Abstract:
A wafer case for holding a wafer includes a case body having an opening for receiving the waver, and a lid for closing said opening of the case body. The case body and lid are made of dust-free paper. Further, the case body has a lid fitting portion, over which said lid fits; and a plurality of through holes are formed in the lid fitting portion at equal interval.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a wafer case for holding a wafer obtained as a result of a single crystal ingot such as Si or the like used as a material of a semiconductor device being cut, and, in particular, to a wafer case which can be manufactured at low cost, is of a light weight, is discardable or reusable and has no adverse effect upon the environment.  
           [0003]    2. Description of the Related Art  
           [0004]    Processes such as ion diffusion, photoetching and so forth are performed on wafers obtained as a result of single crystal ingots of Si or the like being cut, and, thus, various semiconductor devices such as LSI or the like are manufactured. Grown single crystal ingots are cut, the resulting wafers undergo processes such as lapping, edge working, mirror polishing, surface cleaning and so forth, and, thus, the wafers used for manufacturing the semiconductor devices are obtained, and then are shipped. Further, before being shipped, the wafers undergo inspections such as measurement of electric characteristics such as resistivity and so forth; measurement of dimensional precision such as thickness, flatness, and so forth; and whether or not flaws or spots exist on the surfaces, and so forth.  
           [0005]    The performances and reliabilities of semiconductor devices are provided by the manufacturing technologies. However, wafers themselves used as materials of the semiconductor devices should be maintained in a damage-free condition as the wafers have been worked to a high degree of accuracy, and, also, should be kept clean. Further, the air in a room in which the manufacturing processes are performed is required to be clean to a very high degree, that is, high cleanliness is required. For this purpose, the manufacturing operations are performed in a “clean room” which is maintained in a condition in which the dust density is very low. Accordingly, the wafers to be brought into such a clean room should be maintained in a damage-free worked condition, and, also, in a clean condition. Further, cases or containers which hold the wafers should not bring dust into the clean room. For these purposes, when shipping worked wafers, it is necessary to ship the wafers in a condition in which the wafers are held in clean cases which can protect the wafers during transportation.  
           [0006]    Cases using plastic as the material thereof have been used to fulfill the conditions required of cases for holding wafers. The wafer cases using plastic as the material thereof can be said to be satisfactory also because these wafer cases are superior in strength, and, also, it is possible to maintain these wafer cases in a clean condition. However, an expensive mold is used for manufacturing these wafer cases, the raw materials thereof are expensive, and, thereby, the unit price thereof is expensive. Further, at the time of disposal of the used wafer cases, it is environmentally difficult to discard the plastic. An alternative is to collect and reuse the used wafer cases after cleaning them. However, an additional expense is needed for cleaning, and, thereby, the overall cost increases. Further, it is difficult to deal with those wafer cases (re-export, shipping), which were originally exported, in such a manner.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention has been devised to solve these problems, and an object of the present invention is to provide a wafer case which is inexpensive, is of light weight, is small-sized, can be discarded easily, and, also, is suitable for environmental protection.  
           [0008]    In order to achieve this object, according to the present invention, a wafer case is manufactured using dust-free paper. As a result of manufacturing the wafer case using paper, it is possible to reduce the cost required for manufacturing the wafer case, to reduce the weight of the wafer case and to miniaturize the wafer case. Further, because the material of the wafer case is dust-free paper, dust is not created from the wafer case itself, dust is prevented from adhering to the wafer itself, and, also, it is possible to restrain dust from being brought into a room in facilities for manufacturing semiconductor devices when the wafer case is brought into the room. Further, by incinerating the used wafer case, it is possible to perform disposal of the wafer case easily at a low cost, without polluting the environment.  
           [0009]    Further, through holes, through which air inside and outside of the case body can flow, may be formed in a lid fitting portion of the case body of the wafer case according to the present invention. Thereby, when a lid is lifted, air flows into the wafer case, and, as a result, opening and shutting of the lid can be easily performed. 
       
    
    
       [0010]    Other objects and further features of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 shows a perspective view of a wafer case in an embodiment of the present invention;  
         [0012]    [0012]FIG. 2 shows a perspective view for illustrating a condition in which a wafer is received by the wafer case shown in FIG. 1;  
         [0013]    [0013]FIG. 3 shows a perspective view of a wafer case in a variant embodiment of the present invention; and  
         [0014]    [0014]FIG. 4 shows a perspective view of a wafer case in another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    Embodiments of the present invention will now be described together with drawings.  
