Abstract:
An apparatus for holding a rotatable wafer having a wafer side and a wafer edge includes one or more clamps proximally positioned around a wafer perimeter, each of said clamps including a clamp edge adapted to engage said wafer edge.

Description:
[0001]     This invention relates to systems and methods for securing semiconductor wafers during spinning.  
         [0002]     In semiconductor fabrication, various layers of insulating, conducting and semi-conducting materials are deposited to produce semiconductor devices that provide desired electrical functions in an integrated circuit (IC) device.  FIG. 1  shows an exemplary of typical wafer processing apparatus. A wafer  10  is positioned above a wafer chuck  12 , both of which are contained in a shroud  14 . The chuck  12  is connected to one end of a spindle shaft  19 , while the other end of the spindle shaft  19  is connected to a pulley  20 . The shaft  19  is centered in a spindle housing  18  using a plurality of spindle bearings  16 . The pulley  20  is driven by a belt  22 , which in turn is connected to a motor pulley  24 . The motor pulley  24  is connected to a motor  26  which, when activated, rotates the pulley  20  to rotate the shaft  19  and the chuck  12  to spin the wafer  10  resting above the chuck  12 . The wafer is held in place by a wafer retaining device  50 .  
         [0003]     During fabrication, semiconductor processing apparatus treat wafer surfaces by furnishing required treating liquids and gases to a wafer surface while rotating the wafer at a high speed. Such spinning or rotating-type substrate processing requires an arrangement that minimizes slippage between a substrate and retaining members which hold the substrate while the substrate is spinning since slippage causes the substrate surface to be chipped and generated particles, and also causes dust to adhere to the substrate surface. This also causes the processing liquid to flow unevenly, which eventually deteriorates the quality of processing.  
         [0004]     Generally, the wafer retaining mechanism is broadly classified into two types. One is a so called vacuum chuck type that conducts vacuum-suction to one side surface of the wafer, and the other is a type that holds the outer peripheral edge of the wafer by means of three or more chuck pieces. Since the treating can be applied to only one side surface of the wafer according to the former, the latter is chiefly employed when it is desired to treat both side surfaces simultaneously.  
         [0005]     U.S. Pat. No. 4,788,994 discloses a wafer holding mechanism that horizontally holds, one at a time, wafers which are sequentially transported thereto. Wafers are treated with liquids such as an etching, rinsing liquid, and the like, at the same time that the wafer is rotated at a high speed. The mechanism includes a hollow rotary shaft having an upper end thrust into a housing, a rotary plate horizontally mounted on the upper end of the rotary shaft, chuck pieces provided on the rotary plate for holding an outer peripheral edge of the wafer, the chuck pieces being movable in the radial direction of the rotating plate between a holding position wherein the wafer is tightly held by the chuck pieces and a release position wherein the wafer is free to be removed from the chuck pieces.  
         [0006]     U.S. Pat. No. 5,376,216 discloses a plurality of substrate holding members and a substrate pressing member being disposed on a rotation stage at a peripheral portion. The substrate pressing member includes a magnet and is pivotally supported by the rotation stage. A ring-shaped permanent magnet is located below the rotation stage and forms a ring around the rotation axis of the rotation stage. When a substrate mounted on the rotation stage is rotated and processed, the ring-shaped permanent magnet is positioned in the vicinity of the magnet of the substrate pressing member. This creates a magnetic force between the magnets, causing the substrate pressing member to pivot so that the substrate pressing member contacts the edge of the substrate with a predetermined amount of pressure.  
