Abstract:
A system and method for reducing and controlling the number of defects due to carbon inclusions on magnetic media is disclosed. A diamond like carbon protective layer is deposited on magnetic media using a rotary cathode target assembly. The target and cathode are cylindrical in shape and are mounted on holder that allows the target and cathode to rotate while holding a magnet fixed. The target surface is periodically swept in through a plasma which sputters off the surface of the target. This prevents the build up of redeposited material on the target and consequently keeps the target surface cleaner. The reduction of redeposited material on the target surface reduces the number of unwanted particulates which are ejected from the surface, manifesting themselves as disk defects.

Description:
[0001]    This application claims priority from U.S. provisional application serial No. 60/357,042, filed on Feb. 13, 2002 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to the reduction of defects resulting from magnetron sputtering, and, more particularly to reducing and controlling the number of defects due to carbon inclusions on magnetic media.  
           [0004]    2. Description of the Related Art  
           [0005]    Computer disc drives commonly use components made out of thin films to store information. Typical disc drive thin film components include read-write head elements for reading and writing magnetic signals and magnetic media for writing magnetic signals onto. Conventional magnetic media is usually made by depositing a stack of thin film layers over each other as illustrated in FIG. 1A.  
           [0006]    [0006]FIG. 1A is an illustration showing the layers of a conventional magnetic media structure including a substrate  103 , a seed layer  105 , a magnetic layer  107 , a protective layer  109 , and a lube layer  111 . The first layer of the media structure is the substrate  103 , which is typically made of nickel-phosphorous plated aluminum or glass that has been textured. The seed layer  105 , typically made of chromium, is the first thin film deposited onto the substrate  103 . The magnetic layer  107 , typically made of a magnetic alloy containing cobalt (Co), platinum (Pt) and chromium (Cr), is a thin film deposited on top of the seed layer  105 . The protective layer  109 , typically made of carbon and hydrogen, is a thin film that is deposited on top of the magnetic layer  107 . Finally the lube layer  111 , typically made of a polymer containing carbon (C ) and fluorine (F) and oxygen (O), is deposited on top of the protective layer  109 .  
           [0007]    The durability and reliability of recording media is achieved primarily by the application of the protective layer  109  and the lube layer  111 . The protective layer  109  is typically an amorphous film called diamond like carbon (DLC), which contains carbon and hydrogen and exhibits properties between those of graphite and diamond. Thin layers of DLC can be deposited on disks using a variety of conventional thin film deposition techniques such as ion beam deposition (IBD), plasma enhanced chemical vapor deposition (PECVD), magnetron sputtering, radio frequency sputtering or chemical vapor deposition (CVD). During the deposition process, adjusting sputtering gas mixtures of argon and hydrogen varies the concentrations of hydrogen found in the DLC. Since typical thicknesses of protective layer  109  are less than 100 Angstroms, lube layer  111  is deposited on top of the protective layer  109  for added protection, lubrication and enhanced disk drive reliability. Lube layer  111  further reduces wear of the disc due to contact with the magnetic head assembly.  
           [0008]    Although there are several techniques available for depositing DLC films as a protective layer  109  for magnetic recording media, as previously discussed, planar magnetron is the preferred method because of its wide spread use and good resultant film properties. However, there are problems associated with using planar magnetron sputtering including low yields resulting of the high number of defects found on the disk.  
           [0009]    [0009]FIG. 1B is an illustration showing a cross sectional side view of a conventional magnetron sputtering system including a target  110 , a target erosion zone  115 , a redeposition area  120 , a backing plate  125 , a coolant  130 , magnets  135 , a shunt  140 , a cathode  145  and a plasma  150 . Target  110  is a conventional sputtering target that is mounted to the backing plate  125  with indium. Magnets  135  are typically permanent magnets, which are used to confine plasma  150  near the surface of the target. Coolant  130  is typically water which is circulated behind.backing plate  125  to cool the target while it is being sputtered. Shunt  140  diverts the magnetic field to the exterior of the target  110  causing electrons to be trapped and consequently causing sputtering of the target  110 .  
