Patent Application
20120082800
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2010-223216, filed on Sep. 30, 2011, the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to a method for manufacturing a magnetic recording medium.
Recently, in a magnetic recording medium incorporated into a hard disk drive (HDD), enhancement of the track density is inhibited due to interference between adjacent tracks. To enhance the track density, it is important to reduce a writing blur attributable to a fringe effect of a recording head magnetic field.
In view of above, a discrete track-type patterned medium (DTR medium) in which recording tracks are physically separated, and a bit patterned medium (BPM) in which recording bits are physically separated, have been proposed. Such patterned medium can have an increased track density because a side erase during recording and a side read during reproduction can be reduced, and these mediums are promising as a high-density magnetic recording medium. In this specification, the term “patterned medium” includes the DTR medium and the BPM.
When recording or reproducing a medium (patterned medium) having surface convexes/concaves by a flying head, the flying property is important. For example, in a DTR medium, with an attempt to completely separate adjacent tracks, a groove is formed to a total depth of 20 nm by removing a magnetic recording layer composed of a ferromagnetic material of about 15 nm in thickness and a protective layer of about 5 nm in thickness. On the other hand, the designed flying amount of the flying head is about 10 nm. Therefore, ensuring of the flying property of the head by filling the groove with a nonmagnetic material and thereby smoothing the DTR medium surface has been considered. However, such smoothing process is difficult.
Instead, a method of patterning a smooth magnetic recording layer by local transformation has been proposed (JP-2009-087454-A and JP-2008-077756-A).
However, in JP-2009-087454-A and JP-2008-077756-A, the non-recording area for dividing the recording area of the patterned medium is magnetically separated from the recording area by completely omitting a magnetic material or depriving the non-recording area of magnetism through fluorination or reduction in the Co concentration. In the deactivation by fluorination or the like, when the recording layer contains easily volatile elements including fluorine, a free atom incapable of being completely bonded volatilizes to bring about a phenomenon of the deactivation effect being weakened or transfers to the recording layer to cause a problem of corrosion, failing in allowing the finished medium to have sufficiently high environmental resistance.
A general architecture that implements the various feature of the present invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments and not to limit the scope of the present invention.
In general, according to one embodiment, there is provided a method for manufacturing a magnetic recording medium, the method including: depositing a magnetic recording layer on a substrate; forming a mask on a region of the magnetic recording layer corresponding to a recording area; irradiating another region of the magnetic recording layer where the mask is not formed with an ion beam using a C-containing gas as a source gas to deactivate the another region and to thereby form a non-recording area; and forming a protective film over an entire surface of the substrate.
An embodiment will be described below by referring to the drawings.
One example of the method for manufacturing a magnetic recording medium according to an embodiment is described by referring to
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Separately, a stamper 60 having a concave/convex pattern (for example, as shown in
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The characteristic features of this embodiment are described in detail below.
<Medium Having C-Containing Non-Recording Area>
The magnetic recording layer in this embodiment consists of a recording area mainly composed of a magnetic element, and a non-recording area formed by adding a C element to the recording area. In the non-recording area, the addition of C enables deactivating the magnetism and enhancing the fringe performance of the medium. Furthermore, the medium in which C is added has resistance to heat or humidity and exhibits good environmental resistance. The elements constituting the non-recording area contain at least the same element as that in the recording area. By containing the same element, unevenness of the composition can be reduced and the resistance to corrosion can be improved.
The C concentration is preferably 1% or more of the magnetic element in terms of the atomic ratio. When 1% or more of this element is contained, the lattice of the recording layer can be distorted to deactivate the magnetism. Whether 1% or more of the element is contained can be easily measured by an analysis method such as EDX and EELS. Also, when 20% or more of the element is contained, the Ms can be reduced to 20% or less, and this is more preferred in view of fringe characteristics of the medium.
Addition of C is not achieved only by depositing it on the magnetic recording layer by CVD, sputtering or the like method. For example, even when DLC is deposited as a protective film on the magnetic recording layer, C does not diffuse into the recording layer in a concentration of 1% or more. Also, even when the portion corresponding to the non-recording area is etched to half the thickness and concave/convex implanting with C is performed, the characteristics of the present invention are not obtained.