         [0007]     U.S. Pat. No. 5,989,342 discloses a substrate holding apparatus that holds a rotating substrate without idly rotating the substrate and keeps the substrate in proper balance while the substrate is rotated. In a revolvable holding member, a column-shaped holding part is disposed on a top surface of a column-shaped supporting part, at an eccentric position with respect to a rotation axis of the supporting part. The revolvable holding member is supported by a rotation base for free rotation, and linked to a magnet holding part which incorporates a permanent magnet. On the other hand, a ring-shaped magnet which is disposed in a processing liquid collecting cup is freely driven by an air cylinder in a vertical direction. As the ring-shaped magnet is moved upward or downward and crosses a predetermined line as viewed in a positional relationship relative to the permanent magnet, which is at a height where the permanent magnet is disposed, the direction of a magnetic line of flux of the ring-shaped magnet is reversed. As a result, the direction of the revolving force which acts upon the permanent magnet is reversed, whereby the revolvable holding member holds or releases a substrate.  
       SUMMARY  
       [0008]     In a first aspect, an apparatus for holding a rotatable wafer having a wafer side and a wafer edge includes one or more clamps proximally positioned around a wafer perimeter, each of said clamps including a clamp edge adapted to engage said wafer edge.  
         [0009]     In another aspect, an apparatus for holding a rotatable wafer having a wafer side and wafer edge clamp housing and a clamp rotatably positioned in said clamp housing, said clamp having a clamp edge adapted to engage said wafer edge.  
         [0010]     Advantages of the system may include one or more of the following. The clamp provide for a substrate holding apparatus which, with a simple structure and securely holds and releases a substrate. The substrate can be rotated without causing idle rotation of the substrate, while keeping excellent balance.  
         [0011]     These and other features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings. To facilitate this description, like reference numerals designate like structural elements.  
         [0013]      FIG. 1  shows an exemplary prior art of typical wafer processing apparatus.  
         [0014]      FIG. 2  illustrates an exemplary first embodiment of a spin apparatus that can access both sides of a wafer.  
         [0015]      FIGS. 3-4  show a perspective view and enlarged perspective view of the clamp of  FIG. 2  securing a wafer with support pins.  
         [0016]      FIG. 5  illustrates an exemplary wafer processing apparatus with a second embodiment of a wafer clamp in a clamped position.  
         [0017]      FIG. 6  illustrates the second wafer clamp embodiment in an open position.  
         [0018]      FIG. 7  shows top views of the wafer support stands and clamp of  FIGS. 5-6  in a clamped position.  
         [0019]      FIG. 8  illustrates the detail of wafer clamp in  FIGS. 5-6 .  
         [0020]      FIG. 9  shows a perspective view of the wafer support stands and clamp shown in  FIG. 5 .  
         [0021]      FIG. 10  shows a perspective view of a support clamp shown in  FIG. 8 .  
         [0022]      FIG. 11  shows a perspective view of a support stand shown in  FIG. 7   
         [0023]      FIG. 12  shows a cross-sectional view of the wafer clamp in  FIG. 10   
         [0024]      FIG. 13  illustrates an exemplary wafer processing apparatus with a third embodiment of a wafer clamp.  
         [0025]      FIG. 14  shows a perspective view of the clamps in  FIG. 13  securing a wafer.  
         [0026]      FIG. 15  shows a close-up view of the clamp of  FIG. 14  securing a wafer.  
         [0027]      FIG. 16  shows a cross-sectional view of the clamp in  FIG. 15  securing a wafer.  
     
    
     DESCRIPTION  
       [0028]      FIG. 2  shows an exemplary wafer processing apparatus with a first wafer clamp embodiment, in this case a clamp  200  with a pin to secure a wafer  100  at the wafer&#39;s edge. During operation, the wafer  100  is securely held in place by a wafer retaining device  200  and rotated by a drive assembly including a motor  110  mounted to the platform. The motor  110  rotates a pulley  114 , which drives a belt to spin a spinning housing  190  which in turn spins the wafer  100 . The assembly  200  includes an outer housing  132  to collect liquid and drain hole to vent air and liquid to a drainpipe.  
         [0029]     A first tub or bowl  150  collects waste materials during the processing of the wafer  100 , and a second tub or bowl  152  collects material generated during the processing of the bottom side of the wafer  100 . Drains  154 - 156  are provided at the bottom of the first tub or bowl  150  to provide liquid and air exhaust for the first tub  150 . Similarly, a drain  158  is provided at the bottom of the second tub  152  to remove materials from the second tub  152 .  
         [0030]     The bowl  150  has a shroud  140  to collect liquid and drain hole to vent air and liquid to a drainpipe. The shroud  140  can be moved up and down: the shroud  140  is in a lower position during wafer loading and un-loading, and is at an upper position during wafer rotation process sequences. The assembly moves the shroud  140  up and down using magnets located inside the outer housing  132 . A labyrinth seal between inner and outer tub applied to prevent liquid getting into bearing. Additional protection, a felt ring seal is located between outer bearing drive housing to prevent moisture from getting into the bearing. From the outer bearing assembly, positive pressure airline supplies dry air to the bearing assembly. The foregoing protection prevents moisture from getting into the bearing assembly: there is no metallic material, hardware and mechanism that is exposed liquid. Hence, the arrangement advantageously prevents any corrosion and contamination to the substrate or wafer  100 . Although a belt-drive system has been described, the drive system can also be a direct drive motor system.  
         [0031]     The shroud  140  has a mesh that minimizes liquid from flashing back into the wafer during high speed spinning. The spacing between the shroud and mesh can be from 0.125″ to 1.0″, and preferably is 0.25″. The movement of the shroud is actuated by one or more actuators such as air cylinders. The moving end of the actuator is provided with a magnet that magnetically attaches to a corresponding magnet mounted on the shroud  140 . The shroud  140  is at a first position (down position) during wafer loading or unloading and the shroud is at a second position (up position) during wafer rotation or processing.  
         [0032]      FIGS. 3-4  show a perspective view of the clamp of  FIG. 2  securing a wafer. In the configuration shown in  FIG. 3 , six clamps  200  are positioned above the spinning housing  190  to support the wafer  100  during a spin wash cycle. In an alternate configuration, only three clamps  200  are needed to support and secure the wafer  100  at a low-speed such as during cleaning.  FIG. 4  shows more detail a pin  201  extending from the clamp  200  to press against a wafer edge  101 . A plurality of pins  201  extending from clamps  200  effectively constraints and secures the wafer  100  to the housing  190  at a relatively low spinning speed for washing purposes, for example.  
         [0033]      FIG. 5  illustrates an exemplary wafer processing apparatus with a second embodiment of a wafer clamp in a clamped position. In the embodiment of  FIG. 5 , a clamp  300  supports and secures the wafer  100 . The clamp  300  is magnetically activated by a cylinder  303  which moves a head  305  with a magnet mounted thereon. As shown in  FIG. 5 , when the shroud  140  is an up position, the cylinder  303  is at a rest position and exerts no influence on the clamp  300 . In the absence of a contactless force from the head  305 , the clamp  300  urges one or more contact points against a wafer edge to secure the wafer  100  to the wafer processing apparatus of  FIG. 5 . In an open position, the shroud  140  is in a down position which allows the cylinder  303  to move. When the head  305  approaches the clamp  300 , the magnet on the head  305  repels a magnet mounted on the clamp  300 , causing the clamp  300  to pivot to release the wafer  100 .  
         [0034]      FIGS. 7-8  show a top view of the clamped wafer  100  and an enlarged top view of support clamps  300  when the wafer  100  is secured by the clamps  300 .  FIG. 7  shows that a clamp  300  engages the wafer  100  at the wafer edge. As shown therein, the clamp  300  and a plurality of wafer support stands  400  securely engage the wafer  100  during processing operation.  FIG. 8  shows a top view of the clamp  300  in more detail as having clamp edges  351  and  352  that engage the edge of the wafer  100 . Additionally, the wafer  100  rests above a wafer seat  353  provided on the clamp  300 . In one embodiment, the distance between the clamp edges  351  and  352  is longer than the width of a wafer notch  340 . With this configuration, only three clamps  300  are needed to securely hold the wafer  100 .  
         [0035]      FIG. 9  illustrates an exemplary wafer processing apparatus with support clamps and the wafer clamp of  FIGS. 5-6 . As shown therein, the clamp  300  and a plurality of wafer support stands  400  securely engage the wafer  100  during processing operation.  
         [0036]      FIG. 10  shows a perspective view of the clamp shown in  FIG. 9 . As discussed above, the clamp  300  provides the seat  353  that allows the wafer  100  to be initially placed on the clamp  300 . The clamp  300  also has two clamp edges  351  and  352  that engage the wafer  100  at the wafer edge  307 . The clamp  300  is pivotally enclosed in a housing  360  and pivotally engages the wafer  100  through a pivot  362 . A rotating limit pin  364  limits the rotation of the clamp  300  when actuated by the cylinder  303  with its magnetized head  305 .  
         [0037]      FIG. 11  shows a perspective view of a support stand  400  of  FIG. 9 . Similar to the clamp  300 , the stand  400  provides stand edges  402  and  404  that engage the wafer edge. A stand seat  406  supports the wafer  100  at a rest position. The stand  400  has a body with an elevated portion. Further, an opening  382  is provided at the bottom of the stand  400  to secure the stand to the wafer processing apparatus. Together, stands  400  and the clamp  300  support the wafer  100  at rest and securely engages the wafer edge during operation.  
         [0038]      FIG. 12  shows a cross-sectional view showing the support stand  400  and the wafer clamp  300 . A top end of the clamp engages the wafer  100  at clamp contact  361 , while a bottom end rests on a receptacle  363 . A plurality of magnets  366 - 367  are positioned on the sides of the clamp  360 . Correspondingly, an actuator (not shown) such as a cylinder moves an actuating magnet toward and away from the magnet  416  and causes the clamp to pivotally move about a pivot, subject to a limit pin  364  that prevents excessive pivoting. When the actuator moves toward the clamp, repulsive forces between magnets  416  and the actuator magnet (not shown) pivots the clamp into an open position so that the wafer  100  can be removed. When the actuator magnet is moved away from the clamp  360 , an opposing magnet  414  repels the magnet  418  to cause the clamp to move back to a clamping position to securely hold the wafer  100 .  
         [0039]      FIG. 13  illustrates an exemplary wafer processing apparatus with a fourth embodiment of a wafer clamp  500 . The clamp  500  operates by centrifugal forces exerted on the clamp  500  during rotation of the wafer  100 .  FIGS. 14-15  show perspective view of the clamp  500  in securing a wafer, while  FIG. 16  shows a cross-sectional view of the clamp  500  in securing the wafer  100 . The clamp  500  is pivotally attached to a clamp housing  540  through a pivot  506  so that when the clamp  500  pivots toward the wafer  100 , the clamp  500  secures the wafer  100  and vice versa, when the clamp  500  pivots away from the wafer  100 , the wafer  100  can be removed.  
         [0040]     Similar to the clamp  300 , the clamp  500  provides a clamp edge  502  that engages the wafer edge  307 . A seat  503  supports the wafer  100  at a rest position. The clamp  500  has a body with an elevated portion  504  that cooperates with the seat  503  in securing the wafer  100  at low speed. The clamp has a weight  510  mounted on one side. At high rotational speed, the weight  510  experiences a centrifugal force and moves away from the center of the wafer  100 . As the weight  510  moves away from the wafer center, the edge  502  engages the wafer edge  307  to clamp the wafer  100  in place during rotation.  
         [0041]     Although the invention has been described with reference to particular embodiments, the description is only an example of the inventor&#39;s application and should not be taken as limiting. Various adaptations and combinations of features of the embodiments disclosed are within the scope of the invention as defined by the following claims.