Abstract:
A method for drying workpieces in accordance with our invention includes the step of immersing the workpieces in a liquid, holding the workpieces with a first holding mechanism, slowly draining the liquid from the container until a first portion of the workpieces is exposed and dried, holding the workpieces with a second holding means at the first portion, and draining the remainder of the liquid from the container. Because of this, a drying portion of the workpiece is not held by a wet holding mechanism.

Description:
This patent claims priority based on U.S. Provisional Patent Application No. 60/099,159, filed on Sep. 4, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a method and apparatus for drying a workpiece such as a substrate used in magnetic disk or integrated circuit manufacturing. 
     In many manufacturing processes it is necessary to treat a workpiece with a liquid and then dry the workpiece. For example, during the manufacturing of magnetic disks, one typically performs the following manufacturing steps: 
     1. First a nickel-phosphorus layer is plated onto an aluminum substrate; 
     2. The nickel-phosphorus layer is polished and textured; 
     3. The substrate is cleaned, rinsed and dried; 
     4. A series of layers are sputtered onto the substrate, e.g., an underlayer such as sputtered NiP or Cr, a magnetic cobalt alloy, and a protective hydrogenated carbon overcoat. 
     Immediately prior to sputtering, the substrate is cleaned and then dried. It is extremely important that when the substrate is dried, there are no impurities left on its surface. 
     Numerous other manufacturing processes require drying a workpiece. For example, during various semiconductor manufacturing process steps, semiconductor wafers are immersed in a liquid and then dried. It is critical that there be no impurities on the surface of these wafers after drying. 
     One structure for drying semiconductor wafers is discussed in European Patent Application 0 385 536 A1, incorporated herein by reference. In the &#39;536 apparatus, a cassette of wafers is immersed in a liquid and then slowly removed from the liquid in the presence of a vapor that aids in the drying process. The cooperation of this vapor and liquid creates the so-called Marangoni effect which permits drying of the wafer without leaving “drying marks”. 
     During the drying process, a wafer holding mechanism is always in contact with the wafer. This leaves the possibility that there will be a contamination or drying mark at the point where the wafer is held during drying. One object of our invention is to overcome this problem. 
     SUMMARY 
     Drying apparatus in accordance with our invention comprises a container for holding a liquid and first and second structures for holding one or more workpieces. The workpiece is held by the first structure while the workpiece and the first structure are immersed in the liquid. (The second structure is also typically immersed in the liquid.) Thereafter, the liquid is slowly drained from the container until a first portion of the workpiece and a portion of the second structure are exposed and dried. Thereafter, the dry portion of the second structure is used to hold the first portion of the workpiece. The first structure is then removed from contact with the workpiece and the remainder of liquid is drained from the container. After the first structure and the remainder of the workpiece are dried, the first structure withdraws the workpiece from the container. 
    
    
     BRIEF DESCRIPTION 
     FIGS. 1A to  1 D illustrate apparatus for drying a workpiece in accordance with a first embodiment of our invention during a drying process. 
     FIG. 2A is a perspective view of holding members  12   a,    12   b  and  12   c  of FIGS. 1A to  1 D. 
     FIG. 2B is a perspective view of holding members  24   a ,  24   b  and knife  24   c  of FIGS. 1A to  1 D. 
     FIGS. 3A to  3 D illustrate a second embodiment of apparatus for drying a workpiece during a drying process. 
     FIGS. 4A to  4 D illustrate a third embodiment of apparatus for drying a workpiece during a drying process. 
     FIG. 5 illustrates holding member  102  of FIGS. 4A to  4 D 
    
    
     DETAILED DESCRIPTION 
     Referring to FIGS. 1A to  1 D, apparatus  10  in accordance with our invention comprises a holder  12  for holding one or more workpieces such as substrates  14 . In one embodiment, substrates  14  can be substrates used during the manufacture of magnetic disks. Such substrates typically have a diameter of 65, 84, 95 or 130 mm. However, this apparatus may also be used in conjunction with substrates having other shapes and diameters, or in other manufacturing processes, e.g., semiconductor manufacturing. 
