Patent Publication Number: US-6908369-B2

Title: Apparatus for and method of smoothing substrate surface

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to an apparatus for and a method of smoothing the surface of a substrate such as a magnetic disk substrate. 
   A magnetic disk substrate serving as a magnetic memory medium is generally produced by forming a NiP layer on the surface of an aluminum or glass substrate, carrying out a texturing process to form a concentrically circular texturing marks on the surface of this NiP layer, thereafter forming a magnetic layer thereon by a sputtering process or the like and then further forming a lubricating protective membrane. According to such a prior art method of production, abnormal protrusions appear on the disk surface in the final stage and such abnormal protrusions are likely to hit the magnetic head, thereby damaging the magnetic disk surface or to cause foreign objects to become attached to the magnetic head. Debris particles thus generated during the production process are also likely to become attached to the disk surface. 
   In order to remove such abnormal protrusions and debris particles, it has been customary to carry out a surface smoothing process. Japanese Patent Publication Tokko 2-10486, for example, disclosed a smoothing process for the surface of a disk substrate by using a polishing tape with a polishing layer formed thereon and causing it to run while using a rubber roller or the like to apply a pressure for removing the abnormal protrusions on the surface. A smoothing method by running a polishing tape while blowing air from behind the polishing tape, instead of using a roller, has also been practiced. Japanese Patent Publication Tokkai 2001-162504 disclosed another smoothing process by pressing a polishing tape onto the surface of the disk substrate by means of a pad while the disk substrate is caused to rotate and the pad is moved reciprocatingly in a radial direction of the substrate. 
   The smoothing process carried out while a polishing tape is pressed by means of a rubber roller is effective from the point of view of removing the abnormal protrusions from the surface but is not capable of either preventing the generation of debris particles or removing them since the polishing tape and the rubber roller interfere each other during the polishing process. The method with air is capable of preventing the generation of debris particles because there is no interference such as between a rubber roller and the polishing tape but tends to bring in the debris particles from the surrounding areas because of the air movement. The method of using a pad to press the polishing tape is effective not only in removing debris particles but also in preventing their generation because the polishing tape is not caused to run at the time of polishing, unlike the method using a rubber roller, but there is an interference between the edges of the polishing tape and the pad even while the polishing tape is not running. Moreover, the polishing tape and the pad interfere with respect to each other when the polishing tape is run without contacting the disk substrate for the preparation of a next polishing process. Thus, there is a limit to how much the generation of debris particles due to the falling of abrading particles can be prevented. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of this invention in view of the above to provide an apparatus for and a method of preventing the generation of particles when using a polishing tape to smoothen the surface of a substrate. 
   It is another object of this invention to provide an apparatus for and a method of preventing the generation of particles due to the falling of abrading particles when using a polishing tape to smoothen the surface of a substrate. 
   An apparatus embodying this invention for smoothing a surface of a rotatably supported substrate may be characterized not only as comprising a base plate, a block (“the first block”) having an extending arm structure and being attached to the base plate so as to be movable along a surface thereof, a roller (“the first roller”) attached to a tip portion of the arm structure in a direction perpendicular to the surface of the base plate, a mobile member (“the first mobile member”) attached to the arm structure so as to be movable perpendicularly to the axial direction of the roller, a tape-running means (“the first tape-running means”) attached to the base plate for feeding and taking up a polishing tape through the roller so as to advance the tape around the mobile member, and a moving means (“the first moving means”) attached to the arm structure of the block for moving the mobile member but also wherein the mobile member has a pad which presses the polishing tape from backside and wherein the mobile member moves by means of the moving means to a retracted position where the pad does not contact the polishing tape when the polishing tape is being run by means of the tape-running means and to a compressing position where the pad pushes the polishing tape when the substrate is being smoothed by the polishing tape. 
   For smoothing both surfaces of the substrate at the same time, such an apparatus may additionally comprise a second block, a second roller, a second tape-running means, a second mobile member and a second moving means which are structured like and disposed symmetrically to the aforementioned first block, first roller, first tape-running means, first mobile member and first moving means, respectively. 
