  for use in the previous manufacturing step. The pod lid  14  is detached from the wafer pod body  12  after placing the wafer pod. The detachment of the pod lid  14  is performed by means of the lid opening/closing control means  22 . The lid opening/closing control means  22  is also used to fix the pod lid  14  to the wafer pod body  12 . In another case, these procedures may be manually conducted. The lid opening/closing control means  22  is provided with a pod lid shutting device  16  so that the detachment and the attachment of the pod lid  14  is performed by coupling the pod lid shutting device  16  with the pod lid  14 . 
   After the detachment of the pod lid  14  is completed, a wafer transfer means  24  provided for the semiconductor process chamber  26  serves to transfer, one after another, the semiconductor wafers  10  located in the wafer pod body  12  to the semiconductor process chamber  26 . The semiconductor process chamber  26  is used to perform a semiconductor manufacturing step such as the ion-implantation step, the diffusion step, the photolithography step, the thin film formation step, the etching step or the like. After completion of the manufacturing step, the semiconductor wafer  10  is then transferred from the semiconductor process chamber  26  to the wafer pod body  12  by means of the wafer transfer means  24 . When all the wafers  10  have been processed in the current manufacturing step and transferred to the wafer pod body  12 , the pod lid  14  is sealingly fixed again to the wafer pod body  12  by means of the lid opening/closing control means  22 . The wafer pod is then transported to the next semiconductor process chamber for the subsequent manufacturing step, for example, by means of operator&#39;s hands, a transportation machine on the floor such as AGV(Automated Guided Vehicle), RGV(Rail Guided Vehicle) or the like, or a transportation machine on the ceiling such as OHT(Overhead Transpotation) or the like. 
     FIG. 3A  is a schematic diagram showing the wafer transportation by means of the semiconductor wafer transportation pod which is designed in accordance with a first embodiment of the present invention and placed on the wafer pod table  20  for carrying in or out the semiconductor wafers  10 .  FIG. 3B  is a schematic diagram showing the semiconductor wafer transportation pod in accordance with the first embodiment of the present invention which is transported between the process chambers. 
   As illustrated in  FIG. 3A , the semiconductor wafer transportation pod in accordance with the first embodiment of the present invention is composed of the wafer pod body  12  for accommodating and storing the wafers  10  and transporting the semiconductor wafers  10  between the process chambers, and the pod lid  14   a  sealingly fixed to the wafer pod body  12  in order to tightly close the interior of the wafer pod body  12 . The wafer pod body  12  is provided with an opening located on a side wall for carrying in/out the semiconductor wafers  10  and composed of an appropriate material which outputs few particles. The opening is adapted to be engaged with the pod lid  14   a  in order to sealingly close the interior of the wafer pod body  12 . Not shown in the figure, the wafer pod body  12  is provided with a plurality of grooves aligned in the horizontal direction and arranged in parallel to each other with a constant interval in order to directly accommodate a plurality of the wafers  10 , for example, 13 wafers, 25 wafers and so on. The wafer pod body  12  is also provided with a handling grip(s) located on the other side walls, the upper wall, or the bottom wall. An operator or a transportation robot can carry the wafer pod for transportation by means of the handling grip. 
   The pod lid  14   a  is formed with a gas holding vessel  28  which constitutes the important feature of the present invention. The gas holding vessel  28  is provided for temporarily holding an sealing gas with which the wafer pod body  12  is filled. The sealing gas is injected to the gas holding vessel  28  by the lid opening/closing control means  22 . After the pod lid  14   a  formed with the gas holding vessel  28  is detached from the wafer pod body  12 , the attachment  18  is connected to the pod lid  14   a  through the pod lid shutting device  16   a . The sealing gas is transferred to the pod lid  14   a  from the lid opening/closing control means  22  through the attachment  18  and injected to the gas holding vessel  28  through a conduit formed inside of the pod lid  14   a . The gas holding vessel  28  serves to temporarily hold a sufficient amount of the sealing gas for completely replacing the resident gas in the wafer pod body  12 . The sealing gas is held in the gas holding vessel  28  in a compressed condition at a constant pressure. The sealing gas is an inactive gas such as nitrogen, argon. 
