Patent Application
20150302877
The disclosure is related to the field of magnetic recording media.
One type of recording media that is used in modern disk drive systems is perpendicular magnetic recording (PMR) media. PMR media includes a magnetic recording layer that has an easy axis of magnetization oriented substantially perpendicular to the substrate. Hexagonal Close Packed (HCP) Co-alloys are typically used as the magnetic recording layer for perpendicular recording. The easy axis of magnetization for these materials lies along the c-axis or <0001> direction.
PMR media is generally formed on a substrate with a soft magnetic underlayer (SUL), one or more interlayers, and a perpendicular magnetic recording layer. The soft magnetic underlayer (SUL) serves to concentrate a magnetic flux emitted from a main pole of a write head and to serve as a flux return path back to a return pole of the write head during recording on the magnetic recording layer. The interlayers (also referred to as seed layers) serve to control the size of magnetic crystal grains and the orientation of the magnetic crystal grains in the magnetic recording layer. The interlayers also serve to magnetically de-couple the SUL and the magnetic recording layer. The magnetic recording layer is the layer in which bit data is stored based on the orientation of the magnetization of individual magnetic grains.
Because the magnetic recording layer has a magnetization that is oriented parallel to magnetic fields used to write to the media, reversing the magnetization of the magnetic recording layer may be difficult. To assist in reversing the magnetization of the magnetic grains in the magnetic recording layer, PMR media may also include a cap layer that is exchange coupled to the magnetic recording layer. The cap layer is typically formed from a CoPt alloy, such as CoPt, CoPtCr, CoPtCrB, etc. The cap layer may directly contact the magnetic recording layer, or a coupling layer may be fabricated between the cap layer and the magnetic recording layer. When a coupling layer is used, the structure is sometimes referred to as an exchange spring structure.
As the areal bit density of a magnetic recording media increases, the magnetic regions in the recording layer that encode bit data become smaller. This may reduce the read signal generated in a read head of the disk drive system. One solution to improve the read signal is to reduce a thickness of the carbon overcoat that is typically applied to the cap layer. The carbon overcoat is a non-magnetic layer applied to the cap layer to protect the media from corrosion and/or damage. Thus, reducing the carbon overcoat thickness potentially reduces the relative distance between the read head and the cap layer. However, as the carbon overcoat becomes thinner, the corrosion resistance of the disk may degrade, especially if the overcoat is rough.
Another solution for improving the read signal is to reduce the clearance between the read head and the top surface of the disk. However, one consequence of a reduced clearance is head-to-disk contact, which is undesirable. Head-to-disk contact occurs when a slider that includes the read head makes contact with the disk. Head-to-disk contact may cause damage to the slider, the disk, or both. It therefore remains an ongoing challenge to improve the performance of magnetic media.
Embodiments described herein provide improvements in magnetic recording media by utilizing Xenon plasma to polish the cap layer prior to depositing a carbon overcoat onto the cap layer. Polishing the cap layer reduces a roughness of the top surface of the cap layer, and therefore, the resulting roughness of the carbon overcoat that is formed on the cap layer is reduced. A smoother carbon overcoat on the disk improves the clearance between the slider and the disk. Also, a smoother carbon overcoat on the disk improves the corrosion resistance of the disk, and the carbon overcoat may be made thinner without sacrificing the corrosion resistance of the disk. A thinner carbon overcoat reduces the relative distance between the read head and the cap layer.
One embodiment comprises a method of operating a carbon overcoat deposition station. The method comprises inserting a magnetic recording disk into the deposition station that includes a cap layer that is exchange coupled to a magnetic recording layer. The method further comprises supplying a source of Xenon gas to the deposition station, and applying a negative bias voltage to the cap layer. The method further comprises ionizing the Xenon gas in the deposition station to generate Xenon plasma, and to polish the cap layer utilizing the Xenon plasma to a roughness of 5 angstroms or less.
