Abstract:
A hermetic substrate transportation container permitting storage of an electronic substrate is provided, keeping a rise of internal moisture concentration low, thus preventing generation of natural oxidation film on the surface of the electronic substrate and allowing detection of the contents inside the substrate transportation container, from outside. A container body having an aperture for loading and unloading an electronic substrate, the substrate transportation container comprising a lid for sealing such aperture, in which the container body and the lid are made of a material having an amorphous polyolefin as its main constituent. By constituting the container body and the lid using the amorphous polyolefin with low hygroscopic characteristic as a main constituent, it is possible to keep discharge of moisture from the internal wall thereof low and also to prevent an increase of moisture concentration in the sealed compartment.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a substrate transportation container and, more specifically, to a hermetic substrate transportation container used for transportation of electronic substrates such as semi-conductor wafers or liquid crystal substrates.  
           [0003]    2. Description of the Related Art  
           [0004]    Conventionally, an electronic appliance using an electronic substrate, such as a semi-conductor wafer, a liquid crystal substrate or a magnetic disc, is fabricated in a clean room that is free of dust. However, transportation of the electronic substrate between processing apparatuses during fabrication is done by housing an electronic substrate into a cassette inside a portable and sealable clean container (in other words, a substrate transportation container). By means of that, the electronic substrate can be transported without being exposed to dust in the air, both inside and outside of the clean room. Such a substrate transportation container is commercialized under a trade name of SMIF (Standard Mechanical Interface) pod (a trademark of Assist Technologies, Inc.).  
           [0005]    Although such SMIF pod has its interior sealed so as to prevent contamination by dust from the air, small molecules such as oxygen, water moisture or volatile organic substances can easily infiltrate. As a consequence, such small molecules infiltrated during transportation between processes contaminate the electronic substrate inside. For example, natural oxide film grows in the surface of the semi-conductor wafer and molecular adsorption contamination by an organic substance, boron, phosphor and the like is originated. For an advanced technology device, such contamination greatly affects the properties of the device.  
           [0006]    In view of such problems, a flange is provided in borders of an aperture of the container&#39;s body and by sealing with an O-ring provided in a rim of a base lid to such flange, the sealing properties of the substrate transportation container&#39;s interior are improved. Japanese Patent Laid-Open No. 10-56050 discloses a substrate transportation container that limits infiltration of small molecules. Still, when transporting an electronic substrate that requires high cleanliness, like a semi-conductor wafer, the interior of the substrate transportation container containing the substrate is filled with an inert gas (hereinafter referred to simply as inert gas), such as argon (Ar) or nitrogen gas (N 2 ). At this event, replacement of the interior ambient atmosphere of the container with inert gas is done each time of the open-close of a bottom lid and, as a result, contamination of the electronic substrate by molecular adsorption of organic substances, boron or phosphor as well as formation of natural oxide film on the electronic substrate surface is prevented.  
           [0007]    However, a substrate transportation container of the construction mentioned above is constructed using plastics material such as polycarbonate, for example. Because polycarbonate is a high hygroscopic material with a water absorption rate of 0.2%, water moisture is gradually ejected from the internal wall according to time course. As a result, the moisture concentration in the interior of the sealed substrate transportation container cannot be kept low for a long time, thus causing formation of natural oxide film in the surface of the electronic substrate placed inside.  
           [0008]    In addition, although the container has to be cleaned up when the interior of the container is contaminated by fine particles, there is a problem that IPA (isopropanol), which is a washing liquid having electron-removing effect, cannot be employed, as IPA is corrosive to polycarbonate.  
           [0009]    On the other hand, when constituting a substrate transportation container by means of metallic material with the purpose of controlling moisture discharge from the internal wall, the moisture concentration within the substrate transportation container can be kept low. However, it is hard to consider that a substrate transportation container made of metallic material is suitable for transportation because it is heavily. Furthermore, as the substrate transportation container made of metallic material is formed from a cutting process, productivity is low, and cost is high. Besides, there is the problem that an electronic substrate stored inside cannot be detected from outside, like through infrared radiation.  