   On the other hand, as illustrated in  FIG. 3B , the sealing gas in the gas holding vessel  28  is then injected to the wafer pod body  12  during the transportation of the wafer pod. While the sealing gas is injected to the wafer pod body  12  through the conduit  30  inside of the pod lid  14   a , the residual gas inside of the wafer pod body  12  is exhausted to the outside through a conduit  32  inside of the pod lid  14   a . By this configuration, the residual gas inside of the wafer pod body  12  is completely replaced by the sealing gas after a certain time elapses. 
   Next, the operation of the first embodiment of the present invention will be explained with reference to  FIG. 3A  and  FIG. 3B . The operation of the first embodiment of the present invention consists generally of the following two operations.
     (1) Injection of the sealing gas to the gas holding vessel  28 .   (2) Injection of the sealing gas to the wafer pod body  12 .   

   Firstly, in accordance with the first embodiment of the present invention, the procedure of the injection of the sealing gas to the gas holding vessel  28  is performed during the step of carrying out the semiconductor wafers  10  from the wafer pod body  12 , the step of processing the semiconductor wafers  10  and the step of carrying the semiconductor wafers  10  into the wafer pod body  12  as illustrated in  FIG. 3A . In the prior art technique, the pod lid  14   a  is left supported by the pod lid shutting device  16   a  without any operation during the step of carrying out, the step of processing the semiconductor wafers  10  and the step of carrying in. However, in accordance with the first embodiment of the present invention, the sealing gas is injected to the gas holding vessel  28  by making use of the inoperative periods in parallel with these steps. The injection step can be completed within the step of processing the semiconductor wafers  10 . Accordingly, there is no need for an extra time as required to complete the injection of the sealing gas to the gas holding vessel  28 . 
   Next, as illustrated in  FIG. 3B , the injection of the sealing gas to the wafer pod body  12  is then performed during the transportation of the wafer pod. After transferring the semiconductor wafers  10 , the wafer pod is transported to the next process chamber used in the subsequent manufacturing step by means of an appropriate transportation system (not shown in the figure). The sealing gas inside of the gas holding vessel  28  is then transferred to the wafer pod body  12  during the transportation. Since the sealing gas is held in the gas holding vessel  28  at a certain pressure, it is transferred to the wafer pod body  12  through the conduit  30  by its pressure when a valve is opened. The residual gas inside of the wafer pod body  12  is exhausted to the outside of the wafer pod at the same time so that the interior of the wafer pod body  12  finally becomes in a sealing gas atmosphere. The gas injection time for injecting the sealing gas to the wafer pod body  12  is about 10 minutes in the case that the semiconductor wafer transportation pod has been designed to accommodate  25  wafer having a diameter of 300 mm. Accordingly, from the overall view point, the injection step can be recognized as completed just after starting the transportation of the wafer pod. In the prior art technique, the injection to the wafer pod body  12  is conducted before the transportation of the wafer pod. Because of this, the transportation of the wafer pod is delayed by the gas injection time and therefore resulting in elongating the cycle time required for completing all the manufacture process. In accordance with the first embodiment of the present invention, the wafer pod body  12  is filled with the sealing gas which has been temporarily stored in the gas holding vessel  28  during the transportation of the wafer pod. By this configuration, there is virtually no additional time required for the injection step to the wafer pod body  12 . 
   In accordance with the first embodiment of the present invention, the injection of the sealing gas to the wafer pod body  12  is carried out in steps of (1) injecting the sealing gas to the gas holding vessel  28  inside of the pod lid  14   a  in order to temporarily store the sealing gas, and (2) transferring the sealing gas as stored in the gas holding vessel  28  to the wafer pod body  12  in order to replace the residual gas inside of the wafer pod body  12 . Also, in accordance with the first embodiment of the present invention, the injection of the sealing gas to the gas holding vessel  28  is performed during the step of carrying out the semiconductor wafers  10  from the wafer pod body  12 , the step of processing the semiconductor wafers  10  and the step of carrying the semiconductor wafers  10  into the wafer pod body  12 . Accordingly, there appears no time required for the injection steps (1) and (2) to be added to the cycle time required for completing all the manufacture process. By this configuration, the cycle time is shortened resulting in the improvement of the production efficiency and reduction of the production cost. 