Another embodiment comprises a method of operating a carbon overcoat deposition station. The method comprises inserting a magnetic recording disk into the deposition station that includes a cap layer that is exchange coupled to a magnetic recording layer. The method further comprises supplying a source of Xenon gas to the deposition station, and applying a negative bias voltage to the cap layer. The method further comprises ionizing the Xenon gas in the deposition station to generate Xenon plasma, and to polish the cap layer utilizing the Xenon plasma. The method further comprises terminating the source of Xenon gas to the deposition station, and supplying a source of carbon carrying gas to the deposition station. The method further comprises depositing a carbon overcoat on the polished cap layer.
Another embodiment comprises a magnetic recording disk. The magnetic recording disk includes a magnetic recording layer that is configured to store bit data for the magnetic recording disk. The magnetic recording disk further includes a cap layer that is polished utilizing Xenon plasma to a roughness of 5 angstroms or less, where the cap layer is formed on and is exchanged coupled with the magnetic recording layer. The magnetic recording disk further includes a carbon overcoat that is formed on the cap layer.
The above summary provides a basic understanding of some aspects of the specification. This summary is not an extensive overview of the specification. It is intended to neither identify key or critical elements of the specification nor delineate any scope particular embodiments of the specification, or any scope of the claims. Its sole purpose is to present some concepts of the specification in a simplified form as a prelude to the more detailed description that is presented later.
Some embodiments of the present invention are now described, by way of example only, and with reference to the accompanying drawings. The same reference number represents the same element or the same type of element on all drawings.
The figures and the following description illustrate specific exemplary embodiments of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within the scope of the invention. Furthermore, any examples described herein are intended to aid in understanding the principles of the invention, and are to be construed as being without limitation to such specifically recited examples and conditions. As a result, the invention is not limited to the specific embodiments or examples described below, but by the claims and their equivalents.
Step 102 comprises depositing a film of a magnetic recording disk. Although not shown, the film may be deposited on a substrate or on another film of the disk that was previously deposited. Some examples of the film are a soft magnetic underlayer (SUL), a magnetic underlayer, a non-magnetic underlayer, a magnetic recording sublayer, a magnetic recording layer, a magnetic cap layer, etc.
In order to achieve some measure of corrosion resistance, disk fabricators desire smoother surfaces, or fabricate thicker protective layers in order to reduce the corrosion rate of the recording media. However, thick protective layers are typically non-magnetic carbon-like layers (Diamond-Like Carbon (DLC), carbon overcoats, etc.) that act to separate the read/write head from the magnetic recording layer used to store bit data on the disk. As this separation increases, which is also referred to as the magnetic spacing, the read signal (for a constant magnetic region size) decreases. This is undesirable and problematic because as the bit density of magnetic recording media increases, the number of magnetic grains (and therefore the size of the magnetic regions used to store data) decreases.
Step 104 (see
Step 106 comprises depositing a subsequent layer on the polished top surface of a film.
Steps 504 and 506 are utilized in performing a polishing process on the top surface of a magnetic recording layer using plasma. Step 504 and 506 are additional exemplary details of the polishing process described previously for step 104 of method 100 (see
During clearance testing, the inventors found that plasma polishing the media resulted in a clearance improvement from 8 nanometers to 8.5 nanometers over standard fabrication processes that did not include plasma polishing. The inventors further found that that standard fabrication processes for a magnetic disk (i.e., that did not use the plasma polishing process described herein) resulted in a carbon overcoat surface roughness of about 6.9 angstroms and a magnetic layer/carbon interfacial roughness of about 8 angstroms. The surface roughness and interfacial roughness were determined by X-ray reflectivity. Similar tests were performed on media that was plasma polished. Both the carbon overcoat surface roughness and the magnetic layer/carbon interfacial roughness were about 5.1 angstroms, which are less than what were found for the standard fabrication process. A smoother carbon overcoat 904 allows fabricators to make carbon overcoat 904 thinner, because the corrosion resistance of disk 602 is improved. When carbon overcoat 904 is thinner, the magnetic spacing between the read/write head and recording layer 606 is reduced. The reduction in the magnetic spacing allows for improved read/write performance when disk 602 is part of a disk drive system. During testing, the inventors found that standard fabrication processes for a magnetic disk (i.e., that did not use the plasma polishing process described herein) resulted in a corrosion product for a 28 angstrom thick carbon overcoat of about 3.6 nanograms. The amount of the corrosion product was determined by measuring a Co (cobalt) extraction count. Similar tests were performed on media that was plasma polished. A plasma polished 28 angstrom overcoat sample resulted in a 0.5 nanogram Co extraction count, which is significantly improved over the standard fabrication process. A 22 angstrom thick overcoat was also fabricated with the plasma polish process. Testing revealed that the Co extraction count for the sample was 0.8 nanograms. Therefore, even though the carbon overcoat in the 22 angstrom sample was thinner, plasma polishing of the media resulted in a corrosion resistance improvement from 3.6 nanograms to 0.8 nanograms over the standard fabrication process.