         SUMMARY OF THE INVENTION  
         [0010]    It is an object of the present invention to provide a substrate transportation container for sealing an electronic substrate by allowing long term conservation of low internal moisture concentration, thus reducing generation of natural oxide film on the electronic substrate surface and permitting recognition of the electronic substrate within the container under the sealed condition.  
           [0011]    A substrate transportation container of the present invention achieving such purpose comprises a container body having an aperture for loading and unloading an electronic substrate, the substrate transportation container including a lid for sealing the aperture and at least one member selected from the container body and the lid is constituted mainly by an amorphous polyolefin.  
           [0012]    In such substrate transportation container, the container body and the lid have a hygroscopic amorphous polyolefin of low moisture adsorption as a main constituent in its composition. As a result, water discharge from an internal wall of the container is reduced and an increase of moisture concentration within the sealed interior is reduced, even when the container is sealed for a long time. In addition, as the amorphous polyolefin has transparency, an electronic substrate placed inside can be detected, even when the container is sealed.  
           [0013]    With such container body and such lid having the hygroscopic amorphous polyolefin of low moisture adsorption as a main constituent in its composition, the moisture discharge from the internal wall of the container is reduced and an increase of moisture concentration within the sealed interior is reduced, thus it is possible to reduce generation of natural oxide over a surface of the electronic substrate stored therein.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The foregoing and other objects, features and advantages of the present invention will be apparent to those skilled in the art from the following description of the preferred exemplary embodiments of the present invention taken in conjunction with the accompanying drawings, in which:  
         [0015]    [0015]FIG. 1 is a diagrammatic view describing a substrate transportation container and a substrate housing method using the container, according to a preferred embodiment of the present invention; and  
         [0016]    [0016]FIG. 2 is a graph showing a change in moisture concentration with time, inside the substrate transportation container according to the preferred embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    A substrate transportation container according to a preferred embodiment of the present invention is described based on FIG. 1 and FIG. 2.  
         [0018]    [0018]FIG. 1 describes a construction of a substrate transportation container and a substrate storage method using the container, according to a preferred embodiment of the present invention.  
         [0019]    A substrate transportation container  1  shown in FIG. 1 comprises a container body  2  for carrying an electronic substrate (for example, a semiconductor wafer) W and a lid  3 .  
         [0020]    The container body  2  has a size sufficient for containing a carrier L holding a plurality of the electronic substrate W, and an aperture  21  on its bottom side for loading and unloading the carrier L. In addition, a rim of the aperture  21  is constituted as a flange  22  bent outwardly and extending throughout the rim.  
         [0021]    The lid  3  has a size enough for blocking the aperture  21  of the container body  2  so that the rim portion is abutted against the flange  22  of the lid  3 , when blocking the aperture  21  of the container body  2 . In such lid  3 , a double O-ring groove  31  is formed extending along the rim of the lid  3  in the rim portion abutted to the flange  22 , with the aperture  21  of the container body  2  blocked. Then, an O-ring  4  is provided inside such O-ring groove  31 .  
         [0022]    Moreover, in a position as interposed within the double O-ring groove  31 , a vacuum groove  32  extending along the rim of the lid  3  is provided so as to have partial communication (not shown in the figure) to the O-ring groove  31 . In addition, two pipe tubes  33 ,  33  are provided on the lid  3  so as to connect an external environment to the vacuum groove  32 , when blocking the aperture  21  of the container body  2 . Then, a valve  34  is provided for the pipe tubes  33 ,  33 .  
         [0023]    A composition of matter having an amorphous polyolefin as its main constituent constitutes the container body  2  and the lid  3 .  
         [0024]    The amorphous polyolefin is, generally, a cyclic olefin resin having a saturated hydrocarbon ring structure in its polymer&#39;s main chain or side-chain, or a ring-opened polymer or a hydride of the ring-opened polymer, of a monomer having a single unsaturated bond among monomers having a monocyclic cycloolefin, a norbornene ring or the like.  
