Abstract:
Read elements and associated methods of fabrication are disclosed. During fabrication of the read element, and more particularly, the fabrication of the hard bias magnets, a non-magnetic sacrificial layer is deposited on top of the hard bias material. When a CMP process is subsequently performed, the sacrificial layer is polished instead of the hard bias material. The thicknesses of the hard bias magnets are not affected by the CMP process, but are rather defined by the deposition process of the hard bias material. As a result, the variations in the CMP process will not negatively affect the magnetic properties of the hard bias magnets so that they are able to provide substantially uniform effective magnetic fields to bias the free layer of the magnetoresistance (MR) sensor of the read element.

Description:
BACKGROUND OF THE INVENTION  
       [0001]    1. Field of the Invention 
         [0002]    The invention is related to the field of magnetic recording heads and, in particular, to using a sacrificial layer that protects hard bias magnets during a chemical mechanical polishing (CMP) process. 
         [0003]    2. Statement of the Problem 
         [0004]    Many computer systems use magnetic disk drives for mass storage of information. Magnetic disk drives typically include one or more magnetic recording heads (sometimes referred to as sliders) that include read elements and write elements. An actuator/suspension arm holds the recording head above a magnetic disk. When the magnetic disk rotates, an air flow generated by the rotation of the magnetic disk causes an air bearing surface (ABS) side of the recording head to fly a particular height above the magnetic disk. The height depends on the shape of the ABS. As the recording head rides on the air bearing, an actuator moves the actuator/suspension arm to position the read element and the write element over selected tracks of the magnetic disk. 
         [0005]    To read data from the magnetic disk, transitions on a track of the magnetic disk emit magnetic fields. As the read element passes over the transitions, the magnetic fields of the transitions modulate the resistance of the read element. The change in resistance of the read element is detected by passing a sense current through the read element, and then measuring the change in bias voltage across the read element to generate a read signal. The resulting read signal is used to recover the data encoded on the track of the magnetic disk. 
         [0006]    The most common types of read elements are magnetoresistive (MR) read elements. A typical MR read element includes a MR sensor fabricated between a pair of shields. The MR sensor may be a Giant MR (GMR) sensor, a Tunneling MR (TMR) sensor, or another type of MR sensor. A GMR sensor implementing two layers of ferromagnetic material (e.g., NiFe) separated by a layer of nonmagnetic material (e.g., Cu) is generally referred to as a spin valve (SV) sensor. A simple-pinned SV sensor generally includes an antiferromagnetic (AFM) pinning layer, a ferromagnetic pinned layer, a spacer layer, and a ferromagnetic free layer. The pinned layer has its magnetization typically fixed (pinned) by exchange coupling with the AFM pinning layer. The pinning layer generally fixes the magnetic moment of the pinned layer perpendicular to the ABS of the recording head. The magnetization of the free layer is not fixed and is free to rotate in response to the magnetic field from the magnetic disk. The magnetic moment of the free layer is free to rotate upwardly and downwardly with respect to the ABS in response to positive and negative magnetic fields from the rotating magnetic disk. The free layer is separated from the pinned layer by the nonmagnetic spacer layer. 
         [0007]    A TMR sensor comprises first and second ferromagnetic layers separated by a thin, electrically insulating, tunnel barrier layer. The tunnel barrier layer is sufficiently thin, that quantum-mechanical tunneling of charge carriers occurs between the ferromagnetic layers. The tunneling process is electron spin dependent, which means that the tunneling current across the junction depends on the spin-dependent electronic properties of the ferromagnetic materials and is a function of the relative orientation of the magnetic moments, or magnetization directions, of the two ferromagnetic layers. In the TMR sensor, the ferromagnetic pinned layer has its magnetic moment pinned, while ferromagnetic free layer has its magnetic moment free to rotate in response to an external magnetic field from the magnetic disk. When a sense current is applied, the resistance of the TMR sensor is a function of the tunneling current across the insulating layer between the ferromagnetic layers. The tunneling current flows perpendicularly through the tunnel barrier layer, and depends on the relative magnetization directions of the two ferromagnetic layers. A change of direction of magnetization of the free layer causes a change in resistance of the TMR, which is reflected in voltage across the TMR sensor. 
         [0008]    Designers of read elements use different techniques to stabilize the magnetic moment of the free layer. Although the magnetic moment of the free layer is free to rotate upwardly or downwardly with respect to the ABS in response to positive and negative magnetic fields from the magnetic disk, it is important to longitudinally bias the free layer (biased parallel to the ABS and parallel to the major planes of the layers of the read element) to avoid unwanted movement or jitter of the magnetic moment of the free layer. Unwanted movement of the magnetic moment adds noise and unwanted frequencies to the signals read from the read element. 
         [0009]    One method used to stabilize the magnetic moment of the free layer is to bias the free layer using first and second hard bias magnets that are adjacent to the sides of the MR sensor. Examples of hard bias magnets are CoPt or CoPtCr. The magnetic moments of the hard bias magnets stabilize the magnetic moment of the free layer of the MR sensor. 
         [0010]    To fabricate a read element with hard bias magnets, MR material is deposited on a first shield, and a first photoresist is patterned on the MR material to define a stripe height of an MR sensor. An ion milling process is then performed to remove the portions of MR material exposed by the first photoresist, and refill material is deposited. The first photoresist is then removed. Next, a chemical mechanical polishing (CMP) stop layer is deposited on the top surface of the MR material and the refill material. The CMP stop layer may be a diamond-like carbon (DLC) or another type of material. A bottom anti-reflective coating (BARC) layer is then deposited on the CMP stop layer, and a second photoresist is patterned on the BARC layer. The second photoresist is used to define the track width of the MR sensor. A reactive ion etching (RIE) process is then performed to remove the BARC layer and the CMP stop layer exposed by the second photoresist. An ion milling process is then performed to remove the portions of the MR material and the refill material exposed by the second photoresist. After the milling process, the stripe height and track width of the MR sensor is defined. 
         [0011]    To form the hard bias magnets on either side of the MR sensor, a thin layer of insulation material is deposited. Next, hard bias material, including one or more seed layers and magnetic material, for the hard bias magnets is deposited. The hard bias material is typically deposited so that the top surface of the hard bias material is above the top surface of the CMP stop layer. A CMP process is then performed down to the CMP stop layer to planarize the top surface of the layers. The CMP process removes the second photoresist, and also removes the hard bias material that extends above the CMP stop layer. Thus, the CMP process defines the final thickness of the hard bias magnets. A second shield may then be deposited to form the read element. 
         [0012]    When the thicknesses of the hard bias magnets on each side of the MR sensor are defined with the CMP process, the hard bias magnets on each side of the MR sensor may unfortunately have non-uniform thicknesses due to variations in the CMP process. The thickness variations may be between magnets on each side of the MR sensor, or between magnets on different read elements. Also, the top surfaces of the hard bias magnets on each side of the MR sensor may not be planar. When the hard bias magnets on each side of the MR sensor have non-uniform thicknesses and differently-shaped top surfaces, the hard bias magnets unfortunately have different effective magnetic fields. Thus, the hard bias magnets do not uniformly bias the magnetic moment of the free layer. 
         [0013]    It would therefore be desirable to define the thickness of hard bias magnets in a different way. 
       SUMMARY  
       [0014]    Embodiments of the invention solve the above and other related problems by depositing a non-magnetic sacrificial layer on top of the hard bias material during fabrication of the read element. The CMP process then polishes the sacrificial layer instead of the hard bias material. The thicknesses of the hard bias magnets are not affected by the CMP process, but are rather defined by the deposition process of the hard bias material. As a result, variations in the CMP process will not negatively affect the magnetic properties of the hard bias magnets so that they are able to provide substantially uniform effective magnetic fields to bias the free layer of the MR sensor. This advantageously leads to improved stability in the read element. 
         [0015]    One embodiment of the invention comprises a method of fabricating a read element of a magnetic recording head. The method includes forming a magnetoresistance (MR) sensor on a first shield using a photoresist to define the track width of the MR sensor. The method further includes depositing an insulating layer on the photoresist and side regions of the MR sensor, and depositing hard bias material on the insulating layer. The method further includes depositing a non-magnetic sacrificial layer on the hard bias material. The method further includes performing a chemical mechanical polishing (CMP) process which removes the photoresist and planarizes the top surface of the sacrificial layer. The result of the method is that the sacrificial layer is polished during the CMP process, and not the hard bias material. Thus, the thicknesses of the hard bias magnets are not affected by the CMP process. 
