Patent Document

[0001]     This application claims the benefit under 35 U.S.C 119(e) of U.S. Provisional Application No. 60/349,059 filed on Jan. 15, 2002. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates to wafer carriers. More particularly it relates to sealable wafer enclosures having doors with latching mechanisms.  
         [0003]     Processing of semi-conductor wafers into finished electronic components typically requires many processing steps where the wafers must be handled and processed. The wafers are very valuable, and are extremely delicate and easily damaged by physical and electrical shocks. In addition, successful processing requires the utmost in cleanliness, free of particulates and other contaminants. As a result, specialized containers or carriers have been developed for use during processing, handling and transport of wafers. These containers protect the wafers from physical and electrical hazards, and are sealable to protect the wafers from contaminants. It is important that the containers remain sealed when in use to prevent damage to the wafers from contaminants. It is also important from a process efficiency standpoint that carriers be easily useable and cleanable.  
         [0004]     Various configurations of door enclosures and latching mechanisms for sealable wafer carriers are known in the art. Some known latching mechanisms use rotary members for actuating the latch, such as a cam. A problem, however, with such mechanisms is that the cam member can self-rotate at undesirable times. This self-rotation can cause unlatching of the door and exposure of the wafers to contaminants. When the door is not in place on the carrier, self-rotation can cause extension of the latches, making it difficult to reinstall the door on the carrier. Other latching mechanisms use systems of interlinked latching arms actuated by a rotary or sliding element. Such systems can have similar problems with actuation of the latching mechanism at undesired times and by intended means.  
         [0005]     Previous methods used with cam actuated latching mechanisms for restraining cam rotation have typically involved a simple leaf spring with a bent tip arranged tangential to the cam. As the cam is rotated near the rotational limit of travel where it is to be held, a surface or projection of the cam slides past the bent tip of the leaf spring. The cam is then held in position at a favored position by the spring force of the leaf spring and friction between the parts. Such a mechanism does not generally urge or spring-bias the cam member toward the favored position to prevent further cam rotation should the cam be dislodged from the detent. Moreover, if two favored positions are provided corresponding to the latch-open and latch-closed position, two separate leaf springs are needed to adequately address both conditions. This adds complexity to the mechanism and complicates assembly of the parts. The leaf springs, if formed from plastic material, do not generally have sufficient rigidity in bending to generate enough friction to hold the cam in position. Alternatives, such as metallic materials, are undesirable in that sliding contact between such materials can generate damaging particulates. Other known methods involve simple detent systems, involving for example, projections from the cam member that engage structures on the door. Such simple detents, however, can become disengaged at unintended times and by unintended means. Once a detent is disengaged, the simple detent mechanism provides no biasing force urging the cam member back toward the detent to prevent latching or unlatching of the door.  
         [0006]     Accordingly, what is needed is a device or apparatus that provides favored positions for a wafer carrier door latching mechanism, and that also provides some type of biasing force urging the latching mechanism toward the favored positions to resist further movement of the latch in the event it is dislodged from the favored positions.  
       SUMMARY OF THE INVENTION  
       [0007]     A wafer container with a door having at least one latching mechanism, wherein the latching mechanism has a spring member that holds the latching mechanism at one or more desired positions that preferably correspond to latch-open and latch-closed conditions. In a preferred embodiment, the spring member has an over-center condition that urges the latching mechanism towards the favored positions, thereby resisting unintended actuation of the latching mechanism. Moreover, in preferred embodiments, the latching mechanism has soft stops at the latch open or latch closed condition that minimizes abrupt snapping into position of the latching mechanism. Preferred embodiments utilize a rotatable member configured as a cammed member with an elongate rigid plastic member having at least one node, forming a plastic spring. The spring is pivotally mounted on the rotatable member and pivotally mounted to the door structure. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a perspective view of a wafer carrier with a machine interface on a piece of processing equipment;  
         [0009]      FIG. 2  is a perspective view of a pair of latch assemblies of a wafer carrier door;  
         [0010]      FIG. 2   a  is a perspective view of a latch assembly of a wafer carrier door;  
         [0011]      FIG. 3  is a view of a preferred embodiment of a latch assembly of a wafer carrier door showing the latch in the open position;  
         [0012]      FIG. 4  is a view of a preferred embodiment of a latch assembly of a wafer carrier door showing the latch in the closed position;  
         [0013]      FIG. 5  is a view of an alternative embodiment of a latch assembly of a wafer carrier door;  