It is preferred to aggressively add C by the following method.
Although both of the non-recording area (C-containing layer 51a) and the DLC protective layer 52 contain C, it is possible to distinguish them from each other, because only the non-recording area contains an element which is used in the magnetic recording layer 51. For example, a boundary between the non-recording area (C-containing layer 51a) and the DLC protective layer 52 may be determined by performing the point analysis with the cross-sectional TEM-EELS to analyze the spectrum.
<Patterning of Magnetic Recording Layer>
The step for patterning the magnetic recording layer, included in the manufacturing method of this embodiment, can be performed by irradiating with an ion beam and thereby deactivating the magnetic recording layer. By deactivation of the magnetism, the fringe characteristics of the magnetic recording medium are enhanced. By implanting a C element in the non-recording area of the magnetic recording layer, particularly the mechanical strength of the recording layer can be increased.
The magnetism deactivation step in this embodiment indicates a step of weakening the magnetism in the area exposed by the mask of the magnetic recording layer, compared with the magnetism in the area covered with the mask. Weakening of the magnetism means to effect soft magnetization, non-magnetization or diamagnetization. Such a change in the magnetism can be observed by measuring Ms, Hn, Hs, Hc or the like value by means of VSM (vibrating sample magnetometer) or a Kerr (magneto-optical Kerr effect) measuring apparatus.
In the method of this embodiment, the magnetism deactivation step can be performed by irradiating with an ion beam. Upon ion beam irradiation, a C element is caught between lattices of elements constituting the magnetic recording medium or caused to substitute for the recording layer element, whereby the magnetism can be weakened. The ion beam irradiation is performed is irradiated at an accelerating energy of approximately from 500 eV to 20 keV by plasma conversion using an ECR (electron cyclotron resonance) system or an RF power source. By this irradiation, the magnetic recording layer can be implanted with a C element and deprived of the magnetism.
When performing the deactivation by directly irradiating the magnetic recording layer with an ion beam, CO, CO2, CH4, C2H2, C2H4, C2H6, C3H6, C3H8, C4H6, C4H8, C4H10, HCN or CH3F is preferably used as the ion beam source.
By using such a gas, a C element can be efficiently implanted into the exposed magnetic recording layer. A gas species having a large molecular weight brings about etching of the magnetic recording layer and its use is not preferred. It is also disadvantageous to contain many corrosive elements such as fluorine and chlorine, because a problem of corrosion is caused due to their reaction with an element constituting the recording layer.
At the time of implanting a C element, it is effective to mix an assist gas such as He, Ne, Ar, Kr, Xe, H2, N2, O2 and O3. By mixing such a gas, the magnetic recording layer can be amorphized and the deactivation effect can be more increased. To obtain the C implanting effect, the partial pressure ratio of the assist gas may be set to 75% or less.
Deactivation may also be performed by depositing a C-containing layer on the magnetic recording layer and irradiating with an ion beam. In this case, in order to obtain a sufficiently high C implanting effect, the layer deposited is preferably composed to have a C concentration of 50% or more in terms of atomic ratio. As for the layer deposited, the effect is obtained as long as 50% of C is contained, but when any one of C, CN, AlC, SiC, TiC, VC, CrC, ZrC, NbC, MoC, TaC and WC or a mixture thereof is used, the effect is high, and above all, C, CN, CrC and VC are more preferred.
The film thickness of the deposited layer is preferably 30 nm or less and preferably 3 nm or more. If the film thickness is too large, C is excessively implanted and the C element diffuses even into the recording area, whereas if the thickness is too small, the total amount of C implanted is deficient.
After depositing the C layer, ion beam irradiation is performed to deactivate the magnetic layer in the non-recording area. The ion beam is preferably formed by generating plasma from a gas composed of He, Ne, Ar, Kr, Xe or a mixture thereof.
Gases such as N2 and O2 react with and gasify C and therefore, are not preferred. The ion beam irradiation is continued until the C-containing layer is convexed or concaved to a depth of about 5 nm or less and depending on the case, even the magnetic recording layer is convexed or concaved.