   An apparatus according to another embodiment of this invention may be characterized not only as comprising a base plate having an extending first arm structure (“the first arm structure”), a roller (“the first roller”) attached to a tip portion of the arm structure perpendicularly to the base plate, a block (“the first block”) having a mobile member (“the first mobile member”) which extends along the arm structure and being attached to the base plate so as to be movable along the base plate, a tape-running means (“the first tape-running means”) attached to the base plate for feeding and taking up a polishing tape through the roller so as to advance the tape around the mobile member, and a moving means (“the first moving means”) attached to the base plate for moving the mobile member but also wherein the mobile member has a pad which presses the polishing tape from backside and wherein the mobile member moves by means of the moving means to a retracted position where the pad does not contact the polishing tape when the polishing tape is being run by means of the tape-running means and to a compressing position where the pad pushes the polishing tape when the substrate is being smoothed by the polishing tape. 
   For smoothing both surfaces of the substrate at the same time, this apparatus may also additionally comprise a second arm structure extending from the base plate parallel to the first extending arm structure such that the substrate can be disposed between the two arm structures as well as a second block, a second roller, a second tape-running means, a second mobile member and a second moving means which are structured like and disposed symmetrically to the aforementioned first block, first roller, first tape-running means, first mobile member and first moving means, respectively. 
   It is preferable that the pads be narrower than the polishing tapes. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a plan view of a double side smoothing apparatus embodying this invention. 
       FIG. 2  is an enlarged diagonal view of one of the mobile members which are components of the apparatus of FIG.  1 . 
       FIG. 3  is a plan view of another apparatus embodying this invention. 
       FIG. 4  is a diagonal view of one of the blocks of the apparatus shown in FIG.  3 . 
       FIGS. 5A and 5B  are sectional views for showing the operations of the block-moving mechanism of the apparatus shown in  FIG. 3 ,  FIG. 5A  showing when the block-moving rod is pushed forward such that the blocks and the mobile members have moved away from each other, and  FIG. 5B  showing when the block-moving rod is retracted such that the blocks and the mobile members have moved close to each other and the pads have been pressed against the tapes. 
   

   Throughout herein, components that are like or equivalent to each other are indicated by the same numerals and may not be repetitiously described. 
   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a smoothing apparatus  10  embodying this invention adapted to simultaneously smoothen both surfaces of a substrate  60  (say, of a magnetic disk) but this may be used for the smoothing of only one surface at a time. The smoothing apparatus  10  is shown attached to a support table  40 , together with a spindle  48  for supporting and rotating the substrate  60 . The apparatus  10  has a base plate  11  which is affixed to a reciprocating table  16  having leg parts  17  provided with female screw holes elongated in the front-back direction indicated by double-headed arrow T. The base plate  11  of the apparatus  10  is attached to the support table  40  by way of a male screw  41  which is rotatably supported by block tables  40 ′ attached to the support table  40 , penetrates and engages these female screw holes. Each of these block tables  40 ′ consists of a fixed part  40 ′ a  and a mobile part  40 ′ b  which is mobile in the vertical direction (perpendicular to the drawing). It is the mobile parts  40 ′ b  of the block tables  40 ′ that the male screw  41  penetrates. As the male screw  41  is rotated by its motor  42 , the apparatus  10  attached to the reciprocating table  16  can undergo a reciprocating motion in the direction of arrow T. Similarly, the apparatus  10  can be caused to undergo a reciprocating motion in the vertical direction (perpendicular to the drawing) as the mobile parts  40 ′ b  of the block table  40 ′ are caused to move vertically by a similar mechanism (not shown). As the spindle  48  attached to the support table  40  is rotated while holding the substrate  60 , its entire surface can be efficiently smoothed with the apparatus  10  thus moved reciprocatingly. 