         [0016]    The invention may include other exemplary embodiments described below. 
     
    
     
       DESCRIPTION OF THE DRAWINGS  
         [0017]    The same reference number represents the same element or same type of element on all drawings. 
           [0018]      FIG. 1  is a flow chart illustrating a method of fabricating a read element of a magnetic recording head in an exemplary embodiment of the invention. 
           [0019]      FIG. 2  is a cross-sectional view of a read element with a first shield formed according to the method of  FIG. 1 . 
           [0020]      FIG. 3  is a cross-sectional view of a read element with MR material deposited according to the method of  FIG. 1 . 
           [0021]      FIG. 4  is a cross-sectional view of a read element with a first photoresist patterned according to the method of  FIG. 1 . 
           [0022]      FIG. 5  is a cross-sectional view of a read element after an ion milling process of the method of  FIG. 1 . 
           [0023]      FIG. 6  is a cross-sectional view of a read element with refill material deposited according to the method of  FIG. 1 . 
           [0024]      FIG. 7  is a cross-sectional view of a read element with a first photoresist removed according to the method of  FIG. 1 . 
           [0025]      FIG. 8  is a cross-sectional view of a read element with a CMP stop layer deposited according to the method of  FIG. 1 . 
           [0026]      FIG. 9  is a cross-sectional view of a read element with a BARC layer deposited according to the method of  FIG. 1 . 
           [0027]      FIG. 10  is a cross-sectional view of a read element with a second photoresist patterned according to the method of  FIG. 1 . 
           [0028]      FIG. 11  is a cross-sectional view of a read element after a RIE process of the method of  FIG. 1 . 
           [0029]      FIG. 12  is a cross-sectional view of a read element after an ion milling process of the method of  FIG. 1 . 
           [0030]      FIG. 13  is a cross-sectional view of a read element with an insulation layer deposited according to the method of  FIG. 1 . 
           [0031]      FIG. 14  is a cross-sectional view of a read element with hard bias material deposited according to the method of  FIG. 1 . 
           [0032]      FIG. 15  is a cross-sectional view of a read element with a sacrificial layer deposited according to the method of  FIG. 1 . 
           [0033]      FIG. 16  is a cross-sectional view of a read element after a CMP process of the method of  FIG. 1 . 
           [0034]      FIG. 17  is a cross-sectional view of a read element after a RIE process of the method of  FIG. 1 . 
           [0035]      FIG. 18  is a cross-sectional view of a read element with a second shield formed according to the method of  FIG. 1 . 
           [0036]      FIG. 19  illustrates a magnetic disk drive system in an exemplary embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0037]      FIGS. 1-19  and the following description depict specific exemplary embodiments of the invention to teach those skilled in the art how to make and use the invention. For the purpose of teaching inventive principles, some conventional aspects of the invention have been simplified or omitted. Those skilled in the art will appreciate variations from these embodiments that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific embodiments described below, but only by the claims and their equivalents. 
         [0038]      FIG. 1  is a flow chart illustrating a method  100  of fabricating a read element of a magnetic recording head in an exemplary embodiment of the invention.  FIGS. 2-18  illustrate the results of the steps of method  100  to fabricate a read element  200  in exemplary embodiments of the invention. Method  100  is just one example of how to fabricate a read element, as other methods may be performed in other embodiments to fabricate read element  200 . 
         [0039]    Step  102  comprises forming a first shield  202  (see  FIG. 2 ).  FIG. 2  is a cross-sectional view of read element  200  with first shield  202  formed according to step  102 . First shield  202  may be formed by depositing electrically conductive material, such as NiFe, full-film on a substrate (not shown) and plagiarizing the top surface of the conductive material. 
         [0040]    Step  104  of  FIG. 1  comprises depositing magnetoresistance (MR) material on the first shield  202 . Depositing MR material is a multi-layer deposition process for depositing a pinning layer, a pinned layer, a spacer/barrier layer, a free layer, etc.  FIG. 3  is a cross-sectional view of read element  200  with MR material  302  deposited according to step  104 . 