           [0010]    The sputtering process removes target material from the target erosion zone  115  and deposits that material throughout the chamber including the substrate, chamber walls and target  110 . If reactive gases such as ethylene or methane are used then additional material other than the sputtered material is deposited throughout the chamber and substrate. The area on the target  110  where sputtered material gets redeposited and any film grows as a result of using reactive gasses is called the redeposition area  120 . This redeposited material, located in the redeposition area  120 , is sometimes ejected from the target  110  surface and bombards the substrate creating a defect, as explained in more detail below.  
           [0011]    [0011]FIG. 1C is a block diagram showing a front view of typical planar sputtering cathode including a target  110 , a target erosion zone  115  and a redeposition area  120 . The target erosion zone  115 , resembling a racetrack, is the area of the target  110  where material is sputtered off. The redeposition area  120  is the area on the target where carbon is redeposited during the sputtering process. Redeposition area  120  includes the rectangular area in the center of the target erosion zone  115  as well as the outer part of the target  110  between the target erosion zone  115  and the edge of the target  110 .  
           [0012]    [0012]FIG. 1D is an illustration showing a top view of a conventional magnetron sputtering system including a first chamber wall  155 , a second chamber wall  160 , a top view of eight planar cathode mounted sputtering targets with redeposition areas  120 , a top view of eight plasma patterns  165  and a top view of a transport mechanism  170 . First chamber wall and second chamber wall are both conventional walls of a vacuum chamber typically constructed out of stainless steel. The eight sputtering patterns represent the material sputtered from the erosion pattern  115  along with ionized sputtering gas atoms (argon). Transport mechanism  170  is a transportation device that moves disks or pallets full of disks in front of plasma  150  as further described with reference to FIG. 1E below.  
           [0013]    [0013]FIG. 1E is an illustration showing a front view of one side of a conventional magnetron sputtering system including four targets  110  with erosion zones and redeposition areas and a transport  170  located within a vacuum chamber  180  as well as disks  185 , a pallet  187  and a beam  191 . Vacuum chamber  180  is a conventional chamber, typically made of stainless steel, that houses targets  110  and transport  170 . Disks  185  are substrates  103  with seed layer  105  and magnetic layer  107  already on them and ready for depositing protective layer  109  to be deposited. Pallet  187  is typically made of aluminum and is machined to hold disks  185  in an upward position. Beam  191  is typically a stainless steel beam from which pallet  187  hangs and is transported in vacuum chamber  180 .  
           [0014]    A significant disadvantage with conventional planar magnetron sputtering techniques, such as the one described with reference to FIGS.  1 A- 1 E, is the high number of particulates that are produced on the substrate. If too many particulates are deposited on a substrate then the substrate is defective and cannot be used. Although defects resulting from excessive particulates on a substrate can occur when sputtering any material, the problem is enhanced when sputtering carbon.  
           [0015]    Typical carbon defects include particulates containing carbon and traces of the sputtering gases used (typically argon) that range in size from sub micron to micron in diameter. These defects, which have a high content of SP2/SP3 hybridization, are often found embedded deeply into the NiP coated aluminum substrate manifesting themselves as glide height asperities and/or thermal asperities when the magneto-resistive recording head glides over them. The rate at which these defects are generated is time dependent. New or recently resurfaced targets have a low emission rate for these defects. As the targets are sputtered, the rate increases to a maximum, and then decreases over time to a stable level. For this example of planar magnetrons, the maximum defect rate takes approximately 60 hours to be reached and then decreases over the next 120 hours of operation. The final defect rate maintains at 2-3% product loss until the targets are replaced or resurfaced.  
           [0016]    In one model explaining the formation of particulates on a carbon surface, particulates are ejected from the redeposition area of a sputtered target and are deposited on the substrate. In this model, the defects arising out of carbon particulates increase as the redeposited material on the target increases. During the sputtering process, some of the sputtered material is redeposited back on the areas of the target material. Redeposited material is defined as the material that is sputtered off of a target and lands back on the target. This can include the target material plus other materials such as argon, hydrogen or other impurities that get commingled with the target material during the sputtering process. As the redeposited material builds up over time, stress fracturing occurs in the redeposition area  120  resulting in ejection of particulate material and a roughening of the redeposition area. Since the trajectory of these high velocity particles is random, statistically some of the particles collide with the surface of the substrate being coated. During this collision, the high velocity particles impart to the substrate sufficient energy to melt the Nickel phosphate (NiP) coating on the substrate at the contact site and to deform the surface of the substrate sufficiently to embed the particle or a proportion of the particle deeply into the NiP material. Finally, these defects manifest themselves as glide height asperities and/or thermal asperities when a magneto-resistive recording head glides over the defect, which can result in unacceptable recording media. If enough defects are found on a recording disk then the disk is rejected resulting in lower yields and higher cost.  