   The pod lid  14   a  in accordance with the first embodiment of the present invention is designed for example as illustrated in  FIG. 4 .  FIG. 4  is a cross sectional view showing the configuration of the pod lid  14   a  in accordance with the first embodiment of the present invention. As illustrated in  FIG. 4 , the pod lid  14   a  in accordance with this embodiment of the present invention is composed therein of the gas holding vessel  28 , the conduit  30  for injecting the sealing gas inside of the gas holding vessel  28  to the wafer pod body  12 , an opening/closing valve  34  and a filter  36  which are provided in the middle of the conduit  30 , a conduit  40  for injecting the sealing gas to the gas holding vessel  28 , an opening/closing valve  42  provided in the middle of the conduit  40 , and a conduit  32  for communicating the side of the pod lid  14   a  facing the wafer pod body  12  with the opposite side of the pod lid  14   a , and a pressure valve  38  provided in the middle of the conduit  32 . 
   In  FIG. 4 , when the opening/closing valve  42  is opened, the gas holding vessel  28  receives the sealing gas through the conduit  40 . The conduit  40  is designed to be able to make connection with the attachment  18  of the lid opening/closing control means  22  through the pod lid shutting device  16   a  in order to transfer the sealing gas as supplied from the attachment  18  to the gas holding vessel  28 . These procedures is conducted with the pod lid  14   a  being detached from the wafer pod body  12  and fixed to the pod lid shutting device  16   a.    
   On the other hand, when the opening/closing valve  34  is opened, the sealing gas contained inside of the gas holding vessel  28  is injected to the wafer pod body  12  through the conduit  30 . As explained above, since the sealing gas is held compressed in the gas holding vessel  28 , the sealing gas flows by itself into the wafer pod body  12  through the conduit  30  with the opening/closing valve  34  being opened. The filter  36  serves to improve the purity of the sealing gas temporarily stored in the gas holding vessel  28  in advance of the injection to the wafer pod body  12 . By this configuration, the purity of the semiconductor wafers  10  inside of the wafer pod body  12  can be furthermore improved. While the pressure in the wafer pod body  12  is gradually elevated as the sealing gas is flowing into the wafer pod body  12 , the pressure valve is opened when the pressure in the wafer pod body  12  reach a certain level. The residual gas inside of the wafer pod body  12  is exhausted to the outside of the wafer pod through the conduit  32  when the pressure valve  38  is opened. As a result, after a predetermined time elapses, the residual gas inside of the wafer pod body  12  is completely replaced by the sealing gas. These procedures are conducted with the pod lid  14   a  being sealingly fixed to the wafer pod body  12 . 
   The procedure as described above is preferably conducted in response to the opening action and the closing action of the pod lid  14   a . Namely, when the pod lid  14   a  is detached from the wafer pod body  12 , the opening/closing valve  42  is operated to open while the opening/closing valve  34  is operated to close, followed by the injection of the sealing gas to the gas holding vessel  28 . Also, when the pod lid  14   a  is fixed to the wafer pod body  12 , the opening/closing valve  34  is operated to open while the opening/closing valve  42  is operated to close, followed by the injection of the sealing gas to the wafer pod body  12 . This is an effective sequence. 
   In accordance with the first embodiment of the present invention, therefore, it is proposed to control the opening/closing operation of the opening/closing valves  34  and  42  in response to the opening/closing operation of the pod lid  14   a . In practice, the pod lid shutting device  16   a  for attaching and detaching the pod lid  14   a  is designed, for example, as described in the followings. 