         [0041]    Step  106  of  FIG. 1  comprises patterning a first photoresist on MR material  302  to define a stripe height of an MR sensor.  FIG. 4  is a cross-sectional view of read element  200  with first photoresist  402  patterned according to step  106 . Step  108  of  FIG. 1  comprises performing an ion milling process, or another type of removal process, to remove the MR material  302  exposed by photoresist  402 .  FIG. 5  is a cross-sectional view of read element  200  after the ion milling process of step  108 . Step  110  of  FIG. 1  comprises depositing refill material. Refill material comprises some type of insulating material, such as alumina.  FIG. 6  is a cross-sectional view of read element  200  with refill material  602  deposited according to step  110 . Step  112  of  FIG. 1  comprises removing the first photoresist  402 . Photoresist  402  may be removed with a Chemical Mechanical Polishing (CMP) assisted lift-off process.  FIG. 7  is a cross-sectional view of read element  200  with photoresist  402  removed according to step  112 . The removal of photoresist  402  also removes the refill material  602  deposited on top of photoresist  402 , which exposes MR material  302 . 
         [0042]    Step  114  of  FIG. 1  comprises depositing a CMP stop layer on the top surface of the MR material  302  and the refill material  602 . The CMP stop layer may be comprised of a diamond-like carbon (DLC) material or another type of material.  FIG. 8  is a cross-sectional view of read element  200  with CMP stop layer  802  deposited according to step  114 . Step  116  of  FIG. 1  comprises depositing a bottom anti-reflective coating (BARC) layer on the CMP stop layer  802 . The BARC layer may be comprised of DURIMIDE® or another type of material.  FIG. 9  is a cross-sectional view of read element  200  with BARC layer  902  deposited according to step  116 . Step  118  of  FIG. 1  comprises patterning a second photoresist on the BARC layer  902 .  FIG. 10  is a cross-sectional view of read element  200  with a second photoresist  1002  patterned according to step  118 . The second photoresist  1002  is patterned with openings that are used to define the track width of the MR sensor. 
         [0043]    Step  120  of  FIG. 1  comprises performing a reactive ion etching (RIE) process to remove the BARC layer  902  and the CMP stop layer  802  exposed by the second photoresist  1002 .  FIG. 11  is a cross-sectional view of read element  200  after the RIE process of step  120 . Step  122  of  FIG. 1  comprises performing an ion milling process, or another type of removal process, to remove the MR material  302  exposed by photoresist  1002 .  FIG. 12  is a cross-sectional view of read element  200  after the ion milling process of step  122 . After the ion milling process, the MR sensor  1202  is defined in read element  200  from the MR material  302 . The milling process also removes the second photoresist  1002 . 
         [0044]    Step  124  of  FIG. 1  comprises depositing an insulation layer on the second photoresist  1002  and on side regions of MR sensor  1202 .  FIG. 13  is a cross-sectional view of read element  200  with insulation layer  1302  deposited according to step  124 . Insulation layer  1302  may comprise an alumina material that is formed using an atomic layer deposition (ALD) process. Insulating layer  1302  may be deposited to have a thickness less than about 80 Å (e.g., in the range of 20 Å to 80 Å). 
         [0045]    Step  126  of  FIG. 1  comprises depositing hard bias material on the insulation layer  1302 . The hard bias material is used to form hard bias magnets on side regions of MR sensor  1202 .  FIG. 14  is a cross-sectional view of read element  200  with hard bias material  1402  deposited according to step  126 . The hard bias material  1402  is used to longitudinally bias a free layer (not shown) in MR element  1202 . The hard bias material  1402  may be deposited in step  126  by depositing multiple layers of material. For instance, a first seed layer of NiTa or a similar material may be deposited, with a second seed layer of a non-magnetic Cr alloy (e.g., CrMo) deposited on the first seed layer. The hard bias magnetic layer of a magnetic material (e.g., CoPt or CoPtCr) may then be deposited on the seed layers. The hard bias material may be formed with other materials in other embodiments. 
         [0046]    In step  126 , the hard bias material  1402  is deposited to a threshold thickness so that a height of the top surface of the hard bias material  1402  is less than the height of CMP stop layer  802 . In other words, the threshold thickness of the hard bias material  1402  should be such that the top surface of the hard bias material  1402  should be below the CMP stop layer  802  so that a subsequently-performed CMP process does not polish the top surface of the hard bias material  1402 . 
