Abstract:
A wafer container comprising a base and a cover that nest together. The base includes a staggered wall structure composed of inner and outer walls. The staggered wall structure is arranged so that forces from side impacts are absorbed principally by outer wall segments. A rib on the cover restrains the outer wall segments from flexing beyond the inner wall diameter. Reference tabs on the base facilitate alignment of the base to the cover.

Description:
This application claims benefit of Provisional application No. 60/998,678, filed on Oct. 12, 2007. 
    
    
     BACKGROUND OF THE INVENTION 
     Semiconductor wafers are fragile substrates that can easily become scratched or damaged if not properly protected during transport. Each semiconductor wafer is patterned with numerous integrated circuits on a silicon substrate. Numerous containers have been developed to protect semiconductor wafers from damage during shipping and handling. 
     Frequently, the top and bottom half of wafer containers are improperly combined by an operator or become misaligned by forces that impact the containers during shipping. Such misalignment may contaminate, crack, or otherwise damage the valuable wafers stored within the containers. 
     Among the variety of horizontal wafer containers for semiconductor wafers, are containers having a dual wall structure. U.S. Pat. No. 6,193,068 (Lewis) is one example. The double walls in Lewis were designed to protect wafers from forces that may contact the outer wall of the base. However, in Lewis the outer wall is directly behind the inner wall and is aligned in a similar angular sector. Inner walls in such wafer containers are generally rigid and inadequately shock absorbent. An external force may be substantial enough to flex the outer wall into the inner wall, which in turn would damage the wafers stored within the wafer container. 
     There remains a need for a wafer container that is less prone to becoming separated and that is sufficiently robust to protect semiconductor wafers from forces transmitted during shipping and handling. 
     SUMMARY OF THE INVENTION 
     The present invention concerns a wafer container having a dual wall structure on the base. The wall structure comprises multiple outer walls and multiple inner walls. Each inner wall shares a minimal percentage of a common angular sector with each adjacent outer wall. 
     The present invention also concerns an alignment system for facilitating the proper alignment of a cover with a base. The alignment system includes reference tabs that are received by the cover and a visual identifier for guiding an operator in the proper alignment of the two halves of the container. 
     Another embodiment of the invention concerns a locking mechanism for securing two halves of a wafer container together. The bottom half comprises a wall structure perpendicular to the base. The wall structure comprises segmented inner and outer walls, each portion of the wall structure has a distinctive arc length. The arc length of each inner wall does not completely overlap with the arc length of any outer wall. 
     Yet another embodiment of the invention concerns a cover for a wafer container that engages to a base. The cover includes one or more notches, each having a ramp that easily receive latches from the base. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the container of the present invention showing wafers interposed between both halves of the container; 
         FIG. 2  illustrates reference tabs on the base in alignment with the cover. 
         FIG. 3A  illustrates reference tabs in alignment with a cover. 
         FIG. 3B  illustrates reference tabs in misalignment with a cover. 
         FIG. 3C  illustrates a cover with alignment arrows to facilitate proper orientation to a base. 
         FIG. 4A  illustrates the height dimension of the hook portion of the latch. 
         FIG. 4B  illustrates the height dimension of the reference tabs of  FIG. 2 . 
         FIG. 5  illustrates the container of  FIG. 1  with the top cover being secured to the bottom half. 
         FIG. 6A  is a side view of the closed container of  FIG. 5 . 
         FIG. 6B  is an alternate side view of the closed container of  FIG. 5 . 
         FIG. 7  illustrates the location of angular sectors on the base of the present invention. 
         FIG. 8  is a top view of the base. 
         FIG. 9  is a perspective view of the base of the present invention. 
         FIG. 10  is a perspective view of the interior of the top cover. 
         FIG. 11  is an exploded view of the ramp in  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The container of the present invention stores semiconductor wafers, or semiconductor film frames.  FIG. 1  illustrates the two halves of the container, a base  100  and its corresponding cover  200 . A ribbed pattern  30  on the floor  10  of deck  60  serves to reinforce the integrity of base  100 . The storage area of base  100  is defined by inner walls  80 , floor  10 , and outer walls  90 A,  90 B,  92 A, and  92 B. Interposed between cover  200  and base  100  are wafers  30 ,  32  and wafer separators  37 - 39 . 
     Upon impact, outer wall segments  90 A,  90 B,  92 A, and  92 B will flex to the inner diameter  12  of inner wall segments  80 . Outer wall segments  90 A,  90 B,  92 A, and  92 B absorb the bulk of energy from side impact, thereby transferring a reduced amount of energy to the inner wall segments  80 . Consequently, wafers  30  and  32  are sheltered from the brunt of forceful impact by the staggered wall structure of the invention. 