In another embodiment, Xenon can be used as a polishing ion for the plasma polishing process rather than Argon. In plasma polishing, ionized gas atoms (e.g., Xenon and/or Argon) are accelerated towards a layer on the disk that has already been deposited. For example, plasma polishing may be performed on a cap layer prior to depositing a carbon overcoat on the cap layer. The polishing ions collide with the top surface of the cap layer, transfer momentum and energy to the atoms of the cap layer, and remove them away from the top surface of the cap layer.
The energy transfer between the polishing ions and the atoms in the top surface of the magnetic recording layer is most efficient when they have the same mass. In PMR media and in Shingle Magnetic Recording (SMR) media, the top magnetic layer is referred to as a cap layer, which is exchange coupled to an underlying magnetic recording layer. Cap layers typically comprise Platinum (Pt), Cobalt (Co), Chromium (Cr), and/or Boron (B) along with possible oxides of these elements. Table 1 below lists the atomic number of the cap layer elements along with possible polishing ions that may be used in a plasma polishing process of the cap layer.
Based on the atomic number, the removal of Platinum atoms would be more efficient when using Xenon as the polishing ion rather than Argon as the polishing ion because the atomic number of Xenon (54) is closer to that of Platinum (78) than that of Argon (18). Although the atomic number of Radon (86) is closer still, Radon is radioactive and may not be practical for use in a manufacturing environment.
In the embodiments described below, a carbon overcoat deposition station is used to plasma polish the cap layer using Xenon prior to depositing the carbon overcoat onto the cap layer. One example of a carbon overcoat deposition station is a New Carbon
Technology (NCT) station. NCT stations are manufactured by Intevac. NCT stations are designed for deposition of ultra-thin, high-density carbon overcoats onto magnetic media, such as disks. Carbon overcoats may also be referred to as DLC overcoats or DLC layers. To deposit a carbon overcoat using an NCT station, a filament is heated to a high temperature to emit electrons. These electrons ionize gas molecules or atoms to form a plasma. Gases that comprise Carbon and Hydrogen elements are supplied to the NCT station, which decompose into Carbon and Hydrogen ions and atoms. A carbon overcoat is then grown by the deposition of Carbon ions and atoms onto the cap layer of the disk.
For plasma polishing in a NCT station, a disk is inserted into the NCT station that includes a cap layer deposited onto a magnetic recording layer, and Xenon is supplied to the NCT station rather than the gases used to form a carbon overcoat on the disk (e.g., gases that comprise Carbon and Hydrogen elements).
As shown in
The filament in the deposition station (e.g., a NCT station) is heated to a high temperature to emit electrons. These electrons ionize the Xenon gas to generate Xenon plasma (see step 1108). The negative bias voltage applied to cap layer 1004 accelerates the positive Xenon ions toward cap layer 1004, plasma polishing top surface 1008 of cap layer 1004 to generate a smooth surface. Top surface 1008 of cap layer 1004 may be polished to roughness of 5 angstroms or less (see step 1110). Polishing top surface 1008 of cap layer 1004 allows for a subsequent layer (e.g., a carbon overcoat) to be grown on a smoother surface than would be possible without plasma polishing cap layer 1004. Since the subsequent layer grows on a smoother surface, a top surface of the subsequent layer will have a smoother surface.