   A pair of feed rollers  13  for feeding a polishing tape  50  and a pair of take-up rollers  12  for winding it up are disposed on the base plate  11  in a symmetrical manner to the left-hand and right-hand sides. 
   The base plate  11  is further provided with a pair of mutually oppositely disposed blocks  20  on its side of the spindle  48  so as to be able to slide along a surface of the base plate  11 , being each connected to a block-moving means  21  affixed to the base plate  11 . These block-moving means  21  may comprise, for example, a cylinder operated by air. As air is supplied to the cylinders, the pair of blocks  20  moves towards each other along guide rods  20 ′. As air is removed from these cylinders, the pair of blocks  20  moves away from each other. 
   As shown more clearly in  FIG. 2 , each of the blocks  20  is provided with an arm  22  extending in the direction of the spindle  48 . A plurality of direction-reversing rollers  23  are rotatably attached to the tip of the arm  22  perpendicularly to the horizontal main surface of the base plate  11 , and each of the polishing tapes  50  is adapted to pass over these rollers  23 . In other words, each polishing tape  50 , unwound from corresponding one of the feed rollers  13 , reaches these rollers  23  through a plurality of rollers on the base plate  11  as shown in  FIG. 1 , changes its direction of motion thereby and is taken up by corresponding one of the take-up rollers  12  through another plurality of rollers on the base plate  11  as shown in FIG.  1 .  FIG. 2  shows two such direction-reversing rollers  23  separated from each other by a distance S such that a sufficiently large gap is maintained between the portions of the tape  50  moving in one direction and in the opposite direction between the feed roller  13  and the take-up roller  12 . A similar effect can be obtained by using a single roller with a large diameter. Alternatively, three or more such rollers may be provided. 
   Within this space of width about S formed between the two portions of the tape  50 , there is disposed a mobile member  30  having a pad  31  affixed to its bottom surface (as seen in  FIG. 2 ) for compressing the tape  50  and an extended part  32  which extends upward (as seen in  FIG. 2 ) between the tape  50  and the arm  22 . As shown in  FIG. 1 , the two mobile members  30  are disposed symmetrically to the two arms  22  such that their extended parts  32  extend away from each other. A cylinder  33  is affixed to each arm  22  and is connected to the extended part  32  of corresponding one of the mobile members  30  such that the mobile members  30  can be moved as air is introduced into and removed from these cylinders  33 . The pads  31  are narrower than the width of the tapes  50  such that abrading particles can be prevented from falling off from the edges of the tapes  50  to generate debris particles as the pads  31  contact the tapes  50 . 
   As the cylinders  33  retract their pistons, the mobile members  30  are each pulled towards the corresponding one of the cylinders  33  such that the pads  31  are separated from the tapes  50 , as shown in FIG.  1 . The tapes  50  are forwarded from the feed rollers  13  to the take-up rollers  12  without contacting the pads  31  while the mobile members  30  are at their retracted positions. This means that the production of debris particles due to the interference (or contact) between the tapes  50  and the pads  31  can be prevented as the tapes  50  are advanced. 
   As the cylinders  33  extend their pistons, the mobile members  30  are pushed such that each pad  31  not only contacts the corresponding tape  50  but also pushes it further outward as shown in FIG.  2 . Thus, as explained below, the tape  50  can contact and polish the substrate  60 . 
   The polishing tapes  50  may preferably be one produced by applying a resin binder (for example, of polyester or polyurethane type) on the surface of a plastic film (for example, of polyester or polyethylene terephthalate (PET)) of thickness 5 μm-100 μm and dispersing and fixing abrading particles (for example, of aluminum oxide, diamond or silicon carbide) with average diameter of 0.1 μm-10 μm, or by forming a polishing layer on the surface of a plastic film by covering it with a coating material with a resin binder having abrading particles dispersed therein, forming an antistatic membrane of thickness 0.1 μm-0.3 μm by applying an antistatic agent on the back surface of this plastic film, if necessary, and slitting it into the form of a tape. The tape is preferably of a width of about 12.6 mm (½ inch). In such a case, the width of the pads  31  is preferably about 10 mm, that is, smaller than the width of the tape. 