         [0047]    Step  128  of  FIG. 1  comprises depositing a sacrificial layer on the hard bias material  1402 .  FIG. 15  is a cross-sectional view of read element  200  with sacrificial layer  1502  deposited according to step  128 . Sacrificial layer  1502  is formed from any material that has a good polishing rate. Sacrificial layer  1502  may be formed with a material that is already used in the read element  200  so that a new material does not need to be introduced into the fabrication stations. For example, Cr or CrMo may be used as sacrificial layer  1502  in addition to being used as a seed layer for the hard bias magnets. 
         [0048]    Step  130  of  FIG. 1  comprises performing a CMP process down to CMP stop layer  802 .  FIG. 16  is a cross-sectional view of read element  200  after the CMP process of step  130 . The CMP process removes the BARC layer  902  and planarizes the top surface of sacrificial layer  1502 . After the CMP process, hard bias magnets  1601 - 1602  are formed on each side of MR sensor  1202  from the hard bias material  1502 . 
         [0049]    During CMP, the sacrificial layer  1502  is in direct contact with the CMP pads, and not the hard bias material  1402 . Therefore, the thickness of the hard bias magnets  1601 - 1602  is defined by the deposition process of step  126 , and is not defined by the CMP process of step  130 . The CMP process only reduces the thickness of the sacrificial layer  1502 , and does not reduce the thickness of hard bias magnets  1601 - 1602 . Any variations in the CMP process only affect the sacrificial layer  1502  and do not affect the hard bias magnets  1601 - 1602 . As a result, the magnetic performance of the hard bias magnets  1601 - 1602  is not affected by the CMP process. The hard bias magnets  1601 - 1602  on each side of MR sensor  1202  will thus have substantially uniform effective magnetic fields, which advantageously lead to improved stability in read element  200 . 
         [0050]    Step  132  of  FIG. 1  comprises performing a reactive ion etching (RIE) process to remove the CMP stop layer  802 .  FIG. 17  is a cross-sectional view of read element  200  after the RIE process of step  132 . Step  134  of  FIG. 1  comprises forming a second shield.  FIG. 18  is a cross-sectional view of read element  200  with second shield  1802  formed according to step  134 .  FIG. 18  thus illustrates a completed read element  200  fabricated according to method  100 . Read element  200  may comprise a GMR element, a TMR element, or CPP GMR element. 
         [0051]    Read element  200  as illustrated in  FIG. 18  may be implemented in a magnetic disk drive system.  FIG. 19  illustrates a magnetic disk drive system  1900  in an exemplary embodiment of the invention. Magnetic disk drive system  1900  includes a spindle  1902 , a magnetic recording disk  1904 , a motor controller  1906 , an actuator  1908 , an actuator/suspension arm  1910 , and a recording head  1914 . Spindle  1902  supports and rotates magnetic recording disk  1904  in the direction indicated by the arrow. A spindle motor (not shown) rotates spindle  1902  according to control signals from motor controller  1906 . Recording head  1914  is supported by actuator/suspension arm  1910 . Actuator/suspension arm  1910  is connected to actuator  1908  that is configured to rotate in order to position recording head  1914  over a desired track of magnetic recording disk  1904 . Magnetic disk drive system  1900  may include other devices, components, or systems not shown in  FIG. 19 . For instance, a plurality of magnetic disks, actuators, actuator/suspension arms, and recording heads may be used. 
         [0052]    When magnetic recording disk  1904  rotates, an air flow generated by the rotation of magnetic disk  1904  causes an air bearing surface (ABS) of recording head  1914  to ride on a cushion of air at a particular height above magnetic disk  1904 . The height depends on the shape of the ABS. As recording head  1914  rides on the cushion of air, actuator  1908  moves actuator/suspension arm  1910  to position a read element (not shown) and a write element (not shown) in recording head  1914  over selected tracks of magnetic recording disk  1904 . The read element in recording head  1914  may comprise a read element  200  (see  FIG. 18 ) as described herein in the above FIGS. 
         [0053]    Although specific embodiments were described herein, the scope of the invention is not limited to those specific embodiments. The scope of the invention is defined by the following claims and any equivalents thereof.