In the case where etching occurs in the magnetic recording layer by the ion beam irradiation, in view of head flying, the concave/convex height of the magnetic recording layer is preferably 15 nm or less, more preferably 10 nm or less.
<Hard Mask>
The hard mask for use in the method of this embodiment preferably contains carbon as a main component. The atomic ratio of carbon preferably exceeds 75%. If the ratio of carbon is 75% or less, the etching selectivity tends to decrease, failing in processing the magnetic layer with good profile.
The hard mask can be deposited by sputtering or CVD. Also, other than carbon, Al, Si, Ta or Ti can be used as the hard mask. The film thickness of the hard mask is preferably from 4 to 50 nm. If the film thickness is too large, etching takes a long time when separating the hard mask and this gives rise to a damage in the side of the patterned film, whereas if it is excessively small, the film cannot fulfill the function as a hard mask during etching.
The hard mask functions also as a protective film of the raw material medium before processing and therefore, an oxide film between the magnetic recording layer and the hard mask may be omitted. Furthermore, a wet release layer may be deposited between the hard mask and the magnetic recording layer, if desired.
<Sub-Mask Between Hard Mask and Resist Layer>
For the sub-hard mask in the method of this embodiment, a material ensuring etching selectivity with respect to the hard mask is used and is preferably Si, SiO2, SixNy, SiON, Al, Ta, Ti or a material mainly composed of Ag, Au, Co, Cr, Cu, Ni, Pd, Pt or Ru, which are resistant to an O2 or O3 gas. Also, an elemental substance, nitride, oxide, alloy or mixture thereof may be used.
The film thickness of the sub-hard mask is preferably from 1 to 15 nm, more preferably from 2 to 5 nm. If the film thickness is too large, the magnetic recording layer may be damaged when removing the sub-hard mask, whereas if it is excessively small, the mask cannot be deposited as a uniform film.
The step of patterning and separating the sub-hard mask is performed by plasma etching with a gas containing a fluorine-based gas including CF4, C2F6, C3F8, C4F8, SF6, NF3, CHF3 and HF or with a gas mainly composed of a rare gas including He, Ne, Ar, Kr and Xe.
<Wet Release Layer>
For the wet release layer in the method of this embodiment, a metal layer capable of being removed by a wet release process with water, an acid, an alkali, an organic solvent or the like is used. For example, the layer is preferably formed of Mg when the releasing solution is water, Mo, Al, Sc, Ti, V, Mn, Y, Zr, Nb, La, Ce, Nd, Sm, Eu, Gd or Hf for an acid, Al, Zn Sn, Pb, Ga or In for an alkali, and photocurable or thermosetting resins for an organic solvent.
<Patterning of Sub-Hard Mask>
In the case of using a sub-hard mask, after imprinting and removal of the resist residue, the hard mask is patterned based on the pattern of the imprinted resist. For the patterning of the sub-hard mask, RIE may be used or an ion beam etching method with He, Ne, Ar, Kr, Xe or the like may be employed. For example, when the main component of the sub-hard mask is Si, SiO2, SixNy, SiON, Al, Ta or T, a gas mainly composed of a fluorine-based gas including CF4, C2F6, C3F8, C4F8, SF6, NF3, CHF3 and HF is suitably used.
In the case where the main component of the hard mask is Ag, Au, Co, Cr, Cu, Ni, Pd, Pt or Ru, ion beam etching with a fluorine-based gas such as CF4 or a rare gas such as He, Ne, Ar, Kr and Xe is suitable. The patterning of the sub-hard mask is terminated at a stage when the surface of the hard mask is exposed.
<Patterning of Hard Mask>
In the case of using a sub-hard mask, the hard mask is patterned based on the pattern of the sub-hard mask. In the case of not using a sub-hard mask, after imprinting and removal of the resist residue, the hard mask is patterned based on the pattern of the imprinted resist. For the patterning of the hard mask, RIE may be used, or an ion beam etching method with He, Ne, Ar, Kr, Xe or the like may be employed.
