Abstract:
A wafer carrying structure is provided that allows more efficient operation of the opening and closing mechanisms. More specifically, the wafer carrier includes pressure relief structures that provide appropriate pressure equalization during the opening and closing operations of the wafer carrier. This allows doors on the wafer to be more easily opened and closed while also providing significant environmental isolation for the wafers during transport operations. Relief structures specifically designed to remain closed except for those brief periods of time where pressure relief is necessary to equalize pressure during opening and closing of the carrier.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to wafer handling techniques used during the fabrication of integrated circuits. More specifically, the present invention provides a carrier, and method for using, which protects wafers from contamination during transportation while also allowing easy opening and closing. 
       BACKGROUND OF THE INVENTION 
       [0002]    Careful control of the manufacturing environment for integrated circuits is critical to the success of the process. With this in mind, considerable steps are typically taken to protect wafers, including performing the manufacturing processes in clean rooms, providing controlled environments, ensuring that processing equipment does not contribute to potential contamination, and ensuring employees are careful throughout the process. Although the particular processing steps may be readily controlled, one additional area for concern is the transportation of wafers from one process to the next. Naturally, this step of transporting the wafers requires movement between environments, which creates potential exposure to uncontrolled environments, and a potential for contamination. 
         [0003]    To address transportation concerns, wafers are typically transported in sealed carriers. Naturally, these sealed carriers can protect wafers from contamination due to undesired particles, humidity, gases, general foreign matter or material, or any other potential sources of contamination or damage. The sealed carriers are specifically designed to control their internal environments, thus are typically sealed to avoid any undesired conditions. In some versions, this includes very tight seals to effectively prevent any airflow (gas flow) into or out of the carrier. Other versions may include filtered vents which allow airflow but prevent particles from entering the carrier. 
         [0004]    Complications exists, however, when it is necessary to access wafers within these tightly sealed carriers. For example, when a sealed environment is created inside the carrier, it can be difficult to open existing doors or covers due to pressures within. This may create additional concerns due to the fact that these carriers are typically robotically handled, and opening forces are yet an additional consideration for these systems. Thus, it is desirable to provide a mechanism to equalize pressures and allow easy door opening. One approach to this problem is to provide vents within the carrier, thus allowing pressure within the carrier to be equalized. In order to allow such pressure equalization, while also protecting the internal atmosphere, present carriers utilize filtering mechanisms to catch any particles or undesired foreign matter which may be carried by the ambient atmosphere. Unfortunately, this venting approach cannot prevent undesirable gases from entering the internal chamber. Consequently, an alternative approach is needed to provide appropriate operability of the carrier while also prohibiting undesirable gases or contamination. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    In order to provide a controlled environment for the transportation of wafers, the present invention provides a carrier that may easily be accessed while also providing sufficient levels of wafer protection. The present invention addresses the opening and closing of the carrier by incorporating appropriate pressure equalizing valves which are specifically configured to open and close during appropriate conditions. More specifically, the valve is specifically designed to open and to provide pressure relief when door opening activities create a vacuum within the carrier. By equalizing pressures at the desired point in time, the doors may be easily opened by an individual user or a robotic system attempting to access the internal portion of the carrier. Similarly, a second relief valve is incorporated, which is specifically configured to deal with closing pressures. This second relief valve opens under those conditions where increased pressure is generated within the carrier due to the closing of the carrier doors. Using these valves, the carrier provides a controlled environment by eliminating the vents previously used, while also allowing prompt access to the interior of the carrier. 
         [0006]    Although the concepts of the present invention may be applied to a carrier typically referred to as a front opening unified pod (FOUP), similar conditions and characteristics may be encountered by other carriers that likewise may benefit from the present invention. The concepts of the invention may further be applied to virtually any carrier that may provide protection to wafers during the processing and manufacturing of integrated circuits. 
         [0007]    As previously describe, the relief valves of the present invention are specifically designed to open at very precise pressure conditions. To achieve this operation, the valves are primarily configured to include a valve housing, a pressure sensitive plate which will be exposed to the internal pressures of the carrier, and a spring configured to hold the pressure plate in a predetermined position. The spring and plate themselves are specifically configured to be responsive to very specific pressures, and calibrated to be relatively precise. In addition, the valve housing includes an adjustment structure for adjusting and calibrating the operating characteristics of the relief valve. Lastly, a filter structure is included downstream to provide filtering while the relief valve is open. 
         [0008]    The relief valve of the present invention is generally designed to be closed for a majority of the time during operation, and is only opened at those times when the carrier doors are being opened or closed. As such, this approach allows for easy operation of the carrier while providing an additional level of environment protection. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Further objects and advantages of the present invention will be seen by reading the following detailed description, in conjunction with the drawings in which: 
           [0010]      FIG. 1  is a perspective view of the carrier; and 
           [0011]      FIG. 2  includes a front view and cross sectional view of the airflow relief valve utilized in the carrier. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    As illustrated in  FIG. 1 , the present invention employs the use of a wafer carrier  10  which is generally illustrated in an open state. In this particular embodiment, wafer carrier  10  is intended to be a front opening type carrier, typically referred to as a front opening unified pod (FOUP), but the present invention may be applied to other carrier types as well. In this particular example, wafer carrier  10  includes a front door  20  and a main housing  30 . Front door  20  is primarily planar, but it does include a seal  22  positioned on an interior surface thereof. Seal  22  is configured to interface with a front edge  32  of main housing  30 . In this particular embodiment, seal  22  is an O-ring configured and designed to fit within appropriate ridges in door  20 . Multiple different configurations are possible to achieve a desired seal between housing  30  and front door  20 . 
