Abstract:
A magnetic head including a magnetoresistive junction and an oxide layer. The magnetoresistive junction includes a pinned layer, a free layer, and a barrier layer residing between the pinned and free layer. The magnetoresistive junction includes at least one side having a smooth profile. The oxide layer is on the at least one side. The oxide layer is less than one nanometer thick at the free layer.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 12/147,450, filed on Jun. 26, 2008, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
       FIG. 1  depicts a conventional magnetoresistive transducer  1  including a conventional magnetoresistive junction  10 . For clarity,  FIG. 1  is not drawn to scale. Magnetoresistive junctions  10 , such as tunneling magnetoresistive (TMR) junctions, are used as read sensors in the conventional read transducer  1 . Typically, conventional magnetoresistive junctions are formed by blanket depositing the layers for the conventional magnetoresistive junctions. This stack of layers typically includes layers for pinning layer  12  such as an antiferromagnetic (AFM) layer, a magnetic pinned layer  14 , a nonmagnetic spacer layer  16 , and a magnetic free layer  18 . Other layers (not shown) might also be included in the magnetoresistive junction. For a conventional TMR junction  10 , the nonmagnetic spacer layer  16  is a tunneling barrier layer. The barrier layer  16  is typically an insulator, for example aluminum oxide. After formation of the stack, a mask (not shown) is provided. The mask is typically a single layer photoresist mask with no undercut. The mask substantially covers the portion of the stack which is to become the conventional magnetoresistive junction  10 . A remaining portion of the layers in the stack are then removed to define the conventional magnetoresistive junction  10 . In such conventional methods, ion milling is the prevailing mechanism for defining the conventional magnetoresistive junction  10 . 
     A single milling angle, φ1, is typically selected for defining the conventional magnetoresistive junction  10 . This milling angle is typically at least five degrees and not more than thirty degrees from normal to the surface of the transducer. The single-angle milling proceeds until the stack has been completely milled through. Thus, the conventional magnetoresistive junction  10  is substantially defined. Because this single-angle ion milling often leads to redeposition of removed material on the sides of the conventional junction  10  and mask, a second, cleanup ion mill may be performed. This second ion mill is typically short in duration and performed at a high angle milling angle, φ2. For example, the angle is typically greater than sixty degrees from normal to the surface of the read transducer. 
     Although the conventional ion milling may define the conventional magnetoresistive junction  10 , there are drawbacks. Ion milling may cause damage to the layers in a stack, particularly to oxide layers. Thus, the first, single-angle ion mill may damage the barrier layer  16  when the conventional magnetoresistive junction  10  is defined. This damage to the barrier layer  16  may adversely affect performance of the magnetoresistive junction  10 . In addition, if the redeposition is not cleaned by the second ion milling, then metallic redeposition across the barrier layer  16  may result in shorting of the magnetoresistive junction  10 . However, if the redeposition is cleaned, then the additional ion mill may further damage the barrier layer  16 . 
     In addition, the damage due to ion milling may vary based on junction angle, θ, of the magnetoresistive junction  10  as well as on the milling angle, φ. The ion milling damage to the barrier layer  16  of the conventional magnetoresistive junction  10  occurs when the junction width is close to its final value. This is because portions of the stack damaged far from the final width of the conventional magnetoresistive junction  10  are removed during ion milling. As a result, ion milling damage is generally smaller for a shallow magnetoresistive junction (small junction angle θ and large milling angle φ) than for a steep magnetoresistive junction (large junction angle θ and small milling angle φ). This is because the shallow junction  10  is typically milled using a high milling angle φ1. As a result, the junction width for a shallow magnetoresistive junction  10  reaches its final value only when the single-angle milling comes towards its end. In contrast, for a larger junction angle θ formed using a small milling angle φ1, the width quickly gets close to its final value. As a result, the barrier layer  16  is exposed to more milling during the single-angle mill and experiences greater damage. Thus, a conventional magnetoresistive junction that has a steep (large) junction angle and/or which is formed using a small milling angle is more likely to be damaged during ion milling that defines the junction. 
     The conventional ion mill process may also create an undesirable junction profile. The single-angle ion mill or the single-angle ion mill in combination with the second ion mill may result in a kink  19 , or step, at the barrier layer  16 . This profile is due to the redeposition during the single-angle ion mill and different milling rates of the stack layers. For example, the barrier layer  16  typically mills at a different rate than the pinned layer  14  or free layer  18 . Consequently, especially for a shallow junction angle, the kink  19  may occur. This junction profile with a kink  19  at the barrier layer  16  is undesirable because it adversely affects biasing of the magnetoresistive junction  10  by the hard bias structure (not shown). Consequently, performance of the read transducer  10  may be adversely affected. 