         [0016]    [0016]FIG. 1 shows a wafer case  1  for holding an Si wafer in an embodiment of the present invention. The wafer case  1  is made of cardboard, the material of which is dust-free paper, and consists of a case body  2  and a lid  3 , the cross section of each of them having a circular shape. The dust-free paper used as the material is one such that creation of dust therefrom is restricted to a very high degree, and is also called “clean paper”. This dust-free paper can be made from paper stock obtained as a result of resin binder (for treatment for preventing dust from being created) and sizing agent (for preventing ink from running) being mixed with pulp, which is the raw material, during the paper manufacturing process, for example.  
         [0017]    The above-mentioned pulp is natural pulp used as the raw material of ordinary paper, and is a mass of cellulosic fiber obtained as a result of a plant product such as wood or the like being processed. Rubber latex such as SBR, NBR, MBR, polyurethane or the like, resin latex such as polyacrylate, polyvinyl acetate or the like, or the like can be used as the above-mentioned binder. The binder content of the dust-free paper is higher than that of ordinary paper (for example, the binder content of the dust-free paper is present in the range of 5 to 40 parts by weight with respect to 100 parts by weight of the natural pulp). Thereby, it is possible to restrain creation of dust.  
         [0018]    The case body  2  of the wafer case  1  includes a cylindrical body portion  2   a  having an opening  2   d  at the top thereof, a wafer being received by the case body  2  through the opening  2   d , having a bottom  2   e  and having an inner diameter slightly larger than the outer diameter of a wafer to be held by the wafer case  1 . A thin-wall lid fitting portion  2   b  is formed at the end, adjacent to the opening  2   d , of the body portion  2   a , the lid  3  fitting over the lid fitting portion  2   b . The lid  3  consists of a circular top plate  3   a  and a surrounding cylindrical portion  3   b , and has an opening  3   c  at the bottom thereof, the lid fitting portion  2   b  of the case body  2  fitting into the lid  3  through the opening. The inner diameter of the cylindrical portion  3   b  is slightly larger than the outer diameter of the lid fitting portion  2   b , and, the cylindrical portion  3   b  is caused to fit over the lid fitting portion  2   b  so that the opening  2   d  of the case body  2  is closed.  
         [0019]    Round through holes  2   c  are formed in the lid fitting portion  2   b  of the case body  2  at three places at equal intervals so as to horizontally pierce the lid fitting portion  2   b , as shown in FIG. 1. These through holes  2   c  are provided so that, when the lid  3  is being removed from the case body  2 , and, thus, the wafer case  1  is being opened, air is quickly introduced into the wafer case  1 , the partial vacuum created when the lid  3  is being lifted is released at an early stage, and, thereby, the lid  3  is easily lifted.  
         [0020]    [0020]FIG. 2 shows a way in which an Si wafer is held by the above-described wafer case  1 . A sponge  5 , used as a shock absorbing member, is placed inside the case body  2  on the bottom  2   e , and the wafer  4  is set on the sponge  5 . Then, on the wafer  4 , a sponge  7 , used as a shock absorbing member, is placed, a thin sheet  6  for protecting the surface of the wafer  4  being interleaved therebetween. Then, in this condition, the lid  3  is put on the case body  2 , and, thus, the wafer case  1  is shut up by means of the lid  3 .  
         [0021]    Because dust-free paper is used as the material of the wafer case  1  in the embodiment, dust is not created by the wafer case  1  itself, and, thereby, dust is prevented from adhering to the wafer  4 . Further, when the wafer case containing the wafer  4  is conveyed into a clean room for manufacturing semiconductor devices, the wafer case  1  itself is free from creating dust and bringing it into the clean room.  
         [0022]    Further, although paper is used as the material, the strength of the cardboard enables the wafer case  1  to have a sufficient strength such that the wafer case  1  can be used as a case for holding a wafer. For example, as a result of using cardboard having a thickness on the order of 1.6 mm, no dent develops either in the top plate  3   a  of the lid  3  or in the bottom  2   e  of the body  2 , even when the wafer case  1  is vacuum-packed (the wafer case  1  is covered by a vinyl bag, a vacuum is formed therein and, thus, the wafer case  1  is packed). Further, as a result of a test being performed in which the wafer case  1  is put into a hexahedral packing box, and, in this condition, the packing box is caused to fall  1  meter, no damage such as a crack is caused to the wafer  4  present inside the wafer case  1 . Further, when a load on the order of 80 kgf is applied perpendicularly against the side of the wafer case  1 , the amount of compression caused to the wafer case  1  is on the order of 10 mm.  
