Abstract:
The method and system for providing a magnetic element are disclosed. The method and system include providing a magnetic element stack that includes a plurality of layers and depositing a stop layer on the magnetic element stack. The method and system also include providing a dielectric antireflective coating (DARC) layer on the stop layer, forming a single layer mask for defining the magnetic element on a portion of the DARC layer, and removing a remaining portion of the DARC layer not covered by the single layer mask. The portion of the DARC layer covers a portion of the stop layer. The method further includes removing a remaining portion of the stop layer and defining the magnetic element using at least the portion of stop layer as a mask.

Description:
FIELD OF THE INVENTION 
     The present invention relates to magnetic recording technology, and more particularly to a method and system for providing a magnetic element capable of having a smaller critical dimension using a single layer mask. 
     BACKGROUND 
       FIG. 1  depicts a conventional method  10  for providing a conventional magnetic element, such as magnetoresistive elements used in read transducers.  FIGS. 2-3  depict the conventional magnetic element during fabrication. Referring to  FIGS. 1-3 , the layers for the conventional magnetic element are deposited, via step  12 . For a conventional tunneling magnetoresistance (TMR) stack that may be used in a read transducer, step  12  may include depositing a pinning layer such as an antiferromagnetic (AFM) layer, a pinned layer, a nonmagnetic spacer layer, and a free layer. The pinned and free layers are typically ferromagnetic or synthetic antiferromagnetic layers including two ferromagnetic layers separated by a nonmagnetic, conductive layer. For a conventional TMR stack, the nonmagnetic spacer layer is an insulator, such as Al 2 O 3 , crystalline MgO, and/or titanium oxide, that provides a tunneling barrier. 
     A conventional undercut bilayer structure is provided on the conventional magnetic element layers, via step  14 .  FIG. 2  depicts the conventional magnetic element layers  20  and the conventional undercut bilayer structure  30 . The conventional magnetic element layers  20  include an AFM layer  22 , a pinned layer  24 , an insulating, nonmagnetic spacer layer  26 , and a free layer  28 . Other layers, such as seed or capping layers, might also be used. The conventional undercut bilayer structure  30  includes two layers  32  and  34 . The lower layer is typically a PMGI layer  32 , while the upper layer is typically a photoresist layer  34 . The PMGI layer  32  is narrower than the photoresist layer  34  to provide the undercut  36 . 
     The pattern provided by the conventional undercut bilayer structure  30  is transferred to the underlying magnetic element layers  20 , via step  16 . In step  16 , therefore, the magnetic element is defined.  FIG. 3  depicts the conventional magnetic element  20 ′ that has been formed prior to removal of the conventional undercut bilayer structure  30 . The conventional magnetic element  20 ′ has been defined from the layers  22 ′,  24 ′,  26 ′, and  28 ′. 
     Processing is completed for the conventional magnetic element  20 ′ and the conventional device in which the conventional magnetic element  20 ′ resides, via step  18 . Step  18  includes lifting off the conventional undercut bilayer structure  30 , which exposes the underlying conventional magnetic element  20 ′. Step  18  may also include providing subsequent layers and processing steps. For example, insulating layers, hard bias layers, fillers, and contacts to the conventional magnetic element  20 ′ may be provided in step  18 . Typically, these layers are provided prior to lift-off of the conventional undercut bi-layer structure  30  so that the conventional undercut bi-layer structure  30  can act as a mask for the conventional magnetic element  20 ′. Thus, the conventional magnetic element  20 ′ in a conventional device, such as a read transducer and/or merged head, may be formed. 
     Although the conventional method  10  and the conventional magnetic element  20 ′ can function, one of ordinary skill in the art will readily recognize that the trend in magnetic recording technology is toward higher densities and smaller sizes. Thus, the critical dimensions in write or read heads are currently below those in semiconductor processing. Further, as sizes shrink to provide areal densities above 120 Gb/in 2 , the lift-off performed in step  18  becomes more difficult. For printed critical dimensions of the photoresist layer  34  below 0.1 micrometer, it is difficult to provide a small enough the PMGI layer  32  to generate a sufficient undercut for lift-off. For example, the undercut  36  must typically be greater than at least 0.03 micrometer for complete liftoff of the conventional undercut bilayer structure  30 . This means that the PMGI layer  32  is only 0.04 micrometers in width for a 0.1 micrometer photoresist layer  34 . For smaller geometries having critical dimensions of less than 0.1 micrometer, the PMGI layer  32  may become too thin to support the photoresist layer  34 , causing the conventional undercut bilayer structure  30  to collapse. Thus, transfer of the pattern of the conventional undercut bilayer structure  30  to the conventional magnetic element  20 ′ and liftoff of the conventional undercut bilayer structure  30  become difficult. For areal densities of 200 Gb/in 2  and track widths of 0.08 micrometer or less, the conventional method  10  and conventional undercut bilayer structure  30  may be incapable of fabricating the conventional magnetic element  20 ′. 
