Abstract:
An apparatus for plating a magnetic film on a substrate includes: a track including a plurality of stopping points along the track; a permanent magnet placed on the track such that the permanent magnet can be moved along the track towards and away from the stopping points; at least one plating tank positioned on the stopping point; and a removable high permeability iron flux concentrator inserted into gaps between the substrate and inside walls of the plating tank, substantially surrounding the substrate and extending around and under the substrate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a division of, and claims priority from, U.S. patent application Ser. No. 11/844,587, filed on Aug. 24, 2007, and incorporated by reference in its entirety herein. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED-RESEARCH OR DEVELOPMENT 
       [0002]    None. 
       INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
       [0003]    Not Applicable. 
       FIELD OF THE INVENTION 
       [0004]    The invention disclosed broadly relates to the field of magnetic film plating and more particularly relates to scalable magnetic film plating. 
       BACKGROUND OF THE INVENTION 
       [0005]    In the semiconductor industry the wafer size on which devices are fabricated has been steadily increasing, which has resulted in a dramatic decrease of cost per unit cell. The maximum size of wafers used in the fabrication of magnetic thin film heads has remained a steady size, between five and six inches in diameter, for many years. One of the key reasons for this is that it is necessary to provide a 1000 oersted (Oe) magnetic field at the center of the wafer during plating and also during annealing to overcome the demagnetizing field in the individual tiny devices and to achieve intrinsic magnetic anisotropy in the deposited magnetic films. The demagnetizing field greatly depends on the size, shape and thickness of the head features. Some assistance in overcoming the demagnetizing field is achieved by plating magnetic films through narrow photo resist frames providing pseudo continuous film but even that is not sufficient when the dimensions of the pattern become very small and at the same time it is necessary to make films relatively thick. The demagnetizing field at such edges, unless the films are laminated by a non-magnetic material, can reach the value of the saturation magnetization of the film and it becomes very difficult to achieve any degree of the intrinsic magnetic anisotropy in the deposited magnetic films. 
         [0006]    Electroplating is typically performed in an electrolytic cell having an anode (positive electrode) and a cathode (negative electrode). The anode can have the same chemical composition as the material being plated, or it may contain only one element of the material being plated. The cathode is usually the object to be electroplated (usually a metal, ceramic, or polymer structure). The anode and cathode are enveloped in an electroplating solution or bath containing plating ions of the metals being plated. In the electroplating process, metallic plating cations fix on the cathode to form a thin layer of metal plating (such as chromium, copper, nickel, iron, silver, and/or cobalt) when an electric current is passed through the solution. The solution is generally a salt aqueous mixture. 
         [0007]    Magnetic sensors and heads on disk drives and tape drives use magnetically anisotropic films formed by electroplating a magnetic alloy under the influence of an orienting magnetic field. The electroplated film exhibits magnetic anisotropy in the plane of the film, the direction of the orienting field applied during deposition becoming the longitudinal, preferred, or easy axis of magnetization in the plated coating; and the orthogonal direction becoming the transverse or hard axis of magnetization. It is desirable for the electrodeposited magnetic film to have a large high frequency magnetic permeability. Such magnetic films have a magnetic anisotropy; directional fields are typically used to switch the device from one direction to another. 
         [0008]    The magnetic field used in electroplating is usually provided by a permanent magnet built around the plating tank so that the plating tank and the cathode holder with the wafer are sitting in the center of the horse shoe-shaped magnet. The cathode holder is generally stainless steel. To maximize the magnitude of the magnetic field the top surface of the wafer is placed at approximately the level of the pole tips of the magnet. 
         [0009]    Using even the highest commercially available permanent magnets it has not been possible to achieve 1000 Oe in the middle of a plating tank capable of accommodating an 8-inch wafer. The magnetic field can be increased to 1000 Oe and beyond only by using an electromagnet. Electromagnetic use has its drawbacks. Electromagnets are much more costly than permanent magnets, much too big (they occupy ten to twenty times the volume of the permanent magnet), and they require such a high current and dissipate so much heat that it is necessary to water cool the magnet. This greatly increases the square foot area of the manufacturing plant. The electromagnets also require a much higher operating cost (cost of high current electricity and of the cooling water). 
         [0010]    This is the key reason why the entire thin film magnetic head industry has used permanent magnets with a maximum wafer size of 6 inches. Electroplating is done in a magnetic field when plating magnetic films such as permalloy. An applied field in the plane of the plated film creates a uniform magnetic easy axis in the film. The magnet gap must be large enough to span the wafer and plating tank. This introduces a major limitation in the field strength and uniformity for magnets of reasonable cost with available hard magnet materials. For electromagnets, large coils are needed. Another drawback with permanent magnets is that the magnets are expensive and the magnetic field interferes with the insertion and removal of the anode, which is usually a magnetic material such Nickel or Cobalt. 
