Abstract:
A method is disclosed for defining discrete magnetic and non-magnetic regions on the magnetic film layer of a storage media substrate. The method applies anodic oxidation of a cobalt-containing magnetic film layer to remove cobalt, followed by controlled deposition of a non-magnetic matrix into the regions where the cobalt has been removed. Deposition may either be electrodeposition, collimated vacuum deposition, or other methods depending upon the composition of the non-magnetic matrix being deposited. The method may be performed in a single electrochemical cell.

Description:
FIELD 
     This disclosure relates generally to the formation of patterned media or discrete track media for use in storage media. Specifically, this disclosure relates to the deposition of a non-magnetic matrix to form patterned media or discrete track media. 
     BACKGROUND 
     Bit patterned media (BPM) and discrete track media (DTR) are becoming more popular media for storage because of their inherent abilities to store more data in a smaller area. The goal of BPM and DTR and other patterned media is to increase bit density. However, manufacturing methods for BPM and DTR are complicated, expensive and inconsistent. 
     BPM media are typically formed by using lithography to define the pattern on the media substrate. Once the pattern is defined, the translation of the pattern to the media substrate is typically an additive or subtractive process. An additive process, e.g., electrodeposition and lift-off, requires steps of creating a resist pattern and then depositing a magnetic film layer. In contrast, the subtractive process begins with the deposition of a magnetic film layer followed by resist patterning. The resist pattern may serve as an etch mask such that the surrounding magnetic film may be removed by ion milling, reactive ion etching (RIE), wet chemical etching or other processes. An issue with these types of etching is that they are not very selective in defining magnetic and non-magnetic regions on the magnetic film layer. As a result, etching does not always result in consistently higher bit densities. 
     Other methods have been reported with varying results. For example, focused ion beams (FIB) poisoned with gallium (Ga + ) have been used in order to created discrete magnetic islands (also referred to as “dots” or “bits”) smaller than 70 nm in diameter. However, magnetic film layer modification using FIB is not readily scalable to mass production. 
     What is therefore needed is a way to define discrete magnetic and non-magnetic regions on a magnetic film layer that is both efficient and scalable to mass production. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Embodiments of this disclosure are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements, and in which: 
         FIG. 1  is a perspective view of individual bit cells in a bit-patterned media. 
         FIG. 2  is an exemplary flow diagram illustrating the steps of an embodiment of the disclosure. 
         FIG. 3  is an image illustrating an embodiment. 
         FIG. 4  is an image illustrating an embodiment. 
         FIG. 5  is a cross-sectional view of a medium undergoing a method embodiment. 
         FIG. 6  is an exemplary chart illustrating an embodiment. 
         FIG. 7  is an exemplary chart illustrating an embodiment. 
         FIG. 8  is an exemplary chart illustrating an embodiment. 
         FIG. 9  is an exemplary flow diagram illustrating the steps of an embodiment. 
         FIG. 10  is a cross-sectional view of a medium undergoing a method embodiment. 
     
    
    
     SUMMARY OF THE DISCLOSURE 
     An embodiment includes a method for forming patterned media by selectively oxidizing a cobalt-containing magnetic film layer on a medium substrate, then depositing or “backfilling” a non-magnetic matrix in the regions of the cobalt-containing magnetic film layer where the cobalt was removed. An embodiment includes an electrochemical cell for selectively oxidizing a cobalt-containing magnetic film layer to remove cobalt, and then backfilling the removed cobalt with a non-magnetic matrix. 
     DETAILED DESCRIPTION 
     A method for forming patterned media is disclosed herein. The patterned medium is formed by selective anodic oxidation of a cobalt-containing magnetic film layer on the medium substrate, then depositing or backfilling a non-magnetic matrix in the regions of the cobalt-containing magnetic film layer where cobalt was removed. By way of example,  FIG. 1  depicts an exemplary storage medium  104  comprising an array of magnetic dots  108  in a magnetic film layer. Each magnetic dot  108  is capable of storing a single bit of information. A typical magnetic film layer may be comprised of cobalt (Co) and platinum (Pt). 
       FIG. 2  is a flowchart illustrating the steps of an exemplary oxidation-reduction method in which the removal of cobalt from the media substrate and backfilled with a non-magnetic matrix in a single electrochemical cell, or “one-pot” method. As will be explained further below, the progress of the reaction may be attenuated by lowering the current applied to the single electrochemical cell. In  FIG. 2 , the electrochemical cell contains an electrolyte solution comprised of H 2 PtCl 6 , H 3 BO 3  and NH 4 Cl. The PtCl 6   −2  species in the electrolyte solution may act as the oxidizing agent while at the same time providing the Pt species for the non-magnetic matrix. In an embodiment, the pH level of the electrolyte solution is 5.0. 
