Abstract:
An apparatus and method for sputter depositing a magnetic film on a substrate to produce a magnetic device such as magnetic recording heads for reading digital information from a storage medium. The apparatus of the invention includes a sputtering chamber containing a target and a substrate, and a magnet array disposed within the chamber to form a substantially parallel magnetic field at a surface of the substrate. The sputtering chamber reduces interference between the magnetron and the magnet array by providing a long throw distance and/or a grounded collimator. The magnet array is preferably a circular ring.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an apparatus and method for forming magnetic recording heads. More particularly, the present invention relates to providing a parallel magnetic field at a substrate during sputter deposition of a metal film onto the substrate. 
     BACKGROUND OF THE INVENTION 
     Magnetic read-write heads are used in the recording and retrieval of digital information from magnetic discs, magnetic tape, or other information storage devices. The magnetic heads typically include one or more thin layers of magnetic material that is oriented to generate a magnetic field that alters the recording media, or to sense a magnetic field on the recording media without interference. The thin layer of magnetic material is typically deposited on a substrate that is used to prepare the magnetic recording head. 
       FIG. 1  (prior art) illustrates a typical magnetoresistive head  5  that reads information from magnetic medium  6 . The magnetoresistive head  5  includes a soft magnetic layer  7  (e.g., 80% nickel, 20% iron) that functions as the magnetoresistive sense layer, and a hard magnetic layer  8  (e.g., 75% nickel, 20% iron, 5% chromium). The magnetic layers are deposited on a non-magnetic substrate  4  such as aluminum oxide or an alloy of aluminum/titanium/carbon. The soft magnetic layer  7 , and the hard magnetic layer  8 , are separated by a spacer layer  9  (e.g., tantalum). The magnetic layers are typically manufactured by sputtering a target comprising the metal alloy to deposit particles of the metal alloy onto a substrate positioned within a magnetic field. The magnetic field orients the depositing particles and magnetizes the deposited film. Performance of the magnetic heads is enhanced by depositing the thin film within a substantially parallel magnetic field, as described in U.S. Pat. No. 5,589,039. Sputtering of the target can occur within a magnetic field as known in the art. However, uniform magnetic fields having a high degree of parallelism at a substrate are difficult to maintain within a sputtering chamber because of interference between the magnetic field at the substrate and a plasma generated within a magnetic field at the target. 
     U.S. Pat. No. 5,660,744 describes a circular magnet array that is located outside an etch chamber and includes a plurality of magnets that form a parallel magnetic field. In the &#39;744 patent, two external circular magnet arrays are used in conjunction with an electric field to enhance an etching process. The circular magnet arrays generate parallel magnetic fields that are out of phase and are not positioned to form a parallel magnetic field at a surface of a substrate. 
     Elimination of interference between a plasma generated adjacent a metal alloy target and a parallel magnetic field at the surface of a substrate would substantially improve the manufacture of magnetic films such as used in magnetoresistive heads. Therefore, there is a need for a sputtering chamber that provides a parallel magnetic field at the substrate surface without substantial interference from charged particles. 
     SUMMARY OF THE INVENTION 
     The present invention provides an apparatus and method for sputter depositing a magnetic film on a substrate to produce a magnetic device such as a magnetic recording head for reading and writing digital information on a storage device. The apparatus of the invention includes a sputtering chamber containing a target and a substrate, and a magnet array disposed within the chamber to form a substantially parallel magnetic field at a surface of the substrate. The target and the magnet array are separated by distance and/or a grounded collimator to reduce interference with the parallel magnetic field. The target can be any material that retains magnetic properties when deposited on a substrate positioned in a magnetic field. However, the target preferably comprises a nickel/iron alloy, such as Permalloy metals, suitable for forming magnetic recording heads. 
     In one embodiment, a sputtering process deposits a magnetic film in a chamber containing a grounded collimator that reduces interference between a plasma generated in a magnetic field adjacent the target and the parallel magnetic field at the surface of the substrate. Preferably, the parallel magnetic field is generated by a circular magnet array. In another embodiment of the invention, a long throw sputtering process deposits a magnetic film in a chamber having a long throw distance between the target and the magnet array disposed adjacent the substrate. The long throw process may optionally include a grounded collimator and the circular magnet array. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. 