     Further, the trend in magnetic recording is to higher densities and, therefore, smaller junction widths. For example, current ultra-high density magnetic recording of approximately five hundred GB/in 2  or more utilizes a TMR junction  10  having a width of not more than fifty nanometers. The junction width is desired not only to be small, but to have limited variations in order to maintain performance. Using the conventional single-angle ion milling, the junction width is primarily determined by the width of the mask used during ion milling. This is generally true whether or not the second ion mill is performed. At higher densities, the photolithography utilized to repeatably obtain a mask having a small width with limited variations may be difficult to achieve. Consequently, fabrication of the conventional magnetoresistive junction  10  may be more problematic. 
     There are conventional mechanisms for accounting for ion mill induced damage. Damage caused by the single angle ion mill that defines the junction and the second, cleanup ion mill may be repaired by an oxidation. However, such an oxidation may result in a relatively thick oxidation layer on the sides of the conventional magnetoresistive junction  10 . Consequently, biasing of the magnetoresistive junction using a hard bias layer (not shown in  FIG. 1 ) may be adversely affected. 
     Accordingly, what is needed is a system and method for providing an improved magnetoresistive junction. 
     BRIEF SUMMARY OF THE INVENTION 
     A method and system define a magnetoresistive junction in a magnetic recording transducer. The method and system include performing a first mill at a first angle from a normal to the surface of the magnetic recording transducer. A second mill is performed at a second angle from the normal to the surface. The second angle is larger than the first angle. A third mill is performed at a third angle from the normal to the surface. The third angle is not larger than the first angle. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  depicts a conventional magnetic read transducer. 
         FIG. 2  is a flow chart of an exemplary embodiment of a method for defining a junction. 
         FIG. 3  depicts another exemplary embodiment of a method for defining a junction. 
         FIGS. 4-8  depict an exemplary embodiment of a magnetoresistive junction during fabrication. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 2  is a flow chart of an exemplary embodiment of a method  100  for defining a magnetoresistive junction. For simplicity, some steps may be omitted. The magnetoresistive junction may be part of a read transducer (not shown in  FIG. 1 ). The read transducer may be part of a merged head that also includes a write transducer (not shown in  FIG. 1 ) and resides on a slider (not shown in  FIG. 1 ). The method  100  also may commence after formation of other structures of the read and/or write transducer. The method  100  is also described in the context of providing a single magnetoresistive junction. However, the method  100  may be used to fabricate multiple magnetoresistive junctions at substantially the same time. The method  100  is also described in the context of particular layers. However, in some embodiments, such layers may include sub-layer(s) and the magnetoresistive junction may include additional layers. For example, a free or pinned layer may be a synthetic layer including multiple ferromagnetic layers separated by nonmagnetic spacer layers. Similarly, the magnetoresistive junction may be a TMR junction. The method  100  commences after formation of a stack of layers for the magnetoresistive junction is formed. In one embodiment, these layers are formed on a shield. In one embodiment, the stack includes at least a pinning layer such as an AFM layer, a magnetic pinned layer, a nonmagnetic spacer layer that may be a barrier layer, a free layer, and optional seed and/or capping layer(s). The method  100  also begins after a mask has been formed on the stack. The mask is used to cover the portion of the stack from which the magnetoresistive junction is formed. 
     A first mill is performed at a first angle from normal to the surface of the read transducer, via step  102 . Thus, for an ion mill performed in step  102 , the ions are incident on the magnetoresistive stack at the first angle from the normal. In one embodiment, the first angle is at least twelve degrees and not more than thirty degrees from normal. In one such embodiment, the first angle is at least seventeen degrees and not more than twenty-five degrees from normal. In one embodiment, the first mill is terminated after at least a portion of the junction including the barrier layer is defined. Thus, the first mill exposes at least the free layer and the barrier layer in a TMR junction in which the pinned layer is closer to the underlying substrate. In one such embodiment, the first ion mill is terminated after the layer immediately below the barrier layer is defined. Stated differently, the first mill would be terminated before another portion of the magnetoresistive junction including the layer immediately below the barrier layer is completely defined. In one embodiment, therefore, the first mill may be terminated before the pinned layer is milled through and this portion of the junction completely defined. 
     After termination of the first mill, a second mill is performed at a second angle from normal to the surface of the read transducer, via step  104 . For an ion mill performed in step  104 , the ions are incident on the magnetoresistive stack at the second angle from the normal. This second angle is greater than the first angle. In one embodiment the second angle is at least sixty degrees and not more than eighty degrees. In one such embodiment, the second angle is at least seventy degrees from normal. In one embodiment, the second mill is terminated before the junction is completely defined. Thus, in such an embodiment, the second mill is terminated before the pinning layer is completely milled through. 
