Abstract:
A package for the transportation of contamination vulnerable articles is provided, comprising a closeable plastic container which is loaded with the respective articles, a first bag made from plastic surrounding said container, and a second bag made from plastic wrapping said first bag, wherein said first bag is provided with a valve-filter arrangement in order to allow a controlled air stream into said first bag when opening said valve-filter arrangement.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates in general to packages for contamination vulnerable articles. More specifically the invention relates to such packages for the transportation of semiconductor wafers. The invention also pertains to a transportation device for such contamination vulnerable articles. 
         [0002]    Semiconductor wafers are generally dispatched from the manufacturer to the purchaser&#39;s premises. During transportation, long distances often have to be covered and the means of transport may have to be changed frequently. Therefore, there is a considerable risk that the sensitive semiconductor wafers may be damaged. Even without any visible damage caused by scratches or fracturing, impurities may have a considerable adverse effect on the semiconductor wafers or even make them un-useable for the desired purpose, namely the fabrication of electronic components. 
         [0003]    It had been found that after transportation wafer substrates show significantly higher particle contamination values as compared to the level right after fabrication. This fact can be easily explained via the following mechanism: 
         [0004]    Usually, wafer substrates are delivered in transport boxes, known as Front Opening Shipping Box (FOSB), each containing 25 wafers. The boxes are double bagged to avoid particle contamination. The bags are individually evacuated during sealing in order to prevent bursting during, e.g., aircraft transportation. Examples of such methods can be found, e.g., in US 2002/023413 A1, JP 54043461 A2, JP 60167414 A2 and JP 60167415 A2. 
         [0005]    When the bags are opened at the customer&#39;s premises (usually by a simple cut with a knife), the pressure gradient between the exterior of the bag and the interior of the bag causes particles residing at the bag surface to be sucked in. A fraction of these particles finally ends up on the wafer box itself, and some of those consequently also on the wafers through the seal and on the wafers once the box is opened. 
         [0006]    Additional box cleaning procedures will not completely cure this problem since particles present in the sealed gap between the box body and the lid of the FOSB will not be cleaned off but drop into the boxes interior when the door is removed. 
         [0007]    U.S. Pat. No. 6,131,739 discloses a shock-absorbing package for a plurality of containers holding semiconductor wafers, consisting of two half-shells of foamed plastic configured with recesses into which the containers are placed in a positive-fitting manner. A container of the FOSB type is described, for example, in U.S. Pat. No. 6,581,264. A shock-absorbing package of this type is suitable for reducing the risk of mechanical damage to the semiconductor wafers during transport. 
         [0008]    In U.S. Pat. No. 6,155,027 there is described an encased and evacuated container for semiconductor wafers, which should protect the wafers from contaminating particles during transport. 
         [0009]    U.S. Pat. No. 6,119,865 discloses a container for stacking of framed wafers comprising means for binding moisture. 
         [0010]    In U.S. 2002/0153526 A1, there is described an encased container for wafers arranged between shock-absorbing elements in an outer packaging. 
         [0011]    Finally, DE 10 2004 019 664 B4 and DE 10 2004 063 912 A1 disclose a ready-for-dispatch package for semiconductor wafers and a method for the ready-for-dispatch packaging of semiconductor wafers, respectively, comprising a) a closeable plastic container which is loaded with the semiconductor wafers and has a lid and a body, a seal between the lid and the body and a particle filter which is integrated with the container and allows exchange of gas between the interior space of the container and the external environment of the container; b) a first sheath made from plastic, which surrounds the container and rests closely against the container with the aid of reduced pressure; c) a means for binding moisture; d) a second sheath made from coated plastic, with a coating which blocks the passage of moisture and rests closely against the first sheath and against the container with the aid of reduced pressure; e) a shock-absorbing structure which embeds the sheathed container in a positive-fitting manner; and f) an outer packaging which surrounds the double-sheathed and embedded container in a positive-fitting manner. 
         [0012]    However, these containers and packages do not solve the problem that the sensitive wafers are damaged by contaminating particles when opening the bags at the customer&#39;s premises. Accordingly, there is still a need for packages that do overcome this disadvantage. 
       SUMMARY OF THE INVENTION 
       [0013]    It is therefore an object of the present invention to provide a method for packaging contamination vulnerable articles that overcomes the above mentioned disadvantage. 
         [0014]    It is a further object of the present invention to provide a package for use in the above method. 
         [0015]    These and other objects and advantages are achieved by the method disclosed in claim  1  and the transportation device disclosed in claim  8 . 
         [0016]    Advantageous embodiments of the invention are disclosed in the dependent claims. 