         [0011]    Further processing of the magnetic films by heating the films in the presence of the in-plane field is used to further enhance the magnetic axis uniformity and magnetic permeability of the films. The drawback is that yet another magnet is needed for the annealing station. Existing systems use a magnet in a fixed location for each plating tank and an annealing station where the magnetic materials are entirely external to the plating tank. 
         [0012]    There is a need for a method of fabricating magnetic storage heads to overcome the shortcomings of the prior art. 
       SUMMARY OF THE INVENTION 
       [0013]    Briefly, according to an embodiment of the invention a method for enhancing a magnetic field when plating magnetic film on a substrate includes: loading the substrate into a plating tank; and introducing a conformable magnetic material into the plating tank. The conformable magnetic material acts as a high permeability iron flux concentrator and is inserted into gaps between the substrate and walls of the plating tank, substantially surrounding the substrate and extending around and under the substrate. The method proceeds with insertion of the anode, which is usually ferromagnetic, such as Nickel or Cobalt. The substrate is then electroplated using a permanent magnet surrounding the plating tank, wherein the permanent magnet magnetizes the conformable magnetic material; removing the magnetic anode from the plating tank; removing the electroplated substrate from the plating tank; and removing the conformable magnetic material from the plating tank. 
         [0014]    According to an embodiment of the present invention, a tool for plating a magnetic film on a substrate includes: a track including a plurality of stopping points along the track; a permanent magnet placed on the track such that the permanent magnet can be moved along the track towards and away from the stopping points along the track; at least one plating tank positioned on the stopping point along the track; and a removable high permeability iron flux concentrator inserted into gaps between the substrate and inside walls of the plating tank, substantially surrounding the substrate and extending around and under the substrate. The method can also include a removable electroplating anode. According to another embodiment, the removal of the electroplating anode is facilitated by moving the permanent magnet away from the stopping point where the magnet is positioned close to the anode. 
         [0015]    According to another embodiment of the present invention, a method for plating magnetic film on a substrate includes: mounting a permanent magnet on a track including a plurality of stopping points, wherein the permanent magnet is movable along the track; positioning a first cell on a first stopping point; positioning a second cell on a second stopping point; and moving the permanent magnet along the track to the first and second stopping points wherein the magnet surrounds the first and second cells, respectively, when positioned; and wherein the permanent magnet magnetizes the substrate disposed within the first and second cells. Further, a conformable magnetic material is introduced into the first and second cells, substantially surrounding the substrate. Further, the removal and insertion of a plating anode may be facilitated by repositioning the permanent magnet. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    To describe the foregoing and other exemplary purposes, aspects, and advantages, we use the following detailed description of an exemplary embodiment of the invention with reference to the drawings, in which: 
           [0017]      FIG. 1  is an illustration of soft magnetic poles, according to an embodiment of the present invention; 
           [0018]      FIG. 2  is an illustration of another view of the soft magnetic poles of  FIG. 1 , according to an embodiment of the present invention; 
           [0019]      FIG. 3  shows a first position of the moveable magnet, according to an embodiment of the present invention; 
           [0020]      FIG. 4  shows a second position of the moveable magnet, according to an embodiment of the present invention; 
           [0021]      FIG. 5  shows a third position of the moveable magnet, according to an embodiment of the present invention; 
           [0022]      FIG. 6  is a flow chart of the process for plating a wafer using the moveable magnet, according to an embodiment of the present invention; 
           [0023]      FIG. 7  is a flow chart of the process for annealing the plated wafer, according to an embodiment of the present invention; 
           [0024]      FIG. 8  shows a cut-away perspective drawing of the soft magnetic poles, showing the shaping of the soft magnetic material, according to an embodiment of the present invention; 
           [0025]      FIG. 9  shows the moveable magnet on a track above the plating tanks, according to another embodiment of the present invention; and 
           [0026]      FIG. 10  shows a stationary magnet with the plating tanks and annealing oven positioned on the moveable track, according to another embodiment of the present invention. 
       
    
    
       [0027]    While the invention as claimed can be modified into alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the scope of the present invention. 