   Next, a method of using the smoothing apparatus  10  described above is explained for smoothing both surfaces of the magnetic disk substrate  60  but it is to be understood that the methods embodying this invention include situations where only one of the surfaces of the substrate  60  is smoothed. 
   The magnetic disk substrate  60  to be processed is set on the spindle  48  which serves not only to support the substrate  60  but also to rotate it. As the male screw motor  42  is activated, the base plate  11  of the apparatus  10  approaches the substrate  60  supported by the spindle  48 . At this time, air is out of the cylinders of both block-moving means  21  such that the two blocks  20  are separated from each other by leaving a sufficiently wide gap in between for having the substrate  60  positioned in this gap. Air is also out of the cylinders  33  affixed to the arms  22  such that the mobile members  30  are at their retracted positions. Under this condition, the polishing tapes  50  are run from the feed rollers  13  to the take-up rollers  12  through the direction-reversing rollers  23  such that unused portions of the tapes  50  will contact the substrate  60 . 
   Since the mobile members  30  are both retracted as the tapes  50  are caused to run, the tapes  50  contact only the rotatably supported rollers and do not rub against the pads  31 . Thus, debris particles are not generated from the abrading particles that may fall off. 
   When the base plate  11  has moved to a specified position, each of the block-moving means  21  stops at a position close to the substrate  60  as air is supplied to the corresponding cylinder. Air is supplied then to the cylinders  33  affixed to the arms  22  such that the mobile members  30  move from their retracted positions to the compressing positions and the pads  31  press the tapes  50  from their back sides onto the surfaces of the substrate  60 . 
   The substrate  60  is rotated by the spindle  48  while the block tables  40 ′ move reciprocatingly in the vertical direction such that both surfaces of the substrate  60  are smoothed by the tapes  50 . If the base plate  11  is additionally caused to undergo its reciprocating motion in the horizontal direction (in the direction of arrow T shown in  FIG. 1 ) by means of the male screw motor  42 , the polishing can be accomplished even more effectively. Since the pads  31  are somewhat narrower than the tapes  50 , the pads  31  do not interfere with the edge parts of the tapes  50 . This serves to prevent the abrading particles from falling off the tapes  50 . Although the tapes  50  are generally stopped during the smoothing process described above, the tapes  50  may be caused to run in order to improve the smoothing efficiency even more. 
   After the smoothing process is completed, air is removed from each cylinder such that the mobile members  30  are moved back to their retracted positions and the pair of blocks  20  moves away from each other. The substrate  60  may then be removed from the spindle  48 . 
     FIG. 3  shows another apparatus embodying this invention. Components that are similar to those shown in  FIG. 1  are indicated by the same numerals and may not be repetitiously described. The apparatus shown in  FIG. 3  is distinguishable from the one in  FIG. 1  in that a block-moving rod  62  for moving the blocks  20  is provided between the pairs of feed rollers  13  and take-up rollers  12  which are symmetrically disposed so as to be able to move in the direction of arrow T by means of a motor  61  at one end of the rod  62 . The blocks  20  are adapted to move away from each other if the block-moving rod  62  is moved towards them and to approach each other if the block-moving rod  62  is moved away from them. 
   As shown in  FIG. 4 , each block  20  according to this embodiment of the invention is movable parallel to the surface of the base plate  11  along guide rods  70  which are provided between two protruding members  71  and  72  from an end part of the base plate  11  and by which the block is penetrated. Numeral  73  indicates a block-moving mechanism for moving the block  20  along these guide rods  70 . 
   As shown in  FIG. 5A , the block-moving mechanism  73  has a screw  90  which engages in a hole provided through the member  71 . A knob  91  is provided at one end of this screw  90 . As the screw  90  is rotated by handling the knob  91 , the screw  90  is moved either towards or away from the block  20 . A cylindrical tubular body  92  is attached to the other end of the screw  90 , supporting a piston rod  93  inside this tubular body  92  so as to be movable in the axial direction inside the tubular body  92 . A plate  94  is attached to the end of this piston rod  93  outside the tubular body  92  and a spring  95  is inserted between the plate  94  and the tubular body  92 . The biasing force of this spring  95  operates on the piston rod  93  in the outward direction, normally keeping the plate  94  in contact with the block  20 . 