For example, when the main component of the hard mask is C, a gas mainly composed of O2 or O3 is suitably used. In the case where the main component of the hard mask is Al, Si, Ta or Ti, ion beam etching with a fluorine-based gas such as CF4 or a rare gas such as He, Ne, Ar, Kr and Xe is suitable. The patterning of the hard mask is terminated at a stage when the surface of the magnetic recording layer (in the case of using a wet release layer, the surface of the wet release layer) is exposed.
<Patterning of Wet Release Layer>
In the case of using a wet release layer, the wet release layer is patterned based on the pattern of the hard mask. For the patterning of the wet release layer, RIE with a fluorine-based gas including CF4, C2F6, C3F8, C4F8, SF6, NF3, CHF3 and HF, or RIE with a gas mainly composed of O2 or O3 may be used. An ion beam etching with He, Ne, Ar, Kr and Xe may also be employed.
<Removal of Mask Layer>
After the patterning of the magnetic recording layer, the mask layer is removed.
In the case of using a wet release layer, the mask with the overlying hard mask is separated by a wet process.
In the case of not using a wet release layer, the hard mask can be separated by plasma ashing with a gas mainly composed of O2, O3 or H2 or a gas mainly composed of a fluorine-based gas or by ashing using RIE.
A DTR medium was manufactured by the method of Example 1. In order to vary the amount of C implanted, the CH4 gas ion beam irradiation time is changed in the range from 0 seconds to 100 seconds as shown in Table 1. As Comparative Example, a medium subjected to magnetism deactivation by CF4 irradiation but not by CH4 irradiation was prepared.
The relationship between the CH4 irradiation time and the medium characteristics is shown in Table 1.
The C content (%, atomic ratio to Co) in the non-recording area was measured by XPS, and the results are shown in Table 1. The medium was mounted on a drive and subjected to a fringe test. The error ratio was measured after performing adjacent recording 1,000 times under the conditions that the magnetic land width of the medium was 54 nm, the groove width was 16 nm, the effective recording head width (MWW) was 80 nm and the effective reproduction head width (MRW) was 50 nm.
In a medium where the CH4 irradiation time is from 2.2 to 100 seconds, the error ratio was 10−5 or less and the medium was confirmed to operate as a DTR medium without problem. In a medium where the irradiation time was 1.3 seconds and the C content was 0.7%, magnetization remained in the non-recording area and the error ratio could not be measured. Similarly, in a medium not irradiated with CH4, the error ratio could not also be measured. In the medium with a low C content, the fringe test is considered to result in NG due to insufficient deactivation of the magnetism.
Furthermore, an environmental test was performed. Each medium was placed under high-temperature high-humidity conditions at 80° C. and a humidity of 80% and the time until the error ratio could not be measured was examined, as a result, an environmental resistance of 400 hours or more was confirmed except for Comparative Example 1.
In the drive of Comparative Example 1, measurement of the error ratio became impossible in 24 hours. It is presumed that fluorine migrates out of the non-recording area and deteriorates the magnetism of the recording area.
These results reveal that the medium containing C in the non-recording area is good in fringe characteristics and environmental resistance and exhibits sufficient performance as a DTR medium.
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Separately, a stamper 60 having a concave/convex pattern (for example, as shown in
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This process is performed, for example, in an inductively coupled plasma (ICP) RIE apparatus by using O2 as the process gas and setting the chamber pressure to 0.1 Pa, the coil RF power and the platen RF power to 100 W and 50 W, respectively, and the etching time to 30 seconds.
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The manufactured magnetic recording medium is mounted on a drive, and the error ratio is measured and found to be 10−6.4, and continuous driving over 100 hours is confirmed. The medium manufactured by the process in this Example has good performance as a magnetic recording medium.
Magnetic recording mediums were manufactured by the same method as in Example 1 except that CO, CO2, C2H2, C2H4, C2H6, C3H6, C3H8, C4H6, C4H8, C4H10, HCN or CH3F was used in place of CH4 as the ion beam source. Also, as Comparative Example, a medium whose magnetism deactivation was performed by CF4 irradiation was prepared.
The relationship between the ion beam irradiation time and the medium characteristics is shown in Table 2.
