BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
The invention will be described in more detail below in connection with the accompanying drawings, in which
FIG. 1 schematically shows one particular embodiment of the invention;
FIG. 2 depicts a well-shut tubing according to the invention;
FIGS. 3A and 3B depict a filter element according to the invention; and
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
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.
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.
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. 3B. It may consist of a plastic tube 22 showing an integrated holder 24 for the filter sheet 20.
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.
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.
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.
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.
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'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.
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'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.
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).
Patent Application
20070289896