     FIG. 5  is a plan view showing the configuration of the pod lid shutting device  16   b  having been used in the prior art technique. Also,  FIG. 6A  and  FIG. 6B  are plan views showing the configuration of the pod lid  14 ( 14   a ,  14   b ).  FIG. 6A  is a plan view showing the configuration of the pod lid  14   b  in accordance with the prior art technique while  FIG. 6B  is a plan view showing the configuration of the pod lid  14   a  in accordance with the first embodiment of the present invention. As illustrated in  FIG. 5 , the pod lid shutting device  16   b  is provided with a locking/unlocking control mechanism  44 , a gas injection connecting aperture  48  to which the attachment  18  is connected, a gas exhaustion connecting aperture  50  for exhausting the residual gas inside of the wafer pod body  12 , and a valve opening/closing control mechanism  46  for controlling the opening/closing operation of the gas injection connecting aperture  48  and a gas exhaustion connecting aperture  50 . Meanwhile, in accordance with the first embodiment of the present invention, there is no need for the gas exhaustion connecting aperture  50 . 
   In accordance with the prior art technique, the opening/closing operation of the pod lid  14  is conducted by means of the locking/unlocking control mechanism  44  of the pod lid shutting device  16   b . When the pod lid shutting device  16   b  is engaged with the pod lid  14   b , the locking/unlocking control mechanism  44  is connected to the locking/unlocking mechanism  54  of the pod lid  14   b  as illustrated in  FIG. 6A . The locking/unlocking mechanism  54  is rotated by turning the locking/unlocking control mechanism  44  in the same direction. Linking bars  56  serves to move locking pins  58  in the vertical direction when the locking/unlocking mechanism  54  rotates. The locking pins  58  are then projected from the pod lid  14   b  in order to sealingly fix the pod lid  14   b  to the wafer pod body  12 . On the other hand, when the pod lid  14   b  is detached from the wafer pod body  12 , the locking pins  58  are controlled to be drawn back into the pod lid  14   b.    
   Furthermore, in accordance with the first embodiment of the present invention, the opening/closing valves  34  and  42  are controlled by making use of the locking/unlocking mechanism  54 . As illustrated in  FIG. 6B , in the case of the pod lid  14   a  according to this embodiment, the opening/closing operation of the opening/closing valves  34  and  42  is controlled by linking bars  62  when the locking/unlocking mechanism  54  rotates. More specifically speaking, when the locking pins  58  are drawn back into the pod lid  14   b  by means of the linking bars  56  in response to the rotation of the locking/unlocking mechanism  54 , the linking bars  62  also serve to close the opening/closing valve  34  and open the opening/closing valve  42  at the same time. On the other hand, when the locking pins  58  are projected from the pod lid  14   b  by means of the linking bars  56  in response to the rotation of the locking/unlocking mechanism  54 , the linking bars  62  also serve to open the opening/closing valve  34  and close the opening/closing valve  42  at the same time. By this controlling mechanism, when the pod lid  14   a  is detached from the wafer pod body  12 , the injection of the sealing gas to the gas holding vessel  28  can be started with the opening/closing valve  42  being opened and the opening/closing valve  34  being closed. Also, when the pod lid  14   a  is fixed to the wafer pod body  12 , the injection of the sealing gas to the wafer pod body  12  can be started with the opening/closing valve  42  being closed and the opening/closing valve  34  being opened. 
   In accordance with the first embodiment of the present invention, the pod lid  14   a  is implemented with the gas holding vessel  28  so that the sealing gas can be injected to the gas holding vessel  28  during the period after the semiconductor wafers  10  are carried out from the wafer pod body  12  and before the semiconductor wafers  10  are carried in the wafer pod body  12 . The sealing gas having been injected to the gas holding vessel  28  is then transferred to the wafer pod body  12  during the transportation of the wafer pod. By this configuration, the sealing gas injection step to the wafer pod body  12  can be recognized to virtually disappear. Accordingly, there is no need for an extra time as required to inject the sealing gas to the wafer pod body  12  so that the transportation of the wafer pod can be accelerated by the extra time which has been dispensed with. As a result, the cycle time required for completing all the manufacture process can be shortened to realize the improvement of the production efficiency and the reduction of the production cost. 