         [0014]      FIG. 6  is a view of another alternative embodiment of a latch assembly of a wafer carrier door;  
         [0015]      FIG. 7  is a view of yet another alterative embodiment of the latch assembly of the wafer carrier door;  
         [0016]      FIG. 8  is a perspective view of yet another embodiment of a latch assembly of a wafer carrier door;  
         [0017]      FIG. 9  is a view of the embodiment of  FIG. 8  showing the latch in an open position;  
         [0018]      FIG. 10  is a view of the embodiment of  FIG. 8  showing the latch in a closed position;  
         [0019]      FIG. 11  is a view of yet another embodiment of a latch assembly of a wafer carrier door with the latch in an open position;  
         [0020]      FIG. 12  is a view of yet another embodiment of a latch assembly of a wafer carrier door with the latch in a closed position; and  
         [0021]      FIG. 13  is a view of yet another embodiment of a latch assembly of a wafer carrier door.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     Referring to  FIG. 1 , a wafer carrier  20 , is seated on automated processing equipment  22 . The wafer carrier comprises a container portion  24  including a top  26 , a bottom  28 , a back  30 , a pair of opposing sides  32  and  34 , and an open front  36 . Inside the container portion  24  are supports  38  for holding a plurality of horizontally aligned and spaced wafers. A machine interface  30  is attached to the exterior of the bottom  28  of the container. Open front  36  is defined by a door frame  40  with latch receptacles  42 . The container portion  24  further has a robotic flange  44  on the top  26  of the container portion. A wafer carrier door  46  fits into the door frame  40  to close the open front.  
         [0023]     Referring to FIGS. ______, door  46  generally includes door chassis  48 , latching mechanisms  50 ,  52 , and mechanism covers  54 ,  56 . FIG. ______, depicts a partial view of latching mechanism  50  in exemplary fashion. The mechanism shown has a rotary actuating member in the form of cam member  68 . Latching arms  58 ,  60 , each have a cam follower portion  62 ,  64 , respectively, engaged with the periphery  66  of cam member  68  at cam portions  70 ,  72 . As depicted in FIG. ______, each of latching arms  58 ,  60 , has a latching portion  74 ,  76 , at the end opposite from cam follower portions  62 ,  64 . When key  78  is inserted into key slot  80  and rotated, cam follower portions  62 ,  64 , slide along cam portions  70 ,  72 . Due to the shape of cam member  68 , latching arms  58 ,  60 , are translated radially, extending or retracting latching portions  74 ,  76 , through latch openings  82 ,  84 . Latching portions  74 ,  76 , are received by latch receptacles  42  in the wafer carrier, allowing the door to be secured in place.  
         [0024]     which are provided to protect the latching mechanisms  50 ,  52  from physical damage and contamination, and to serve as guides for latching arms  110 ,  112 ,  114 , and  116 .  
         [0025]     In the preferred embodiment of the invention as shown in FIGs. ______, latching mechanism  50  is shown in the open position with latching arms  58 ,  60 , fully retracted. Spring member  86  is pivotally attached to cam member  68  at pivot  88  and is also pivotally attached to door chassis  48  at spring pivot  90 . Spring member  86  restrains cam member  68  rotationally and is neutrally biased, exerting no biasing force on cam member  68  in the position shown. Thus, spring member  86  provides a favored position for latching mechanism  50  in this position. If cam member  68  is rotated clockwise, however, spring member  86  will be biased in tension and will exert a steadily increasing biasing force in a counter-clockwise direction. This counter-clockwise biasing force serves as a “soft” rotational stop for cam member  68  in the clockwise rotational direction from the favored position. If cam member  68  is rotated further in the clockwise direction, cam follower portions  62 ,  64 , eventually contact mechanical stops  92 ,  94 , on cam member  68 .  
         [0026]     If cam member  68  is rotated counter-clockwise from the neutral position as shown, spring member  86  is biased in compression and initially exerts a steadily increasing rotational biasing force on cam member  68  in a clockwise rotational direction. As cam member  68  is rotated further counter-clockwise and reaches the mid-point of its rotational travel range, the biasing force of spring member  86  is directed through the center of cam member  68 . In this position, spring member  86 , although compressed, exerts no rotational biasing force on cam member  68 . As cam member  68  is further rotated in the counter-clockwise direction past the mid-point of its rotational travel range, spring member  86  exerts a biasing force, now urging cam member  68  in the counter-clockwise direction. As cam member  68  rotates further in the counter-clockwise direction, the rotational biasing force exerted by spring member  86  steadily decreases as spring member  86  decompresses. Once cam member  68  reaches the fully latched position as shown in FIG. ______, spring member  86  once again reaches a neutral position and exerts no rotational biasing force in either direction. Thus, spring member  86  has another favored position in this location. As before, if cam member  68  is rotated further counter-clockwise from this neutral position, spring member  86  is loaded in tension and exerts a steadily increasing rotational biasing force urging the cam member clockwise. Eventually, as cam member is turned further counter-clockwise, cam follower portions  62 ,  64 , contact mechanical stops  96 ,  98 , on cam member  68 .  
