Abstract:
Systems and methods for forming magnetic recording media with improved columnar growth for energy assisted magnetic recording are provided. In one such method, a first sub-layer of a magnetic layer is formed on a substrate, the magnetic layer including a magnetic material and a plurality of non-magnetic segregants, a top surface of the first sub-layer is etched to substantially remove the non-magnetic segregants accumulated on the top surface, and a second sub-layer of the magnetic layer is formed on the first sub-layer.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 13/436,596, filed on Mar. 30, 2012, which is hereby incorporated by reference in its entirety. 
     
    
     FIELD 
       [0002]    Aspects of the present invention relate to heat assisted or energy assisted magnetic recording, and, more particular, systems and methods for forming magnetic recording media with improved columnar growth for heat assisted or energy assisted magnetic recording. 
       BACKGROUND 
       [0003]    Due to the increasing demand for more data storage, heat assisted or energy assisted magnetic recording concepts have been pursued as ways to achieve higher density magnetic recording well over a Terabit/in t  in media design. Among the many available magnetic materials, FePt is often chosen as one of the suitable materials for a magnetic recording layer. This material is shown to have a desired thermal gradient near the Curie point for heat assisted magnetic recording. 
         [0004]    To achieve magnetic material (e.g., FePt, FePd) with high densities, non-magnetic segregants (e.g., C, Cr, B, SiO 2 , TiO 2 , Cr 2 O 3 , Ag, BN, V 2 O 5 , ZrO 2 , Nb 2 O 5 , HfO 2 , Ta 2 O 5 , WO 3 , MgO, B 2 O 3 , ZnO, etc.) can be added in order to attain smaller grain sizes of the magnetic material with sufficiently low grain size distributions (e.g., &lt;20%). Carbon has been found to be one of the effective additives which shows the above mentioned properties. However, as the grain sizes get smaller, it becomes difficult to make the magnetic recording layer thicker. For example, in an FePt-C system, a ratio t/D (where t is the thickness, and D is the grain diameter) is found to be limited to approximately 1. This leads to severe reduction in read-back amplitude and hence poor recording performance at high densities. Therefore, it is desirable to improve the performance of existing magnetic recording layers and methods for forming the same. 
       SUMMARY 
       [0005]    Embodiments of the present invention are directed to magnetic recording media with improved columnar growth of the magnetic grains. Embodiments of the present invention are also directed to methods for forming the improved magnetic recording media. 
         [0006]    According to an embodiment of the present invention, a method for fabricating a magnetic recording medium is provided. According to the embodiment, a first sub-layer of a magnetic layer is formed on a substrate, the magnetic layer including a magnetic material and a plurality of non-magnetic segregants, a top surface of the first sub-layer is etched to substantially remove the non-magnetic segregants accumulated on the top surface, and a second sub-layer of the magnetic layer is formed on the first sub-layer. 
         [0007]    According to another embodiment of the present invention, a magnetic recording medium is provided. According to the embodiment, the magnetic recording medium includes a substrate and a magnetic recording layer on the substrate, the magnetic recording layer including a magnetic material and a plurality of non-magnetic segregants. In the embodiment, the magnetic material includes a plurality of grains having substantially continuous columnar crystal growth. In one embodiment, the magnetic recording layer has a thickness of t, a diameter of the plurality of grains is D, and a ratio of t/D may be greater than 1. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The above and other features and aspects of the present invention will become more apparent by describing in detail embodiments thereof with reference to the attached drawings in which: 
           [0009]      FIG. 1  illustrates a cross-sectional functional view of a layer stack of a magnetic recording medium for energy assisted magnetic recording (EAMR) according to an embodiment of the present invention. 
           [0010]      FIG. 2  conceptually illustrates a process for fabricating an EAMR medium with an elongated columnar grain structure without the formation of an undesirable layer of segregant particles, according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    As the present invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to particular modes of practice, and it is to be appreciated that all changes, equivalents, and substitutes that do not depart from the spirit and technical scope of the present invention are encompassed in the present invention. 