       FIG. 2  illustrates an alternative embodiment for the base  100  of wafer container  250 . In this more preferred embodiment, a series of reference tabs are mounted on deck  60  of base  100 . Reference tabs  20 A,  20 B,  22 A,  22 B,  24 A,  24 B,  28 A, and  28 B are designed to help align base  100  with cover  200  in the following manner. Cover  200  has support brackets that are designed to register with tabs  20 ,  22 ,  24 , and  28 . In particular, recess  70 A of bracket  70  loosely fits over tab  20 A, while recess  70 B loosely fits over tab  20 B. Similarly, recess  78 A fits over tab  28 A (not shown), while recess  78 B slips over tab  28 B. Recesses  74 A and  74 B fit over tabs  24 A and  24 B respectively. Preferably, none of the recesses of support brackets  70 ,  72 ,  74 ,  78  will snugly fit onto tabs  20 ,  22 ,  24 , and  28 . In the most preferred embodiment, each of the four support brackets will be identical and have the appearance of support bracket  70 .  FIG. 3C  illustrates cover  200  where the all of the support brackets have an identical structure. 
     In  FIG. 3A , a top view of base  100  is shown along with a skeletal view of cover  100 . A hatched outline is used to indicate cover  200  and how cover  200  is properly aligned to base  100 . A latch  25  on each corner is also shown in  FIG. 3A . Adjacent to each latch is an opening  31  which provides latch  25  latitude for moving into a latched or unlatched position. Pairs of references tabs are located on each side of an upper surface of base  100 . For example, in  FIG. 3A , tabs  24 A and  24 B are located on one side of base  100  between openings  31 C and  31 D, while tabs  28 A and  28 B are located on an adjacent side of base  100  between openings  31 A and  31 D. Similarly, tabs  22 A and  22 B are located on a different side of base  100  between openings  31 B and  31 A. Tabs  20 A and  20 B are located on a fourth side of base  100 .  FIG. 3B  illustrates cover  200  of  FIG. 3A  after it has been rotated 90°. In the position of  FIG. 3B , cover  200  is misaligned with its base  100 . Cover  200  can not properly fit onto base  100  because recess  70 A and recess  78 A do not register with reference tab  20  A and reference tab  28 A respectively. That is, the recesses of support brackets  70  and  78  do not slide freely onto tabs  20 A and  28 A, thereby preventing cover  200  from being improperly positioned onto base  100 .  FIG. 3B  also illustrates orientations arrows  35  and  37 . Orientation arrows  35 ,  37  provide a visual reference to assist an operator in properly aligning cover  200  with base  100 . In a preferred embodiment, cover  200  will also have a pair of orientation arrows as shown in  FIG. 3C  that coincide with the arrows on base  100  when the two halves are in proper place relative to each other. Instead of an arrow, any other type of visual mark may be used to assist an operator in identifying when the cover and the base are properly aligned. 
     The height dimension H 1  of the latch hook is shown in  FIG. 4A . The height dimension H 2  of reference tab is shown in  FIG. 4B . H 2  should have a height that will prevent latch  25  from engaging to cover  200  if cover  200  is not adequately pressed down onto base  100 . In a preferred embodiment, H 2 &gt;H 1 . 
       FIG. 5  illustrates a perspective view of the closed wafer container  250 . Specifically, sidewall  75  and support brackets  70  and  74  of cover  200  enclose the exterior of wall structure  80 ,  90 , and  92  to form closed container  250 . The major surface  50  of cover  200  has a pattern that provides structural strength as well as stiffness to the top portion of container  250 . In particular, it was found that adding a star shaped pattern  33  on cover  200  and concentric ribs  52 ,  54 , resulted in a stiff and lightweight cover  200 . The star-shaped pattern  33  is not limited to four arms, but it can have more than four arms as shown in  FIG. 3B . Base  100  also has a latch  25  mounted on each corner of a deck  60 . The two halves of container  250  are secured when each latch  25  locks onto a respective notch  43  of cover  200  as shown in  FIG. 5 . Also visible in  FIG. 5  is a lip  27  on the periphery of cover  200 . This lip  27  enables the container  250  to be stacked on a second container identical to the first one. 
     To illustrate how the segmented wall structure of base  100  mates with its cover  200 , a side view of container  250  is shown in  FIGS. 6A and 6B . Wall segment  81  fits inside sidewall  75  of cover  200 . Sidewall  75  has slots  35 , which allow a portion of outer walls  81  and  85  to be exposed. Similarly, outer wall  85  will fit inside sidewall  75  of cover  100  when the two halves  100 ,  200  are engaged. In addition, support brackets  70 A and  70 B nest outside outer walls  83  and  87  of base  100 , providing a stable storage area for the wafers stored inside. 