     Accordingly, what is needed is a system and method for providing a magnetic element having smaller critical dimensions. 
     SUMMARY 
     A method and system for providing a magnetic element are disclosed. The method and system comprise providing a magnetic element stack that includes a plurality of layers and depositing a stop layer on the magnetic element stack. The method and system also comprise providing a dielectric antireflective coating (DARC) layer on the stop layer, forming a single layer mask for defining the magnetic element on a portion of the DARC layer, and removing a remaining portion of the DARC layer not covered by the single layer mask. The portion of the DARC layer covers a portion of the stop layer. The method further includes removing a remaining portion of the stop layer and defining the magnetic element using at least the portion of stop layer as a mask. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a flow chart depicting a conventional method for providing a conventional magnetic element. 
         FIG. 2  depicts a conventional magnetic element during fabrication. 
         FIG. 3  depicts a conventional magnetic element during fabrication. 
         FIG. 4  is a flow chart depicting a method in accordance with an exemplary embodiment of the present invention for fabricating a magnetic element. 
         FIG. 5  is a diagram of a magnetic element during fabrication in accordance with an exemplary embodiment of the present invention. 
         FIG. 6  is another diagram of the magnetic element during fabrication in accordance with an exemplary embodiment of the present invention. 
         FIG. 7  is another diagram of the magnetic element during fabrication in accordance with an exemplary embodiment of the present invention. 
         FIG. 8  is another diagram of the magnetic element during fabrication in accordance with an exemplary embodiment of the present invention. 
         FIG. 9  is another diagram of the magnetic element during fabrication in accordance with an exemplary embodiment of the present invention. 
         FIG. 10  is another diagram of the magnetic element during fabrication in accordance with an exemplary embodiment of the present invention. 
         FIG. 11  is another diagram of the magnetic element during fabrication in accordance with an exemplary embodiment of the present invention. 
         FIG. 12  is another diagram of the magnetic element during fabrication in accordance with an exemplary embodiment of the present invention. 
         FIG. 13  is another diagram of the magnetic element during fabrication in accordance with an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 4  is a flow chart depicting a method  100  in accordance with another exemplary embodiment of the present invention for fabricating a magnetic element.  FIGS. 5-13  depict a magnetic element residing in a transducer  200  during fabrication in accordance with an exemplary embodiment of the present invention. The method  100  is described in the context of a particular magnetic element, a TMR stack. However, one of ordinary skill in the art will readily recognize that the method  100  can be used in conjunction with other magnetic elements such as spin valves. In addition, steps may be omitted or combined for ease of explanation. Further, fabrication of the magnetic element is described in the context of a transducer  200 . However, in an alternate embodiment, the magnetic element may be used in a different device. 
     The layers for the magnetic element are deposited, via step  102 . In a preferred embodiment, step  102  includes depositing a pinning layer such as an AFM layer, a pinned layer, a spacer layer, and a free layer. The pinned layer and free layer may be simple ferromagnetic layers or may by synthetic antiferromagnets including ferromagnetic layers separated by conductive nonmagnetic layer(s). The spacer layer is preferably an insulator and acts as a tunneling barrier. In addition, seed and/or capping layers may be provided in step  102 . Although the magnetic element layers provided in step  102  are preferably for a TMR stack, in another embodiment, the layers could be for another magnetic element. 
     A stop layer is deposited on the magnetic element layers, via step  104 . The stop layer is preferably used as a chemical mechanical polish (CMP) stop. In a preferred embodiment, the stop layer provided in step  104  is a diamond-like carbon (DLC) layer. However, in another embodiment, other material(s) may be used. A dielectric antireflective coating (DARC) layer is provided on the stop layer, via step  106 . As its name suggests, the DARC layer is an antireflective layer configured to reduce reflections during photolithographic processes. In addition, the DARC layer preferably improves adhesion of a subsequent mask layer. Also in a preferred embodiment, the DARC layer is resistant to etches used to remove the subsequent mask layer. 
