Patent Publication Number: US-9431040-B1

Title: Magnetic recording transducer

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 12/560,669, filed on Sep. 16, 2009, now U.S. Pat. No. 8,233,248, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
       FIG. 1  depicts a conventional method  10  for fabricating a magnetoresistive sensor in magnetic recording technology applications.  FIGS. 2-3  depict a conventional transducer  50  during fabrication using the method  10 . The method  10  typically commences after a conventional magnetoresistive, or MR, stack has been deposited. The conventional magnetoresistive stack typically includes an antiferromagnetic (AFM) layer, a pinned layer, a nonmagnetic spacer layer, and a free layer. In addition, seed and/or capping layers may be used. The pinned layer may be a synthetic antiferromagnetic (SAF) layer including magnetically coupled ferromagnetic layers separated by a nonmagnetic spacer layer. The nonmagnetic spacer layer may be a conductive layer for a giant magnetoresistive sensor or an insulator for a tunneling magnetoresistive sensor. The free layer is ferromagnetic and has a magnetization that is free to change in response to an external magnetic field, for example from a media. 
     The conventional method  10  commences providing a conventional organic mask, via step  12 . The conventional organic mask provided in step  12  is typically a photoresist mask. The conventional photoresist mask covers the region from which the conventional magnetoresistive sensor is to be formed, as well as the field region of the transducer  50 . However, part of the device region adjoining the magnetoresistive sensor is left uncovered. The magnetoresistive sensor is defined, via step  14 . Step  14  typically includes ion milling the transducer  50 . Thus, the portion of the magnetoresistive stack exposed by the conventional photoresist mask is removed.  FIG. 2  depicts air-bearing surface (ABS) and plan views of a conventional, magnetic recording read transducer  50  after step  14  is completed. For clarity,  FIG. 2  is not drawn to scale and only certain structures are depicted. The conventional transducer  50  magnetoresistive layers  54  which have been defined to provide a conventional magnetoresistive sensor  56 . Because the regions adjacent to the conventional magnetoresistive sensor  56  were exposed, the conventional magnetoresistive sensor  56  has been formed. Also shown is conventional photoresist mask  58  which has a first portion  62  covering the magnetoresistive sensor  56  and remaining portions  60  that cover the remaining device and field regions. The photoresist mask  58  used is typically very thick. For example, the photoresist mask may be on the order of one hundred sixty nanometers or higher. 
     The hard bias material(s) are deposited, via step  16 . In addition, seed and/or capping layers may be provided in step  16 . The hard bias material(s) and other layers are deposited while the conventional photoresist mask  58  is in place. A lift-off of the conventional photoresist mask  58  is then performed, via step  18 .  FIG. 3  depicts the conventional transducer  50  after step  18  is performed. Thus, the hard bias material(s)  64  are shown. The hard bias material(s) to the left are denoted  64 L, while the hard bias material(s) to the right of the magnetoresistive sensor  56  are denoted  64 R. Fabrication of the conventional transducer  50  may be completed. 
     Although the conventional method  10  allows the conventional transducer  50  to be fabricated, there are several drawbacks. In particular, there may be asymmetries in the conventional transducer  50 . As can be seen in  FIGS. 2-3 , the conventional magnetoresistive sensor  56  is asymmetric. These asymmetries may become significant at smaller track widths, for example thirty to forty nanometers or less. In particular, the junction angles θ and φ may differ significantly. Further, multiple transducers  50  are typically fabricated from a single wafer. There may also be variations in the junction angles between transducers  50  fabricated on the same wafer. Transducers closer to the center may have a smaller variation in junction angles than transducer  50  closer to the edge. For conventional transducers  50 , the average difference between the left junction angle φ and the right junction angle θ may be seven or more degrees. Further, as can be seen in  FIG. 3 , the hard bias  64 L and  64 R are asymmetric. Again, this asymmetry may vary across a wafer. These variations between conventional transducers  50  may adversely affect performance and/or yield. 
     Accordingly, what is needed is a system and method for improving the fabrication of a magnetic recording read transducer. 