         [0013]    Illustrated within main housing  30  are a plurality of slots  34  shown within a sidewall  38 . These slots are configured to receive wafers in a convenient manner, thus maintaining separation between the various wafers within main housing  30  while also holding them in a desired position. Again, those skilled in the art will recognize that many different configurations are possible for this holding type structure. Further, a holding structure may be utilized which is separate from the sidewalls and simply inserted into or coupled with main housing  30 . 
         [0014]    In addition, main housing  30  includes handling structures  36  existing on a top portion. This handling structure is just one example of a device which will assist in the mechanical handling of wafer carrier  10 . Also shown in  FIG. 1  are an input relief valve  40  and an output relief valve  60 . In this particular context, “input” and “output” are utilized to designate the direction of airflow which is permitted by the respective valve relative to the internal portion of housing  30 . As will be recognized by those skilled in the art, different positioning and different configurations of the relief valves is possible. 
         [0015]    Referring now to  FIG. 2 , a more detailed illustration of input relief valve  40  is shown. This particular embodiment of input relief valve  40  is illustrated and discussed herein in considerable detail with reference to  FIG. 2 . It will be understood that output relief valve  60  is configured in a substantially similar manner. Both of these valves are intended to be poppet valves which will open upon a predetermined pressure condition, but will remain closed when the pressure condition does not exist.  FIG. 2  includes a front view ( FIG. 2A ) and a cross sectional view ( FIG. 2B ) of input relief valve  40 . As seen in these illustrations, input relief valve  40  includes an outer shell  42 , a spring  44 , a movable disk  46  and a retainer  48 . Further, movable disk  46  includes a gasket  52  positioned on a front surface thereof. Gasket  52  provides an appropriate coupling and sealing between retainer  48  and movable disk  46 . As can be appreciated, when pressure on the spring side of movable disk  46  becomes lower than the pressure on the opposite side thereof, force is created which will attempt to compress spring  44 . Once this force becomes sufficient to move spring  44 , the movable disk  46  will become unseated from retainer  48 , thus opening an airway. This will thus allow air to pass through input relief valve  40 . In the illustration of  FIG. 2 , air will move through relief valve  40  in a direction to the right, as oriented in  FIG. 2B . 
         [0016]    Although not specifically illustrated, output relief valve  60  is similarly configured with the spring and housing members slightly modified to allow reverse pressures to enable airflow. Those skilled in the art will recognize that a slight reconfiguration of components is easily achieved to accomplish this reverse operation. 
         [0017]    Also illustrated in  FIG. 2B  are inner connecting threads  54  which provide a coupling mechanism between outer shell  42  and retainer  48 . By having a threaded connection, the spring itself can be compressed more or less and adjusted once the valve is installed. Providing this threaded connection allows the force and other operating characteristics of spring  44  to be slightly adjusted due to the biases placed upon spring  44 . Once installed, input relief valve  40  can thus be calibrated to open upon desired pressure conditions by achieving the desired force in the spring. Similar calibration of output relief valve  60  is also possible, thus allowing for carefully controlled operation. 
         [0018]    By incorporating appropriate relief valves  40  and  60  into main housing  30 , appropriate pressure relief is achieved which can easily allow the opening and closing of door  20 . As mentioned above, further protection is provided by also incorporating a filter element  70 . The filter is positioned in the airflow path, to cause any airflow to pass therethrough. Various suitable alternatives may be applied for the inclusion of the filter elements. In one embodiment, filter elements  70  are captured between outer shell  42  of valve  40  and the carrier housing  30 . 
         [0019]    Referring now specifically to  FIG. 2A , a unique configuration for movable disk  46  is illustrated. More specifically, a plurality of slots  56  are shown. These slots include indentations in the outer portion of movable disk  46  to more easily accommodate airflow. In this particular configuration, movable disk  46  includes four different slots  56  equally spaced around the circumference of the movable disk. These slots provide free and clear openings for the movement of air at those times when relief is required. 
         [0020]    In the configuration described above, the valve structure can be adapted to fit existing carriers. As discussed, carriers may include filtered vent openings to provide pressure equalization. To refit these existing carriers, outer shell  42  of valve  40  can be configured to tightly fit within existing vent openings and create a seal therewith. Thus, existing carriers can be easily modified by inserting valves into appropriate vent openings to create a better functioning carrier. 
         [0021]    While certain embodiments of the invention have been described above, these specific configurations are not considered to be limiting in any way, but rather illustrative of the concepts of the present invention. The applicants intends the invention to include all variations and modifications coming within the scope and spirit of the following claims.