         [0025]    As the monocyclic cycloolefin, there is, for example, cyclobutene, 1-methylcyclopentene, 3-methylcyclobutene, 3,4-diisopropenylcyclobutene, cyclopentene, 3-methylcyclopentene, cyclohexene, cyclooctene, 1-methylcyclooctene, 5-methylcyclooctene, cyclooctatetraene, cyclododecen and the like.  
         [0026]    In addition, as the monomer having a single unsaturated bond among monomers having the norbornene ring, there is, for example, 2-methyl-bicyclo[2.2.1]hepta-2-ene, 2,2-dimethyl-bicyclo[2.2.1]hepta-2-ene, 2-ethyl-bicyclo[2.2.1]hepta-2-ene, 2-butyl-bicyclo[2.2.1]hepta-2-ene, 2-hexyl-bicyclo[2.2.1]hepta-2-ene, 2-phenyl-bicyclo[2.2.1]hepta-2-ene, 2-octyl-bicyclo[2.2.1]hepta-2-ene, 2-octadecyl-bicyclo[2.2.1]hepta-2-ene.  
         [0027]    A construction of a substrate carrying apparatus  5  used for housing the electronic substrate W in the substrate transportation container  1  of such construction is described below.  
         [0028]    Such substrate carrying apparatus  5  is provided together with the processing apparatus not shown in the figures, and comprises a lift  6  moving up and down when carrying the lid  3  of the substrate transportation container  1 . A gas introduction pipe  7  and an air exhaust pipe  8 , connected to the pipe tubes  33 ,  33  of the lid  3  loaded on the lift  6 , are fixed to the lift  6 , and a pump  81  is provided for the air exhaust pipe  8 .  
         [0029]    In addition, such lift  6  is arranged within a housing  9  having a top aperture larger than the lid  3 . Such housing  9  is constituted so as to support a most external contour portion of the flange  22  of the container body  2  with its upper end under the condition of having the substrate transportation container  1  loaded on the lift  6 , and to have its top aperture blocked by means of the container body  2 . In addition, although illustration has been omitted, the housing  9  has communication to an electronic substrate introduction chamber of a processing apparatus, and has an air exhaust pipe and an inert gas introduction pipe provided.  
         [0030]    Next, description is made of a procedure for housing the electronic substrate W in the substrate transportation container  1  by means of using the substrate carrying apparatus  5 .  
         [0031]    After finishing process at the processing apparatus, the electronic substrate W housed within the cassette L on the lid  3  is loaded on the lift  6 . In such condition, the gas introduction pipe  7  and the air exhaust pipe  8  are connected to the pipe tube  33 ,  33  of the lid  3 . In addition, the container body  2  is carried on the housing  9  of the substrate carrying apparatus  5 , with the flange  22  supported on the upper end of the housing  9 .  
         [0032]    Firstly, after an internal portion of the container body  2  and the housing  9  are filled with inert gas or after the internal portion thereof is depressurized, the lift  6  loaded with the electronic substrate W is raised. As a result, the cassette L is housed into the container body  2  kept under inert gas atmosphere or depressurized, whereby the O-ring groove  31  of the lid  3  and the vacuum groove  32  are blocked by means of the flange  22  of the container body  2 .  
         [0033]    Next, the valve  34  of the pipe tube  33  of the lid  3 , connected to the air exhaust pipe  8  is opened, and then the pump  81  provided for the air exhaust pipe  8  is activated. As a result, the gas in the vacuum groove  32  communicating to the pipe tube  33  and in the O-ring groove  31  gas is exhausted whereby depressurizing, thus making the lid  3  vacuum-adsorbed against the container body  2 , as well as sealing the container body  2  by pushing the O-ring  4  under pressure against the flange  22 . Then, the pump  81  is stopped and the valve  34  of the pipe tube  33  is closed, thus the electronic substrate W within the substrate transportation container  1  is kept sealed under an inert gas atmosphere (or, under a depressurized atmosphere).  
         [0034]    Moreover, the substrate transportation container  1  in which the electronic substrate W is stored sealed is separated from the substrate carrying apparatus  5 . At this event, if the housing  9  is depressurized, the adherence of the substrate transportation container  1  to the housing  9  is released by means of returning the housing  9  to an environment atmospheric pressure. Afterwards, the substrate transportation container  1  is conveyed to a subsequent step.  