     BRIEF SUMMARY OF THE INVENTION 
     A method and system for fabricating a magnetic transducer is described. The transducer has a device region, a field region, and a magnetoresistive stack. The method and system include providing a hard mask on the magnetoresistive stack. The hard mask is an inorganic mask and includes a sensor portion and a line frame. The sensor portion covers a first portion of the magnetoresistive stack corresponding to a magnetoresistive structure. The line frame covers a second portion of the magnetoresistive stack in the device region. The method and system also include defining the magnetoresistive structure in a track width direction using the hard mask and providing at least one hard bias material after the magnetoresistive structure is defined. A first portion of the at least one hard bias material is substantially adjacent to the magnetoresistive structure in the track width direction. The method and system also include removing a second portion of the at least one hard bias material. In one aspect, the magnetoresistive structure is characterized by a junction angle difference between junction angles on opposing sides of the magnetoresistive structure, In such an aspect, the average junction angle difference does not exceed six degrees. In addition, the track width in this aspect is less than or equal to one hundred nanometers. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a flow chart depicting a conventional method for fabricating a magnetic recording transducer. 
         FIG. 2  depicts plan and ABS views of a conventional magnetic recording transducer during fabrication. 
         FIG. 3  depicts plan and ABS views of a conventional magnetic recording transducer during fabrication. 
         FIG. 4  is a flow chart depicting an exemplary embodiment of a method for fabricating a magnetic recording transducer. 
         FIG. 5  depicts plan and ABS views of an exemplary embodiment of a magnetic recording transducer. 
         FIG. 6  is a flow chart depicting another exemplary embodiment of a method for fabricating a magnetic recording transducer. 
         FIGS. 7-16  depict plan and ABS view of another exemplary embodiment of a magnetic recording transducer during fabrication. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 4  is an exemplary embodiment of a method  100  for providing magnetic recording transducer. For simplicity, some steps may be omitted. The method  100  is also described in the context of providing a single recording transducer. However, the method  100  may be used to fabricate multiple transducers at substantially the same time. The method  100  is also described in the context of particular layers. A particular layer may include multiple materials and/or multiple sub-layers. The method  100  also may start after formation of other portions of the magnetic recording transducer. For example, the method  100  commences after deposition of magnetoresistive layer(s) for a magnetoresistive stack. The magnetoresistive layers may includes a pinning layer, a pinned layer, a nonmagnetic spacer layer, and a free layer. In addition, seed and/or capping layers may be used. The pinning layer may be an AFM or other layer configured to fix, or pin, the magnetization of the pinned layer. The pinned layer may be a synthetic antiferromagnetic (SAF) layer including magnetically coupled ferromagnetic layers separated by a nonmagnetic layer. The ferromagnetic layers may be termed pinned and reference sub-layers. The nonmagnetic spacer layer may be a conductive layer for a giant magnetoresistive structure, an insulator for a tunneling magnetoresistive structure, or may have another structure. The free layer is ferromagnetic and has a magnetization that is free to change in response to an external magnetic field, for example from a media. The free layer may have multiple sub-layers, as may the pinned and reference sub-layers. Further, the transducer may be considered to have a device region, in which the magnetoresistive structure is to be formed, and a field region distal from the magnetoresistive structure. 
     A hard mask is provided on the magnetoresistive stack, via step  102 . The hard mask is inorganic and includes a structure portion and a line frame. In some embodiments, for example in which the structure is a magnetoresistive sensor, the structure portion of the hard mask may also be termed a sensor portion. The structure portion of the hard mask covers a part of the magnetoresistive stack corresponding to the magnetoresistive structure being formed. The line frame covers a second portion of the magnetoresistive stack in the device region. In some embodiments, the line frame may be significantly wider than the sensor portion. For example, the line frame may have a width on the order of at least two hundred nanometers, while the structure portion has a width on the order of sixty nanometers or less. In some embodiments, the width of the sensor portion may be thirty to forty nanometers or less. Step  102  may include depositing a hard mask layer, then patterning the hard mask layer to form the hard mask. The hard mask provided in step  102  should be resistant to removal in the process used to define the magnetoresistive structure in step  104 , described below. For example, in some embodiments, the hard mask includes one or more of diamond-like carbon (DLC), SiC, and SiN. Further, the hard mask may be relatively thin. In one embodiment, the hard mask has a thickness of not more than seventy nanometers. In one such embodiment, the hard mask has a thickness of not more than sixty nanometers. In some embodiments, the hard mask is also configured to provide a magnetoresistive structure having a small width of not more than one hundred nanometers. In some such embodiments, the width may be smaller, for example not more than sixty nanometers. In some embodiments, the width may be thirty to forty nanometers or less. 
     The magnetoresistive structure is defined at least in a track width direction using the hard mask, via step  104 . In one embodiment, step  104  includes performing an ion mill to remove exposed portions of the magnetoresistive stack. 