   As the knob  91  is rotated such that the tubular body  92  approaches the block  20 , the spring  95  begins to press the piston rod  93  against the block  20 . Since the plate  94  on the piston rod  93  applies a force on the block  20  through a pressure sensor  96  buried inside the block  20 , this compressive force can be detected by means of this pressure sensor  96 . 
   The protruding member  72  has a hole  74  therethrough, as shown in FIG.  5 A. The block  20  has a rounded protrusion  20   a  formed at an end position on the side facing the member  72  so as to penetrate the hole  74  completely and to protrude outward, as shown in FIG.  5 B. The tip of the block-moving rod  62  is tapered and is adapted to contact the rounded end portion of the protrusion  20   a  as the rod  62  is advanced by means of the motor  61  at its end, thereby pushing the protrusion  20   a  back into the hole  74  and causing the block  20  to move toward the protruding member  71  against the biasing force of the spring  95 . When the rod  62  is retracted, the biasing force of the spring  95  causes the block  20  to approach the protruding member  72  and its protrusion  20   a  is again pushed out of the hole  74 . 
   As shown in  FIG. 4 , the base plate  11  has an arm structure  80  extending from an end portion behind the block  20 . (This is different from the arm  22  affixed to the block  20  shown in  FIGS. 1 and 2 .) A plurality of rollers  83  are supported by this arm structure  80 , as shown in  FIG. 1 , for allowing a tape  50  to run smoothly. 
   A mobile member  81  extending parallel to the arm structure  80  is attached to the block  20 , as shown in  FIGS. 4 and 5 . As the two blocks  20 , symmetrically disposed as shown in  FIG. 3 , move towards or away from each other, the associated mobile members  81  also move towards or away from each other. A pad  82  is attached to each of these mobile members  81  for pressing the tape  50  onto the substrate  60 . This pad  82  is also made narrower than the tape  50  so as to prevent interference between the pad  82  and the edges of the tape  50 . 
   When the apparatus  10  shown in  FIGS. 3-5  is used for smoothing the substrate  60 , the arm structures  80  are moved towards the substrate  60  and the rod  62  is retracted backward as shown in  FIG. 5B  such that the blocks  20  are pressed against the protruding members  72  by means of the mechanisms  73 . The mobile members  81  are accordingly moved such that their pads  82  operate to press the tapes  50  against the substrate  60 . Since the blocks  20  are subjected to the biasing forces of the springs  95 , the forces with which the pads  82  press the tapes  50  against the substrate  60  depends on the biasing forces of the springs  95 . Since the forces of the springs  95  on the blocks  20  can be detected by means of the pressure sensors  96 , the forces with which the tapes  50  are pressed onto the substrate  60  can also be detected by the pressure sensors  96 . The user can thus turn the knobs  91  of the block-moving mechanisms  73  appropriately to the right or to the left on the basis of the detection signals received from the pressure sensors  96  so as to adjust the compressive forces of the tapes  50  on the substrate  60  by way of the pads  82  on the arm structures  80 . 
   When the substrate  60  is not being processed, the rod  62  is inserted between the protrusions  20   a  as shown in  FIG. 5A  so as to force them back into their holes  74  such that the blocks  20  move away from each other and the mobile members  81  retreat to their retracted positions. This releases the pads  82  from pressing the tapes  50  onto the substrate  60  and the pads  82  are separated from the tapes  50 . Thus, also with the apparatus shown in  FIG. 3 , the pads contact the tapes when the apparatus is operated for smoothing the substrate  60  but they are separated and do not interfere with each other when the apparatus is not being operated. Thus, the tapes can be run without generating any debris particles.