       DETAILED DESCRIPTION 
       [0028]    We describe a tool and method for enhancing a magnetic field used in the plating of magnetic film. This tool and method overcomes the shortcomings of the prior art by increasing the magnetic field around a wafer. This in turn enables the use of a larger wafer, with no subsequent loss of magnetic strength as measured in oresteds (Oe). Also by improving the magnetic flux distribution, we achieve better magnetic orientation and magnetic anisotropy, thereby improving the operation of the magnetic heads. The increase in wafer size yields an increase in the number of magnetic heads which can be produced, while at the same time reducing manufacturing costs. The embodiments of the proposed tool and method, as will be described fully herein, can be advantageously used in any process involving the plating of magnetic films where an applied magnetic field is desired during plating, such as tape head manufacturing. For clarity, however, we focus our discussion on wafers in the fabrication of magnetic thin film heads. 
         [0029]    According to one embodiment of the present invention, the magnetic field around a wafer is enhanced by replacing parts of the traditional stainless steel cathode on which the wafer is mounted with soft iron pieces surrounding the wafer. 
         [0030]    These “floating magnetic pole pieces” act as very high permeability iron flux concentrators all around the wafer. Since wafers are round there is space surrounding the wafer to be plated but clear of the mixing paddles or fountains. In addition there is usually space below the mixing paddles. According to this embodiment, the plating magnet still spans the exterior of the plating tank (electrolytic cell) but the magnetic field strength and uniformity around the wafer are enhanced by incorporating these additional magnetic poles between the tank walls and the wafer. 
         [0031]    Shaping the soft iron or other soft magnetic material so that the pieces extend along the width of the entire wafer can double the magnitude of the measured magnetic field in the center of a plating tank (which is the center of the wafer) used to plate 6-inch wafers from 1000 to 2000 Oe. The soft iron is approximately 1.5 inches wide, and 0.5 inches thick. Proper shaping of the soft iron not only enables an improved magnetic flux concentration but it also provides a better uniformity of the magnetic field along the wafer and along the length of the tank. Note that in this example we use iron, but in actuality any conformable magnetic material may be used. 
         [0032]    The iron pieces are said to be “floating” because they are not attached to either the wafer or the tank; they are simply placed around the wafer in the gaps between the wafer and the tank. This allows for the soft iron to be easily introduced into the tank and then subsequently removed. 
         [0033]    Alternatively, according to another embodiment of the present invention, we embed the “floating magnet pole pieces” into the substrate wafer holders. We again use the term “floating” here because they are not attached, merely placed in the aqueous solution of the tank. The pole pieces may also be embedded in the substrate holder. 
         [0034]    Referring now in specific detail to the drawings, and particularly  FIG. 1 , there is illustrated an embodiment according to the present invention wherein the magnetic poles  150  are shaped pieces of soft magnetic material extending around a wafer  108 . The poles  150  are soft magnetic material added between the tank walls and wafer  108 . The poles  150  are magnetized by the external magnet  100 . 
         [0035]      FIG. 1  shows such a magnet and tank-internal soft poles or flux concentrators  150  in a half-section at the midpoint of the magnet as they would appear crosswise relative to a tank. In the complete magnet  100  the parts shown are mirrored around the front (XY) plane. The tank walls are not shown but pass between the black hard magnet components  170  and the internal soft poles  150  shown as the smaller cross-hatched structures surrounding the wafer  108 . The external horseshoe of soft magnet material (diagonal lines)  180  and hard magnet poles (black)  170  make up the external, moveable magnet  100  part of the invention. The wafer  108  lies in the X-Z plane centered on the axis arrows. 
         [0036]    The internal soft poles or flux concentrators  150  extend around the wafer  108  in the plane of the wafer  108  (X, Z) and under the wafer  108  (Y) direction. The desired magnetic field is in the X direction. For an external tank dimension of 12 inches the soft poles  150  in the drawing provide a field enhancement of 30% and a significant improvement in field uniformity over the wafer volume. A plating anode  120  is shown disposed over the substrate  108 . The anode  120  is a removable plate of material made up of the magnetic material to be plated. The anode  120  is not attached to the substrate  108  and must be removed after plating.  FIG. 2  shows a closer view of the tank poles  150  of  FIG. 1 . 
         [0037]    Mathematical modeling of field distribution with the flux concentrators  150  is done to estimate the shape and the position in which the floating soft iron magnet poles or flux concentrators  150  would have to be placed in this commercially built magnet  100  to achieve the desired minimum 1000 Oe field in the center of an 8-inch wafer. The shape of the pole tip or flux concentrators  150  must also be calculated to provide a uniform magnetic field in the wafer area inside the plating tank. 