     A third mill is performed at a third angle from normal to the surface of the read transducer after termination of the second mill, via step  106 . Thus, for an ion mill performed in step  106 , the ions are incident on the magnetoresistive stack at the third angle from the normal. The third angle is not larger than the first angle. In one embodiment, the third angle is smaller than the first angle. In one embodiment, the third angle is not more than twelve degrees. In one such embodiment, the third angle is at least three degrees and not more than nine degrees from normal. In one embodiment, the third mill is terminated after the magnetoresistive junction is completely defined. 
     Using the method  100 , the magnetoresistive junction may be defined. Moreover, the magnetoresistive junction, particularly the barrier layer, may exhibit less damage. The first mill may be performed at a relatively large angle. The second mill is performed at an even larger angle. As described above, a larger angle from normal results in less damage to the junction. Using the method  100 , therefore, less damage may be done to the junction while a significant portion of the junction is being defined. For example, in one embodiment, at least the free and barrier layers are defined substantially defined in the first and second mills. Thus, these layers may exhibit less damage due to ion milling. Further, the second mill may be performed at a sufficiently high angle to remove redeposition that has built up during the first mill. Thus, less damage and less redeposition may be result in the final device. Because less damage may be done during definition of the magnetoresistive junction, oxidation steps meant to repair such damage may be skipped or reduced in strength. For example, a natural oxidation instead of a plasma oxidation may be sufficient. Consequently, processing may be simplified and thick oxide layers at the sides of the junction may be reduced or avoided. Furthermore, the third mill may be performed at a lower angle from normal to the surface. Although this third mill may be more likely to damage the magnetoresistive junction, it may be performed for a relatively short time. This is because the first two mills have already defined a significant portion of the junction. The third mill allows the junction angle and the width for the magnetoresistive junction to be tailored substantially as desired. In particular, a steeper junction may be achieved. Further, the width of the magnetoresistive junction may be adjusted in the second mill without reducing the size of the mask used in defining the junction. As a result, photolithography parameters may be relaxed. Fabrication may, therefore, be simplified. 
       FIG. 3  depicts another exemplary embodiment of a method  150  for defining a junction. For simplicity, some steps may be omitted.  FIGS. 4-8  depict an exemplary embodiment of a magnetoresistive junction that is part of a read transducer  200  during fabrication.  FIGS. 4-8  are not drawn to scale. The method  150  is described in the context of the read transducer  200 . Referring to  FIGS. 3-8 , the read transducer  200  may be part of a merged head that also includes a write transducer (not shown in  FIGS. 4-8 ) and resides on a slider (not shown in  FIGS. 4-8 ). The read transducer also includes a shield  202 . The method  150  also may commence after formation of other structures of the read and/or write transducer. The method  150  is also described in the context of providing a single magnetoresistive junction. However, the method  150  may be used to fabricate multiple magnetoresistive junctions at substantially the same time. 
       FIG. 4  depicts the read transducer  200  before the method  150  commences. Thus, a stack  210  of layers for the magnetoresistive junction is shown. In the embodiment shown, these layers are formed on the shield  202 . The stack includes at least a pinning layer such as an AFM layer  222 , a magnetic pinned layer  224 , a nonmagnetic spacer layer that may be a barrier layer  226 , a free layer  228 , and optional seed and/or capping layer(s) (not shown). The stack  210  shown includes particular layers. However, in some embodiments, such layers may include sub-layer(s) and the stack  210  may include additional layers. For example, a free layer  228  and/or pinned layer  224  may be a synthetic layer including multiple ferromagnetic layers separated by nonmagnetic spacer layers. Similarly, the magnetoresistive junction formed from the stack  210  may be a TMR junction. Alternatively, a conductive spacer layer might be used. Also shown in  FIG. 4  is a mask  204  formed on the stack  210 . The mask  204  is used to cover the portion of the stack  210  from which the magnetoresistive junction is formed. In one embodiment, the mask  204  is a single layer photoresist mask with no undercut. 
     A first ion mill is performed at a first angle, Φ1 of at least twelve and not more than thirty degrees from normal to the surface of the read transducer, via step  152 . In one embodiment, the first angle is at least seventeen degrees and not more than twenty-five degrees from normal. Also in step  152 , the first mill is terminated after at least a portion of the junction including the barrier layer  224  is defined but before the pinned layer  222  has been completely milled through.  FIG. 5  depicts the read transducer  200  during step  152 . Thus, the ions are incident on the magnetoresistive stack  210 ′ at the first angle, Φ1, from the normal. In addition, free layer  228 ′ and barrier layer  226 ′ have been substantially defined from the stack  210 ′. A portion of the pinned layer  224 ′ has also been defined. However, a portion of the pinned layer  224 ′ remains unmilled. In addition, redeposition  230  has built up on the mask  204 . Although not specifically shown, redeposition may also reside on the portion of the stack  210 ′. 