   Next, an exemplary modification of the first embodiment of the present invention will be explained. This exemplary modification is described to show an example which is capable of improving the sealing ability of the wafer pod by enhancing the sealable connection of the pod lid  14   a  to the wafer pod body  12  according to the first embodiment.  FIG. 7A  and  FIG. 7B  are schematic diagrams showing the wafer transportation by means of a semiconductor wafer transportation pod which is designed in accordance with this exemplary modification of the first embodiment of the present invention and placed on the wafer pod table  20  for carrying in or out the semiconductor wafers  10 . As illustrated in  FIG. 7A  and  FIG. 7B , in accordance with this exemplary modification, the pod lid  14   a  of the first embodiment is replaced by a pod lid  14   c  which is provided with two rubber gaskets on the contact surface at which the pod lid  14   c  comes into contact with the wafer pod body  12 . Also, in accordance with this exemplary modification, the space defined between the two rubber gaskets and the contact surface is put at a pressure which is lower than the pressure of the atmosphere to some extent, i.e., “a negative pressure” as conventionally and technically expressed. The negative pressure is referred to as “vacuum condition” in the following description, unless otherwise described, for convenience. 
     FIG. 7B  is a schematic diagram showing the procedure of exhausting the space defined between the two rubber gaskets and the contact surface by placing, on the wafer pod table  20 , the semiconductor wafer transportation pod in accordance with this exemplary modification of the first embodiment of the present invention. As illustrated in  FIG. 7B , in accordance with this exemplary modification, the space defined between the two rubber gaskets and the contact surface is evacuated in advance of the transportation of the wafer pod into which the semiconductor wafers  10  have been transferred. The evacuation of the space is performed by means of a vacuum pump P located on the lid opening/closing control means  22 . The vacuum pump P is connected to the attachment  18 , which is connected in turn to the conduit inside of the pod lid  14   c  through the pod lid shutting device  16   c . Meanwhile, while the rubber gaskets are usually made of an O-ring whose cross section is circular, the rubber gaskets may be formed of a semicircular ring, rectangular ring and so on. 
   The pod lid shutting device  16   c  and the pod lid  14   c  in accordance with this exemplary modification are designed, for example, as illustrated in  FIG. 8A  and  FIG. 8B .  FIG. 8A  is a plan view showing the configuration of the pod lid shutting device  16   c  in accordance with this exemplary modification.  FIG. 8B  is a plan view showing the configuration of the pod lid  14   c  in accordance with this exemplary modification. As illustrated in  FIG. 8A , the pod lid shutting device  16   c  in accordance with this exemplary modification is provided with the locking/unlocking control mechanism  44  in the same manner as the first embodiment of the present invention, and also provided with gas inlet ports  66 , a vent port connector  68 , a valve opening/closing control mechanism  70  for controlling the opening/closing operation of the gas inlet ports  66  and the vent port connector  68 . On the other hand, as illustrated in  FIG. 8B , the pod lid  14   c  in accordance with this exemplary modification is provided with the locking/unlocking mechanism  54  and the linking bars  56  in the same manner as the first embodiment of the present invention, and furthermore provided with gas inlet port connectors  72  and a vent port  74 . Also, the rubber gaskets made of an O-ring are attached to the contact surface between the pod lid  14   c  and the wafer pod body  12 . When the pod lid  14   c  and the pod lid shutting device  16   c  are aligned with each other, the gas inlet port connectors  72  of the pod lid  14   c  and the gas inlet ports  66  of the pod lid shutting device  16   c  are coupled with each other while the vent port  74  of the pod lid  14   c  and the vent port connector  68  of the pod lid shutting device  16   c  are coupled with each other. The evacuation of the space is performed from the gas inlet ports  66  by means of the vacuum pump P through the attachment  18 . On the other hand, when the pod lid  14   c  is detached from the wafer pod body  12 , the space is vented to the atmosphere by passing air from the vent port  74  through the vent port connector  68 . 
   In the case of the modification of the first embodiment of the present invention, the sealing ability of the pod lid  14   c  to the wafer pod body  12  is effectively enhanced in addition to the advantages of the first embodiment. Accordingly, the airtightness of the wafer pod is improved so as to elevate the purity of the interior of the wafer pod. Also, the loss of the sealing gas as contained in the wafer pod can be effectively avoided. By this configuration, it is possible to maintain the semiconductor wafers  10  in a highly purified environment to protect the semiconductor wafers  10  from generation of natural oxide films. 