     One or more hard bias materials are provided after the magnetoresistive structure is defined, via step  106 . Thus, a portion of the hard bias material(s) is substantially adjacent to the magnetoresistive structure in the track width direction. If the magnetoresistive structure is to be used in a current-perpendicular-to-plane (CPP) configuration, then an insulator might be provided prior to the hard bias material(s) in step  106 . In addition, seed and/or capping layers may also be provided in step  106 . For example, the capping layer(s) may include a trilayer having Ru sub-layer sandwiched between Ta layers. 
     A portion of the hard bias material(s) is removed in step  108 . Step  108  includes removing the hard bias materials at least in the field region of the magnetic recording transducer. In such an embodiment, the device region of the transducer may be covered, for example by an organic mask. The hard bias material(s) in the exposed, field regions may then be removed. In addition, step  108  may include removing any hard bias material(s) residing on the magnetoresistive structure. Further, portions of the hard mask may also be removed, for example using a reactive ion etch having the appropriate chemistry. Fabrication of the transducer may then be completed. 
       FIG. 5  depicts plan and ABS views of an exemplary embodiment of a magnetic recording transducer  120  fabricated using the method  100 . For clarity,  FIG. 5  is not drawn to scale. Further, although described in the context of layers, structures in the magnetic recording transducer  120  may include one or more sub-layers. For simplicity, only portions of the transducer  120  are shown. In some embodiments, the transducer  120  may be part of a head. The head may be a merged head including at least one write transducer (not shown) in addition to at least one read transducer  120 . Further, the head may reside on a slider (not shown) and be part of a disk drive including the head, slider and media (not shown) on which data is written. 
     The transducer  120  includes a substrate  122  and magnetoresistive layers  124  defined from a magnetoresistive stack. In addition, the transducer  120  includes magnetoresistive structure  130  and hard bias structures  140 . The magnetoresistive structure  130  is a read sensor. The MR layers  124  and read sensor  130  may be deposited as a full film. The read sensor  130  is then defined using step  104 . The hard bias  130  may be provided as a full film. However, because the hard mask and/or other structures may be removed during fabrication, the hard bias  140  adjacent to the magnetoresistive structure  130  and magnetoresistive layers  124  remains. In the embodiment shown, the magnetoresistive sensor  130  is to be used in a CPP configuration. Consequently, an insulating layer  142  is also provided between the hard bias material(s)  140  and the magnetoresistive sensor  130 . 
     The magnetoresistive sensor  130  has a track width, w. The track width corresponds to a characteristic distance between the right and left sides. In some embodiments, the magnetoresistive sensor  130  has a track width of not more than one hundred nanometers. In some embodiments, the track width may be smaller. For example, in one embodiment, the track width, w, is not more than sixty nanometers. In other embodiments, w is not more than thirty to forty nanometers. 
     The magnetoresistive sensor  130  had has a left side having a junction angle α and a right side having a junction angle β. The junction angles for the magnetoresistive sensor  130  and others formed in a similar manner may be characterized by an average junction angle difference. The average junction angle difference is the average of the differences between the junction angles α and β for a number of transducers  120 . The average junction angle difference being not more than six degrees. In some embodiments, the average junction angle difference is not more than four degrees. In another embodiment, the average junction angle difference is not more than three degrees. In yet another embodiment, the average junction angle difference is not more than two degrees. 
     Using the method  100 , the transducer  120  may be formed. As discussed above, the transducer  120  is symmetric. Thus, the junction angles α and β may be closer in size. In particular, it has been determined that asymmetries in the portion  62  of the thick photoresist mask  58  shown in  FIG. 2  may result in the asymmetries in the conventional sensor  56  and hard bias  64 . More specifically, it has been determined that variations in the junction angles may be due to the directional nature of the ion beam used in defining the conventional sensor  56 , the large height of the photoresist mask  58 , and the asymmetric shape of the top of the portion  62  of the photoresist mask. In contrast, the hard mask provided in step  102  is thinner, and remains substantially unchanged and substantially symmetric. Thus, use of the hard mask in steps  102  and  104  may improve the symmetry of the magnetoresistive sensor  130 . The junction angles α and β may, therefore, be significantly more symmetric. In other words, the difference between the junction angles, as well as the average junction angle difference across multiple transducers  120 , may be reduced. Further, the thicknesses of the hard bias material(s)  140  adjacent to the left and right sides of the sensor  130  may be more symmetric. Consequently, asymmetries in the transducer  120  may be reduced. In addition, because a line frame is used, removal of a portion of the hard bias may be facilitated. Thus, performance of the transducer  120  and yield using the method  100  may be improved. 