The C content (%, atomic ratio to Co) of the non-recording area was measured by XPS, and the results are shown in Table 2. The medium was mounted on a drive, and the same fringe test as in Example 2 was performed. In all mediums, the error ratio was confirmed to be 10−5 or less and it is revealed that the non-recording area was deactivated without problem.
Also, each medium was subjected to an environmental test. The medium was placed under high-temperature high-humidity conditions at 80° C. and a humidity of 80% and the time until the error ratio could not be measured was examined, as a result, an environmental resistance of 400 hours or more was confirmed except for Comparative Example 1 and CH3F.
In the drive of Comparative Example 1, measurement of the error ratio became impossible in 24 hours. In the case of CH3F, although not so bad as in Comparative Example 1, measurement of the error ratio became impossible in 200 hours. It is presumed that fluorine migrates out of the non-recording area and deteriorates the magnetism of the recording area.
These results reveal that when the gas of Examples above is used for the source, the medium is good in fringe characteristics and environmental resistance and exhibits sufficient performance as a DTR medium.
Magnetic recording mediums were manufactured by the same method as in Example 1 except that an assist gas He, Ne, Ar, Kr, Xe, H2, N2, O2 or O3 was mixed with CH4 as the ion beam source. The assist gas was mixed in a ratio to give a partial pressure ratio of 50%.
Also, as Comparative Examples, a medium manufactured without using an assist gas and a medium whose magnetism deactivation was performed by CF4 irradiation were prepared.
The relationship between the assist gas species and the medium characteristics is shown in Table 3.
The C content (%, atomic ratio to Co) of the non-recording area was measured by XPS, and the results are shown in Table 3. The medium was mounted on a drive, and the same fringe test as in Example 2 was performed. In all mediums, the error ratio was confirmed to be 10−5 or less and it is revealed that the non-recording area was deactivated without problem.
Also, in all mediums except for Comparative Examples, despite a short irradiation time compared with CH4 alone, the error ratio is equal to or smaller than that when using CH4 alone and this proves the assist gas effect.
Also, each medium was subjected to an environmental test. The medium was placed under high-temperature high-humidity conditions at 80° C. and a humidity of 80% and the time until the error ratio could not be measured was examined, as a result, an environmental resistance of 400 hours or more was confirmed except for Comparative Example 1. In the drive of Comparative Example 1, measurement of the error ratio became impossible in 24 hours. It is presumed that fluorine migrates out of the non-recording area and deteriorates the magnetism of the recording area.
Not only CH4 but also other C-containing gases were tested, but the results were the same. These results reveal that when the gas described in claim 10 is used, the medium is good in fringe characteristics and environmental resistance and exhibits sufficient performance as a DTR medium.
Magnetic recording mediums were manufactured by the same method as in Example 1 except that an assist gas He was mixed with CH4 as the ion beam source to give a partial pressure ratio of 25%, 50%, 75% or 85%.
Also, as Comparative Examples, a medium manufactured without using an assist gas and a medium whose magnetism deactivation was performed by CF4 irradiation were prepared.
The relationship between the assist gas species and the medium characteristics is shown in Table 4.
The C content (%, atomic ratio to Co) of the non-recording area was measured by XPS, and the results are shown in Table 4. The medium was mounted on a drive, and the same fringe test as in Example 2 was performed. In all mediums where the He partial pressure was 75% or less, the error ratio was confirmed to be 10−5 or less and it is revealed that the non-recording area was deactivated without problem.
Also, the assist gas effect was confirmed. In the medium where the He partial pressure of 85%, the C content is smaller than in other mediums with a lower He partial pressure, Ms in the non-recording area is liable to remain and in turn, the error ratio is slightly inferior to that in the case of CH4 alone.
Furthermore, each medium was subjected to an environmental test. The medium was placed under high-temperature high-humidity conditions at 80° C. and a humidity of 80% and the time until the error ratio could not be measured was examined, as a result, an environmental resistance of 400 hours or more was confirmed except for Comparative Example 1. In the drive of Comparative Example 1, measurement of the error ratio became impossible in 24 hours. It is presumed that fluorine migrates out of the non-recording area and deteriorates the magnetism of the recording area.