   Second Embodiment 
   Next, the second embodiment of the present invention will be explained. The second embodiment of the present invention is described to show an example which is capable of improving the sealing ability of the wafer pod and also improving the leak-proof structure of the wafer pod by evacuating the interior of the wafer pod into a vacuum condition. 
     FIG. 9A  is a schematic diagram showing the wafer transportation by means of a semiconductor wafer transportation pod in accordance with the second embodiment of the present invention which is placed on a wafer pod table  20  for carrying in or out the semiconductor wafers  10 .  FIG. 9B  is a schematic diagram showing the semiconductor wafer transportation pod in accordance with the second embodiment of the present invention which is transported between the process chambers. As illustrated in  FIG. 9A , in the case of the semiconductor wafer transportation pod according to the second embodiment of the present invention, the pod lid  14   a  according to the first embodiment is replaced by a pod lid  14   d  which has a different configuration. 
   The pod lid  14   d  in accordance with the second embodiment of the present invention is provided with a vacuum chamber  76  located within the pod lid  14   d . The vacuum chamber  76  is evacuated in advance for the purpose of evacuating the wafer pod body  12 . In the first step, the evacuation of the vacuum chamber  76  is performed by the lid opening/closing control means  22 . The attachment  18  is then connected to a conduit located inside of the pod lid  14   d  through a pod lid shutting device  16   d  by means of the lid opening/closing control means  22  after detaching the pod lid  14   d  implemented with the vacuum chamber  76  from the wafer pod body  22 . The attachment  18  is connected to a vacuum pump P provided for the lid opening/closing control means  22  so that the evacuation of the vacuum chamber  76  is performed by means of the vacuum pump P. A vacuum is formed in the vacuum chamber  76  by this procedure. On the other hand, as illustrated in  FIG. 9B , the vacuum chamber  76  serves in turn to evacuate the wafer pod body  12  during the transportation of the wafer pod. The interior of the wafer pod body  12  is therefore rendered to be in a vacuum condition after a certain time elapses. 
   Next, the operation of the second embodiment of the present invention will be explained with reference to  FIG. 9A  and  FIG. 9B . The operation of the second embodiment of the present invention consists generally of the following two operations.
     (1) Evacuation of the vacuum chamber  76 .   (2) Evacuation of the wafer pod body  12 .   

   Firstly, in accordance with the second embodiment of the present invention, the procedure of the evacuation of the vacuum chamber  76  is performed during the step of carrying out the semiconductor wafers  10  from the wafer pod body  12 , the step of processing the semiconductor wafers  10  and the step of carrying the semiconductor wafers  10  into the wafer pod body  12  as illustrated in  FIG. 9A . In the prior art technique, the pod lid  14   d  is left supported by the pod lid shutting device  16   d  without any operation during the step of carrying out, the step of processing the semiconductor wafers  10  and the step of carrying in. On the other hand, in accordance with the second embodiment of the present invention, the vacuum chamber  76  is evacuated in parallel with these steps. The evacuation can be completed within the step of processing the semiconductor wafers  10 . Accordingly, there is no need for an extra time as required to evacuate the vacuum chamber  76 . 
   Next, as illustrated in  FIG. 9B , the evacuation (2) of the wafer pod body  12  is then performed during the transportation of the wafer pod. The wafer pod is transported to the next process chamber used in the subsequent manufacturing step by means of an appropriate transportation system (not shown in the figure) after transferring the semiconductor wafers  10  to the wafer pod. The vacuum chamber  76  as evacuated is then functioning to evacuate the interior of the wafer pod body  12  during the transportation. Since the vacuum chamber  76  is in a vacuum condition, the gas inside of the wafer pod body  12  is transferred to the vacuum chamber  76  through the appropriate conduit by its pressure when the appropriate valve is opened. The evacuation time for evacuating the wafer pod body  12  is about several second or several minutes in the case that the semiconductor wafer transportation pod has been designed to accommodates  25  wafer having a diameter of 300 mm. Accordingly, from the overall view point, the evacuation step can be recognized as completed just after starting the transportation of the wafer pod. 