     A single layer mask is provided, via step  108 . Step  108  includes depositing and developing the single layer mask where photoresist is used for the single layer mask. In a preferred embodiment, step  108  optionally also includes trimming the single layer mask to further reduce the critical dimension of the single layer mask. 
       FIG. 5  depicts the transducer  200  after at least a portion of step  108  has been performed. The transducer  200  is depicted before trimming, if any, in step  108  is performed. Shown in  FIG. 5  are magnetic element layers  210 , stop layer  220 , DARC layer  230 , and single layer mask  240 . In the embodiment shown, the magnetic element layers  210  reside on a shield  202 . In the embodiment shown, the magnetic element layers  210  include an AFM layer  212 , a pinned layer  214 , an insulator spacer layer  216 , and a free layer  218 . Note that although a particular orientation of the layers  212 ,  214 ,  216 , and  218  with respect to the shield  202  is shown, another orientation could be used. For example, the orientation of the layers  212 ,  214 ,  216 , and  218  could be reversed. The stop layer  220  depicted is preferably a DLC layer. However, in an alternate embodiment, the stop layer  220  could include other materials such as Ta, W, alumina, and/or silicon dioxide. The DARC layer  230  preferably includes at least one or more of SiO 3 , Si x N 4  and SiO x N y . However, in another embodiment, the DARC layer  230  may include other materials or combinations of materials such as SiO 3 , Si x N 4  and SiO x N y . In a preferred embodiment, the DARC layer  230  improves adhesion of the single layer mask  240 . The single layer mask  240  is preferably a deep ultraviolet (DUV) photoresist mask. The DARC layer  230  is, therefore, preferably configured to reduce reflections of the DUV light used in developing the single layer mask  240 . In one embodiment, the single layer mask  240  is developed to have a critical dimension, d, of approximately 0.1 μm, at the lower limit of photolithography using DUV photoresist. In another embodiment, the single layer mask  240  may have a different critical dimension. 
       FIG. 6  depicts the transducer  200  after step  108  has been completed. Thus, the transducer  200  is depicted after the trimming has been performed in a preferred embodiment of step  108 . If DUV photoresist is used for the single layer mask  240 , the trimming of the single layer mask may be performed using an oxygen plasma reactive ion etch (RIE). As a result, the single layer mask  240 ′ is still present, but has a smaller critical dimension. In one embodiment, the critical dimension of the single layer mask  240 ′ is approximate 0.08 μm. In a preferred embodiment, the underlying DARC layer  230  is also resistant to the oxygen plasma used in the RIE. Consequently, trimming of the single layer mask  240 ′ in step  108  does not significantly affect the DARC layer  230 . 
     A portion of the DARC layer  230  that does not reside under the single layer mask  240 ′ is removed, via step  110 . Thus, the pattern of the single layer mask  240 ′ is transferred to the DARC layer  230 . In a preferred embodiment, step  110  is performed using a fluorine plasma (e.g. CF 4 ) RIE. Also in a preferred embodiment, the stop layer  220  is resistant to the etch used to remove the DARC layer  230 , such as the fluorine plasma RIE. As a result, step  110  may overetch the DARC layer  230  without adversely affecting the underlying magnetic element layers  210 . Such an overetch ensures complete removal of the exposed portions of the DARC layer  230 . 
       FIG. 7  depicts the transducer  200  after step  110  has been performed. As can be seen in  FIG. 7 , the pattern of the single layer mask  240 ″ has been transferred to the DARC layer  230 ′. Because an overetch may be performed, the exposed portion of the DARC layer has been completely removed. Thus, only the portion  230 ′ of the DARC layer under the single layer mask  240 ″ remains. In addition, some portion of the single layer mask  240 ″ may remain after the etch of the DARC layer. 
     The exposed portion of the stop layer is removed, via step  112 . Stated differently, the pattern of the single layer mask  240 ′ is transferred to the stop layer  220 . If the stop layer  220  is a DLC layer, then step  112  is preferably performed using an oxygen plasma RIE. However, for other materials, a different etch process might be used. For example, a carbon monoxide or fluorine etch might be used if the stop layer  220  includes materials such as Ta, W, alumina or silicon dioxide. 
       FIG. 8  depicts the transducer  200  after step  112  has been performed. Because of the etch performed in step  112 , only a portion of the stop layer  220 ′ remains. In addition, the single layer mask  240 ′ may be removed during step  112 , for example using an oxygen plasma RIE or solvent. However, a portion of the DARC layer  230 ″ remains, acting as a mask for the underlying stop layer  220 ′. This is because the DARC layer  230 ″ is preferably resistant to the etch performed in step  112 . 
     The magnetic element is defined, via step  114 . The pattern is thus transferred to the underlying magnetic element layers  210 . In a preferred embodiment, step  114  is performed by ion milling the magnetic element layers, generally using Ar ions. The stop layer  220 ′ is preferably insensitive to the process that defines the magnetic element and, therefore, functions as a mask during step  114 . 
       FIG. 9  depicts the transducer  200  after the magnetic element  210 ′ has been defined in step  114 . In the embodiment shown, the DARC layer is removed during step  114  and is thus not depicted. The magnetic element  210 ′ having the desired profile and desired critical dimension, d′, may thereby be formed. For example, in one embodiment, the magnetic element  210 ′ may have a critical dimension of less than or equal to 0.08 μm, as typically measured at the free layer  218 ′. 
     Processing then continues. If a read head is being formed, then an insulator is deposited on the magnetic element  210 ′, via step  116 . The insulator is preferably alumina, but may include other materials, such as SiO 2 . A hard bias layer is provided, via step  118 . Step  118  include providing a hard magnet used in biasing the magnetic element  210 ′. In addition, a filler is provided, via step  120 . The filler is preferably Cr. However, in another embodiment, the filler provided in step  120  could include other materials such as alumina, silicon dioxide, or silicon nitride.  FIG. 10  depicts the transducer  200  after step  120  has been completed. Thus, the magnetic element  210 ′ and remaining stop layer  220 ″ have been covered in an insulator  250 , a hard bias layer  252 , and a filler  254  that is preferably Cr. The filler  254  is used to protect the underlying hard bias layer  252  from subsequent processing. 
     The device is planarized, via step  122 . In a preferred embodiment, the planarization is performed using a CMP step. Also in a preferred embodiment, the CMP is continued until the stop layer  220 ″ is exposed. 
       FIG. 11  depicts the transducer  200  after a portion of step  122  has been performed. Consequently, part of the filler layer has been removed, leaving portions  254 ′. A portion of the hard bias layer has also been removed, leaving remaining portion  252 ′. The exposed surface is, therefore, planar. However, as discussed above, the planarization may be continued to overpolish the device  200 .  FIG. 12  depicts the transducer  200  after completion of step  122 . Thus, portions of the filler  254 ″ and hard bias  252 ″ remain. In addition, the insulator  250 ′ is exposed. However, the stop layer  220 ′″ remains substantially intact. Consequently, the stop layer  220 ′″ may still mask the underlying magnetic element  210 ′, protecting the magnetic element  210 ′ from damage. 
     The surface of the magnetic element  210 ′ is exposed, via step  124 . Step  124  may be carried out using the same etch as step  112 . If the remaining portion of the stop layer  220 ′″ is a DLC layer, step  124  is preferably performed using an oxygen plasma RIE. However, for other materials, a different etch might be used. For example, a carbon monoxide or fluorine etch might be used if the remaining portion of the stop layer  220 ′″ includes materials such as Ta, W, alumina or silicon dioxide.  FIG. 13  depicts the transducer  200  after step  124  has been performed. The top surface of the magnetic element  210 ′ is thus exposed. 
     Processing of the device may be completed, via step  126 . For the transducer  200 , step  126  may include providing contacts on the top surface of the exposed magnetic element  210 ′. Additional insulating and shield layers may also be provided. If the transducer  200  is part of a merged head, then step  126  may include providing other structures, such as a write transducer. If the magnetic element  210 ′ and method  100  are used for another device, then other layers and/or additional layers having different structures and functions may be provided in step  126 . 
     Thus, the method  100  can provide the magnetic element  210 ′. Because a single layer mask  230 ′ is utilized, issues due to problems with lift-off and collapse of a bilayer photoresist structure can be avoided. Further, the single layer mask  230 ′, and thus the magnetic element  210 ′, can be made smaller than the critical dimensions of photolithography. As a result, the magnetic element can be made smaller than is possible using conventional photolithography. In one embodiment, the magnetic element  210 ′ can have a critical dimension of 0.08 μm or less. As a result, the method  100  and magnetic element  210 ′ may be suitable for higher density recording applications.