     The various wall segments on base  100  occupy specific areas within a circumference on base  100 . These areas are referred to herein as angular sectors.  FIG. 7  illustrates one example of the angular sectors R 1 -R 6  that may exist within a circumference  50  located on base  100 . R 1 , R 3 , and R 5  represent angular sectors where an inner wall segment is to be located, while R 2 , R 4 , and R 6  represent areas where an outer wall segment is to be located. The outermost boundary of each angular sector is defined by an arc. Outermost arcs are indicated as  41 B,  41 D and  41 F. The innermost arcs within circumference  50  are  41 A,  41 C, and  41 E. Arc  41 A is shown as extending into angular sector  41 F by an angle γ of approximately 2°. Arc  41 C is shown as extending into both adjoining sectors R 4  and R 2  by an angle θ 1  and θ 2 , wherein θ 1  is approximately 3° and θ 2  is approximately 4°. Arc  41 E extends from sector R 5  by an angle α, which is approximately 5°. Although only six angular sectors are shown, the container can have eight or more angular sectors. 
       FIG. 8  is a top view of base  100 , showing both the segmented walls  80 ,  82 ,  84 ,  86 ,  90 A,  90 B,  92 A,  92 B and angular sectors R 1 -R 8 . The floor  10  of deck  60  is shown without any ribbed pattern  30  to illustrate a more clarified view of angular sectors R 1 -R 8 . However, it is understood that the ribbed pattern  30  is present in a preferred embodiment. Perpendicular, or nearly perpendicular, to base  100  are a series of inner walls,  80 ,  82 ,  84  and  86 . In addition, a series of outer walls  90 A,  90 B,  92 A,  92 B are also perpendicular, or nearly perpendicular, to base  100 . Each of the walls shown has an arc with a specific arc length. For example, inner wall  86  has an arc  59  with an arc length  58 . Similarly, outer wall  92 A has an arc  53  with an arc length  56 . Each inner and outer wall occupies one of angular sectors R 1 -R 8 . Between 50 and 99.5% of the inner wall arc is not located in the same angular sector as the arc of an adjacent outer wall. For example, over 90% of the inner wall arc  59  is located in R 7 , and occupies virtually none of the adjoining angular sectors R 6  or R 8 . Outer wall  92 A is located on arc  53 , and is located almost entirely within angular sector R 4 . Consequently, approximately 95% of outer wall  92 A is not located in adjoining angular sector R 3  or R 5 . 
     Since inner wall segments alternate with outer wall segments, the arc of an inner wall may encroach into an adjoining angular sector. In a preferred embodiment of the invention, the arc length of each inner wall segment encroaches approximately 0 to 50% of the arc length of an adjoining angular sector of an outer wall. In a more preferred embodiment of the invention, inner wall  82  occupies angular sector R 3  and shares between 0.1% to 25% of angular sector R 4  with outer wall  92 A; inner wall  82  also shares between 0.1% to 25% of angular sector R 2  with outer wall  90 A. Most preferably, inner wall  82  shares between 0.1% to 10% of angular sector R 4  with outer wall  92 A and between 0.1% to 10% of angular sector R 2  with outer wall  90 A. Similarly, inner wall  80 , which principally occupies angular sector R 1 , preferably shares between 0 to 50% of angular sector R 2  with outer wall  90 A and between 0-50% of angular sector R 8  with outer wall  92 B. More preferably, inner wall  80  shares between 0.1% to 25% of angular sector R 2  with outer wall  90 A; inner wall  80  also shares between 0.1% to 25% of angular sector R 8  with outer wall  92 B. Most preferably, inner wall  80  shares between 0.1% to 10% of angular sector R 2  with outer wall  90 A and between 0.1% to 10% of angular sector R 8  with outer wall  92 B. 
     The invention is not limited to a container that has only the eight angular sectors R 1 -R 8  shown in  FIG. 8 . The invention will work with a base having fewer than eight angular sectors, as well as a base with more than eight angular sectors. The number of sectors will equal the total number of inner and outer wall segments. The arc of each wall segment defines an outermost boundary of each angular sector. Although each wall ( 80 ,  82 ,  84 ,  86 ,  90 A,  90 B,  92 A, and  92 B) in  FIG. 8  separately occupies less than 90° of the base circumference (i.e., each wall preferably has an arc length less than (Π/2 radius)), it is not necessary that this always be the case for the invention to work. In other words, each wall can occupy a greater angular portion of the circumference. Moreover, each inner wall ( 80 ,  82 ,  84 ,  86 ) need not have the same arc length as every other inner wall. Similarly, it is not essential for each outer wall ( 90 A,  90 B,  92 A, and  92 B) to have the same arc length as every other outer wall on base  100 . Also shown in  FIG. 8  is a latch  25  mounted on each corner of base  100 . On the rear of latch  25  is a rib  23 . Rib  23  is an optional feature for strengthening latch  25 . Although four latches are shown in  FIG. 5 , the invention will work satisfactorily if only two latches are present. 