   In the case of the first embodiment of the present invention, the evacuation of the wafer pod body  12  is conducted before the transportation of the wafer pod. Because of this, the transportation of the wafer pod is delayed by the evacuation time. In the case of the second embodiment of the present invention, the evacuation of the wafer pod body  12  is performed during the transportation of the wafer pod. By this configuration, there is virtually no additional time required for the evacuation of the wafer pod body  12 . 
   Furthermore, in the case of the second embodiment of the present invention, it is possible to improve the leak-proof structure of the wafer pod. Generally speaking, the pressure P 1 ( t ) in a sealed box after evacuation is expressed by the following equation,
 
 P   1 ( t )=( Q/V )× t+P   0 ( t )
 
where “V” is the volume of the box; “Q” is the leak volume; and “P 0 ( t )” is the pressure just after evacuation.
 
   As understood from the equation as described above, the increase in the pressure of P 1 ( t ) in the sealed box is kept limited to a smaller level as the volume V of the sealed box is larger even in the case that the leak volume becomes substantial. Namely, the leak-proof characteristic of the sealed box is furthermore improved, as the volume of the sealed box is larger, in order to elongate the time for which the sealed box is maintained in a vacuum condition.  FIG. 10  is a graphical diagram showing the leak-proof characteristic in the case of the second embodiment of the present invention in contrast to the leak-proof characteristic in the case of the modification of the first embodiment of the present invention. In the case of the modification of the first embodiment, what is evacuated is the tiny space defined between the two rubber gaskets and the contact surface as illustrated in  FIG. 7B . However, in the case of the second embodiment of the present invention, all the spaces of the vacuum chamber  76  and interior of the wafer pod body  12  are rendered to be in a vacuum condition so that a higher leak-proof characteristic can be obtained. Accordingly, in accordance with the second embodiment, it is possible to maintain the sealed structure of the wafer pod for a longer time and therefore the semiconductor wafers  10  as stored in the wafer pod can be maintained in a highly purified environment even if the transportation requires a longer time. Also even in the case that the wafer pod is temporarily stored in a stocker, the semiconductor wafers  10  can be maintained in a highly purified environment in the same manner. 
   The pod lid  14   d  in accordance with the second embodiment of the present invention is designed for example as illustrated in  FIG. 11A .  FIG. 11A  is a cross sectional view showing the configuration of the pod lid  14   d  in accordance with the second embodiment of the present invention. As illustrated in  FIG. 11A , the pod lid  14   a  in accordance with the second embodiment is composed therein of the vacuum chamber  76 , a conduit  78  for evacuating the vacuum chamber  76 , an opening/closing valve  80  located in the middle of the conduit  78 , a conduit  84  for drawing the gas inside of the wafer pod body  12  into the vacuum chamber  76 , an opening/closing valve  86  located in the middle of the conduit  84 , a conduit  90  for communicating the side of the pod lid  14   d  facing the wafer pod body  12  with the opposite side of the pod lid  14   d , and an opening/closing valve  92  and a filter  96  which are located in the middle of the conduit  90 . In  FIG. 11A , when the opening/closing valve  80  is opened, the vacuum chamber  76  is evacuated through the conduit  78  by means of the vacuum pump P as illustrated in  FIG. 9A . The conduit  78  inside of the vacuum chamber  76  is then communicating with an inlet port  82 , which is connected to the attachment  18  provided for the lid opening/closing control means  22  through the pod lid shutting device  16   d . These procedures is conducted with the pod lid  14   d  detached from the wafer pod body  12  and fixed to the pod lid shutting device  16   a.    
   On the other hand, when the opening/closing valve  86  is opened, the vacuum chamber  76  serves to evacuate the wafer pod body  12  through the conduit  84 . As described above, since the vacuum chamber  76  is in a vacuum condition, the gas inside of the wafer pod body  12  is transferred to the vacuum chamber  76  through the conduit  84  when the opening/closing valve  86  is opened. 