       It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefor not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  (prior art) is a schematic view of a typical magnetic recording head utilizing a magnetoresistive sense layer produced by sputtering metal alloys onto a non-magnetic substrate; 
         FIG. 2  is a schematic sectional view of a sputtering chamber having a grounded collimator that reduces interference with a parallel magnetic field formed at the surface of a substrate by a circular magnet array; 
         FIG. 3  is a schematic view of the circular magnet array that surrounds a substrate surface in the deposition chamber of  FIG. 2 ; 
         FIG. 4  is a schematic sectional view of a long throw sputter deposition chamber that substantially reduces interference with a parallel magnetic field formed by a circular magnet array without a collimator; 
         FIG. 5  illustrates the effect of chamber pressure on the easy axis coercivity of a magnetic film deposited in a parallel magnetic field; 
         FIG. 6  illustrates the effect of chamber pressure on the magnetoresistance of a magnetic film deposited in a parallel magnetic field; and 
         FIG. 7  is a B-H curve for an oriented Nickel/Iron Film deposited in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The apparatus and method of the invention substantially improves deposition of magnetic films on a substrate by reducing interference with a parallel magnetic field provided at the surface of the substrate. The magnetic films are deposited in a sputtering chamber typically comprising a sputtering target and a magnet array that magnetizes a thin film of the target material deposited on a surface of the substrate.  FIG. 2  is a schematic sectional view of a preferred sputtering chamber of the present invention having a metal alloy target positioned to deposit a thin film on the surface of a substrate, and further including a grounded collimator that reduces interference with the parallel magnetic field. 
     The Sputtering Chamber 
     Referring to  FIG. 2 , a grounded collimator  12  is disposed between a sputtering target  14  and a semiconductor substrate  16  in a sputter deposition chamber  10 . The collimator  12  can comprise a one or more cells as shown in  FIG. 2 , two or more concentric rings, or other configurations known in the art. The collimator  12  blocks a portion of the target particles traveling obliquely with respect to the substrate surface to provide a more uniform and symmetrical flux of deposition material to each location on the substrate. In addition, the collimator  12  assists in trapping charged particles that interfere with a parallel magnetic field positioned adjacent the substrate  16  as described below. 
     Referring still to  FIG. 2 , the sputtering chamber  10  for practicing the invention generally includes a vacuum chamber enclosure wall  24  having at least one gas inlet  26  connected to a gas source (not shown) and an exhaust outlet  28  connected to an exhaust pump (not shown). A substrate support pedestal  20  is disposed at one end of the chamber  10 , and the sputtering target  14  is mounted to the other end of the chamber  10 . The target  14  is electrically isolated from the enclosure wall  24  by an insulator  18 , and the enclosure wall  24  is preferably grounded, so that a negative voltage may be applied and maintained on the target with respect to the grounded enclosure wall  24 . In operation, the substrate  16  is positioned on the support pedestal  20  and a plasma is generated in the chamber  10 . Charged particles from the target  14  are substantially neutralized by the grounded collimator  12  prior to deposition on the substrate  16 . 
     The Magnet Array 
       FIG. 3  is a schematic view of a permanent magnet array  50  having a circular shape that preferably surrounds a substrate surface in the deposition chamber of  FIG. 2 . The permanent magnet array  50  is located within the chamber  10  and provides a parallel magnetic field at a surface of the substrate  16 . The permanent magnet array  50  is known as a Halbach array, and can be an electromagnet or a permanent magnet. 
     The permanent magnet array  50  comprises segments having different magnetic orientations that combine to form a parallel magnetic field as described in U.S. Pat. No. 5,660,744. The circular magnet array is well known for producing parallel magnetic fields in electric motors. The circular magnet array  50  preferably has 12 or more segments to provide a uniform magnetic field. Placement of the circular magnet array  50  within the chamber walls  24  provides a limited magnetic field that is not substantially impaired by the magnetron  30 . Referring to  FIG. 2 , placement of the grounded collimator  12  between the magnetron  30  and the magnet array  50  in the long throw chamber  10  as shown eliminates interference by the magnetron  30  with the parallel field at the substrate. 