These results reveal that, when the gas of this embodiment is used as an assist gas with the concentration of 75% or less, the medium is good in fringe characteristics and environmental resistance and exhibits sufficient performance as a DTR medium.
Another example of the method for manufacturing a magnetic recording medium according to this embodiment is described below by referring to
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On the third hard mask 55, a resist 56 is spin-coated to have a thickness of 50 nm. Separately, a stamper 60 having a concave/convex pattern (for example, as shown in
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This process is performed, for example, in an inductively coupled plasma (ICP) RIE apparatus by using O2 as the process gas and setting the chamber pressure to 0.1 Pa, the coil RF power and platen RF power to 100 W and 50 W, respectively, and the etching time to 20 seconds.
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A DTR medium was manufactured by the above-described method, and the C content (%, atomic ratio to Co) in the non-recording area of the medium obtained was measured by XPS and found to be 52%. The medium was mounted on a drive, and the same fringe test as in Example 2 was performed.
The error ratio was 10−6.0. Furthermore, the same environmental test as in Example 2 was performed, and an environmental resistance of 400 hours or more was confirmed.
These results reveal that the DTR medium manufactured by this method has sufficient performance.
Magnetic recording mediums were manufactured by the same method as in Example 7 except that CN, AlC, SiC, TiC, VC, CrC, ZrC, NbC, MoC, TaC or WC was used in place of C as an implantation layer.
The relationship between the implantation layer and the medium characteristics is shown in Table 5.
The C content (%, atomic ratio to Co) in the non-recording area was measured by XPS, and the results are shown in Table 5. The medium was mounted on a drive and subjected to the same fringe test as in Example 2. In all mediums except for Comparative Example 1, the error ratio was confirmed to be 10−5 or less and it is revealed that the non-recording area was deactivated without problem.
Also, each medium was subjected to an environmental test. The medium was placed under high-temperature high-humidity conditions at 80° C. and a humidity of 80% and the time until the error ratio could not be measured was examined, as a result, an environmental resistance of 400 hours or more was confirmed except for Comparative Example 1. In the drive of Comparative Example 1, measurement of the error ratio became impossible in 24 hours. It is presumed that fluorine migrates out of the non-recording area and deteriorates the magnetism of the recording area.
These results reveal that when the material described in claim 12 is used for the implantation layer, the medium is good in fringe characteristics and environmental resistance and exhibits sufficient performance as a DTR medium.
Magnetic recording mediums were manufactured by the same method as in Example 6 except that Ne, Ar, Kr or Xe was used in place of He as the ion beam source for implantation.
The relationship between the beam source and the medium characteristics is shown in Table 6.
The C content (%, atomic ratio to Co) of the non-recording area was measured by XPS, and the results are shown in Table 6. The medium was mounted on a drive, and the same fringe test as in Example 2 was performed. In all mediums except for Comparative Example 1, the error ratio was confirmed to be 10−5 or less and it is revealed that the non-recording area was deactivated without problem.
Furthermore, each medium was subjected to an environmental test. The medium was placed under high-temperature high-humidity conditions at 80° C. and a humidity of 80% and the time until the error ratio could not be measured was examined, as a result, an environmental resistance of 400 hours or more was confirmed except for Comparative Example 1. In the drive of Comparative Example 1, measurement of the error ratio became impossible in 24 hours. It is presumed that fluorine migrates out of the non-recording area and deteriorates the magnetism of the recording area.
The test was performed for other implantation layers, but the results were the same. These results reveal that when the above material is used for the implantation layer, the medium is good in fringe characteristics and environmental resistance and exhibits sufficient performance as a DTR medium.
According to the above-described embodiment, a method capable of manufacturing a magnetic recording medium in which the environmental resistance of the non-recording area is increased while surely deactivating the non-recording area, the flying property of the recording/reproducing head is ensured with good head-positioning precision, the SN ratio is good, and high reliability is exhibited even in a high-temperature high-humidity environment, can be provided.
| Number | Date | Country | Kind |
|---|---|---|---|
| P2010-223216 | Sep 2010 | JP | national |