         [0035]    Furthermore, a procedure for unloading the sealed electronic substrate W from the substrate transportation container  1  is done as follows. Firstly, the substrate transportation container  1  is loaded on the lift  6  of the substrate transportation apparatus  5  provided for the processing apparatus of the subsequent process. At this event, the pipe tubes  33 ,  33  of the lid  3  are connected to the gas introduction pipe  7  and the air exhaust pipe  8 . Then, the valve  34  of the pipe tube  33  connected to the gas introduction pipe  7  is opened, the inert gas is introduced to the pipe tube  33  from the gas introduction pipe  7 , whereby the inert gas is supplied to the vacuum groove  32  communicated to the pipe tube  33  and the O-ring groove  31 . Then, the interior of the vacuum groove  32  and the O-ring groove  31  are pressurized, thus releasing the status of adherence of the lid  3  to the flange  22  of container body  2 .  
         [0036]    After the above, the lift  6  of the substrate transportation apparatus  5  is descended. As a result, with the container body  2  supported on the upper end of the housing  9 , the lid  3  descends into the housing  9  along with the lift  6 , so that the electronic substrate W is carried out from within the container body  2  to the housing  9 .  
         [0037]    The substrate transportation container  1  used as discussed above has the container body  2  and the lid  3  constituted mainly by an amorphous polyolefin of low hygroscopic property, so that it allows a moisture discharge on its internal wall to be controlled to a small amount. Therefore, even if sealed for a long time, an increase of moisture concentration within the sealed interior can be controlled, thus preventing formation of natural oxidation film on the surface of the electronic substrate stored sealed inside. As a result, for a product (a semiconductor device, for example) formed by means of the electronic substrate stored sealed in such substrate transportation container  1 , a quality of the product such as electrical properties can be preserved, and yield of the process can be improved.  
         [0038]    Furthermore, an anamorphous polyolefin has transparency such that even if the substrate transportation container  1  is sealed, it is possible to detect from the outside the electronic substrate W stored inside. In addition, in contrast to a substrate transportation container made of polycarbonate, the substrate transportation container  1  constituted by an amorphous substance polyolefin does not suffer corrosion by IPA. As a result, when the substrate transportation container  1  is contaminated by fine particles, it is possible to provide a cleaning process making use of IPA, which has electron-removing effect.  
         [0039]    Besides, the substrate transportation container  1  having resin material as its main constituent has lighter weight and better formability in comparison with the case of a substrate transportation container using metallic material. As a result, the substrate transportation container  1  can be transported easily, the productivity becomes high and the fabrication cost becomes cheaper compared with a conventional substrate transportation container.  
         [0040]    Furthermore, FIG. 2 is a graph showing a change in moisture concentration with, time inside the sealed substrate transportation container according to the preferred embodiment of the present invention. Measurement was done for the substrate transportation container having an amorphous substance polyolefin as its main constituent according to the preferred embodiment of the invention, and a conventional substrate transportation container having polycarbonate as its main constituent. After the atmosphere of the interior of the substrate transportation container body is substituted by nitrogen gas until moisture concentration is reduced to approximately 10 ppm and then sealed, a change with time of moisture concentration was measured. The water absorption rate for the amorphous polyolefin is approximately 0.01%, while for the polycarbonate, the water absorption rate is approximately 0.2%.  
         [0041]    As shown in the graph, when compared with the moisture concentration {circle over (1)} for a conventional substrate transportation container (made of polycarbonate), an increase of moisture concentration {circle over (2)} for the substrate transportation container of the preferred embodiment of the invention (made of an amorphous polyolefin-based material) is controlled low, thus confirming a smaller moisture discharge from the container&#39;s internal wall in the later case of the preferred embodiment of the invention as compared to the former conventional case.  
         [0042]    Finally, the configurations and structures of respective units and portions described specifically with respect to the preferred embodiments of the present invention are only examples of realization of the present invention, so the embodiments thereof should not be construed as to limiting the technical scope of the present invention.