           [0017]    Therefore what is needed is a system and method that reduces the amount of redeposited material on the target, consequently reducing the number of particulates ejected from the surface of the target and creating defects on the substrate. Although such a system and method for reducing substrate defects is needed in all areas of thin film growth the need is especially high in the area of recording media manufacture. Defects produced on magnetic media during the thin film deposition process are usually carried through to the finished product because subsequent processes, such as lubrication, coat and conform to the defect geometry. Defects on magnetic media often cause thermal asperities and head crashes resulting in unusable magnetic media and consequently low yields and higher cost in manufacturing magnetic media.  
         SUMMARY OF THE INVENTION  
         [0018]    In order to reduce the number of defects per disk arising from particulates produced in the magnetron sputtering processes, a rotary magnetron sputtering system and method is used for depositing thin films. The rotary magnetron cathode target assembly consists of a magnet, a cylindrical cathode, a cylindrical target, a shaft for connecting to a rotary drive mechanism for rotating the assembly and a coolant. The magnet is located inside the cylindrical cathode and remains stationary as the cathode and target rotate around it. The cathode and target are coupled to the shaft which is attached to a rotary drive mechanism that rotates the shaft and coupled cathode and target.  
           [0019]    The method of using the rotary magnetron cathode to reduce the number of defects per disk includes igniting a plasma at the surface of the target causing the target surface closest to the magnet and exposed to the plasma to be sputtered off. Next, the target and cathode are rotated around the shaft, the magnet remains stationary. The stationary magnet forces the plasma to remain stationary as the target moves around. Therefore, rotating the cathode and target about the shaft produces the effect of sweeping the target surface in front of the plasma so that only the portion of the target surface that is exposed to the plasma is sputtered off. This prevents build up of redeposited material because the entire surface gets sputtered off. As the target surface rotates, the material that is redeposited onto the surface is again sputtered off as that portion of the surface with redeposited material enters the plasma. The effect of this rotary cathode target assembly is that the entire surface is repeatedly being sputtered off so that redeposited material is not allowed to get so thick that it eventually dislodges from the surface. This dislodged material then enters the plasma where it is superheated and explodes into smaller high-energy particles that collide and embed into the disk causing a defect on the disk. This method of depositing carbon onto disks prevents the redeposited material from dislodging from the surface and entering the plasma.  
           [0020]    These and various other features as well as advantages which characterize the present invention will be apparent upon reading of the following detailed description and review of the associated drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE INVENTION  
       [0021]    [0021]FIG. 1A is a block diagram showing a prior art conventional magnetic media structure;  
         [0022]    [0022]FIG. 1B is a block diagram showing a cross sectional side view of a typical planar magnetron sputtering cathode with target;  
         [0023]    [0023]FIG. 1C is a block diagram showing a front view of typical planar magnetron sputtering cathode;  
         [0024]    [0024]FIG. 1D is a top view of the prior art planar magnetron sputtering cathode and target incorporated into a deposition chamber;  
         [0025]    [0025]FIG. 1E is a side view of the prior art planar sputtering cathode and target incorporated into a deposition chamber;  
         [0026]    [0026]FIG. 2 is a block diagram showing a rotary sputtering cathode target assembly in accordance with an embodiment of the invention;  
         [0027]    [0027]FIG. 3 is a block diagram showing a side view of the rotary sputtering cathode target assembly in accordance with an embodiment of the invention;  
         [0028]    [0028]FIG. 4 is a block diagram showing a thin film deposition system used to deposit the magnetic media;  
         [0029]    [0029]FIG. 5 is a top view of a rotary sputtering cathode incorporated into carbon overcoat deposition chamber  425  in accordance with an embodiment of the invention;  
         [0030]    [0030]FIG. 6 is a front view of one side of a rotary sputtering cathode incorporated into carbon overcoat deposition chamber  425  in accordance with an embodiment of the invention;  
         [0031]    [0031]FIG. 7 is a flowchart showing the process steps used to deposit a carbon overcoat in deposition chamber  425  in accordance with one embodiment of the invention; and  
         [0032]    [0032]FIG. 8 is a yield chart comparing levels of defects due to carbon inclusions both with conventional magnetron sputtering and rotary cathode sputtering techniques.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]    The invention provides a system and method for reducing defects resulting from sputtering including but not limited to magnetron sputtering. In particular, the invention provides a system and method for reducing the number of defects due to carbon inclusions on magnetic media.  