       FIG. 9  illustrates the bottom half of the wafer container  250 , also referred to herein as base  100 . The wall structure of base  100  includes segmented inner walls and segmented outer walls. A continuous wall structure is disadvantageously very stiff, even in the presence of one or two lateral openings. By providing a segmented wall structure, inner walls  80 ,  82 ,  84  and  86  are more flexible and shock absorbent. As a result, walls  80 ,  82 ,  84  and  86  sufficiently cushion wafers within container  250  if the container is dropped or otherwise subjected to forceful impact. 
     Outer walls  90 A,  90 B,  92 A and  92 B are staggered relative to inner walls  80 ,  82 ,  84  and  86  as shown in  FIG. 9 . This staggered double wall structure provides maximum protection from shock to wafers stored in container  250 . In addition, outer walls  90 A,  90 B,  92 A, and  92 B have a greater flexible tolerance when their angular sector has minimum overlap with the angular sector of an adjacent inner wall. Outer walls  92 A and  92 B each have a slot  15 . Preferably the lower portion of slot  15  does not extend to the same level as deck  60 . Slot  15  enables an operator arm to more easily access wafers stored within base  100 . 
     The deck  60  of  FIG. 9  also includes latches  25  for securing base  100  to cover  200 . Each latch  25  has a proximal end that is mounted on a corner region  60  of base  100 . The distal end of each latch  25  terminates in a hook  25 A that grasps onto cover  200 . 
     A detailed view of the cover  200  is shown in  FIG. 10 . On the interior surface  44  of cover  200  are a series of concentric ribs  51 ,  52 ,  54 . Outermost rib  54  may contact a portion of the wall structure on base  100  if wafer container  250  is subjected to external forces. During shipping or handling, when closed container  250  encounters a forceful side impact, outer wall segments  90 A,  90 B,  92 A and  92 B absorb the bulk of the impact by flexing inward toward the inner diameter  12  of inner wall segments  80 . The outer wall segments  90 A,  90 B,  92 A and  92 B are restrained from flexing beyond diameter  12  by rib  58  on the interior of cover  200 . 
     In addition to ribs, cover  200  contains a sidewall  75  that extends perpendicularly from surface  44 . In a preferred embodiment, two slots  35  are present in sidewall  75 . Slots  35  are each surrounded by support bracket  71  or  73 . Support brackets  70 A and  70 B are also attached to sidewall  75  on cover  200 . Support brackets  70 ,  71  and  73  serve to orient cover  200  into a proper position on base  100 . Bracket  73  has two fins  77 A and  77 B connected together by a narrow tie  74  so as to form recesses  72 A and  72 B. In addition, located within support bracket  71  are recesses  74 A and  74 B. The four corner regions  60  of cover  200  each have a notch  43  for receiving a respective latch  25 . To enhance the security of cover  200  from becoming disengaged from base  100 , notch  43  is provided with a ramp  85 . 
       FIG. 11  illustrates an exploded view of the locking mechanism of the invention that secures cover  200  to base  100 . A notch  43  is shown having a rectangular shape. The longer edge of notch  43  has a ramp  85 . Suitable angles for ramp  85  range from 5°-30° from the planar surface of cover  200 . To secure cover  200  to base  100 , notches  43  are aligned above their corresponding latches so that hook  25 A can enter notch  43 . Latch hooks  25 A then slip downward over the positive slope of a ramp  85 , i.e. positive relative to the top surface  50  of cover  200 . Once latch  25  locks into place, cover  200  is securely engaged to base  100 . To disengage cover  200  from base  100 , an operator pushes back on hook  25 A until it clears notch  43 , and then the cover  200  is lifted away from base  100 . Although notch  43  is shown to be rectangular, it can also have other shapes, such as a “T” or an ellipsoidal shape. 
     The examples described herein of the various segmented walls are solely representative of the present invention. It is understood that various modifications and substitutions may be made to the foregoing examples and methods of operation of the wafer container without departing from either the spirit or scope of the invention. In some instances certain features of the invention will be employed without other features depending on the particular situation encountered by the ordinary person skilled in the art. It is therefore the intent that the scope of the invention is to be defined by the appended claims.