     
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0017]    The invention will be described in more detail below in connection with the accompanying drawings, in which 
           [0018]      FIG. 1  schematically shows one particular embodiment of the invention; 
           [0019]      FIG. 2  depicts a well-shut tubing according to the invention; 
           [0020]      FIGS. 3A and 3B  depict a filter element according to the invention; and 
           [0021]      FIGS. 4A and 4B  are flow charts comparing the process of handling the packaged wafers according to the state of the art as compared to the inventive process. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    First of all, it has to be mentioned that the present invention is not restricted to wafers, but can be used with any articles that are contamination vulnerable and thus need protection during shipment. However, in the following, the invention is described in more detail in view of semiconductor wafers as an example. 
         [0023]    As has been described before, the boxes containing the wafers are double-bagged to avoid particle contamination. According to the invention, the bags are modified in such a way that the first bag, i.e., the bag wherein the wafer box is packed (or, in the following called the inner bag), carries a valve as well as a filter element attached thereto. In a special embodiment, the second bag, i.e., the bag wrapped around the first bag (or, in the following called the outer bag) is provided with such a valve and filter element as well. 
         [0024]      FIG. 1  schematically shows one particular embodiment of the invention. It has to be mentioned that the skilled worker will readily think of other embodiments to realize such a valve-filter. Such designs are usually cost-driven and  FIG. 1  shows an economically priced embodiment. In a corner portion  2  of the inner standard vacuum sealing bag  4 , a valve  6  is arranged. This valve can also be arranged elsewhere in the bag, however, arranging it in a corner portion is advantageous because it is easier to attach and easier to access in order to open the bag. The valve  6 , advantageously formed of one single piece, consists of an elongated flexible plastic tubing part  8  that is mounted to the sealing bag  4  by welding or glueing or is directly integrated into the packaging. The tubing part  8  consists of a lower part  10  arranged so as to extend into the bag  4 , and an upper part  12  protruding from the bag. The upper part  12  is closed at its top. According to  FIG. 2 , the flexible plastic tubing  8  (also called weld shut tubing) consists of a plastic tube  14  closed on one side, i.e., having a U-shape. Welded into said plastic tube is a filter element  16 , shown in detail in  FIGS. 3A and 3B . This filter element may be a commercially available filter element such as, e.g., an Ultra Low Penetration Air (ULPA) filter sheet. The filter holder  18 , wherein the filter sheet  20  is arranged, may have a design as shown in FIG.  3 B. It may consist of a plastic tube  22  showing an integrated holder  24  for the filter sheet  20 . 
         [0025]    The first bag gets removed through pressure release by cutting off the sealed end of the filter valve along line  26  (cf.  FIG. 1 ), thus allowing a controlled air stream into the second bag. The filter secures that only particle free air is released from the evacuated bag. The same procedure is used to open the inner bag. In case also the inner bag is provided with the inventive valve, the desired effect is increased. 
         [0026]    The plastic tubing  8  in combination with the filter element  16 , built into the bag  4 , has the function of a valve filtering the air from particles. The filter pore size determines the particle limit filtered, which should satisfy regular class  1  clean room conditions. After opening the weld-shut, the pressure release goes fairly slow due to the filter resistance. 
         [0027]    As has already been described above, in the old packaging process, the FOSB is packed into two bags, one after the other, and each bag gets evacuated to achieve shipment protection. 
         [0028]    In the new, inventive method, the wafers are loaded into the FOSB for transportation in the packaging area. The FOSB then gets closed and is put into the first bag being provided with a filter wave included in a corner portion of the bag. The bag then gets evacuated to protect the box during shipment. For additional protection a second bag is used that may also include the filter-valve. The second bag is evacuated as well to additionally protect the box during shipment. 
         [0029]      FIGS. 4A and 4B  depict flowcharts comparing the old ( FIG. 4A ) and the new ( FIG. 4B ) packaging process flow. The typical problem is that after sorting from an FOSB into a Front Opening Unified Pad (FOUP) at the customer&#39;s premises, at least the wafers in the first and the last slot of the containers show increased particle contamination. This is pretty much a common problem in industry caused, as has already been explained, by the pressure difference and the leaky seals of the boxes. The typical action to resolve this problem up to now is that the wafers have to see wet cleaning, which is an additional process step with remaining risk, due to handling and treatment. 
         [0030]    The controlled opening by cutting off the valves according to the invention causes slow pressure release in the bag(s). This prevents particles which are located on the outer bag&#39;s surface from being sucked onto the inner bag or the FOSB surface, respectively. From the box surface the particles reach into the box through the seals, which, in the prior art, are not designed to stay the rapid pressure difference. Thus, the controlled opening of the bag(s), using the valves including a filter, has the positive effect that the wet cleaning of the wafers can be eliminated. 
         [0031]    The advantages of the inventive device and method are as follows:
       No additional inspection, rework and further cleaning required.   Improvement of yield and substrate phase in the process.   Prevention of particle contamination, triggered through bag opening, the filter pore size depending on the cleanliness requirements.   very simple application, only air filters have to be added to the bag(s).