         [0034]    [0034]FIG. 2 is an illustration showing a top view of one embodiment of the rotary cathode target assembly, for sputtering, including a rotatable holder  205 , target  210 , a target surface  212 , a cathode  215 , an axis of rotation  220 , a shaft  225 , a magnet  230 , coolant  240  and a plasma region  250 . Rotatable holder  205 , which holds and supports target  210 , cathode  215  and coolant  240 , is made from a sturdy metal such as stainless steel or aluminum. Moreover, rotatable holder  205  is built to allow target  210  and cathode  215  to rotate about the axis of rotation  220  while magnet  230  remains stationary. Target  210  and target surface  212  can be made of any material that can be sputtered. Some common materials include carbon, silicon, chromium, cobalt and cobalt alloys. Target  210  and target surface  212  are formed into a rotationally symmetric shape such as a cylinder. Target  210  and target surface  212  are rotated about an axis of rotation  220 , which coincides with the symmetry axis of target  210 . Magnet  230 , can be a permanent magnet or an electrical magnet, which is located near target  210  and is separated from plasma region  250  by target  210 . Typical permanent magnets include SmCo and NdFeB while typical electrical magnets include conventional copper windings attached to a power supply. Magnet  230  must be chosen so that the magnetic field lines originating from the magnet  230  penetrate the target  210  and target surface  212  and are present in the plasma region  250 . The magnetic field is considered present in the plasma region  250  when it&#39;s magnitude is a measurable value that is non-zero. There are no other restrictions on the magnetic field including the direction of the magnetic field vector except that its magnitude is non-zero. Coolant  240  can be any liquid or gas effective in conducting heat away from the target  210  and cathode  215  including water and argon, for example. Coolant  240  is circulated over cathode  215  and magnet  230  to carry away heat generated during the sputtering process. Plasma region  250  is a conventional plasma typically made of ionized gas including argon, xenon or nitrogen used to bombard and. sputter target  210 .  
         [0035]    In order to rotate target  210  and cathode  215  about an axis of rotation  220  without affecting the sputtering process both target  210  and cathode  215  are built to be rotationally symmetric. In this embodiment, both target  210  and cathode  215  are cylindrical in shape. Cathode  215  has a cylindrical inner surface  255 , cylindrical outer surface  260 , a first sealed end (not shown) and a second sealed end (not shown). Inner surface  255  contacts the coolant  240  while the outer surface  260  contacts the target  210 . First sealed end is typically an attached plate that forms a seal keeping coolant  240  from leaking out. Similarly, second sealed end is typically an attached plate that forms a seal keeping coolant  240  from leaking out of the second end of the cathode. First sealed end also has coolant inlet and coolant outlet for flowing coolant  240  through the inside of the cathode for cooling during the sputtering process. Both coolant inlet and coolant outlet are typically attached onto first sealed end in a manner that is compatible with ultrahigh vacuum system.  
         [0036]    In an alternative embodiment, the coolant is not used to cool the cathode and target during the sputtering process. The coolant can be eliminated when low powers are used for sputtering because heating is not a problem. When the heating rate is low, sufficient cooling can be achieved with the use of direct mechanical link such as copper, eliminating the need for using harder to control liquids and gases. This system is advantageous because liquids and gasses are kept out of the vacuum chamber. In this alternative embodiment the first sealed end and the second sealed end of the cathode  215  are replaced with a first open end and a second open end respectively. The coolant inlet and the coolant outlet are also eliminated. This alternative embodiment is advantages because it is easier to build and maintain.  