     Holder  12  comprises three cylindrical members  12   a  and  12   b ,  12   c , having notches  16  formed therein (FIG. 2A) for supporting substrates  14 . One end of members  12   a  to  12   c  is connected to a plate  15   a  and the other end to a plate  15   b . Members  12   a  to  12   c  are on a carrier  17  FIG.  2 A. As shown in FIG. 1B, substrates  14  are then lowered by holder  12  into a container  18  containing a liquid  20  such as deionized water. In one embodiment, carrier  17  rides on a threaded screw (not shown) which is rotated by a motor (not shown) to raise and lower holder  12 . When being raised and lowered, carrier  17  rides along a ball or cross roller slide  19 . 
     Container  18  is typically filled to overflowing with liquid  20 . An overflow channel  21  surrounds the top of container  18  to receive overflowing excess water. Container covers  22   a ,  22   b  close over the top of container  18  after substrates  14  are immersed in liquid  20 . 
     Although our invention can be used in conjunction with numerous manufacturing processes at a variety of temperatures, in one manufacturing process, water  20  is at room temperature. After being immersed in water  20  for a suitable length of time, the water is slowly drained from container  18  while a drying gas is pumped into container  18  by gas manifolds  23 . In one embodiment, the gas provided by manifolds  23  comprises isopropyl alcohol (“IPA”) vapor and nitrogen at one atmosphere of pressure and room temperature. The IPA concentration can vary from 0.5 to 4.0 ml/run. 
     The top surface  20   a  of water  20  is lowered at a rate between 0.1 and 3 mm/sec, and preferably about 1 mm/sec. The drain rate is precisely controlled by a drain or needle valve. Referring to FIGS. 1A to  1 D and  2 B, also within container  18  is a holder  24  comprising first and second elongated holding members  24   a ,  24   b  and knife support  24   c . Holding members  24   a ,  24   b  have notches  26  formed therein for supporting substrates  14 . After the surface  20   a  of water  20  falls below the top of holding members  24   a ,  24   b , and the top of holding members  24   a ,  24   b  are dry, holder  12  is lowered so that substrates  14  rest against and are supported by holder  24  (FIG.  1 C). Holder  12  must be lowered at a rate slower than the rate surface  20   a  of water  20  is falling. This permits surface  20   a  of water  20  to continue to fall relative to substrate  14  while lowering holder  12 . Of importance, at this time, substrates  14  are supported entirely by dry surfaces (with the exception of knife support  24   c ). This helps prevent staining or “drying marks” from remaining on substrates  14  after drying. 
     Referring to FIG. 1D, the remainder of water  20  is drained from container  18  while substrates  14  are supported by holder  24 . 
     In one embodiment, after water  20  is drained from container  18 , a heated dry vapor can be sprayed through manifolds  23  (or other manifolds within the apparatus) to further guarantee substrate  14  dryness. The heated gas can be nitrogen between room temperature and 160° F., and preferably between 80 and 160° F. 
     As soon as holder  12  is dry, container covers  22   a  and  22   b  open and holder  12  is raised in a direction A, and carries substrates  14  upwardly and outside of container  18 . 
     In the embodiment of FIGS. 1A to  1 D, knife support  24   c  remains in contact with substrates  14  as water surface  20   a  recedes below the knife-substrate contact point. Knife  24   c  is used because we believe that knife  24   c  may aid in permitting water to flow off of substrates  14  during drying. 
     Cylindrical members  12   a  to  12   c  of holder  12  can be made of any appropriate solid material. In one embodiment, members  12   a  to  12   c  are made from UHMWPE (ultra high molecular weight poly ethylene) formed around stainless steel cores (FIG.  2 A). In addition, holding members  24   a ,  24   b  can also be made from UHMWPE. Knife  24   c  can be made from PEEK (polyether etherketone). 
     While holder  12  holds substrate  14  at three points of contact, other embodiments comprise a holder which supports substrate  14  at two, four, or another number of contact points. Holder  12  can be made using single or multiple piece construction. 