         [0012]      FIG. 1  illustrates a layer stack of a magnetic recording medium for energy assisted magnetic recording (EAMR). Referring to  FIG. 1 , the magnetic recording medium includes a substrate  10 , an adhesion layer  20  on the substrate  10 , one or more heatsink layers  30  on the adhesion layer  20 , one or more under layers  40  on the heatsink layers  30 , a magnetic layer  50  on the under layers  40 , and a protective coat on the magnetic layer  50 . The substrate  10  may be a glass substrate, a metal substrate, or any other suitable substrates. The adhesion layer  20  may include CrTa, NiP, NiTa, or other suitable materials. The one or more heatsink layers  30  may include Cu, W, Ru, Mo, Ag, Au, Cr, Mg, Rh, Be, or alloys thereof, or other suitable materials. The one or more under layers  40  may include MgO, TiN, TiC, AIRu, VC, HfC, ZrC, TaC, NbC, CrC, NbN, CrN, VN, CoO, FeO, CaO, NiO, MnO, or other suitable materials. 
         [0013]    In  FIG. 1 , the magnetic layer  50  includes a first magnetic sub-layer  50   a  and a second magnetic sub-layer  50   b.  The second magnetic sub-layer  50   b  is formed on the first magnetic sub-layer  50   a  after performing an etching process on the first magnetic sub-layer  50   a.  The etching process removes an accumulation of segregants such as carbon on a top surface of the first magnetic sub-layer  50   a.  The accumulation of segregants will be discussed below in more details. Each of the first and second magnetic sub-layers ( 50   a  and  50   b ) may include a magnetic material such as Fe, Co, and/or combinations thereof, according to several embodiments of the present invention. For example, the magnetic material may include FePt, FePd, CoPt, or other suitable materials. In one embodiment, the magnetic layer  50  has a ratio of t/D greater than 1, where t is a thickness of the magnetic layer  50 , and D is a diameter of the grains of the magnetic layer  50 . 
         [0014]    In one embodiment, the magnetic layer  50  includes L10 FePt, and the under layers  40  include MgO on which FePt can grow with the desired texture. The substrate  10  can be a high temperature glass substrate or a metal substrate that facilitates the growth of the layers formed thereon for obtaining a good crystallographic texture growth for L10 FePt. In order to grow the FePt magnetic layer, carbon is added to segregate the grains of FePt because FePt and carbon are immiscible. 
         [0015]    While not bound by any particular theory, when an FePt layer is grown to be thicker than a certain thickness (e.g., about 5 nm), a layer of carbon forms on a top surface of the formed FePt layer. The carbon layer will decouple the FePt grains vertically when the FePt layer is grown to be thicker than the certain thickness. It was found that carbon atoms cover the top of the FePt grains after the FePt layer is grown to the certain thickness, thus preventing the columnar growth of the FePt grains. Therefore, when the thickness of the FePt layer is grown to be thicker than, e.g., about 5 nm, an upper FePt layer is separated from a bottom FePt layer by a layer of carbon formation between the upper FePt layer and the bottom FePt layer. This phenomenon makes the epitaxial columnar growth of the FePt layer very difficult above a certain thickness (e.g., 5 nm). As such, the control of grain distributions and magnetic properties of the magnetic layer become difficult. 
         [0016]      FIG. 2  conceptually illustrates a process for fabricating an EAMR medium with an elongated columnar grain structure without the formation of an undesirable layer of segregant particles (e.g., C), according to an embodiment of the present invention. Referring to  FIG. 2 , in a block S 100 , the process forms a first sub-layer  110  of a magnetic layer (e.g., FePt layer) on a suitable substrate (not shown in  FIG. 2 ), where the magnetic layer includes a magnetic material (e.g., FePt) and non-magnetic segregants (e.g., C, Cr, B, SiO 2 , TiO 2 , Cr 2 O 3 , Ag, BN, V 2 O 5 , ZrO 2 , Nb 2 O 5 , HfO 2 , Ta 2 O 5 , WO 3 , MgO, B 2 O 3 , ZnO, etc.). The first sub-layer  110  is grown to a preselected thickness (e.g., 5 nm). At this preselected thickness, a segregant layer  112  (e.g., carbon layer) forms on the top surface of the first sub-layer  110 . The presence of this undesirable segregant layer  112  prevents further vertical columnar growth of grains of the magnetic layer because the segregant layer  112  decouples the magnetic grains vertically. 