         [0027]     The latching mechanism illustrated in  FIGS. 3 and 4  has a number of distinct advantages. First, spring member  86  provides two favored positions for cam member  68  corresponding to the neutral positions described above. These favored positions are created with a single spring member and without the need for sliding contact between parts that can cause undesirable particulates. Secondly, spring member  86  provides a rotational biasing force, urging cam member  68  toward either of the favored positions, depending on the rotational position of cam member  68 . In operation, cam member  68  experiences about 90 degrees of rotational travel range. Spring member  86  provides a rotational biasing force over nearly the entire range, exerting no biasing force only when cam member  68  is at the mid-point of its rotational range, and when it is at either of the two favored positions. Thus the effective rotational range where spring member  86  provides a rotational biasing force urging cam member  68  toward its favored positions is nearly 45 degrees in each direction. Finally, as explained above, spring member  86  provides a biasing force resisting rotation of cam member  68  beyond each of its favored positions. As a result, when cam member  68  is rotated to either of its favored positions, it is decelerated in a controlled fashion by spring member  86  as it moves past the favored position, and its momentum is absorbed. Once the momentum has been absorbed, spring member  86  contracts, pulling cam member  68  to its favored position. The result is that the favored positions are “soft”, and do not involve the collision of mechanical parts, which can generate vibrations. Such vibrations are undesirable in that they can tend to “launch” any particulate matter present on the door or in the container, creating the possibility of contamination of the wafers. Another advantage of avoiding the collision of mechanical parts as in “hard” favored positions is that such collisions can themselves generate undesirable particulates.  
         [0028]     The material and geometry of spring member  86  may be selected so that sufficient bias force is exerted to effectively prevent unintended rotation of cam member  68 , but is not excessive so as to unduly hinder intended rotation of cam member  68  when operated in use. In the preferred embodiment of FIGs. ______, spring member  86  may be comprised of thermoplastic material, but could be made from any compatible resilient material suitable for use in a wafer container. The material may also be made electrically conductive if desired, for instance, by the addition of carbon fiber fill, to provide electrical conductivity for a grounding path.  
         [0029]     It will be appreciated that, by varying the length, cross-section and material used for spring member  86 , it is possible to achieve a range of the amount of spring biasing force exerted by spring member  86 . It is preferable that the spring biasing force be effective for at least 5 degrees of the rotational travel range of cam member  68  proximate to each favored position, but a range of up to nearly 45 degrees of the rotational travel range proximate to each favored position is possible as described above In addition, although spring member  86  is depicted as having an arcuate shape, other geometries are possible and are within the scope of the invention, such as the s-shaped spring  100  of FIG. ______ or the coil spring  102  of  FIG. 6 . Two or more spring members  104 ,  106 , of smaller dimension may be used if desired, as depicted for example in FIG. ______. In addition, one or more torsion springs disposed within cam member  68  could be used to similar effect.  
         [0030]     Another embodiment of the invention is depicted in FIGs. ______. In this embodiment, cam member  68  has radial protuberance  108 . Arcuate shaped spring member  110  is rigidly mounted to mechanism cover  118  at a point intermediate to tips  194  and  198 . Spring member  190  has a v-shaped bends  192  and  196  proximate to tips  194  and  198  respectively. Tips  194  and  198  are shaped conformingly to protuberance  180 . When mechanism cover  118  is installed on door chassis  102 , tips  194  and  198  are proximate to the periphery of cam member  108 . When cam member  108  is at a position corresponding to a latch-closed condition as shown in  FIG. 8 , radial protuberance  180  of cam member  108  is engaged and captured with tip  194 , providing a favored position for cam member  108 . Spring member  190  is not loaded and thus has a neutral bias in this position. As cam member  108  is rotated clockwise, v-shaped bend  192  rides over protuberance  180 , biasing spring member  190  in bending. The resilience of spring member  190  exerts a biasing force acting through v-shaped bend  192 , tangential to protuberance  180 . This biasing force urges cam member  108  in a counter-clockwise direction, resisting the clockwise rotation. As cam member  108  is rotated further clockwise, protuberance  180  clears v-shaped bend  192 , and spring member  190  returns to an unloaded condition. Spring member  190  remains out of contact with cam member  108  and exerts no rotational biasing force on it until cam member  108  nears a position corresponding to a latch-open condition, and protuberance  180  contacts v-shaped bend  196 . As cam member  108  is rotated further clockwise, v-shaped bend  196  rides over protuberance  180  again loading spring member  190  in bending. Once protuberance  180  clears v-shaped bend  196 , the resilience of spring member  190  acting through v-shaped bend  196  urges cam member  108  clockwise. Protuberance  180  is captured and held by the shape of tip  198 , constituting a favored position for cam member  108  corresponding to a latch-open condition. Spring member  190  once again has a neutral bias in this position. If cam member  108  is rotated further clockwise from this position, the distal end of tip  198  is pressed radially outward by protuberance  180 , biasing spring member  190  in bending. Consequently, spring member  190  exerts a biasing force directed radially inward, increasing the sliding friction between the distal end of tip  198  and radial protuberance  180 . Thus, a force resisting rotation of cam member  108  clockwise beyond the favored position is provided. If cam member  108  is rotated still further clockwise, cam follower portions  130  and  132  contact mechanical stops  150  and  152  on cam member  108 , but before the distal end of tip  198  clears protuberance  180 .  