       FIG. 6  is a flow chart depicting another exemplary embodiment of a method  150  for fabricating a magnetic recording transducer.  FIGS. 7-16  depict plan and ABS view of another exemplary embodiment of a magnetic recording transducer  200  during fabrication. The method  150  is described in the context of the transducer  200 . For simplicity, some steps of the method  150  may be omitted. The method  150  is also described in the context of providing a single recording transducer  200 . However, the method  150  may be used to fabricate multiple transducers at substantially the same time. The method  150  and transducer  200  are also described in the context of particular layers. A particular layer may include multiple materials and/or multiple sub-layers. The method  150  also may start after formation of other portions of the magnetic recording transducer  200 . 
     A magnetoresistive stack is deposited, via step  152 . The magnetoresistive layers may includes a pinning layer, a pinned layer, a nonmagnetic spacer layer, and a free layer. In addition, seed and/or capping layers may be used. Examples of such layers are described above. Further, the transducer may be considered to have a device region, in which the magnetoresistive structure is to be formed, and a field region distal from the magnetoresistive structure. 
     A hard mask layer is provided on the magnetoresistive stack, via step  154 . Step  154  includes blanket depositing an inorganic hard mask layer, such as DLC, SiN, and/or SiC on the magnetoresistive stack. In one embodiment, step  154  includes depositing a hard mask layer having a thickness of not more than seventy nanometers. In another embodiment, the hard mask layer provided in step  154  has a thickness of not more than sixty nanometers. 
     A photoresist mask is provided, via step  156 . The photoresist mask is used in patterning the hard mask layer to form the hard mask. Thus, the photoresist mask covers a first portion of the hard mask layer corresponding to the sensor portion of the hard mask and a second portion corresponding to the line frame of the hard mask.  FIG. 7  depicts the transducer  200  after step  156  is performed. Thus, a substrate  202  and magnetoresistive stack  204  are shown. In addition, the hard mask layer  206  is shown as being blanket deposited on the magnetoresistive stack. Further, the photoresist mask  208  is also shown. The photoresist mask  208  has portions  208 A and  208 B corresponding to the magnetoresistive structure and the line frame, respectively. The portion  208 A corresponding to the magnetoresistive sensor may be printed with a critical dimension at the limit of the photo process used for the photoresist mask  208 . However, the width of the line frame may be larger, for example on the order of two hundred nanometers or more. 
     A portion of the hard mask layer is removed to form the hard mask, via step  158 . Thus, the pattern of the mask  208  is transferred to the hard mask layer  206 . In one embodiment, step  158  is performed using a reactive ion etch (RIE).  FIG. 8  depicts the transducer  200  after step  158  is performed. Thus, a hard mask  206 ′ has been formed. The hard mask  206 ′ corresponds to the locations of portions of the mask  208 . The portion of the hard mask  206 ′ under the mask portion  208 A corresponds to the sensor in the device region. The portion of the hard mask  206 ′ under the mask portion  208 B corresponds to the line frame. Also in step  208 , the photoresist  165  may be removed, for example via a photoresist strip. Thus, through steps  154 - 158 , the hard mask  206 ′ is provided. 
     The magnetoresistive structure is defined in the track width direction, via step  160 . In step  160 , the hard mask  206 ′ is used to protect portions of the magnetoresistive stack  204  from the process. In one embodiment, defining the magnetoresistive structure in a track width direction includes performing an ion mill.  FIG. 9  depicts the transducer  200  after step  160  is performed. Thus, a magnetoresistive structure  210  has been defined. In one embodiment, the structure, magnetoresistive layers  204 A′ corresponding to the line frame of the hard mask have been defined from the magnetoresistive stack  204 . In addition, magnetoresistive layers  204 ′ in the field region have also been defined. The sensor  210  has a track width of not more than one hundred nanometers. In other embodiments, the track width may be smaller. For example, in one embodiment, the track width, w, is not more than sixty nanometers. In other embodiments, w is not more than thirty to forty nanometers. In contrast, the width of portions  204 A′ may be larger as these portions correspond to the line frame. In some embodiments, the portions  204 A′ may be two hundred nanometers or more in width. 
     An insulator is optionally provided after the magnetoresistive structure  210  is defined, via step  162 . Step  162  is performed if the sensor  210  is to be used in a CPP configuration. At least one hard bias material after the insulator is provided, via step  164 . A first portion of the hard bias material(s) is substantially adjacent to the magnetoresistive structure in the track width direction. In some embodiments, capping layer(s) for the hard bias material(s) may also be provided in step  164 . In some embodiments, the capping layer may have sub-layer(s). For example, providing a plurality of sub-layers may include providing a first Ta sub-layer, a Ru sub-layer, and a second Ta sub-layer. In such an embodiment, the Ru sub-layer resides between the Ta sub-layers.  FIG. 10  depicts the transducer  200  after step  164  is performed. Thus, hard bias layer  220  and capping layer(s)  222  are shown. 