         [0023]    Further, in a case of overseas transportation of the wafer case  1 , the wafer case  1  is transported in a vacuum-packed condition. It has been experimentally verified that, in a case where, for example, the ambient temperature is 40° C. and humidity is 80%, the interior humidity of the wafer case  1  is kept low without being affected by the external conditions for a period on the order of two weeks.  
         [0024]    Further, because the material of the wafer case  1  is paper which can be obtained at low cost, it is possible to prevent the cost from increasing even when the wafer case  1  is miniaturized and each wafer  4  is held by a respective wafer case  1 . Further, because the weight of the wafer case  1  is very light, handling thereof can be easily performed. Further, because the wafer case  1  is made of dust-free paper, it is possible to perform printing, on the wafer case  1  itself directly, for indicating what is contained thereby, for example. Further, because the dust-free paper contains the sizing agent for preventing ink from running, the ink used in the printing is prevented from running, and, also, the ink is prevented from becoming dust, and adhering to, and, thus, staining the wafer  4  and/or wafer case  1 . Furthermore, because the material of the wafer case  1  is paper, it is possible to dispose of the used wafer case  1  by incinerating it. Thereby, a problem such as environmental pollution does not occur.  
         [0025]    Furthermore, the through holes  2   c  are formed in the lid fitting portion  2   b  of the case body  2  of the wafer case  1 , through which holes air inside and outside of the case body  2  can flow. Thereby, lifting of the lid  3  from the case body  2  can be easily performed, handling of the lid  3  can be smoothly performed, and, as a result, it is possible to prevent dust from being created. The through holes  2   c  are formed at the three places at equal intervals in the embodiment as described above. This is because, even if, when the lid  3  is lifted, the lid  3  does not move upwardly in a condition in which the top plate  3   a  of the lid  3  is horizontal but is moved in an inclined condition, air flows in through any of the through holes  2   c . Accordingly, when the wafer case is a cylindrical one, it is advantageous to provide the through holes  2   c  in the lid fitting portion  2   b  at least at three places at equal intervals.  
         [0026]    [0026]FIG. 3 shows a variant embodiment of the embodiment shown in FIG. 1. A wafer case  10  in this variant embodiment is the same as the wafer-case  1  except that through holes  12   c  formed in a lid fitting portion  12   b  are triangular ones.  
         [0027]    Other than these, the through holes  12   c  may be oval-shaped ones or quadrangular ones. By changing the shape of the through holes, it is possible to identify the wafer cases. Therefore, it is possible to change the shape of the through holes to correspond to a particular type of a wafer to be held by the wafer case or a particular lot of manufactured wafer cases.  
         [0028]    [0028]FIG. 4 shows a wafer case  20  in another embodiment of the present invention. The wafer case  20  is made of cardboard of dust-free paper, has a square cross section, and consists of a case body  22  and a lid  23 . Similar to the above-described embodiments, through holes  22   c  are formed in a lid fitting portion  22   b  of the case body  22  for the respective sides thereof. The depth of the case body  22  is larger than that of the embodiments shown in FIGS.  1 - 3 . Thereby, the wafer case  20  can hold a plurality of wafers using sponges interleaved with these wafers, respectively.  
         [0029]    Because the wafer case  20  has a shape of cubic (a square bottom (cross-section)) although wafers to be held thereby are circular ones, when a corrugated cardboard box having a shape of a rectangular parallelepiped is filled with a plurality of wafer cases  20  so that the box contains the wafer cases, it is possible for the wafer cases  20  to be contained by the box in an aligned condition, in comparison to cylindrical ones. Thereby, it is possible to effectively use the space in the box, and, also, to prevent the wafer cases contained by the box from moving therein.  
         [0030]    As described above, the wafer cases according to the present invention are made of cardboard of dust free paper and have the strength needed to be used as wafer cases. Although the wafer cases according to the present invention are inferior in strength in comparison to plastic wafer cases, the wafer cases according to the present invention can be used for ordinary preservation and transportation of wafers without occurrence of any particular problems. When a large number of the wafer cases are transported, there is an effective method in which these wafer cases are transported in a condition in which the wafer cases are contained by a container or a plastic receptacle which can contain a predetermined number of the wafer cases.  
         [0031]    Further, the present invention is not limited to the above-described embodiments and variations and modifications may be made without departing from the scope of the present invention.  
         [0032]    The present application is based on Japanese priority application No. 11-43671, filed on Feb. 22, 1999, the entire contents of which are hereby incorporated by reference.