         [0037]    [0037]FIG. 3 is an illustration showing a side view  300  of one embodiment of the rotary sputter cathode target assembly including a target  210 , a first shaft end  310 , a second shaft end  315 , a first coupler  320 , a second coupler  325 , a first rotary vacuum feed-through  330 , a second rotary vacuum feed-through  335 , a module  340 , a coolant inlet  345  and a coolant outlet  350 . Target  210  encloses the cathode, magnet and coolant as was described with reference to FIG. 2 above. Module  340  supports the rotary drive mechanism as well as electrical connections and power supplies.  
         [0038]    In one embodiment, there is a shaft  225  along the axis of rotation  220 , which runs the entire length of target  210 . First shaft end  310  and second shaft end  315  are the ends of the shaft that extend past the target  210  and which are attached to first coupler  320  and second coupler  325 . The shaft material is made out of a metallic material such as copper or aluminum which is both conductive and durable enough to support the torque put on the shaft due to rotation of the cathode and target material. The first shaft end  310  and the second shaft end  315  are attached to first coupler  320  and second coupler  325  respectively. First coupler  320  and second coupler  325  are used to connect shaft  225 , which supports target  210  and cathode  215  through rotatable holder  205 , to first vacuum feed-through  330  and second vacuum feed-through  335 . This type of connection allows for removal of the target  210  and cathode  215  from a vacuum chamber without removal of the feed-throughs and therefore minimizing the chances of developing vacuum leaks. Module  340 , which is coupled to first vacuum feed-through, contains a rotary drive mechanism for rotating the target  210  and cathode  215  as well as an electrical connection for supplying power to target  210  and cathode  215 . The electrical connection to the rotating cathode is done through brushes located in module  340 , which is positioned outside of the vacuum process so that particles generated by the brush contact do not generate defects.  
         [0039]    First vacuum feed-through  330  and second vacuum feed-through  335  are used mainly when the rotary drive mechanism is located outside of the process chamber. Rotary drive mechanism generates rotary motion of the target  210  and cathode  215  about the axis of rotation  220 . Rotary motion involves rotating the target  210  and cathode  215  at about one revolution per minute about its axis of rotation  220 . There are however no restrictions on the rate of rotation. In another embodiment, where the rotary drives are located inside the chamber, the vacuum feed-throughs  330  are omitted.  
         [0040]    In an alternative embodiment second shaft end  315 , second coupler  325  and second vacuum feed-through  335  are omitted. This type of design can be advantage if the entire cathode-target assembly is light enough and sturdy enough to remain stable during rotary motion. The advantages are that it has fewer components and is therefore less expensive, easier to use and less likely to malfunction.  
         [0041]    [0041]FIG. 4 represents a multilayer thin film deposition system  400  equipped with a rotary sputter cathode for depositing diamond like carbon (DLC) protective layers  109 . System  400  preferably includes a loader  410 , a PREP  415 , a magnetic thin film depositor  420 , an overcoat depositor  425 , an unloader  430 , a controller  435 , a power system  440 , a pumping system  445  and a gas flow system  450 . Although, this embodiment is described in terms of using rotary cathode sputtering for depositing carbon in the overcoat depositer  425 , the rotary cathode target assembly  300  can be used to replace any planar magnetron sputter target assembly and consequently can be used in PREP  415  or magnetic thin film depositor  420 .  
         [0042]    Loader  410  and unloader  430  represent conventional load locks that allow substrates to be transferred into and out of a vacuum chamber without venting the entire vacuum system. PREP  415  represents a preparation chamber and can be heaters, coolers additional thin film deposition chambers, etc. The generic term PREP  415  is used to describe processes before the deposition of the magnetic layer  107  because conventional processes such as heating of the substrate  103  and deposition of the seed layer  105  are well known in the art. Magnetic thin film depositor  420  represents the deposition of the magnetic thin film stack including the magnetic layers and any spacers needed for magnetic properties. Typically magnetic thin film depositor  420  includes several planar magnetron-sputtering apparatuses that sputter Co based targets. Overcoat depositor  425  represents a thin film deposition chamber using rotary cathode target assembly  300  for sputter depositing DLC protective layer  109  in accordance with an embodiment of the invention. Power system  440  represents power supplies used to power the system  400  and include power supplies for heaters, conveyers, DC magnetrons, rf sources, etc. Pumping system  445  represents all pumps and valves used to evacuate the vacuum chambers including mechanical pumps, turbo pumps, cryogenic pumps and gate valves. Gas flow system  450  represents the gas delivery equipment such as mass flow controllers, valves, piping and pressure gauges.  