   Meanwhile, when the pod lid  14   d  is detached from the wafer pod body  12 , the wafer pod body  12  and the vacuum chamber  76  are vented to the atmosphere by passing air from the conduit  90 . Air is introduced to the wafer pod from the vent port  94  through the conduit  90  when the opening/closing valve  96  is opened. Furthermore, the filter  96  is provided for the purpose of improving the purity of air as introduced to the wafer pod body  12 . By this configuration, the purity of the semiconductor wafers  10  inside of the wafer pod body  12  can be maintained in a highly purified environment. 
   The procedure as described above is preferably conducted in response to the opening action and the closing action of the pod lid  14   d . Namely, the evacuation of the vacuum chamber  76  is started when the pod lid  14   d  is detached from the wafer pod body  12  while the evacuation of the wafer pod body  12  is started when the pod lid  14   d  is attached again to the wafer pod body  12 . In accordance with the second embodiment of the present invention, therefore, it is proposed to perform two operations in response to the opening/closing operation of the pod lid  14   d.    
   In practice, the pod lid  14   d  is designed, for example, as described in  FIG. 11B .  FIG. 11B  is a plan view showing the configuration of the pod lid  14   d  in accordance with the second embodiment of the present invention. As illustrated in  FIG. 11B , in accordance with the pod lid  14   d  of the second embodiment, the opening/closing operation of the opening/closing valves  80 ,  86  and  92  is performed by linking bars  98  and  100  in response to the rotation of the locking/unlocking mechanism  54 . More specifically speaking, when the locking pins  58  are drawn back into the pod lid  14   d  by means of the linking bars  56  in response to the rotation of the locking/unlocking mechanism  54 , the linking bar  98  serves to close the opening/closing valve  86  while the linking bar  100  serves to open the opening/closing valves  80  and  92  at the same time. On the other hand, when the locking pins  58  are projected from the pod lid  14   d  by means of the linking bars  56  in response to the rotation of the locking/unlocking mechanism, the linking bar  98  serves to open the opening/closing valve  86  while the linking bar  100  serves to close the opening/closing valves  80  and  92  at the same time. Accordingly, when the pod lid  14   d  is detached from the wafer pod body  12 , it is possible to start venting the wafer pod body  12  and evacuating the vacuum chamber  76  with the opening/closing valves  80  and  92  being opened and the opening/closing valve  86  being closed. On the other hand, when the pod lid  14   d  is fixed to the wafer pod body  12 , the evacuation of the wafer pod body  12  is started with the opening/closing valves  80  and  92  being closed and the opening/closing valve  86  being opened. 
   In accordance with the second embodiment of the present invention, the pod lid  14   d  is provided with the vacuum chamber  76  so that the vacuum chamber  76  is evacuated in advance during the period after the semiconductor wafers  10  are carried out from the wafer pod body  12  and before the semiconductor wafers  10  are carried in the wafer pod body  12  while the wafer pod body  12  is then evacuated by means of the vacuum chamber  76  during the transportation of the wafer pod. By this configuration, the evacuation step of the wafer pod body  12  can be recognized to virtually disappear. Accordingly, there is no need for an extra time as required for the evacuation of the wafer pod body  12 . As a result, the cycle time required for completing all the manufacture process can be shortened to realize the improvement of the production efficiency and the reduction of the production cost. Furthermore, in accordance with the second embodiment, it is possible to maintain the sealed structure of the wafer pod for a longer time and therefore the semiconductor wafers  10  as stored in the wafer pod can be maintained in a highly purified environment for a longer time. 
   While the gas holding vessel and the vacuum chamber are described as implemented within the pod lid in accordance with the first and second embodiments of the present invention, it is possible to make use of the structure in which the gas holding vessel and the vacuum chamber are implemented in any other suitable location. For example, the gas holding vessel and the vacuum chamber may be implemented within the wafer pod body. Furthermore, not limited to the built-in structure, the gas holding vessel and the vacuum chamber are separately designed to be freely attached or detached to certain positions of the wafer pod. 
   Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof.