Abstract:
An apparatus is disclosed for drying wafer substrates in a process tank having an object supporting member for supporting one or more wafer substrates, the object supporting member having apertures through which “vacuum force” can be applied to essentially remove trace amounts of liquid from object contact points formed by the support of the wafer substrate by the object supporting member. Also disclosed is a method of implementing the disclosed apparatus comprising transferring a wafer substrate from an object transporting member to the object supporting member, providing an aperture at or near each contact point, and applying a “vacuum force” through the apertures to remove any trace amounts of liquid. Also disclosed and claimed are wafer substrates resulting from application of the disclosed drying process and apparatus.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of Provisional Application No. 60/275,933 filed Mar. 15, 2001. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to apparatus and processes for drying substrates, especially silicon wafer substrates, flat panel display substrates, and other types of substrates which must be cleaned, rinsed, and dried during the manufacture of an object. The invention especially relates to removing trace amounts of water from silicon wafer substrates in a process tank during the manufacture of integrated circuits.  
           [0003]    Many systems and methods have been devised to dry objects. With certain types of objects, such as silicon wafers and flat panel displays where high yields are desired, very sophisticated systems and methods have been devised to dry the object as quickly and as completely as possible.  
           [0004]    For example, in the field of manufacture of semiconductors and integrated circuits from silicon wafers, hundreds of circuits can be made from each wafer substrate by process which require many cycles of cleaning, rinsing, and drying.  
           [0005]    Due to deficiencies of prior art systems and methods of drying substrates, it is impossible to completely remove all traces of liquid from the points where the drying apparatus contacts the edges of the substrates. For example, in process tanks where a supporting member is used to lift a substrate off of a transporting member so that most of the water can drain from the substrate, it is a well recognized problem in the art to quickly and effectively remove traces of water from the contact points. Therefore, there is a certain very valuable portion of the substrate which is wasted due to what is known in the art as “edge exclusion,” a term referring to the portion near the edges which cannot be completely dried and must be discarded.  
           [0006]    There have been many attempts by others to improve dryer systems and drying methods so as to eliminate the need for edge exclusion by completely drying the wafer substrate. However, none have fully solved the problem of water residue at edge contact points.  
           [0007]    For example, Mohindra, et al., U.S. Pat. No. 5,571,337, teach pulsing a drying fluid such as nitrogen gas directed at the edge of the partially completed semiconductor to remove the liquid from the edge. Application of the Mohindra et al process results in evaporation of the liquid at the contact points. Evaporation is undesirable because particles and water spots are left behind, both of which decrease yields. McConnell, et al., U.S. Pat. No. 4,984,597, teach using large amount of IPA to replace water and enhance drying. Such process requires special tanks and elaborate support equipment.  
           [0008]    Many other systems and methods have been proposed to try to solve the edge exclusion problem resulting from inability to efficiently remove water residue from the contact points between the edges of objects and the supporting members of dryers in a clean, low cost, or timely manner, but none have completely solved the problem.  
         SUMMARY OF THE INVENTION  
         [0009]    It is therefore an objective of the present invention to eliminate water residue at the edges of objects for the drying thereof.  
           [0010]    Another objective of the invention is to provide a quicker method of drying high value objects.  
           [0011]    A further objective is to eliminate defects at the contact points between dryer equipment and the object being dried.  
           [0012]    A still further objective is to improve yields of high value integrated circuits from silicon wafers.  
           [0013]    Additional objects, advantages and other novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the claims.  
           [0014]    To achieve the foregoing and other objects, the invention comprises three aspects, a system for drying objects, a method for drying objects, and the resultant dried object produced by implementing a particular drying method.  
           [0015]    System For Drying Objects  
           [0016]    In one aspect, the invention is a system for use in drying objects in a process tank. The system comprising an object supporting member having at least one contact point for each object supported, at least one aperture at or near each contact point, and a source of negative pressure fluidly connected to each aperture.  
           [0017]    Preferably, the object supporting means is adapted to support a plurality of wafer substrates and the objects to be dried are wafer substrates. Also, the source of negative pressure is preferably one or more vacuum or eductor pumps.  
           [0018]    In one embodiment of the system of invention, the object supporting member is in a fixed position at or near the bottom of the process tank. The system further includes an object transporting member for delivering the object to the fixed object supporting member, the object transporting member preferably being a wafer basket. The wafer basket is adapted to carry a plurality of wafer substrates. In this embodiment of the system, the object supporting member has two outside lifters, a center lifter, and a base plate. The outside lifters and center lifter extend upward from the base plate and the center lifter is shorter than the outside lifters. The outside lifters and center lifter are so positioned on the base plate so that wafer substrates in a wafer basket can be engaged, removed from the wafer basket, and supported by the object supporting member. For each wafer supported by the object supporting member, three contact points are formed. Each contact point is located at or near at least one aperture which is fluidly connected to the one or more eductor pumps.  
           [0019]    In another embodiment of the system of invention, the object supporting member is movable between a loading position at or near the top of the process tank and a position at or near the bottom of the process tank. The object supporting member remains fluidly connected to the one or more vacuum or eductor pumps over the entire range of motion. Such fluid connection is made possible by means of flexible vacuum tubing. Preferably, the object supporting member has two side support tubes and a bottom support tube. When a wafer substrate is loaded into the object supporting member, three contact points are formed for each wafer substrate supported. Each contact point is located at or near at least one aperture which is fluidly connected to the one or more eductor pumps.  
           [0020]    Method of Drying Objects  
           [0021]    In another aspect, the invention is a method of drying objects in a process tank having an object supporting member having at least one contact point for each object supported and an object transporting member. The process comprising the steps of providing at least one aperture at or near each contact point of the object supporting member and a source of negative pressure fluidly connected to each aperture, filling the process tank with a liquid, transferring the objects from the object transporting member to the object supporting member, applying a vacuum force through the apertures so as to essentially remove trace amounts of liquid from each contact point, draining the liquid from the process tank so as to substantially dry the objects, and transferring the resultant fully dried objects from the object supporting member to the object transporting member.  
           [0022]    Preferably, the object transporting member is a wafer basket and the objects to be dried are wafer substrates. The wafer basket is adapted to carry a plurality of wafer substrates and the object supporting member is adapted to support the plurality of wafer substrates. Also preferably, the source of negative pressure is one or more vacuum or eductor pumps.  
           [0023]    In one embodiment of the method of invention, the object supporting member is in a fixed position at or near the bottom of the process tank. The object supporting member has two outside lifters, a center lifter, and a base plate. The outside lifters and center lifter extend upward from the base plate and the center lifter is shorter than the outside lifters. The outside lifters and center lifter are so positioned on the base plate so that wafer substrates that are in a wafer basket can be engaged, removed from the wafer basket, and supported by the object supporting member. For each wafer supported by the object supporting member, three contact points are formed with the object supporting member. Each contact point is located at or near at least one aperture which is fluidly connected to the one or more vacuum or eductor pumps.  
           [0024]    In this embodiment of the method of invention, the process tank is filled with DI water. The wafer basket, which has one or more wafer substrates contained therein, is lowered into the process tank, submersing the wafer substrates in the DI water. The wafer basket is lowered until the wafer substrates are contacted by the object supporting member, removed from the wafer basket, and supported solely by the object supporting member. The process tank is then sealed. The remaining volume of the process tank is then pumped full of nitrogen gas and some liquid IPA forming a nitrogen-IPA vapor in the process tank. The DI water is drained from the process tank by opening a slow drain valve located at or near the bottom of the process tank. When the slow drain valve is opened, the vacuum or eductor pumps are also activated, creating a vacuum force at all of the apertures on the object supporting member. The DI water continues to drain from the process tank while nitrogen-IPA vapor continues to form in the process tank. When the DI water level gets to a level just below the apertures located on the outside lifters of the object supporting member, the vacuum force for those apertures is discontinued. The DI water continues to be drained from the tank until it reaches a point at or below the wafer substrates. At this point, large piston valves are actuated to an open position thus quickly draining the remaining liquids. The IPA liquid flow is then discontinued and pure nitrogen gas continues to be pumped into the tank. The vacuum force of the apertures on the center lifter of the object supporting member is discontinued. The resultant fully dried wafer substrates are then transferred from the object supporting member to the wafer basket by raising the wafer basket. The loaded wafer basket is then removed from the tank.  
           [0025]    In another embodiment of the method of invention, the object supporting member is movable between a loading position at or near the top of the process tank and a position at or near the bottom of the process tank. The object supporting member remains fluidly connected to the one or more vacuum or eductor pumps over the entire range of motion. Such fluid connection is made possible by means of flexible vacuum tubing. In this embodiment, the object supporting member has two side support tubes and a bottom support tube. When a wafer substrate is loaded into the object supporting member, three contact points are formed with the object supporting member for each wafer substrate. Each of these contact points are located at or near at least one aperture which is fluidly connected to the one or more vacuum or eductor pumps.  
           [0026]    In this embodiment of the method of invention, the process tank is filled with DI water. The object supporting member is moved to the loading position at or near the top of the process tank. The wafers are then transferred from an active gripper to the object supporting member. The object supporting member, which has one or more wafer substrates contained therein, is then lowered into the process tank, submersing the wafer substrates in the DI water. The object supporting member is continued to be lowered until it reaches a position at or near the bottom of the process tank. The process tank is sealed. The remaining volume of the process tank is pumped full of nitrogen gas and some liquid IPA forming a nitrogen-IPA vapor in the process tank. The DI water is drained from the process tank by opening a slow drain valve located at or near the bottom of the process tank. When the slow drain valve is opened, the vacuum or eductor pumps are also activated, creating a vacuum force at all of the apertures on the object supporting member. The DI water continues to drain from the process tank while nitrogen-IPA vapor continues to be formed in the process tank. When the DI water level gets to a level just below the apertures located on the two side support tubes of the object supporting member, the vacuum force for those apertures is discontinued. The DI water continues to be drained until it reaches a point at or below the wafer substrates, large piston valves are then actuated to an open position thus quickly draining the remaining liquids. At this point, the IPA liquid flow is discontinued and pure nitrogen gas continues to be pumped into the tank. The vacuum force of the apertures on the bottom support tube of the object supporting member is discontinued. The object supporting member then raises the resultant fully dried wafer substrates from the position at or near the bottom of the process tank to the loading position at or near the top of the process tank. The wafer substrates are then transferred from the object supporting member to the active gripper.  
           [0027]    The Objects Produced  
           [0028]    In yet another aspect, the invention is a wafer substrate dried in a process tank having an object supporting member having at least one contact point for each wafer substrate supported and an object transporting member. The wafer substrate being dried by a drying process comprising the steps of providing at least one aperture at or near each contact point of the object supporting member and a source of negative pressure fluidly connected to each aperture, filling the process tank with a liquid, transferring the objects from the object transporting member to the object supporting member, applying a vacuum force through the apertures so as to essentially remove trace amounts of liquid from each contact point, draining the liquid from the process tank so as to substantially clean then dry the objects, and transferring the resultant fully dried objects from the object supporting member to the object transporting member. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]    FIG. 1 is a side elevational view of an object transporting member, illustrated as a wafer basket, with an object, illustrated as a wafer substrate, being lowered into the object transporting member.  
         [0030]    FIG. 2 is a top view of the object transporting member, illustrated as a wafer basket.  
         [0031]    FIG. 3 is a side elevational view of a fixed supporting member.  
         [0032]    FIG. 4 is a side elevational view of the top portion of an outside lifter of the fixed supporting member.  
         [0033]    FIG. 5 is a side view of the outside lifter.  
         [0034]    FIG. 6 is a cross-sectional view of the outside lifter taken along line VI-VI in FIG. 5.  
         [0035]    FIG. 7 is a bottom view of the outside lifter.  
         [0036]    FIG. 8 is a schematic cross-sectional view of a process tank implementing the fixed supporting member.  
         [0037]    FIG. 9 is a schematic cross-sectional view of a process tank implementing the fixed supporting member where the object is in an object transporting member and is being lowered into the process tank.  
         [0038]    FIG. 10 is a schematic cross-sectional view of a process tank implementing the fixed supporting member where the object transporting member is fully lowered and the object is no longer in contact with the object transporting member, (i.e., is solely supported by the supporting member).  
         [0039]    FIG. 11 is a side cross-sectional view of the fixed supporting member in the process tank as it supports the object.  
         [0040]    FIG. 12 is a flowchart summarizing the claimed substrate aspiration drying process utilizing the fixed supporting member.  
         [0041]    FIG. 13 is a side elevational view of a modified supporting member with an object being slidably inserted therein.  
         [0042]    FIG. 14 is a side elevational view of a bottom support tube of the modified supporting member.  
         [0043]    FIG. 15 is a cross-sectional view of the modified supporting member with an object, in the form of a wafer substrate, slidably inserted therein.  
         [0044]    FIG. 16 is a schematic cross-sectional view of a process tank implementing the modified support member in the fully lowered position.  
         [0045]    FIG. 17 is a schematic cross-sectional view of a process tank implementing the modified support member in the fully raised position.  
         [0046]    FIG. 18 is a flowchart summarizing the claimed substrate aspiration drying process utilizing a movable supporting member. 
     
    
     DETAILED DESCRIPTION  
       [0047]    The figures depict a preferred embodiment of the present invention for purposes of illustration only. One, skilled in the art will readily recognize from the following discussion that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the invention described herein.  
         [0048]    Referring to FIG. 1, an object transporting member  1  is illustrated in the embodiment of a wafer basket  1 . The wafer basket  1  has a front panel  2 , a rear panel  3 , two side panels  4 , two bottom support panels  5 , and a plurality of object separating guides  6  protruding from both side panels  4  and bottom support panels  5 . The object separating guides  6  are so aligned that a wafer substrate  7  can be slidably placed between and supported by said object separating guides  6 .  
         [0049]    Referring now to FIG. 2, wafer basket  1  also has two side opening holes  8  and a bottom opening hole  9 .  
         [0050]    FIG. 3 illustrates a fixed supporting member  10  which is capable of aspiration and includes two outside lifters  11  and a shorter center lifter  12 . Both the outside lifters  11  and the center lifter  12  are constructed so as to have a plurality of jagged wafer holding combs  13  along the top portion of each outside lifter  11  and center lifter  12 . The jagged wafer holding combs  13  are so aligned on the outside lifters  11  and the center lifter  12  so that a wafer substrate  7  can be slidably inserted between and supported by the outside lifters  11  and the center lifter  12 . The fixed supporting member  10  further includes a base plate  14  which has a plurality of drainage holes  15  located throughout the base plate  14  to facilitate the drainage of liquid from the fixed supporting member  10 .  
         [0051]    Referring to FIG. 4, a view of the center lifter  12  is shown. The top portion of the center lifter  12  has a plurality of vacuum holes  16  located between each of the jagged wafer holding combs  13 .  
         [0052]    Referring now to FIG. 5, each vacuum hole  16  is the opening of an aspiration channel  17  that is fluidly connected to a vacuum tube  18 . All of the aspiration channels  17  are connected to a single vacuum tube  18  that runs through the interior of the outside lifter  11 . FIG. 6 is a cross-sectioned view of these features.  
         [0053]    Referring to FIG. 7, the vacuum tube  18  of the outside lifter  11  also has a manifold connection hole  19  at the bottom surface of the outside lifter  11 .  
         [0054]    Outside lifters  11  have characteristics similar to those disclosed in FIGS. 4, 5, 6, 7 as discussed above. Specifically, the top portion of the outside lifters  11  have a plurality of vacuum holes  16  located between each of the jagged wafer holding combs  13 . Each vacuum hole  16  of the outside lifters  11  being the opening of an aspiration channel  17  that is fluidly connected to a vacuum tube  18 . The vacuum tube  18  of the outside lifters  11  having a manifold connection hole  19  at the bottom surface of the each outside lifter  11 .  