         [0043]    [0043]FIG. 5 is an illustration showing a detailed top view of overcoat processing chamber  425  including a first vacuum chamber wall  510 , a second vacuum chamber wall  515 , a transport  520 , eight rotary cathode targets  530 - 537  respectively, eight sputtering patterns  540 - 547  respectively, in accordance with one embodiment of the invention. Controller  435 , power system  440 , pumping system  445  and gas flow system  450  are also shown coupled to overcoat processing chamber  425 . The eight rotary cathode targets  301 - 308  are arranged into two banks with each bank having four rotary cathode targets each. The first bank consists of rotary cathode targets  530 - 533  and the second bank consists of rotary cathode targets  534 - 537 . The first bank and second bank are arranged to permit substrates to pass in between the two banks so that both sides of the substrates are coated with a thin film of the sputtered target. In an alternative embodiment the two banks of cathode target assemblies only include one cathode target assembly in each bank. In this alternative embodiment the first bank has a target, a magnet and a rotatable holder from the first cathode target assembly and the second bank has a second target, second magnet, and second rotatable holder wherein the second target is positioned to permit movement of the substrate between target and the second target.  
         [0044]    First vacuum chamber wall  510  and second vacuum chamber wall  515  are stainless steel walls of a conventional vacuum chamber which include feed-throughs for electrical connectors, rotary mechanical connectors, gauges, gas lines and pumping lines. Transport  520  is an overhead transportation mechanism that transports a hanging pallet containing disks or substrates through the overcoat-processing chamber  425 . As the pallet containing disks or substrates moves through overcoat processing chamber the disks are coated with carbon as is further discussed with reference to FIG. 7 below. The corresponding confined plasmas generate sputtering patterns  540 - 547  that are conical in shape and are composed of ionized gases used for sputtering such as argon, xenon or ethylene as well as carbon atoms sputtered off the target  210  from the cathode target assembly  300 .  
         [0045]    Controller  435  represents the hardware and software that controls operation of the multilayer thin film deposition system  400 . The portion of controller  435  that controls the rotary cathode target assembly  300  includes a drive rotation mechanism  340  for rotating the cathode target assembly  300  as well as sensors to monitor the rate of rotation, voltage, temperature and rate of coolant flow within cathode target assembly  300 . The rotation mechanism can be a single motor coupled to all eight cathode target assemblies  300  through a conventional chain, for example; several motors wherein each motor is coupled to more than one of the eight cathode target assemblies  300 ; or a single motor for each of the of the eight cathode target assemblies  300 .  
         [0046]    The eight confined plasmas having sputtering patterns  540 - 547  originate at the target surface  212  of each of the eight corresponding cathode target assemblies  300  and spread out according to some distribution which can be conical. The plasma  250  consists of electrons trapped by a magnetic field in the small region near the target surface  212  opposite the side of magnet  230 . The magnetic field from magnet  230  penetrates the target  210  and target surface  212  trapping electrons near the target surface  212 . These trapped electrons then ionize the sputtering gas atoms, which are accelerated towards the target surface  212  because of the potential difference between the plasma  250  and the target  210  and cathode  215 . The accelerated ions bombard the target surface  212  and sputter carbon from the target surface  212 . The sputtered carbon atoms leave the target surface  212  of each of the cathode target assemblies  300  according to a conical distribution pattern, which makes up the confined plasmas and sputtering patterns  540 - 547 . These sputtered atoms are deposited onto the magnetic media disks growing a thin film of DLC protective overcoat  109  on the disk.  
         [0047]    During rotation of cathode target assembly  300 , magnet  230  remains fixed as target  210  sweeps in front of the plasma  250  causing uniform sputtering of the entire cylindrical target surface  212 . By periodically sweeping the target surface  212  in front of the plasma  250 , the carbon target  210  mounted on the cathode target assembly  300  erodes uniformly, minimizing the redeposited material on the target. As previously defined the redeposition area on the target includes sputtered material that gets redeposited and any film that grows as a result of using reactive gasses. In accordance with one embodiment of the invention, a typical erosion pattern at any given time resembles a rectangle which is arced to conform to the cylindrical target surface  210  with an arced width approximately equal to the width of the magnet and a length approximately equal to the length of the target surface  210 . As the cathode target assembly  300  rotates, the target surface  210  sweeps through the plasma, consequently subjecting the target surface to the plasma and cleaning the target surface. Cleaning the target surface includes eliminating the redeposited material by sputtering the redeposited material off of the target, as well as removing oxide layers or other foreign material that end up on the target surface that could affect films grown through the sputtering process. Rotating the target in a plasma so that a substantial portion of the target is sputtered essentially cleans the target surface on a regular periodic basis by sputtering it clean. Since the rotation rate is such that redeposited material is periodically removed from the target surface  210 , before too much accumulates, substantial amounts of redeposited material which can dislodge and get ejected into the plasma are not allowed to form. Ultimately this leads to fewer defects on a disk and higher yields as is further discussed with reference to FIG. 8 below. Additionally, this method of periodically rotating, or sweeping, a target into the sputtering region increases utilization of the target  210  to almost 100% and consequently increases the life of a target because the entire target is eroded rather than just the erosion zone  115  seen in the prior art.  
         [0048]    [0048]FIG. 6 is an illustration showing a detailed side view of a pallet  610 , containing disks  620 , hanging from a second transport  630  going into overcoat processing chamber  425 , which further includes side views of a top vacuum chamber wall  640 , a bottom vacuum chamber wall  645 , a transport  520 , and four rotary cathode targets assemblies  300  in accordance with one embodiment of the invention. Controller  435 , power system  440 , pumping system  445  and gas flow system  450  are also shown attached to overcoat processing chamber  425 .  
         [0049]    Pallet  610  is an aluminum square plate with slots machined into it for holding disks  620  in a vertical position. The slots further include lips to securely hold the disks in the vertical position. Although pallet  610  is shown as a square with fifty-six slots, it can be of any shape and can have any number of slots machined into it provided the number of slots fit within the area of pallet  610 . Typically, pallet  610  is loaded with disks  620  and is hanging from a transport that transports the pallet along with the disk into overcoat processing chamber  425 .  
         [0050]    The rotary cathode target assemblies  300  are rotating before pallet  610  and disks  620  enter the overcoat process chamber  425 . The cathode target assemblies  300  are typically set to rotate at a constant rate of rotation at all times but can be set to rotate only when pallet  610  is passing in front of the cathodes. The rotation rate is chosen so that a substantial portion of the redeposited material on the target surface is removed during one revolution of the target. This rate varies according to sputtering power, pressure, temperature and process gas. For example, a lower sputtering power may require a slower rotation rate. Similarly, different process gasses (such as argon, argon-hydrogen mixtures, argon-ethylene mixtures, argon-methane mixtures, argon-hydrogen-nitrogen mixtures, etc) may require different rotation rates because of the rate at which redeposited material builds up on the target surface. However, a typical range of rotation rates is 1 revolution per minute to 100 revolutions per minute and a typical rotation rate is ten revolutions per minute. Plasma  250  is ignited before pallet  610  enters the overcoat deposition chamber  435 .  
         [0051]    Although plasma  250  can be left on at all times it is preferably ignited shortly before pallet  610  along with disks  620  are transported into overcoat process chamber  435 . After igniting plasma  250  and starting rotation of rotary cathode target assemblies  300 , transport  520  is turned on. External transport  630  is then turned on, transporting pallet  610  and disks  620  through all eight sputtering patterns  540 - 547  and in front of target surfaces  212 . During this transport process, pallet  610  and disks  620  are never stopped. Their motion must be continuous all the way through the eight sputtering patterns  540 - 547  Although this embodiment describes moving disks, it works equally well for moving substrates.  
         [0052]    [0052]FIG. 7 is a flowchart showing the process steps used to deposit a carbon protective overcoat  109  in deposition chamber  425  in accordance with one embodiment of the invention. First in step  705 , pallet  610  arrives to a position in thin film deposition system  400  where it is ready to begin the overcoat deposition process. This typically occurs two chambers before overcoat depositor  425 . Next in step  710 , a decision is made as to whether the cathode target assemblies  300  is rotating at an optimal rate which is set to minimize the amount of redeposited material on the target surface  212 . Typically, all eight cathode target assemblies  300  are rotated at the same speed. This, however, is not necessary and each can be rotated at different speeds, if needed, to optimize the thin film deposition process. If the decision reached in step  710  is yes then the plasma  250  is ignited in step  715  by supplying a voltage to the cathode and target assembly  300 . Voltages used are typically a few hundred volts negative but can vary depending on the deposition rate desired and the gas pressure in the processing chamber. Igniting a plasma typically requires setting appropriate plasma conditions such as 5-10 milli-torr of argon gas and negative 200 volts. Igniting the plasma in step  715  subjects a portion of the outside surfaces of the targets to the plasma. By then rotating the cathode target assemblies  300 , the entire surface of the target is sputtered. This process of rotating the target relative to the plasma cleans the target surface by removing target material from the entire surface of the target. However, if the decision reached in step  710  is that the targets and cathodes are not rotating at the correct speed then an alarm is given in step  712  and the process ends.  
         [0053]    Next in step  720  the speed at which pallet  610  will be transported through the overcoat depositor  425  in front of the cathode target assemblies  300  is determined. The speed is determined by calculating the amount of time needed to grow the desired protective overcoat  109  thickness using the current film growth rate and using that time to estimate the speed of the pallet  610  and disks  620 . After the transport speed is determined, the transports in the process chamber, the preceding chamber and the following chamber are turned on and the pallet  610  along with disks  620  move through the overcoat depositor  425  in front of cathode target assemblies  300 . As the pallet  610  and disks  620  move through the chamber in front of the plasma and cathode target assembly  300 , the pallet&#39;s  610  location is monitored in step  725 . Next in step  735  a decision is made as to whether the pallet  610  is still inside the overcoat depositor  425 . If any part of the pallet  610  is still inside overcoat depositor  425  then the position of the pallet  610  continues to be monitored otherwise the plasma is extinguished in step  740 . Finally, in step  745  the pallet  610  along with disks  620  move to the next process in the film deposition system  400  which is usually the unload station  430  where the pallet  610  and disks  620  are removed from the thin film deposition system  400 . Although the method is described in terms of depositing thin films on disks it will be recognized by those skilled in the art that the deposition can be done on substrates just as well.  
         [0054]    [0054]FIG. 8 is a chart comparing the average errors per disk as a function of service time for both the prior art conventional planar target assembly shown in FIG. 1C and the rotary cathode target assembly  300 . Measurement of the average error is performed using glide test heads that glides over the media, as the media rotates at thousands of revolutions per minute, imitating read-write head in finished disk drives. Among the various factors that trigger an error are glide hits, which occur when glide heads contact defects such as those commonly produced with planar magnetron sputter deposition of carbon. Control group trend  810  shows the average errors per disk for disks made using the prior art planar magnetron sputtering cathode and target  100  to sputter protective overcoat  109  as a function of service time. Similarly, experimental group trend  820  shows the average errors per disk for disks made using the rotary cathode target assembly  300  to sputter protective overcoat  109 , as a function of time. Service time is the time measured in hours starting from when the overcoat-processing chamber  425  was serviced and the targets either changed or resurfaced. The data suggests that sputtering with rotary cathode target assembly  300  instead of conventional planar magnetron sputtering significantly reduces the number of defects on a disk.  
         [0055]    It will also be recognized by those skilled in the art that, while the invention has been described above in terms of preferred embodiments, it is not limited thereto. Various features and aspects of the above-described invention may be used individually or jointly. Further, although the invention has been described in the context of its implementation in a particular environment and for particular applications, those skilled in the art will recognize that its usefulness is not limited thereto and that the present invention can be utilized in any number of environments and implementations.