Carbon and Hydrogen based gasses may then be supplied to the deposition station (e.g., a NCT station) rather than Xenon in order to deposit the carbon overcoat onto the smoothened top surface 1008 of cap layer 1004. Plasma polishing of cap layer 1004 and the deposition of the carbon overcoat onto cap layer 1004 can be performed in the deposition station without removing disk 1002 from the deposition station. In other embodiments, the deposition of the carbon overcoat onto cap layer 1004 can be performed in a different deposition station (e.g., a NCT station) after cap layer 1004 is polished.
During testing of Xenon as a polishing ion for reducing the roughness of cap layers prior to the deposition of a carbon overcoat, it was found that Xenon provided a lower roughness than Argon at the interface between the cap layers and the carbon overcoats.
In some cases, the use of a sputtering target during the plasma polishing process may introduce contamination onto the cap layer from the sputtering target. Further, the bias voltages in a NCT station are lower (−180V) as compared to a DC magnetron sputter station (−600V) which can be desirable for reducing the possibility of arcing and/or localized heating of the disk where electrical connections are made to the disk.
As discussed, reducing the thickness of the carbon overcoat and/or the roughness of the top surface of the carbon overcoat is desirable for a number of reasons. One reason is that a thinner carbon overcoat reduces the magnetic spacing between read/write heads on the slider and the cap layer. This increases the signals sensed by the read head during a read process, and improves the magnetic field gradient applied to disk 1002 during a write process.
Another reason is that reducing the roughness of the carbon overcoat also improves the corrosion resistance of the disk. Typically, a rough carbon overcoat is made thicker to ensure that the corrosion resistance of the disk is sufficient. However, a thicker carbon overcoat increases the magnetic spacing between the read/write heads and the cap layer, which is undesirable. Using Xenon as a polishing ion in a plasma polishing process, the interfacial roughness between the carbon overcoat and the cap layer is reduced, which results in a smoother top surface for the carbon overcoat. This improves the corrosion resistance of the disk and consequentially, the carbon overcoat may be made thinner. Table 2 below illustrates the results of a Cobalt extraction test on magnetic media fabricated using Xenon polishing of the cap layer, which demonstrates that an acceptable corrosion resistance for the media can be achieved using a carbon overcoat thickness of about 20.4 Angstroms.
A recording analysis was performed on media fabricated using Xenon polishing and Argon polishing in a NCT station. Xenon polishing at 10 SCCM was performed on a cap layer of a test media at a bias voltage of −180V prior to depositing a carbon overcoat. Argon polishing at 20 SCCM was performed on a cap layer of another test media at a bias voltage of −180V prior to depositing a carbon overcoat.
Table 3 indicates that with the magnetic spacing reduction that results from Xenon polishing, areal density capacity can be increased by approximately 2%. The recording test was performed in a spin stand using SMR.
In the table, FOM is a recording parameter in the spin stand measurement which has been demonstrated to correlate with Areal Density Capacity (ADC). The 1.9% increase in FOM calculated from the data in the table indicates an approximately 2% increase in ADC. The SMR test was carried out with trimming from the inner diameter of the media. Owi is overwrite, 2TS0NRi is the isolated signal-to-mid frequency noise ratio of the media, and 2TSNRi is the mid frequency signal-to-mid frequency noise ratio of the media. TD is a measurement of the clearance between the media and the read/write head.
The 0.4 dB of 2TSNRi increase of Xenon polished media is a direct result of the magnetic spacing reduction achieved from both clearance increase (TD increases from 7.8 nanometers for Argon polishing to 7.9 nanometers for Xenon polishing), and carbon overcoat thickness reduction. 2TS0NRi is comparable between both Xenon polished and Argon polished media, which indicates that the intrinsic magnetic and recording performance of the media in is not degraded by using Xenon as a polishing ion.
Although specific embodiments were described herein, the scope is not limited to those specific embodiments. The scope is defined by the following claims and any equivalents thereof.
This patent application is a continuation-in-part of co-pending U.S. non-provisional patent application Ser. No. 13/472,854, filed on 16 May 2012 and entitled “PLASMA POLISH FOR MAGNETIC RECORDING MEDIA”, which is incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13472854 | May 2012 | US |
| Child | 14695858 | US |