         [0031]     In the embodiment shown in  FIGS. 8-10 , spring member  190  exerts a biasing force urging cam member  108  toward each of the two favored positions configured as detent stops for a rotational range of cam member  108  of about 5-15 degrees surrounding each detent stop, thus resisting disengagement of the cam member from the detents. In addition, this embodiment also has the advantage of “soft” favored positions configured as soft detent stops, due to the biasing force provided by the distal end of tips  194  and  198  against protuberance  180  as cam member  108  rotates in either direction past the detent stops.  
         [0032]     In the embodiments shown in  FIGS. 8-10 , spring member  190  and cam member  108  are made from thermoplastic material, each preferably having abrasion resistant qualities. As a person of skill in the art will appreciate, however, the scope of the invention includes members made from any suitable and compatible materials.  
         [0033]     The latching arms themselves, rather than the rotating element of a latch assembly, may be provided with a spring bias toward favored positions, as shown for example in  FIGS. 11 and 12 . Although shown here with a rotary actuating member, such an assembly would be particularly well adapted for a latch mechanism having no rotary actuating member, using for instance, a four bar linkage for actuation. Spring members  204  and  214  in this embodiment of the invention function similarly to a Belleville type spring. Two favored positions are provided, corresponding to a latch-open and a latch-closed position. Spring member  204  is mounted between pivots  200  and  202  and is attached to latching arm  114  at center pivot  206 . Similarly, spring member  214  is mounted between pivots  208  and  210 , and is attached to latching arm  116  at center pivot  212 . Each of spring members  204  and  214  is normally straight, but slightly longer than the distance between the pivots to which it is attached. Thus, spring members  204  and  214  take on a slightly arcuate shape when installed between the pivots and with no load applied as shown in  FIGS. 11 and 12 . When cam member  106  is rotated counter-clockwise from the latch-open detent position shown in  FIG. 11 , latching arms  114  and  116  are translated radially outward along the longitudinal axis of each latching arm, causing center pivots  206  and  212  to also move radially outward. Spring members  204  and  214  are consequently loaded in compression, and exert a force acting through center pivots  206  and  212  resisting the radial movement of latching arms  114  and  116 . When center pivot  206  reaches a point on a line directly between pivots  200  and  202 , and center pivot  212  reaches a point on a line directly between pivots  208  and  210 , each spring member  204  and  214  is fully compressed and exerts no radial biasing force on latching arms  114  and  116 . When cam member  106  is rotated further counter-clockwise so that center pivots  206  and  212  move further radially outward, spring members  204  and  214  begin to decompress and exert a force directed radially outward, urging latching arms  114  and  116  toward the latch-closed detent position. When latching arms  114  and  116  are fully extended as shown in  FIG. 12 , spring members  204  and  214  are once again in a neutral position, exerting no biasing force on latching arms  114  and  116 . Those of skill in the art will recognize that, by varying the length, cross-section and material used for spring members  204  and  214 , it is possible to achieve a range of the amount of spring biasing force exerted by spring members  204  and  214 . It is preferable that the spring biasing force be effective for at least 10% of the longitudinal travel range of the latching arms proximate to each favored position, but a range up to nearly 50% of the longitudinal travel range proximate to each favored position is possible.  
         [0034]     Another embodiment wherein a biasing force is provided directly to the latching arms using a spring arrangement having a single pivot on the door chassis is illustrated in  FIG. 13 . Those of skill in the art will recognize that many other such variations are possible and are within the scope of the invention.  
         [0035]     Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of the invention. Thus, the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.

Technology Category: 5