     FIGS. 3A to  3 D illustrate another embodiment of our invention which is the same as the embodiment of FIGS. 1A to  1 D and  2 A to  2 B, except that knife  24   c  is not present. As with the embodiment of FIGS. 1A to  1 D and  2 A to  2 B, substrates  14  are initially held by holder  12  (FIG.  3 A). Substrates  14  are lowered into water  20  by holder  12  (FIG.  3 B). Covers  22   a ,  22   b  are then closed. Water  20  is then slowly drained from container  18  while a drying gas is provided in container  18  via manifolds  23 . After the top of holding members  24   a ,  24   b  are exposed and dry (FIG.  3 C), holder  12  is lowered (in direction B) so that dry portions of substrates  14  are held by dry portions of holding members  24   a ,  24   b . The remainder of water  20  is then drained from container  18  (FIG.  3 D). When substrates  14  and holder  12  are dry, covers  22   a  and  22   b  open and holder  12  lifts substrates  14  out of container  18 . 
     In another embodiment, after substrates  14  are rinsed in water  20 , instead of simply draining water  20  from container  18 , holder  12  pushes substrates  14  above surface  20   a  of water  20  while the top of holding members  24   a ,  24   b  are also pushed above top surface  20   a  of water  20 . As soon as the portions of members  24   a ,  24   b  are dry, members  24   a ,  24   b  are pushed upwardly until they are supporting substrates  14  at a dry portion of substrates  14 . Members  24   a ,  24   b  continue to be pushed upwardly until all of substrates  14  are dry. Holder  12  is then pushed out of water  20 . When holder  12  is dry, it is pushed upwardly until it is supporting substrates  14 . Holder  12  then lifts substrates  14  out of container  18 . Alternatively, instead of pushing holder  12  out of the water, water  20  at that point can be drained from container  18 . 
     FIGS. 4A to  4 D illustrate another embodiment of our invention in which substrates  14  are held at their inner diameter by a holding member  102 . Holding member  102  is shaped to optimize drying (see FIG.  5 ), and comprises notches  104  for holding the inner diameter edge of substrates  14 , e.g., as shown in FIG.  5 . Holding member  102  then immerses substrates  14  in container  18  of water  20  for rinsing purposes (FIG.  4 B). Cover  22   a ,  22   b  are then closed. Thereafter, substrates  14  are left resting against holding members  24   a ,  24   b  while holding member  102  is lowered so that it no longer contacts substrates  14 . Water  20  is then slowly drained from container  18  until the top surface  20   a  of water  20  is below holding member  102 . Concurrently, a drying gas is provided in container  18  by manifolds  23 . Referring to FIG. 4C, as soon as holding member  102  is dry (but before surface  20   a  of water  20  falls below holding members  24   a ,  24   b ), holding member  102  moves upwardly and lifts substrates  14  (at a dry portion of substrates  14 ) so that substrates  14  no longer contact holding members  24   a ,  24   b . Thereafter, the remainder of water  20  is drained from container  18  and the substrates  14  are dried (FIG.  4 D). Covers  22   a ,  22   b  are then opened and substrates  14  are removed from container  18  by holding member  102 . Of importance, at no time during the drying process does a drying portion of substrates  14  contact a wet holding structure. 
     Although holder  24  of FIGS. 4A to  4 D holds substrate  14  at two points of contact with two members  24   a ,  24   b , three or more members can be used in holder  24 , including a knife edge support. 
     While the invention has been described with respect to specific embodiments, those skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the invention. For example, the various holding mechanisms and containers may be constructed from any appropriate material. In lieu of deionized water, our invention can be used in conjunction with other liquids. Such liquids can be used for washing, rinsing or performing other manufacturing processes in conjunction with the substrates. In lieu of isopropyl alcohol, other vapors such as those mentioned in the &#39;536 Application can be used. In lieu of nitrogen, other carrier gases such as helium, argon or other inert gas can be used. In yet another embodiment, a carrier gas is not used. Accordingly, all such changes come within our invention.