     In block  201  of  FIG. 2 , a CoPt magnetic film is sputter or otherwise deposited onto a seed layer of a media substrate. The seed layer may be a ruthenium (Ru) seed layer or other equivalent layer. In block  203  of  FIG. 2 , Co is selectively removed from the magnetic film layer by selective anodic oxidation by lowering the current or potential in the electrolyte solution. This step may also be referred to herein as “anodic removal” or “AR.” AR will leave tracks or bits of 1.0-5.0 nm in the magnetic layer where CoPt is left behind, and grooves or trenches in the magnetic layer where Co has been selectively removed.  FIG. 3  is an example of a transmission electron microscopy (“TEM”) image of DTR media in which Co has been selectively removed from the magnetic film layer, leaving behind a 2.0-3.0 nm groove. One skilled in the art will appreciate that when viewed through a scanning electron microscope (“SEM”), a top-down view of DTR media which has had Co selectively removed using AR will show less dense, more porous, labyrinth-like microstructures in the areas exposed to AR as compared to the areas not exposed to AR. 
     One skilled in the art will appreciate that removing Co from a CoPt-containing magnetic film layer may leave Pt remaining in the grooves or trenches. This may be confirmed by observation with a cross-sectional TEM and nano-energy dispersive X-ray spectrometer (“nano-EDX”), in which the grooves or trenches may show a strong Pt signal as compared to areas not exposed to AR. One will appreciate that as a result of the remaining Pt, the interface between the CoPt bits and the exposed Pt layer may form a galvanic cell that can enhance the corrosion rate of the remaining CoPt between anodic oxidation and the following rinsing or drying steps. However, because the method of  FIG. 2  occurs in a single electrochemical cell, the opportunity for CoPt corrosion is significantly reduced. In block  205  of  FIG. 2 , the Pt in solution will be electrodeposited into the grooves left from the removed Co from block  203  of  FIG. 2 .  FIG. 4  is a TEM image of DTR media in which an overabundance (˜20 nm) of Pt has been electrodeposited into the grooves. One will appreciate that the excess Pt may be stripped in order to provide a substantially flat media surface. 
     One skilled in the art will also appreciate that removing Co from a CoPt-containing magnetic film layer using an oxidation process may leave a non-conductive oxidized film in the groove, as shown in  FIG. 3 . This may inhibit electrodeposition, since it is generally preferred that the surface upon which electrodeposition takes place be generally conductive. In order to encourage electrodeposition of Pt into the grooves, the medium may require pretreatment, such as pre-wet cleaning, chemical activation, cathodic reduction or other methods. Pretreatment may ensure that the surface of the grooves is generally conductive and the surface of the tracks or bits is non-conductive. 
       FIG. 5  is a cross-sectional view of a medium undergoing the method of  FIG. 2 . In block  501  the media substrate may comprised of a photoresist (“PR”) layer, a magnetic layer and one or more underlayers beneath the magnetic layer. The media substrate may be descummed in block  503  in order to remove foreign contaminants or residue. In block  505  of  FIG. 5 , the media substrate undergoes AR as described in block  203  of  FIG. 2 . In block  507  of  FIG. 5 , the trench or groove left from the AR process may be backfilled with the electrodeposition of Pt, NiPt (“NiP”) or other platinum-containing compounds. In block  509  of  FIG. 5 , the media substrate may be stripped to form a substantially flat surface. In block  511  of  FIG. 5 , the carbon overcoat (“COC”) may be deposited onto the media substrate. 
     As mentioned previously, the progress of the electrolyte reaction may be controlled by lowering the electric potential (measured in volts (V) vs. saturated calomel electrode (SCE)). One skilled in the art will appreciate that the voltages applied in the examples disclosed herein are merely exemplary and that other ranges are possible without departing from this disclosure or the scope of the appended claims. For example,  FIG. 6  is a chart of a rotating disc electrode (RDE) voltammetry study run in H 2 PtCl 6  solution at a range from pH 2.0 to pH 5.0, and illustrates that Pt may be deposited at potentials more negative than −0.4 V vs. SCE (shown as −400.0 mV in  FIG. 4 ). As shown,  FIG. 7  illustrates that selective anodic removal of Co from CoPt in an H 2 PtCl 6  solution having a pH of 5.0 occurs at a peak potential of E p =0.018 V vs. SCE. Pt oxidation can occur at E p =0.45 V vs. SCE. One will appreciate that the rate of reaction may also be controlled by varying potential. In an embodiment, the method illustrated in  FIG. 2  may be completed in 20 seconds. During the first 10 seconds at +0.3 V vs. SCE, selective removal of Co from the CoPt magnetic layer occurs by anodic oxidation. During the second 10 seconds, when potential is stepped to −0.4 V vs. SCE, Pt 4+  is reduced to Pt and electrodeposited into the trenches left by the removed Co. This rate of reaction is illustrated in the chart of  FIG. 8 . 