     A portion of the hard bias material(s)  220  is removed, via step  166 . The portion removed resides on the hard mask  206 ′ above the sensor  210  and the line frame  204 A′, Step  166  may include performing a high angle ion mill, for example at an angle of sixty or more degrees from normal to the surface of the transducer  200 .  FIG. 11  depicts the transducer  200  after step  166  is performed. The portions of the hard bias material(s)  220  and capping layer(s)  222  on the hard mask  206 ′ are shrunk. Thus, the hard bias  220 ′ and capping layers  222 ′ are shown. In some embodiments, the portion of the hard bias material(s)  220  above the magnetoresistive structure  210  is completely removed. This situation is shown in  FIG. 11 . However, in other embodiments, some portion of the hard bias material(s)  220  on the sensor  210  remain. 
     An organic device region mask is provided after the portion of the hard bias material(s) is removed, via step  168 . Step  168  may include spinning on a layer of photoresist, then patterning the photoresist using photolithography. The organic device region mask covers at least the device region and leaves at least a portion of the field region uncovered. An exposed portion of the hard bias material(s) is removed while the organic device region mask remains in place, via step  170 . Thus, exposed hard bias in the field region may be removed. In one embodiment, step  170  may be performed using an ion mill.  FIG. 12  depicts the transducer  200  after step  170  is performed. Thus, the device region mask  230  is shown. The organic device region mask  230  covers most the device region of the transducer  200 , but leaves the field region exposed. In addition, the exposed portion of the hard bias material(s)  220 ′ and capping material(s)  222 ′ in the field region have been removed. Thus, hard mask  206 ′ in the field region is exposed. 
     The device region mask is removed after the exposed portion of the hard bias material(s)  220 ′ have been removed, via step  172 . Step  172  may include stripping the photoresist mask  230 .  FIG. 13  depicts the transducer  200  after step  172  is performed. Thus, the device region of the transducer  200  is exposed. 
     A chemical mechanical planarization (CMP) is performed to remove a portion of the material(s) residing on the hard mask, via step  174 . Thus, portions of the hard bias material(s)  220 ′ that protrude from the transducer  200  are removed. As a result, the hard mask  206 ′ is exposed, and may be removed.  FIG. 14  depicts the transducer  200  after step  174  is performed. Thus, the hard mask  206 ″ has been thinned and is exposed. The protruding portions of the hard bias  220 ′ have been removed. The hard bias material(s)  220 ″ and capping layer(s)  222 ″ remain. 
     The hard mask  206 ″ is removed, via step  176 . In one embodiment, step  176  includes performing a RIE to remove the hard mask  206 ″. For example, if a DLC hard mask  206 ′ is used, step  176  may include performing an oxygen RIE.  FIG. 15  depicts the transducer  200  after step  176  is performed. Thus, MR layers  204 A′ that reside under the line portion of the hard mask  206 ′ are exposed. 
     A second CMP may be performed after the step of performing the RIE is completed, via step  178 . Thus, the topology of the transducer  200  may be further smoothed.  FIG. 16  depicts the transducer  200  after step  178 . Thus, hard bias structures  220 ′″ and capping layers  222 ′″ are shown. Thus, through step  174 - 178 , the remaining hard mask has been removed. 
     Using the method  150 , the transducer  200  may be formed. As discussed above, the transducer  200  is symmetric. Thus, the junction angles α and β may be closer is size. In particular, the average difference in junction angles α and β may be not more than six degrees. In some embodiments, average junction angle differences of four degrees or less may be fabricated. In other embodiments, average junction angle differences of four degrees or less may be fabricated. In another embodiment, the average junction angle difference is not more than three degrees. In yet another embodiment, the average junction angle difference is not more than two degrees. Further, asymmetries in the thicknesses of the hard bias structures  220 ′″ to the left and right of the magnetoresistive structure  210  may be reduced. Consequently, asymmetries in the transducer  200  may be reduced. This may be achieved for a magnetoresistive structure  210  having a smaller track width. For example, the track width, w, is less than one hundred nanometers. In some embodiments, the track width may be thirty to forty nanometers or less. In addition, because a line frame is used, removal of the hard bias  220 ′ may be facilitated. Thus, performance of the transducer  200  and yield using the method  150  may be improved.