     In the alternative, the magnet array could have a non-circular configuration as shown in U.S. Pat. No. 5,589,039, particularly when used in combination with the grounded collimator  12  or within a long throw sputtering chamber  10  as described below for an alternate embodiment. 
     The Deposition Process 
     During the deposition process of the present invention, using an apparatus such as described in  FIG. 2 , a process gas comprising a non-reactive species such as Ar, is charged into the vacuum chamber  10  through the gas inlet  26  at a selected flow rate regulated by a mass flow controller (not shown). The chamber pressure is controlled by varying the rate that process gases are pumped through the exhaust outlet  28 . 
     A power source, such as a D.C. power supply  22 , applies a negative voltage to the target  14  with respect to the enclosure wall  24  so as to excite the gas into a plasma state. 
     Ions from the plasma bombard the target  14  and sputter atoms and larger particles of target material from the target  14 . The particles sputtered from the target  14  travel along linear trajectories from the target  14 , and a portion of the particles collide with, and deposit on, the substrate  16 . 
     A conventional magnetron sputtering source employs a rotating magnet  30  above the target  14  to increase the concentration of plasma ions adjacent to the sputtering surface of the target  14 . Rotation of the magnetron  30  during sputtering of the target  14  results in an even erosion profile. 
     The surfaces of the collimator  12  that are perpendicular to the surface of the substrate  16  block particles travelling obliquely to the surface of the substrate  16  as described in U.S. Pat. No. 5,527,438. Thus, the collimator  12  promotes deposition of target particles traveling normal to the surface of the substrate  16 , and such deposition results in columns of deposited material that are easily oriented within the parallel magnetic field maintained at the surface of the substrate. Grounding of the collimator  12  acts as a sink for electrons from the plasma, thus reducing electron bombardment of the substrate, and essentially eliminates interference between the plasma generated by the magnetron  30  and the magnetic field generated by the permanent magnet array  50 . 
     The target  14  comprises a material that retains magnetic properties when deposited in a substantially parallel magnetic field. For deposition of magnetic recording heads, the target preferably consists of an alloy of nickel/iron (NiFe) having from 75 to 85 wt % of Ni. Most preferably the target is formed from Permalloy metal which is an optimum NiFe alloy having 80 wt % Ni. Combinations of magnetic layers can be used as discussed for  FIG. 1 . 
     Preferably, the exposed surfaces of collimator  12  are composed of a material that is non-contaminating to the chamber when exposed to a plasma. Therefore, the collimator  12  is preferably manufactured from the same material as the target  14 . The collimator  12  is supported in the chamber  10  between the substrate  16  and target  14  by conventional means and can be in electrical contact with the chamber walls  24  when both are grounded. The collimator  12  can also be rotated within the chamber  24  if desired to reduce build-up of target material on surfaces that face the target  14 . 
     The collimator  12  provides collimation on a gross scale, i.e., it screens from the stream of target particles passing from the target  14  to the substrate  16  a portion of the target particles which are traveling at highly oblique trajectories with respect to the surface of the substrate  16  (i.e., trajectories at low angles relative to the plane of the substrate surface). 
     An iterative determination of the size and location of the collimator  12 , the optimum substrate and target size and spacing, and the optimal magnetron configuration may be performed through trial and error. However, one skilled in the art could also perform the iterations on the properly programmed computer. 