         [0038]    Referring now to  FIG. 8  there is illustrated a cut-away perspective highlighting the shape and placement of a typical flux concentrator within a plating tank.  FIG. 8  shows the substrate  108  centered in the substrate holder  101 , soft iron pole piece  150 , part of one wall of the plating tank  104 , and one permanent magnet pole  170 . The exact shape of the soft iron flux concentrator  150  is determined by the mathematical modeling just described. As shown in  FIG. 8 , the soft iron pole piece  150  can extend above the substrate  108  (see pole portion  807 ); in the plane of the substrate  108  and into the region left empty by the round shape of the substrate  108  (see pole portion  805 ), and below and under the substrate  108  (see portion  806 ). 
         [0039]    In this illustration the substrate holder  101  is cut away to allow the holder  101  to fit in separately from the soft iron poles  150 . In another implementation, the flux concentrators  150  can be made part of the substrate holder  101 . The flux concentrators  150  can be single pieces or made up of multiple pieces of soft iron assembled. 
         [0040]    This solution enables the creation of a sufficiently large magnetic field inside the plating tank  104  on each side of the wafer  108  to scale the wafer size in fabrication of the tape heads to 8 inch wafers and eventually perhaps to 12 inch wafers. 
         [0041]    The soft iron pole pieces  150 , since they are “soft magnetic material highly permeable flux concentrators,” are used to increase the magnetic field on the surface of the wafer  108 . With proper magnetic flux distribution mathematically modeling the shape, the size and the location of the “floating flux concentrator pole tips” could be used to achieve a very uniform magnetic flux distribution over the entire wafer or to selectively increase the magnetic flux at any part of the surface of the wafer  108  being plated. 
         [0042]    With a much higher magnetic field at the center of the wafer  108  it will be possible to achieve much better magnetic orientation of the deposited magnetic material, better magnetic anisotropy (smaller demagnetizing field at discontinuities) and thereby much better operation of the magnetic heads. 
         [0043]    Moveable Magnet. 
         [0044]    Referring again to  FIG. 1 , in order to facilitate the loading of the iron flux concentrators  150 , and plating anodes  120  another embodiment of the present invention uses a moveable magnet (standard permanent magnets can be used) that exhibits relative movement alternately over and away from the tanks The permanent magnet can be moved over and away from the tanks, or the tanks may be moved under and away from the tank. Large magnetic fields require high forces to move magnetic materials around; this restriction is avoided by moving the magnet away from the tank. 
         [0045]    To describe this, we use an example of magnetic thin film plating of a wafer incorporating a permalloy plating tank, an annealing oven, and a high-moment plating tank. In this exemplary embodiment, the annealing oven is centered between the two plating tanks Note that this embodiment is presented for describing enablement of this tool and should not be construed as a limitation of its configuration. 
         [0046]    All three pieces of equipment and the moveable magnet  100  are placed on one set of rails, or track. This is accomplished in such a way that the magnet  100  can be moved by conventional crank mechanism from the first plating tank, positioned on one end of the rail to the annealing oven (positioned in the center) and then to the second plating tank. In this manner we can use only one magnet to create a magnetic field at a plurality of tanks or stations in different phases of the fabrication process. This approach lowers the cost of fabrication equipment by a considerable amount. 
         [0047]    The moveable magnet  100  is moved along the track away from the plating tank when loading the iron flux concentrating pieces  150  and the nickel anode  120  and then the magnet  100  is moved into place for the plating operation when the cathode holder and the anode are in place. This allows for a very easy introduction of the flux concentrator  150 , anode  120  and substrate holder and substrate  101  into the plating tank and also allows for easy removal. Placing the flux concentrators  150  directly into the tank allows the flux concentrators  150  to wrap around the round shape of the substrate  108  in a way they could not do outside of a rectangular tank. 
         [0048]    In one configuration, the magnet  100  is mounted on a track with a plating tank at each end and an annealing station at the middle. When the magnet is moved away from a tank or station, the magnetic field at the tank or station is removed or reduced so that the substrate and any shaping or field enhancing components (flux concentrators  150 ) can be readily accessed and moved. The cost of the system is reduced since one magnet can be used in conjunction with multiple plating or annealing stations. 
         [0049]    Referring to  FIG. 3  there is shown a first position of the moveable magnet  100  positioned at a first plating station  111 . The magnet  100  is positioned on a magnet track  107 . Note that the track  107  shown here is on the bottom of the tanks In another embodiment the track may be above the tanks The magnet  100  surrounds a permalloy plating tank  104 . Permalloy (Ni 81 Fe 19 ) combines 81% nickel with 19% iron by weight, introduced in the form of a plating anode  120 . Situated in this plating tank  104  is a substrate holder  101  with a substrate  108  positioned in its center. The plating anode  120  can be replaced with anodes of other magnetic materials to plate those magnetic materials. 