         [0055]    FIG. 8, illustrates an embodiment of the invention wherein, the fixed supporting member  10  is rigidly connected to a process tank  20  near the bottom of the process tank  20 . The manifold connection holes  19  of the outside lifters  11  and the center lifter  12  are fluidly connected to a vacuum system  21  capable of producing negative pressure. The process tank  20  has a tank lid  22 , a slow drain valve  23 , one or more large piston valves  39 , and DI water supply valves  24 . A DI water supply system  25  is fluidly connected to the process tank  20  by a DI water supply tube  26 . The tank lid  22  has a porous tube  28  connected thereto. The porous tube  28  is fluidly connected to a nitrogen supply tube  29  and a liquid IPA supply tube  30  that are capable of supplying nitrogen and IPA respectively.  
         [0056]    Referring to FIG. 9, as the wafer basket  1  containing at least one wafer substrate  7  is lowered into the process tank  20 , the wafer basket  1  is so positioned that the outside lifters  11  and the center lifter  12  of the fixed supporting member  10  are respectively aligned with the two side opening holes  8  and bottom opening hole  9  of the wafer basket  1 .  
         [0057]    Referring now to FIG. 10, when the wafer basket  1  is in the fully lowered position the outside lifters  11  and center lifter  12  respectively extend through the two side opening holes  8  and bottom opening hole  9  of the wafer basket  1 , engaging and supporting any wafer substrates  7  that are in the wafer basket  1 . The wafer substrates  7  are removed from, and no longer in contact with, any part of the wafer basket  1 . At this point, the wafer substrates  7  are captured between corresponding jagged wafer holding combs  13  of the outside lifters  1   1  and center lifter  12  and are solely supported thereby.  
         [0058]    Referring now to FIG. 11, when the wafer substrate  7  is captured and supported by the outside lifters  11  and center lifter  12  of the fixed supporting member  10 , each wafer substrate  7  is in contact with exactly three points of the fixed supporting member  10 , referred to herein as aspiration contact points  31 . Each of the three aspiration points  31  for each wafer substrate  7  is at or near a vacuum hole  16  for the corresponding outside lifters  11  and center lifter  12 .  
         [0059]    FIG. 12 summarizes the above described steps of loading the wafer substrates  7  onto the fixed supporting member  10  and further summarizes the remaining steps performed in practicing the claimed aspiration drying process when utilizing a fixed supporting member  10 . At step  100 , as discussed in detail above, a wafer basket  1  with at least one wafer substrate  7  therein is lowered into the process tank  20  which is filled with DI water. Thereafter, at step  101 , the fixed supporting member  10 , which is located near the bottom of the process tank  20 , contacts the wafer substrates  7  and fully removes the wafer substrates  7  from the wafer basket  1 . Now that the wafer substrates  7  are fully submersed in the DI water and in sole contact with the fixed supporting member  10 , the wafer substrates are wet and need to be dried.  
         [0060]    At step  102 , the tank lid  22  is put in place and the remaining volume of the sealed process tank  20  is filled with nitrogen and liquid IPA through the porous tube  28  which is supplied by the nitrogen supply tube  29  and liquid IPA supply tube  30  respectively. Next, at step  103 , the slow drain valve  23  is then opened and the vacuum system  21  is activated. Activating the vacuum system  21  creates a vacuum force at the vacuum holes  16  and sucks DI water into said vacuum holes  16 . As the DI water drains from the tank, the nitrogen-IPA vapor takes its place by occupying the volume of the process tank  20  previously occupied by the DI water.  
         [0061]    At step  104 , once the DI water level is just below the aspiration contact points  31  of the outside lifters  11 , the vacuum force for those two aspiration contact points  31  is discontinued. The DI water in the process tank  20  continues to drain as a result of the slow drain valve  23  being open and the vacuum force being applied by the vacuum hole  16  at the aspiration contact point  31  of the center lifter  12 . At step  105 , when the DI water level gets to a level at or below the wafer substrates, large piston valves  39  are actuated to an open position thus quickly draining the remaining liquids. When the DI water is totally drained from the process tank  20 , the tank is completely filled with a nitrogen-IPA vapor.  
         [0062]    Finally, at step  106 , the liquid IPA supply tube  30  is then closed and the process tank  20  becomes completely filled with nitrogen. The entire time the nitrogen is filling the process tank  20 , the slow drain valve  23  and large piston valves  39  are open and vacuum hole  16  located on the center lifter  12  is producing a vacuum force. At this point, the wafer substrates  7  are completely dry, including at every aspiration contact point  31 , and are ready for removal from the process tank  20 .  
         [0063]    In another embodiment of the invention illustrated in FIG. 13, the need to use the object transporting member  1  is eliminated. A modified supporting member  32  is used. The modified supporting member  32  includes a bottom support tube  33  and two side support tubes  34 .  
         [0064]    Referring to FIG. 14, the bottom support tube  33  and the two side support tubes  34  have a plurality of teeth  35  along their surfaces that form slots in which a wafer substrate  7  can be slidably inserted and supported. A vacuum hole  16  is located between each pair of teeth  35  present on the bottom support tube  33  and the two side support tubes  34  of the modified supporting member  32 .  
         [0065]    Referring to FIG. 15, when a wafer substrate  7  is slidably inserted and supported by the modified supporting member  32  it contacts the modified supporting member  32  in exactly three aspiration contact points  31 , one on each side support tube  34  and bottom support tube  33 . Each aspiration contact point  31  on the modified supporting member  32  is located at or near a vacuum hole  16 . Each vacuum hole  16  is an opening that leads to a vacuum passage  36 . The vacuum passages  36  of the bottom support tube  33  and the two side support tubes  34  are fluidly connected to a flexible vacuum tube hole  37  (FIG. 13).  
         [0066]    Referring to FIG. 16, in this embodiment of the invention, the modified supporting member  32  is not rigidly connected to the process tank  20 . Instead, the modified supporting member  32  is capable of vertical movement. The modified supporting member  32  is fluidly connected to the vacuum system  21  by flexible vacuum tubing  38  that fluidly connects to the flexible vacuum tube hole  37 . The flexible vacuum tubing  38  is constructed so that the modified supporting member  32  can be vertically raised above the top of the tank while remaining fluidly connected to the vacuum system  21  (FIG. 17).  
         [0067]    FIG. 18, summarizes the steps of performing the claimed drying process with this embodiment of the invention. At step  200 , the DI water supply valves  24  are opened and the process tank  20  is filled with DI water. At step  201 , the tank lid  22  is removed, the modified supporting member  32  is positioned so that it is above the DI water level and protrudes from the top of the process tank  20 , and at least one wafer substrate  7  is slidably inserted into the modified supporting member  32 . Next at step  202 , the modified supporting member  32  is lowered into the process tank  20  to a position where the wafer substrate  7  is fully submersed in the DI water and the tank lid  22  is put back on.  
         [0068]    At step  203 , the remaining volume of the sealed process tank  20  is filled with nitrogen and liquid IPA which enters the tank through the porous tube  28  which is supplied by the nitrogen supply tube  29  and liquid IPA supply tube  30  respectively. At step  204 , the slow drain valve  23  is then opened and the vacuum system  21  is activated. Activating the vacuum system  21  creates a vacuum force at the vacuum holes  16  and sucks DI water into said vacuum holes  16 . As the DI water drains from the tank, the nitrogen IPA vapor takes its place by occupying the volume of the process tank  20  previously occupied by the DI water.  
         [0069]    At step  205 , once the DI water level is just below the aspiration contact points  31  of the two side support tubes  34 , the vacuum system  21  for those two aspiration contact points  31  is discontinued. The DI water in the process tank  20  continues to drain as a result of the slow drain valve  23  being open and the vacuum force being applied by the vacuum hole  16  at the aspiration contact point  31  of the bottom support tube  33 . At step  206 , when the DI water level gets to a level at or below the wafer substrates, large piston valves  39  are actuated to an open position thus quickly draining the remaining liquids. When the DI water is totally drained from the process tank  20 , the process tank  20  is completely filled with a nitrogen-IPA vapor. At step  207 , the liquid IPA supply tube  30  is then closed and the process tank  20  is completely filled with nitrogen. The entire time the nitrogen is filling the process tank  20 , the slow drain valve  23  and large piston valves  39  are open and the vacuum hole  16  located on the bottom support tube  33  is producing a vacuum force. At this point, the wafer substrates  7  are completely dry, including at every aspiration contact point  31 , and are ready for removal from the process tank  20 .