     One will appreciate that electrodeposition may be used to backfill other non-magnetic matrices containing other metals besides Pt. For example, a metal or alloy containing Pt, Ru, Ni, P, Cu, NiPt, CuNi, etc., may be electro-deposited into the trenches formed by the anodic removal of Co in block  203  of  FIG. 2 . electrodeposition may be more desirable than other deposition methods, such as vacuum deposition, since it may provide an even deposition of certain non-magnetic matrices without disturbing the tracks or bits left from the oxidation step. As a result, a low cost media fabrication process is provided because the need for post backfill lift-off or other CMP processes is obviated. 
     Even though electrodeposition may be a preferred method for backfilling the magnetic layer, one will appreciate that vacuum deposition methods may be used as well. For example, if a media manufacturer wants to use a metal or alloy containing Cr, Ta, NiTa, Ni, Ti and/or Cu, or use other non-magnetic matrices, it may employ alternative methods without departing from the scope of the appended claims or this disclosure.  FIG. 3  illustrates a method using collimated vacuum deposition of Cr. In the method of  FIG. 3 , the anodic oxidation step may not occur in the same reaction vessel, or “one-pot” as the deposition step because it requires different conditions. 
     In block  901  of  FIG. 9 , a CoPt magnetic film is sputter deposited onto a seed layer, which may be a Ru seed layer or other equivalent layer. In block  903  of  FIG. 9 , Co is selectively removed from the magnetic film layer by selective anodic oxidation to leave tracks or bits in the magnetic layer where CoPt is left behind, and grooves or trenches in the magnetic layer where Co has been selectively removed. In block  905  of  FIG. 9 , Cr is deposited into the trenches using collimated vacuum deposition techniques. 
       FIG. 10  is a cross-sectional view of a medium undergoing the method of  FIG. 9 .  FIG. 10  is similar to  FIG. 5 , except that Cr is deposited using collimated vacuum deposition rather than electrodeposition. In block  1001 , the media substrate may comprised of a photoresist (“PR”) layer, a magnetic layer and one or more underlayers beneath the magnetic layer. The media substrate may be descummed in block  1003  in order to remove foreign contaminants or residue. In block  1005  of  FIG. 10 , the media substrate undergoes AR as described in block  903  of  FIG. 9 . In  1007  of  FIG. 10 , the trench or groove left from the AR process may be backfilled with the collimated vacuum deposition of Cr. In block  1009  of  FIG. 10 , the media substrate may be stripped to form a substantially flat surface. In block  1011  of  FIG. 10 , the carbon overcoat (“COC”) may be deposited onto the media substrate. 
     One will appreciate that the methods describe herein disclose methods for controlled deposition into a trench formed by anodic oxidation of a cobalt-containing magnetic film layer. Because the deposition is controlled, little to no planarization of the magnetic film layer is required following deposition. This offers a significant advantage over milled (IBE) patterned media which typically has a trench depth of about 20 nm. 
     According to an embodiment, a result of one or more of the methods described above is a cobalt-containing magnetic film layer overlaying a medium substrate, the cobalt-containing magnetic film layer containing a plurality of magnetic portions separated from each other by a nonmagnetic matrix. One will appreciate that the magnetic film layer does not have to be directly deposited upon or in contact with the medium substrate, and the magnetic film layer may be separated from the underlying medium substrate by one or more interlayers. Using one or more of the methods described above, the nonmagnetic matrix may comprise an electrodeposited metal selected from the group consisting of platinum, ruthenium, nickel and copper. In addition, the nonmagnetic matrix may comprise a vacuum deposited metal selected from the group consisting of chromium, tantalum and nickel. 
     One will appreciate that in the description above and throughout, numerous specific details are set forth in order to provide a thorough understanding. It will be evident, however, to one of ordinary skill in the art, that an embodiment may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form to facilitate explanation. The description of the preferred embodiments is not intended to limit the scope of the claims appended hereto. Further, in the methods disclosed herein, various steps are disclosed illustrating some of the functions. One will appreciate that these steps are merely exemplary and are not meant to be limiting in any way. Other steps and functions may be contemplated without departing from this disclosure or the scope of the appended claims.