         [0017]    Still referring to  FIG. 2 , in block S 102 , the process etches a top surface of the first sub-layer  110  to substantially remove the segregants accumulated on the top surface. The segregant layer  112  can be etched away by a suitable etching process. During the etching process of the first sub-layer  110 , a portion of the first sub-layer  110  proximate to the top surface is removed. The removed portion of the first sub-layer  110  has a concentration of the segregants higher than that of the other portions of the first sub-layer  110 . In one embodiment, an inductively coupled plasma (ICP) etching process can be used to etch out the segregant layer  112  to expose the grains of the first sub-layer  110  below. The ICP etching process can be performed with an ICP etch gas mixture selected from the group consisting of Ar, H 2 , O 2 , Xe, Ne, N 2 , and other suitable etching gases. However, the present invention is not limited to the above described etching process, and other suitable etching processes, such as ion milling, sputter etching, reactive ion etching, etc., may be used in various embodiments. 
         [0018]    Still referring to  FIG. 2 , in block S 104 , after the removal of the segregant layer  112 , the process grows a second sub-layer  114  of the magnetic layer on the exposed grains of the etched first sub-layer  110  to increase the total thickness of the resultant magnetic layer. Because the segregant layer  112  has been removed by etching, a thicker magnetic layer  200  can be fabricated (e.g., greater than 5 nm or 7 nm) with continuous columnar growth than if the segregant layer  112  were not removed. In several embodiments of the present invention, the magnetic layer  200  include FePt that can be grown from about  10  nm to about  15  nm in thickness with good epitaxy. According to the embodiment of  FIG. 2 , the resultant magnetic layer (i.e., FePt layer) can have a ratio of t/D greater than about 1, where t is the thickness of the magnetic layer and D is a diameter of the FePt grains. 
         [0019]    In several embodiments, the magnetic layer  200  include FePt that has grain sizes between about 4 nm and about 9 nm in diameter, inclusive. In other embodiments, the magnetic layer  200  include FePt that has grain sizes between 5 nm and about 6 nm, inclusive. In several embodiments, the first sub-layer  110  has a thickness between about 3 nm and about 6 nm, inclusive, and the second sub-layer  114  has a thickness between about 3 nm and about 10 nm, inclusive. In several embodiments, the first sub-layer  110  has a thickness between about 3 nm and about 4 nm, inclusive. It should be appreciated that the above described materials and processes used for forming the EAMR medium are illustrative only, and the present invention is not limited thereto. In several embodiments, the EAMR medium may include other suitable magnetic materials and segregants. 
         [0020]    In some embodiments, the above described processes can be used to form additional sub-layers of the magnetic layer  200 . For example, after forming the second sub-layer  114 , a top surface of the second sub-layer  114  can be etched to substantially remove a second segregant layer (not shown in  FIG. 2 ) accumulated on the top surface of the second sub-layer  114 . Then, a third sub-layer (not shown) of the magnetic layer  200  is formed on the second sub-layer  114 . In addition, an adhesion layer, a heatsink layer, and an under-layer can be formed between the magnetic layer  200  and the substrate. 
         [0021]    In the above described embodiments, the process or method can perform the sequence of actions in a different order. In another embodiment, the process or method can skip one or more of the actions. In other embodiments, one or more of the actions are performed simultaneously or concurrently. In some embodiments, additional actions can be performed. 
         [0022]    According to the above described embodiments of the present invention, magnetic layers with smaller grain sizes can be grown thicker to provide sufficient read-back signal and good signal-to-noise ratio (SNR). Also, the above described processes can significantly improve the surface roughness of a magnetic medium. 
         [0023]    While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims and their equivalents.