         [0050]      FIG. 4  shows the moveable magnet  100  at the annealing station  113 . 
         [0051]    The magnet  100  surrounds an annealing station heater  106 . Within the heater  106  is a substrate holder  102  with a substrate  109 . 
         [0052]      FIG. 5  shows the moveable magnet  100  positioned at the second plating station  112 . The magnet  100  surrounds a plating tank  105 . The high moment plating tank  105  contains a substrate holder  103  with a substrate  110 . 
         [0053]    In another embodiment, the permanent magnet  100  is placed on one track  107 , and the tanks are placed on a separate track, parallel to and underneath the first track. In yet another embodiment, only the permanent magnet  100  is placed on a track  107 . The track  107  may be placed above the tanks rather than below the tanks Other configurations of tanks and ovens are possible within the spirit and scope of the invention. 
         [0054]    Referring to  FIG. 6  there is shown a flow chart of the process for plating using the moveable magnet  100  as previously described. The process begins at step  610  when the substrate  108  and holder  101  are placed in the plating tank  104 . Next, the soft magnetic material  150  is introduced into the tank in step  620 . A plating anode  120  may optionally be placed over the substrate  108 . In an alternate embodiment using the anode  120 , the substrate  108  is placed over the anode  120 ; therefore, the anode  120  is positioned first, then the substrate  108  is placed in the tank  104 . 
         [0055]    In step  630  the magnet  100  is slid along the track  107  until the magnet  100  straddles the tank  104  at the location of the substrate  108 . There can be more than one location for substrates within the tank  104 . Referring back to  FIG. 5  it is shown that the substrate in tank  104  is located in a different position than the substrate in tank  105 . 
         [0056]    In step  640  the film  108  is electroplated using conventional means and in step  650  the magnet  100  is then moved away from the tank  104  along the track  107  so that the magnetic field at the substrate  108  is removed or reduced. Then, in step  660  the pole pieces  150  are removed from the tank  104  and the anode  120  is also removed. Lastly, in step  670  the electroplated film  108  is then removed. By having two or more plating tanks, one tank can be used for plating while the other tank is accessible for maintenance or substrate addition or removal. 
         [0057]    Continuing, the magnet  100  is moved to another tank for the annealing process. Referring to  FIG. 7  there is shown a flow chart of the process for annealing plated films in a field using the moveable magnet  100 . The process begins at step  710  when the substrate  109  with plated film is placed on a heating station  106 . In step  720  the magnet  100  is moved to straddle the heating station  106 . In step  730  the heater  106  is turned on and the plated film  109  experiences a raised temperature while within the magnetic field of the magnet  100  Annealing is a known process, accomplished at temperatures ranging from 120 degrees Celsius to 300 degrees Celsius. 
         [0058]    In step  740  the heater  106  is turned off. Once the heater  106  is turned off the magnet  100  can then be moved away in step  750  so that the magnetic field at the substrate  109  is removed or reduced. Lastly, in step  760  the annealed substrate  110  is removed. 
         [0059]    The substrate  110  can then be moved to another plating station  112  where it is placed in a plating tank  105 . In this embodiment, the tank  105  is a high moment plating tank for subsequent plating of the annealed film  110 . The annealed film  110  is centered on a substrate holder  103 . The process then continues just as described with respect to  FIG. 6 . 
         [0060]      FIG. 9  shows another embodiment wherein the magnet  100  is mounted on a moveable track  907  situated above the plating tanks, rather than beneath the tanks In another embodiment, as shown in  FIG. 10 , the magnet  100  remains stationary and the tanks move along the moveable track  107 . 
         [0061]    This invention allows magnetic storage head manufacturers to move from 6-inch diameter wafers to 8-inch diameter wafers and eventually to 12-inch wafers, each time utilizing the just abandoned fabrication areas by the semiconductor device manufacturers. At the same time with proper mathematical modeling it is possible to achieve magnetic fields on the wafer which can be at least double the magnetic fields used in the industrial plants today. 
         [0062]    Therefore, while there has been described what is presently considered to be the preferred embodiment, it will understood by those skilled in the art that other modifications can be made within the spirit of the invention. The above descriptions of embodiments are not intended to be exhaustive or limiting in scope. The invention, as described above, can be advantageously used in any process involving the plating of magnetic films where an applied magnetic field is desired during plating. The embodiments, as described, were chosen in order to explain the principles of the invention, show its practical application, and enable those with ordinary skill in the art to understand how to make and use the invention. It should be understood that the invention is not limited to the embodiments described above, but rather should be interpreted within the full meaning and scope of the appended claims.