     Long Throw Sputtering Chamber 
       FIG. 4  is a schematic sectional view of a long throw sputtering chamber that substantially reduces interference with the parallel magnetic field at the surface of the substrate without a collimator. Referring to  FIG. 4 , the long throw sputtering chamber  110  for practicing an embodiment of the invention generally includes the vacuum chamber enclosure wall  124  having the gas inlet  126  and the exhaust outlet  128  connected to an exhaust pump (not shown). The substrate support pedestal  120  is disposed at one end of the chamber  110 , and the sputtering target  114  is mounted to the other end of the chamber  110 . The target  114  is electrically isolated from the enclosure wall  124  by an insulator  118 , and the enclosure wall  124  is preferably grounded, so that a negative voltage may be maintained on the target with respect to the grounded enclosure wall  124 . In operation, the substrate  116  is positioned on the support pedestal  120  at a long throw distance from the target  114  of at least 50 mm, preferably at about 80 to 175 mm. 
     A conventional magnetron sputtering chamber employs the rotating magnet  130  above the target  114  to increase the concentration of plasma ions adjacent to the sputtering surface of the target  114 . The magnetron  130  produces a magnetic field that is separated by distance from a parallel magnetic field maintained at the surface of the substrate by the circular magnet array  150  as described above with reference to  FIG. 3 . The long throw distance facilitates reducing interference with the parallel magnetic field. A grounded collimator (not shown) could be included to further reduce interference as described above. Rotation of the magnetron  130  during sputtering of the target  114  results in an even erosion profile. 
     Method of Depositing Magnetic Films 
     The apparatus of the invention deposits a magnetic film on the substrate  16 ,  116  by sputtering the target  14 ,  114  with a plasma generated adjacent the target, and by maintaining a surface of the substrate  16 ,  116  substantially outside the plasma. The substrate  16 ,  116  is maintained in a magnetic field that is substantially parallel at the substrate surface. The target  14 ,  114  and the parallel magnetic field is separated by distance and/or a grounded collimator to reduce interference with the substantially parallel magnetic field at the surface of the substrate. 
     During deposition of a magnetic film, the chamber pressure is maintained below 15 mTorr, preferably below 5 mTorr, to reduce collision of molecules within the chamber  10  and prevent dispersion of the deposited film. The reduced pressure also results in deposited films having a lower content of the processing gas such as argon. Lower argon content significantly improves the deposited film by reducing the easy axis coercivity of the magnetic film.  FIG. 5  illustrates the effect of chamber pressures ranging from 1 to 20 mTorr on the easy axis coercivity of NiFe magnetic films (80% Ni, 20% Fe) having a thickness ranging from 200 to 1000 Å. Lower argon content also significantly improves the deposited film by increasing the magnetoresistance of the magnetic film.  FIG. 6  illustrates the effect of chamber pressures ranging from 1 mTorr to 20 mTorr on the magnetoresistance of the NiFe magnetic films of  FIG. 5 . 
     Nickel/iron alloys, such as Permalloy metal films, are typically deposited on substrates at a thickness less than about 200 Å for magnetoresistive head applications. The magnetic films are deposited on a non-magnetic substrate such as described for  FIG. 1 . The strength of the second magnetic field for a 4 inch substrate is preferably from 50 to 100 gauss, and such a parallel magnetic field is readily provided by a permanent magnet array having an outside diameter less than 12 inches. The combination of reduced interference and the permanent magnet array as described herein results in a parallel magnetic field at the surface of the substrate that is easily aligned with the substrate with less than 1% dispersion. 
     EXAMPLE 
     The present invention was reduced to practice by placing a permanent magnet array within an ENDURA™ PVD chamber in combination with a Permalloy metal target and a substrate comprising aluminum, titanium, and carbon. The substrate had a diameter of 4 inches and the Permalloy metal target had a diameter of 12 inches. The distance between the target and the substrate was 120 mm during processing. The permanent magnet array was a commercially available Halbach array that had an inside diameter of 9 inches and an outside diameter of 11 inches. 
     The PVD chamber included a magnetron that generates a magnetic field of 30 gauss adjacent the target. D.C. power of 100 W was applied to the target during deposition. 
     The deposited film had excellent magnetic properties as shown in  FIG. 7  indicating that the Halbach array maintain a parallel magnetic field at the surface of the substrate and deposited a highly oriented film. The easy axis hysteresis loop  200  and the hard axis hysteresis loop  210  are well defined in  FIG. 7 , and establish that the deposited film is magnetically oriented. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow.