US20160372146A1

US20160372146A1 - Magnetic Disk of a Data Storage Device with Tempered Growth of Magnetic Recording Layer

Info

Publication number: US20160372146A1
Application number: US15/032,963
Authority: US
Inventors: Vignesh SUNDAR; Jian-Gang Zhu; David E. Laughlin
Original assignee: Carnegie Mellon University
Current assignee: Carnegie Mellon University
Priority date: 2013-11-01
Filing date: 2014-10-31
Publication date: 2016-12-22
Also published as: US20160293197A1; US10026431B2; WO2015066469A1

Abstract

In one aspect, a magnetic data storage device comprises a template layer, an underlayer, and a magnetic recording layer. The template layer includes a patterned array of protruding features. The underlayer is formed on the patterned array of protruding features of the template layer. The underlayer includes an array pattern of protruding features that aligns with the patterned array of protruding features of the template layer. The magnetic recording layer is formed on the underlayer. The magnetic recording layer includes columnar grains of magnetic material separated by grain boundaries of non-magnetic material, with each columnar grain being on a protruding feature of the array pattern of the underlayer, and the grain boundaries being in trenches between the protruding features of the array pattern of the underlayer.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. §119(e) to provisional U.S. Patent Application No. 61/962,172, filed Nov. 1, 2013, the entire contents of which are hereby incorporated by reference.

FIELD OF USE

The present disclosure relates to magnetic data storage devices.

BACKGROUND

A magnetic data storage device, such as a hard disk drive, includes a disk of magnetic materials for storing digital data. Magnetic data storage devices can offer high storage capacities at low costs as compared to some other available data storage devices.

SUMMARY

The present disclosure describes a magnetic disk of a data storage device and a method relating to fabricating a magnetic disk of a data storage device. The magnetic disk may include a template layer that is pre-patterned into an array of protruding features, such as dome-shaped or cone-shaped features. The morphology of the template layer may be fabricated using self-assembling nanostructures, such as a block of a block copolymer, which can be used to pattern a hexagonal array of nano-sized posts or pillars into a mask layer. The array pattern may be transferred from the mask layer into the template layer. The magnetic disk may include a suitable underlayer for defining a crystallographic orientation of magnetic material of a magnetic recording layer. The magnetic disk includes an etch-free magnetic recording layer with a grain boundary free of magnetic material in order to obtain low transition noise and high signal-to-noise ratio. The magnetic recording layer is grown on the array of protruding features such that the grains of magnetic material are positioned on the protruding features and the grain boundaries are positioned in trenches between the protruding features and in the spaces among the grains. The magnetic disk may be fabricated with better control of microstructure in terms of grain positions and lower distributions of grain size and grain boundary thickness as compared to other magnetic disks fabricated using other techniques.
In one aspect of the present disclosure, a magnetic disk of a data storage device comprises a template layer with a patterned array of protruding features; an underlayer formed on the patterned array of protruding features of the template layer, the underlayer having an array pattern of protruding features that aligns with the patterned array of protruding features of the template layer; and a magnetic recording layer formed on the underlayer, the magnetic recording layer comprising columnar grains of magnetic material separated by grain boundaries of non-magnetic material, with each columnar grain being on a protruding feature of the array pattern of the underlayer, and the grain boundaries being in trenches between the protruding features of the array pattern of the underlayer.
Implementations of the disclosure can include one or more of the following features. The magnetic disk may include a substrate comprising a single-crystal silicon wafer, a wafer with one or more oxide layers, an aluminum substrate, or a glass substrate; and an adhesion layer deposited on the substrate; and the template layer may be formed on the adhesion layer. The magnetic disk may include a substrate comprising a single-crystal silicon wafer, a wafer with one or more oxide layers, an aluminum substrate, or a glass substrate; a second underlayer formed on the substrate; a non-magnetic exchange break layer formed on the second underlayer; and one or more intermediate layers formed on the non-magnetic exchange break layer, the one or more intermediate layers configured to manage heat flow through the magnetic storage device; and the template layer may be formed on the one or more intermediate layers. The template layer may have a crystalline orientation that matches a lattice orientation of the underlayer. The template layer may include one or more of platinum, nickel, tungsten, magnesium, oxygen, ruthenium, aluminum, titanium, or molybdenum. The patterned array may be fabricated using self-assembled nanostructures to define positions of the dome-shaped features. The self-assembled nanostructures may include a copolymer of a block copolymer. The block copolymer may include poly(styrene-block-dimethyl siloxane), poly(styrene-block-methyl methacrylate), poly(styrene-block-isoprene), poly(styrene-block-vinyl pyridine), poly(styrene-block-ferrocenyl dimethylsilane), poly(ethylene oxide-block-isoprene), poly(ethylene oxide-block-butadiene), or poly(ethylene oxide-block-styrene). The patterned array may be fabricated using self-assembled nanoparticles or nanoimprint lithography. The underlayer may include one or more of ruthenium, magnesium oxide, aluminum, titanium carbide, tungsten, titanium nitride, or molybdenum. The magnetic material may include one or more of cobalt, chromium, platinum, iron, palladium, manganese, aluminum, or nickel, and the non-magnetic material comprises silicon oxide, tantalum oxide, titanium oxide, yttrium oxide, carbon, or boron. The patterned array of protruding features may include a patterned array of dome-shaped features, cone-shaped features, or a combination of dome-shape features and cone-shaped features. The columnar grains may have a pitch of 35 nanometers or less. The magnetic recording layer may have a thickness between 5 nanometers and 15 nanometers.
In another aspect of the present disclosure, a method for fabricating a magnetic disk of a data storage device comprises providing a template layer; transferring an array pattern of self-assembled nanostructures into the template layer to form a patterned array of protruding features in the template layer, with the template layer retaining the patterned array of protruding features during fabrication of other layers of the magnetic disk; depositing, onto the patterned array of protruding features of the template layer, an underlayer to have an array pattern of protruding features that aligns with the patterned array of protruding features of the template layer; and depositing, onto the underlayer, a magnetic recording layer to grow columnar grains of magnetic material on the protruding features of the array pattern of the underlayer and grain boundaries of non-magnetic material in trenches between the protruding features of the array pattern of the underlayer.
Implementations of the disclosure can include one or more of the following features. The method may include providing a substrate; depositing, onto the substrate, an adhesion layer; and depositing, onto the adhesion layer, at least 5 nanometers of one or more of platinum, nickel, tungsten magnesium oxide, ruthenium, aluminum, titanium, or molybdenum to form the template layer. The method may include providing a substrate; depositing, onto the substrate or an adhesion layer on the substrate, a second underlayer; depositing, onto the second underlayer, an non-magnetic exchange break layer; and depositing, onto the non-magnetic exchange break layer, at least 5 nanometers of one or more of platinum, nickel, tungsten magnesium oxide, ruthenium, aluminum, titanium, or molybdenum to form the template layer. Transferring the array pattern of self-assembled nanostructures into the template layer may include depositing, onto the template layer, a mask layer that may include one or more of carbon, silicon, silicon nitride, or tungsten; depositing, onto the mask layer, a block copolymer layer that may include a block copolymer dissolved in a solution, the solution may include one or more of toluene, acetone, chlorohexane, or propylene glycol monomethyl ether acetate, and the block copolymer may include poly(styrene-block-dimethyl siloxane), poly(styrene-block-methyl methacrylate), poly(styrene-block-isoprene), poly(styrene-block-vinyl pyridine), poly(styrene-block-ferrocenyl dimethylsilane), poly(ethylene oxide-block-isoprene), poly(ethylene oxide-block-butadiene), or poly(ethylene oxide-block-styrene), with one block of the block copolymer being nanostructures that self-assemble into the array pattern; treating the block copolymer to direct self-assembly of the nanostructures into the array pattern and to stabilize positions of the self-assembled nanostructures on the mask layer; etching the block copolymer layer to expose portions of the mask layer while retaining the self-assembled nanostructures; etching the exposed portions of the mask layer to transfer the array pattern of the self-assembled nanostructures into the mask layer to form a patterned array of pillars in the mask layer; removing the self-assembled nanostructures of the block copolymer layer; milling the template layer to transfer the patterned array of pillars into the template layer to form the patterned array of protruding features in the template layer; and removing remaining portions of the mask layer. Treating the block copolymer layer may include directing micro-phase separation or ordering of the block copolymer, with the nanostructures self-assembling into the array pattern. Each nanostructure of the array pattern may include one of a sphere or a cylinder positioned in a matrix of another block of the block copolymer. The array pattern may have a pitch less than 35 nanometers. Treating the nanostructure layer may include annealing the nanostructure layer using an elevated temperature. Treating the nanostructure layer may include annealing the nanostructure layer using a solvent vapor that may include one or more of toluene, acetone, dimethyl formamide, or hexane. Milling the template layer to transfer the patterned array of pillars into the template layer may include milling the template layer using a directional ion beam. The directional ion beam may have an angle of 5 to 40 degrees between the directional ion beam and a normal to a surface of the template layer into which the patterned array of protruding features is formed.
In yet another aspect of the present disclosure, a magnetic disk of a data storage device comprises a substrate; a template layer attached to the substrate layer, the template layer comprising a platinum film with face-centered cubic structure and (111) crystallographic texture, with the template layer retaining a patterned array of protruding features in the template layer during fabrication of other layers of the magnetic disk, with the patterned array fabricated using self-assembled nanostructures to define positions of the protruding features, wherein the self-assembled nanostructures comprise a copolymer of a poly(styrene-block-dimethyl siloxane) block copolymer; an underlayer grown on the patterned array of protruding features of the template layer, the underlayer comprising ruthenium film having a hexagonal close packed structure and (002) crystallographic texture and a thickness of 10 nanometers or less, the underlayer having an array pattern of protruding features that aligns with the patterned array of protruding features of the template layer, the underlayer defining a crystallographic orientation of magnetic material comprising a cobalt-chromium-platinum alloy; and a magnetic recording layer grown on the underlayer to have a thickness between 9 nanometers and 11 nanometers, the magnetic recording layer comprising columnar grains of the magnetic material separated by grain boundaries of non-magnetic material comprising an oxide, with the columnar grains having a pitch of 35 nanometers or less, with each columnar grain grown on a protruding feature of the array pattern of the underlayer, and the grain boundaries grown in trenches between the protruding features of the array pattern of the underlayer.
The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, object, and advantages will be apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows an example of a magnetic disk of a data storage device.

FIG. 2 is a flowchart of a process for fabricating a magnetic disk of a data storage device.

FIG. 3 shows cross-sectional views of a magnetic disk of a data storage device during different stages of fabrication.

FIG. 4 shows plane-view scanning electron micrographs of a magnetic disk of a data storage device during different stages of fabrication.

FIG. 5 shows microscopic images of a magnetic disk of a data storage device after templated growth of the magnetic recording layer.

FIG. 6 shows a microscopic image of a cross-section of a magnetic disk of a data storage device after templated growth of the magnetic recording layer.

DETAILED DESCRIPTION

FIG. 1 shows an example of a magnetic disk or magnetic recording media 100 of a data storage device. The magnetic disk 100 may be, for example, a perpendicular magnetic recording media, a heat assisted magnetic recording (HAMR) media, a microwave assisted magnetic recording (MAMR) media, or a bit-patterned media (BPM).
The magnetic disk 100 includes a substrate 102. The substrate 102 may include, for example, a single-crystal silicon wafer, a wafer with one or more oxide layers, an aluminum substrate, a glass substrate, or other suitable substrates.
The magnetic disk 100 includes a template layer 106 attached to the substrate 102. Depending on the substrate 102, the magnetic disk 100 may include an adhesion layer 104 for attaching the template layer 106 to the substrate 102. As an example, for the substrate 102 that includes a single-crystal (100) Si wafer with native oxide, the adhesion layer 104 may include a thin layer of an adhesive such as tantalum (Ta).
In some implementations, the magnetic disk 100 includes a soft underlayer (not shown) formed on the substrate, a non-magnetic exchange break layer (not shown) formed on the soft underlayer, and one or more intermediate layers (not shown) formed the non-magnetic exchange break layer. The intermediate layers may include suitable materials that facilitate the structural, magnetic, and thermal properties of subsequent layers deposited on the intermediate layers. The intermediate layers may include a film stack that is configured to manage heat flow through the magnetic disk 100.
The template layer 106 may be pre-patterned to have an array of protruding features 116. The protruding features 106 may be dome-shaped, cone-shaped, or a combination of a dome-shape and a cone-shape. The template layer 106 retains the patterned array of protruding features during fabrication of other layers of the magnetic disk 100. The template layer 106 may be used to control the structure of subsequent layers, such as an underlayer 108 and a magnetic recording layer 110, of the disk 100.
The underlayer 108 may have a topography that is similar to or conforms to the patterned array of protruding features 116 of the template layer 106. For example, the template layer 106 may be pre-patterned to have an array of dome-shaped features, and the underlayer 108 may be deposited on the template layer 106 to have an array of dome-shaped features in the underlayer 108 that aligns with the array of dome-shaped features in the template layer 106. As another example, the template layer 106 may be pre-patterned to have an array of cone-shaped features, and the underlayer 108 may be deposited on the template layer 106 to have an array of dome-shaped features in the underlayer 108 that aligns with the array of cone-shaped features in the template layer 106.
The magnetic recording layer 110 includes a single layer of columnar grains of magnetic material 112 that are separated by grain boundaries of non-magnetic material 114. The magnetization within each grain of magnetic material 112 is essentially uniform, and a bit of data may consist of one or more of these grains. The non-magnetic material 114 of the grain boundaries cut off the exchange coupling between neighboring grains.
The template layer 106 may contribute to the coherent growth of the magnetic recording layer 110 on the underlayer 108. The morphology of the template layer 106 may govern the positioning of subsequently grown magnetic material 112 and non-magnetic material 114 of the magnetic recording layer 110. When the magnetic recording layer 110 is grown on the underlayer 108, the morphology of the template layer 106 causes the magnetic material 112 to grow as a single layer of columnar grains on the protruding features 116 and the non-magnetic material 114 to grow as grain boundaries in the trenches 118 among the protruding features 116 to fill spaces among the columnar grains of magnetic material 112.
The template layer 106 may include a material that has a high resistance to oxidation so that surface characteristics and morphology of the template layer 106 are retained and not modified when exposed to atmosphere or during processing, such as reactive ion etching, to prevent negatively impacting the growth of the underlayer 108 and the magnetic recording layer 110 of the disk 100. The template layer 106 may include, for example, platinum (Pt), nickel (Ni), oxygen, magnesium oxide (MgO), aluminum (Al), titanium carbide (TiC), titanium nitride (TiN), tungsten (W), molybdenum (Mo), ruthenium (Ru), or a combination, such as NiW or RuAl. Other suitable materials may be used for the template layer 106.
The underlayer 108 may include a material that facilitates appropriate crystallographic texture in the magnetic material 112 of the magnetic recording layer 110. The underlayer 108 may include, for example, ruthenium (Ru), magnesium oxide (MgO), aluminum (Al), titanium carbide (TiC), tungsten (W), titanium nitride (TiN), molybdenum (Mo), or a combination, such as RuAl. Other suitable materials may be used for the underlayer 108.
The magnetic material 112 in the magnetic recording layer 110 may include, for example, cobalt (Co), chromium (Cr), platinum (Pt), iron (Fe), palladium (Pd), manganese (Mn), aluminum (Al), nickel (Ni), or a combination, such as CoCrPt alloys, FePt alloys, FePd alloys, MnAl alloys, CoPt alloys, or FeNi alloys. The non-magnetic material 114 in the magnetic recording layer 110 may include, for example, silicon oxide (SiO_x), tantalum oxide (Ta_xO_y), titanium oxide, yttrium oxide, other such oxides, carbon, or boron. The non-magnetic material 114 may have low solubility in the materials used for the template layer 106, the underlayer 108, and the magnetic recording layer 110. Other suitable materials may be used for the magnetic material 112 and the non-magnetic material 114 of the magnetic recording layer 110.
A material for the template layer 106 may be selected depending on materials selected for the underlayer 108 and the magnetic recording layer 110. The selected template material may have a crystalline orientation that substantially matches the lattice orientation of the underlayer 108 to achieve good texture with a low rocking angle, e.g., αθ₅₀=4 degrees, of the underlayer 108.
For example, the magnetic material 112 may include a CoCrPt alloy, the underlayer 108 may include ruthenium, and the template layer 106 may include platinum. Platinum, having a face-centered cubic (FCC) crystal structure, may favor film growth with (111) texture. In the (111) plane, the lattice mismatch with ruthenium (002) in the underlayer 108 may be approximately 2.5%. Platinum with (111) texture can thus be used in the template layer 106 for growing the underlayer 108 that includes ruthenium epitaxially with (002) texture.
As another example, for HAMR media, the template layer 106 may include Mo or Pt for templated growth of the magnetic recording layer 110 with MgO as an underlayer 108. The Pt may have a (100) texture, the Mo may have a (100) texture, and the MgO may have a (100) texture.
FIG. 2 is a flowchart of a process 200 for fabricating a magnetic disk of a data storage device, such as the magnetic disk 100 of FIG. 1. Briefly, the process 300 includes providing a substrate (202), depositing a template layer (204), transferring an array pattern of self-assembled nanostructures into the template layer to form a patterned array of protruding features in the template layer (206), depositing an underlayer to have a an array pattern of protruding features that aligns with the patterned array of protruding features in the template layer (208), and depositing a magnetic recording layer to grow columnar grains of magnetic material on the protruding features of the array pattern of the underlayer and grain boundaries of non-magnetic material in trenches between the protruding features of the array pattern of the underlayer to fill spaces separating the columnar grains (210). The process 200 will now be described in more detail with reference to FIG. 3.
FIG. 3 shows cross-sectional views of a magnetic disk during different stages (a)-(j) of fabrication. In stage (a), a substrate 141 is provided, and a template layer 143 is attached to the substrate 141. The template layer 143 may be attached to the substrate 141 using an adhesion layer 142 that includes an adhesive. The adhesive may be sputtered onto the substrate 141 to have a thickness of approximately 3 nanometers (nm). In some implementations, a suitable template material may be sputtered onto the substrate layer 141 or the adhesion layer 142 to create a thin film for the template layer 143. The template layer 143 may have a thickness of at least 5 nm.
In some implementations, a soft underlayer may be deposited on the substrate 141 or the adhesion layer 142. A non-magnetic exchange break layer may be deposited on the soft underlayer, and one or more intermediate layers may be deposited on the exchange break layer. The template material may be sputtered onto the intermediate layers to create the thin film for the template layer 143.
In stages (b)-(g), an array pattern of self-assembled nanostructures is transferred into the template layer 143 to form a patterned array of protruding features in the template layer 143. To transfer the array pattern, a mask layer 321 is deposited onto the template layer 143 at stage (b). The mask layer 321 may include amorphous carbon, diamond-like carbon, silicon, silicon nitride, or any other suitable mask material such as tungsten, or a combination of materials. The mask layer 321 may include one or more layers of material to aid the transfer of the array pattern to the template layer 143. For example, a thin film stack that includes different materials such as silicon nitride, amorphous silicon, or silicon oxide can be used in combination with carbon to improve transfer of the array pattern into the template layer 143.
The mask material may be sputtered onto the template layer 143 to have a thickness of approximately 20 nm. In some implementations, the mask layer 321 includes amorphous carbon. Carbon may have a low ion-milling rate as compared to the ion-milling rate of the material used in the template layer 143. Carbon may have a high etch rate using oxygen plasma in reactive ion etching (RIE), which may enable pattern transfer into the mask layer 321.
In stage (c), a nanostructure or block copolymer layer 331 is deposited onto the mask layer 321. The nanostructure layer 331 may be spin-coated onto the mask layer 321. The nanostructure layer 321 may include a block copolymer. Block copolymers consist of two or more “blocks” of polymer chains A and B that are usually energetically incompatible with each other. These polymer chains are connected by a covalent bond. At equilibrium, the two chains do not mix since mixing is energetically unfavorable, and thus the chains phase separate. However, since the chains are connected by a covalent bond, the phase separation can only occur on a micro-scale.
Block copolymers form different morphologies depending on the relative volume fractions of the two blocks. The size of the features obtained is related to the chain length or the molecular weight. The phase-segregating tendency of block copolymers is related to the product of the Flory-Huggins parameter χ and the degree of polymerization (which is related to molecular weight). Block copolymers which form a hexagonal array of the nanostructures 342, such as cylinders (oriented perpendicular to plane of the mask layer 321) or spheres, of one block in the other block's matrix can be used in the nanostructure layer 331. Suitable block copolymers may include, for example, poly(styrene-block-dimethyl siloxane), poly(styrene-block-methyl methacrylate), poly(styrene-block-isoprene), poly(styrene-block-vinyl pyridine), poly(styrene-block-ferrocenyl dimethylsilane), poly(ethylene oxide-block-isoprene), poly(ethylene oxide-block-butadiene), or poly(ethylene oxide-block-styrene).
Block copolymer may be dissolved in a suitable solution 341 and may be deposited onto the mask layer 321 from the solution 341. The choice of solution 341 may depend on the block copolymer. The solution 341 may include, for example, toluene, acetone, dimethyl formamide, hexane, chlorohexane, or propylene glycol monomethyl ether acetate. The concentration of the solution 341 and speed of deposition are such that one layer of nanostructures 342, such as spheres or cylinders, suspended in the solution 341 is obtained in the nanostructure layer 331. The nanostructure layer 331 may be deposited by spin coating, dip coating, spray coating, or other suitable polymer thin film fabrication techniques.
In some implementations, the nanostructure layer 331 includes poly (styrene-b-dimethyl siloxane) (PS-b-PDMS). PS-b-PDMS may have a high Flory-Huggins parameter χ, which may enable fabrication of array patterns with small pitch of around 15 nm. With this block copolymer, there may be further potential to obtain sub-10 nm features. PS-b-PDMS may have a high etch selectivity between the two blocks in reactive ion etching using an oxygen plasma, where PS etches faster than PDMS, which may enable the pattern transfer. In some implementations, PS-b-PDMS with a molecular weight of 13.9 kg/mol, and a PDMS volume fraction of 17.2% may be used to create a pattern with approximately 15 nm pitch. For this volume fraction, PS-b-PDMS micro-phase separates into PDMS spheres in a PS matrix. The block copolymer may be pre-diluted in a solution of toluene. The PS-b-PDMS may be spin coated onto the mask layer 321 from the toluene solution, using a dynamic dispense method, with a spread step of 600 rpm for 6 seconds and a spin step of 6200 rpm for 60 seconds.
Since spin-coating may not be an equilibrium process, the arrangement of the nanostructures 342 after spin coating may be disordered. The nanostructure layer 331 may be treated to direct self-assembly of the nanostructures 342 into the array pattern to stabilize positions of the self-assembled nanostructures 342 on the mask layer 331 at stage (d). For fabricating bit patterned media, the nanostructure layer 331 may be treated to obtain long range ordering of the nanostructures 342. To direct self-assembly (e.g., micro-phase separation or ordering) of the nanostructures 342, polymer chain mobility is increased by either subjecting the nanostructure layer 331 to an elevated temperature in a process such as thermal annealing or subjecting the nanostructure layer 331 to a solvent vapor in a process such as solvent annealing. To maximize the favorable polymer-solvent interactions, the polymer film absorbs the solution and swells, resulting in a larger free-volume and higher mobility for the polymer chains. The partial pressure of solvent vapor and annealing time may be optimized to improve the ordering of the polymer domains. For example, PS-b-PDMS film may be exposed to toluene vapor for 3 hours to facilitate micro-phase separation.
At stage (c), the nanostructure layer 331 may be etched to expose portions of the mask layer 321 while retaining the self-assembled nanostructures 342. The technique used to etch the nanostructure layer 331 may depend on the materials selected for the nanostructure layer 331 and the mask layer 321. Techniques such as reactive ion-etching (RIE) can be used to selectively etch one block of the block copolymer. Other wet etching techniques (such as selective solubility in particular solvents) or dry-etching techniques (such as exposure to radiation or reactive gases followed by dissolution of the damaged or etched block) may also be suitable depending on the polymer selected for the nanostructure layer 331.
For example, PDMS, due to its low surface energy, may form a thin layer at the top of the nanostructure layer 331, and this thin layer may be etched away using a CF4 plasma in RIE. PS matrix surrounding the nanostructures 342 may be subsequently etched away in a directional fashion using a low-bias oxygen plasma. The low-bias may minimize the physical etching in RIE, resulting in optimal pattern transfer although directionality may be lowered. During this process, the nanostructures 342 may become partially oxidized and may be used as an etch-mask to transfer the array pattern using O₂plasma into the underlying mask layer 321.
At stage (f), the exposed portions of the mask layer 321 may be etched to transfer the array pattern of the self-assembled nanostructures 342 into the mask layer 321 to form a patterned array of pillars in the mask layer 321. After etching the mask layer 321, the self-assembled nanostructures 342 of the etched nanostructure layer 331 may be removed. For example, RIE using oxygen plasma with a bias of around 200V in a Plasma-Therm 790 RIE system can be used to etch the mask layer 321 and transfer the pattern of the nanostructure layer 331 into the mask layer 321. For a nanostructure layer 331 that includes PS-b-PDMS, reactive ion etching (RIE) may be used to remove the nanostructures 342 of the nanostructure layer 331. Although the above describes transferring an array pattern into the mask layer 321 using self-assembled nanostructures, the array pattern may be transferred into the mask layer 321 using other suitable techniques such as patterning using self-assembling nanoparticles and nanoimprint lithography.
At stage (g), the template layer 143 may be milled or etched to transfer the patterned array of pillars of the mask layer 321 into the template layer 143 to form the patterned array of protruding features in the template layer 143, and remaining portions of the mask layer 321 are removed. Pattern transfer into the template layer 143 can be accomplished by ion-milling or methanol etching.
In the case of ion-milling, a directional argon beam may be used. Other suitable gases include, for example, xenon, neon, or krypton. The angle between the ion-beam and the plane of the template layer 143 may be optimized to minimize re-deposition and shadowing effects. Ion-milling may be applicable to a wide range of metals that can be used as template layers. By varying the ion-milling angle, height of mask, beam voltage, current and other parameters, the morphology of the template layer can be varied. The mask layer 321 may be removed by optimizing the milling time, through a separate etching process, or both.
In some implementations, ion-milling using a Commonwealth Scientific Ion Mill may be performed to pattern the template layer 143. The template layer 143 may be oriented at an angle of 5 to 40 degrees, e.g., 12.5°, to the ion beam and rotated in order to ensure uniform milling. Milling may be performed at a bias of 500V and current of 40 mA. These conditions may be optimized based on the choice of materials for the template layer 143 and the mask layer 321, and the settings of the individual ion-mill systems.
In some implementations, the template layer 143 may be subjected to a short sputter-etch to clean the surface of the template layer 143. Other suitable cleaning techniques may be used to clean the surface of the template layer 143. Sputter-etching of the template layer 143 may result in damage and loss of the patterned morphology in the template layer 143 within a very short time. Using platinum for the template layer 143 may minimize the damage to the template layer 143, as platinum may not be susceptible to oxidation.
At stage (h), an underlayer 144 is deposited onto the patterned array of protruding features of the template layer 143 to have an array pattern of protruding features that aligns with the patterned array of protruding features of the template layer 143. A thin underlayer film may be deposited by, for example, sputtering. In some implementations, Ru is used as the underlayer 144 in conjunction with a magnetic recording layer that includes CoCrPt magnetic material. A thin layer of the underlayer film, approximately 5 nm to 6 nm in thickness, may be sputtered onto the template layer 143 using RF sputtering in a Leybold Heraeus Z-400 sputtering system. The underlayer 144 is kept thin enough so that the morphology of the template layer 143 created after ion-milling is maintained. This thin layer of Ru may be used to obtain the correct crystal structure (HCP) of the CoCrPt magnetic material of the magnetic recording layer. If Pt with a (111) texture was previously deposited as the template layer 143, Ru may grow epitaxially with (002) texture under optimized sputtering conditions.
In some implementations, a few monolayers of non-magnetic material 145 may be sputtered onto the underlayer 144 at stage (i). The non-magnetic material 145 may prefer to go into the trenches of the patterned array to form a segregant layer. The segregant layer may be maintained thin enough so that the non-magnetic material 145 does not cover the patterned array in a conformal fashion.
At stage (j), a magnetic recording layer is deposited onto the underlayer 144 to grow columnar grains of magnetic material 146 on the protruding features of the patterned array and grain boundaries of the non-magnetic material 145 in spaces separating the columnar grains. The magnetic recording layer may be grown on the underlayer 144 using sputtering, which may result in a granular microstructure defined by the microstructural and morphological properties of the template layer 143. DC, RF sputtering or their magnetron counterparts can be used. Sputtering parameters, such as pressure of Ar gas in the chamber, bias voltage, and rate of deposition, may be optimized to obtain columnar growth of the grains of magnetic material. In some implementations, CoPt may be used as the magnetic material 146 and SiO₂may be used as the non-magnetic material 145. The magnetic recording layer may have a thickness of between 5 nm and 15 nm, e.g., approximately 10 nm, and sputtered using RF sputtering in a Leybold Heraeus Z-400 sputtering system. The grains of magnetic material 146 may have a pitch of 35 nm or less, e.g., 15 nm.
Sample morphology may be characterized at various stages of fabrication using a FEI Sirion 600 Scanning Electron Microscope. Magnetic hysteresis loops may be studied using a Princeton Alternating Gradient Force Magnetometer. Further microstructural analysis may be carried out using a 200 kV FEI Tecnai F20 Super-Twin Transmission Electron Microscope, using both the Bright Field, and High Angle Annular Dark Field (HAADF) Scanning Transmission Electron Microscopy (STEM) modes. Both plane-view and cross-sectional microstructure may be characterized.
FIG. 4 shows plane-view scanning electron micrographs 402, 404, 406, 408 of a magnetic disk during different stages (c), (e), (f), (g) of fabrication. Micrograph 402 shows the disordered nature of the polymer blocks after deposition of the nanostructure layer 331 at stage (c). Because spin-coating may not be an equilibrium process, the nanostructure layer 331 may be treated by, for example, annealing to increase chain mobility and improve ordering of the nanostructures 342. The improvement in ordering is shown in micrograph 404. The center-to-center spacing (pitch) of the array pattern may be approximately 15 nm or less. As shown in micrographs 406 and 408, the diameter of a protruding feature in the template layer 143 may be larger than the diameter of a pillar in the mask layer 321 because ion-milling may be performed at an angle to avoid re-deposition issues. Thus, instead of vertical side-walls which are obtained by RIE after pattern transfer into mask layer 321 at stage (f), the morphology of the template layer 143 at stage (g) is an array of protruding features, which may be used for obtaining templated growth of the magnetic recording layer at stage (j).
After deposition of the underlayer 144 and the magnetic recording layer, transmission electron microscopy may be used to study the microstructure of the magnetic recording layer. FIG. 5 shows micrographs 502 and 504 of a magnetic disk after templated growth of the magnetic recording layer. As shown in micrographs 502 and 504, the magnetic recording layer follows the morphology set by the template layer 143. The non-magnetic material 145, which appears as a lighter gray in the micrographs 502 and 504, is observed around the grains of magnetic material 146.
The cross-section microstructure of the magnetic disk may be observed using scanning transmission electron microscopy. FIG. 6 shows a microscopic image 602 of a cross-section of a magnetic disk after templated growth of the magnetic recording layer. In the high angle annular dark field mode, the contrast observed may be due to atomic number or ‘Z’ contrast. Thus, Pt, which may be the heaviest among the materials included in the magnetic disk, may have the maximum brightness. CoPt and Ru may have similar contrast since the signal from Co and Pt may be averaged. SiO₂may appear the darkest. As shown in the image 602, grains of magnetic material, e.g., CoPt, grows on the protruding features, e.g., Pt domes, as defined by the template layer, while the non-magnetic material, e.g., SiO₂, grows between the grains of magnetic material.
A number of implementations have been described. Nevertheless, various modifications can be made without departing from the spirit and scope of the processes and techniques described herein. In addition, the processes depicted in the figures do not require the particular order shown, or sequential order, to achieve desirable results. In addition, other steps can be provided, or steps can be eliminated, from the described processes, and other components can be added to, or removed from, the describe apparatus and systems. Accordingly, other embodiments are within the scope of the following claims.

Claims

What is claimed is:

1. A magnetic disk of a data storage device, the magnetic disk comprising:

a template layer with a patterned array of protruding features;

an underlayer formed on the patterned array of protruding features of the template layer, the underlayer having an array pattern of protruding features that aligns with the patterned array of protruding features of the template layer; and

a magnetic recording layer formed on the underlayer, the magnetic recording layer comprising columnar grains of magnetic material separated by grain boundaries of non-magnetic material, with each columnar grain being on a protruding feature of the array pattern of the underlayer, and the grain boundaries being in trenches between the protruding features of the array pattern of the underlayer.

2. The magnetic disk of claim 1, further comprising:

a substrate comprising a single-crystal silicon wafer, a wafer with one or more oxide layers, an aluminum substrate, or a glass substrate; and

an adhesion layer deposited on the substrate;

wherein the template layer is formed on the adhesion layer.

3. The magnetic disk of claim 1, further comprising:

a substrate comprising a single-crystal silicon wafer, a wafer with one or more oxide layers, an aluminum substrate, or a glass substrate;

a second underlayer formed on the substrate;

a non-magnetic exchange break layer formed on the second underlayer; and

one or more intermediate layers formed on the non-magnetic exchange break layer, the one or more intermediate layers configured to manage heat flow through the magnetic storage device;

wherein the template layer is formed on the one or more intermediate layers.

4. The magnetic disk of claim 1, wherein the template layer has a crystalline orientation that matches a lattice orientation of the underlayer, and the template layer comprises one or more of platinum, nickel, tungsten, magnesium, oxygen, ruthenium, aluminum, titanium, or molybdenum.

5. The magnetic disk of claim 1, wherein the patterned array is fabricated using self-assembled nanostructures to define positions of the dome-shaped features, and wherein the self-assembled nanostructures comprise a copolymer of a block copolymer, the block copolymer comprising poly(styrene-block-dimethyl siloxane), poly(styrene-block-methyl methacrylate), poly(styrene-block-isoprene), poly(styrene-block-vinyl pyridine), poly(styrene-block-ferrocenyl dimethylsilane), poly(ethylene oxide-block-isoprene), poly(ethylene oxide-block-butadiene), or poly(ethylene oxide-block-styrene).

6. The magnetic disk of claim 1, wherein the patterned array is fabricated using self-assembled nanoparticles or nanoimprint lithography.

7. The magnetic disk of claim 1, wherein the underlayer comprises one or more of ruthenium, magnesium oxide, aluminum, titanium carbide, tungsten, titanium nitride, or molybdenum.

8. The magnetic disk of claim 1, wherein the magnetic material comprises one or more of cobalt, chromium, platinum, iron, palladium, manganese, aluminum, or nickel, and the non-magnetic material comprises silicon oxide, tantalum oxide, titanium oxide, yttrium oxide, carbon, or boron.

9. The magnetic disk of claim 1, wherein the patterned array of protruding features comprises a patterned array of dome-shaped features, cone-shaped features, or a combination of dome-shape features and cone-shaped features.

10. The magnetic disk of claim 1, wherein the columnar grains have a pitch of 35 nanometers or less.

11. The magnetic storage device of claim 1, wherein the magnetic recording layer has a thickness between 5 nanometers and 15 nanometers.

12. A method for fabricating a magnetic disk of a data storage device, the method comprising:

providing a template layer;

transferring an array pattern of self-assembled nanostructures into the template layer to form a patterned array of protruding features in the template layer, with the template layer retaining the patterned array of protruding features during fabrication of other layers of the magnetic disk;

depositing, onto the patterned array of protruding features of the template layer, an underlayer to have an array pattern of protruding features that aligns with the patterned array of protruding features of the template layer; and

depositing, onto the underlayer, a magnetic recording layer to grow columnar grains of magnetic material on the protruding features of the array pattern of the underlayer and grain boundaries of non-magnetic material in trenches between the protruding features of the array pattern of the underlayer.

13. The method of claim 12, further comprising:

providing a substrate;

depositing, onto the substrate, an adhesion layer; and

depositing, onto the adhesion layer, at least 5 nanometers of one or more of platinum, nickel, tungsten magnesium oxide, ruthenium, aluminum, titanium, or molybdenum to form the template layer.

14. The method of claim 12, further comprising:

providing a substrate;

depositing, onto the substrate or an adhesion layer on the substrate, a second underlayer;

depositing, onto the second underlayer, an non-magnetic exchange break layer; and

depositing, onto the non-magnetic exchange break layer, at least 5 nanometers of one or more of platinum, nickel, tungsten magnesium oxide, ruthenium, aluminum, titanium, or molybdenum to form the template layer.

15. The method of claim 12, wherein transferring the array pattern of self-assembled nanostructures into the template layer comprises:

depositing, onto the template layer, a mask layer comprising one or more of carbon, silicon, silicon nitride, or tungsten;

depositing, onto the mask layer, a block copolymer layer comprising a block copolymer dissolved in a solution, the solution comprising one or more of toluene, acetone, chlorohexane, or propylene glycol monomethyl ether acetate, and the block copolymer comprising poly(styrene-block-dimethyl siloxane), poly(styrene-block-methyl methacrylate), poly(styrene-block-isoprene), poly(styrene-block-vinyl pyridine), poly(styrene-block-ferrocenyl dimethylsilane), poly(ethylene oxide-block-isoprene), poly(ethylene oxide-block-butadiene), or poly(ethylene oxide-block-styrene), with one block of the block copolymer being nanostructures that self-assemble into the array pattern;

treating the block copolymer to direct self-assembly of the nanostructures into the array pattern and to stabilize positions of the self-assembled nanostructures on the mask layer;

etching the block copolymer layer to expose portions of the mask layer while retaining the self-assembled nanostructures;

etching the exposed portions of the mask layer to transfer the array pattern of the self-assembled nanostructures into the mask layer to form a patterned array of pillars in the mask layer;

removing the self-assembled nanostructures of the block copolymer layer;

milling the template layer to transfer the patterned array of pillars into the template layer to form the patterned array of protruding features in the template layer; and

removing remaining portions of the mask layer.

16. The method of claim 15, wherein treating the block copolymer layer comprises:

directing micro-phase separation or ordering of the block copolymer, with the nanostructures self-assembling into the array pattern, with each nanostructure of the array pattern comprising one of a sphere or a cylinder positioned in a matrix of another block of the block copolymer, with the array pattern having a pitch less than 35 nanometers.

17. The method of claim 15, wherein treating the nanostructure layer comprises:

annealing the nanostructure layer using an elevated temperature.

18. The method of claim 15, wherein treating the nanostructure layer comprises:

annealing the nanostructure layer using a solvent vapor comprising one or more of toluene, acetone, dimethyl formamide, or hexane.

19. The method of claim 15, wherein milling the template layer to transfer the patterned array of pillars into the template layer comprises: milling the template layer using a directional ion beam, with the directional ion beam having an angle of 5 to 40 degrees between the directional ion beam and a normal to a surface of the template layer into which the patterned array of protruding features is formed.

20. A magnetic disk of a data storage device, the magnetic disk comprising:

a substrate;

a template layer attached to the substrate layer, the template layer comprising a platinum film with face-centered cubic structure and (111) crystallographic texture, with the template layer retaining a patterned array of protruding features in the template layer during fabrication of other layers of the magnetic disk, with the patterned array fabricated using self-assembled nanostructures to define positions of the protruding features, wherein the self-assembled nanostructures comprise a copolymer of a poly(styrene-block-dimethyl siloxane) block copolymer;

an underlayer grown on the patterned array of protruding features of the template layer, the underlayer comprising ruthenium film having a hexagonal close packed structure and (002) crystallographic texture and a thickness of 10 nanometers or less, the underlayer having an array pattern of protruding features that aligns with the patterned array of protruding features of the template layer, the underlayer defining a crystallographic orientation of magnetic material comprising a cobalt-chromium-platinum alloy; and

a magnetic recording layer grown on the underlayer to have a thickness between 9 nanometers and 11 nanometers, the magnetic recording layer comprising columnar grains of the magnetic material separated by grain boundaries of non-magnetic material comprising an oxide, with the columnar grains having a pitch of 35 nanometers or less, with each columnar grain grown on a protruding feature of the array pattern of the underlayer, and the grain boundaries grown in trenches between the protruding features of the array pattern of the underlayer.