     After termination of the first ion mill, a second ion mill is performed at a second angle of at least sixty degrees from normal to the surface of the magnetoresistive stack  210 ′, via step  154 . In one such embodiment, the second angle is at least seventy degrees and not more than eighty degrees from normal. Also in step  154 , the second mill is terminated before the pinning layer  222  is completely milled through.  FIG. 6  depicts the read transducer  200  during step  154 . Definition of the magnetoresistive stack  210 ″ has continued. Thus, the ions are incident on the magnetoresistive stack  210 ″ at the second angle, Φ2, from the normal. In addition, to the free layer  228 ″ and barrier layer  226 ″ being defined, the pinned layer  224 ″ has been substantially defined from the stack  210 ″. However, in the embodiment shown, a portion of the pinning layer  224 ″ remains unmilled. In another embodiment, a portion of the pinned layer  224 ″ may also remain unmilled. Further, because the second milling is performed at a higher milling angle, the redeposition  230  has been substantially removed. 
     After termination of the second mill, a third mill is performed at a third angle of not more than nine degrees from normal to the surface of the magnetoresistive stack  210 ″, via step  156 . The third mill continues in step  156  until the magnetoresistive junction is completely defined.  FIG. 7  depicts the read transducer  200  as step  156  is performed. Thus, the ions are incident on the magnetoresistive stack  210 ′″ at the third angle, Φ3, from the normal. In addition, to the free layer  228 ′″, barrier layer  226 ′″, and pinned layer  224 ′″ being defined, the pinning layer  222 ″ is substantially defined. Stated differently, the magnetoresistive junction  210 ′″ is defined. Further, the width, w, of the magnetoresistive junction  210 ′″ may be adjusted during the second mill and, to an extent, the first mill. The first and third mills may be used to adjust the junction angle, Θ. In one embodiment, the junction angle, Θ, may be at least forty and not more than eighty degrees. Similarly, in one embodiment, the width is not more than sixty nanometers. In another embodiment, the width is not more than fifty nanometers. 
     Using the method  150 , the magnetoresistive junction  210 ′″ may be defined. Moreover, the magnetoresistive junction  210 ′″, particularly the barrier layer  226 ″, may exhibit less damage. Because less damage may be done during definition of the magnetoresistive junction, oxidation steps meant to repair such damage may be skipped or reduced in strength. For example, a natural oxidation instead of a plasma oxidation may be sufficient. Consequently, processing may be simplified and thick oxide layers at the sides of the junction may be reduced or avoided. In addition, redeposition  230  has been removed. Furthermore, a larger junction angle may be achieved and the width of the magnetoresistive junction  210 ′″ adjusted. As a result, photolithography parameters may be relaxed. Fabrication may, therefore, be simplified. In addition, as can be seen in  FIG. 7 , the sidewalls of the magnetoresistive junction  210 ′″ may be free of kinks. 
       FIG. 8  depicts an exemplary embodiment of a magnetic head  250  that may be fabricated using the method  100  and/or  150 . The magnetic head may also include a write transducer (not shown) and a slider. In addition, the magnetic head  250  may reside in a disk drive. The read transducer  260  is shown. The read transducer  260  includes a shield  262 , a read sensor  264 , an insulator  266 , seed layer  268 , hard bias layer  270 , a hard bias capping layer  274 , a metal layer  276  and an additional shield  278 , which may also act as a pole for the write transducer that is not shown. The read sensor  264  is a magnetoresistive junction, such as the TMR junction  210 ′″. Thus, in one embodiment the read sensor  264  has a junction angle of at least forty and not more than eighty degrees. Similarly, in one embodiment, the track width of the read sensor  264  is not more than sixty nanometers. In another embodiment, the width is not more than fifty nanometers. In addition, as can be seen in  FIG. 8 , the sidewalls of the sensor are free of kinks. 
     In addition, an oxide layer  272  is shown. Because the method  100  or  150  is used, the oxide layer  272  may be thin. In particular, the oxide layer  272  is not more than one nanometer thick at the free layer (not shown in  FIG. 8 ). In the present application, a thickness of less than one nanometer at the free layer includes a zero thickness. Stated differently, the oxide layer  272  may not be present. 
     Because the method  100  or  150  is used, the read sensor  260  may exhibit less damage. Further, little or no redeposition may reside on the read sensor  260 . Thus, shorting of the read sensor  260  may be less likely. The junction angle and track width of the read sensor  260  may also be better controlled. As a result, photolithography parameters may be relaxed. Fabrication may, therefore, be simplified. Further, because less damage may be done during definition of the read sensor  260 , oxidation steps meant to repair such damage may be skipped or reduced in strength. For example, a natural oxidation instead of a plasma oxidation may be sufficient. For example, the oxide layer  272  may have a thickness of less than one nanometer. Consequently, the read sensor  272  may be better coupled with the hard bias  270 . Performance of the magnetic head  250  may, therefore, be improved.